Hydrogen-induced cracking in welds

Hydrogen-induced cracking occurs when the conditions outlined in 

This is inevitably present, derived from moisture in the fluxes used in welding and from other sources. It is absorbed by the weld pool and some is transferred to the HAZ by diffusion. 

These arise inevitably from thermal contractions during cooling and may be supplemented by other stresses developed as a result of rigidity in the parts to be joined. 

That part of the HAZ which experiences a high enough temperature for the parent steel to transform rapidly from ferrite to austenite and back again produces microstructures which are usually harder and more susceptible to hydrogen embrittlement than other parts of the HAZ. Hydrogen cracks, when present, are invariably found in these transformed regions. 

The greatest risk of cracking occurs when temperatures near ambient are reached and cracking may thus take place several 

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