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PETRONAS TECHNICAL STANDARDS

DESIGN AND ENGINEERING PRACTICE

MANUALS

INSTRUMENTATION OF DEPRESSURISING SYSTEMS

PTS 32.45.10.10

NOVEMBER 2009

2010 PETROLIAM NASIONAL BERHAD (PETRONAS)All rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted in any form or by any means

(electronic, mechanical, photocopying, recording or otherwise) without the permission of the copyright owner.

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PTS Circular

This revision of PTS 32.45.10.10 Instrumentation of Depressur ising Systemshas been updatedincorporating PETRONAS Lessons Learnt, Best Practice and new information issued by relevantindustry code and standards. All updates in the document are highlighted in italicfont.

The previous version of this PTS (November 2003) will be removed from PTS binder/ e-repositoryfrom herein onwards.

Document Approval

Name Designation Date Signature

Initiator Yusof b Hj Siraj Custodian Engineer,Instrument & Control(Upstream),PCSB

Reviewed SKG14 TPs PTS SKG14 ChallengeSession 1 (July 2009) andFinal Circulation (End October2009)

Approved V. R. Harindran Custodian Engineer,Instrument & Control,PA&O, GTS

Verified Saifol Mualim bAhmad Yahaya

Senior Manager,PA&O Engineering -GTS

Verified Pau Kiew Huai General Manager,Engineering - GTS

Endorsed Pau Kiew Huai Acting, SeniorGeneral Manager,GTS

Revision History

Date Version Descript ion of Updates Author

2009 - 007

PTS No: 32.45.10.10Publication Title: Instrumentation of Depressurising Systems

Base PTS Version:

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SUMMARY OF CHANGES

Section Description of Changes

2. GENERAL Added following clause in Para 2

On Exploration and Production facilities, high rate emergency depressuringsystem should consist of an on/off actuated ball valve (ABV). For a processsystem where its components are sensitive to the depressuring rate and/or highnoise level exceeding local authority requirements, a restriction orifice (RO) maybe used as a rate adjusting device. In the event that the noise level still exceedslocal authority requirements with ABV and RO, a control valve should beconsidered, subject to the approval of the Principal.

Added following clause in Para 4 (bold)

The implementations for high-rate emergency depressurising systems areprimarily distinguished by the use of normally energised or normally de-energised solenoid valves. Normally de-energised solenoids are preferred

for depressurizing valves to prevent inadvertent depressurizing, in eventof solenoid failure.

3.2.2 Valverequirements

Rephrase item 2 (bold)

2) The valve should have a metal seat and shall be tight shut-off in the forwardflow direction in accordance with IEC 60534-4 leakage class V; (therequirement of fire safe valves subject to the approval of thePrincipal).

4.1.1 Systemrequirements

Rephrase as follows (bold):

(1) Starting at the maximum upstream process pressure and the minimumdownstream process pressure, the depressurising valve shall stroke from

fully closed to fully open and vice versa within 30 s from initiation, whenoperated from thepneumatic manual station and within 20 s from initiationwhen electricallyoperated

(2) The manual control station shall be located at a safe and remote location(usually the control room);

6.4 SIGNALSEGREGATION

Rephrase as follows (bold):

Redundant IPS inputs from the depressurising initiating device shall not sharethe same power supply units, input cards, racks and field and/or system cablingin order to min imise common mode failure.

6.5 SIA BUFFERVESSEL

Following note were removed:

Note 2. Air buffer vessels may require a safety relief device, if located in aso-called fire area. (Depending on the size of the buffer vessel it mayneed ASME certificate to operate as a pressure vessel this is aDOSH requirements)

APPENDIX 1 Added and/or rephrase note 7, 11 and 12 as follows (changes bold):

7. A relief valve on the SIA buffer vessel is only required if located in a so-called fire area or when stipulated by local authority requirement egDOSH.

11. To improve reliability, followings are options:a) use of dual NE solenoid valves in series using separately routed cable,and segregated outputs from IPS to minimize common mode failure.However, this must be installed with a test panel to execute regular on-

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Section Description of Changes

line testing to ensure zero solenoid failure on demand.b) use of solenoid valves with dual coils.

12. The depressuring valve(s) shall be provided with two limit switches, one for

fully open position and one for fully closed position. SIL Class for the limitswitches as the initiators for trip function (if any), shall be done todetermine the final configuration (1001, 2003 etc).

APPENDIX 2 Added and/or rephrase note 7, 12 and 14 as follows (changes bold):

NOTES:7. A relief valve on the SIA buffer vessel is only required if located in a so-

called fire area or when stipulated by local authority requirement egDOSH.

12. Input and output circuit fault alarms shall be equipped with linemonitoring facilities and be able to distinguish between open circuits,short circuits and earth faults.

