L52243 Modeling of Delayed Hydrogen Cracking for In-Service Welds

Abstract

The objective of this research project was to demonstrate and develop a means of predicting the inspection delay time such that hydrogen cracking would not occur after inspection for in-service welds. Hydrogen cracking is an issue for in-service welding since this form of cracking may occur a significant time after the weldment has cooled to ambient temperatures. Hydrogen cracking has three necessary conditions including a tensile stress, the presence of hydrogen and susceptible microstructure. After weld cooling the microstructure is stable and it was assumed that the local weld stress state is constant, therefore, the potential for cracking is only affected by the change in local hydrogen concentration. It was asserted that after the peak local hydrogen concentration is reached the risk of cracking is over. The current project described the theory, validation and use of the BMT Hydrogen Diffusion and Cracking model. The results of this project was the demonstration of peak hydrogen delay time trends with in-service welding conditions and the development of formulae that estimate the time to peak hydrogen in a weldment as a surrogate for the time to hydrogen cracking. The results of this project provide information useful in establishing in-service weld inspection delay times for fillet weld applications.