dep 80.36.00.30 relief valve - selection, sizing and specification

DEP SPECIFICATION

RELIEF DEVICES - SELECTION, SIZING AND SPECIFICATION

DEP 80.36.00.30-Gen.

February 2012

(Amendment A01 incorporated – September 2012)

DESIGN AND ENGINEERING PRACTICE

DEM1

© 2012 Shell Group of companies All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, published or transmitted, in any form or by any means, without the prior

written permission of the copyright owner or Shell Global Solutions International BV.

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This document has been supplied under license by Shell to:Shell [email protected] 03/01/2013 10:24:34

DEP 80.36.00.30-Gen. February 2012

PREFACE

DEP (Design and Engineering Practice) publications reflect the views, at the time of publication, of Shell Global Solutions International B.V. (Shell GSI) and, in some cases, of other Shell Companies.

These views are based on the experience acquired during involvement with the design, construction, operation and maintenance of processing units and facilities. Where deemed appropriate DEPs are based on, or reference international, regional, national and industry standards.

The objective is to set the standard for good design and engineering practice to be applied by Shell companies in oil and gas production, oil refining, gas handling, gasification, chemical processing, or any other such facility, and thereby to help achieve maximum technical and economic benefit from standardization.

The information set forth in these publications is provided to Shell companies for their consideration and decision to implement. This is of particular importance where DEPs may not cover every requirement or diversity of condition at each locality. The system of DEPs is expected to be sufficiently flexible to allow individual Operating Units to adapt the information set forth in DEPs to their own environment and requirements.

When Contractors or Manufacturers/Suppliers use DEPs, they shall be solely responsible for such use, including the quality of their work and the attainment of the required design and engineering standards. In particular, for those requirements not specifically covered, the Principal will typically expect them to follow those design and engineering practices that will achieve at least the same level of integrity as reflected in the DEPs. If in doubt, the Contractor or Manufacturer/Supplier shall, without detracting from his own respons bility, consult the Principal.

The right to obtain and to use DEPs is restricted, and is granted by Shell GSI (and in some cases by other Shell Companies) under a Service Agreement or a License Agreement. This right is granted primarily to Shell companies and other companies receiving technical advice and services from Shell GSI or another Shell Company. Consequently, three categories of users of DEPs can be distinguished:

1) Operating Units having a Service Agreement with Shell GSI or another Shell Company. The use of DEPs by these Operating Units is subject in all respects to the terms and conditions of the relevant Service Agreement.

2) Other parties who are authorised to use DEPs subject to appropriate contractual arrangements (whether as part of a Service Agreement or otherwise).

3) Contractors/subcontractors and Manufacturers/Suppliers under a contract with users referred to under 1) or 2) which requires that tenders for projects, materials supplied or - generally - work performed on behalf of the said users comply with the relevant standards.

Subject to any particular terms and conditions as may be set forth in specific agreements with users, Shell GSI disclaims any liability of whatsoever nature for any damage (including injury or death) suffered by any company or person whomsoever as a result of or in connection with the use, application or implementation of any DEP, combination of DEPs or any part thereof, even if it is wholly or partly caused by negligence on the part of Shell GSI or other Shell Company. The benefit of this disclaimer shall inure in all respects to Shell GSI and/or any Shell Company, or companies affiliated to these companies, that may issue DEPs or advise or require the use of DEPs.

Without prejudice to any specific terms in respect of confidentiality under relevant contractual arrangements, DEPs shall not, without the prior written consent of Shell GSI, be disclosed by users to any company or person whomsoever and the DEPs shall be used exclusively for the purpose for which they have been provided to the user. They shall be returned after use, including any copies which shall only be made by users with the express prior written consent of Shell GSI. The copyright of DEPs vests in Shell Group of companies. Users shall arrange for DEPs to be held in safe custody and Shell GSI may at any time require information satisfactory to them in order to ascertain how users implement this requirement.

All administrative queries should be directed to the DEP Administrator in Shell GSI.



TABLE OF CONTENTS

1. INTRODUCTION ........................................................................................................ 4 1.1 SCOPE ........................................................................................................................ 4 1.2 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS ......... 4 1.3 DEFINITIONS ............................................................................................................. 5 1.4 CROSS-REFERENCES ............................................................................................. 5 1.5 SUMMARY OF MAIN CHANGES ............................................................................... 5 1.6 COMMENTS ON THIS DEP ....................................................................................... 6 1.7 DUAL UNITS ............................................................................................................... 6

2. RELIEF DEVICE SELECTION ................................................................................... 7 2.1 GENERAL CRITERIA ................................................................................................. 7 2.2 MECHANICAL DESIGN .............................................................................................. 7 2.3 SPECIFIC SELECTION CRITERIA ............................................................................ 7

3. RELIEF DEVICE SIZING CALCULATIONS ............................................................ 13 3.1 GENERAL CRITERIA ............................................................................................... 13 3.2 PRESSURE RELIEF VALVE SIZING ....................................................................... 13 3.3 NON-RECLOSING RELIEF DEVICE SIZING .......................................................... 15

4. REQUISITIONING .................................................................................................... 15 4.1 GENERAL ................................................................................................................. 15 4.2 PRESSURE RELIEF VALVES.................................................................................. 15 4.3 RUPTURE DISKS ..................................................................................................... 16

5. RELIEF DEVICE SPECIFICATIONS ....................................................................... 16 5.1 GENERAL ................................................................................................................. 16 5.2 PRESSURE RELIEF VALVE SPECIFICATION ....................................................... 16 5.3 SET PRESSURE CONSIDERATIONS ..................................................................... 16 5.4 ADDITIONAL REQUIREMENTS FOR SPECIFIC SERVICES ................................. 17

6. PRESSURE RELIEF VALVES INSPECTION AND TESTING ................................ 17 6.1 GENERAL ................................................................................................................. 17

7. PAINTING ................................................................................................................. 17 7.1 GENERAL ................................................................................................................. 17

8. IDENTIFICATION ..................................................................................................... 17 8.1 PRESSURE RELIEF VALVES.................................................................................. 17 8.2 RUPTURE DISKS ..................................................................................................... 17

9. PROTECTION AND PACKAGING........................................................................... 18 9.1 GENERAL ................................................................................................................. 18 9.2 PRESSURE RELIEF VALVES.................................................................................. 18 9.3 RUPTURE DISKS ..................................................................................................... 18 9.4 BUCKLING PINS ...................................................................................................... 18

10. DOCUMENTATION .................................................................................................. 18 10.1 MANUFACTURER .................................................................................................... 18 10.2 ELECTRONIC FILES ................................................................................................ 18 10.3 EQUIPMENT FILES .................................................................................................. 19

11. REFERENCES ......................................................................................................... 20



1. INTRODUCTION

1.1 SCOPE

This DEP specifies requirements and gives recommendations for the selection, sizing, and specification of relief devices.

