Carbon steel is a common construction material for many equipment items in oil refineries, gas plants, storage tanks, etc. Numerous weld failures in pressure vessels, heat exchangers, tanks, and piping have been documented in NACE publications. Many of these weld failures were caused by sulfide stress cracking in "sour" service and were a form of hydrogen stress cracking (HSC). It should be noted, however, that sulfides are not the only cause of such failures, since corrosion reactions resulting from other corrosive media can introduce hydrogen into metal with similar results.

Since such weld failures can result in safety problems for personnel, expensive mechanical repairs, and substantial process losses in production and products, this NACE recommended practice was developed to provide the industry with a method of minimizing risk of failure in all equipment constructed of P-11 classification steels having a minimum specified tensile strength of 70,000 psi (480 MPa) or less. Alloyed steels and/or steels having minimum specified tensile strengths higher than 70,000 psi (480

MPa) are also subject to hydrogen induced cracking, but they are outside the 'scope of this recommended practice, which simply imposes a hardness limitation.

This recommended practice, issued by NACE under the auspices of Group Committee T-8 on Refinery Industry Corrosion, was prepared by NACE Task Group T-8-7 composed of corrosion consultants, corrosion engineers, and other specialists associated with the petroleum refining industry. API Recommended Practice 942, Controlling Weld Hardness of Carbon Steel Refinery Equipment to Prevent Environmental Cracking, addresses the same problem and closely parallels this document.

Carbon steel is a common construction material for many equipment items in oil refineries, gas plants, storage tanks, etc. Numerous weld failures in pressure vessels, heat exchangers, tanks, and piping have been documented in NACE publications. Many of these weld failures were caused by sulfide stress cracking in "sour" service and were a form of hydrogen stress cracking (HSC). It should be noted, however, that sulfides are not the only cause of such failures, since corrosion reactions resulting from other corrosive media can introduce hydrogen into metal with similar results.

Since such weld failures can result in safety problems for personnel, expensive mechanical repairs, and substantial process losses in production and products, this NACE recommended practice was developed to provide the industry with a method of minimizing risk of failure in all equipment constructed of P- 11 classification steels having a minimum specified tensile strength of 70,000 psi (480 MPa) or less. Alloyed steels and/or steels having minimum specified tensile strengths higher than 70,000 psi (480 MPa) are also subject to hydrogen induced cracking, but they are outside the 'scope of this recommended practice, which simply imposes a hardness limitation.

This recommended practice, issued by NACE under the auspices of Group Committee T-8 on Refinery Industry Corrosion, was prepared by NACE Task Group T-8-7 composed of corrosion consultants, corrosion engineers, and other specialists associated with the petroleum refining industry. API Recommended Practice 942, Controlling Weld Hardness of Carbon Steel Refinery Equipment to Prevent Environmental Cracking, addresses the same problem and closely parallels this document.

1.1 This recommended practice establishes guidelines to prevent in-service cracking of welds on P-1 steel equipment. Information is also given on the three primary factors believed to be related to in-service cracking of carbon steel welds: (1) corrosive environment, (2) hardness, and (3) total stress.  Historical Document 1987