Process Sizing Criteria: Plant
Process Sizing Criteria: Plant
Process Sizing Criteria: Plant
DOC. N. PLANT :
2017 30 000 R SP SP 20003 ONSHORE FACILITIES
Snamprogetti DOC. N.
JOB. 308700 - DOC. 999-ZA-E-03003 DB 2017 999 P312 205
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CONTENTS
1 SCOPE .................................................................................................................................... 5
2 PURPOSE ............................................................................................................................... 5
3 DESIGN BASIS........................................................................................................................ 5
4 GENERAL................................................................................................................................ 6
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7 PIPING ................................................................................................................................... 28
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9 SOFTWARE........................................................................................................................... 37
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1 SCOPE
This procedure outlines the basic sizing/ design criteria to be applied as a minimum in the
equipment specification for the design of ONSHORE FACILITIES of SOUTH PARS FIELD
DEVELOPMENT (Phases 4 & 5) Project which are located at ASSALUYEH, IRAN. In the event of
a conflict between this specification and any of the Licensers sizing/design criteria, the Licensers
shall prevail.
2 PURPOSE
3 DESIGN BASIS
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4 GENERAL
4.1 APPLICABILITY
The process design shall apply to new installations and to major modifications or extensions of
existing installations, both onshore and offshore. It is also applicable to supplier’s packages.
PROCESS: Discipline(s) in charge to study the process units, but also all associated off sites and
utility fluids.
PFD (PROCESS FLOW DIAGRAM): It presents the succession of the operations in the fluid
processing to reach the required products specifications set in the objective of the plant processing
including associated off-sites and utility fluids. The succession of operations are pictorially
represented by equipment symbols and all lines for a good understanding.
The controls are indicated by a simplified symbolic representation of control loops.
The equipment reference is given closed to the symbolic representation.
In the upper part of the sheet, the equipment reference is remind to indicate the function of each
equipment.
The operating pressure, temperature, flow rate, and heat duty values are indicated in separated
sheet by means of fluid number inside a diamond. Operating pressure and temperature in the
appropriate square shape are indicated on PFD.
PROCESS DATA SHEET : data sheet for equipment, packages, etc…, containing the process
information required for sizing and given sometime the sketch with sizes for some equipment such
as vessels, columns. It is issued by process.
It is different of the mechanical data sheet which defines additional information for construction and
it is issued by specialists and/or vendors.
5.1.1 General
The design pressure is the value used for the mechanical sizing of equipment.
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The design pressure of a piece of equipment (excluding storage tanks, atmospheric tanks and
pipelines) shall be taken as the following:
(*) 2.0 barg for PSV discharging to atmosphere, 3.5 barg for PSV discharging to flare networks.
(**) 2 or 3.5 barg as minimum design pressure
For the minimum design pressure has to be considered that:
• Unless otherwise noted, the design pressure specified by Process applies to the vapour phase
at the top of the vessel.
• Minimum design pressure not applicable for thin wall equipment such as silos, storage tanks. In
that case the governing parameter is full of liquid.
• The design pressure shall also account for upset or transient conditions such as start-up,
pressure surge, settle-out pressure at compressor suction, etc. ..
• Vapour pressure at design temperature should be considered as design pressure except when
safety relief valves are provided.
• Equipment subject to operate at pressure below atmospheric pressure will also be designed for
full vacuum.
• Equipment that could face vacuum under abnormal conditions such as :
Ø vacuum conditions during start-up, shut down and/or regeneration purges.
Ø normally operated full of liquid but can be blocked in and cooled down
Ø containing condensable vapor but can be blocked in and cooled down
Ø could undergo a vacuum condition through the loss of heat input.
will be treated case by case. They will be designed for full vacuum unless fully reliable
protective devices are provided (vacuum breaker, pressurisation gas, low pressure switch,....)
• For equipment in equilibrium with flare, the design pressure of the equipment is the flare design
pressure.
• Hydraulic pressure due to the relative elevation between equipment and also the PSV's
location shall be considered.
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• A margin of 10% is generally adequate in order to ensure protection of the equipment with one
conventional pressure relief valve (PSV), one pressure alarm (PAH) and one pressure switch
(PSHH). It is reminded that the following tolerances are generally admitted for conventional
instrumentation.
