line sizing philosophy.pdf

Document Nu Number

PEC-EN-GDE-P-1756

Revision

1

Applicability

Sharjah, Mumbai, Chennai, Delhi & Jakarta

Document Type

Guidelines

LINE SIZING PHILOSOPHY

REVISION / APPROVAL HISTORY

1

24-May-2012

Complete Updated and Approved

Sunil Kumar

K Jain

K Ramachandran

N Nagarajan L Venkatesh V Aggarwal Handian

0

04-Dec-2006

Rev

Date

Approved

Description of Change

Hamid Arabashahi

Robert Page

Robert Page

Originator

Reviewer

Approver

Records of approval are retained in the BMS/Quality Department

Page Page 1 of 21 21

This document is an uncontrolled copy when printed or saved. Viewed by:  Parvathy C M 18-Jan-2013

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CONTENTS 1.0

PURPOSE...... PURPOSE........... ........... ........... ........... ............ ........... .......... ........... ........... ........... ............ ........... ........... ............ ........... ........... ...........4 .....4

2.0

SCOPE SCOPE ........... ................ ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... .......... ....4 4

3.0

DEFINITI DEFINITIONS... ONS........ ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ............ ............ ........... ........... .......... ....4 4

4.0

REFERENC REFERENCES ES ........... ................ ........... ........... ........... ............ ........... ........... ............ ........... ........... ............ ........... .......... ........... ........... ....... 5

5.0

RESPONSI RESPONSIBILI BILITY TY & AUTHORIT AUTHORITY Y ........... ................ ........... ........... ........... ............ ........... ........... ............ ........... ........... ............ ......5 5

6.0

DESCRIP DESCRIPTION....... TION............. ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ............ ............ ........... ........... ..........6 ....6

6.1

Standard Standard and Minimum Minimum Line Sizes Sizes ........... ................ ........... ............ ............ ........... ........... ........... .......... ........... ............ .......6 .6

6.2

Sizing Sizing Methods........ Methods............. ........... ........... ........... ............ ........... .......... ........... ........... ........... ............ ........... ........... ............ ........... .....6 6

6.2.1 Liquid Hydraulics....................................................................................... Hydraulics.........................................................................................6 6.2.2 Vapor Vapor Hydrauli Hydraulics cs .......... ................ ........... ........... ............ ........... ........... ............ ........... ........... ............ ........... .......... ........... ...........7 .....7 6.2.3 Two-Phas Two-Phase e Hydraulic Hydraulicss ........... ................ ........... ........... ........... ............ ............ ........... ........... ........... ........... ........... ........... .......... ....7 7 6.3

Pipe Sizing Sizing Criter Criteria ia for for Single Single Phase Fluid........... Fluid................ ........... ........... ........... ........... ........... ........... ........... .......... ....7 7

6.3.1 Sizing Criteria for Liquid Phase Flow.............................................................. Flow ................................................................. ...8 8 6.3.2 Sizing Criteria for Vapor Phase Flow .............................................................. ................................................................. ...9 9 Incompressible Incompressible Vapor Flow ........................................................... .................................................................................... .........................9 9 Compressible Compressible Vapor Flow ............................................................. .................................................................................... ....................... 11 6.3.3 Design Design Margin Margin ........... ................ ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........... ........ .. 11 6.4

Pipe Sizing Sizing Crite Criteria ria for Two Two Phase Phase Fluid............. Fluid.................. ........... ........... ........... ........... ........... ........... ........... ........ .. 11

6.4.1 Flow Regime Regime ........... ................ ........... ........... ........... ........... ........... ........... ........... ........... ........... ............ ............ ........... ........... ........ .. 11 6.4.2 Line Sizing Criteria................................................... Criteria.................................................................................... ................................. 15 6.4.3 Accepted Accepted Flow Regimes Regimes ........... ................ ........... ............ ............ ........... ........... ........... ........... ............ ............ ........... .......... ..... 16 6.4.4 Simple Pressure Drop Models ............................................................ ........................................................................ ............ 16 6.4.5 Piping Arrangement Arrangement for Two-Phase Flow .......................................................... 16 6.5

Line Line Sizing Sizing Crite Criteria ria for Flare Flare and and Relievi Relieving ng Device Devicess ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ... 17

