Fracture mechanics hydrogen embrittlement

In neutral solutions the application of cathodic polarisation prevents crack initiation and this could be taken to indicate that hydrogen embrittlement is not the operative mechanism, since the discharge and entry of hydrogen might be expected to fracture the specimen more readily. The beneficial effect of cathodic polarisation has been interpreted , however, to result from more rapid film repair in the alkaline catholyte generated by the cathode reaction. The film serves as a barrier to rapid hydrogen entry. Consistent with this is the observation that in an environment of low pH (e.g. 10 N HCl) where film formation would not be expected, cathodic polarisation has no effect upon crack propagation. 

Althongh hydrogen embrittlement is more severe at high gas pressnres and in high-strength steels, strnctnres can still be designed with steels nnder these conditions by using fracture mechanics. Provided material data are available for steels... 

Wei, R. P., Klier, K., Simmons, G. W., and Chou, Y. T., Fracture Mechanics and Surface Chemistry Investigations of Environment-Assisted Crack Growth, in Hydrogen Embrittlement and Stress Corrosion Cracking, Ronald Gibala, et al., eds., American Society for Metals, Metals Park, OH (1984), 103. 

DM Symons, A comparison of internal hydrogen embrittlement and hydrogen environment embrittlement of X-750 , Engineering Fracture Mechanics, vol. 68, 2001, pp. 751-71. 

On high-strength steel used in prestressed concrete (but not with common reinforcing steel) under very specific environmental, mechanical loading, metallurgical and electrochemical conditions, hydrogen embrittlement can occur, which may lead to brittle fracture of the material (Chapter 10). 

This type of attack does not require any specific environment to take place, since it can take place simply in neutral or acidic wet environments. Failure due to hydrogen is named hydrogen embrittlement since it leads to a brittle-Uke fracture surface. Indeed, the ductility of the bulk metal does not change, but the propagation of the crack is due to the mechanical stresses induced in the lattice by hydrogen accumulated near the crack tip. If hydrogen is present in the metal lattice before the application of loads a delayed fracture may occur, i. e. the steel does not fail when the load is applied, but after a certain time. 

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