Sulfide Stress Cracking (SSC)
Definition
Hydrogen-assisted cracking specific to H2S-containing environments. Sulfide ions poison the recombination reaction at the steel surface, forcing more atomic hydrogen to enter the metal rather than evolving as molecular H2.
- Mechanism
- Hydrogen-assisted cracking
- Trigger environment
- H2S-containing environments
- Effect of sulfide ions
- Poisons hydrogen recombination at steel surface
- Material affected
- Steel
Common questions
Why does hydrogen sulphide make cracking worse than plain hydrogen exposure?+
Sulfide ions adsorb onto the steel surface and block atomic hydrogen from recombining into harmless H2 gas, which is the normal escape route. With recombination poisoned, more atomic hydrogen diffuses into the metal lattice, increasing the embrittling hydrogen concentration compared to an H2S-free environment.
What does SSC failure look like in a forensic materials examination?+
SSC typically produces brittle, intergranular or quasi-cleavage fracture surfaces in high-strength steel components exposed to sour (H2S-bearing) service conditions, such as oilfield tubulars or pipelines. Fractography combined with knowledge of the service environment distinguishes it from purely mechanical overload failure.
Related terms
- Hydrogen-Assisted Cracking (HAC)
- The general term for crack initiation and propagation facilitated by absorbed atomic hydrogen. Encompasses hydrogen embrittlement, sulfide stress cracking, and hydrogen-induced cracking.
- Hydrogen Embrittlement (HE)
- Loss of toughness and ductility in a metal due to absorbed atomic hydrogen, resulting in brittle fracture at stress intensities below the...
- Hydrogen-Induced Cracking (HIC)
- Planar crack arrays that form parallel to the steel rolling direction when high levels of hydrogen are absorbed. Common in pipeline steels...
- Liquid-Metal Embrittlement (LME)
- Brittle fracture of a normally ductile metal when it is in contact with a specific liquid metal. Not hydrogen-related but mechanistically analogous:...
- NACE MR0175/ISO 15156
- The international standard for materials selection and qualification for sour oil-and-gas service. Sets hardness limits, alloy restrictions, and testing requirements to prevent...