14. The depressuring valve(s) shall be provided with two limit switches , onefor fully open position and one for fully closed position. SIL Class for thelimit switches as the initiators for trip function (if any), shall be doneto determine the final configuration (1001, 2003 etc).

APPENDIX 4 Rephrase Note 7

7. A relief valve on the SIA buffer vessel is only required if located in a so-called fire areaor when stipulated by local authority requirement eg (DOSH

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PREFACE

PETRONAS Technical Standards (PTS) publications reflect the views, at the time of publication,ofPETRONAS OPUs/Divisions.

They are based on the experience acquired during the involvement with the design, construction,

operation and maintenance of processing units and facilities. Where appropriate they are based on,or reference is made to, national and international standards and codes of practice.

The objective is to set the recommended standard for good technical practice to be applied byPETRONAS' OPUs in oil and gas production facilities, refineries, gas processing plants, chemicalplants, marketing facilities or any other such facility, and thereby to achieve maximum technical andeconomic benefit from standardisation.

The information set forth in these publications is provided to users for their consideration anddecision to implement. This is of particular importance where PTS may not cover every requirementor diversity of condition at each locality. The system of PTS is expected to be sufficiently flexible toallow individual operating units to adapt the information set forth in PTS to their own environment andrequirements.

When Contractors or Manufacturers/Suppliers use PTS they shall be solely responsible for thequality of work and the attainment of the required design and engineering standards. In particular, forthose requirements not specifically covered, it is expected of them to follow those design andengineering practices which will achieve the same level of integrity as reflected in the PTS. If indoubt, the Contractor or Manufacturer/Supplier shall, without detracting from his own responsibility,consult the owner.

The right to use PTS rests with three categories of users:

1) PETRONAS and its affiliates.2) Other parties who are authorised to use PTS subject to appropriate contractual arrangements.3) Contractors/subcontractors and Manufacturers/Suppliers under a contract with users referred

to under 1) and 2) which requires that tenders for projects, materials supplied or - generally - workperformed 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,PETRONAS 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 PTS, combination of PTS or any part thereof. The benefit of thisdisclaimer shall inure in all respects to PETRONAS and/or any company affiliated to PETRONAS thatmay issue PTS or require the use of PTS.

Without prejudice to any specific terms in respect of confidentiality under relevant contractualarrangements, PTS shall not, without the prior written consent of PETRONAS, be disclosed by usersto any company or person whomsoever and the PTS shall be used exclusively for the purpose they

have been provided to the user. They shall be returned after use, including any copies which shallonly be made by users with the express prior written consent of PETRONAS.

The copyright of PTS vests in PETRONAS. Users shall arrange for PTS to be held in safe custodyand PETRONAS may at any time require information satisfactory to PETRONAS in order to ascertainhow users implement this requirement.

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TABLE OF CONTENTS

1. INTRODUCTION ........................................................................................................11.1 SCOPE........................................................................................................................11.2 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS .........11.3 DEFINITIONS .............................................................................................................1

1.4 ABBREVIATIONS.......................................................................................................21.5 CROSS-REFERENCES .............................................................................................2

2. GENERAL...................................................................................................................3

3. HIGH-RATE EMERGENCY DEPRESSURISING.......................................................43.1 GUIDANCE ON THE SELECTION OF SYSTEM IMPLEMENTATION......................43.2 HIGH-RATE EMERGENCY DEPRESSURISING SYSTEM.......................................4

4. LOW-RATE OPERATIONAL DEPRESSURISING.....................................................64.1 LOW-RATE OPERATIONAL DEPRESSURISING SYSTEM.....................................64.2 LOW-RATE OPERATIONAL DEPRESSURISING SYSTEM WITH

ADDITIONAL ..............................................................................................................7

5. DEPRESSURISING VALVE CALCULATIONS ..........................................................9

6. SPECIFIC DESIGN REQUIREMENTS ....................................................................106.1 VALVES ....................................................................................................................106.2 FIRE PROOFING......................................................................................................106.3 LINE MONITORING..................................................................................................106.4 SIGNAL SEGREGATION .........................................................................................116.5 SIA BUFFER VESSEL..............................................................................................116.6 TESTING...................................................................................................................12

7. REFERENCES .........................................................................................................13

APPENDICES

APPENDIX 1 TYPICAL ARRANGEMENT FOR HIGH-RATE EMERGENCYDEPRESSURISING SYSTEM WITH AIR FAILURE OPEN VALVE(NORMALLY ENERGISED)................................................................................1

APPENDIX 2 TYPICAL ARRANGEMENT FOR HIGH-RATE EMERGENCYDEPRESSURISING SYSTEM WITH AIR FAILURE OPEN VALVE(NORMALLY DE-ENERGISED)..........................................................................2

APPENDIX 3 TYPICAL ARRANGEMENT FOR LOW-RATE OPERATIONALDEPRESSURISING SYSTEM ............................................................................1

APPENDIX 4 TYPICAL ARRANGEMENT FOR LOW-RATE OPERATIONALDEPRESSURISING SYSTEM WITH ADDITIONAL PROTECTIVEFUNCTION 2

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1. INTRODUCTION

1.1 SCOPE

This PTS specifies requirements and gives recommendations for the instrumentation ofdepressurising systems, taking into consideration high-rate emergency depressurising and

low-rate operational depressurising.

