Embrittlement by Internal and by External Hydrogen

By use of equations developed by the author, hydrogen pressures are calculated in nascent microcracks producing delayed failure. The results suggest a high degree of similarity between internal cracking due to dissolved hydrogen and external cracking due to environmental molecular hydrogen. This supports the surface adsorption and lattice decohesion models of hydrogen embrittlement rather than the planar pressure theory. The latter may be applicable under extreme charging conditions leading to blistering and cracking in the absence of an applied stress, especially at elevated temperatures.