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.

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.