Corrosion & Corrosion Control
Corrosion & Corrosion Control
Corrosion & Corrosion Control
Corrosion Control
1
Table of contents
I. Basics of Corrosion 3
II. Engineering Material 28
I. Families of Alloys 41
III. Corrosion Monitoring & Control 65
I. Material Selection 68
II. Improved Design 109
III. Corrosion Control Techniques 116
IV. Protective Coating 153
V. Cathodic Protection 189
2
I. Basics of Corrosion
3
What is Corrosion?
• Corrosion is defined as the
degradation of a material
due to its reaction with the
Oxides, Ore thermodynamically
environment. stable
• In case of metallic
corrosion, corrosion is
related to the law of
conservation of energy. Corrosion
(Smelting)
(Corrosion)
4
Why we study Corrosion?
5
Cost Of Corrosion
LEAKAGE LEADING TO
ENVIRONMENTAL POLLUTION
CATASTROPHIC FAILURE 6
Corrosion Mechanism
7
Corrosion Mechanism
A e
Flow of
Flow of
Electrical Electrons
- Current +
H2O
CATHODE
H+ Fe Cl- Cu
Na+ H2O
Na+ 2e
H2O Cl-
H+ 2e H+
Cl- OH- Fe+ OH- H2O
2e + OH-
Fe++ 2e Na+
H2O OH-
Na+ Cl- H2O
H 2O
8
Corrosion Mechanism
At anode, metal dissolves producing electrons
4M = 4M++ + 8e
At cathode electrons are consumed
4H2O + 2O2 + 8e = 8OH-
The faster that electrons are consumed at the cathode, the
faster will the metal go into solution at the anode (corrode).
This keeps the reaction in equilibrium.
Overall reaction is:
4M + 4H2O + 2O2 = 4M(OH)2
9
Standard EMF Series
Standard EMF series represents a ranking of metals in terms of its
natural potential reference to a hydrogen electrode.
Readiness to Corrode
Aluminum Al Al+++ + 3e -1.67
(Reconvert to Ore)
Ease of Smelting
Zinc Zn Zn++ + 2e -0.76
Iron Fe Fe++ + 2e -0.44
Nickel Ni Ni++ + 2e -0.25
Tin Su Su++ + 2e -0.14
Lead Pb Pb++ + 2e -0.13
Hydrogen 2H 2H+ + 2e 0.00
Copper Cu Cu++ + 2e 0.34
Silver Ag Ag++ + 2e 0.79
Platinum Pt Pt++ + 2e 1.20
Gold Au Au+++ + 3e 1.42
10
Standard Galvanic Series
11
THE GALVANIC SERIES OF METALS IN SEA WATER
Magnesium ACTIVE
Zinc
Aluminum
Couple Mildly Iron
Corrosive for Iron
Lead
Tin
Nickel (Active)
Brass Couple Severely
Corrosive for Iron
Copper
Nickel (Passive)
410 Stainless
Titanium
304 Stainless
Silver
Gold
Platinum NOBLE
12
Factors Affecting Corrosion
• pH of environment
• Concentration of corrosive
species
• Stream Velocity
• Oxygen Content
• Temperature
13
Forms of Corrosion
14
Forms of Corrosion
Uniform Corrosion
Uniform Corrosion
15
Forms of Corrosion
Localized Corrosion
Takes place on specific locations:
• Is hard to predict
• Is hard to monitor
• Can lead to catastrophic failures
• Has numerous forms the most important are:
• Pitting
• Crevice
• Stress Corrosion Cracking
• Erosion Corrosion
• Galvanic 16
Forms of Corrosion
Uniform Corrosion – Pitting Corrosion
Pitting corrosion of SS
17
Forms of Corrosion
Uniform Corrosion – Crevice Corrosion
Crevice or contact corrosion is the corrosion produced at the
region of contact of metals with metals or metals with
nonmetals.
