Hydrogen embrittlement failure process

In considering the various theories it is also apparent that many of them may be considered as alternative descriptions of essentially the same physical process, or as descriptions of parallel processes which collaborate in the failure. Thus a complete description of hydrogen embrittlement in a given situation will almost inevitably incorporate aspects of several of the following theories. 

Hydrogen has a low solubility in solvents for example, at ambient conditions, only 0.018 and 0.078 mL of gaseous H2 dissolves into each milliliter of water and ethanol, respectively. However, the solubility is much more pronounced in metals. Palladium is particularly notable in this respect, which dissolves about 1000 times its volume of the gas. The adsorption of hydrogen in steel may cause "hydrogen embrittlement," which sometimes leads to the failure of chemical processing equipment [4],... 

Hydrogen embrittlement is brought about, when the material absorbs evolved hydrogen during some processes. Some examples are acid pickUng, electrolysis, and uses in various vaporized atmospheres. It sometimes leads to fractures. Usually, the phenomenmi nfight occur after a long time. Therefore, it is often called delayed fracture or delayed failure . 

In addition to hydrogen embrittlement, brittle failure can occur as a result of stress corrosion, liquid metal attack, or strain-age hardening. The last mentioned cause is well known and can occur on strained steel of any strength but seldom actually occurs in modem steels it is adequately documented in Appendix E of BS 729 (British Standards Institution, 1971 reaffirmed in 1986) users often erroneously refer to this effect as hydrogen embrittlement. This clearly states that strain-age embrittlement is the only type of embrittlement that can be aggravated by the hot dip galvanizing process. 

In processes using certain chemicals stresses have been shown to make the parts prone to corrosive attack which can reduce their strength. Similarly failures have occurred where a chemical in contact with the part has affected its ability to carry stresses through causing embrittlement such as zinc embrittlement of stainless steel and hydrogen embrittlement of grade T chain. ... 

Several tests are not related to any particular part of the corrosion process, but involve only a specific test specimen that responds to corrosion by complete failure. These tests are used in the measurement of certain forms of corrosion involving factors such as stress. Examples are corrosion fatigue, stress corrosion cracking, and hydrogen embrittlement In designing such corrosion tests, the variety of test specimens parallels the number of apphcations. 

Hydrogen embrittlement has also been observed in steel structural components exposed to aqueous environments (Sheinker and Wood 1971). Termed stress corrosion cracking, this natural process can result in the failure of a component from the combined action of stress and chemical attack. It is now fairly well established that stress corrosion cracking of steels in aqueous solutions is governed, at least to some extent, by a series of electrochemical reactions at the surface which permit the entry of hydrogen into the metal (Parkins 1964). 

Later work on aluminium alloys has also focused more closely upon the role of hydrogen which had not previously been widely considered as an embrittling species in the stress-corrosion cracking process for these alloys. The idea was not new, however. Reports of intergranular failure under cathodic charging conditions had been made at a much earlier time . A reduction in stress-corrosion life and alloy ductility in a high purity Al-5Zn-3Mg alloy had been found in specimens pre-exposed to a 2% NaCI solution" , an effect that was accentuated if specimens were stressed". ... 

Specific segments of process piping handling flammable liquids or gases in mixtures known to promote pipe failures through erosion, corrosion, or embrittlement. These include hydrocarbons, streams that may contain entrained catalyst, caustics, acids, hydrogen, or similar materials where development of an appropriate scenario envelope is feasible. 

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