The selection, sizing, and specification of relief devices shall be in accordance with the following standards, as clarified, amended or supplemented by this DEP:

a) ASME Section 1; ASME Sect. IV; ASME Sect. VIII, Divisions 1 or 2;

b) API Standard 520, Part I and Recommended Practice 520, Part II;

c) ISO 23251;

d) API Standard 526;

e) API Standard 527;

f) ISO 28300.

g) ISO 4126

h) Pressure Equipment Directive (97/23/EC) NOTES: 1. API Standard 521, 5th edition is identical to ISO 23251:2006.

2. API Standard 2000, 6th edition is identical to ISO 28300:2008.

This DEP does not cover pressure surge valves, these valves protect liquid filled lines from overpressures caused by water hammer.

Refer to DEP 80.45.10.10-Gen. and DEP 80.45.10.11-Gen. to determine the hydraulics and other requirements of the relief and flare system.

This DEP contains mandatory requirements to mitigate process safety risks in accordance with Design Engineering Manual DEM 1 – Application of Technical Standards.

This is a revision of the DEP of the same number dated February 2011; see (1.5) regarding the changes.

1.2 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS

Unless otherwise authorised by Shell GSI, the distribution of this DEP is confined to Shell companies and, where necessary, to Contractors and Manufacturers/Suppliers nominated by them. Any authorised access to DEPs does not for that reason constitute an authorization to any documents, data or information to which the DEPs may refer.

This DEP is intended for use in facilities related to oil and gas production, gas handling, oil refining, chemical processing, gasification, distribution and supply/marketing. This DEP may also be applied in other similar facilities.

When DEPs are applied, a Management of Change (MOC) process shall be implemented; this is of particular importance when existing facilities are to be modified.

If national and/or local regulations exist in which some of the requirements could be more stringent than in this DEP, the Contractor shall determine by careful scrutiny which of the requirements are the more stringent and which combination of requirements will be acceptable with regards to the safety, environmental, economic and legal aspects. In all cases, the Contractor shall inform the Principal of any deviation from the requirements of this DEP which is considered to be necessary in order to comply with national and/or local regulations. The Principal may then negotiate with the Authorities concerned, the objective being to obtain agreement to follow this DEP as closely as possible.



1.3 DEFINITIONS

1.3.1 General definitions

The Contractor is the party that carries out all or part of the design, engineering, procurement, construction, commissioning or management of a project or operation of a facility. The Principal may undertake all or part of the duties of the Contractor.

The Manufacturer/Supplier is the party that manufactures or supplies equipment and services to perform the duties specified by the Contractor.

The Principal is the party that initiates the project and ultimately pays for it. The Principal may also include an agent or consultant authorised to act for, and on behalf of, the Principal.

The word shall indicates a requirement.

The capitalised term SHALL [PS] indicates a process safety requirement.

The word should indicates a recommendation.

1.3.2 Specific definitions

For pressure relief valve (PRV) terminology and related terms, refer to API Std 520 and DEP 80.45.10.10-Gen.

1.4 CROSS-REFERENCES

Where cross-references to other parts of this DEP are made, the referenced section number is shown in brackets ( ). Other documents referenced by this DEP are listed in (11).

1.5 SUMMARY OF MAIN CHANGES

This DEP is a revision of the DEP of the same number dated February 2011. The following are the main, non-editorial changes.

The “SHALL [PS]” elements in this DEP were critically reviewed and updated as required. The updates are summarized below.

Section Paragraph Change

2.2.1 1 Removed SHALL [PS] because requirement is covered by DEP 31.38.01.11-Gen.

2.3.3 1 Removed SHALL [PS] where the risk ranking did not meet the criteria for a SHALL [PS]


2.3.4.2 Table 1, note 2

Removed SHALL [PS] where the risk ranking did not meet the criteria for a SHALL [PS],

2.3.7.2 a 1 Removed SHALL [PS] where the risk ranking did not meet the criteria for a SHALL [PS]


2.3.10.1 1 Added SHALL [PS] to be consistent with DEP 34.51.01.31-Gen.

3.1 Added paragraph “General criteria”


3.2.4.4 2 Removed section inclusive SHALL [PS]. Section is part of DEP 80.45.10.11-Gen. and requirement is covered by this DEP



Section Paragraph Change

3.2.5.2 1 There was no SHALL [PS] statement in this section, removed from the SHALL [PS] list in the informative.

3.1.7.3 c 1 The SHALL [PS[ statement in this section has been deleted as this is redundant with the SHALL [PS] in (4.1)

5.3.1 2 Added SHALL [PS] to be consistent as with other DEPs and design assumption

This update achieves harmonization and rationalisation by including relevant design and engineering practices from the following regional and local standards:

a) 12-GS-2 Design of Pressure Relief System Hardware

b) 12-GS-10 Testing of New Pressure Relief Valves

c) BSP-12-Standard-500 Brunei Shell Petroleum Company, Process Safeguarding Standard

d) ES/099 Engineering Reference Document Standard Safety Relief Valves

e) NSP 12-G-7-30 Overhaul and test procedure for safety valves

1.6 COMMENTS ON THIS DEP Amendment A01

Comments on this DEP may be submitted to the Administrator using the DEP Feedback Form by:

• Entering comments directly in the DEP Feedback System on the Technical Standards Portal http://sww.shell.com/standards (mandatory for users with access to Shell Wide Web);

• Clicking on the DEP Feedback Form button on the DEPs DVD-ROM main page (for users without access to Shell Wide Web);

• Requesting a copy of the DEP Feedback Form from the Administrator at [email protected] (for users without access to Shell Wide Web).