Crevice corrosion of SS
18
Forms of Corrosion
Uniform Corrosion – Galvanic Corrosion
20
Forms of Corrosion
Uniform Corrosion – Galvanic Corrosion
21
Hydrogen Blistering
Grain Boundaries 22
Hydrogen Blistering
23
Hydrogen Embrittlement
24
Intergranular Corrosion
•Intergranular corrosion
occurs preferentially along
grain boundaries for some
alloys and in specific
environments
25
Erosion Corrosion
26
Stress Corrosion Cracking
• Stress corrosion cracking
(SCC) is caused by the
simultaneous effects of
tensile stress and a
specific corrosive
environment. Stresses
may be due to applied Stress corrosion cracking of stainless steel
loads, residual stresses
from the manufacturing
process, or a
combination of both.
28
ENGINEERING MATERIALS
Materials are classified into two groups; metals and non
metals
International materials
standards and codes
30
Material Properties
Physical Properties
- Density
- Thermal Expansion
- Thermal Conductivity
Mechanical Properties
- Strength (ultimate, yield)
- Ductility
- Elasticity
- Hardness
- Toughness (Impact resistance)
- Wear Resistance
- Creep resistance & rupture
31
Mechanical Properties of Material
Yield Strength
Material resistance to yield (start of plastic deformation)
Ultimate Strength
Maximum strength prior to fracture
Fracture
Material Failure
32
Mechanical Properties of Material
Hardness
Material resistance to notch formation, however, more hard
materials are more susceptible to cracking during processing,
forming, or welding
33
Mechanical Properties of Material
Toughness
Toughness is defined as a materials capacity to absorb energy,
which, is dependant upon strength as well as ductility
Test Methods
- Charpy V-notch
-Most applicable method
34
Mechanical Properties of Material
- Chemical composition
- Materials processing
- Heat treatment
Ductile-to-Brittle Transition
35
Mechanical Properties of Material
Ductile-to-Brittle Transition
36
Mechanical Properties of Material
Classification of Wear
- Metallic against non-metallic abrasive (erosion)
-Erosion of impellers by sands contained in flowing liquid
-Erosion of earth removing devices by abrasives in dry sand
39
Mechanical Properties of Material
Creep
Creep is defined as a very slow plastic strain increased by time and
temperature (time and temperature dependant) for stressed
materials.
Rupture
Rupture is material failure due to creep
40
I. Families of Alloys
41
Materials Categories
42
6. Carbon Steel
• High availability
• Economic
43
Carbon Steel Materials
Carbon Steels
Iron-Base alloys contain certain percentage of carbon as a main
alloying element, however, some elements may be contained as
residuals.
- Low-carbon steels
Contain upto 0.3% C
- Medium-carbon steels
Contain 0.3 to 0.6% C
- High-carbon steels
Contain 0.6 to 1.0 % C
44
Carbon Steel Materials
Iron-Carbon Diagram
45
Carbon Steel
• High availability
• Economic
46
7. Stainless Steel
47
7. Stainless Steel (Cont.)
Is known of its superior resistance against corrosion
48
7. Stainless Steel (Cont.)
Stainless Steel families are:
49
7.1 Austenitic Stainless Steel
50
7.1 Austenitic Stainless Steel (Cont.)
Austenitic SS Grades
51
7.2 Ferritic Stainless Steel
• Is included within the AISI 400 series
• Cr is 11-30%
• Ferro-magnetic
• Not hardened by heat treatment
• Used for nitric acid services, water, food processing, automobile
trims and architectural applications.
• Their impact resistance is poor
• Their weldability is poor
• The general-purpose grade of this stainless steel family is grade 430
which contains 17% Cr.
• Contains Cr and Mo as the major alloying elements
52
7.3 Martensitic Stainless Steel
53
7.3 Martensitic stainless steel(Cont.)
Martensitic SS Grades
54
7.4 Super Stainless Steel
55
7.5 Duplex Stainless Steel
Is a noble metal, this is why it is known of it superior
resistance to corrosion
Ni forms a protection layer of nickel oxide
Ni and Ni alloys are being used extensively in industry
57
8. NICKEL AND NICKEL ALLOYS (Cont.)
58
8.1 Ni (alloys 200 &201)
59
8.2 Ni-Cu alloys (alloys 400, K-500, Cupro-
Nickels 90/10 & 70-30)
60
8.3 Nickel-Molybdenum alloys (Alloy B-2)
Addition of molybdenum ensures good resistance to
chloride pitting and to reducing acids in general. Also
alloy B-2 is known of its immunity against stress
corrosion cracking.
