本文件适用于减压和蒸汽减压系统。虽然是有意的 主要用于炼油厂，也适用于石化设施、天然气厂、液化石油气厂 天然气（LNG）设施和油气生产设施。提供的信息是经过设计的 帮助选择最适合所涉及风险和环境的系统 各种装置。 本文件补充了API Std 521第6版（2014），其要求适用 本文件规定的例外情况除外。购买本文件时可获得的所有当前修订均包含在购买本文件中。

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.All current amendments available at time of purchase are included with the purchase of this document.