6.5.1 Lines Upstream Upstream of Relievin Relieving g Devices Devices ........... ................. ........... ........... ............ ............ ........... ........... ........... ........... ........ 17 Pressure Safety Valves ( PSV) : ....................................................... ............................................................................. ...................... 17 Depressurization Depressurization Devices ............................................................. .................................................................................... ....................... 17 6.5.2 Lines Downstream of Relieving Devices, Flare Headers ......................................... 17 Lines downstream downstream relieving devices devices and sub-headers: .................................................. 18 Headers:........................................................................................................ Headers:........................................ ................................................................ 18 6.6

Utility Utility Line Sizing Sizing ........... ................. ........... ........... ............ ............ ........... ........... ........... ........... ............ ............ ........... ........... ...... 18 Page Page 2 of 21 21


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6.6.1 Steam Lines ............................................................................................ 18 6.6.2 Condensate Lines ..................................................................................... 19 6.6.3 Cooling Water/Sea Water Lines..................................................................... 19 6.6.4 Fire Water Lines....................................................................................... 19 6.6.5 Oily Water Lines....................................................................................... 19 6.6.6 Chemical Lines ........................................................................................ 20 6.6.7 Instrument Air, Plant Air and Nitrogen ............................................................ 20 6.7

Special Cases .......................................................................................... 20

6.7.1 Reboiler Lines ......................................................................................... 20 6.7.2 Miscellaneous Fluids .................................................................................. 20

7.0

RECORDS.................................................................................................. 21

8.0

APPENDICES .............................................................................................. 21

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1.0

PURPOSE

The purpose of this document is to provide a guideline for plant line sizing.

2.0

SCOPE

Plant lines are pipe segments within the plant whether onshore or offshore facilities. Plant Line sizing is usually done with respect to pressure drop and velocity criteria. Engineering judgment can be used when selecting line sizes based on past experience of similar facilities. This document describes the line sizing criteria for both single phase (Gas or Liquid) and two phase flow of fluids. If project specific line sizing criteria is available in FEED documents or Licensor package the recommendations from these documents will be followed for sizing. This document provides description of the various considerations for Line size and the criteria used for designing them. This guide is applicable to Sharjah, Mumbai,Delhi, Chennai and Jakarta. If any philosophy described in this document conflicts with any part of the regulation, requirement, policy or directive name, this document shall be superseded by the regulation, requirement, policy or directive name.

3.0

DEFINITIONS

This section defines those words, phrases, terms, acronyms, and abbreviations that apply specifically to the guide

API ASTM atm bar a bar g

American Petroleum Institute American Society of Testing Material Atmospheres bar absolute bar gauge

cm

Centimeters

cP CS cSt Cu

centipoises Carbon Steel centistokes Copper

DEP

Design Engineering Practice

DN

Deutesche Normales (Pipe Diameter)

EOS FRP

Equation of State Fiberglass Reinforced Plastic

ft GRP

feet Glass Reinforced Plastic

hr

hour Page 4 of 21


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kg

kilograms

km lb Le LTCS m mm MAOP NACE

kilometers pounds Equivalent Length Low Temperature Carbon Steel meters millimeters Maximum Allowable Operating Pressure National American Corrosion Engineers

NaCl

Sodium Chloride

NB ppb ppm PR PSV

Normal Bore Parts per Billion Parts per Million Peng-Robinson Pressure safety valve

PVC

Polyvinyl Chloride

s SRK SS TEMA

second Soave-Redlich-Kwong Stainless Steel Tubular Exchangers Manufacturer’s Association

4.0

REFERENCES

Reference 1 - Shell DEP 31.38.01.11-Gen, “Piping-General Requirement”, February 2012. Reference 2 - Shell DEP 31.40.00.10-Gen, “Pipeline Engineering”, November, 1993. Reference 3 - Ludwig, E.E., “Applied Process Design for Chemical and Petrochemical Plants”, Vol. I, 2nd Edition. Reference 4 - “Recommended Practice for Design and Installation of Offshore Production Platform Piping Systems”, API RP-14E, 5th Edition, October 1991. Reference 5 -“Sizing, Selection, and Installation of Pressure-Relieving Devices in Refineries”, API RP 520, Part II, 4th Edition, December, 1994. Reference 6 -“Perry’s Chemical Engineers’ Handbook”, Section 2, Physical & Chemical Data, 7th Edition, McGraw Hill, 1999. Reference 7 - Crane, “Flow of Fluids”, Appendix A, 7th Edition, March 1988. Reference 8 - Shell DEP 20.0010.10-Gen, “Basic Data and Phase Behavior Methods”, April 2003.