For the last two options, the completed DEP Feedback Form can be attached to an email and submitted to the Administrator at [email protected]. Only feedback that is entered into the Feedback Form will be considered.

1.7 DUAL UNITS

This DEP contains both the International System (SI) units, as well as the corresponding US Customary (USC) units, which are given following the SI units in brackets. When agreed by the Principal, the indicated USC values/units may be used.


http://sww.shell.com/standards

mailto:[email protected]

mailto:[email protected]


2. RELIEF DEVICE SELECTION

2.1 GENERAL CRITERIA

Technical requirements for pressure relief valves (PRVs) and thermal expansion relief valves (TERVs) shall conform to MESC SPE 77/135. Outlet flange ratings for PRVs that relieve to a flare system or atmosphere shall be in accordance with API 526. For PRVs that relieve to a pressurised system, the outlet flange shall be selected according to the maximum back pressure and temperature it is subjected to.

Material selection for PRV and TERV components shall be compatible with the associated piping class material selection.

The minimum inlet flange rating should be class 300; the minimum outlet flange rating shall be class 150.

2.2 MECHANICAL DESIGN

2.2.1 Inlet and outlet connection

The inlet and outlet connections including flange face finish shall be consistent with the pipe specifications for the systems to which they connect. PRVs having threaded inlet connections shall not have threaded inlet bushing connections that may unscrew from the body during installation.

2.2.2 Threaded connections

Limitations to threaded connections shall conform to DEP 31.38.01.11-Gen.

2.2.3 Pressure relief device design temperature

2.2.3.1 The design temperature SHALL [PS] be determined by the inlet and outlet temperatures that result from extreme operating and relieving conditions. The temperature reduction resulting from possible internal valve leakage (e.g., flashing of liquid) shall be included in the determination of the design temperature. For the definition of design conditions reference is made to DEP 01.00.01.30-Gen. Elevated temperature arising from an external fire is not a basis for the design temperature or material selection.

2.2.3.2 To determine the minimum temperature at the throat of the relief device, an isentropic flash calculation to the choking pressure should be carried out.

2.3 SPECIFIC SELECTION CRITERIA

2.3.1 General

PRVs shall normally be of the spring-loaded type. For special applications, pilot-operated PRVs, buckling pin valves, and where permitted by local regulations, assisted PRVs may be employed.

Capacities established and guaranteed by the relief device Manufacturer for the applicable service conditions shall be used for selecting the relief device.

2.3.2 Conventional spring-loaded pressure relief valves Amendment A01

If the built-up back pressure plus the variable superimposed back pressure does not exceed the allowable overpressure, PRVs shall be conventional safety relief valves unless considerations other than back pressure justify the use of a different type of relief device. The set pressure and CDTP may require adjustment for constant backpressure, see API Std 520 Part 1, Paragraph 5.3.2.

Spring-loaded PRVs connected to a closed discharge system shall always have a closed bonnet.

2.3.3 Balanced type pressure relief valves

Balanced PRVs (or alternatively pilot operated PRVs) SHALL [PS] be used when the built-up back pressure plus the variable superimposed back pressure is higher than that allowed



for a non-balanced valve. The maximum permissible back pressure specified by the Manufacturer shall be in excess of the back pressure supplied in the requisition.

The bonnet of a balanced PRV shall be vented to atmosphere at all times. Balanced-bellows valves, with a bonnet vent open to atmosphere, shall not be used with fluids which may cause the valve to freeze if there is a leak. In clean service, pilot-operated PRVs, of which the pilot stays relatively warm, may be selected.

Balanced-bellows valves shall not discharge to the suction side of reciprocating equipment since pressure pulsation may result in fatigue of the bellows.

Balanced-bellows valves shall not be used in coking or fouling services because the bellows can become fouled and may not operate properly.

A suitably corrosion-resistant material shall be specified for the bellows since, in the event of a bellows failure, fluid could enter the bonnet space and escape through the bonnet vent. If no suitable corrosion-resistant material can be selected or if no suitable bellows can be specified, then use of an auxiliary balancing piston should be considered.

2.3.4 Pilot-operated pressure relief valves

Use of pilot-operated PRVs requires approval by the Principal.

2.3.4.1 For proper operation, pilot-operated PRVs shall only be selected for clean gas or liquid service so that the pilot valve or sensing line cannot be blocked with hydrates, ice, wax, solids or dirt. The pilot valve shall be of the non-flowing type except as noted in 2.3.4.3(e). Heat tracing or purging SHALL [PS] be installed where cooling of process fluids to temperatures as low as the Lowest One-Day Mean Ambient Temperature (LODMAT) can cause plugging in the pilot, sensing line, pilot-operated valve (POV) inlet, or dome. Where single tracing and/or purging are installed, alarms SHALL [PS] also be installed to alert operators of any problem with these systems

2.3.4.2 Situations in which pilot-operated PRVs may be suitable are:

a) where the pressure loss between the protected equipment and the inlet flange of the PRV exceeds 3 % of the set pressure of the PRV. In such situations the pilot sensor tapping should be located close to the protected equipment. The sensing line shall be free draining to the protected equipment without any pockets. The sensing line shall also be as short as practical.

b) where seat leakage may be a problem with spring loaded relief devices, since pilot operated relief devices have better sealing qualities;

c) where high back pressures limit even the applicability of balanced valves;

d) in large capacity and high set-pressure service due to their smaller size and weight and where, especially for the larger sizes, a higher operating pressure is allowed;

e) if the margin between the maximum operating pressure (MOP) of the protected system and the PRV set pressure is less than 10% of the PRV set pressure, since the process pressure provides a higher seating force than if a spring were used;

f) where operating pressure is pulsating.

If pilot-operated PRVs are used, the options in Table 1 shall be followed when the option comment is applicable.

Table 1 Options for pilot-operated pressure relief valves

Option Provided Comments

Modulating pilot Normally Less disruptive to process

Field test connections No (1) If required, special installation precautions are required to assure that the test connection is not plugged.