§ PSV opening : +/- 3%
§ PSV closing : +/- 5%
§ PSV recommended leak test : 10% below set point
§ Pressure switch and transmitter : +/- 1%
• In case of absolute necessity (for example in case of high pressure), the use of piloted PSV
(tolerance of +/- 1% on set point) could help to reduce the design pressure.
• If two or more PSV are in service, the set pressure will be staggered to avoid chattering. The
difference between set points shall be less than 5% of the design pressure.
5.1.3 Pipelines
For pipelines, the design pressure is function of the maximum Allowable Operating Pressure
(MAOP) and the design factor which depends on the class location.
Process determines only the MAOP.
MAOP is normally the design pressure of the last equipment upstream the pipeline plus the
hydrostatic pressure due to the pipeline profile.
Particular attention shall be paid to the transient conditions such as equilibrium pressure plus
hydrostatic pressure, water hammer, etc. …
5.1.4.1 Compressors
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5.1.4.2 Pumps
a- Centrifugal pumps
• Generally no PSV's are provided at the discharge of centrifugal pumps and the design pressure
shall be the discharge pressure of the pumps at no flow with the maximum suction pressure
and the maximum specific gravity.
• When the discharge pressure of the pumps at no flow is not available, this pressure can be
estimated :
b- Volumetric pumps
• At discharge of volumetric pumps :
MOP + 1 bar for MOP < 10 bar g.
MOP + 10% for MOP > 10 bar g.
PSV's are required.
• In case of two pumps in series, the maximum differential head will be the sum of the maximum
differential head of each pump if there is no pressure relief valve between the pumps.
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Full vacuum conditions should be added to design conditions since vacuum can happen during
cooling of such equipment (if it is not connected to atmosphere) unless fully reliable protective
devices are provided (vacuum breaker, pressurisation gas, low pressure switch...).
5.1.6 Columns
• For columns, the same design pressure will be selected for the top of a fractionation tower and
associated condenser, reflux drum and inter connecting piping.
• The design pressure at the bottom of a fractionation column (vapour phase) is determined by
adding the column pressure drop at the column overhead design pressure.
• Liquid density and maximum liquid height in the bottom will be specified on the process data
sheet to allow the vessel designer to calculate the bottom thickness.
5.1.7 Tanks
Atmospheric tanks shall be designed full of water or full of product if product specific gravity >1 as
a minimum. Depending on the type of tank, higher design pressures could be specified. To be
treated case by case depending on tank type.
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• The design temperature is the value used for the mechanical sizing of equipment.
• The design temperatures shall be specified as follows; with due consideration for the special
cases discussed at section 5.2.4 :
Max. design temperature = max. operating temperature + 15°C or maximum exceptional
operating temperature, whichever is the greater.
Note: Exceptional operating temperature is to be considered for operations duration exceeding
a total of 100 hours per year.
• Minimum design temperature should be 85°C due to the solar radiation. This value should be
examined case by case for equipment on which dilatation problem can occur (such as
doublewall tank, fixed tubesheet, plate heat exchanger) and for insulated high pressure vessels
(not to increase wall thickness).
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• Various pressure and temperature conditions sets will be specified for each phase of
equipment operation.
• Mixing of extreme conditions of pressure and temperature shall not be considered.
• Typical example is related to molecular sieves vessel design conditions specification. The sets
of conditions of each phase of the operating cycle will be specified, e.g. design conditions of
the adsorption phase, of the regeneration phase, etc.
• The minimum design temperature must take into account any depressurisation and
repressurisation (depending of material selection) of the equipment / piping that may occur
either during emergency or shutdown situation or gas blow-by from one equipment to another
equipment and to the possible consequence of change of material.
• The emergency depressurizing shall impact the material selection as follows:
§ Piping material
Piping material will be selected taking into account the temperature occurred during
depressurisation. Piping repressurisation shall be considered as to be performed with the
minimum depressurisation temperature.
§ Vessel material
The minimum temperature due to the blowdown conditions shall be associated with design
pressure. Although depressurization of any section of the plant cannot be performed unless the
section is isolated and permissive is obtained, repressurization may take place by operator’s
fault or a valve failure, therefore the minimum temperature shall be associated with design
pressure. No special devices are foreseen to ensure that the plant shall remain isolated and
depressurised.
In addition the above criteria will ensure safe operation also in case of residual piping stress is
present (in particular for low diameter nozzle/piping).
