API RP 941 pdf download Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants 4 Forms of HTHA 4.1 General High temperature hydrogen can attack steels in two ways: a) surface decarburization, and b) internal decarburization and fissuring. The combination of high temperature and low hydrogen partial pressure favors surface decarburization without internal decarburization...