Option Provided Comments

Pilot filters and/or purge

Yes Unless the service is absolutely clean. Pilot filters require periodic maintenance in order to control the risk of blockage. Where a spare filter is used, the switching valve shall be designed and installed so that it can be flow tested to ensure proper line-ups. Operating procedures for switching filters shall be developed to avoid inadvertent closure of the pilot sensing line.

Pressure spike snubbers

Yes Cyclic services (e.g., positive displacement rotating equipment)

Backflow preventors Yes Shall be used whenever discharging into closed header systems or when operating conditions may be below atmospheric pressure

NOTE: 1. Where in-situ pop-testing is required, field test connections shall be provided. The valve Manufacturer should be contacted for details of field testing.

2.3.4.3 If pilot-operated PRVs are used, the following issues should be considered:

a) Minimum process pressure required to seat the main valve to accommodate the elasticity of the seat.

b) Pilot-operated valves are more complex than spring-loaded valves. This can result in lower reliability and more opportunities for error during repair.

c) The soft goods for main valve and pilot shall be compatible with the process composition including upset conditions, temperature (relieving and heat tracing temperatures, if applicable), and pressure. Soft goods can be affected by substances in the process at low concentration. Some materials are susceptible to explosive decompression in certain process environments.

d) Low temperature service can cause brittle failure or loss of elasticity of several soft goods.

e) Use of diaphragm-style pilot-operated PRVs should normally be limited as an alternative to pressure/vacuum vents described in (2.3.10). Diaphragm-style pilot-operated PRVs should only be used on process equipment with approval by the Principal.

2.3.5 Assisted pressure relief valves

Assisted PRVs are spring-loaded PRVs equipped with a pneumatic actuator. The function of the actuator is to reduce the operating margin between set pressure and maximum operating pressure.

Assisted pressure relief valves are not ASME VIII certified and shall only be used with the approval of local authorities. The application shall follow ISO 4126-5.

For design purposes, use an operating margin of 5%. To achieve this goal, the following options are possible:

2.3.5.1 The actuator assists to open the PRV exactly at set pressure. In this case, the spring setting of the PRV is 105 % of design pressure.

2.3.5.2 The actuator assists to keep the PRV closed up to the latter's set point (supplemental load). The spring setting of the PRV is 100 % of design pressure. However, in the event of instrumentation malfunction (including e.g., instrument air supply) the PRV shall act as a spring-loaded PRV with requirement of this DEP specification.



2.3.5.3 The action of the actuator is a combination of (2.3.5.1) and (2.3.5.2). But since a supplemental load is applied, the spring setting of the PRV may be 100 % of design pressure.

The assist instrumentation should be classified as an Instrumented Protective Function. An assisted pressure relief valve in toxic or hazardous medium service shall have a bellows to ensure tightness to the atmosphere.

The PRV Manufacturer is responsible for the overall PRV assembly (valve complete with actuator and/or accessories).

2.3.6 Thermal expansion relief valves (TERVs)

The standard TERV size for piping systems shall be (25 mm x 25 mm) or (20 mm x 25 mm) [(1 in x1 in) or (¾ in x 1 in)], flanged, with a minimum orifice area of 0.71 cm2 (0.110 in2).

2.3.7 Rupture disks

2.3.7.1 General

a) Rupture Disks are non reclosing relief devices and are typically not preferred when selecting the relief device type.

b) Rupture disks (also known as “bursting disks”) should be considered to accomplish a fast response time, which cannot be achieved with a PRV. This could be required to cope with a sudden gas breakthrough due to a heat exchanger tube burst or malfunctioning of a level control valve into a liquid-filled system;

c) Rupture disk installations with burst pressures less than 100 kPa (ga) [15 psig] shall be analyzed for their susceptibility to fatigue failure due to pressure fluctuations at the inlet piping (including vortex shedding).

d) Rupture disks SHALL [PS] be sized and specified in accordance with the disk Manufacturer’s recommendations and the relevant design code. Additional detail on rupture disk sizing is given in (3.3.1).

e) The specified rupture disk burst temperature shall be the ambient temperature, unless the system is heat traced or unless specific data (field temperature measurements on comparable systems) supports using a different temperature.

f) Superimposed back pressure shall be part of the disk design specification.

g) Rupture disks shall be designed so that process pressure pulsations or spikes do not cause premature failure of rupture disks.

h) If a rupture disk is used in lieu of a PRV, the risk of disk failure (e.g., pin hole or premature burst) shall be reduced by:

(i) Selecting rupture disks that are resistant to fatigue, creep, and corrosion in the specific application.

(ii) Consulting the Manufacturer to determine an initial time-based replacement interval.

(iii) Providing an alarm to alert operations personnel that a disk has burst (whether premature or legitimate). Where a large liquid flow could be passed, this alarm shall inform the operators in the unit containing the protected equipment and the operators managing the flare KO drum.

(iv) Where it is important to limit further the possibility of premature burst, specifying a properly engineered system consisting of two disks in series.

(v) To indicate when a rupture disk has burst or is leaking, a pressure gauge or a pressure alarm should be provided between the two disks in dual disk applications. If bursting or leaking of the first rupture disk could lead to downstream fouling, then installation of an alarm between the rupture disks should be considered.



2.3.7.2 Rupture disk selection

a) Rupture disks shall be adequate for any constant or variable vacuum and for the maximum back pressure conditions. This may require the use of vacuum support.

b) Non-fragmenting rupture disk designs shall be used where fragmentation could affect the proper operation of equipment downstream of the disk such as PRVs, control valves, and exchangers.

To avoid premature failure, a sufficient operating margin shall be provided between the maximum operating pressure of the protected equipment and the design bursting pressure of the disk.

c) The disk Manufacturer's recommended operating ratio (the ratio of maximum operating pressure to marked burst pressure) shall be indicated on the disk data sheet. If the marked burst pressure is less than 2.75 barg (40 psig), subtract 14 kPa (2 psi) from the lower limit of the marked burst pressure to determine the allowable operating ratio.

The specified burst pressure shall be determined, taking into account the operating ratio, the manufacturing range, and superimposed back pressure. The minimum burst pressure shall be recorded in the rupture disk data sheet.

d) Reverse buckling rupture disks are generally preferred on account of their smaller operating margins and manufacturing tolerances.