IPF classification according to PTS 32.80.10.10 defines the implementation and testingrequirements for instrumented protective functions, including depressurising systems.Where IPF classification results in more stringent requirements than the typical designarrangements specified in this PTS, the design shall be modified accordingly.

This PTS is a revision of the PTS of the same title and number dated December 1994 andshall be used in conjunction with other PTS documents, particularly PTS 32.31.00.32,PTS 32.36.01.17 and PTS 32.80.10.10.

1.2 DISTRIBUTION, INTENDED USE AND REGULATORY CONSIDERATIONS

Unless otherwise authorised by PETRONAS, the distribution of this document is confined tocompanies forming part of or managed by PETRONAS, and to Contractors nominated bythem.

This PTS is intended for use in oil refineries, chemical plants, gas plants, supply/marketinginstallations and in exploration and production facilities.

If national and/or local regulations exist in which some of the requirements may be morestringent than in this PTS, the Contractor shall determine by careful scrutiny which of therequirements are the more stringent and which combination of requirements will beacceptable as regards safety, environmental, economic and legal aspects. In all cases theContractor shall inform the Principal of any deviation from the requirements of this PTS

which is considered to be necessary in order to comply with national and/or localregulations. The Principal may then negotiate with the Authorities concerned with the objectof obtaining agreement to follow this PTS as closely as possible.

1.3 DEFINITIONS

1.3.1 General definit ions

The Principal is the party that initiates the project and ultimately pays for its design andconstruction. The Principal will generally specify the technical requirements. The Principalmay also include an agent or consultant, authorised to act for, and on behalf of, thePrincipal.

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

The Principal may sometimes undertake all or part of the duties of the Contractor.

The Manufacturer/Supplier is the party which manufactures or supplies equipment andservices to perform the duties specified by the Contractor.

The word shallindicate a requirement.

The word should indicate a recommendation.

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1.3.2 Specific defini tions

DepressurisingReducing the pressure in process equipment at a controlled rate either due to emergencyconditions or for operational purposes.

Instrumented Protective Function (IPF)A function comprising the initiator function, logic solver function and final element functionfor the purpose of preventing or mitigating hazardous situations.

Instrumented Protective System (IPS)The (electrical and/or electronic and/or programmable electronic) logic solver component ofthe Instrumented Protective Function complete with input and output equipment.

Probability of Failure on DemandThe probability of the IPF failing to respond to a demand. Dimensionless.

Safe FailureA failure whose occurrence does not have the potential to place an IPF in a dangerous

state. Formerly known as revealed failure.

1.4 ABBREVIATIONS

Cv Control valve (flow) capacity, as defined in IEC 60534-1.DCS Distributed Control SystemDN Diameter Nominal, the size being indicated in millimetres, e.g. DN 15

(which is the metric equivalent of inch nominal size).ESD Emergency ShutdownHAZOP Hazard and Operability studyHSE Health, Safety and EnvironmentIA Instrument Air

IEC International Electro-technical CommissionIPF Instrumented Protective FunctionIPS Instrumented Protective SystemNDE Normally de-energisedNE Normally energisedPFD Probability of Failure on DemandSIA Secure Instrument AirSIL Safety Integrity Level according to IEC 61508 & IEC 61511TSO Tight shut-off (to Class V or Class VI, in accordance with IEC 60534-4)

1.5 CROSS-REFERENCES

Where cross-references are made, the number of the section or sub-section referred to isshown in brackets.

All publications referred to in this PTS are listed in (7).

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2. GENERAL

High-rate emergency depressurising of plant facilities is typically used in order toimmediately and quickly evacuate equipment inventory in an emergency.

On Exploration and Production facilities, high rate emergency depressuring system should

consist of an on/off actuated ball valve (ABV). For a process system where its componentsare sensitive to the depressuring rate and/or high noise level exceeding local authorityrequirements, a restriction orifice (RO) may be used as a rate adjusting device. In theevent that the noise level still exceeds local authority requirements with ABV and RO, acontrol valve should be considered, subject to the approval of the Principal.

