20019.MAT - COR.PRG Selezione Maeriali Servizio Marino Rev. 0 - Aprile 2009

Eni S.p.A.
Exploration & Production Division
COMPANY STANDARD
MATERIAL SELECTION FOR

SEAWATER HANDLING SYSTEMS
20019.MAT.COR.PRG
Rev. 0 – April 2009
ENGINEERING COMPANY STANDARD
Documento riservato di proprietà di Eni S.p.A. Divisione Agip. Esso non sarà mostrato a Terzi né utilizzato per scopi diversi da quelli per i quali è stato inviato.
This document is property of Eni S.p.A. Divisione Agip. It shall neither be shown to Third Parties not used for purposes other than those for which it has been sent.
Eni S.p.A. 20019.MAT.COR.PRG
Rev. 0 April 2009
Exploration & Production Division Page 2 of 45
PREMISE
Rev. 0 ISSUE
The present document cancels and replaces the previous ENI norms:
- 03580. MAT.COR.PRG Design criteria. Internal corrosion. Metallic materials in contact with
sea water
- 03581. MAT.COR.PRG Design criteria. Materials and corrosion control methods for circuits
with sea water.
The document, which merges the two above, has been significantly updated considering:
- new available materials and techniques;
- updated knowledge in the fields of material performance and corrosion control methods;
- updated corrosion management criteria adopted in seawater handling systems, including
feedbacks from ENI Fields.
Rev. 0 April 2009
TABLE OF CONTENTS
MATERIAL SELECTION FOR SEAWATER HANDLING SYSTEMS

1. GENERAL
1.1 Scope
1.2 Document organization
1.3 Reference Standards
1.4 ENI Company Standards
1.5 Symbols and abbreviations
2. INTRODUCTION
2.1 Seawater
2.2 Seawater handling systems
2.2.1 Seawater injection
2.2.2 Seawater cooling systems
2.2.3 Seawater fire-fighting systems
2.3 Seawater treatments
2.3.1 Filtration
2.3.2 Deaeration
2.3.3 Disinfection
2.3.3.1 Chlorination
2.3.3.2 Copper ion for bio-fouling control
2.3.4 Other chemical treatments
2.3.4.1 Oxygen scavengers (residual oxygen and chlorine content control)
2.3.4.2 Biocide
2.3.4.3 Corrosion inhibitor
2.3.4.4 Other treatments
2.4 Seawater corrosion
2.4.1 Dissolved oxygen
2.4.2 Chlorine
2.4.3 Temperature
2.4.4 Flow conditions
2.4.5 Pollution by sulphides
2.4.6 Microbial activity
2.4.7 Contaminants
2.4.8 Galvanic corrosion
2.4.9 Stress Corrosion Cracking
3. METALLIC MATERIALS
3.1 Forewords
3.2 Carbon and low alloy steels
3.2.1 Corrosion performance
3.3 Cast Irons
3.3.1 Low alloy cast iron
3.3.2 High-alloy cast iron
3.4 Stainless steels
3.4.1 High-alloy austenitic stainless steels
3.4.2 Duplex stainless steels
3.4.3 Localised corrosion resistance
3.5 Copper alloys
3.5.1 Aluminium and nickel-aluminum bronzes
3.5.2 Copper nickel alloys
3.6 Nickel alloys
3.7 Titanium alloys
4. NON METALLIC. COMPOSITES. LINERS
4.1 Plastic lining
Rev. 0 April 2009
4.2 Cement linings

4.3 Rubber linings and coatings
4.4 Glass fiber reinforced plastic
4.5 Thermoplastics
5. MATERIAL SELECTION IN SEAWATER HANDLING SYSTEMS
5.1 Material selection
5.1.1 Criteria for the selection of applicable corrosion prevention methods
5.1.2 Options evaluation and costs comparison
5.2 Seawater handling systems. Material selection and corrosion control requirements
5.2.1 Seawater piping
5.2.1.1 Aerated seawater
5.2.1.2 Deaerated seawater
5.2.1.3 Piping material selection summary
5.2.2 Electro-chlorination unit
5.2.3 Submersible Lift Pumps
5.2.4 Centrifugal Pumps
5.2.5 Valves
5.2.6 Exchangers and coolers
5.2.7 Deaeration tower
5.2.8 Filters
5.2.9 Pipelines
5.3 Seawater fire-fighting systems
ANNEX A – METAL COMPOSITION DATA
Stainless steels
Copper alloys
Nickel alloys
Titanium and its alloys
Rev. 0 April 2009
1. GENERAL
1.1 Scope
This document deals with metallic, non-metallic and composite materials to be used in process
facilities handling seawater and associated corrosion control techniques.
The aims of the document are:

- to identify the applicable materials in seawater handling units;
- to review the relevant corrosion and degradation mechanisms;
- to review the typical issues associated to the use of applicable materials, including design,
fabrication, installation, procurement and costs;
- to provide the requirements for corrosion control and monitoring of the applicable materials;
- to provide guidelines for material selection in seawater handling units.
1.2 Document organization
Section 1 Defines the scope of the document and provides general information for its
use.
Section 2 Illustrates the parameters of natural seawater affecting corrosion and

material performances and their variability.
Illustrates the process units handling seawater in oil and gas production; in
particular the water injection systems, the seawater cooling systems, and
the fire-fighting systems.
Reviews the main factors affecting corrosion and degradation mechanisms.
Section 3 Reviews the metallic materials families applicable in seawater, providing

specific information on their performance in seawater.
Section 4 Reviews the non-metallic materials and liners applicable in seawater.
Section 5 Provides criteria for material selection.

Specify recommended materials for main components met in seawater
handling systems together with applicability limitations and associated
corrosion control requirements.
ANNEX A Reports tables with metal alloys chemical composition.
1.3 Reference Standards
ISO 8044 Basic Terms and Definitions on Corrosion

ISO 14692 Glass Reinforced Plastics (GRP) Piping
ISO 15156/NACE MR0175 Petroleum and Natural gas industries – Materials for use in H2S
containing environments in oil and gas production
Part 1 General principles for selection of cracking resistant materials
Part 2 Cracking resistant carbon and low alloy steels
Part 3 Cracking resistant CRAs
ISO 15663-1 Life Cycle Costing – Part 1 Methodology
API RP-14E Design and Installation of Offshore Production Platform Piping
System
Rev. 0 April 2009
ASTM G 78-46 Standard Test Method for Pitting and Crevice Corrosion Resistance
of Stainless Steels and Related Alloys by the Use of Ferric Chloride
Solutions
ASTM E 527 Standard Practice for Numbering Metals and Alloys (UNS)
NORSOK M-001 Materials Selection
1.4 ENI Company Standards
02555.VAR.COR.PRG Internal Corrosion – Fluid Classification and Corrosion Parameters

Definition
20555.VAR.COR.PRG Internal Corrosion Monitoring
14351.PIP.MEC.SDS Guidelines for the Use of Glassfiber Reinforced Plastic (GRP) Piping
20312.VAR.COR.PRG Guidelines for Chemical Treatments of Pipelines
1.5 Symbols and abbreviations
ABS Acrylonitrile Butadiene Styrene

BP Bio Probe
cO2 Dissolved Oxygen concentration
cCl2 Free Chlorine concentration
CRA Corrosion Resistant Alloys
CSCC Chloride Stress Corrosion Cracking
CuNi Copper Nickel alloy
ECTFE Ethylene Chlorotrifluoroethlyene
ETFE Ethylene Tetrafluoroethylene
GRP Glass Glass-fiber Reinforced Plastic
HAZ Heat Affected Zone
MIC Microbial Induced Corrosion
PE Polyethylene
PP Polyprophylene
PRE/PRNEN Pitting Resistance Equivalent Number
PTFE Polytetrafluoroethylene
PVC Polyvinyl chloride
PVDF Polyvinylidene Fluoride
S Salinity
SCE Saturated Calomel Electrode
SHE Standard Hydrogen Electrode
SRB Sulphate Reducing Bacteria
SSC Sulphide Stress Cracking
Rev. 0 April 2009
2. INTRODUCTION
2.1 Seawater
The chemical composition of seawater is remarkably constant in most of geographical area;

concentrations values of the main constituents are shown in Table 2.1. Furthermore, with the
exception of inorganic carbon, the principal constituents have almost fixed ion concentration ratios
(column 4 in the table); their concentrations vary primarily in response to a comparatively rapid
exchange of water (precipitation and evaporation), with relative concentrations remaining nearly
constant.
Table 2.1 - Principal constituents of seawater.

Ions Concentrations at salinity equal to 35 g/l
g/kg of seawater moles/kg relative concentr.
-
Chloride, Cl 19.2 0.54 1.0000
+
Sodium, Na 10.7 0.464 0.8593
2+
Magnesium, Mg 1.28 0.0526 0.0974
2-
Sulphate, SO4 2.68 0.0279 0.0517
2+
Calcium, Ca 0.41 0.0102 0.0189
+
Potassium, K 0.40 0.0101 0.0187
Carbon (inorganic) 0.028 0.0023 0.0043
-
Bromide, Br 0.066 0.00083 0.00154
Boron 0.0044 0.00041 0.00075
Salinity is used as a measure of the total salt content of seawater; it affects the electrical conductivity
and the seawater density. Salinity is about 34 ÷ 35 g∙l-1, with variations observed in some local area
and closed basins; Figure 1 is the salinity map in the Caspian Sea, in winter and summer; Baltic Sea
is a mixture of sea water from the North Sea and fresh water from rivers and rainfall, and salinity
-1 -1
varies from 2 to 20 g∙l ; high salinity values are met in Red Sea and Persian Gulf, of about 40 g∙l ,
caused by the high evaporation rates.
Figure 2.1 – Salinity map – winter and summer cases – in the Caspian Sea
Carbon dioxide dissolved from the atmosphere reacts with water in seawater to form carbonic acid
- 2-
(H2CO3), bicarbonate ions (HCO3 ) and carbonate ions (CO3 ); approximately 90 percent of the total
organic carbon in seawater is present as bicarbonate ions. Bicarbonates and carbonates provide
buffer capacity to seawater, with pH between 7.4 and 8.3.
Rev. 0 April 2009
The concentration of dissolved oxygen, cO2, in ppm, in seawater in equilibrium with atmosphere
depends on temperature and salinity, with values in the order of a few ppm (8 ÷ 10 ppm); if the local
datum is not available, it can be predicted by using the following empirical equation:
c O2 = 14.59 - 0.397 × T + 0.008 × T 2 - 8 ×10 -5 × T 3 - 6.0443 × S × (0.0167 - 0.00059 × T + 10 -5 × T 2 )
-1
where T is the seawater temperature in Celsius and S is the salinity in g∙l (see Figure 2.2).
14
13
)
m12
p
p
( 11
n 10
e
g
y 9
x
o 8 S=15g/l ppm
d
e 7 S=25g/l ppm
v
l
o 6
s S=35g/l ppm
s
i 5
d S=45g/l ppm
4
3
2
1
0
0 5 10 15 20 25 30 35 40 45 50
temperature (\C)
Figure 2.2 – Oxygen solubility in equilibrium with atmosphere as a function of temperature and
salinity.
For deep water applications it is important to consider the variation of key parameters with depth: the
typical trends of the dissolved oxygen content and other parameters as temperature, salinity and pH
is qualitatively shown in the below figure.
Figure 2.3 – Typical variation of key parameters as a function with depth in deep water
Rev. 0 April 2009
2.2 Seawater handling systems
In oil and gas production seawater is handled in the following main systems:
- water injection;
- cooling circuits;
- fire-fighting.
Other typical uses of seawater include fresh water generation, ballast, pressure testing.
2.2.1 Seawater injection
A typical offshore seawater injection system is illustrated in Figure 2.4. The process is based on the
treatments of filtration, sterilization and deaeration (or deoxygenation).
ELECTROCHLORINATION
PACKAGE
OXYGEN SCAVENGER
BIOCIDE
COARSE FINE DEAERATION BOOSTER INJECTION

FILTERS FILTERS TOWER PUMPS PUMPS
FLOWLINES
SEAWATER
LIFT PUMPS
Figure 2.4 - Typical offshore seawater injection system.
In onshore systems, from water intakes, seawater is sent to water plant facilities where treatments
are performed.
In raw seawater injection systems, aerated seawater is directly injected into the reservoir thus
eliminating the deoxygenation treatment.
In some fields, seawater is mixed, continuously or intermittently, to formation water from separation
units or to water from other sources like aquifer water or surface water (commingled systems). In
these cases, water properties and corrosivity can be significantly modified, depending on the
composition of the water mixed to seawater, and its aggressivity shall be evaluated case by case.
2.2.2 Seawater cooling systems
Seawater cooling systems are similar to injection systems except for deaeration treatment, which is
normally missed with water returned to sea from cooling units. The circuit is typically a raw water
systems with water entering at ambient temperature and leaving at a higher temperature after
circulation through the heat exchangers.
The filtration and the disinfection (or sterilization) treatments are required to prevent fouling and
bacterial growth.
Rev. 0 April 2009
2.2.3 Seawater fire-fighting systems
Typical seawater fire-fighting system is illustrated in Figure 2.4. Differently from water injection and
cooling systems, seawater circulation is intermittent, and stagnant or low velocity are experienced.
Some parts of the circuit are maintained dry.
ELECTROCHLORINATION HYDRANTS
PACKAGE (INTERNAL)
HYDRANTS
FOAM MIXER
TANK
SEAWATER LIFT PUMPS