5.0

RESPONSIBILITY & AUTHORITY

Lead Process Engineer is responsible for the Line Sizing system Philosophy.

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6.0

DESCRIPTION

The following sections describe the line sizing methods and criteria applicable in various cases.

Standard and Minimum Line Sizes The line sizes shall be limited to available standard sizes of pipes. In general these are ¼, ½, ¾, 1, 1½, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32,36, 40, 42, 48 inches etc. For any limitations on pipe sizes, project specifications should be referred. The following lines sizes are not standard and shall not be used: 1 ¼”, 2 ½”, 3 ½”, 5”, 7”, 9” The following guideline shall be used when selecting the minimum line sizes:        

2" NB 2" NB 1½" NB ¾" NB 1” NB 2” NB 4" NB 4” NB

Minimum Minimum Minimum Minimum Minimum Minimum Minimum Minimum

nozzle size for vessels, tanks, heat exchangers process (hydrocarbon) line size utility line size bridle drain or pump casing vent / drain chemical injection. on pipe rack or pipe sleeper for (wrapped and coated) underground lines. for storm water runoff sewer drain lines

Sizing Methods Single phase line sizing can be done using different correlations for friction factor. The following roughness coefficients are typically considered for different pipe material:

Pipe Material Carbon steel pipe Carbon steel corroded - pipe) Note-1 Stainless steel pipe Galvanized Steel Plastic Brass, Aluminum, Copper

Roughness (mm) 0.0457 0.457 0.0254 0.13 0.005 0.03

Note-1 : Higher roughness to be used for brownfield projects. Crane Data Book may be referred for selecting the pipe roughness. Crane Data Book may be referred for the equivalent length of pipe fittings and valves. DEP 31.38.01.11-Gen can also be referred to information is not available in crane handbook.

for Shell projects or in cases where such

For special pipe materials like GRE, cladded / coated pipes; Vendor provided data should be used. Liquid Hydraulics Spreadsheet ( Line Sizing.xls) or preferably Korf hydraulic software shall be used for estimating pressure drop for single-phase liquid flow. Page 6 of 21


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Vapor Hydraulics Spreadsheet (Line Sizing.xls) or preferably Korf hydraulic software shall be used for estimating pressure drop for single-phase vapour or gas flow.

Two-Phase Hydraulics The following tools shall be used : 

Petrofac in-house Excel spreadsheet Line Sizing.xls



KORF Hydraulic Software

It is recommended that the in-house spreadsheet is used for preliminary sizing of two phase lines. Critical two phase lines can be finalized after comparing the results with Korf hydraulic software. Pipesim shall be used for off-plot and long lines where significant changes in fluid properties are expected due to change in pressure and temperature.

Pipe Sizing Criteria for Single Phase Fluid The recommended velocities are based on vibration, noise and erosion considerations. The recommended pressure drop limitations are based on economic considerations and reasonable pump heads. It is difficult to establish the exact limits of min/max velocities and pressure drops analytically. The recommended values are based on common established engineering practices prevalent in the industry. Large size headers and bulk line pipes for pipeline transport are selected based on economic analysis of investment and operating cost, the guidelines in this document may not entirely apply to such situations. Line sizing criteria for both liquid phase and vapour phase flow regimes are described below.

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Sizing Criteria for Liquid Phase Flow For a specific duty, line sizing criteria for liquid phase is tabulated below: SERVICE

Pump suction, bubble point

LINE SIZE

 3”

RECOMMENDED MAXIMUM VELOCITY (m.s- ) 1.1

ALLOWABLE PRESSURE DROP MAX. (bar/100m) 0.045

(Note- 2,5) 4” – 8”

Pump suction, subcooled

1.4 – 1.8 ( Note-1)

0.045 to 0.05 ( Note-1)

10”

1.8

0.07

 3”

1.1

0.136

(Note-5) 4” - 8”

10”

Pump discharge

1.4-1.8 ( Note-1) 1.8

0.136 to 0.226 ( Note-1) 0.226

 3”

1.8

4” – 8”

2.4-4.3

0.339-0.453

10”

4.9

0.453

Unit line liquid bubble point

 3”

