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Hydrogen can diffuse into metals and alloys from several sources during processing and subsequent service. These sources include the dissociation of moisture during casting and welding, thermal decomposition of gases, and pickling and plating operations. Hydrogen can also be generated from cathodic reactions during corrosion in service and from cathodic protection measures by sacrificial anodes and impressed current.

The effects of hydrogen are well known in ferritic and martensitic steels, where it can diffuse to suitable sites in the microstructure and develop local internal pressure resulting in the characteristic form of hydrogen embrittlement. In low carbon steels, which have inherent ductility, hydrogen may not give rise to cracking but will cause blisters to develop at inclusions. This can lead to delamination in‐plate due to the directional nature of the inclusions. Steels for sour gas service, where the environment contains wet hydrogen sulfide, must have very low sulfur levels or have been treated with additions to control the shape of the inclusions during deoxidation to minimize the danger of hydrogen embrittlement and blistering.