Reverse buckling rupture disks shall not be used in liquid full systems unless the disk is designed for such service.

Reverse buckling rupture disks that use knife blades in the disk holder shall not be used, because blunt knife blades could prevent the 100% rupture of the disk.

2.3.7.3 Disk holders

a) Rupture disks shall be installed in the corresponding Manufacturer’s rupture disk holder.

b) The Manufacturer’s holder installation instructions SHALL [PS] be followed.

c) The rupture disk holder shall shield the disk from contact with the piping flanges, when inserted.

2.3.8 Rupture disk and pressure relief valve combinations

This combination should be considered for the following situations:

a) to prevent PRVs in vacuum service from drawing gas or air back into the process;

b) to protect PRVs from being in continuous contact with a corrosive, solidifying, or polymerizing process fluid;

c) to protect PRVs from accumulation of solids and dusts;

d) to prevent leakage of very toxic substances through the PRV that discharges to the atmosphere;

e) to prevent leakage of very corrosive substances through the PRV that discharges to a closed system.

In pressure service, the compartment between the disk and the PRV should have an open outlet through a restriction orifice or excess flow check valve to the atmosphere at a safe location. Additionally, where a rupture disk is installed upstream of a PRV to safeguard the integrity of the system, a pressure gauge or a pressure alarm shall be provided between the disk and the PRV. If bursting or leaking of the rupture disk could lead to downstream fouling, then installation of an alarm between the rupture disk and PRV shall be considered.

When a rupture disk is installed upstream of a PRV, the combination capacity factor (derating factor) for the specific rupture disk/PRV combination, in accordance with ASME Section VIII, Division 1, UG-127 and API Std 520 Part I, shall be used in sizing the



PRV. If a derating factor for the rupture disk/PRV combination is not available, a combination capacity factor of 0.9 shall be used.

2.3.9 Buckling pin pressure relief valves

Buckling pin pressure relief valves are non reclosing relief devices and are typically not preferred when selecting the relief device type.

Buckling pin relief valves may be used in place of other relief valves or rupture disks as long as their limitations, i.e., non-reclosing and possible seal issues, are taken into consideration by the designer. The advantages of buckling pin pressure relief valve over a rupture disk is that it can be reclosed more easily and changing out the buckling pin does not require removing the device from the piping or having any process openings.

2.3.10 Pressure/vacuum vents

2.3.10.1 The set points for pressure/vacuum vents (PVVs) SHALL [PS] be below the tank design (high) pressure and above the tank design (vacuum) pressure.

2.3.10.2 PVV data sheets shall clearly state the maximum relieving pressure limit and vacuum limit of the protected equipment.

2.3.10.3 Flame arrestors shall not be used in conjunction with PVVs, unless required by local regulation or justified by risk analysis.

2.3.10.4 If PVV screens are required, they shall be of the same material as the PVV body or higher grade.

2.3.10.5 Moderate pressure storage tanks that can have pressures exceeding 18 kPa (ga) [2.5 psig] and all refrigerated storage tanks shall have pipe-away PVVs to limit the thermal radiation at the tank roof or other affected structure to 15 kW/h/m2 (4758 Btu/h/ft2) or less.

2.3.10.6 Direct acting PVV are not balanced and shall be evaluated for the downstream pressure if connected to a downstream system.

2.3.11 Manhole covers

2.3.11.1 Manhole covers that have a dual function as emergency tank vents shall be provided with ASME flange bolt patterns or API Std 650 flange bolt patterns, or as specified by the tank design standard. The flange face type (raised or flat) of the manhole cover shall match that of the manway nozzle.

2.3.11.2 Manhole covers shall be suitably restrained so that the cover cannot be blown off from the tank.

2.3.12 Small relief valves

For small valves that are not used for thermal expansion relief (2.3.6) the maximum orifice size shall be 71 mm2 (0.110 in2).

These valves are not covered by API 526 for constructional details. They shall be procured only from Manufacturers approved by the Principal, and full manufacturer drawings and parts lists shall be required for each individual valve. Capacity certification shall be to ASME requirements, or to other equivalent standards as approved by the Principal.

The Principal should indicate blowdown requirement. Most compact small relief valves have fixed blowdown that is greater than 10%.

In normal operating mode i.e., valve closed, the only valve parts contacting the fluid shall be of stainless steel type 316 or better.



3. RELIEF DEVICE SIZING CALCULATIONS

3.1 GENERAL CRITERIA

For each relief device, the size SHALL [PS] be determined from the largest relief area required for overpressure protection for all scenarios as established in accordance with DEP 80.45.10.11-Gen.

3.2 PRESSURE RELIEF VALVE SIZING

3.2.1 General

Combinations of a PRV with a rupture disk or a PRV with a buckling pin have capacity reduction factors as described in (2.3.8) and (3.3.2), respectively.

For reporting the calculations of the PRV size for single-phase flow, the standard calculation sheet DEP 31.36.90.94-Gen. shall be used.

For reporting the calculations of the PRV size for two-phase flow, calculation sheet DEP 31.36.90.95-Gen. shall be used. Thermodynamic calculations should be used to check for the formation of two phase flow.

Use of alternative calculation sheets requires approval by the Principal.

3.2.2 Vapour and gas

For calculating the PRV size for single phase vapour or gas flow, the formulae in the current API Std 520 Part I SHALL [PS] be applied. If the vapour or gas is outside the compressibility range 0.8 to 1.1, the integral method shall be used assuming ideal gas specific heat at relieving conditions (or standard if data is not available) and with Z=1. See API-520 B.3.5 for details.

3.2.3 Liquid

Where liquid certified valves are specified, the sizing method for certified relief valves (refer to API Std 520 Part I) SHALL [PS] be used.

If a vapour trim valve is specified and there is a liquid relief scenario, then the non-certified valve equation from API Std 520 Part I shall be used to determine the required liquid relief capacity for the liquid relief scenario – see also (5.2.2).

3.2.4 Two-phase fluids

3.2.4.1 General

For flashing and two-phase flow through a PRV, the integral equation of API Std 520 Part 1 Appendix C SHALL [PS] be used. Two common methods acceptable for solving the integral equation are described in (3.2.4.2) and (3.2.4.3).