61
8.4 Nickel-Chromium-Iron alloys
(Alloys 600 & 800)
62
8.5 Nickel-Chromium-Molybdenum alloys
(C-276, C-4 & alloy 625)
resistance properties of the last two families they
considered like the super-nickel alloys where they are
resistant to nearly every single environment and hence
their cost is considerably higher than the other Ni alloys.
63
9. TITANIUM AND TITANIUM ALLOYS
Is widely used in aerospace, medical and petroleum
industries
Is known of its excellent corrosion resistance properties
Used in seawater cooling, seawater valves and fittings, data
logging systems, cathodic protection anodes, pumps and
valves as well as underwater operations.
64
III. Corrosion Monitoring &
Control
65
How we control Corrosion?
66
Corrosion Control Techniques
67
I. MATERIALS SELECTION
68
Corrosion Control Techniques
Materials Selection
Corrosion Resistance
Mechanical Cost
Effectiveness
Properties
Availability
69
Corrosion Control Techniques
Materials Selection
70
INTRODUCTION
71
1- Materials Selection
Introduction
Is made to ensure proper resistance against the intended
service environment.
72
Introduction (cont.)
Materials selection is made either using a degradable
material (carbon steel) with the addition of a “corrosion
allowance” with or without the addition of a corrosion
control technique (e.g. coating, cathodic protection, etc.)
Or using a corrosion resistant alloy (a material that doesn’t
readily corrode in the environment) such as the use of
stainless steel or nickel alloys.
73
Introduction (cont.)
Materials selection for corrosion control depends upon
1. Knowledge of materials properties and corrosion control
2. Knowledge of corrosion process, mechanism and theory
3. Knowledge of service (environment, its operating
conditions)
4. Knowledge of materials behavior with the environment
5. Knowledge of lifetime required
6. Knowledge of economics
7. Knowledge of corrosion control techniques
8. Case histories in same application
74
Introduction (cont.)
A. Information needs
• Process flow diagrams (PFD) showing design/ operating/ upset
conditions of:
• Temperature (min. & max.)
• Pressure
• Stream chemical analyses showing the corrosive constituents
and their concentrations:
• H2O
• Dissolved gases (O2, CO2, H2S)
• Cl-
• TDS (total dissolved salts)
• pH
• TAN (total acid number ) for crude oil
• Total Sulfur Content
75
Introduction (cont.)
3. Stream Velocity
Corrosion rate and corrosion type are function of flow
velocity
CORROSION RATE
76
Introduction (cont.)
MSPR = highlights:
77
Effect of temperature on material selection
78
MATERIALS SELECTION
Process flow
Stream analyses Operation Dept.
Service conditions
Codes, standards,
specifications, textbooks, Materials Selection Inspection Dept.
handbooks, vendor & Corrosion Control Dept.
recommendations
Past experience, case studies Corrosion
Monitoring
79
Materials Selection (cont.)
80
Materials Selection (cont.)
1. Corrosion Theory
2. Corrosion Forms
3. Criticality of Service
4. Lifetime Required
5. Corrosion Control Techniques
6. Corrosion Resistance of Materials
81
2. Corrosion Allowance
82
Corrosion Allowance (Cont.)
CA= CR x LT
Where CA is the Corrosion allowance in mils (1/1000 inch)
or in mm
CR is the estimated corrosion rate in such an environment in
mil/year or mm/year
LT is the required lifetime in years.
83
Corrosion Allowance (Cont.)
CA involvement in codes
84
3. Materials Selection in Selected Environments
85
3.1. HIGH TEMPERATURE SULFUR CORROSION
86
3.1. HIGH TEMPERATURE
SULFUR CORROSION (CONT.)
Crude oils and their fractions contain sulfur compounds
including polysulfides, hydrogen sulfide, mercaptans,
aliphatic sulfides, disulfides and thiophenes. At temperatures
in the range 260°C to 540°C steels are significantly corroded
by these compounds.
87
3.1. HIGH TEMPERATURE SULFUR
CORROSION (CONT.)