1.1

0.1

or liquid with dissolved gas

4” – 8”

1.4 – 1.8 ( Note-1)

0.1

10”

1.8

0.1

(Note-6)

(Note-4) Gravity run lines

0.6 -2.5

0.339

0.04 to 0.09

Amine Solution: Rich Amine

1.5

Lean Amine

2.0

Sour water Service water (Note- 3)

2.0  2”

1.5

0.35

3”-6”

2.0 – 3.0

0.35

8”- 12”

2.5 -4.2

0.35

 12”

3.0 - 5.0

0.35

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Notes : 1)

Lower limit of velocity and pressure drop corresponds to lower sizes of pipe.

2)

Applicable to liquid feeding to thermosiphon reboiler and liquid containing dissolved gas.

3)

Higher velocity can be used in pipe if water quality is good.

4)

Unit subcooled liquid lines will be sized similar to pump discharge.

5) 6)

Line size must meet the pump NPSH requirement. Higher pressure drop and velocity can be allowed in Alloys/SS lines .

Sizing Criteria for Vapor Phase Flow Vapor flows in process piping can be split into two general categories: 1. Incompressible flow 2. Compressible flow The correct line sizing criteria must be selected, depending on the vapor flow type. Incompressible Vapor Flow Vapor flow is considered incompressible, when both the following criteria are met: Vapor velocity is less than 60 m/sec. Total pressure drop is less than 10% of the initial pressure.

Normal in plant process and utility vapor flows fall in this category and the lines are sized for isothermal incompressible flow. Process and utility lines in vapor service (excluding flare, vent, PSV and depressurization lines) fall in isothermal incompressible flow. These lines can be sized in accordance with the criteria presented in the following table. The v2 criteria are governed by consideration of vibration and forces on piping supports. The v3 criteria are governed by consideration of noise levels. By exceeding these criteria, the energy of the fluid can damage the material (piping, fatigue of pipe supports, etc.) and personnel in the form of excessive noise. Line size to be selected based on recommended velocity and allowable pressure drop. Lines where pressure drop is not critical for compression power, should be sized based on maximum velocity.

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For a specific duty, line sizing criteria for Gas phase is tabulated below: SERVICE

ALLOWABLE PRESSURE DROP MAX. (bar/100m)

RECOMMENDED MAXIMUM VELOCITY ms-

RECOMMENDED MAXIMUM v² (kg.m- .s- )

15,000

Gas ; General (Note- 1,2) P  Atm

0.06

38 or 122/1/2

Atm < P  7 bar g

0.12

Whichever is

7 < P  70 bar g

0.45

lower

0.6% of upstream

= density in

pressure

kg/m3

0.011-0.022

40-60

atm < P  3.5 bar g

0.033

18-30

P > atm

0.15

12-15

P >70 bar g

Column gas outlet P  Atm

Compressor suction (Note-2) 0.07

Compressor discharge (Note-

0.12 to 0.22

2) Refrigerant Suction lines

4.5-10.7

Refrigerant discharge lines

10.7-18

Intermittent operation (antisurge, startup etc)

25,000

Notes : 1) The above indicated line sizing criteria are valid for continuous operation. In general, the pressure drop should be less than 10 % of the static terminal absolute pressure for long pipe segments and 5% for short segments.

For intermittent

operation, these limits may be exceeded, on a case by case analysis. 2) In addition to these criteria, flowing limitations on a noise point of view have to be considered (maximum V3 = 200,000 kg.s-3). V3 > 100,000 kg.s-3 may need acoustic induced vibration analysis. This requirement should be checked.