The method requires a suitable equation of state and thermodynamic/physical property data to calculate the fluid specific volume using an isentropic expansion. The two acceptable methods both are based on the classical homogeneous equilibrium model (HEM), which assumes Vapour-Liquid Equilibrium and no slip between the liquid phase and the vapour phase.

The sum-of-the-areas method for two-phase relief sizing that appeared in API Std 520 Part I through the 6th Edition has been shown to be non-conservative and is superseded by that of the 7th edition.

3.2.4.2 Integral method (numerical)

The direct integration method in API Std 520 Part I Appendix C.2.1 is preferred.

3.2.4.3 Omega method

An alternative method specified in API Std 520 Part I Appendix C.2.2, the Leung Omega method, may be used as an approximate solution of the above integral.



3.2.4.4 Special considerations

Dissolved gas: Since depressurization of a fluid with solubilised gas produces an effect similar to flashing, API Std 520 Part 1, Appendix C, Equation C.12 shall be used to calculate ω when using the Omega method with process simulator data.

Two-phase sizing tools: Only packages meeting the DIERS (Design Institute for Emergency Relief Systems) two phase benchmarks and approved by the Principal shall be used (many applications have been found to be incorrect).

3.2.5 Supercritical fluid

3.2.5.1 General

For fluids that do not undergo a phase change upon heating while at relieving conditions, the relief load and required relief area during external fire exposure are based on accommodating thermal expansion of the fluid. The relief device SHALL [PS] be able to accommodate the maximum volumetric expansion rate as determined using the method of DEP 80.45.10.11-Gen.

3.2.5.2 Pressure relief valve sizing

Use the same method as described in (3.1.4.2).

Omega should be evaluated with a process simulator by flashing the fluid at its choke pressure (if that is not known, 70 % of the relieving pressure should be taken).

3.2.5.3 Near-critical liquid

Common practice is to assume a latent heat of vaporization of 116 kJ/kg (50 Btu/lb) as a conservative basis for relief load. For revamping or expansion of existing facilities or for new facilities, a more-rigorous evaluation should be performed, accounting for changes in fluid heat of vaporization, heat capacity, and density in response to possible fluid heating and surpassing of the critical temperature.

3.2.6 Discharge coefficients

For preliminary sizing, the discharge coefficients given in API Std 520 Part I (or the Manufacturer’s certified discharge coefficients with corresponding orifice area, if available), shall be used, as summarized in Table 2.

Table 2 Discharge coefficients

Discharge Coefficient, Kd Vapour certified Liquid certified

For gas/vapour only relief 0.975 N/A

For all subcooled liquid relief (including non-flashing liquids)

0.62 0.65

For two-phase relief (including saturated liquids) in non-reactive service

0.85 N/A

More detail regarding PRV certification can be found in (5.2). For any of the above cases, the Manufacturer is responsible for verifying the sizing and substitutes its device-specific discharge coefficients, as applicable. The Manufacturer is responsible for the verification of the sizing based upon the specifications provided.

Other regional or local codes might require different discharge coefficients.

3.2.7 Back pressure

3.2.7.1 General

For calculation of the back pressure, refer to DEP 80.45.10.10-Gen.

For the impact of back pressure on PRV selection (conventional vs. balanced), refer to (2.3).



3.2.7.2 Pressure relief valve back pressure correction factor

a) Balanced PRVs: For preliminary sizing, methods in API Std 520 Part I should be used. Where available, the Manufacturer’s published capacity correction factor due to back pressure (Kb or Kw) can be used. The Manufacturer is responsible for the verification of the sizing based upon the inputs and specifications provided by the Contractor.

b) Conventional PRVs: For critical flow, the allowable built-up back pressure for a conventional PRV is limited to the allowable overpressure and the back pressure correction factor (Kb) is 1. For subcritical flow, the allowable built-up back pressure is still limited to the allowable overpressure; in this case, the coefficient of subcritical flow (F2) described in API 520 Part I or the PRV Manufacturer’s curves shall be used. For conventional PRVs in liquid service, the built-up back pressure is limited to the allowable overpressure and the back pressure correction factor (Kw) is 1.

c) Pilot Operated Valves (POVs): For critical flow, the back pressure correction factor (Kb) for a pilot-operated pressure relief valve is 1. For subcritical flow, the coefficient of subcritical flow (F2) described in API 520 Part I or the PRV Manufacturer’s curves shall be used. For POVs in liquid service, the back pressure correction factor (Kw) is 1.

3.3 NON-RECLOSING RELIEF DEVICE SIZING

3.3.1 Rupture disks

3.3.1.1 General

For calculating the size of a rupture disk, the formulae in the current API Std. 520 Part I, Paragraph 5.11.1 SHALL [PS] be applied.

3.3.2 Buckling pins

Either a “UV” or a “UD” stamped buckling pin device can be used as a relief device for overpressure protection in lieu of a PRV or a rupture disk. A “UD” stamped buckling pin device can be installed between a PRV and the protected equipment.

Buckling pin devices SHALL [PS] be sized and specified in accordance with the device Manufacturer’s recommendations, ASME Section VIII, Division 1. The same considerations SHALL [PS] also apply to capacity reduction factors for combinations of a PRV and a buckling pin device.

4. REQUISITIONING

4.1 GENERAL

The information and specifications for the pressure relief valves (PRVs) shall be entered into data sheet DEP 31.36.90.93-Gen. The information and specifications for the rupture disks shall be entered into data sheet DEP 80.46.20.93-Gen. These data sheets shall be used to requisition the relief devices. Use of alternative data sheets requires approval by the Principal.

The choice of relief device Manufacturer shall be subject to the approval of the Principal.

The Manufacturer is responsible for the design and construction of the supplied relief devices for the services and conditions specified in the requisition. Available capacities of the selected relief devices SHALL [PS] be those established and guaranteed by the relief device Manufacturer for the applicable service conditions and be greater than the required capacities.

4.2 PRESSURE RELIEF VALVES

If a PRV is provided with an actuator and/or accessories from another source, but supplied as part of the PRV requisition, the PRV Manufacturer alone is responsible for the overall valve assembly (valve complete with actuator and/or accessories).