88
3.2. HYDROGEN ATTACK
Hydrogen service is defined as one in which the partial
pressure of hydrogen exceeds 100 psig
89
3.2. HYDROGEN ATTACK(CONT.)
90
3.3. NAPHTHENIC ACID CORROSION
91
3.4. Wet Hydrogen Sulfide Attack
Wet H2S service is one in which liquid water with
sufficient dissolved hydrogen sulfide is present to cause
sulfide stress corrosion cracking (SSCC) and/ or hydrogen
induced cracking (HIC) of vulnerable materials.
The threshold conditions above which precautions have
to be taken to avoid SSCC are defined in NACE MR0175
92
3.4. Wet Hydrogen Sulfide Attack
CS shall:
- contain Ni < 1% and S < 0.02
- be normalized and thermally stress relieved
- Have hardness < 22 HRC
- have reasonable corrosion allowance
93
3.4. Wet Hydrogen Sulfide Attack
SCC Pitting
Hydrogen embrittlement
94
3.4. Wet Hydrogen Sulfide Attack
95
3.5. POLYTHIONIC ACID CORROSION
Is a mixture of sulfurous acids formed by the interaction
Two strategies to avoid PTA are available. The most
resistant grades of stainless steel, type 347 and 321, can
be selected or the equipment can be provided with an
alkaline wash on shutdown, as outlined in NACE RP0170
96
3.6. AMINE SERVICE
Amine service is one containing aqueous solutions of
monoethalomine (MEA), or diethanolamine (DEA), or
methyldiethanolamine (MDEA), or di-isopropanolamine
(DIPA), usually in about 30 % concentrations. DEA is to be
used mainly in hydrogen sulfide removal units.
Some precautions shall be made for the use of materials
in amine units where amine solutions are capable of
causing stress corrosion cracking of welded or cold-
formed steel parts
97
3.6. AMINE SERVICE (CONT.)
item requirements
Carbon and carbon manganese Fully killed steel (i.e. contains > 0.1% Is)
steel equipment (vessels, “Requirements for Wet H² S Service” apply
exchangers, filters etc.), paperwork in the case of Rich Amine Service.
and instrumentation (wetted parts). Cold formed items, including exchanger
tubing bends shall be stress relieved.
Post weld heat treat irrespective of
thickness and operating temperature,
including attachment and repair welds.
Screwed connections Not permitted
98
3.7. CAUSTIC SERVICE
Care should be made on using carbon steel for caustic
service
99
3.8. WET CO2 CORROSION
Carbonic acid is corrosive to carbon and low alloy steels,
corrosivity being dependent on a range of factors
including CO2 partial pressure, temperature, and liquid
phase composition and flow velocity. Corrosion rates
have been calculated using de Waard et al formulae
100
CARBON DIOXIDE CORROSION
Use of austenitic stainless steel if water contains less than 400ppm Cl-
and temperature less than 50 Deg C
101
3.8. WET CO2 CORROSION (CONT.)
The standard 300 series austenitic stainless steels are
potentially at risk of stress corrosion cracking in chloride
containing environments at temperatures above about
60C. It is common to apply external coatings, or foil
wrapping under insulation, to such pipework in marine
environments to prevent access of chlorides from
rainwater and concentration at the metal surface.
104
3.9. Chlorides Corrosion
Formation water is the main source of salts
105
CHLORIDES PITTING
106
3.9. CHLORIDE PITTING, CREVICE AND STRESS
CORROSION OF STAINLESS AND HIGH ALLOY
MATERIALS(CONT.)
108
II. Improved Design
109
Improved Design
Examples of avoiding
impingement corrosion by design
111
Improved Design
Bad Examples of
avoiding crevice Good
corrosion by design
112
Improved Design
t (required) = t min + CA
113
Improved Design
• Incorporation of corrosion allowance
114
Improved Design
Non-metallic Gasket
Non-metallic
Sleeve
Non-metallic Washers
115
III. Corrosion Control Techniques
Chemical Treatment
116
Corrosion Control Techniques
Chemical Treatment
Chemical treatment involves injecting chemicals that
Retard the corrosion of a metal.
