The specific temperatures at which different materials undergo high-temperature hydrogen corrosion

For many years, the selection of materials for equipment operating in high-temperature and high-pressure hydrogen environments has been based on what was originally called the “Nelson curve”. This curve was originally drawn from empirical data collected in 1949 by G.A. Nelson, and it was proposed by API (American Petroleum Institute). Before 1967, copyright belonged to G. A. Nelson ； Subsequently, the copyright was transferred by G.A. Nelson to API, who published it in 1970 as APL Publication 941 (First Edition). Since 1949, based on numerous experimental data from laboratories and various cases in actual production where materials considered to be in the safe zone according to the Nelson curves at that time suffered hydrogen corrosion damage when used in a hydrogen environment, the curves have been revised seven times. The current latest version is API RP (Recommended Practice) 941, 5th edition, \"Steels for High-Temperature and High-Pressure Hydrogen Service in Refineries and Petrochemical Plants\". APL 941 has always been a valuable guiding document for selecting materials resistant to high-temperature hydrogen corrosion. It should be noted that APL 941 deals only with high-temperature hydrogen corrosion of materials; it does not take into account damage caused by other important factors at high temperatures, such as the presence of other corrosive agents like hydrogen sulfide in the system, as well as damages such as temper embrittlement that may occur, or damages that can act in conjunction with high-temperature hydrogen corrosion.

For specific details, you can refer to API RP941-2008 Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants

There is a discussion on this. Could someone tell me what a “Nelson curve” is? https://bbs.hcbbs.com/thread-212910-1-1.html (Source: Haichuan Chemical Industry Forum)