ISO/TC 67/SC 6/WG 12 - Pressure-relieving and depressuring systems

This document is applicable to pressure-relieving and vapour depressuring systems. Although intended for use primarily in oil refineries, it is also applicable to petrochemical facilities, gas plants, Liquefied Natural Gas (LNG) facilities and oil and gas production facilities. The information provided is designed to aid in the selection of the system that is most appropriate for the risks and circumstances involved in various installations. This document supplements API Std 521, 6th edition (2014), the requirements of which are applicable with the exceptions specified in this document.

ISO 28300:2008 covers the normal and emergency vapour venting requirements for aboveground liquid petroleum or petroleum products storage tanks and aboveground and underground refrigerated storage tanks designed as atmospheric storage tanks or low-pressure storage tanks. Discussed in ISO 28300:2008 are the causes of overpressure and vacuum; determination of venting requirements; means of venting; selection, and installation of venting devices; and testing and marking of relief devices. ISO 28300:2008 is intended for tanks containing petroleum and petroleum products but it can also be applied to tanks containing other liquids; however, it is necessary to use sound engineering analysis and judgment whenever ISO 28300:2008 is applied to other liquids. ISO 28300:2008 does not apply to external floating-roof tanks.

ISO 23251:2006 is applicable to pressure-relieving and vapour-depressuring systems. Although intended for use primarily in oil refineries, it is also applicable to petrochemical facilities, gas plants, liquefied natural gas (LNG) facilities and oil and gas production facilities. The information provided is designed to aid in the selection of the system that is most appropriate for the risks and circumstances involved in various installations. ISO 23251:2006 is intended to supplement the practices set forth in ISO 4126 or API RP 520-1 for establishing a basis of design. ISO 23251:2006 specifies requirements and gives guidelines for examining the principal causes of overpressure; and determining individual relieving rates; and selecting and designing disposal systems, including such component parts as piping, vessels, flares, and vent stacks. ISO 23251:2006 does not apply to direct-fired steam boilers.