(MAIN AND JOCKER) DELUGE
SYSTEMS
Figure 2.5 - Typical offshore fire-fighting system.
2.3 Seawater treatments
In seawater handling systems treatments are performed that affect its corrosivity. The main ones are:
- filtration;
- deaeration (or deoxygenation);
- disinfection.
2.3.1 Filtration
Seawater filtration is first performed with self cleaning filters. In offshore systems, coarse filters with
backwash facilities are located downstream the lifting pumps to avoid particles larger than 2 mm to
enter the system.
Further filtration if performed by sand filters and cartridge filters, with residual solid particle size below
50 microns.
Poly-electrolytes are often added to promote solid separation.
2.3.2 Deaeration
Deaeration is aimed to remove oxygen dissolved in seawater and to reduce oxygen corrosion in
particular of carbon and low alloy steels.
Physical deaeration is performed by vacuum in a deaeration tower or by gas stripping in an

exchange tower. Re-circulating nitrogen stream as gas stream is also used.
If gas stripping is performed using available gas containing corrosive constituents, like CO 2 or H2S,
the seawater corrosivity can be enhanced.
Rev. 0 April 2009
Physical deaeration is completed by injection of chemicals, i.e. oxygen scavenger, like ammonium or
sodium bisulphite; a catalyser is added to speed up the reaction. Dosage of oxygen scavenger shall
be based on residual concentration of oxygen and chlorine; excessive dosages could increase the
corrosion rate.
Deoxygenation by oxygen scavenger only, i.e. without physical deaeration, is discouraged because
of the excessive consumption of chemical product.
The requirement for the deaeration treatment is a maximum residual oxygen content never
3
exceeding 20 ppb (or mg/m ). A strict control is required to avoid significant excursions, in time and
peak value, beyond this threshold, which is a particular thread for localised corrosion initiation of
corrosion resistant alloys.
2.3.3 Disinfection
Seawater disinfection is performed to prevent marine growth and fouling. Applicable techniques
include:
- chlorination, usually electro-chlorination;
- ultra violet (UV) sterilization;
- injection of biocides, continuous or batch.
- copper ions, supplied by copper anodes electro dissolution.
2.3.3.1 Chlorination
Chlorination represents the base treatment in water injection and cooling systems, performed
immediately downstream the lifting pumps.
The dosage of chlorine is controlled by the residual chlorine concentration. The residual chlorine
concentration shall be high enough to guarantee sterilization, but, in the mean time, excessive
chlorine concentrations shall be avoided. Residual chlorine, in fact, exerts the following effects:
- as oxygen, chlorine behaves as an oxidant, causing uniform corrosion on active metals like steel;
based on the equivalent weight values (16 for O2 and 35.4 for Cl2), 1 ppm in weight of Cl2
corresponds to about 0.22 ppm of O2. The oxygen equivalent is therefore calculated with the
following formula: OEQ = O2 + 0.22 ´ Cl2;
- residual chlorine reacts with the oxygen scavenger where it is used; excessive dosage of
chlorine lead to high consumption of oxygen scavenger; furthermore, chlorine reacts with the
oxygen scavenger before oxygen;
- the semi-reaction chlorine/chloride (Cl 2/Cl ) has a very high equilibrium potential (+1.36 V vs.
-
SHE compared with about +0.8 V of the semi-reaction O2/H2O at neutral seawater pH). Residual
chlorine causes an increase of the free corrosion potential of exposed metals and this represents
an aggravating factor for localized corrosion initiation. In particular many corrosion resistant
alloys may suffer pitting and crevice corrosion when exposed to seawater with residual chlorine,
particularly above ambient temperature.
Reference concentration values for residual chlorine are:

- upstream deaeration: 0.5 ÷ 1 ppm;
- downstream deaeration: 0.2 ÷ 0.5 ppm max.
Concentration of residual chlorine shall be monitored on a regular basis, tentatively daily, and
injection rate adjusted according to residual values.
2.3.3.2 Copper ion for bio-fouling control
Treatment with chlorination can be integrated by addition of copper ions. Copper ions permit to limit
the residual chlorine content.
The principle of these systems is to place anodes made of copper and aluminium at seawater system
inlets. A low-voltage electric current releases ions from these sacrificial anodes by electrolysis.
Copper ions prevent biocides growth and aluminium ions capture the copper ions in excess by
precipitating with copper oxides forming a film which is protective for the pipe internal surfaces.
Rev. 0 April 2009
2+
Copper as an ion (Cu ) at proper concentrations is toxic and is used to control algae and bacteria.
Because of its toxic effects, copper discharge to surface water is a concern. If a copper biocide
treatment is used for ballast discharge, then this discharge water needs to be regulated.
1,2
Test results shown that the use of copper ion as biocide is only partially effective at about 70 ppb in
reducing bacteria in simulated seawater experiments, suggesting that at the tested concentrations,
copper treatment was not fully reliable. In order to fully effective, higher concentrations are required,
which exceed the allowable discharge concentration levels (2 to 50 ppb). Furthermore, copper
effectiveness is influenced by the natural geochemical behaviour of copper in the environment. Being
a particle reactive chemical, it tends to be adsorbed by sediments, whether suspended or settled,
thereby being subtracted to copper available as a biocide. Copper in solution is also influenced by
the presence of dissolved organic matter, bicarbonate, and carbonate in water, and for this reason
different amounts of copper may be needed to accomplish its function as biocide. Copper ion at
concentration in water above 20 to 50 ppb can cause severe corrosion of aluminium alloys.
In summary, the toxicity data suggest that in fairly high concentrations, copper ion could be an
effective biocide. However, at the concentrations needed to achieve the desired effectiveness, the
copper level could be too high to allow discharging to the sea which may render this method not
practical as an alternative biocide.
Combined treatment with copper and chlorine is typically with 5 ppb of Cu and 0.1 residual chlorine.
2.3.4 Other chemical treatments
Treatments for corrosion prevention may include the following chemicals:

- oxygen scavenger,
- biocide,
- corrosion inhibitor (for carbon and low alloy steels).
2.3.4.1 Oxygen scavengers (residual oxygen and chlorine content control)
Oxygen scavengers are typically used to complete oxygen removal after physical deaeration.
Ammonium bisulphite (NH4)HSO3, molecular weight 99, is the most used oxygen scavenger in water
injection systems; it is available as concentrated liquid solution. Sodium sulphite, Na2SO3 , molecular
weight 126, is also used combined with inorganic catalysers.
Dosage shall be based on the concentrations values of dissolved oxygen and chlorine. Chlorine
reacts first: accordingly, chlorine concentration shall be kept as low as possible to avoid excessive
consumption of scavenger.
Excessive dosage of oxygen scavenger shall be also avoided as it can enhance the seawater
corrosivity.
Procedures for monitoring of residual concentration of the oxygen scavenger shall be established in
accordance with the product suppliers and performed on a regularly basis.
2.3.4.2 Biocide
Injection of biocide may be considered downstream of deaeration tower to prevent biological activity,
MIC and corrosion under deposit in pipelines.
1
Gracki, J.A., R.A. Everett, H. Hack, P.F. Landrum, D.T. Long, B.J. Premo, S.C. Raaym akers, G.A. Stapleton and K.G.
Harrison “Critical Review of a Ballast Water Biocide Treatment Demonstration Project Using Copper and Sodium Hypochlorite”
September 2002. Michigan Environmental Science Board, Lansing. xii + 30p.
2
BMT Fleet Technology, Ltd. and ESG International, Inc. [2002]. [Draft] Final Report: Ballast Water Treatment “Evaluation
Using Copper and Sodium Hypochlorite as Ballast Water Biocides” April 12, 2002. Kanata, Ontario. 730p.
Rev. 0 April 2009
Biocides injection shall be considered in particular in case seawater is commingled with produced
water for water injection purposes.
2.3.4.3 Corrosion inhibitor
Corrosion inhibitor injection may be considered to control corrosion of carbon steel pipelines in case
corrosive produced water (e.g. containing CO2) is commingled with seawater for water injection
purposes (see also ENI Company Standard 02555.VAR.COR.PRG). Corrosion inhibitors are not
normally considered for routine treatment of seawater alone.
2.3.4.4 Other treatments
Seawater handling systems typically include packages for the injection of the following chemicals:
- antifoam;
- polyelectrolyte;
- scale inhibitors.
2.4 Seawater corrosion
Some parameters and factors have a significant impact on material selection in seawater systems;
main ones are:
- dissolved oxygen;
- microbial activity;
- chlorine;
- temperature;
- flow conditions;
- contaminants (as CO2 and H2S);
The forms of corrosion that metallic materials may experience in seawater service include:
- general corrosion;
- localised corrosion;
- galvanic effects;
- stress corrosion cracking;
- microbial corrosion.
The above aspects are briefly reviewed hereinafter; additional information are available in the ENI
Company Specification 02555.VAR.COR.PRG.
2.4.1 Dissolved oxygen
The oxygen dissolved in seawater has a strong oxidizing capacity and it is responsible of uniform
corrosion of carbon and low alloy steels and of localized corrosion on susceptible passive alloys.
In aerated seawater, oxygen corrosion of carbon and low alloy steels depends on oxygen
concentration, on temperature and on flow velocity (see the norm ENI 02555.VAR.COR.PRG for
algorithms available to calculate corrosion rate for different values of these parameters). Indicative
penetration rates are in the order of 0.1 0.5 mm/y or greater depending on water velocity and
temperature. Local penetration rates in the order of 1 mm/y can are experienced under deposits and
in correspondence to welds.
In deaerated seawater oxygen corrosion of carbon and low alloy steels is acceptable, provided the
deoxygenation treatment is properly performed and maintained.
2.4.2 Chlorine
Chlorine is almost invariably added to seawater as a biocide to prevent bio fouling and microbial
corrosion as discussed at paragraph 2.3.3.1. The dosage of the injected chlorine is such that a
residual amount survive in the system after being consumed by reaction with living organisms and
other organic compounds, deaeration process and oxygen scavenger. This residual chlorine should
Rev. 0 April 2009
be controlled in order to be maintained above a minimum value, to avoid any bacterial activity, and
below a maximum to avoid drawbacks on the materials and the environment.
Presence of chlorine has an important effect on the corrosion of materials. For carbon and low alloy
steels, chlorine enhances general corrosion adding up its oxidising contribution to the oxygen’s, in
the proportion given at paragraph 2.3.3.1. For most of the corrosion resistant alloys, the presence of
chlorine is critical in combination with the maximum temperature that the system may experience,
and is key for proper material selection. The synergistic effect of temperature with the high oxidizing
power of chlorine may promote pitting and crevice corrosion to many corrosion resistant alloys, which
are otherwise resistant to seawater (e.g. superduplex stainless steels).
2.4.3 Temperature
For carbon and low alloy steels, general corrosion by oxygen moderately increases with temperature.
The effect of temperature on localised corrosion of corrosion resistant alloys is more critical. The
occurrence of pitting and crevice corrosion of stainless steels and nickel alloys is in fact strongly
affected by temperature, particularly in combination with chlorine presence.
The typical stainless steel alloys that are considered for seawater service are those characterised by
a PREN ³ 40 (e.g. superduplex stainless steels and 6Mo austenitic stainless steels). These materials
are suitable for this service only within certain limits: at ambient temperature (within 20-30°C), they
resist also in presence of free chlorine and in stagnant conditions. At higher temperature (30 to 60°C)
a safe use of these materials may be considered provided that no chlorine is present. At higher
temperature, stainless steels are not resistant to hot seawater and alternative alloys as titanium
alloys or high nickel-molybdenum alloys are required.
Most seawater injection and fire-fighting systems operate at ambient temperature, but in seawater
cooling systems higher temperature can be met and material selection upgrading is required (e.g.
heat exchangers and downstream pipework).
2.4.4 Flow conditions
At stagnant or low velocity conditions marine growth easily develop with formation of solid deposits.
Presence of deposits promotes corrosion of carbon and low alloy steels by establishing anaerobic
conditions favourable to the growth of sulphate reducing bacteria (SRB). H2S is also produced by
microbial metabolism.
Stagnant condition is an aggravating factor for initiation of localised corrosion attacks (pitting and
crevice) on corrosion resistant alloys.
In flowing conditions, higher flow velocities enhance oxygen corrosion of carbon and low alloy steels
by increasing the oxygen flux diffusing to the corroding surface according to Fick’s law. Exceeding a
critical flow velocity threshold, erosion-corrosion condition may set-up, which result in metal wastage
by mechanical removal of protective layers of corrosion products or of the passive layer, with a sharp
increase of corrosion rate. The critical flow velocity depends on the metallic materials.
In carbon and low alloy steels piping systems conveying deaerated seawater a maximum flow
velocity of 8 ÷ 10 m/s is admitted, provided the fluid is free from solid particles.
For other metals the following limits apply (aerated and deaerated seawater):
- stainless steels:
3
no limits for corrosion
- copper-nickel alloys: 3-4.5 m/s;
- aluminium bronze: 2.5 m/s;
- aluminium brass: 2.4 m/s;
- titanium alloys no limits for corrosion.
3
Velocity limits can be needed for vibrations and noise.
Rev. 0 April 2009
2.4.5 Pollution by sulphides
Seawater contamination by sulphides is a frequent issue which may have different origins, as
industrial effluents, organic decomposition or sulphate reducing bacteria activity and is usually
accompanied by the reduction in the dissolved oxygen concentration, which increase in particular the
corrosion of copper alloys. Pollution may be systematic or cyclic, the former being evidently more
critical. In aerated seawater, even modest sulphides content, in the order of 1 ppm, can severely
accelerate the corrosion rates of copper alloys, including brasses and copper-nickel alloys. The
systematic contamination by sulphides leads to a breakdown of the passive layers that copper alloys
form in aerated seawater. In deaerated water the effect of sulphides are remarkably less severe.
2.4.6 Microbial activity
Sessile bacteria, dwelling on metallic surfaces, have the greatest impact on corrosion. Sulphate-
reducing bacteria (SRB) develop in anaerobic conditions and produce sulphides; they enhance
corrosion by the cathode of the local corrosion cells. SRB are found in the biofilms growing on metal
surfaces. The extent of the SRB colonization is estimated by the population density.
Microbial activity in seawater systems is controlled by chlorination and biocide injection.
Targets for bacterial population density:

sessile bacteria:
- SRB:
2 -2
< 10 cm
- aerobic bacteria:
2 -2
< 10 cm
planktonic bacteria:
- SRB:
-1
< 1 ml
- aerobic bacteria:
4 -1
< 10 ml .
2.4.7 Contaminants
In commingled systems with seawater mixed to produced water, corrosion can be enhanced by the
presence of dissolved CO2 and H2S. Corrosion forms shall be evaluated individually by dedicated
corrosion studies.
2.4.8 Galvanic corrosion
Galvanic corrosion occurs by electrically coupling different metals exposed to the same electrolytic
environment (see the norm ENI 02555.VAR.COR.PRG for mechanism and influencing parameters).
Raw seawater represents a severe environment for galvanic corrosion because of presence of
oxidizing compounds, like dissolved oxygen and chlorine, and because of the low resistivity.
Free corrosion potential depends on metallic material, dissolved oxygen concentration and
temperature. Indicative ranges for alloy families used in aerated seawater systems are shown in
Figure 2.6. Graphite, used for gaskets, in seawater has a free corrosion potential higher than
titanium, of about +500 mV vs. SCE.
Rev. 0 April 2009
4
Figure 2.6 – Free corrosion potential in aerated seawater.
Galvanic corrosion effects in aerated seawater are low and acceptable in the following cases:
- coupling of different types of stainless steels;
- coupling of titanium with superduplex and 6 Mo stainless steels,
and they are risky in the following cases:

- copper alloys coupled to stainless steels and to titanium;
- carbon and low alloy steels coupled to any passive metals.
To prevent galvanic corrosion in aerated seawater, insulating spools shall be installed between
dissimilar metals. The insulating spool shall be made of the most noble metal of the couple and it
shall be coated inside with an organic coating resistant to the exposure environment. The length of
the isolated spool shall be designed based on coupled metals, fluid resistivity and pipe diameter.
In presence of galvanic couples, the use of organic coatings, or other lining systems that may fail or
damages, applied onto the less noble metal in the couple to prevent corrosion is to be avoided,
unless supported by careful corrosion assessment.
In same cases, e.g. for components such as valves and pumps, material selection takes advantage
from galvanic effects to use material not resistant to pitting corrosion (typically steels with PREN < 40
as AISI 316) but that result cathodically protected by electrically coupled components made in a less
noble material (typically copper alloy or cast iron), whereby localised corrosion is prevented. This
solution is viable provided the area ratio is such that the accelerated corrosion onto the less noble
material is acceptable.
Use of corrosion allowance extra-thickness to prevent galvanic corrosion is not normally a viable
solution. Only in particular cases, where the corrosion rates resulting from galvanic effect are not
severe due to favourable area ratio, the use of corrosion allowance as a mitigation action can be
considered if supported by a documented corrosion analysis.
4
Re-elaborated from R. Johnsen, ‘Experience with the use of copper alloys in seawater in the Norvegian Sector of the
North Sea’, Proceedings of the EuroCorr 2004 Conference, Nice, September 12-16, 2004.
Rev. 0 April 2009
2.4.9 Stress Corrosion Cracking
Stress corrosion cracking is a well known issue in presence of H2S (sulphide stress cracking “SSC”)
and in presence of chlorides (chloride stress corrosion cracking “CSCC”).
The main influencing parameters are:

- presence of dissolved oxygen;
- tensile stress conditions;
- cold-working conditions;
- welds are preferential sites for CSCC initiation because of residual stress conditions and because
of their metallurgical criticality.
For seawater service, sulphide stress cracking “SSC” is normally not an issue due to the absence of
H2S. In some particular cases however H2S may be present, e.g. seawater commingled with
produced water, material application limits and material requirements shall comply with the
requirements provided by the ENI Company Specification 02555.VAR.COR.PRG and by the ISO
Standard 15156 / NACE MR0175.
Chloride stress corrosion cracking “CSCC” is a potential concern for stainless steels in seawater at
high temperature (above some 60-80°C). However, in practice, CSCC is rarely a factor limiting
materials applicability, because sensitive materials often fails by pitting or crevice corrosion at
conditions promoting CSCC.
The AISI 300 series austenitic stainless steels (i.e. AISI 304 and 316), are highly sensitive to
localised corrosion and CSCC, and for this reason they shall not be applied in seawater service.
High alloy austenitic stainless steels, characterised by a nickel content above 15%, display a higher
resistance to CSCC, which is comparable to duplex stainless steels.
Duplex stainless steels display a higher resistance than austenitics: grades suitable for aerated
seawater are superduplex (PREN > 40) within the domain of applicability for localised corrosion, i.e.
at ambient temperature for chlorinated water, and up to some 70-80°C in the absence of chlorine.
Within these envelope of service conditions they are also resistant to CSCC, which occurs in the
range 80-100°C and above.
Nickel alloys are not sensitive to CSCC in seawater service.

Rev. 0 April 2009
3. METALLIC MATERIALS
3.1 Forewords
The metallic materials normally considered for the main processing items (e.g. pipework and
equipment) in seawater service include:
- carbon and low alloy steels (limitedly to deaerated seawater or in special cases for aerated
seawater),
- duplex stainless steels,
- high-alloy austenitic stainless steels,
- copper-nickel alloys,
- titanium alloys.
For specific components or ancillary parts of the main processing items (e.g. pumps components,
cast bodies, valve trims etc.) the following materials may also be used:
- nickel alloys;
- cast iron;
- copper alloys (brasses and bronzes).
3.2 Carbon and low alloy steels
Carbon and low alloy steels include a number of products providing a wide range of mechanical
properties and applications. From the viewpoint of the resistance to general corrosion, however, they
all show similar performance. A slightly higher resistance to general corrosion is indeed attributed to
low alloy steels containing an amount of chromium of about 0.5-1%. However the gain in corrosion
resistance imparted by this small amount of chromium (which should not be exceeded to avoid risk of
localised corrosion) is limited and not clearly quantified. It may represents a preference criteria but it
is not so substantial to represent a consideration factor in deciding the applicability of this class of
materials. For these reason, in this document no distinction is made among the specific steel types or
products with respect to corrosion performance. The term carbon steel will be hereinafter used to
intend plain carbon steels and low alloy steels
General corrosion of carbon steel in seawater is controlled by the availability of oxygen to the metal
surface. In stagnant aerated seawater, carbon steels corrode uniformly at a rate of 0.1 ÷ 0.2 mm/y,
reflecting the oxygen level and temperature variations in different locations, but local corrosion
attacks at higher rates may also occur. In flowing systems, corrosion rate is enhanced by flow
velocity and an average penetration rate in the order of 0.5 ÷ 1 mm/y may be assumed. Local
penetration rates in the order of 1 mm/y or greater can are experienced under deposits. Welds are
also preferential sites of attack, due to the possible formation of deposits, hold by the weld beam,
local turbulence and possibly by galvanic effects between the base metal and the weld deposit.
The above corrosion rate values can hardly be handled by corrosion allowance, and in consideration
of the risk of localised attacks above highlighted carbon steel are normally not considered for aerated
seawater service. In this service, they may be taken in consideration only in particular cases, e.g.
when the requested service life is very limited and with low reliability requirements.
Alternative methods to control internal corrosion such as chemical treatments and internal
galvanizing are poorly effective and represent at best a modest palliative rather than sound design
solutions. Galvanizing confers only limited benefit as corrosion of zinc is very sensitive to chlorides
and increases with flow velocity. The zinc layer, normally used in piping, may extend the life of the
pipe for about six months. Internal organic coatings, by itself, are not a reliable barrier for corrosion
(subject to breakdown and/or local damages) and can be considered only in combination with
cathodic protection. This is typically the case of tanks or vessels, but not for pipe systems where
internal CP is not practical.
Cement lined carbon steel pipe was used in the past for aerated seawater with poor success, due to
problem at field joints and local detachment of the cement lining with consequent accelerated
Rev. 0 April 2009
corrosion due to galvanic effect between the passive steel covered by the alkaline cement and the
active bared steel.
In deaerated seawater oxygen corrosion is acceptable provided the deoxygenation treatment was
properly performed, by limiting the maximum residual oxygen content within some 20ppb, and strictly
controlled, by avoiding substance fluctuation and permanence above the target threshold. Their main
area of application is in water injection systems downstream deoxygenation treatment.
Microbial corrosion occurs on un-treated seawater at corrosion rate as high as 1 mm/y.
In summary, the following considerations can be drawn for carbon and low alloy steels in seawater
service:
- they are not normally applicable for aerated seawater service, with some particular exceptions,
e.g. short design life and low reliability requirements;
- they represent a cost effective choice in deaerated seawater service, provided effective
deoxygenation is guaranteed;
- in case of seawater commingled with production water, suitability to CO2 and H2S corrosion shall
be verified by corrosion assessment (see ENI Company Standard 02555.VAR.COR.PRG)
- the use of internal coating, chemical treatments for corrosion control or internal galvanising to
extend the domain of applicability is to be careful evaluated for the limited benefits which may be
achieved
- the use of carbon steel with internal liners is discussed at Section 4.
Application limits for carbon and low alloy steels are summarized in the below table.
Table 3.1 - Carbon and low alloy steels. Application limits in seawater systems.
Corrosion rate Applicability
Service Corrosion forms Remarks
mm/y limitations
Localised corrosion expected at
oxygen corrosion
welds and under deposits
normally not
Can be considered for short
erosion corrosion 0.3 - 0.5 uniform applicable for
Aerated seawater service life
≈ 1.0 localised aerated seawater
service Limited benefits with internal
MIC organic coatings, galvanising or
corrosion inhibitors
Physical deaeration treatment
cO2 < 20 ppb
oxygen corrosion completed with oxygen
cCl2 < 0.2÷0.3 ppm
< 0.10 scavenger
biocide treatment Periodical cleaning to avoid
Deaerated seawater MIC
performed microbial growth under deposits
Flow velocity limit corresponding
erosion corrosion - flow vel. < 10 m/s to an erosion constant of 300
2 ½
(kg/m∙s ) in the API model.
3.3 Cast Irons
Cast irons are iron carbon silicon alloys with carbon, present as graphite (free carbon) or iron carbide
(cementite), at a content between 2 to 4%.
From corrosion viewpoint, cast irons can be classified as:

- plain cast iron or low-alloy cast irons;
- high-alloy cast irons (in particular austenitic, “Ni-Resist” type),
while, based on microstructure, they are classified as:

- white cast iron: carbon is present as cementite (FeC3);
- malleable cast iron: carbon is transformed from cementite to graphite nodules by means of a
suitable heat treatment;
- grey cast iron: most of carbon is present as graphite flakes;
- spheroidal cast iron: carbon is transformed in graphite spheroids during solidification.
Chemical composition of some cast irons for seawater applications are reported in ANNEX A.
Rev. 0 April 2009
3.3.1 Low alloy cast iron
Characteristic corrosion form of plain or low-alloy cast iron in sea water is the general type, both
uniform and non-uniform. Main corrosion causes are: oxygen and bacteria (in particular: sulphate
reducing bacteria).
From the point of view of the corrosion behaviour, low alloy cast iron can be considered equivalent to
carbon or low alloy steels, examined in paragraph 3.2.1; however they show a lower corrosion rate in
seawater (for example: in aerated sea water corrosion rates range between 50 to 100 mm/y).
A corrosion related effect is the superficial graphitization that concerns mainly spheroidal, malleable
grey cast iron types, and also, to a lesser degree, white cast iron.
Graphitization occurs through the selective dissolution of ferritic phase that leads to the superficial
graphite enrichment. In this condition, cast iron becomes cathodic to many materials, for instance
copper alloys, then giving galvanic corrosion when coupled.
3.3.2 High-alloy cast iron
Among this family, cast irons containing nickel above 13%, commercially designated as “Ni-Resist”
are of particular interest for their corrosion resistance properties.
The high nickel content provides a resistance to general corrosion; in aerated sea water, corrosion
rate is in the order of 20-50 mm, i.e. an order of magnitude lower than carbon and low alloy steels and
about half compared with low-alloy cast iron. Their austenitic microstructure is not susceptible to
graphitization.
Coupled with stainless steels (typically in valves and pumps), austenitic cast irons provide suitable
cathodic protection, preventing pitting and crevice attack with no major drawbacks on corrosion rate.
3.4 Stainless steels
Austenitic stainless steels (type 316 and similar) may resist to flowing seawater but are rapidly prone
to localised corrosion in stagnant or low flow conditions, particularly at crevices such as flange
surfaces and under deposits (even in deaerated systems pitting attack may occur in case of
temporary upsets or loss of control of the deaeration unit).
The applicability of stainless steels for seawater service is restricted to alloy with adequate resistance
to localized corrosion, which is identified by a Pitting Resistance Equivalent Number PREN which
shall not be lower than 40 (see paragraph 3.4.3). An exception to this general rule is permitted if the
material is cathodically protected (e.g. by coupling with less noble materials or sacrificial anodes or
impressed current systems), in which case pitting corrosion is prevented and plain stainless steels or
low-molybdenum nickel-base alloys may be considered.
Applicable stainless steels fall into three categories:

- ferritic stainless steels containing 25 to 29 % chromium, 3 to 4 % molybdenum with titanium or
niobium for stabilisation and possibly up to 4 % nickel.
- high alloy austenitic steels containing about 18 to 25 % nickel, 20 % chromium, 6 % molybdenum
and 0.1 to 0.2 % nitrogen.
- superduplex steels containing 25% chromium, 5 to 7% nickel, 3 % molybdenum and 0.15 to 0.2 %
nitrogen.
The main advantages of these materials in seawater service are their immunity to impingement
attack at high velocity and their good mechanical properties, with consequent weight/cost saving by
reduced pipe size and thinner wall compared with competitive materials, the pipe size being
governed by considerations of the economics of pumping, noise generation, vibration (number of
supports), etc. rather than by material limitations.
Rev. 0 April 2009
Limitations in the selection of the stainless steels containing molybdenum are:

- The resistance of the materials to crevice corrosion and pitting in hot service is not well defined
(hot seawater and chlorination).
- There may be some doubts about the availability from sufficient reputable suppliers, or requisite
quantities of materials, including all the components that go to make up complete systems
fabricated from compatible materials. Workability and weldability of ferritic stainless steels.
- Stainless steels readily suffer micro and macro bio-fouling in natural seawater and unless steps
are taken to control fouling, systems would readily foul. If chlorination is applied as a fouling
control, the susceptibility of the stainless steels to crevice corrosion and pitting is increased and is
a strict limit at temperature above 30°C.
Stainless steels for seawater applications is therefore restricted to high-alloy austenitic grades with
6% Mo and superduplex. Martensitic stainless steels shall not be used for their poor resistance to
localised corrosion, particularly in stagnant condition. Ferritic stainless steels have limited application,
mostly due to their fabricability limitations.
3.4.1 High-alloy austenitic stainless steels
High-alloy austenitic grades include a number of alloys with higher contents of chromium, nickel and
molybdenum compared with convention austenitic stainless steels as type 316; some grades are
classified as nickel alloys. They offer improved resistance to localised corrosion and to chloride
stress corrosion cracking.
High-alloy austenitic stainless steels that can be considered for seawater service are those
characterised by a PREN equal or above 40. The most common grade used for this service is the
6Mo type and its derivations (e.g. 254SMO UNS S31254 and 654SMO UNS S32654 for improved
localised corrosion resistance). Chemical composition data for a several alloys are reported in Annex
A.
The 6Mo type materials have been specifically developed for application in aerated seawater. Their
chemical composition, with 19-22% Cr, 6% Mo min. and addition of N and Cu guarantees a PREN
(see Par. 3.4.3) above 40, which is considered the lower limit for applicability in aerated seawater at
ambient temperature. Their corrosion behaviour is comparable to superduplex stainless steels, and
also in this case the presence of chlorine at temperature above 20-30°C compromises their
resistance to localised corrosion. The same domain of applicability of superduplex stainless steels
are proposed for 6Mo type austenitics.
3.4.2 Duplex stainless steels
Duplex (austenitic-ferritic) stainless steels are classified into the following types:
- duplex (22Cr),
- superduplex,
- lean duplex,
- hyper duplex.
22Cr duplex are the most common grades of the duplex family, with about 70 % of the total delivery.
Typical grades have 21 to 23 % Cr, 2.5 to 3.5 % Mo and 4.5 to 6.5 Ni. New generation alloys contain
N and the tendency is to increase the N content. Nitrogen allows a better control of the metallurgical
structure in the HAZ, to keep the C content at low levels, to maintain the ferrite/austenite ratio in the
correct range and as an overall result it contributes increasing the pitting resistance. 22Cr provide a
resistance to localized corrosion and to stress corrosion cracking in chloride containing environments
remarkably higher than austenitic type 316, but still not sufficient for aerated seawater service.
Superduplex stainless steels are characterised by an increased contents of Cr, Ni and Mo (about
25% Cr, 4% Mo and 7% Ni) and the addition of N, such that it result a PREN which is not lower than
40, which is the lower limit to provide corrosion resistance to aerated seawater at ambient
temperature.
It worth mention that alloys with a composition similar to superduplex but with a PREN lower than 40
(and with no nitrogen), also designated 25Cr duplex stainless steels, represent old fashion
Rev. 0 April 2009
improvements of 22Cr duplex now superseded by superduplex types and not adequate for raw
seawater application.
Lean duplex types represent an attempt to match the properties of the standard 22Cr grade by alloy
modifications to minimise the use of expensive alloying elements. The prototype alloy is the grade
known as 2304, with 23% Cr, 4% Ni and 0.2 Mo. New alloys are under development and evaluation,
with low Cr+Mo contents, N around 0.2% and with Ni replaced by Mn (average price of Ni and Mo
has significantly increased in last years). The target for lean duplex is to compete with the austenitic
grades type 316 and even 304.
Hyper duplex are new generation alloys with improved mechanical properties and corrosion
resistance. With a PREN much above 40, they extend the application of duplex in seawater at
temperature greater than ambient.
Duplex stainless steels have higher mechanical properties than austenitics (see Table 3.2), which
provides cost and weight benefits by thickness reduction.
Table 3.2 – Stainless steels. Mechanical properties of representative grades.

0.2% Yield strength Tensile strength Elongation
Type UNS
MPa (min.) MPa (min) % (min.)
316L S31603 220 515 45
904L N08904 220 500 35
6 Mo S31254 300 650 35
28 Cr N08028 215 550 40
S31803 450 680 25
Duplex 22Cr
S32205 550 760 15
Superduplex S32750 550 800 25
S32760 550 750 25
Hyper duplex S32906 650 800 25
3.4.3 Localised corrosion resistance
Differently from carbon and low alloy steels, stainless steels exhibit a full resistance to general
corrosion in seawater. The typical occurring corrosion mechanisms affecting stainless steels are
localized corrosion, pitting and crevice, and stress corrosion cracking.
Localised pitting and crevice corrosion is mainly associated with the presence of chlorides in the sea
water and is the primarily concern using CRAs in seawater systems. Chlorides promote local
depassivation of the oxide layer and develop localised corrosion which in particular conditions, not
frequently met in seawater systems, may also initiate stress corrosion cracking.
Comparative resistance of stainless steels to localised corrosion is assessed using the pitting
resistance equivalent number (PRE or PREN), calculated from the alloy chemical composition. The
following formula is used (see also ENI 02555.VAR.COR.PRG).
PREN = Cr + 3.3(Mo + 0.5W) + 16N (stainless steels)
where molybdenum and nitrogen contents are 'weighted' to take account of their influence on pitting
corrosion resistance. Some formulas weight nitrogen more, with factors of 30, but as the actual
nitrogen levels are quite modest in most stainless steels, this does not have a dramatic effect on
ranking.
The above formula was setup to fit iron base stainless steels. For high nickel alloys it yields results
that are not reliable and its use is not recommended, particularly for high molybdenum alloys, where
its contribution tends to be overrated.
Rev. 0 April 2009
In seawater a minimum PREN value of 40 is required. Duplex steels grades with a PREN of 40 or
more are known as superduplex.
Table 3.3 – PREN calculated for main stainless steel.

PREN
UNS Type Material
min max nominal
Austenitic 316L
S31603 24 29 25
Stainless Steel
S31803 Duplex (22Cr) 31 38 35
2205
S32205 Stainless Steel 34 38 35
S32750 2507 38 44 42
S32760 Superduplex Zeron 100 40 46 44
S32520 Stainless Steel 52N+ 37 48 44
S39274 DP3W 39 47 44
S32304 Lean duplex 2304 24 30 25
S32101 Stainless Steel LDX 2101 29 32 30
Hyper duplex
S32707 2707 - - 49
Stainless Steel
S31254 6Mo High-Alloy 6Mo (254SMO) 42 45 43
Austenitic Stainless
S32654 Steel 654SMO - - 54
High-Alloy Austenitic
N08904 904L 32 40 35
Stainless Steel
N08028 Alloy 28 - - 32
Nickel Alloy
N08825 Alloy 825 - - 33
Chemical composition of most common copper alloys used in seawater service are reported in
ANNEX A.
3.5 Copper alloys
Copper (alloys with 99.3 min. of copper) is not used in seawater applications, mainly because of its
poor resistance to erosion. Several alloys, however, are available for marine application, like
brasses, bronzes and copper-nickels (see Table 3.4).
Rev. 0 April 2009
Table 3.4 – Copper alloys families.

Cu alloy Families Main features Types and alloying elements
Brasses Alloys containing zinc as main Wrought alloys:
alloying element, up to 45% - Cu-Zn-Pb (leaded brasses);
maximum. - Cu-Zn-Sn (tin brasses).
Cast alloys:
- Cu-Sn-Zn (red, semi-red and yellow brasses)
- Cu-Mn and Cu-Mn-Pb bronze (high strength yellow brasses);
- Cu-Zn-Si (silicon brasses and bronzes);
- Cu-Bi and Cu-Bi-Se.
Bronzes The term originally indicated Wrought alloys:
alloys with tin as principal alloying - Cu-Sn-P (phosphor bronzes)
element; today, it is used to - Cu-Sn-Pb-P (leaded phosphor bronzes)
identify other alloys containing up - Cu-Al (aluminum bronzes)
to 12% of any alloy element, - Cu-Al-Ni (nickel aluminum bronzes)
except zinc. - Cu-Si (silicon bronzes)
Cast alloys:
- Cu-Sn (tin bronzes);
- Cu-Sn-Zn (gunmetal);
- Cu-Sn-Pb (leaded and high leaded tin bronzes)
- Cu-Sn-Ni (nickel-tin bronzes)
- Cu-Al (aluminum bronzes)
- Cu-Al-Ni (nickel aluminum bronzes)
Copper-Nickel Alloys with nickel as main alloying Wrought alloys:
element, with or without other - CuNi 90/10
designated alloying elements. - CuNi 70/30
Cast alloys:
- CuNi 70/30
Leaded coppers Include a series of cast alloys of
copper with 20% or more lead,
sometimes with a small amount of
silver, but without tin or zinc.
In the UNS designation system, numbers from C10000 through C79999 denote wrought alloys and
numbers from C80000 through C99999 denote cast alloys. Designation of main families are reported
hereinafter.
alloys (wrought) UNS number composition

- copper C10100-C15760 >99% Cu
- brass C20500-C28580 Cu-Zn
- tin brass C40400-C49080 Cu-Zn-Sn-Pb
- phosphor bronze C50100-C52400 Cu-Sn-P
- aluminium bronze C60600-C64400 Cu-Al-Ni-Fe-Si-Sn
- others copper-zinc alloys C66400-C69900 -
- copper-nichel C70000-C79900 CuNi-Fe
alloys (cast) UNS number composition

- red brass (gunmetal) C83300-C85800 Cu(75-89%)-Zn-Sn-Pb
- yellow brass C85200-C85800 Cu(57-74%)-Zn-Sn-Pb
- aluminium bronze C95200-C95810 Cu-Al-Fe-Ni
Chemical composition of most common copper alloys used in seawater service are reported in
ANNEX A.
Although several copper alloys are used with seawater, especially for valves and pumps
components, two groups of materials are particularly used for seawater service in the oil and gas
industry, that are:
- nickel aluminum bronzes,
- copper nickel alloys.
Rev. 0 April 2009
3.5.1 Aluminium and nickel-aluminum bronzes
Aluminium bronze (duplex Cu Al alloy with 8 ÷ 11 % Al) is one of the most used materials for valves
and pumps fabrication.
In nickel aluminium bronzes, Ni (4 ÷ 6 %) and Fe (4 ÷ 5.5 %) are added to improve the mechanical
properties. They offer an excellent resistance to corrosion-erosion and to oxidation at high
temperature.5 Nickel also provides resistance to dealuminization in seawater.
Bronzes shall not be used in sulphide contaminated environments.
3.5.2 Copper nickel alloys
The most common alloy of the family is the alloy CuNi 90/10 (C70600), with 9.0 to 11.0 % Ni. Small
quantities of Fe (1.0 to 1.8 %) and manganese are important additions to provide the best
combination of resistance to flowing seawater and corrosion. It has ha single phase with face
centered cubic structure that provides complete hot and cold workability. No phase transformations
occur during welding with no need of post weld heat treatments.
The alloy has been extensively used for aerated seawater piping in offshore platforms. It provides
adequate corrosion resistance, good mechanical properties and tenacity, good weldability.
In aerated seawater CuNi 90/10 alloy provides high resistance to general corrosion (less than 10
µm/y by long term exposure) and to localized corrosion, and it is fully resistant to stress corrosion
6
cracking. The main issues for corrosion are:
- localized corrosion in sulphides polluted water: pitting corrosion occurs in form of shallow attacks,
- erosion at high flow velocities,
- effect of high contents of residual chlorine,7
- galvanic corrosion by coupling with more noble alloys, in particular stainless steels and titanium
(see Par. 2.4.8 in this document).
Alloy CuNi 70/30 contains some 30% of nickel and, as per the 90/10 type, the same additions of iron
and manganese. Compared with the cheaper 90/10, the 70/30 displays higher mechanical properties
and withstands higher flowing velocities, and similar corrosion resistance.
Copper-nickel alloys suitable for welding shall be limited in their content of Fe, Mn, C, Zn, Pb and S.
These elements, and particularly iron, can also arise from external contamination and therefore
precautions are required in controlling the forming and welding environment to avoid an impairment
of the corrosion resistant properties at weld areas. Otherwise, these alloys are readily weldable by
most common methods using 70/30 consumables in both cases. For their larger tolerance to iron
dilution effects, 65% nickel-copper consumables are used to weld copper-nickel with steel.
In aerated sea water copper alloys form a layer of corrosion products that ensures a good resistance
to general corrosion (average penetration rate is less than 50 mm/year). Formation of the protective
film depends on alloy composition, temperature and flow rate. At low ambient temperature it may
take a period of weeks or months, whereas few hours are sufficient at higher ambient temperature
(about 30°C): this aspect may worth consideration.
Copper alloys are susceptible to pitting corrosion, in particular at low flow velocity (below 0.6-0.9 m/s)
and if sulphides are present (polluted waters).
5
J.R.C. Strang, Cast valve materials for seawater service: nickel-aluminium bronze and its rivals’. Valve World 2006
Conference, 7-9 November 2006, Maastricht, Netherlands.
6
For an updated review on corrosion performance of CuNi 90/10, see: W. Schleich, “Application of copper-nickel alloy
C70600 for seawater service”, Corrosion 2005 Conference, NACE Int., paper N. 05222.
7
The effect of residual chlorine un flow resistance of CuNi 90/10 is debated. Tests results reported by Shleich et al. seem to
negate the effect of chlorine on erosion corrosion occurrence (see: W. Schleich, R. Feser, G. Shmitt, T. Gommlich, S.
Gunther “Effect of seawater on the erosion corrosion behaviour of copper-nickel alloy CuNi90/10”, Corrosion 2008
Conference, NACE Int., paper N. 08231.
Rev. 0 April 2009
The alloys containing more than 15% of zinc (brasses), are susceptible to selective corrosion of the
zinc, causing the formation of a porous superficial layer of copper and copper oxides; the progressive
penetration of the attack can lead to the failure of the component.
In presence of ammonia, ammonic salts or mercury salts, copper alloys and especially brass, are
susceptible to stress corrosion cracking.
Copper alloys offer excellent resistance to microbial corrosion.
As far as erosion corrosion is concerned, copper alloys are more susceptible than stainless steels;
the typical corrosion attack morphology is the so-called horse shoe. Application limits are reported as
critical admitted velocity to prevent erosion corrosion initiation. Typical values are reported here
below.
Alloy UNS number max flow rate (m/s)