High-rate emergency depressurising can be initiated automatically and/or manually,depending on the type of plant or emergency and the safeguarding strategy.

The implementations for high-rate emergency depressurising systems are primarilydistinguished by the use of normally energised or normally de-energised solenoid valves.Normally de-energised solenoids are preferred for depressurizing valves to preventinadvertent depressurizing, in event of solenoid failure.

The consequences of failure on demand and unintended depressurisation (safe failure)define the acceptable implementation(s).

NOTE: In addition to failure on demand assessment, the IPF classification methodology includes theprobability of inadvertent opening and its consequences (e.g. environmental damage, production loss,damage to plant equipment, such as reactor internals or cladding, disturbance to reactor beds).

For additional requirements for emergency depressuring, refer to PTS 80.45.10.10.

Low-rate operational depressurising of plant facilities is typically used for process control orother operational reasons. It is initiated automatically and/or manually. Low-rate operationaldepressurising systems shall be equipped with air failure closed valves to minimise the riskof inadvertent depressurising.

In most applications, a low-rate operational depressurising valve is required in parallel witha high-rate emergency depressurising valve. Where simultaneous opening of both valveswould cause the acceptable blowdown rate (typically limited by rate-of-depressurising andby flare capacity) to be exceeded, the low-rate operational depressurising valve shall beautomatically closed upon opening of the high-rate emergency depressurising valve.

Where multiple high-rate emergency depressurising systems and/or multiple low-rateoperational depressurising systems are installed, simultaneous opening of these valvesmight cause the acceptable flare capacity to be exceeded. Such cases might requireprocess sectioning as described in PTS 80.45.10.10 and need to be addressed separatelyby a risk assessment (e.g. QRA, Hazop and/or Technical Desk HSE review). Measures toprevent flare capacity being exceeded are not covered by these PTS.

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3. HIGH-RATE EMERGENCY DEPRESSURISING

3.1 GUIDANCE ON THE SELECTION OF SYSTEM IMPLEMENTATION

IPF classification in accordance with PTS 32.80.10.10 will ultimately define the acceptablearrangement(s).

3.2 HIGH-RATE EMERGENCY DEPRESSURISING SYSTEM

3.2.1 System requirements

The minimum system requirements for an air failure open high-rate emergencydepressurising system are:

1. Instrument air supply to the depressurising valve shall be assured by the use ofanSIA buffer vessel

2. Starting at the maximum upstream process pressure, the minimum downstreamprocess pressure and with the actuator loaded at the upper design pressure of the

SIA system, the depressurising valve shall be fully open within 20 s from initiation.3. Initiation and reset shall be possible from a safe and remote location, usually the

control room.4. Electrical power shall be supplied from the vital power supply system.5. Design requirements as detailed in (6).

(Appendix 1) shows a typical arrangement of a high-rate emergency depressurising systemwith an air failure open valve and one normally energised solenoid valve.

NOTE: A normally energised solenoid valve means in this context that the solenoid is energised under normaloperating conditions, i.e. with the depressurising valve closed.

(Appendix 2) shows a typical arrangement of a high-rate emergency depressurising system

with an air failure open valve and two normally de-energised solenoid valves in series.

NOTE: Normally de-energised solenoid valves mean in this context that the solenoids are de-energised undernormal operating conditions, i.e. with the depressurising valve closed.

3.2.2 Valve requirements

The minimum requirements for a high-rate, air failure open emergency depressurising valveare:

1) The body nominal size should not be less than DN 50;

2) The valve should have a metal seat and shall be tight shut-off in the forward flowdirection in accordance with IEC 60534-4 leakage class V; (the requirement of fire

safe valves subject to the approval of the Principal);

NOTES: 1. The TSO requirement is an economic environmental consideration, and is not safetyrelated if the valve discharges into a closed relief system;

2. The frequency of testing the TSO performance of the depressurising valve is establishedon environmental and economic grounds and is not related to the test requirements formeeting the SIL classification. The demand rate used for the IPF classification of the valvedoes not apply to the TSO requirement because there is a permanent requirement for thevalve to be TSO.

3) The actual capacity (Cv factor) of the valve should not be less than the calculatedvalue, nor should it exceed this value by more than 10 %, refer to (5). This may resultin a non-standard trim size or a special construction. In this case the actual valve C vshall be demonstrated by a test in accordance with the control valve capacity test

procedure of IEC 60534-2-3;

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4) The Mach number in the valve body outlet shall not exceed 0.7;

5) The noise generated by the depressurising valve shall comply with the criteria for theabsolute noise limit (sound power level) defined in PTS 31.10.00.31;

If a 'low-noise' valve design is applied, it shall be verified to ensure that fouling will not

cause the valve to plug;

To prevent plugging, no filter shall be installed upstream and no low-noise restrictionplate or silencer downstream of the depressurising valve;

6) The valve actuator shall be of the single-acting, spring-to-open type, preferably withmultiple springs (for redundancy). Double-acting piston actuators shall not be used;

7) For actuator requirements and sizing, see PTS 32.36.01.17;

8) High rate emergency depressurising devices require periodic testing and hence thedepressurising valve with its accessories should be located to allow easy access;

9) The valve actuator shall be sized for travelling from the fully closed to the fully openposition and vice versa at the maximum upstream process pressure, the minimumdownstream process pressure and the minimum SIA pressure. The Manufacturer shallsubmit the actuator sizing calculation to the Principal for approval.

