One of these chemical reactions involves hydrogen sulfide in sulfide stress cracking (SSC), a significant problem for the oil and gas industries. This methane does not diffuse out of the metal, and collects in the voids at high pressure and initiates cracks in the steel.  Austempered iron is also susceptible, though austempered steel (and possibly other austempered metals) display increased resistance to hydrogen embrittlement. Understanding how materials behave, degrade and relate to each other is a fundamental part of the research that takes place at TWI. •Liquid Metal Embrittlement. During hydrogen embrittlement, hydrogen is introduced to the surface of a metal and individual hydrogen atoms diffuse through the metal structure. Higher rates of absorption are experienced in molten material and this means that casting and welding operations can provide particular opportunities for the entry of hydrogen into metallic materials. Tests such as ASTM F1624 can also be used to rank alloys and coatings during materials selection to ensure (for instance) that the threshold of cracking is below the threshold for hydrogen-assisted stress corrosion cracking. The formation of brittle hydrides with the parent material allows cracks to propagate in a brittle fashion. The severity of hydrogen embrittlement is a function of temperature: most metals are relatively immune to hydrogen embrittlement, above approximately 150°C. •Hydrogen Embrittlement. •Corrosion Fatigue. Vacancy production can be increased in the presence of hydrogen but since vacancies cannot be readily eliminated this proposal is inconsistent with observations the removal of hydrogen reduces the embrittlement. Hydrogen embrittlement can be prevented by minimising contact between the metal and any sources of atomic hydrogen. The emphasis in hydrogen-related work has now shifted to include ways in which environmental exposures create embrittlement and cracking due to hydrogen. For steels, it is important to test specimens in the lab that are at least as hard (or harder) than the final parts will be. Then the same test can be used as a quality control check to evaluate if baking was sufficient on a per-batch basis. Laboratory facilities address issues relating to: sour service in oil and gas production; performance in other corrosive environments; effects of cathodic protection on the behaviour of subsea dissimilar joints and the influences of both high pressure and high temperature hydrogen on materials which will provide equipment for the ‘hydrogen economy’. There are a number of different forms including: •Environmentally Induced Cracking. Hydrogen embrittles a variety of substances including steel, aluminium (at high temperatures only), and titanium.  Tests such as ASTM F1624 can be used to rapidly identify the minimum baking time (by testing using design of experiments, a relatively low number of samples can be used to pinpoint this value). Phase transformations: This is specifically done with high-strength steels and low alloy steels such as the chrome/molybdenum/vanadium alloys. Hydrogen enhanced dislocation emission: The hydrogen embrittlement phenomenon was first described in 1875.. Because the solubility of hydrogen increases at higher temperatures, raising the temperature can increase the diffusion of hydrogen. National Structural Integrity Research Centre, Granta Park, Great Abington, Cambridge, CB21 6AL, UK, Hydrogen-induced Cracking (HIC) or Hydrogen Pressure-induced Cracking (HPIC). Copper alloys which contain oxygen can be embrittled if exposed to hot hydrogen.
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