• The following conditions mentioned hereafter will be applied generally up to the next process
equipment.
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• Consideration for design temperature definition should be given to cooling medium failure when
coolers are used. Downstream of an air cooler, the design temperature is determined
considering that 20% of the duty is provided by natural draft.
• For bypassed air cooler, the design temperature of the downstream equipment, if any, will be
the maximum upstream operating temperature of the bypassed exchanger
• Downstream of other coolers, the design temperature will be the upstream maximum operating
temperature.
• Consideration to be given to conditions and fluids used for cleaning (e.g. steam). In this case,
both pressure and temperature conditions have to be provided.
• The steam out conditions for vessels are 150°C / ATM. This information is considered by
Vessel Department but will be also specified on SPP.
• Steam out will be not applied for units 104/105/106/111/147/148/149 and 150. For these units
nitrogen purging shall be considered.
• For equipment subjected to steam out operation full vacuum condition shall be specified.
• Consideration for upset and transient conditions such as start-up, shut-down,...In this case,
both pressure and temperature conditions have to be provided.
• The exceptional temperature generated by fire will not be considered for design temperature
selection.
• A specific design temperature will be given with the specified vacuum design pressure.
• The following considerations shall not prevail on § 5.2.4.2 regarding cooling medium failure.
§ The accidental temperature which may occur in emergency situations such as loss of
utilities, valve closure, air cooler failure or any abnormal operation corresponding to a short
duration are not to be taken into account as long as the temperature increase does not
exceed the codes limits (Investigation has to be followed with specialists on a case by case
basis).
§ However equipment containing parts which can be damaged by abnormal high temperature
has to be designed for this temperature. This mainly concerns equipment internals.
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H2S and CO2 corrosion results in metal loss and in metal embrittlement (cracking).
Regarding the stress craking corrosion, this occurrence can be limited by using material listed in
the NACE MR 01.75.
Regarding the hydrogen induced cracking corrosion, its occurrence is directly linked to the material
quality that is to say the possible presence of elonged inclusions, microsegregations. Therefore,
the HIC control is a matter of material specification.
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Sour service definition is based on NACE MR 01.75 criteria considered as a minimum requirement.
The H2S service definition is to base the maximum pressure criteria, mentioned in the NACE,
either on equipment design pressure when no PSHH protection is implemented on the concerned
system, or on PSHH level when existing.
The limits of TEP sour service specifications SP-TCS-612 (wet sour service SSCC & HIC) and SP-
TCS-622 (wet sour service SSCC only) are as follows:
A. When equipment is classified in sour service under the normal operating conditions of the plant
as per definition of NACE standard, specification SP-TCS-612 (i.e. SSCC & HIC) shall be
applied.
B. For equipment operating under transient sour service conditions only (i.e. upset, start-up, ..),
the use of specification 612 vs. 622 will be based on the expected occurrence of the sour
service conditions, as follows :
• for series 600# and above, specification 622 will be applied if transient sour service
conditions are expected to represent less than 10% of the total operating time. Otherwise
spec 612 shall be used.
• For series below 600#, specification 622 will normally be applied, unless the expected
duration of the transient sour service conditions represents more than 20% of the operating
time.
• Vessel department has developed two job specifications amending the Company sour service
specifications :
§ RP 2017 999 6300 02 amends Company spec. SP-TCS-612
§ RP 2017 999 6300 03 amends Company spec. SP-TCS-622
• On process data sheets, a note has to be added on material specification to define which RP is
applicable.
• Flare systems :
§ FA system (high pressure flare) will be “sour service” following Company spec. SP-TCS-
612.
§ FS flare (wet MP flare) is out of NACE conditions (maximum back-pressure is 2.2 bar abs),
FS network will not be “sour service”.
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§ FB network operating at very low pressure and with low H2S partial pressure does not
require sour service definition.
• Cladded carbon steel equipment (or weld overlay) in sour service conditions :
Specifications SP-TCS-612 or 622 shall not be applied to carbon steel, underlining a cladded
vessel in sour service or nozzles fitted with weld overlay.
• For caustic soda and amine service, a postweld treatment for stress relief will be specified to
avoid corrosion cracking. SP-TCS-622 may be applied for this service.
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The pressure vessel code requires to classify the equipment in accordance with lethal service.