NOTES: 1. The maximum upstream process pressure is the set pressure of the upstream systemrelief valve.

2. The upper design pressure of the SIA system shall equal at least the upper designpressure of the IA header.

3. To prevent excessive instrument air consumption, no instrument air pressure regulatorsshall be installed downstream of the non-return valves.

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4. LOW-RATE OPERATIONAL DEPRESSURISING

4.1 LOW-RATE OPERATIONAL DEPRESSURISING SYSTEM


In certain applications, such as in smaller Exploration and Production facilities, low-rateoperational depressurising is initiated by manually opening the valves. The minimumsystem requirements are:

(1) Starting at the maximum upstream process pressure and the minimum downstreamprocess pressure, the depressurising valve shall stroke from fully closed to fully openand vice versa within 30 s from initiation, when operated from the pneumatic manualstation and within 20 s from initiation when electrically operated

(2) The manual control station shall be located at a safe and remote location (usually thecontrol room);

Design requirements as detailed in (6).

(Appendix 3) shows a typical arrangement of a low-rate operational depressurising systemwith an air failure close valve with positioner and one normally energised solenoid valve.

Note: A normally energised solenoid valve means in this context that the solenoid is energised under normaloperating conditions, i.e. the valve position is controlled from the manual control station via the valvepositioner.


The minimum requirements for a low-rate operational depressurising valve are:

1) The valve body nominal size should not be less than DN 50;

2) The valve should have a metal seat and shall be tight shut-off in the forward flowdirection as per IEC 60534-4 leakage class V; fire safe valve.

NOTES: 1. The TSO requirement is an economic/environmental consideration, and is not safetyrelated when released to a closed relief system;

2. The frequency of testing the TSO performance of the depressurising valve is establishedon economic grounds and is not related to the test requirements for meeting the SILclassification. The demand rate used for the IPF classification of the valve does not applyto the TSO requirement because there is a permanent requirement for the valve to beTSO.

3) The actual capacity (Cv factor) of the valve should not be less than the calculatedvalue, nor exceed this value by more than 10%, refer to (5). This may result in a non-standard trim size or a special construction. In this case the actual valve Cvshall be

demonstrated by a test in accordance with the control valve capacity test procedure ofIEC 60534-2-3;

NOTE: The application of a mechanical maximum limit stop adjustment to limit the actual Cv of thevalve requires the written approval of the Principal.

4) The Mach number in the valve body outlet shall not exceed 0.7. For applicationswhere the valve will be used more than 10 times per year, the Mach number shall notexceed 0.3;

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5) The noise generated by the depressurising valve shall comply with PTS 31.10.00.31;

If a low-noise valve design is applied, it shall be verified to ensure that fouling will notcause the valve to plug;

To prevent plugging, no filter shall be installed upstream and no low-noise restriction

plate or silencer downstream of the depressurising valve;

6) The valve actuator shall be of the single-acting, spring-to-close type. Double-actingpiston actuators shall not be used;

7) For actuator requirements and sizing, see PTS 32.36.01.17;

8) As indicated in (Appendix 3), the solenoid valve shall be installed between thepositioner and the valve actuator so that when high-rate emergency depressurising isinitiated, the low-rate operational depressurising valve closes irrespective of theoutput of the manual control station.

4.2 LOW-RATE OPERATIONAL DEPRESSURISING SYSTEM WITH ADDITIONALAUTOMATIC INITIATION


This low-rate operational depressurising system is in the operational safeguarding of plantunits, such as platformers, hydrotreaters and hydrocrackers, where automatic initiation fromthe process is required.

The minimum system requirements are:

1) Instrument air supply to the depressurising valve shall be assured by the use of an SIA

buffer vessel;

2) Starting at the maximum upstream process pressure and the minimum downstreamprocess pressure, the depressurising valve shall stroke from fully closed to fully openand vice versa within 30 s from initiation, when operated from the manual station;

3) Starting at the maximum upstream process pressure, the minimum downstreamprocess pressure and with the actuator fully unloaded, the depressurising valve shallbe fully open within 20 s from initiation via any of the solenoid valves;

4) The manual control station shall be located at a safe and remote location, usually thecontrol room;

Design requirements as detailed in (6).

