Recommendations for Relief Valves on Gas Carriers 3rd Edition

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Published Date

February 2020

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Recommendations for Relief Valves on Gas Carriers 3rd Edition

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Relief valves perform a safety critical function. Proper design and robust maintenance procedures are essential to ensure that this equipment will function as required. The purpose of this document is to provide information to support this goal.

This publication is the third edition of SIGTTO’s guidance on relief valves and it updates the previous edition An Introduction to the Design and Maintenance of Cargo System Pressure Relief Valves on Board Gas Carriers, 1998.

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These recommendations are for liquefied petroleum gas (LPG) carriers and liquefied natural gas (LNG)

carriers. For the purposes of this document, the term LPG refers to liquefied gas cargoes carried between the

temperature range of 0°C to -104°C.

These recommendations do not apply to existing ships, and there is no suggestion that existing ships should be


It is recognised that some gas carrier designs may not be able to conform to all of the recommendations in this

document. However, this document is intended to serve as a starting point with a view to minimising differences

as much as possible.

1 Introduction and Scope

2 Relief Valve Types

2.1 Pilot Operated Relief Valves

2.2 Spring Loaded Relief Valves

2.3 Comparison of Pilot Operated and Spring Loaded Relief Valves

2.4 Vacuum Operation of Pilot Operated Relief Valves

3 Relief Valve Requirements

3.1 General Requirements

3.2 Basic Design Requirements

3.3 Installation Design

3.4 Materials

4 Recommendations

4.1 Selection and Design

4.2 Operational

4.3 Maintenance

4.4 Maintenance and Care of Diaphragms

4.5 Routine Testing

4.6 Field Test Kit

5 Operating Problems and Faults

5.1 Operating Problems

5.2 Faults

5.3 Chloride Stress Corrosion Cracking

5.4 Emergency Closure of Relief Valves


Annex 1 – Auxiliary Setter Installation Procedure

Annex 2 – Metal to Metal Valve Seats

Annex 3 – Glossary of Terms and Abbreviations

Annex 4 – Reference List

The purpose of SIGTTO is to promote shipping and terminal operations for liquefied gases which are safe, environmentally responsible and reliable. To fulfil this mission it will:

  • Proactively develop best operating practices and guideline

  • Sustain a learning environment by sharing lessons learned

  • Promote training and development of all within the industry

  • Foster mutually beneficial relationships with regulatory authorities and other stakeholders

  • Conduct its business with professionalism and integrity

Title: Recommendations for Relief Valves on Gas Carriers 3rd Edition
Number of Pages: 52
Product Code: WS1734K
ISBN: ISBN 13: 978-1-85609-825-0 (9781856098250), ISBN 10: 1-85609-825-7 (1856098257)
Published Date: February 2020
Binding Format: Paperback
Weight: 0.70 kg

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