In order to carry out this classification, the mention “lethal service” will be specified on equipment
data sheets handling a fluid with H2S content higher than 1000 ppm wt or where mercaptan level is
exceeding 100 ppm in release gas.
6.1 PUMPS
The minimum margin between the normal and rated flow for a pump will be as below :
• reflux pump = +20% of normal flow
• other process pump = +10% of normal flow
• utility pump = +10% of normal flow
• loading pump = 0% of normal flow
• export pump from storage (continuous operation ) = +15% of normal flow
• Boiler feed water pump = See applicable codes but not less than 10% of normal flow
To be noted that:
• When a non automatically controlled minimum flow protection has been installed, the
permanent re-circulation flow (if required) must be added to the net process flow.
• Normal and rated flows will be identical in such instance as:
Ø intermittent service pumps : sump pump
Ø when the pump has been overrated to allow for a centrifugal type and if overrating is ≥ 10%
Ø re-circulation flow such as for product loading lines or through amine filtration system.
• Automatic start
• As base case, pump automatic start will be done generally through FSLL (if flow transmitter
already exists).
• Automatic start is determined considering the following rules :
Ø personnel safety : for example flare KO drum pump will be started in order to avoid liquid in
flare tips. In that case, considering the non continuous operation of flare drum pumps, the
start of the spared pump can be performed by LSH or by DCS logic.
Ø equipment safety : for example BFW pump will be started in order to protect the steam
drum and the steam coil.
Ø severe process upset : pump generating by its shutdown one process unit trip or generating
an off spec product shall be spared automatically.
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Ø flaring: automatic start shall NOT be considered to minimize the flaring. For example, reflux
pumps unless a severe process upset is faced.
6.2 COMPRESSORS
• Normally no margin is taken if the flow is constant, a 10% margin can be used if the flow is
directly coming from a production separator to take into account slugging regime.
• The variations of gas compositions, molecular weight, Cp/Cv,..., and the operating
conditions(mainly suction pressure and temperature ) shall be taken into account to determine
the sizing case.
6.4 VESSELS
• 1st separation equipment (plant inlet): 10% on inlet gas flow rate.
• Other drums : 0% unless specific requirements
• Fractionation column : 0% unless specific requirements
• The following excludes the flare/vent drums, desalters and electrostatic dehydrators.
• If internals are installed, the common vapour internal shall be a wire mesh but for some
services vane pack can be used after discussion with Company
• The use of others vapour internals such as cyclones, etc. .. requires a Company approval.
• The basis of sizing is the critical velocity Vc
0.5
ρl − ρg
VC = 0.048
ρg
with ρl = liquid density in kg/m3
ρg = vapour density in kg/m3
The maximum gas velocity is K*Vc.
K is a coefficient depending of the service, and the use or the absence of wire mesh.
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• If a vane pack internal is used, the recommended K value is 3.3. This has to be confirmed with
the supplier.
• For horizontal vessels without vapour internal ( wire mesh, vane pack, .... ), the minimum
distance between the top of the vessel and the LSHH is the largest of 300 mm or 0.2 internal
diameter.
• Vessels handling paraffin oil shall not be equipped with gas internals.
A high efficiency inlet distributor can be considered to improve gas / liquid separation provided that
EPC contractor verify pressure drop through distributor and dimensions between inlet
distributor/mesh and inlet distributor/HLA
• If the vessel is sized to receive a slug, that slug volume shall be taken between NLL and HLA.
• The residence time corresponds to half of the hold-up time, the Normal Liquid Level (NLL)
being set at 50% of the HLL-LLL range. Exceptions will be specified on data sheet.
• The minimum liquid hold up time between LLA and HLA are as follows :
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Note 1: Liquid hold up time is based on one deaerator in shutdown associated with the normal
liquid flowrate
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To be noted that:
• Exception is made for vertical vessel with negligible liquid on clean service with manual or
on/off liquid outlet valve ; in that case volume of the hemi-spherical head can be used : LLL (or
LLLA/LLLS) location to be still compatible with SDV or control valve closing time.
• The distance between HLL and LLL will be in the typical range of 1 to 3.5 meters.
• When applicable, the hold up time below the very low liquid level ( LLLA or ILLLA) has to be
compatible with the time required to close a SDV.
• For three-phase separators, the retention time for the two liquid phases shall be considered.