Types of Treatment :
Neutralization ( pH control )
Removal of dissolved gases ( scavengers )
Corrosion inhibitors
Biocides
117
A. pH Control
118
A. pH Control
Steel corrosion rate related to hydrogen ion
concentration in electrolyte
To avoid acid corrosion, the pH of the
medium shall be raised up to about 7
by injection of
• Caustic Soda NaOH
• Ammonia NH3
119
Crude Oil Fractional Distillation
120
Corrosion Control Techniques
Chemical Treatment
Chemical injection
system for a crude
distillation column
overhead
121
B. Removal of Dissolved Gases
122
C. Corrosion Inhibitors
NACE definition :
• Metal
• Environmental chemical composition
• Service condition (e.g. temperature, flow rate)
123
Application of Corrosion Inhibitors
- Oil refineries
- Petrochemical plants
- Oil and gas production
- Desalination plants
- Cooling water installations
- storage facilities
- Hydro tests
A Cooling Tower Unit
124
Classification of Inhibitors
pH < 5
pH 5 – 10
125
A. Inhibitors for Acid Media
Usually organic compounds with long hydrocarbon chains with polar
(charged) head
126
B. Inhibitors for Near Neutral Media
Anodic
Cathodic, or
127
C. Inhibitors for Near Neutral Media
Safe or Dangerous
128
Mixed Inhibitors
Compatible mixture
129
Efficiency of Inhibitors
Expressed as :
Protective Power ( Z)
Where,
Z = [(RO-R) / RO] X 100
130
Efficiency of Inhibitors
Corrosion rate
concentration
Corrosion inhibitor
concentration
131
D. Biocides
Definition
A substance that is capable of killing a certain
micro-organism or spectrum of Micro-organisms
Biocidal activity
The concentration needed to kill the micro- organisms
132
Biocides role in corrosion control
133
Control of Microbial Corrosion
USE OF BIOCIDES IN CLOSED SYSTEMS
134
Chemical Injection
Non-metallic Tanks
137
Corrosion Control Techniques
Chemical Treatment
138
Corrosion Control Techniques
Chemical Treatment
139
Corrosion Control Techniques
Chemical Treatment
Corrosion Monitoring
Definition :
“ the systematic measurement or evaluation of the
corrosion rate and type of corrosion occurring on an
equipment “ .
140
Corrosion Control Techniques
Chemical Treatment
141
Corrosion Control Techniques
Chemical Treatment
Coupons
Electrical Probes
142
Corrosion Control Techniques
Chemical Treatment
Corrosion Coupons
143
Corrosion Control Techniques
Chemical Treatment
144
Corrosion Control Techniques
Chemical Treatment
Coupon Handling
145
Corrosion Control Techniques
Chemical Treatment
Wire-Loop
Flush
Cylindrical
146
Corrosion Control Techniques
Chemical Treatment
A. In corrosive media
B. In non-corrosive media
A
B
147
Corrosion Control Techniques
Chemical Treatment
Usually includes:
Corrosion Coupon ; mainly for visual evaluation of corrosion
type
Electrochemical Probe ;
for more accurate
instantaneous corrosion
rate determination, e.g.
ER probe
148
Corrosion Control Techniques
Chemical Treatment
149
Corrosion Control Techniques
Chemical Treatment
151
Corrosion Control Techniques
Chemical Treatment
152
IV. PROTECTIVE COATINGS
153
3. Protective Coatings
Definition of a COATING
154
Types of Coatings
155
Wrapping & Sleeves
156
Wrapping & Sleeves
157
Corrosion Control Techniques
3. Protective Coatings
Paints
Definition :
“ a liquid material, which can be applied on a surface, and
which – after drying – forms a thin, cohesive,
non-porous film with good adhesion to the surface’’.
158
Surface Preparation
Criteria :
• Surface Cleanliness
Surface Roughness
159
Surface Profile
THREE PARAMETERS ARE IMPORTANT
TO OBTAIN ACCEPTABLE SURFACE PROFILE :
3-Density 160
Surface Cleanliness International Standards
161
Surface Cleanliness
Sand blasting
Grit blasting
162
Water Jetting
163
Abrasive Blasting
Sand blasting
SAND BLASTING
164
Grit Blasting
By using metal shots with sharp
edges
Recyclable
165
Chemical Composition of Paints
Primary Components :
Resin ( binder / vehicle / base )
Hardener ( curing agent )
Solvent ( thinner )
Secondary Components :
Color Pigments
Cementing Particles
Corrosion Inhibitors
166
Painting Application
167
Paint Application Techniques
BRUSH:
VERY EFFECTIVE
VERY SLOW
ROLLER:
INEFFECTIVE
POROUS FILM
SLOW
168
Spray Application
Fan
SPRAYING = ATOMIZATION
169
Spraying (cont.)