- copper C12200 0.6
- silicon bronze C65100 0.9
- admiral brass C44300 1.2
- aluminium brass (As) C68700 2.4
- aluminium bronze C60800 2.5
- cupronickel 90-10 C70600 3.0
- cupronickel 70-30 C71500 4.5
Copper alloys in sea water promote galvanic corrosion to carbon and low alloy steels (see Par. 2.4.8
in this document).
3.6 Nickel alloys
Nickel base alloys are highly resistant to general corrosion and stress corrosion cracking. Resistance
to localised corrosion depends on the specific alloys within this family of materials and it is the key
property for the selection of this class of materials in seawater applications.
The class of nickel base alloys represents a continuity with that one of high-alloy austenitic stainless
steels, and in some cases the classification within these two categories is not clearly defined. The
category of nickel base alloys may be sub-grouped based on their chemistry or based on the heat
treatment. One method to identify the main groups is based on the Mo content in the alloy, which
distinguishes three groups:
- alloys with some 3%Mo,
- alloys with some 6-9%Mo,
- alloys with 16%Mo.
A further group of nickel alloys used with seawater is represented by Monel alloys, which are nickel-
copper alloys with about 70%Ni, 30%Cu. They are resistant to localised corrosion but not immune to
pitting in stagnant conditions which may promote biofilms formation and pit initiation. The likelihood of
pitting initiation is low and the pitting penetration rate is in any case limited within some 75 µm/y and
therefore acceptable in most cases. When coupled with stainless steels in raw seawater severe
galvanic corrosion may occur. They are sensitive to localised corrosion and cracking in presence of
sulphides (e.g. polluted water)
Low molybdenum types (indicatively lower than 3-4%) are prone to localised corrosion at
unfavourable combinations of temperature, chlorides concentration and presence of oxidising agents,
i.e. oxygen and particularly chlorine.
Similarly than in the case of stainless steels, only the alloys with a molybdenum content above some
6% (PREN > 40) may be applied in raw seawater, where they withstand also stagnant conditions.
Their limitations in temperature and presence of free chlorine are similar to stainless steels with
comparable PREN, but at a cost that does not justify their use.
Rev. 0 April 2009
In general terms, from the point of view of localised corrosion, the nickel alloys with about 3Mo
behaves similarly to duplex 22Cr, the 6-9Mo types similarly to superduplex (and high-alloy austenitic
steels with similar Mo content) and the alloys with 16%Mo are intermediate between the superduplex
or highest alloyed stainless steels and titanium. Considering the cost of key elements in the alloy,
they do not generally offer advantages over the correspondent group of the duplex stainless steels,
which are therefore normally preferred (i.e. 22Cr or lean duplex for deaerated seawater and
superduplex for raw aerated seawater).
Nickel base alloys find application in seawater service when the use of duplex stainless steels or
titanium is limited by fabrication reasons or in presence of H2S beyond the levels tolerated by
stainless steels for sulphide stress cracking.
Monel are used as an expensive alternative to copper alloys when a high resistance to impingement
attack or cavitation is required. They are also used for heat exchanger tubes.
In the above cases the following nickel alloys are selected:
- weld overlaid components: typical nickel alloy used for weld deposits are Alloy 625 or Alloy 725
- clad components
· in raw seawater: typical nickel alloy solution is Alloy 625
· in treated (deaerated) seawater: Alloy 825 may be considered
- ancillary components (e.g. valve trims, pump’s shaft and impeller)
· in raw seawater: typical nickel alloy solution is Alloy 625 or 725/716, Monel
· in treated (deaerated) seawater: typical nickel alloy solution is Alloy 825, 718 or 925
- chlorinated seawater at warm temperature (30-50°C): typical nickel alloy solution is Alloy C276
Main alloys used for seawater service are reported in ANNEX A.
3.7 Titanium alloys
3.7.1 General
Titanium is a material combining high strength, low density and excellent corrosion resistance.
Titanium, like stainless steels, displays a passive behaviour. The oxide film is more protective than in
the case of stainless steel, and it typically performs well in highly oxidizing media, e.g. hot chlorinated
seawater, that cause pitting and crevice corrosion in stainless steels and high nickel alloys. Pure
titanium is however not immune to seawater corrosion if the temperature exceeds about 110°C, in
which case alloying is required.
Titanium can be strengthened greatly through alloying and, in some of its alloys, by heat treatment.
Among its advantages for specific applications are: good strength-to-weight ratio, low density, low
coefficient of thermal expansion, excellent corrosion resistance, good toughness, and low heat-
treating temperature during hardening.
Titanium is fully resistant to natural seawater regardless of chemistry variations. In the sea, titanium
alloys are immune to all forms of localized corrosion and microbiological induced corrosion, and can
withstand seawater impingement and flow velocities in excess of 30 m/s, abrasion and cavitation.
Fatigue strength and toughness of most titanium alloys are also unaffected in seawater and many
titanium alloys are immune to seawater stress corrosion.
When in contact with other metals, titanium alloys are not subject to galvanic corrosion in seawater.
However, titanium may accelerate attack on active metals such as steel, aluminium and copper
alloys. The most successful strategies eliminate this galvanic couple by using more resistant
compatible passive metals with titanium, all-titanium construction, or dielectric (insulating) joints.
Other approaches for mitigating galvanic corrosion have also been effective: coatings, linings and
cathodic protection. Embrittlement conditions for titanium alloys can result in presence of a galvanic
contact with carbon or low alloy steel, in particular above room temperature, aggravated by presence
of H2S due to titanium hydride formation. Normally, titanium alloys induce galvanic corrosion on
coupled alloys.
Rev. 0 April 2009
3.7.2 Titanium and its alloys
Titanium and its alloys are typically divided into groups which take into account unalloyed titanium
(commercially pure titanium) and three groups of alloys based on their microstructure which in turn
result in differences in fabrication and property characteristics.
Table 3.5 – Titanium and its alloys
Unalloyed Titanium Commercially Pure Titanium

Ti-5A1-2.5Sn (Alpha)
Alpha and Near-Alpha Titanium Alloys Ti-6A1-2Sn-4Zr-2Mo (Near-Alpha)
Ti-8A1-1Mo-1V (Near-Alpha)
Ti-6A1-4V
Alpha-Beta Titanium Alloys Ti-6A1-6V-2Sn
Ti-4.5Al-3V-2Fe-2Mo
Ti-13V-11Cr-3A1
Beta, Near-Beta, and Metastable Titanium
Ti-15V-3Cr-3Sn-3A1
Alloys
Ti-10V-2Fe-3A1
The material properties of titanium and its alloys are determined mainly by their alloy content and
heat treatment, both of which are influential in determining its allotropic forms. Under equilibrium
conditions, pure titanium has an “alpha” structure up to 880°C, above which it transforms to a “beta”
structure. The inherent properties of these two structures are quite different. Through alloying and
heat treatment, one or the other or a combination of these two structures can be stabilised and made
to exist at ambient or service temperature, and the properties of the material vary accordingly.
Titanium Grade 1 to 4 are commercially pure (CP) titanium with specific limitation of O, N, C, H, Fe
and residuals. Grade 2 is the most widely used commercially pure titanium grade. Grades 7, 11, 16,
17 are CP titanium with small addition of palladium (some 0.2%). Grades 26 and 27 are CP versions
with small additions of ruthenium with improved resistance to localised corrosion.
Grade 5 is a Ti-6Al-4V alpha/beta alloy which is by far the most widely used titanium alloy. Grade 23
and 29 are Extra Low Interstitial “ELI” (O, N, C) versions of Grade 5 offering improved stress
corrosion cracking resistance and the latter, with additions of ruthenium, improved resistance to
localised corrosion.
Grade 12 is a Ti-0.3Mo-0.8Ni near alpha alloy exhibiting superior crevice corrosion resistance.
Grade 19 (Beta C) is a Ti-4Al-8V-6Cr-4Mo-4Zr meta-stable alloy age-hardenable to a wide range of

strength with superior resistance to localised corrosion and stress corrosion cracking at high
temperature.
Titanium and its alloys recently expanded their application in the oil and gas industry, particularly in
offshore systems. Main feature of titanium are:
- low density (about 60% with respect to steel based alloys); this allows to reduce weight on
offshore platforms;
- high resistance to general and pitting corrosion up to 100°C or more, with no need of corrosion
allowance;
- resistance to crevice corrosion up to 70 ÷ 80 °C. Grade 2 is susceptible to crevice corrosion if T >
70°C and pH < 5; Grade 12 is resistant up to pH = 3 and up to 300°C.
Main alloys are reported in ANNEX A.

Rev. 0 April 2009
4. NON METALLIC. COMPOSITES. LINERS
Plastics or reinforced plastics may be attractive solutions, but in some applications there are serious
doubts about the suitability of these materials. These are mainly centred around:
a) Availability of satisfactory jointing and fabrication procedures.
b) The long term durability under a range of environmental conditions.
c) The vulnerability of the materials in the event of fire.
d) Poor shock-resistance.
Because of these considerations plastics are likely to be of restricted importance for seawater
systems, but may be of use for some non-critical applications.
4.1 Plastic lining
Plastic-lining consists of a plastic liner fit into a metallic (usually carbon steel) body, thus combining
the mechanical properties of metal with the inherent corrosion resistance of the properly selected
plastic liner. The technology is well established in the chemical process industries, especially for
piping and valves handling corrosive or highly pure fluids. A number of plastic materials are available;
the most common ones are:
- PE (polyethylene),
- PP (polypropylene),
- PVDF (Kynar , Fluoroline , etc;),
® ®
- ECTFE (Halar , Norton , etc;),

® ®
- ETFE (Tefzel®, Chemfluor®, etc;),

- PTFE (Teflon®, Fluon®, etc;).
Several manufacturers are available supplying pipes, flanges and fittings. Flanged plastic lined
piping, however, are often not cost effective in seawater handling systems.
In welded pipes, the critical issues is represented by the protection of the metal substrate in
correspondence to the girth welds. Patented systems, however, are available allowing to join stalks
in reeled plastic lined pipes, and this represents a viable option for subsea water injection flowlines. 8
Plastic-lined reel pipes are available in pipe sizes ranging from 8 to 16 inches, suitable for design
pressure up to 200-250 bar.
In seawater handling systems, polyethylene provides adequate performance in most applications.

Use of fluoro-polymers is restricted to protection of valve internals.
4.2 Cement linings
Internal cement lining have been used in the past to protect steel pipes. Cement establish alkaline
conditions at the inner steel surface, providing passivity, and a permanent barrier to oxygen diffusion
from bulk seawater to the steel/cement interface.
In case of break-off of pieces of the liner, a macro-cell establishes between lined steel (passive) and
bare steel (active) in correspondence to the lining fault, with potential differences as high as 0.4 –
0.5V and severe corrosion occurring at bare spots. Once started, steel corrosion tends to further
spall off the cement lining.
Cement lined steel pipe are not recommended solution for durable pipeline and piping systems.
4.3 Rubber linings and coatings
Internal organic coating and linings are used for internal corrosion protection of carbon steel vessels,
filters and valves. This material solution represent a cost effective option for vessels in combination
with sacrificial anodes, to provide protection at areas where the coating or lining may result
damaged.
8
S. Booth, S. McIntyre, J. Baker, D. Leslie , ‘Jointing Method for Pipe-by-pipe Installation of Plastic Lined Pipelines’, Deep
Offshore Technology Conference, November 28-30, 2006, Houston, Texas.
Rev. 0 April 2009
Several problems have been experienced with glass flake vinyl ester coatings, often used for
seawater filters or water boxes, with accelerated corrosion at coating breakdown. This solution is not
recommended unless it is combined with sacrificial anodes.
Neoprene rubber linings offered satisfactory service experience for limited service life.
Coating or lining for valves internal is not in general a recommended solution, and it may be
considered only for limited service life. Galvanic consideration between valve components shall be in
particular considered for the following reasons: a) in some valves the applicability of materials used
for valve trim or stem relies on the cathodic protection of the less noble valve body, which will lead to
rapid failure of these component if coated; b) more noble metal used for the valve trim may lead to
accelerated galvanic corrosion and loss of containment of the valve body at coating damages.
Superduplex stainless steel or Alloy 625 weld overlay represent a reliable solution at ambient
temperature with the lowest risk of corrosion for valves and other items that may not be efficiently
protected by sacrificial anodes.
Internal lining is a viable option for vessels (typically the deaeration tower) with simple internal
geometry that can easily accommodate sacrificial anodes for an efficient distribution of the cathodic
protection current.
4.4 Glassfiber reinforced plastic
Glassfibre reinforced plastic (GRP) are composite non-metallic materials made of a thermosetting
polymeric resin reinforced with glass fibre. The glass fibre normally used to reinforce GRP is E-glass,
consisting mainly of SiO2, Al2O3 and MgO.
GRP products are covered by several norms, including:

- ENI 14351.PIP.MEC.SDS
- ISO 14692 (Parts 1, 2, 3 and 4);
- DNV OS C501;
- Norsok M-622
Different resin types are used, with different properties and temperature limitation (see Table 4.1).
Table 4.1 - Resin types and temperature limitations (from ISO 14692 Parts 1)
Max.
Resin type
temperature
Polyester 70 °C
Vinyl ester 100 °C
Epoxy 110 °C
Phenolic 150 °C
With respect to metallic materials, GRP provides the following main advantages:
- they are not affected by corrosion;
- the allow significant weight reduction.
GRP have been increasingly used in offshore seawater handling systems, in particular for aerated
seawater piping and in fire fighting systems, in alternative to metallic alloys options. They display
good mechanical properties, however the maximum pressure ratings of GRP pipes should be limited
in order to avoid maximum hoop stress in excess of permissible values that ranges indicatively
between 20 MPa and 40 MPa (which may indicatively correspond to pressure in the order of 10 to 20
bar). In any case the above values are only indicative and mechanical design, shall be performed in
accordance with applicable codes (see also ENI Company Standard 14351.PIP.MEC.SDS
“Guidelines for the use of GRP piping”)
Rev. 0 April 2009
Cost effectiveness with respect to metal alloys options shall be evaluated based on Project design
requirements. GRP is normally not cost effective for small diameter pipes.
It is recommended to select a unique Contractor for GRP systems covering detail design, fabrication
of the components, installation and commissioning.
4.5 Thermoplastics
The following thermoplastic types may be considered for solid plastic pipe:
- ABS, acrylonitrile butadiene styrene
- PVC, polyvinyl chloride,
- PE, polyethylene,
- PP, polypropylene.
Polyethylene pipe "PE" are then distinguished between high density polyethylene "HDPE", which is
the most largely employed, low density polyethylene "LDPE" and the cross-linked polyethylene
"XPE", which extends the application of polyethylene in hot service.
The advantages of these materials are:

- immune to internal corrosion,
- do not require protection from external corrosion,
Disadvantages and concerns include:

- low strength,
- low impact resistance,
- temperature limitations,
- propagation of cracks,
- need of a high number of supports and thermal expansion control devices,
- require the extension of plastic pipes usage also for the 2" lines connecting the drain boxes to the
headers,
- possible long-term material degradation mechanisms, due to UV exposure or ageing
- cost may be high.
Joining of thermoplastic pipes can be carried out through butt welding (butt fusion/electrofusion
socket in pipe length).
An accurate design of thermoplastic pipework system which takes into appropriate account of any
possible need for thermal expansion, clearances etc; may be not straightforward, particularly in
presence of a complicated piping route and layout (elbows, tees etc;). Manufacture of pipework shall
be supplied on site in factory tested prefabricated spools with the manufacturer's CAD overlay
drawing marked to show item code numbers and installed route, together with dimensional
diagrammatic sketches. Expansion joints ("O" ring thermal expansion joints) shall be foreseen and
installed, fitted as shown on the manufacturers drawing.
The use of thermoplastics is more typical for drainage systems, whereas in seawater service in
general the window of applicability of this material option remains at present quite limited.
Rev. 0 April 2009
5. MATERIAL SELECTION IN SEAWATER HANDLING SYSTEMS
The present Section is intended to provide guidelines for material selection of the main components
in seawater handling systems.
Recommendations on materials are integrated with the requirements that define the application
limits. Remarks are also provided for the correct management of internal corrosion.
5.1 Material selection
5.1.1 Criteria for the selection of applicable corrosion prevention methods
Criteria for material selection shall reflect all the requirements detailed in the Project design
Premises.
Hereinafter a number of factors is listed that shall be taken into account in all the design phases for
material selection of any given Project.
- Assessment of the operating corrosion conditions based on:

- process description and requirement, including temporary operations;
- design and operating conditions;
- nature of the fluids and treatments performed;
- environmental conditions;
- any other aspect impacting on corrosion.
- Design life;
- Plant location, if offshore or onshore;
- Space and weight constraints.
- Environmental conditions.
- Mechanical requirements and fabrication constraints.
- Lowest design temperature, including cooling caused by depressurization conditions further than
minimum ambient temperature (evaluate impact on mechanical properties).
- External corrosion requirements.
- Impact of cathodic protection, where applied.
- Impact of thermal insulation, where applied.
- Occurrence of sour conditions, also if temporary.
- Exposure conditions during hydro-testing and start-up operations.
- Exposure conditions during upsets and shutdowns.
- Maximum allowed corrosion allowance (for carbon steel only).
- Human resources availability for inspections, monitoring, maintenance and repair.
- Safety and environmental issues.
- Compliance to applicable Project Standards.
- Compliance to local Government regulations.
- Cost effectiveness.
Material selection shall be strictly integrated with other corrosion prevention methods, including:
- internal corrosion allowance, for carbon steel only;
- process treatments;
- treatment with chemicals (in particular oxygen scavenger and biocide);
- use of internal coating and liners;
- internal cathodic protection;
- any other applicable technique.
Corrosion monitoring shall be regarded as part of the corrosion control strategy.
5.1.2 Options evaluation and costs comparison
In case more option are technically acceptable, preference shall be given to the most cost effective
option.
Rev. 0 April 2009
Comparison among different material options shall be based on capital and operating costs, and
preferably on the Life Cycle Cost approach.
Capital costs shall include the following costs:

- costs for material (pipes, sheets, fitting, etc.);
- costs for joining;
- costs for inspections;
- costs for supports.
Material cost comparisons shall be performed considering the actual thickness values calculated for
each option based on mechanical properties and corrosion allowance, if any.
5.2 Seawater handling systems. Material selection and corrosion control requirements
This Chapter deals with recommended materials for seawater handling systems. Materials options
are specified based on typical components, i.e. piping, pumps, valves, vessels, etc.
Recommendations for materials are integrated with specific requirements, if needed. Additional
information are also provided as remarks associated to the reviewed material options.
5.2.1 Seawater piping
Reference is made here to piping part of process seawater handling systems, typically water injection
units, cooling units, etc. Pipelines and flowlines are covered by a dedicated paragraph.
Materials for piping are specified distinguishing between aerated, or raw, seawater and deaerated
seawater. Deaeration treatment is typically performed in water injection systems, onshore or
offshore.
5.2.1.1 Aerated seawater
Materials for aerated seawater piping evolved moving toward corrosion resistant materials. Carbon
steel have been used in the past as piping material, mainly protected by cementitious layers or by
organic coating or galvanized. Experiences, however, have been negative and steel was replaced by
Cu/Ni 90/10. Performance of Cu/Ni alloys was generally adequate, although some failure were
9
reported, mainly due to high flow velocities and by sulphides water contamination.
The preferred choice is represented by superduplex stainless steel (with PREN above 40), with
temperature limitation for chlorinated seawater at 30°C. Nickel alloys with an adequate content of
molybdenum such as alloy 625 or alloy 718 are also used in lieu of superduplex, especially for
products presenting fabrication issues for the latter. The temperature limitation is to prevent
occurrence of localised corrosion, in particular crevice attacks. Austenitic stainless steels type 6Mo
provide corrosion resistance comparable to superduplex; however, they do not result cost effective.
Titanium Grade 2 are required for chlorinated systems at temperature exceeding 30°C and up to
85°C.
GRP and carbon steel with internal thermoplastic lining are not subject to corrosion, and convenience
with respect to CRA shall be assessed based on costs, fabrication and erection issues, mechanical
requirements and safety issues. Same is true for plastic lined (flanged) piping.
Use of carbon steel in aerated seawater is discouraged. Evaluation of this solution should be limited
to the following applications:
- onshore plants;
- temporary facilities with limited design life;
- low-reliability systems.
9
R. Johnsen, ‘Experience with the use of copper alloys in seawater in the Norvegian Sector of the North Sea’, Proceedings
of the EuroCorr 2004 Conference, Nice, September 12-16, 2004.
Rev. 0 April 2009
5.2.1.2 Deaerated seawater
Carbon and low alloy steel represents the base material for piping conveying deaerated seawater,
with the limitations inherent to the deaeration and sterilization treatments (see ). CRA can be
preferred in system where a high reliability is requested.
Use of CRA shall be evaluated in commingled systems where seawater is mixed with process water.
Duplex stainless steels, type 22Cr or 25Cr are typical candidate materials; selection, however, shall
be performed based on Project data and fluid corrosivity assessment.
In water injection systems use of GRP is usually not considered because of pressure limitations.
5.2.1.3 Piping material selection summary
Recommended materials and related additional requirements are summarized in Table 5.1.
Table 5.1 – Seawater piping. Material selection table.

Additional requirements and
Service Material options Remarks
limitations
Superduplex Temperature should be limited
within 20°C
6Mo - T £ 30°C Residual chlorine should be limited
below 0.7 mg/l
Alloy 625 - T £ 30°C Residual chlorine should be limited
below 0.7 mg/l
CuNi 90/10 sensitive to erosion
- max flow velocity 3 m/s
Coupling to different metals to be
- solid particles (sand) absent; carefully evaluated to avoid galvanic
sensitive to corrosion with sulphides corrosion.
- avoid with polluted water
(presence of sulphides as H2S)
GRP - T < 95°C
- maximum flow velocity 5 m/s
aerated seawater - limited pressure (see 4.4)
Plastics and - T < 30°C
thermoplastics (PVC, Safety issues (fire) to be
ABS) - low temperature limitations investigated
- low pressure systems Cost effectiveness to be evaluated
case by case
- crack propagation issue
Installation issues
- limited applications Limits for complex piping route and
Plastic-lined flanged - T < 30-60°C (depends on liner size
piping mat.)
- safety issues (fire resistance)
- fabrication issues
- low temperature limitations
Titanium (Grade 2) - T < 85° C (with chlorine)
- T < 95° C (no chlorine)
Carbon steel - cO2 < 20 ppb Minimum corrosion allowance: 3 mm
- cCl2 < 0.2÷0.3 ppm Corrosion monitoring
deaerated seawater - treatment with biocide Chemical treatment
22Cr Duplex SS -
25Cr Duplex SS - Costly option
Rev. 0 April 2009
5.2.2 Electro-chlorination unit
Exposure environment is a solution of hypochlorite in seawater at ambient temperature. Resistant

materials are:
- titanium;
- solid PVC or polypropylene;
- GRP with PVC or polypropylene;
- nickel alloy type C-276.
Electro-chlorination units are normally supplied as package and material selection is under the
responsibility of the Supplier. The list of adopted materials shall be submitted for review or approval
to the Company.
5.2.3 Submersible Lift Pumps
Submersible vertical pumps are typically used in seawater systems to lift seawater:
- in offshore platforms or FPSO for local seawater supply,
- into an intake basin and from here to the seawater service facilities.
Submersible vertical pumps include the external caisson, the column enclosing the shaft, the pump
unit enclosing the impeller, a suction strainer at the column bottom to filter seawater and a motor
which may be located on the top or at the bottom of the column.
The service is aerated seawater which is chlorinated by injection of chlorine at the bottom for bio-
fouling prevention.
The connection at the top of the pump with the seawater piping shall be designed considering
possible galvanic effects if dissimilar metal are connected (e.g. typically superduplex and copper-
nickel alloys) that shall be prevented by insulating joints or internal painting (applied onto the more
noble material for a suitable distance) or by non-metallic spool interposed between the two metals.
Cathodic protection is to be provided to protect either the external and the internal surface of the
caisson, if made in carbon steel.
Table 5.2 – Submersible pumps. Material Selection Table

Component Material Remarks
Cathodic protection with sacrificial anodes and painting is
- Carbon steel required (in offshore platform this item is considered part of
Caisson the jacket)
- GRP -
- Superduplex External sacrificial anodes are required to protect the

internal side of carbon steel caisson in the caisson/column
annulus, due to aerated seawater flowing at high velocity
Column - Ni-Al Bronze and turbulence and enhanced by galvanic contact with the
column. Either the caisson internal and the column should
- Titanium be coated to reduce anode consumption.
Primary option if the shaft is in contact with seawater.
- Superduplex Alternative material may be considered if the shaft is
Shaft isolated from the seawater environment
- Monel -
- Superduplex -
Pump Unit (impeller) Coupling with less noble material is to be avoided unless
- Ni-Al Bronze cathodic protection is applied
Electrical motor casing (if - Superduplex -
located at the pump
bottom) - Ni-Al Bronze
- Superduplex -
Suction strainer
- Ni-Al Bronze -
Rev. 0 April 2009
5.2.4 Centrifugal Pumps
Centrifugal pumps are normally used in seawater systems.
The pump impeller is exposed to fast flowing, highly turbulent seawater and should be made from a
material with high resistance to these conditions.
The use of cast iron or mild steel can only be considered for limited service.
Most copper-alloys are rapidly damaged by high flow velocity. For other pump components, not
exposed to high flow velocities, copper-based alloys are used in combination with copper alloy
piping. In copper alloy pumps, a clearance is left between the impeller and the casing so that the
water flowing from the impeller does not impinge directly on the casing. Provided direct impingement
is avoided, gunmetals (red brass), aluminium bronze and cast 70/30 copper-nickels perform
satisfactorily.
With stainless steel piping systems, similar materials are used for pump components. Stainless steel
pumps can be made from cast versions of duplex grades.
Where pump parts are fabricated by welding from nickel aluminium bronze plate, there is a risk of
selective phase corrosion (de-aluminification) in the heat affected zone of the weld. This can crack if
stressed.
Monel alloys 400 and K-500 and stainless steels have a high resistance to flowing seawater, and
cast versions of these alloys are preferred for pump impellers. These alloys resist impingement
attack but may pit when the pump is left in stand-by and full of seawater. The risk of pitting of is
however minimal compared with the risk of impingement corrosion of copper-base alloy impeller and
hence stainless steel or cast Monel Alloy 400 are preferred for this application. Alloy 20, and duplex
stainless steel may be used.
For stainless steel pumps, the impeller can be made from the same material as the casing.
Table 5.3 – Seawater Pumps. Material selection table

