Effect of Postweld Heat Treatment and Temper Bead Welding on the Hydrogen Induced Cracking Susceptibility in the Heat Affected Zone of SA-508 Pressure Vessel Steel

Abstract

Abstract ASME Case N-888, Similar and Dissimilar Metal Welding Using Ambient Temperature SMAW and Machine GTAW Temper Bead Technique, requires a 48-hour hold time before nondestructive examination (NDE) can be performed to ensure hydrogen induced cracking (HIC) did not occur. The objective of this work is to evaluate the effect of postweld heat treatment (PWHT) and temper bead welding (TBW) on the HIC susceptibility in the coarse-grained heat affected zone (CGHAZ) in welds of SA-508 pressure vessel steel. A previously published study used the Gleeble™ thermo-mechanical simulator to recreate six CGHAZ microstructural conditions: as-welded (AW), PWHT-ed, and single TBW reheats to 675°C, 700°C, 725°C, and 735°C. Detailed microstructural characterization of all microstructural conditions and preliminary HIC results were reported. The HIC susceptibility was evaluated using the Delayed Hydrogen Cracking Test (DHCT) at a diffusible hydrogen level significantly exceeding those introduced by the GTAW and SMAW processes. This study completed the HIC susceptibility evaluation of the six CGHAZ conditions and generated a “worst-case scenario” ranking of the TBW@700°C, TBW@725°C, and TBW@735°C as highly resistant, PHWT as resistant, TBW@675 °C as slightly susceptible, and as-welded CGHAZ as susceptible to HIC. Ongoing research is evaluating the HIC susceptibility of the six CGHAZ microstructural conditions at diffusible hydrogen levels corresponding to GTAW and SMAW processes and aiming to determine the critical hydrogen content that would cause HIC. The results from this study will be used to consider potential elimination of the NDE hold time requirement in Case N-888.