• The effective retention volume in a vessel is that portion of the vessel in which the two liquid
phases remain in contact with one another. As far as the two liquid phases separation is
concerned, once either substance leaves the primary liquid section, although it may remain in
the vessel in a separate compartment, it cannot be considered as a part of the retention
volume.
• The highest density liquid retention volume is taken between the bottom and the normal
interface level ( INLL).
• The lightest density liquid retention volume is taken between the INLL and the normal liquid
level (NLL).
• Stand pipe shall be installed on clean service when at least 3 level instruments have to
installed (independently from level instrument required for safety actions) e.g. : one level
transmitter with two level gauges
• Minimum size for stand pipe: 3”
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6.4.4 Diameter
6.4.5 Manholes
• size of manholes
§ for vessel diameter < 1000 mm
− flanged vessel will be considered if equipement contains internals
− otherwise, size of manhole = 18”
§ for vessel diameter ≥ 1000 mm
− toxic service size of manhole =24"
− non toxic service size of manhole =20"
• location of manholes
at the opposite side of the utility connection for horizontal vessel
• number of manholes
Vessel
For vessel length/height less than 6 m a single manhole will be provided. For other vessel
(length/height > 6m), two manholes to be provided at least ; one manhole each 6 m for
longer/higher vessel. If vessel is equipped with internals (baffle..), one manhole to be
provided on each compartment.
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Trayed column
Manhole will be provided at the top, below the bottom tray, at the feed tray, at any other tray
at which removable internals are located, and at intermediate points so that the maximum
spacing of manholes does not exceed 15 trays. Tray spacing with manhole in the internal
will be at least 900 mm.
6.4.6 Handhole
Handhole size = 8". Handhole to be installed on vessel with diameter lower than 800 mm or on
vessel where severe fouling of internals is expected.
6.4.8 Drains
• location
The drain of the vessel shall be connected to the outlet line at low point for vertical vessel
and directly on the capacity for horizontal vessel or for vertical vessel with outlet line
entering inside vessel.
• Vent and drain diameter shall be defined as follows :
• Drain number :
For horizontal drums having a length greater than 6 m TL to TL, additional drain connections
are required . Additional drain is also required on each compartment of the vessel.
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On toxic service, a open drain connection (washing out) to be provided with blind flange (not
connected to outside).Size of open drain will be in the same diameter as drain connection.
As a conventional rule for a vessel containing a product at its boiling temperature, a minimum
elevation of 5000 mm will be specified when a recovery bottom centrifugal pump is provided. The
elevation will be updated when NPSH requirements are defined with rotating equipment specialist.
If there is no process requirement regarding the elevation, a note on PID will be indicated
"minimum for piping”.
6.5.1 Oversizing
• Shell and tubes heat exchangers and air coolers : 10% on surface.
The following gives some fouling factors for process and utility fluids which can be reviewed case
by case.
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• Utilities
Sea water 0.00050
Chilled water 0.00020
Potable water 0.00020
Saturated steam / LP condensate 0.00017
BFW/Demineralized water 0.00017
Nitrogen 0.00017
Instrument air 0.00017
Fuel gas 0.00017
Diesel light: 0.00030
heavy: 0.00035
For Plate Frame Heat Exchangers, a general fouling factor of 0.00005 m²°C/W shall be taken for
all fluids (or Process Licenser recommendation).
For Plate Fin heat Exchangers, no fouling factor shall be applied but an extra surface of 15% to be
added on calculated area.
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The temperature approach shall be optimised for heat exchangers but it shall not be smaller than:
• 5°C for TEMA type heat exchangers (shell and tube)
• 10°C for air coolers
• 3°C for plate type heat exchangers.
• 3°C for kettle type
TEMA R will be generally used for all shell and tubes and air pin type heat exchangers.
Fixed tube sheet exchangers are acceptable for non fouling service on the shell side. In this case,
Licenser or EPC Contractor shall define all exceptional operating conditions ( start-up, shutdown,...
) to check the necessity to provide an expansion bellow on the shell.
Air cooler to be induced type when air cooler is installed on pipe rack. Forced draft type shall be
considered
• if air cooler is installed at grade
• if inlet process temperature is above 175°C or air outlet over 93°C
or for multiple purpose exchangers, several sections stacked.