(Appendix 4) shows a typical arrangement of a low-rate operational depressurising systemwith an air failure close valve with positioner, one normally energised solenoid valve andone normally de-energised solenoid valve.

Note: Refer to Appendix 4: One normally energised (110UZV-121) and one de-energised solenoid valve(110UZV-102) means in this context that 110UZV-121 is energised and 110UZV-102 is de-energisedunder normal operating conditions, i.e. the valve position is controlled from the manual control stationvia the valve positioner.

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The minimum requirements for the low-rate operational depressurising valve for thisarrangement shall be as defined in (4.1.2), with the following exception:

1) As indicated in (Appendix 4), the NDE solenoid valve shall be installed between the

NE solenoid and the valve actuator and the NE solenoid shall be installed between thepositioner and the NDE solenoid to create the following command hierarchy: High-rateemergency depressurising closes the valve - other instrumented protective functionsopen the valve - manual control allows operator manipulation.

2) The valve actuator shall be sized for travelling from the fully open to the fully closedposition and vice versa at the maximum upstream process pressure, the minimumdownstream process pressure and the minimum SIA pressure.

3) To prevent instrument air consumption, no instrument air pressure regulator shall beinstalled downstream of the non-return valves.

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5. DEPRESSURISING VALVE CALCULATIONS

Considerations for determining flow rates and depressurising rates for high-rate emergencydepressurising systems are given in PTS 80.45.10.10. Flow rates and depressurising ratesfor low-rate operational depressurising systems are dictated by the operational ormaintenance requirements.

For valve calculations, refer to PTS 32.36.01.17. The Cvof the selected valve, when fullyopen, shall be equal to the calculated Cvwithin 0 % and plus 10 %.

For high-rate emergency depressurising valves, the flow rate, inlet pressure, temperatureand molecular weight shall be plotted against time, based on the actual Cvof the selectedvalve. This plot and the Cv calculations require the approval of the Principal. It shall beverified, either by calculation and/or by testing in the field, that high-rate emergencydepressurising takes place within the specified time.

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6. SPECIFIC DESIGN REQUIREMENTS

6.1 VALVES

Special attention shall be paid to depressurising valves in which the differential pressureacross the valve results in a temperature drop which causes freezing of the stuffing box and

ice formation on the stem. Valves shall be provided with an extended bonnet for thiscondition.

Low-rate operational depressurising valves, unless designed to be locally operatedmanually, shall be supplied without handwheel and without mounting facilities for ahandwheel, such as brackets or threaded holes.

For remote valve status display, a high-rate emergency depressurising valve shall beprovided with a limit switch for the both fully closed position and fully open position. SILClass for the initiators (limit switch) if require to trip the unit shall determine the final limitswitches configuration (either 1oo1, 2oo3 etc).

6.2 FIRE PROOFING

In normally de-energised high-rate emergency depressurising systems, the valve, thesecure instrument air supply buffer vessel and all associated accessories shall be of fireresistant construction. The fire resistance duration shall, as a minimum, enable the systemto perform its function within the time required for depressurising.

Above ground signal cable in the field shall be of fireproof construction, in accordance withIEC-60331-21, i.e. able to withstand temperatures of at least 750 C for a period of 90 min.

NOTE: If the depressurising system is located outside the fire risk area, the above fire resistant requirementsmay be relaxed subject to the approval of the Principal.

In normally energised systems, fire proofing and/or protection is optional due to the 'failsafe' nature of the system.

For all systems, the above-ground instrument air supply lines downstream of the isolationvalve on the main instrument air header and pneumatic signal lines shall be made up ofstainless steel tubing and compression fittings.

6.3 LINE MONITORING

For normally de-energised high-rate emergency depressurising systems, the IPS inputcircuits from the depressurising initiating device and the IPS outputs circuits to thesolenoid valves shall be permanently monitored for open circuits, short circuits and earthfaults. These faults shall generate alarms, but shall not result in opening of the high-rateemergency depressurising valve. The method of circuit monitoring and alarming requiresthe approval of the Principal.

The line monitoring circuit shall use encapsulated resistors in parallel with values suitableintended use.

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6.4 SIGNAL SEGREGATION

Redundant IPS inputs from the depressurising initiating device shall not share the samepower supply units, input cards, racks and field and/or system cabling in order to minimisecommon mode failure.

For a high-rate emergency depressurising system employing two solenoid valves, thesignal wiring and cabling in the control/auxiliary room and in the field shall run via separateroutes. Each output shall be initiated via separate power supply units, output cards, racksand field and/or system cabling. The Principal shall approve the philosophy of separation.

