Hydrogen Embrittlement Caused by Acid Cleaning
It is quite common to use acid solutions to clean metal surfaces, either as paint or coating preparation, water scale removal or cleaning protein-based soiling. In these circumstances these acids work exceptionally well, nevertheless, acids in solution dissociated releasing hydrogen ions (H+) which are particularly aggressive. Incidentally the common measure of the acidity (or alkalinity) of a solution is the concentration of the hydrogen ions. The hydrogen ions can penetrate the protective surface film and are even small enough to absorb into the metal lattice, where they are reduced to hydrogen. The absorbed hydrogen starts to exert an influence to the metal lattice, although the mechanism is not fully understood, it is likely that hydrogen creates pressure leading to microscopic deformation of the metal lattice. If the metal is under stress, these deformation can lead to the propagation of cracks, eventually leading to complete failure.