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Compressible Vapor Flow When piping pressure drop is between 10% and 40% of the upstream pressure, the application of compressible or incompressible flow needs to be reviewed case by case. This situation occurs in relief and blow down lines and long pipelines. For proper sizing criteria of compressible flow, refer to the section on “Line Sizing Criteria for Flare and Relieving Devices”. Adiabatic condition is usually considered for short, well-insulated lines; while flow in long pipelines approaches isothermal condition. In general, isothermal pressure drop is greater than or equal to adiabatic pressure drop. If pressure drop in a pipe segment exceeds 10% of the upstream pressure, pipe shall be divided into segments to keep pressure drop in each segment below 10% of the upstream pressure (of each segment). This is usually done using a suitable computer program to account for changes on the vapor physical properties due to pressure change in the pipeline. Design Margin There is inevitably some inaccuracy associated with the line sizing as the design information is not always exactly the same as actual conditions. Therefore, it is a normal practice to consider design margin on the theoretical pressure drop calculations. In instances when there are no project specific requirements, the following design margins should be used over the “Normal Flow Rate” to obtain the “Design Flow Rate”: For all process lines: 10% For intermittent lines used during startup: 5% For all utility main headers and distribution lines: 20% (or future expansion requirements as applicable to specific cases shall be considered). For recirculating flow e.g. heating or hot oil : 25% For two-phase pressure drop calculations, a 50% design margin on the pressure drop is usually considered to allow for inherent inaccuracies in the calculation methodology. For very low pressure systems, margins are individually assessed especially for pipework.

tank vent

Pipe Sizing Criteria for Two Phase Fluid Many two-phase pressure drop correlations are quoted in the literature. However, for piping within plant boundaries where two-phase lines are short, pressure drop based on average density is generally adequate. For longer lines a more complex method such as modified Panhandle equations for wet gases or Beggs and Brill equation or Korf hydraulic software may be more appropriate.

Flow Regime The interaction of the liquid and vapor phases is complex and depending on vapor/liquid ratio, pipe size, and layout, the fluid flows in differing patterns or flow regimes. Where emulsions may form, the actual pressure drop may be higher than anticipated as the viscosity of the continuous phase would increase considerably When phase change is expected, unstable flow regimes may result in hydraulic and vibration problems. Page 11 of 21


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Flow regime inside a pipe depends on flow rate and physical properties of gas and liquid phases as well as the pipe characteristics such as diameter, length and vertical/ horizontal orientation. These parameters decide the flow regime type i.e., mist flow, stratified flow, slug flow, etc. The transition from one flow regime to another is relatively gradual and is depicted in “flow regime map”. The boundaries shown in flow maps separating the different regimes should not be interpreted as sharp changes in flow pattern. The flow maps are generalized by using the gas and liquid Froude numbers based on the feed pipe velocity and diameter. The advantage of this general representation is that the flow maps are then unaffected by variations in flow conditions, physical properties and feed pipe geometry. This means that the flow maps can be used for a wide range of flow conditions, physical properties and feed pipe diameters. The gas and liquid Froude numbers are defined as follows: Gas Froude number: G FrG  v G L   G gD

Liquid Froude number: L FrL  vL  L   G gD

The flow regime map in a horizontal two-phase flow is shown in Figure-1.

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Figure-1

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The flow regime map in a vertical two-phase flow is shown in Figure-2.

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Figure-2 Line Sizing Criteria For a two-phase fluid, the mixture density and velocity can be calculated as follows: ρm =

W WL/ρL + WV /ρV

Vm =

W / 3600 (ρm) (πxD2 / 4)

where:

ρL

Liquid Phase Density, kg/m3

ρV

Vapour Phase Density, kg/m3

ρm

Apparent Mixture Density, kg/m3

WL

Liquid Flow Rate, kg/h

WG

Vapour Flow Rate, kg/h

W

Total Flow Rate, kg/h

Vm

Mixture Velocity, m/s

D

Internal Diameter of the line, m

The fluid erosion velocity (the velocity above which erosion may occur) can be determined by the following empirical equation as per API 14E: V e



C  m

where

Ve = Erosion Velocity, ft/s ρm = Apparent Mixture Density, lb/ft3 C = Empirical Constant

For solid free fluids, C= 100 for continuous service and C=125 for intermittent service are conservative. For solid-free fluids where corrosion is not anticipated or when corrosion is controlled by inhibition or by employing corrosion resistant alloys, values of C= 150 -200 may be used for continuous service. Values upto C=250 have been used successfully for intermittent service. For SI unit conversion, the empirical constant to be multiplied by 1.22. Example: If Ve is m/s, ρm in kg/m3 and empirical constant should 122 in the place of 100. API 14E recommends following: 

The fluid velocity must be lower than the erosion velocity. Page 15 of 21


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

If possible the minimum velocity in two phase lines should be about 10 ft/s (3.05 m/s) to minimize the slugging of separation equipment. This is particularly important in long lines with elevation changes.



If solids production is anticipated fluid velocity should be significantly reduced from above calculated erosion velocity. Different values of Empirical constant C may be used for specific applications if such recommendations are appropriate.