Additional
Service Casing Impeller requirements and Remarks
limitations
Match carbon steel piping
- Cast iron AISI 316L rely on CP Limited service life,
- AISI 316L protection by steel/cast
- Carbon steel iron casing Low reliability required,
Occasional service
- Superduplex - Superduplex T < 30°C (possibly 20) Match superduplex piping
- 6Mo - 6Mo T < 30°C (possibly 20) Match 6Mo piping
- Gunmetals
- AISI 316L Not suitable for direct Match copper alloy piping
- CuNi 7030 impingement conditions Consider galvanic effects
- Alloy 20
- Ni-resist Avoid with sulphides with stainless steels and
- Monel (polluted waters) other more noble alloys
aerated seawater - Ni-Al Bronze
Match copper or nickel alloy
piping
Avoid with sulphides Consider galvanic effects
- Monel - Monel (polluted waters) when coupled with more
noble alloys
Costly option
- Ni Alloy 625
(solid or
clad/weld
- Alloy 625 T < 30°C Match Ni alloy piping
overlay)
- Ni Alloy C276, - Ni Alloy C276, T < 40°C Match titanium piping

Rev. 0 April 2009
Additional
Service Casing Impeller requirements and Remarks
limitations
C22 C22
- Ni Alloy 686, 59 - Ni Alloy 686, 59 T < 60°C
- Titanium - Titanium T < 85°C
- Cast iron AISI 316L rely on CP

- AISI 316L protection by steel/cast Match carbon steel piping
- Carbon steel iron casing
deaerated AISI 316L rely on CP
seawater
- Ni-resist - AISI 316L protection by Ni-resist
casing
- Duplex 22Cr - Duplex 22Cr Match duplex piping
5.2.5 Valves
Valves are critical components in seawater systems, and quite often they are interested by corrosion
problems. Use of carbon steel valves with non-ferrous piping is a typical example, where the limited
durability of carbon steel is further reduced by galvanic corrosion.
In a system with a nominal seawater velocity of a few meters per second flow through the valve, that
the valve, depending on its design, may give rise to turbulence and much higher local velocities,
particularly when the valves are used in a throttling mode.
The entry-level valve used in ferrous pipe systems has a cast iron body with brass internals.
Depending on design, corrosion rates of several millimeters per year can occur on the body. The
body cathodically protects the internals and the valve will function for some few years. Coatings on
valve bodies may be used but their success depends mainly on the valve design. Any break in a
coating can result in severe corrosion and ultimate perforation of the valve body.
Upgrading of valve body materials to give higher reliability requires the use of alloys with good
corrosion resistance. Such materials are Ni-Resist austenitic cast irons and copper base alloys such
as nickel aluminum bronzes, admiralty and leaded gunmetals and cast copper-nickels. All these
alloys display good resistance to quiescent seawater (shut-down conditions or intermittent services)
and to flowing seawater within limited velocities. Where impingement is likely, alloys with high
resistance such as nickel aluminum bronze or cast copper-nickel (plus chromium) should be used.
Ni-Resist valves are often used in ferrous systems to improve the valve reliability. They are also used
in non-ferrous systems but copper-alloy valves are more common. Nickel aluminum bronze has high
strength and this makes it attractive, particularly for large valves. Also, it has high resistance to
impingement attack and this may be of importance in globe valves used under throttling conditions.
Erosion-corrosion is generally not a problem with stainless steels valve bodies. As pitting and crevice
corrosion are important in valves, then alloys with similar resistance to that of the piping are required
for valve bodies. Both cast and wrought versions of several of the high alloy stainless steels are
available and can be used for valve bodies. Internal cathodic protection has been applied
successfully to protect stainless steel valves in non-metallic systems.
Valve seats experience high water velocities. Materials with high resistance to high velocity flowing
seawater are stainless steels, nickel-base alloys and Monel alloy 400. Stainless steels are prone to
pitting when the system is not in use and nickel-copper alloys are a better choice.
Alloy 625 which has high resistance to both static and flowing seawater is used as a weld overlay to
produce highly resistant surfaces in critical areas of valves and shafts and also on pump castings.
This alloy has excellent weld deposition characteristics and can be used as a general purpose
overlay for avoidance of areas of corrosion damage in carbon, low alloy and stainless steel
components.
Rev. 0 April 2009
Valve seats can be machined areas on the valve body, disc, gate or ball, depending on the valve
design.
Stems in stainless steel valves are made of materials with similar corrosion resistance to the body.
The higher strength of duplex stainless steel makes them attractive for stems.
Valves are a relatively expensive part of a seawater system and it is usually more satisfactory to
select reliable materials. Avoiding corrosion problems by lining the valve is a possibility which is
related to the valve design (i.e. simple shape) and the body can be provided with a thick rubber lining
which can be clamped firmly between the flanges joining the valve to the pipes and is not dependent
on perfect adhesion between the rubber and the body.
Carbon steel or cast iron bodies fitted with brass trim provide galvanic protection from the large area
of ferrous material and may give a useful life. Upgrading the body material to copper-base alloys will,
by removing the cathodic protection effect, give rise to corrosion of the trim.
The use of copper-alloy valves is desirable in copper-alloy pipe systems so as to retain galvanic
compatibility. The use of unprotected ferrous valves in non-ferrous systems should be avoided.
Non-ferrous valves are sometimes used in steel piping systems and while this will lengthen the life of
the valve, galvanic corrosion of the piping adjacent to the valve may occur. A better choice of valve
material in steel systems would be Nickel-Resist cast iron as this is galvanically more compatible with
steel.
Rev. 0 April 2009
Table 5.4 – Seawater Valves. Material selection table

Additional
Service Body Trim requirements and Remarks
limitations
Match carbon steel
piping
- Cast iron Avoid coupling with
- Brass Limited service life,
- Carbon steel more noble piping
Low reliability required,
Occasional service
Avoid coupling with
- Gunmetals more noble piping
- CuNi 7030 (e.g. duplex, stainless Match copper alloy
- Monel steels, titanium)
- Ni-resist piping
Avoid with sulphides
- Ni-Al Bronze (polluted waters)
Residual chlorine
Match superduplex
- Superduplex - Superduplex should be limited
piping
aerated seawater below 0.7 mg/l
- 6Mo - 6Mo T ≤ 30°C Match 6Mo piping
Avoid with sulphides

- Monel - Monel (polluted waters)
Costly option
- Ni Alloy 625 (solid - Alloy 725(716), 625

or clad/weld T ≤ 30°C Match Alloy 625 piping
overlay) - Alloy 625
- Ni Alloy C276 - Alloy C276 T ≤ 40°C
- Ni Alloy 686, 59 - Ni Alloy 686, 59 T ≤ 60°C Match titanium piping
- Titanium - Titanium T ≤ 85°C
- Cast iron Limited resistant to Match carbon steel

- Brass
- Carbon steel erosion piping
deaerated seawater AISI 316L trim rely on

Match carbon steel
- Ni-resist - AISI 316L CP protection by Ni-
piping
resist valve body
- Duplex 22Cr - Duplex 22Cr Match duplex piping
5.2.6 Exchangers and coolers
Recommended materials and relevant limitations are summarized in the next tables.
Table 5.5 – Exchangers and Coolers. Material selection table

Service Material Limitations
- Superduplex - T £ 30°C (possibly £ 20°C)

- 6Mo high-alloy austenitic - T £ 30°C (possibly £ 20°C)
- Ni Alloy 625 - T £ 30°C
aerated seawater
- Ni Alloy C276 - T < 40°C
- Ni Alloy 686, 59 - T < 60°C
- Titanium - T < 85°C
deaerated seawater - Duplex 22Cr - residual oxygen control
(below 10 ppb)
Rev. 0 April 2009
Table 5.6 – Seawater Compact Plate Heat Exchangers (PCHE). Material selection table
Service Material Limitations
- 6Mo high-alloy austenitic - T £ 30°C (possibly £ 20°C)

- Copper alloys - Flow velocity
- Ni Alloy 625 - T £ 30°C
aerated seawater
- Ni Alloy C276 - T < 40°C
- Ni Alloy 686, 59 - T < 60°C
- Titanium Grade 2 - T < 85°C
deaerated seawater - 6Mo high-alloy austenitic
5.2.7 Deaeration tower
Carbon steel with high-integrity internal lining and cathodic protection with sacrificial anodes is the
recommended solution for the de-aerator tower and filter vessels. Internals shall be superduplex, or
high austenitic stainless steels / nickel alloys with PRE > 40.
5.2.8 Filters
Recommended material for the shell of seawater filters is superduplex.
Carbon steel protected with glass flake vinyl ester coatings was typically used, but severe galvanic
attacks at coating breakdown is often experienced and for this reason it is not recommended, unless
protected by cathodic protection with galvanic aluminium anodes.
Lining with neoprene rubber is more satisfactorily, but superduplex represents a safer choice.
5.2.9 Pipelines
Reference is made here to seawater conveying pipelines, in particular for water injection purposes,
onshore or offshore. Typically cases are:
- subsea flowlines connecting platforms to subsea injector wells;
- subsea inter-platform pipelines;
- onshore flowlines, trunklines and pipelines.
As per seawater piping, materials are specified distinguishing between aerated, or raw, seawater and
deaerated seawater.
The traditional material for the construction of pipelines for the transportation of deaerated (treated)
seawater is carbon steel with corrosion allowance, where the control of corrosion depends on the
control of residual oxygen after the deaeration unit, which should be systematically kept below 20
ppb, with a desirable target below 10 ppb. Prolonged and repeated excursions above this limit
determine the risk of localised corrosion for passive materials (CRAs) and general corrosion of
carbon and low alloy steels, with characteristic intensifications at the weld and under deposits at the
bottom of the line (corrosion groove at 6 o’clock position).
Recommended materials and related additional requirements are summarized in Table 5.7.
Rev. 0 April 2009
Table 5.7 – Seawater pipelines. Material selection table.

limitations
GRP Pressure limitations to be verified. Installation issues to be considered.
Not suitable for subsea GRP may not be justified for limited
installations pipeline extensions.
Plastic-lined piping pipe size > 8” Suitable protection at joints shall be
Max pressure 200-250bar integral part of the selected system.
Reeling installation for offshore
application of 300-1500m stalks with
aerated seawater use of Ni 625 compression rings at
weld connections.
Superduplex T ≤ 30°C Temperature should be limited within
20°C
Residual chlorine should be limited
below 0.7 mg/l
Titanium T > 30°C Costly alternative. Consider the
possibility to cool seawater below 30°C
and use superduplex.
Carbon steel cO2 < 20 ppb (cCl2 < 0.2÷0.3 ppm) Corrosion allowance: 3 mm
Corrosion monitoring
Tight control of residual oxygen
Chemical treatments (biocides)
Cleaning with pigs for periodical
removal of deposits
deaerated seawater Plastic-lined piping Reeling installation of 300-1500m This costly option may be considered if
stalks with use of Ni 625 oxygen control is a concern to avoid
compression rings at weld groove corrosion at 6 o’clock location
connections
8-16” pipe size covered
Max pressure 200-250bar
22Cr Duplex SS Costly alternative for deaerated
seawater.
5.3 Seawater fire-fighting systems
Materials for fire-fighting systems (piping, sprinklers, deluge pipework and fittings) include copper-
nickel, superduplex, GRP or titanium.
Table 5.8 – Seawater fire-fighting system. Material selection table.

limitations
GRP Pressure limitations to be verified. Installation issues to be considered.
Safety issues to be investigated. GRP may not be justified for minor
pipework installation.
CuNi 9010 Avoid with polluted water (presence
of sulphides as H2S)
Avoid design involving high flow
velocity for prolonged period (should
be indicatively kept below 5 m/s)
aerated seawater
Superduplex T ≤ 30°C Residual chlorine should be limited
below 0.7 mg/l
Hyperduplex T ≤ 40-50°C
6Mo T ≤ 30°C Residual chlorine should be limited
below 0.7 mg/l
Titanium Usually applied when temperature
exceeds 30°C
Rev. 0 April 2009
ANNEX A – METAL COMPOSITION DATA
Stainless steels
0.1 - Designations and chemical composition of austenitic stainless steels used in seawater systems.
Type UNS Common name C max? Si Mn P S Cr Mo Ni Others
316 S31603 316L 0.03 max 1.00 2.00 0.045 0.030 16.0/18.0 2.00/3.00 10.0/14.0 -
6
S31254 254SMO 0.020 0.80 1.00 0.030 0.010 19.5/20.5 6.0/6.5 17.5/18.5 Cu 0.5/1.0; N 0.18/0.22
7
High Alloy N08367 AL-6XN 0.030 1.00 2.00 0.040 0.030 20.0/22.0 6.0/7.0 23.5/25.5 Cu 0.75; N 0.18/0.25
Austenitic SS N08925
10
(6Mo) N08926 Cronifer 1925hMo 0.020 max 0.50 max 1.0 max 0.030 max 0.005 max 20.0/21.0 6.0/6.8 24.5/25.5 Cu 0.8/1.0; N 0.18/0.2
9
N08026 20Mo6 0.03 0.50 1.00 0.03 0.03 22.0/26.0 5.00/6.70 33.0/37.20 Cu 2.0/4.0; N 0.1/0.16
N08904 904L 0.020 1.00 2.00 0.045 0.035 19.0/23.0 4.0/5.0 23.0/28.0 Cu 1.0/2.0
9
N08020 20Cb-3 0.07 1.00 2.00 0.045 0.035 19.0/21.0 2.00/3.00 32.0/38.0 Cu 3/4; Nb 8xC/1.0
9
N08024 20Mo-4 0.03 0.50 1.00 0.035 0.035 22.5/25.0 3.50/5.00 35.0/40.0 Cu 0.5/1.5; Nb+Ta 0.15/0.35
1
N08028 Sanicro 28 0.030 1.0 2.50 0.030 0.030 26.0/28.0 3.0/4.0 30.0/34.0 Cu 0.6/1.4
1
N08028 Sanicro 29 0.030 1.0 2.50 0.030 0.030 26.0/28.0 4.0/5.0 30.0/34.0 Cu 0.6/1.4
High Alloy 7
N08366 AL-6X 0.035 1.00 2.00 0.040 0.030 20.0/22.0 6.00/7.00 23.5/25.5 -
Austenitic SS
N08700 JS700 0.04 1.00 2.00 0.040 0.030 19.0/23.0 4.3/5.0 24.0/26.0 Cu 0.5; Nb8xC/0.4
S31277 27-7 Mo 0.020 0.50 3.00 0.030 0.010 20.5/23.0 6.5/8.0 26.0/28.0 Cu 0.5/1.50; N 0.30/0.40
6
S32654 654SMO 0.020 0.50 2.0/4.0 0.030 0.005 24.0/25.0 7.0/8.0 21.0/23.0 Cu 0.30/0.60; N 0.45/0.55
S34565 Nirosta 4565S 0.030 1.00 5.0/7.0 0.030 0.010 23.0/25.0 4.0/5.0 16.0/18.0 N 0.40/0.60; Nb 10x C / 1.00
S35135 0.08 0.6/1.0 1.00 0.045 0.015 20.0/25.0 4.0/4.8 30./38.0 Ti 0.40/1.00
Rev. 0 April 2009
0.2 - Designations and chemical composition of duplex stainless steels used in seawater systems.
Type UNS Trademarks C Si Mn P S Cr Mo Ni Others