7 PIPING
7.1.1 Line velocity and friction loss for liquid line and gas line.
Line size of each line shall be firstly selected based on the mass flow rate and in accordance with
the velocity range criteria and then be checked in accordance with the friction loss range criteria as
given in paragraph 4.7.3 Line sizing criteria
Except for instrument piping, connections to equipment or piping in which minimum flow velocity
requirements govern, the minimum size shall be :
• ¾" for pipe when located above ground
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Pump suction lines shall be sized to provide available net positive suction head (NPSH) 1 meter
larger than that required by the pump selected.
Pump suction lines shall not be smaller than suction nozzle. Therefore, reducer at pump suction is
acceptable provided that the available calculated NPSH (with pressure loss in the reducer) remains
acceptable regarding the required NPSH.
Pump suction valves shall be in the same diameter as the line.
As a first estimate, the static head used in calculating the available NPSH shall be taken from the
low liquid level (LSLL) or the tangent line in the suction vessel to one of the following:
• The centerline of a horizontal pump or rotary pump
• The suction impeller on a vertical centrifugal pump.
For the value of NPSH specified on process data sheet, the reference elevation shall be indicated.
The design of suction lines from storage tanks shall be based on a NPSH taken from the lowest
specified liquid level in the tank at which rated pump capacity is required.
In sizing suction lines for reciprocating pumps, acceleration head shall be considered.
• The pressure drop of a control valve, which is installed at the discharge of pump, should be a
minimum of 20% of the system dynamic pressure loss at normal flow rate or 0.7 bar whichever
is greater. ( This criteria does not apply to loading pumps ).
• In case of mis-operation, the gas blow-by shall consider the flow rate through the control valve
full open and its by-pass also fully open when it is installed. If that flow rate size the flare, the
manual by-pass could be deleted or a mechanical interlock between the upstream control valve
manual block valve and upstream by-pass valve manual block valve could be installed.
• For control valve arrangement, refer to PID development DB 2017 V 999 P312 203.
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• personnel protection of equipment for operating temperatures above 70°C. A physical barrier
with warning signs attached to hot surface is preferred to thermal insulation if it is not required
for process reasons,
• to avoid external water condensation or ice
• steam or electrical heat tracing
In all cases, insulation shall be minimised in order to limit CUI (Corrosion Under Insulation).
DP (bar/km)
Vapour and steam lines ρv2 max. (kg.m.s –2) Max. Velocity (m/s)
Normal Maxi
- Continuous operation
P <= 20 bar g 6000 )
20 < P <= 50 bar g 7500 )
50 < P < =80 bar g 10000 ) Pressure drop must be
80 < P <= 120 bar g 15000 ) considered compatible
P > 120 bar g 20000 ) with corresponding service
- Discontinuous operation
P <= 50 bar g 10000 )
50 < P <= 80 bar g 15000 ) Pressure drop must be
P > 80 bar g 25000 ) considered compatible
- Column overhead 15000 ) with corresponding service
(high pressure columns)
Steam lines
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DP (bar/km)
Vapour and steam lines ρv2 max. (kg.m.s –2) Max. Velocity (m/s)
Normal Maxi
- P <= 10 bar g
Short line (L <= 200 m) 15000 0.5 0.15
Long line (L > 200 m) 15000 1.0 0.25
- P > 30 bar g
Short line (L <= 200 m) 15000 30 1.2 0.35
Long line (L > 200 m) 15000 30 2.3 1.0
Unit lines
- Liquid at bubble point with
0.6 1.0 0.6 1.0 1.4 1.8
dissolved gas
- Non boiling liquid 2.3 3.5 0.9 1.2 1.8 2.4
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Notes:
(1) 3.0 m/s maxi ( 2 m/s average ) at storage tank inlet or in loading.
(2) Vendor and/or Licenser requirements could supersede maximum velocity values upon
Company approval.
(3) Special considerations can be applied for copper-nickel or glass reinforced plastic piping upon
Company approval.
For preliminary mixed phase fluid line size calculations, the average density method will be used
while considering the following criteria:
• Vm : 10 to 23 m/s
• ρmV2 : 5000 to 10 000 Pa
• ρmV3 : 100 000 to 150 000 kg/s3
where:
• ρm= W / (( W l/rl ) + (W v/rv )) in kg/m3
W = W l + W v = total flow rate in kg/h rl = liquid density in kg/m3
W l = liquid flow rate in kg/h rv = vapour density in kg/m3
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The following criteria are typical and may have to be supported by economical appraisal.
