Cracking Stimulated by Hydrogen

Hydrogen sulfide is a naturally occurring gas found in oil and gas production. Wet hydrogen sulfide is highly corrosive and has been the source of many pipeline and pressure vessel failures. The corrosion process between carbon steel and hydrogen sulfide produces hydrogen, which both in its atomic and molecular form can cause cracking and failure of the steel. Hardness is not always a safe criterion to use, as two of the forms of cracking can occur in ‘soft’ materials. There are three distinct forms of cracking: hydrogen pressure induced cracking (HPIC), stress orientated hydrogen induced cracking (SOHIC) and sulfide stress corrosion cracking (SSCC) which are described together with a brief description of the applicable test methods currently being used to determine a material's resistance or susceptibility to the crack mechanisms noted. Considerable research is still being undertaken on this topic and even the mechanisms particularly of SOHIC, are not yet well understood.