SPRAYING
FAST
VERY EFFECTIVE
UNIFORM FILM
170
Air Spray
171
Airless Spray
172
Electrostatic Painting
173
Electrostatic Spray
174
Painting System (Cycle)
The 3-layer paint system :
Primer :1st layer
Provides corrosion protection
Provides adhesion to metal surface
175
3-Layer Paint System
For internal surfaces, No need for neither top coat Nor color
code. Use extra thicker inter-coat instead
176
Pipeline Coating System
3-Layer System
Polyethylene
Or
Polypropylene
2-3 mm Thick
177
Keys of Coating Success
SURFACE PREPARATION
MATERIALS
COATING APPLICATION
INSPECTION
178
Corrosion Control Techniques
3. Protective Coatings
179
Dew Point Measurement
180
Key to Successful Painting
1. NO RAIN
2. NO DUST
3. RELATIVE HUMIDITY DOES NOT EXCEED 85%
4. NO WIND
5. ATMOSPHERE TEMPERATURE SHOULD BE
BETWEEN 10-50 °C
6. GOOD ACCESSIBILITY FOR THE WORK PIECE
181
Key to Successful Painting
6. PAINT INSPECTION
• INTEGRITY OF CANS
• SHELF-LIFE
• POT LIFE
• INDUCTION TIME
• COLOR CODE (TOP COAT)
182
Key to Successful Painting
8. PAINT TECHNICAL DATA SHEET
• GENERIC TYPE
• CURING TIME
• DFT (DRY FILM THICKNESS) LIMITS
183
Painting Data Sheet
Steel Company
184
Coating Properties
185
Paint Inspection
Surface cleanliness
Surface roughness
Coating adhesion
186
Surface Cleanliness Inspection
187
Surface Cleanliness Inspection
Comparator
188
V. CATHODIC PROTECTION
189
Corrosion Control by Cathodic Protection
Zn
Fe
190
Application of Cathodic Protection
• Ship hulls
• Offshore jackets
• Offshore jetty piles
• Offshore sheet piles
• Offshore pipelines
• Buried piping and pipelines
• On-grade storage tank bottoms
• Buried tanks
• Water tank interiors (as well as water portion of crude storage
tanks)
• Any other electrolyte immersed structure
191
On-Shore Applications of CP Systems
192
Off-Shore Applications of Cathodic Protection
193
CP Codes and References
There are numerous codes and references that shall be referred
to when dealing with cathodic protection among these are:
- NACE RP 0169
- NACE RP 0176
- NACE RP 177
- NACE RP 575
- BS 7361 PART I
- DNV RP B 401
- API 651
- J. Morgan, “Cathodic Protection”
- A.W. Peabody, “Control of Pipeline Corrosion”
194
CP Techniques
There are two cathodic protection Anode e Fe
techniques these are:
-Sacrificial (Galvanic): Involves the
use of a more active metal as a
source of protection current
(anode)
195
CP Techniques
ICCP Sacrificial
196
Sacrificial and Impressed Current CP
Sacrificial Impressed current
No need for external power source Requires an external power source
197
Cathodic Protection Criteria
198
Instant off Potential
199
100mV Potential Shift
200
Sacrificial Anodes
201
High Potential Mg Anodes
202
Standard Mg Anodes
203
Electrochemical Properties of Mg
High Potential
Properties Standard Mg
Mg
Efficiency (%) 50 50
204
Zinc Anodes
Chemical Composition
Zinc anodes are used either Component Composition (%, weight)
for soil cathodic protection at Fe 0.005 max.
205
Sacrificial Anode Backfill
206
ALUMINUM ANODES
• Typical chemical composition of aluminum
anodes is shown
Element Percentage
207
ALUMINUM ANODES
• Electrochemical properties of aluminum anodes can
be seen in the table.
Anode Capacity 1150 amp hours per pound (Minimum)
Potential (Calomel) 1.080 volts (Minimum)
Consumption Rate 7.6 pounds per amp year
208
ALUMINUM ANODES
• Aluminum anodes
come in numerous
shapes. Bracelet,
slender or flush
type are the
aluminum anodes
shapes used.
