Recommendations for Relief Valves on Gas Carriers - 3rd Edition

This publication describes and illustrates the various types of relief valve and sets out general requirements with reference to the IGC Code. It provides recommendations on selection, design, operation and maintenance and advises on common operating problems and faults.

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 document 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).

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 altered.

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.

SIGTTO gratefully acknowledges the assistance of FUKUI SEISAKUSHO CO., LTD. and the Anderson Greenwood Crosby business unit of Emerson in the production of this document.

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

Annexes

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 Society of International Gas Tanker and Terminal Operators (SIGTTO) is an international body established for the exchange of technical information and experience, between members of the industry, to enhance the safety and operational reliability of gas tankers and terminals. Learn more: https://www.sigtto.org/about-us/