4.3 RUPTURE DISKS

If a rupture disk is provided with a holder and/or accessories from another source, but supplied as part of the rupture disk requisition, the rupture disk Manufacturer alone is responsible for the overall disk assembly (disk complete with holder and/or accessories).

5. RELIEF DEVICE SPECIFICATIONS

5.1 GENERAL

The Manufacturer is responsible for supplying relief devices with material grades as specified on the requisition.

Unless otherwise specified, the Pressure Relief Device material SHALL [PS] conform to the project material selection report (instrument materials selection table). If no materials selection report is available, a corrosion and materials engineer SHALL [PS] be consulted.

Any soft goods SHALL [PS] be compatible with the process at normal operating and ambient conditions as well as during relief events and unit upsets.

5.2 PRESSURE RELIEF VALVE SPECIFICATION

5.2.1 General

The pressure relief valve specification shall be according to MESC SPE 77/135.

Pressure Relief Valves (PRVs) used in applications where the MAWP is 1.03 barg (15 psig) or higher shall meet the requirements of ASME I (for power boilers) or ASME IV (for heating boilers) or ASME VIII (for pressure vessels).

5.2.2 Liquid relief

If there are both liquid and vapour relief cases, the dominant liquid relief case and the controlling case for sizing shall be identified in the PRV data/requisition sheet (DEP 31.36.90.93-Gen.).

If chatter is a problem, the application of a friction damper may be considered where allowed by the relevant codes and regulations.

5.2.3 Buckling pins

Either a “UV” or a “UD” stamped buckling pin device can be used as a relief device for overpressure protection in lieu of a PRV or a rupture disk. A “UD” stamped buckling pin device can be installed between a PRV and the protected equipment.

5.3 SET PRESSURE CONSIDERATIONS

5.3.1 General

There shall be an adequate margin between the set pressure and the Maximum Operating Pressure (MOP). DEP 01.00.01.30-Gen. more specifically defines the margins that should be maintained.

Set pressures (SP) and maximum relieving pressures, expressed in relation to the design pressure (DP) of the protected equipment, all expressed in gauge pressures, SHALL [PS] not exceed the DP, except where allowed by the design code. For the definition of design pressure (DP) reference is made to DEP 01.00.01.30-Gen. The maximum allowable working pressure (MAWP) which is used in the ASME Boiler and Pressure Vessel Code is equal to or greater than the DP.

5.3.2 Liquid relief

For vessels in liquid full service, relief device set pressures shall be adjusted to compensate for static head between the relief device and the protected equipment.



For vessels that normally have a vapour space and are subjected to a liquid relief scenario, the relief device set pressure shall not be lowered to compensate for the static head if that result in exceeding the allowable accumulation while relieving.

5.4 ADDITIONAL REQUIREMENTS FOR SPECIFIC SERVICES

5.4.1 Oxygen service and high pressure air service

DEP 31.10.11.31-Gen. and MESC SPE 77/303 SHALL [PS] apply to PRVs in oxygen service and PRVs in air service above 5 MPa (ga) [725 psig].

5.4.2 Wet hydrogen sulphide service

NACE MR0175/ISO 15156-1 SHALL [PS] apply to oil and gas production facilities and natural gas sweetening plants.

NACE MR0103 SHALL [PS] applies to other applications (e.g., oil refineries, LNG plants and chemical plants).

6. PRESSURE RELIEF VALVES INSPECTION AND TESTING

6.1 GENERAL

Inspection/testing and certification shall be in accordance with the requirements as specified in MESC SPE 77/135.

7. PAINTING

7.1 GENERAL

Pressure relief valves (PRVs) shall be prepared and painted according to MESC SPE 77/135. Other relief devices shall be prepared and painted according to the Manufacturer's standard that is suitable for severe service in an industrial and/or marine environment at the operating temperature. High alloy steel, nickel alloy and nickel/copper alloy valves shall not be painted. This standard is subject to engineering review and approval.

8. IDENTIFICATION


Pressure relief valves (PRVs) shall be marked according to MESC SPE 77/135. PRVs for oxygen service SHALL [PS] be tagged: "SUITABLE FOR OXYGEN SERVICE"

8.2 RUPTURE DISKS

Each rupture disk shall have the tag number (e.g., xxx-PSD/RD-xxxx as stated in the requisition) stamped legibly on the Manufacturer’s disk tag attached to the downstream side of the disk by means of die stamps with characters at least 3 mm (1/8 in) high. If the tag cannot be attached to the disk, it should be provided separately with a hole to be attached to the companion flange.

The markings shall be legible from the downstream side of the disk. Blockage of the tag view should be avoided after the full assembly of the disk.

The rupture disk holder shall have a stainless steel nameplate, attached to the outside of the holder by a spot weld or stainless steel wire. At least the following information shall be clearly stamped on the plate:

• Markings specified in ASME VIII, including size, class rating, material.

• Tag number.

The flow direction shall be clearly marked on the disk holder.



9. PROTECTION AND PACKAGING

9.1 GENERAL

All necessary precautions shall be taken for adequate protection of the relief devices during shipment and storage according to API Std 520 Part II. All relief devices shall be handled carefully in order to avoid damaging them or upsetting their adjustment.


The protection and packaging of pressure relief valves shall be according to MESC SPE 77/135.

9.3 RUPTURE DISKS

The Manufacturer is responsible for providing the rupture disk and holder as a single, assembled unit.

The Manufacturer is responsible for riveting or welding together any vacuum supports, seal or disk liners, and protective rings as a single unit and including the required ASME Code data on a permanently attached tab.

Unless otherwise specified, disk shipping covers shall be attached to the packaging instead of to the disk. This is to prevent inadvertent installation of shipping covers with the disk.

9.4 BUCKLING PINS

Precautions shall be taken to prevent damage of the buckling mechanism during transportation and installation. There shall be an obvious indication that the securing device is installed and it shall be removed before commissioning of the buckling pin relief valve.

10. DOCUMENTATION

10.1 MANUFACTURER

The Manufacturer is responsible for submitting the following documents with the quotation:

• Calculations of relief device capacity;

• Dimensional outline drawing of the relief device;

• Details of where the full relief device specifications will be held.