Accepted Flow Regimes 

For two-phase flow lines:  where mixture is essentially gas, gas criteria will be used,  where mixture is essentially liquid, liquid criteria will be used.





For horizontal lines, stratified, mist, annular or bubble flow is acceptable. Slug and plug flow regimes shall be avoided. For vertical lines, mist, annular or bubble flow is acceptable. Slug flow regime shall be avoided.

Simple Pressure Drop Models As per API 14E, the pressure drop for two phase flow in steel piping may be estimated using a simplified Darcy equation. 0.000336f W2

ΔP =

ρm di5 Where:

ΔP

= Pressure Drop, psi/ 100 ft

W

= Mixture Flow Rate, lb/hr

f = Moody friction factor, dimensionless ρm

= Apparent Mixture Density at flowing press and temp, lb/ft3

di

= pipe inside diameter , inches

The use of above equation should be limited to a 10% pressure drop due to inaccuracies associated with changes in density. If the Moody friction factor is assumed to be an average of 0.015 the above equation becomes: ΔP =

5x10-6 W2 ρm di5

Korf hydraulic software specifies several correlation methods to calculate the 2 phase pressure drop. They are Duckler method, Lockhart-Martinelli method, Chenoweth- Martin method etc. Appropriate method should be selected as per pipe geometry and corresponding method as recommended in Korf manual. Piping Arrangement for Two-Phase Flow Piping arrangement for two-phase flow shall consider: Page 16 of 21


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

Adequate support to avoid vibration.



Distribution

from

symmetrical

two-phase

manifolds/

headers

distribution to different branches.

shall

consider

equal/

Branched lines shall be

connected in horizontal direction and shall slope towards the equipment, if possible. Line Sizing Criteria for Flare and Relieving Devices This section describes sizing criteria for relief valve inlet/outlet lines and depressurization lines as well as flare and cold vent headers. Lines Upstream of Relieving Devices

Pressure Safety Valves ( PSV) : Sizing of PSV inlet lines shall be based on the maximum relieving capacity of the PSV for the selected orifice. Line sizing shall be in accordance with the API 520/521 guidelines. 

P between the protected equipment and the PSV shall be less than 3% of PSV set

pressure. 

Inlet Pipe Diameter shall be greater than or equal to the PSV inlet size

Depressurization Devices Lines upstream or downstream of depressurization devices/blowdown valves shall be sized based on the calculated depressurization rates for the system and shall be in accordance with the criteria provided below: 

Minimum Line Size 2"



Max V² shall not exceed 200,000 kg/m/s2 Pressure drop criteria do not apply to these lines, the pressure loss shall be such that it does not impose any restriction on depressurization objectives.



Velocity shall be limited to 0.8 Mach.



Due to high velocities/V2/V3, Acoustic Induced Vibration analysis may be required.

Lines Downstream of Relieving Devices, Flare Headers Lines downstream of PSV, depressurization and other relieving devices and flares headers and sub-headers shall be sized in accordance with the following criteria: 

Minimum line size 2".



Back pressure consistent with relieving capacity of pressure-relieving devices and with design pressure of the protected equipment.

Velocity and V² Sonic velocity is calculated as below: 

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Sonic velocity:

C 

10 5 * k * P 

where: C

Sonic velocity, m/s

k

Cp/Cv

P

Pressure, bara



Density, kg/m3

Mach no

velocity/C

Lines downstream relieving devices and sub-headers: The basic criteria for sizing the discharge piping and relief header is the back pressure which may be developed at any point in the system does not reduce the relieving capacity of any of the relieving devices required to protect the equipment from overpressure. The back pressure must be maintained within specific safety valve stability limits to avoid chatter. 0.8 Mach maximum and V² < 200,000 kg.m-1.s-2 considering the maximum capacity of the relieving devices. The discharge shall be higher than or equal to outlet of relief devices. Flaring line downstream of pressure control valve shall be designed for a maximum velocity of 0.5 Mach (continuous flow) and maximum value of V² < 200,000 kg.m-1.s-2 Headers: 0.7 Mach maximum and V² < 200,000 kg.m-1.s-2 considering the maximum flow rate; however, a velocity of 0.8 Mach could be accepted for a long straight line without elbows and connections (e.g. stack, line on bridge ). The actual back pressure at the PSV outlet shall be checked to make consistent with back pressure limitations. Acoustic induced vibration study may be required for lines where V² values are high. PAM group will address the impact and propose the mitigation measures. If relief is a two phase/multi-phase, the following criteria may be followed: Potential slug/plug flow velocity shall be limited to 50 m/s Homogeneous flow ( i.e there is no slip between phases) maximum mVm² < 200,000 kg.m1.s-2

