Hydrogen damage in metals, particularly in steels

Hydrogen damage examples of practical interest for the engineer are presented, showing the scope of the problem and its importance in relation to technological development, particularly of CANDU reactor and of heavy water production plants. The fundamental triangle of the hydrogen embrittlement is established as follows: presence of hydrogen in the crystalline network, structure susceptible of damage, and effort. The initial collection of examples is classified in function of the observed effects. For the consideration of the causes of said effects three models of hydrogen interaction with the crystalline network are described, indicating their scopes and limitations. Then the use of the models is explained, both in order to obtain practical information (evaluation tests, acceptance and rejection criteria) and for the validation and improvement of the models themselves (study methods). Solutions for attenuating the hydrogen embrittlement and a programme of studies and tests are proposed to be carried out by the National Atomic Energy Commission. Among the latter, the local development of a microimpression method to detect the evaluation of absorbed hydrogen, comparable with the autoradiography of high resolution, and a mechanical test yielding results on fragility comparable with those obtained through the test of standard disks, are described. (M.E.L.)