Analysis of the hydrogen content in particular in molten metal (s. Chapel process, Hot extraction process).
Very high concentrations of hydrogen can be dissolved in liquid aluminum. Since water solubility decreases considerably when melt transforms from liquid to solid state, high concentrations of hydrogen cause gas porosity in the casting. This phenomenon may also occur in die cast parts in areas with thicker walls.
If castings are to be welded, the atomically dissolved hydrogen will escape in the form of gas blisters during remelting. In case of higher concentrations, this will also result in gas formation, and the weld will swell (relevant for vacuum-supported die casting and/or for weldable and heat-treated die castings, see welding of die castings).
It is also important to know the exact hydrogen content of steels. Depending on the cooling conditions of the casting mold and the diffusion paths to be overcome, hydrogen may be enclosed in the solidifying structure causing porosity.