PR-214-144500-R05 Weld Hydrogen Cracking Susceptibility Characterization

Hydrogen cracking has been and continues to be observed in both heat-affected zones and weld metals. High carbon equivalent weldment heat-affected zones (HAZ) combined with rapid cooling have been related to the development of hydrogen cracking susceptible microstructures. Weld metal cracking is observed in both high and low strength weldments and is a particular concern for root passes due to the use of cellulosic electrodes, parent metal dilution, applied load, and weld fault stress riser effects promoting cracking. The risk of HAZ and weld cracking are increased for repair and in-service welds and/or welds deposited on older generation materials (e.g., pipe or fittings) and this can pose a significant risk to the integrity of welded connections.

This report presents the result of research in the application and extension of the “Slow Bend” testing technique used to quantify the hydrogen cracking susceptibility of a weldment. This testing is being used to quantify the susceptibility of a microstructure to hydrogen cracking by defining the critical combinations of strain and hydrogen concentration (i.e. hydrogen embrittlement curves) that result in cracking in a given material. The testing and modelling results have been used to define relationships between the hydrogen embrittlement curve parameters (i.e. ductility and hydrogen embrittlement indices) and the properties of the deposited weld metal. These preliminary relationships were defined separately for cellulosic and basic SMAW electrodes providing insight to the factors that make a weld material susceptible to hydrogen cracking.