209
ZINC ANODES FOR MARINE APPLICATIONS
210
Zinc Anodes
211
Impressed Current Anodes
• Impressed current anodes involves any material.
– FeSiCr
– Graphite
– Platinized
– Elastomeric anodes
212
Fe Si Anodes
213
Fe Si Anodes
Silicon 14.20 - 14.75%
Chromium 3.25 - 5.00%
Manganese 1.50% max
Composition, ASTM A518 Grade 3
Carbon 0.70 -1 .10%
Copper 0.50% max
Molybdenum 0.20% max
Electrochemical properties
Maximum Amps per anode in a Equivalent current density on
Average soil resistitivity along
coke breeze column, 12" OD by surface of coke breeze column,
groundbed, Ohm-cm
60" Milliamps/sq ft
215
Potential Monitoring
electrode.
electrodes.
216
Potential Monitoring
217
Test Stations
218
Cable Connections
• In general cables are connected to structures either mechanically or by
metallurgically (welding)
• CAD welding is made using a crucible, flint gun and thermite weld powder.
• Pin brazing involves the use of pin brazing machine and requires more skilled
labor.
219
Cable to Cable Connection
220
Cable to Cable Connection
221
Electrical Isolation
• Structures to be protected shall be isolated from
portions that doesn’t require protection. Hence
electrical isolation shall be made.
• In case of underground piping, electrical
isolation is made through the use of either
isolating flange kits or through the use of
monolithic joints.
• Isolating flange kits have the disadvantages of
maintainability, can leak at high pressures.
• Isolating flange kits shall not be used in offshore
environments
• Isolating flange kits have the advantage of
having a relatively low cost and is easy to install.
• Monolithic isolating joints can be used at under
any operating pressure.
222
Electrical Isolation
223
Pipeline Metallic Casing
226
Carbonaceous Backfill
• Inorder to minimize the electrical
resistance between groundbed
anodes and earth, carbonaceous
backfill is used.
• Coke breeze comes in many
grades but the most important
factor is the elctrical resistivity
that shall be a minimum of 1
Ω.cm
• Impressed current anodes are
some times cannistered with the
backfill.
• Backfill shall be well tamped to
eliminate air gaps and voids
227
Carbonaceous Backfill
Property 218-L 218-R 251 251-P 4518
• Resistivity,
0.02 0.02 0.01 0.01 0.01
ohm-inch
• Resistivity,
0.05 0.05 0.03 0.02 0.03
ohm-cm
• Carbon
99.0 99.0 99.8% 99.8% 99.9%
(L.O.I. method)
• Moisture 0.10% 0.10% 0.07% 0.07% 0.02%
• Ash 0.35% 0.35% 0.12% 0.13% 0.10%
• VCM 0.30% 0.30% 0.02% 0.02% 0/22%
• Sulfur 3.75% 3.75% 5.8% 5.8% 4.3%
• Bulk Density
46-50 48-53 64-72 64-72 62-66
(lbs/ft3)
• General
Sizing
+4M < 10% +4M 25% +20M <5% 4M 10%
+ 4 Mesh
+8M > 90% +8M > 70% +100M >70% +20M > 80%
+ 8 Mesh
-8M < 10% -8M < 5% -100M Balance -20M 10%
- 8 Mesh
• Applications Use for Ground Beds & Deep Wells
228
Cathodic Protection Surveys
• Cathodic protection surveys are made for:
– Gathering information regarding the electrolyte through
resistivity and pH measurement
– Gathering information with regards to any existing cathodic
protection system
– Information with regards to sources of corrosion hazard
(sources of stray current)
– Information with regards to power sources
– Cathodic protection surveys could be made to existing
underground facilities as means of evaluating the status quo
of the structure survey includes:
• DCVG survey
• Line current survey
• Potential Survey
• Close interval survey
• Interference survey
229
Soil Resistivity Surveys
230
Interference Surveys
• Interference survey is
made to determine the
detrimental effects
caused by the
interference of two
cathodic protection
systems
• Interference is eliminated
in the case of pipelines
through solid bonding or
resistor bonding
231
Stray Current
232
DCVG Surveys
233