The Manufacturer is responsible for making available the results of the inspections and tests to the Principal as part of a package of final certified documents and drawings.

The Manufacturer is responsible for completing a spare parts list and interchangeability record (E-SPIR) for all equipment supplied. See DEP 70.10.90.11-Gen.

10.2 ELECTRONIC FILES

Documentation shall be consistent with the project or asset information management systems.

10.2.1 Documentation produced with PC-based software shall be provided in electronic form.

10.2.2 Microsoft Word and Excel shall be used to produce documentation, as applicable.

10.2.3 Unless otherwise specified, individual electronic documents that require more than one program to produce shall be provided in a single file (e.g., Excel spreadsheet integrated into a Word file).

10.2.4 For software used to size PRVs, the documentation that is included in the PRV folder shall show the underlying equations.



10.2.5 Documents provided in Adobe Acrobat files shall also be provided in the native format (e.g. Word, Excel, AutoCAD) if available to the Manufacturer/Supplier or the Contractor so that future modifications can be made.

10.3 EQUIPMENT FILES

10.3.1 General

10.3.1.1 The Contractor is responsible for submitting the equipment files.

10.3.1.2 Equipment files referred to in this DEP include those for all pressure relief devices (e.g., PRVs, pressure vacuum vents, rupture disks, and buckling pins).

10.3.1.3 Unless otherwise specified, one set of pressure relief device equipment files shall be issued to the Principal.

10.3.2 Calculations and narratives

Equipment files shall include calculations and narratives as follows:

10.3.2.1 A narrative description of any set pressure considerations that result in a cold differential test pressure that is different from the design pressure of the limiting component in the system.

10.3.2.2 All required area calculations or supporting data as specified in (3.2) and (3.3). This includes pressure vacuum vents.

10.3.2.3 The above calculations and narratives shall be combined with documentation of relief scenarios, relief load calculations, and hydraulic calculations derived from DEP 80.45.10.10-Gen. and DEP 80.45.10.11-Gen.

10.3.3 Miscellaneous

Equipment files shall include miscellaneous documentation as follows:

10.3.3.1 New relief device data sheets

a) Data sheets shall be consistent with those used by the Principal.

b) Data sheets shall be provided “as built.

10.3.3.2 Certified drawings of the relief device that identify all components and materials of construction.

10.3.3.3 Certified Material Test Reports and Positive Materials Identification as specified in DEP 31.10.00.10-Gen.

Unless otherwise specified by the Principal, only the minimum necessary quantity of documentation shall be provided.



11. REFERENCES

In this DEP, reference is made to the following publications: NOTES: 1. Unless specifically designated by date, the latest edition of each publication shall be used,

together with any amendments/supplements/revisions thereto.

2. The DEPs and most referenced external standards are available to Shell staff on the SWW (Shell Wide Web) at http://sww.shell.com/standards/.

SHELL STANDARDS

Definition of temperature, pressure, and toxicity levels DEP 01.00.01.30-Gen.

Positive material identification (PMI) program DEP 31.10.00.10-Gen.

Gaseous oxygen systems DEP 31.10.11.31-Gen.

Safety/relief valves (requisition) DEP 31.36.90.93-Gen.

Safety/relief valve calculation sheet DEP 31.36.90.94-Gen.

Safety relief valve calculation sheet for two-phase flow DEP 31.36.90.95-Gen.

Piping - General requirements DEP 31.38.01.11-Gen.

Spare parts DEP 70.10.90.11-Gen.

Design of pressure relief, flare and vent systems DEP 80.45.10.10-Gen.

Overpressure and underpressure – Prevention and protection DEP 80.45.10.11-Gen.

Bursting discs DEP 80.46.20.93-Gen.

Safety/relief valves to API standard 526 MESC SPE 77/135

Valves in special service MESC SPE 77/303

AMERICAN STANDARDS

Sizing, selection and installation of pressure-relieving devices in refineries, Part I - Sizing and Selection

API Std 520 Part I

Sizing, selection, and installation of pressure-relieving devices in refineries Part II—Installation

API RP 520 Part II

Pressure-relieving and depressuring systems API Std 521

Flanged steel pressure relief valves API Std 526

Seat tightness of pressure relief valves API Std 527

Welded tanks for oil storage API Std 650

Venting atmospheric and low-pressure storage tanks API Std 2000

Pipe Flanges and Flanged Fittings NPS 1/2 Through NPS 24 Metric/Inch Standard

ASME B16.5

ASME Boiler and Pressure Vessel Code: Rules for construction of power boilers

ASME Section I

ASME Boiler and Pressure Vessel Code: Rules for construction of heating boilers

ASME Section IV

ASME Boiler and Pressure Vessel Code: Rules for construction of pressure vessels

ASME Section VIII, Division 1

ASME Boiler and Pressure Vessel Code: Alternative Rules - Rules for construction of pressure vessels

ASME Section VIII, Division 2

Omission of lifting device requirements for pressure relief valves on air, water over 140°F, or steam service

ASME Section VIII, Division 1, BPV Code Case 2203-1


http://sww.shell.com/standards/


Materials resistant to sulfide stress cracking in corrosive petroleum refining environments

NACE MR0103

Petroleum and natural gas industries – Materials for use in H2S-containing environments in oil and gas production

NACE MR0175

EUROPEAN STANDARDS

Directive of the European Parliament and of the Council on the approximation of the laws of the member states concerning pressure equipment NOTE: Commonly known as the European Pressure Equipment Directive (PED). Issued by: EU/EC - European Union/Commission Legislative Documents

EC 97/23

INTERNATIONAL STANDARDS

Petroleum and natural gas industries – Materials for use in H2S-containing environments in oil and gas production, Part 1: General principles for selection of cracking-resistant materials

ISO 15156-1

Petroleum, petrochemical and natural gas industries – Pressure-relieving and depressuring systems

ISO 23251

Petroleum, petrochemical and natural gas industries - Venting of atmospheric and low-pressure storage tanks

ISO 28300

Safety devices for protection against excessive pressure ISO 4126 (all parts)


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