Utility Line Sizing

Steam Lines The following sizing criteria may be used for preliminary pipe sizing of steam lines: Max ΔP, bar/100 m Pressure, barg Up to 2.0

Main Headers

Branch Lines

0.06

0.11

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Recommended Max.Velocity m/sec Saturated : 60

Document Number

Document Title

Revision

PEC-EN-GDE-P-1756


1

2–7 7 – 20

0.09 0.11

0.17 0.23

20  P

0.23

0.34

Superheated: 75

For exhaust steam lines, pressure drop upto 0.33 bar/100 m can be considered. Condensate Lines Condensate piping is sized more generously than normal liquid service to provide allowance for flash steam that is generated. The condensate lines should also be checked for the startup load and piping shall be sized to provide adequate pressure drop for traps and control valves in the system, taking into account for flashing. Steam traps are usually sized for 200 to 300 % of normal flow. If significant amount of flash is occurring the two phase flow sizing criteria shall be used. Note: Mixing flashing condensate with sub-cooled condensate can cause a “water hammer” effect resulting in excessive pipe movement. Cooling Water/Sea Water Lines Cooling water headers and distribution piping is sized to keep the pressure drop per 100 m of piping less than 0.44 bar. Maximum velocity should be limited to 3.0 m/s for 12” and below. maximum velocity should be limited to 4.5 m/s.

For 14” and above,

Velocity restrictions may apply for large cement lined pipes and should be checked with suppliers. In general, higher pressure drop can be allowed for Corrosion Resistant Alloy (CRA) lines to reduce cost. Fire Water Lines Sizing of fire water lines shall be based on available system pressure and allowable flow velocities. In the ring main pipe work, the same sizing criteria as presented for “Cooling Water/Sea Water Lines” may be used.

Downstream of the deluge, the flow velocities shall normally not exceed 10 m/s.Some areas may require velocities higher than 10 m/s in order to hydraulically balance the systems which is acceptable provided the reaction force within the system does not cause excessive stress in the pipe work or the supports. Oily Water Lines The lines for oily water to water treatment facilities shall be sized based on pressure drop available. Typically the velocity should not exceed 3 m/s.

Page 19 of 21


Document Number

Document Title

Revision

PEC-EN-GDE-P-1756


1

Chemical Lines Chemical lines are usually designed for a maximum velocity of 1.5 m/s. Recommended maximum velocity in lines carrying chemicals are as below:

Service

Recommended max velocity (m/s)

CS pipe carrying phenolic water

0.9

CS pipe carrying concentrated H2SO4

1.2

CS pipe carrying caustic solution

1.2

Instrument Air, Plant Air and Nitrogen Gas line sizing criteria shall be used for IA, PA and Nitrogen lines. Special Cases Reboiler Lines

Reboiler Feed Line: Allowable pressure drop

0.03 to 0.07 bar/100 m

Allowable velocity

0.9 to 1.5 m/s

Reboiler Return Line: Allowable pressure drop

0.07 bar/100 m

Miscellaneous Fluids The following velocity criteria may be used in special service conditions: 

Liquid with sand: 0.8 m/s as min. velocity; 3 m/s max.



Solid-liquid mixture lines: 1 to 2.75 m/s max.



Pulverized catalyst standpipes (dense-phase flow): 1.7 m/s max.



Pulverized catalyst carrier lines (dilute-phase flow): 12 m/s max. Velocity of 7.5 m/s is preferred. However, for densities under 0.8 kg/m3 higher velocities may be used.



Cement pipe or coal tar Enamel liquid pipe carrying salt water : 4.5 m/s max.



Plastic pipe or rubber lined pipe carrying liquid in general : 3.0 m/s max.

Page 20 of 21


Document Number

Document Title

Revision

PEC-EN-GDE-P-1756


1

7.0

RECORDS

Not Applicable

8.0

APPENDICES

Not Applicable

Page 21 of 21


line sizing philosophy.pdf

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