Bulletin / Circular by Welding Research Council, Inc., 1976

Hydrogen-induced cracking occurs in either the heat-affected zone microstructure or weld metal when four factors interact simultaneously. These factors are defined as (1) presence of hydrogen, (2) welding stresses, (3) a susceptible microstructure, and (4) a low temperature. Hydrogen can be introduced during welding from base and filler materials or external contaminants. With modern steelmaking processes, hydrogen levels have been significantly reduced, particularly in applications within the nuclear industry, where the hydrogen content in weld metal is strictly controlled. However, eliminating hydrogen entirely from initial metallic materials remains challenging. The possibility of introducing hydrogen still exists, for instance, through improperly dried welding fluxes.

Welding stresses are unavoidable and can only be minimized before welding by considering joint geometry, fit-up, external restraint, and the yield strength of the weld metal. The heat-affected zone microstructure depends on the steel composition, hardenability, and post-weld cooling rate, which in turn is influenced by weld heat input, preheating, and thickness. Among these factors, preheat temperature and post-weld holding time are the most controllable during fabrication. Thus, effective preheat control is crucial for reducing hydrogen concentrations (if present) during welding and heat treatment.

#HydrogenInducedCracking | #PressureVesselSteels | #PostweldHeatTreatment | #Preheating | #WeldingTechnology

For a detailed review, you can access the study here.