∆ DP (bar / km)
LINE TYPE Max. velocity (m/s)
Normal Maxi
Long Carbon steel water line 0.58 1.16 -
Bonna line - - 2.5 to 3
Steam condensate (mixture) 0.2 to 0.3 - 10 to 20.
Corrosion
For corrosion resistant material ( SS, Special alloys,... ), no limitation of flowing velocity up to 100
m/s and no requirement for corrosion allowance.
For non corrosion resistant material, in corrosive fluid service, corrosion allowance for a design
service life and corrosion inhibitor injection are required. The flowing velocity is limited by the
inhibitor film integrity.
Erosion
For Duplex, SS or alloy material, the flowing velocity must be limited to:
• 100 m/s in single phase vapour lines and multiphase lines in stratified flow regimes ( 65 m/s for
13% Cr material ),
• 20 m/s in single phase liquid lines and multiphase lines in annular, bubble or hydrodynamic
slug flow regime,
• 70 m/s in multiphase lines in mist flow regimes.
For Carbon Steel material :
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• In case of continuous injection of corrosion inhibitor, the inhibitor film ensure a lubricating effect
which drifts the erosion velocity limit. The corrosion inhibitor erosion velocity limit will be
calculated taking into account the inhibitor film wall shear stress.
• In case of uninhibited fluid, the API RP 14 E recommendation should apply : the flowing
velocity must be maintained below the erosional limit :
Ve = C / (ρm)0.5
With: Ve erosional velocity in ft/s
ρm gas / liquid mixture density at flowing conditions in lb/ft3
C empirical constant equal to 150 to 170. C value up to 200 can be considered on peak
flow rate only in case of absence of abrasive ( solid ) particles such as sand. When solid
and/or corrosive contaminants are present C value shall not be higher than 100.
For flares and cold vents, the tip can be normally conventional or sonic depending on the required
back pressure and noise limitation.
When possible a sonic tip will be preferred. Sonic tip with Coanda effect and/or with variables slots
are prohibited.
The flares shall be generally smokeless.
The analysis of the causes of relief is required and an occurrence flaring loads balance including
each individual relieving rate for each possible cause shall be performed.
The radiation levels criteria shall follow the Basic Engineering Design Data. The minimum relative
humidity stated on the basis of design shall be applied.
When the radiation calculations are performed by a flare vendor it is necessary to check carefully
the emissivity coefficient used. The emissivity coefficient used by vendors does not take into
account the liquid carry over, they consider an ideal gas/liquid separation. The droplets size for the
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flare drum sizing and the expected liquid carry over shall be clearly indicated in the flare tip
process data sheet.
PSV's:
For the line sizing, the maximum capacity of the PSV, even if this figure exceeds the actual
maximum flow rate due to process limitations shall be considered.
• DP between the protected equipment and the PSV < 3% of PSV set pressure ( API RP 520
Part II )
• ∅ ≥ ∅ PSV inlet
• ρV² ≤ 25 000 kg/m/s² for ∅ ≤ 2"
• ρV² ≤ 30 000 kg/m/s² for P ≤ 50 bar g.
• ρV² ≤ 50 000 kg/m/s² for P > 50 bar g.
DEPRESSURISATION DEVICE
• minimum line size 2"
• ρV² criteria are the same as for PSV's
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For flare drum and cold vent drum, the sizing shall follow API RP 521 method with the following
droplets size in microns:
§ remote flare or cold vent offshore : 600µm
• vertical flare or cold vent onshore : 600 µm
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9 SOFTWARE
The following software will be used by Engineering Contractor for process related calculations
during BASIC stage:
• Plant thermodynamic simulations :
§ PRO II, PROVISION 5.10
• Heat exchangers thermal calculations :
§ Shell and tubes :
§ HTRI
§ Air coolers
§ HTRI
§ HTFS
The EPC contractor has to prepare a list of process software -not listed hereafter - they intend to
use; that list shall be approved by Company and shall incorporate software description.
The following softwares are recommended by Company for process related calculations :
• Plant thermodynamic simulations :
§ PRO II, PROVISION, HYSYS
• Multiphase calculations :
§ Steady state :
§ OLGA (1)
§ Transient conditions :
§ OLGA (1)
(1) option “slug tracking” to be used only at Company request
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