5
UR 45N
6
S31803 Avesta 2205 0.030 1.00 2.00 0.030 0.020 21.0/23.0 2.5/3.5 4.5/6.5 N 0.08/0.20
Duplex 22Cr 7
AL 2205
1
S32205 SAF2205 0.030 1.00 2.00 0.030 0.020 22.0/23.0 3.0/3.5 4.5/6.5 N 0.14/0.20
9
S32950 7Mo Plus 0.030 0.60 2.00 0.035 0.010 26.0/29.0 1.00/2.50 3.5/5.2 N 0.15/0.35
S31260 3
DP3 0.03 0.75 1.00 0.030 0.030 24.0/26.0 2.5/3.5 5.5/7.5 N 0.1./0.3; Cu 0.2/0.8; W 0.1/0.5
Duplex 25Cr S39226
5
Uranus 52 N
S32550 4 0.04 1.00 1.50 0.040 0.030 24.0/27.0 2.9/3.9 4.5/6.5 N 0.10/0.25; Cu 1.50/2.50
Ferralium 255
1
S32750 SAF 2507 0.030 0.80 1.20 0.035 0.020 24.0/26.0 3.0/5.0 6.0/8.0 N 0.24/0.32; Cu 0.50
2
S32760 Zeron 100 0.030 1.00 1.00 0.030 0.010 24.0/26.0 3.0/4.0 6.0/8.0 N 0.20/0.30; Cu 0.5/1.00; W 0.50/1.0
1
S32906 SAF 2906 0.030 0.50 0.80/1.50 0.030 0.030 28.0/30.0 1.50/2.60 5.8/7.5 N 0.30/0.40; Cu 0.80
5
Superduplex S32520 Uranus 52N+ 0.030 0.80 1.50 0.035 0.020 24.0/26.0 3.0/4.0 5.5/8.0 N 0.20/0.35; Cu 0.50/2.0
(PREN > 40) 3 N 0.24/0.32; Cu 0.20/0.80; W
S39274 DP3W 0.030 0.80 1.0 0.030 0.020 24.0/26.0 2.50/3.50 6.0/8.0
1.50/2.50
3
S32808 DP28W 0.030 0.80 1.0 0.030 0.020 27.0/28.0 1 7.5/8.0 N 0.35; W 2
S39277 AF918 0.025 0.025 - 0.025 0.002 24.0/26.0 3.0/4.0 6.5/8.0 N 0.23/0.33; Cu 1.2/2.0; W 0.80/1.2
1
Hyperduplex S32707 SAF2707HD 0.03 max - - - - 27 5 6.5 N 0.4
8
S32100 Nitronic 19D 0.030 1.00 4.0/6.0 0.040 0.030 19.5/21.5 0.60 1.00/3.00 N 0.05/0.17; Cu 1.00
7
S32003 AL 2003 0.030 1.00 2.00 0.030 0.020 19.5/22.5 1.50/2.00 3.0/4.0 N 0.14/0.20
6
Lean duplex S32101 LDX 2101 0.040 1.00 4.0/6.0 0.040 0.030 21.0/22.0 0.10/0.80 1.35/1.70 N 0.2/0.25; Cu 0.10/0.80
1
SAF2304
S32304 5 0.030 1.00 2.50 0.040 0.030 21.5/24.5 0.05/0.60 3.0/5.5 N 0.05/0.2; Cu 0.05/0.60
UR 35N
1
Trademark of Sandvik Steel.
2
Trademark of Weir Materials.
3
Trademark of Sumitomo Metal Industry.
4
Trademark Langley Alloys.
5
Trademark of Usinor Industeel.
6
Trademark of Outokumpu (Avesta).
7
Trademark of Allegheny Ludlum.
8
Trademark of AK Steel.
9
Trademark of Carpenter.
10
Trademark of Thyssen Krupp VDM.
Rev. 0 April 2009
Copper alloys
0.3 - Designations and chemical composition of most copper alloys used in seawater systems.
Family UNS Common name Cu Zn Sn Ni Al Fe Pb Others
C23000 red brass 84-86 rem - - - 0.05 max 0.05 max
Brass C27000 yellow brass 63-68.5 rem - - - 0.07 max 0.10 max
C28000 Muntz alloy 59-63 rem - - - 0.07 max 0.30 max
Gunmetal or cast red P=0.05 max; Si and Al 0.005; S 0.08
Gunmetal C83600 (4) 84-86 4-6 4-6 1 max - 0.3 max 4.0-6.0
brass max; Sb 0.25 max;
C44300 admiral brass 70-73 rem 0.8÷1.2 - - 0.06 max 0.07 max As 0,02÷0,06
Tin Brass
C46200 naval brass 62-65 rem 0.5÷1.0 - - 0.10 max 0.20 max
(1)
C60800 Al bronze rem - - - 5÷6.5 0.10 max 0.10 max As 0.2÷0.35
Al Bronze C95200 Al bronze 86 min - - - 8.5-9.5 2.5-4 -
C68700 Al brass As 76-79 rem - - 1.8÷2.5 0.06 max 0.07 max As 0.02-0.06
(2)
C95800 NiAl bronze 79 - 0.1 max 4.0/5.0 8.5-9.5 3.5-4.5 0.03 Mn 0.8-1.5; Si 0.1 max
Ni-Al Bronze (2)
C95500 NiAl bronze 78-80 - - 3-5.5 10-11.5 3-5 - Mn 3.5
(1) (2)
C70600 CuNi 9010 rem 1 max - 9-11 - 1÷1.8 0.05 max Mn 1 max
(1) (2)
C71500 CuNi 7030 rem 1 max - 29-33 - 0.4÷1 0.05 max Mn 1 max
Copper-Nickel
(1) (2) C 0.03 max; Cr 0.30-0.7; Mn 1 max; Si
C72200 CuNi 8515 rem 1 max - 15-18 - 0.5÷1 0.05 max
and Ti 0.03 max;
Tungum C69100 Tungum 81-84 rem 0.1 max 0.7-1.2 0.25 max 0.05 max Si 0.8-1.3
(1)
Ag included
(2)
Co included
(3)
Ni included
(4)
Reported as Gunmetal, valve bronze, leaded bronze (obsolete),
Rev. 0 April 2009
Nickel alloys
0.4 - Designations and chemical composition of nickel alloys used in seawater systems.
C
Family UNS Common name Cr Ni Mo Fe W Others
max
N08825 Alloy 825 19-23 38-46 2.5-3.5 0.05 rem
Nickel-Iron-Chromium-
N07718 Alloy 718 17-21 50-55 2.8-3.3 0.08 rem Nb 5-6 Co, Ti
Molibdenum (3Mo)
N09925 Alloy 925 20-24 38-46 2.5-3.5 0.03 rem
N06975 Alloy G-2 24-25 50-52 6-7 0.024 rem 3.0-4.5
Nickel-Iron-Chromium- N06985 Alloy G-3 21-23.5 35 6-8 0.015 rem 3.0
Molibdenum (6/9Mo) N06030 Alloy G-30 28-31 30 4-6 0.03 rem 3.9
N06950 Alloy G-50 20 50 9 0.02 rem
N06625 Alloy 625 20-23 56 8-10 0.1 5 Cu rem
Nickel-Chromium-
N07725 Alloy 725 19-22.5 55-59 7-9.5 0.03 5
Molibdenum (9Mo)
N07716 Alloy 716 (625+) 19-22 59-63 7-9.5 0.03 rem Nb 2.75-4, Ti 1-1.6, Al
N10276 Alloy C276 14-16 52 15-17 0.02 4/7
Nickel-Chromium- N06022 Alloy C22 22 56 13 0.01 3
Molibdenum (16%Mo) N06686 Alloy 686 20.5 57 16.3 0.01 <1
N06059 Alloy 59 23 59 16 <1
N04400 Monel 400 - 63-70 - 0.03 -
Nickel-Copper (Monel) N04405 Monel R405 - 63-70 - 0.03 -
N05500 Monel K500 - 63-70 - 0.025 -
Titanium and its alloys

0.5 - Designations and chemical composition of titanium alloys used in seawater systems.
C N H O Fe
Family UNS Common name Al V Ni Mo Ru Others
max max max max max
Commercially R50400 Grade 2 0.08 0.03 0.015 0.25 0.30 - - - - - Residuals < 0.4
Pure “CP” Grade 26
R52404 0.08 0.03 0.015 0.25 0.30 - - - - 0.1 Residuals < 0.4
Titanium (Grade 2 + Ru)
Grade 5
R56400 0.08 0.05 0.015 0.20 0.40 5.5-6.75 3.4-4.5 - - - Residuals < 0.4
(Ti-6Al-4V)
Grade 23
R56407 0.08 0.03 0.0125 0.13 0.25 5.5-6.5 3.4-4.5 - - - Residuals < 0.4
(Ti-6Al-4V ELI)
Grade 12
Titanium alloy R53400 0.08 0.03 0.015 0.25 0.30 - - 0.6-0.9 0.2-0.4 - Residuals < 0.4
(Ti-0.3Mo-0.8Ni)
Grade 19 5Cr, 4Zr
R58640 0.05 0.03 0.015 0.12 0.30 3-4 7.5-8.5 - 3.5-4.5 -
(Beta-C) Residuals < 0.4
Grade 29
R56404 0.08 0.03 0.0125 0.13 0.25 5.5-6.75 3.4-4.5 - - 0.1 Residuals < 0.4
(Ti-6Al-4V-0.1Ru ELI)

20019.MAT - COR.PRG Selezione Maeriali Servizio Marino Rev. 0 - Aprile 2009

Uploaded by

Copyright:

Available Formats

20019.MAT - COR.PRG Selezione Maeriali Servizio Marino Rev. 0 - Aprile 2009

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

20019.MAT - COR.PRG Selezione Maeriali Servizio Marino Rev. 0 - Aprile 2009

Uploaded by

Copyright:

Available Formats

Eni S.p.A.

Exploration & Production Division

MATERIAL SELECTION FOR

ENGINEERING COMPANY STANDARD

MATERIAL SELECTION FOR SEAWATER HANDLING SYSTEMS

4.2 Cement linings

The aims of the document are:

1.2 Document organization

Section 2 Illustrates the parameters of natural seawater affecting corrosion and

Section 3 Reviews the metallic materials families applicable in seawater, providing

Section 4 Reviews the non-metallic materials and liners applicable in seawater.

Section 5 Provides criteria for material selection.

ANNEX A Reports tables with metal alloys chemical composition.

1.3 Reference Standards

ISO 8044 Basic Terms and Definitions on Corrosion

1.4 ENI Company Standards

02555.VAR.COR.PRG Internal Corrosion – Fluid Classification and Corrosion Parameters

1.5 Symbols and abbreviations

ABS Acrylonitrile Butadiene Styrene

The chemical composition of seawater is remarkably constant in most of geographical area;

Table 2.1 - Principal constituents of seawater.

c O2 = 14.59 - 0.397 × T + 0.008 × T 2 - 8 ×10 -5 × T 3 - 6.0443 × S × (0.0167 - 0.00059 × T + 10 -5 × T 2 )

2.2 Seawater handling systems

2.2.1 Seawater injection

COARSE FINE DEAERATION BOOSTER INJECTION

Figure 2.4 - Typical offshore seawater injection system.

2.2.2 Seawater cooling systems

2.2.3 Seawater fire-fighting systems

SEAWATER LIFT PUMPS

Figure 2.5 - Typical offshore fire-fighting system.

2.3 Seawater treatments

Poly-electrolytes are often added to promote solid separation.

Physical deaeration is performed by vacuum in a deaeration tower or by gas stripping in an

Reference concentration values for residual chlorine are:

2.3.3.2 Copper ion for bio-fouling control

2.3.4 Other chemical treatments

Treatments for corrosion prevention may include the following chemicals:

2.3.4.1 Oxygen scavengers (residual oxygen and chlorine content control)

2.3.4.3 Corrosion inhibitor

2.3.4.4 Other treatments

2.4 Seawater corrosion

2.4.1 Dissolved oxygen

2.4.4 Flow conditions

2.4.5 Pollution by sulphides

2.4.6 Microbial activity

Microbial activity in seawater systems is controlled by chlorination and biocide injection.

Targets for bacterial population density:

2.4.8 Galvanic corrosion

and they are risky in the following cases:

2.4.9 Stress Corrosion Cracking

The main influencing parameters are:

Nickel alloys are not sensitive to CSCC in seawater service.

3.2 Carbon and low alloy steels

3.2.1 Corrosion performance

Microbial corrosion occurs on un-treated seawater at corrosion rate as high as 1 mm/y.

3.3 Cast Irons

From corrosion viewpoint, cast irons can be classified as:

while, based on microstructure, they are classified as: