General This recommended practice describes procedures for controlling the hardness of carbon steel welds in petroleum refinery pressure vessels@ tankage@ and piping exposed to corrosive environments such as wet hydrogen sulfide. which can cause hydrogen stress cracking. The recommendations apply primarily to welds on mild carbon steels described as P-1 Group No.1 and 2 in Table QW-422 of the ASME Boiler and Pressure Vessel Code@ Section IX@ but excluding all those steels over 70@000 pounds per square inch (482 megapascals) minimum specified tensile strength. For steels of higher strength or higher alloy content@ the purchaser and the fabricator must determine acceptable limitations and procedures. Because of their greater susceptibility to cracking. higher strength steels generally should not be used under conditions capable of causing hydrogen stress cracking. These procedures represent practical methods@ which need not result in a hardship to the knowledgeable fabricator or purchaser. The methods and limitations are based upon the experience and technology of the petroleum refining industry. The basic principles were confirmed by API-sponsored research at BattelleColumbus Laboratories. The purchaser must specify sampling frequencies if those frequencies are different from those described in 3.4 and must specify the hardness limit based on two categories (Class I or Class II) in 3.5. A similar document on this subject@ published by the National Association of Corrosion Engineers@ Standard RP-04-72 (1976 revision)@ limits weld hardness to 200 Brinell hardness number. Recommended Practice 942 concurs in this limitation@ but also recognizes the existence of environmental situations for which a weld hardness of 225 Brinell hardness number is acceptable.
API RP 942-1982 history
1982API RP 942-1982 Controlling Weld Hardness of Carbon Steel Refinery Equipment to Prevent Environmental Cracking (SECOND EDITION)