All redundant inputs/outputs of depressurizing systems shall be segregated from the non-redundant inputs/outputs of other DCS/IPS. The Principal shall approve the philosophy ofsegregation.

6.5 SIA BUFFER VESSEL

Upon instrument air supply failure, the SIA system shall maintain sufficient pressure in the

buffer vessel to allow for at least three valve strokes. Unless otherwise specified, the size ofthe buffer vessel shall be based on a minimum instrument air header pressure of4.2 bar (ga).

NOTES: 1. One stroke of a valve is a movement from the fully open position to the fully closed position or viceversa, i.e. three strokes starting from the closed position means: closed > open, open > closedand closed > open;

The air charges required for three valve strokes of a single-acting emergencydepressurising valve are as indicated below:

Table 1 Number of air charges of a single-acting emergency depressur isingvalve for three strokes

Valvefail-action

Applicable Air consumption Factor b

Appendices stroke 1close to

open

stroke 2open toclose

stroke 3close to

open

number ofair charges

for threestrokes

Fail-open 1,2 None 1 charge None 1

Fail-closed 4 1 charge None 1 charge 2

The following formula can be used to determine the required air buffer vessel volume:

minmin

min

*2**1*

actNRVIA

actuatoract

vesselpPP

VbPaV

+=

where:

= Minimum required net volume of the SIA buffer vessel.Vvessel= Safety factor, use 1.2 unless instructed otherwise;

this factor compensates for additional volume of thepiping/tubing, not covered by the above formula.

a

= Minimum required air pressure for the actuator to stroke thevalve at maximum upstream process pressure and

minimum downstream process pressure, in bar (ga).

Pactmin

= Number of air charges for the required number of valvestrokes (see Table 1), starting from the closed valveposition.

b

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Page 12

Volume of air required for one full actuator stroke againstthe spring force. Volume to be expressed in the same unitas Vvessel.

Vactuator

= Minimum pressure in the IA header in bar (ga).PIAmin

= Differential pressure required to open one non-return valve

upstream of the buffer vessel, in bar.

PNRV

EXAMPLE:

A single-acting, air failure open, high-rate emergency depressurising valve is installed asshown in (Appendix 2) and the following figures apply:

( ) = 2.8 bar (ga); (VPactmin actuator) = 25 litres; ( ) = 4.2 bar (ga); ( PPIAmin NRV ) = 0.2 bar.

For three valve strokes, the actuator needs to be filled with air only once (when strokingfrom open > close), so (b) = 1. With a safety factor (a) of 1.2, the minimum required netvolume of the buffer vessel is:

( )litres

pPP

VbPaV

actNRVIA

actuatoract

vessel 1148.22.022.4

25118.22.1

2

)1

minmin

min=

+=

+=

For each application, the sizing calculations for the capacity of the SIA buffer vessel shallbe submitted to the Principal for approval.

Each depressurising valve that needs an SIA system shall be provided with a dedicatedSIA buffer vessel and a dedicated IA header branch.

6.6 TESTING

IPF calculations define the required test intervals and the test procedure to meet the PFD ofthe SIL.

Depending on the required test intervals, facilities may be required to test the solenoidvalves by initiating them individually (i.e. one-by-one for implementations with two solenoidvalves). Furthermore, a locked-open manually operated valve downstream of theemergency depressurising valve may be required to allow testing (i.e. opening) of thedepressurising valve while the process pressure is present. A locked open upstream valvewith a downstream vent valve should be provided if the replacement of the depressurisingvalve is required during normal operation. The need for such requirements is covered byPTS 32.80.10.10.

The test plan and test facilities require the approval of the Principal.

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7. REFERENCES

In this PTS, 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 PTS and most referenced external standards are available to PETRONAS users.

PETRONAS STANDARDS

Noise control PTS 31.10.00.31

Instrument air supply PTS 31.37.00.11

Instruments for measurement and control PTS 32.31.00.32

Control valves - Selection, sizing and specification PTS 32.36.01.17

Classification and Implementation of instrumented

protective functions

PTS 32.80.10.10

Pressure relief, emergency depressurising, flare andvent systems

PTS 80.45.10.10

INTERNATIONAL STANDARDS

Industrial process control valves:

Part 1:Control valve terminology and generalconsiderations.

IEC 60534-1

Part 2-3:Flow capacity - Test procedures

IEC 60534-2-3

Part 4: Inspection and routine testing IEC 60534-4

Tests for electric cables under fire conditions - CircuitIntegrity:Part 21: Procedures and requirements - Cables ofrated voltage up to and including 0,6/1,0 kV

IEC 60331-21

Functional safety ofelectrical/electronic/programmable electronic safety-related systems, Parts 1 to 7

IEC 61508-1 to -7

Issued by:Central Office of the IEC3, Rue de VarembCH 1211 Geneva 20Switzerland

Copies can also be obtained from national standardsorganizations

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Appendix 1

APPENDIX 1 TYPICAL ARRANGEMENT FOR HIGH-RATE EMERGENCYDEPRESSURISING SYSTEM WITH AIR FAILURE OPEN VALVE(NORMALLY ENERGISED)

NOTES:1. Equipment and tag numbers are shown for reference.

2. IPF classification shall define the safety integrity level.

3. The non-return valves shall be of the ball or poppet type.

4. LO (locked open) valve shall be provided for maintenance purposes.

5. The alarm setting of 110PIA-101 shall equal the minimum pressure required for three strokes of the

depressurising valve. This corresponds with P IA min -2 * P NRV, see (6).For a minimum instrument air pressure of 4.2 bar (ga) and a differential pressure required to open each ofthe non-return valves of 0.2 bar, the alarm setting of 110PIA-101 shall be 4.2 - 2 * 0.2 = 3.8 bar(ga).

6. A normally closed drain valve shall be located at the lowest point.

7. A relief valve on the SIA buffer vessel is only required if located in a so-called fire area or when stipulated bylocal authority requirement eg DOSH.

8. To prevent instrument air consumption, no instrument air pressure regulator shall be installed downstream ofthe non-return valves.

9. IPF and leak test facilities may be required, but are not shown.

10. Upon initiation of the high-rate emergency depressurising from 110HZA-101, the low rate operationaldepressurising valve (if installed) shall be closed.

11. To improve reliability, followings are options:

a) use of dual NE solenoid valves in series using separately routed cable, and segregated outputsfrom IPS to minimize common mode failure. However, this must be installed with a test panel toexecute regular on-line testing to ensure zero solenoid failure on demand.

b) use of solenoid valves with dual coils

12. The depressuring valve(s) shall be provided with two limit switches, one for fully open position and one for

fully closed position. SIL Class for the limit switches as the initiators for trip function (if any), shall be done todetermine the final configuration (1001, 2003 etc).

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Appendix 3

APPENDIX 3 TYPICAL ARRANGEMENT FOR LOW-RATE OPERATIONALDEPRESSURISING SYSTEM

110

UZV-

102

From high-rate

depressuring system

(if applicable)

(note 3)

110

HC

121

Valve

positioner

Instrument air

Manual control station

(NE)

110HCV-121

SIL ....

TSO (V/-)

L.O.

L.C.

L.O.

Low-rate operational

depressuring valve

NOTES:

1. Tag numbers are shown for reference.


3. Upon initiation of the high-rate emergency depressurising, the low rate operational depressurising valve shallbe closed.

4. An air pressure regulator of the reducing-relief valve type may be required, but is not shown.

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Appendix 4

APPENDIX 4 TYPICAL ARRANGEMENT FOR LOW-RATE OPERATIONALDEPRESSURISING SYSTEM WITH ADDITIONAL PROTECTIVE FUNCTION

110HCV-121

SIL ....

TSO (V/-)

Low-rate operational

depressuring valve

110

UZV

102

From high-rate

depressuring system

(if applicable)

(note 12)110UZ-120

(NDE)

110

HC

121

Valve

positioner

Instrument air

Manual control station

110

UZV-

121(NE)

L.O.

L.C.

L.O.

From low-rate

depressuring system

(note 7)

L (note 5)

110

PIA

101

L.C.

110RV-

101

XXABC

L.O.

(note 4)

Non-return valves(note 3)

IA header

L.O.

Air filter

V-1108

SIAbuffer

vessel

(note 6)

(note 8)

NOTES:

1. Equipment and tag numbers are shown for reference.


3. The non-return valves shall be of the ball or poppet type.

4. LO (locked open) valve shall be provided for maintenance purposes.

5. The alarm setting of 110PIA-121 shall equal the minimum pressure required for three strokes of the

depressurising valve. This corresponds with P IA min -2 * P NRV, see (6).

For a minimum instrument air pressure of 4.2 bar (ga) and a differential pressure required to open each ofthe non-return valves of 0.2 bar, the alarm setting of 110PIA-101 shall be 4.2 - 2 * 0.2 = 3.8 bar(ga).

6. A normally closed drain valve shall be located at the lowest point.

7. A relief valve on the SIA buffer vessel is only required if located in a so-called fire areaor when stipulated bylocal authority requirement e.g. DOSH.

8. To prevent instrument air consumption, no instrument air pressure regulator shall be installed downstream ofthe non-return valves.

9. IPF and leak test facilities may be required, but are not shown.

10. Upon initiation of the high-rate emergency depressurising (if applicable), the low rate operationaldepressurising valve shall be closed.

32451010 Nov 09

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