Equivalent holding time to reduce NDT delay and prevent hydrogen-induced cold cracking

Abstract Cold cracking is delayed in nature, driven by the presence of diffusible hydrogen. Current standards on welding of structural steels therefore require a minimum delay time before non-destructive testing is conducted, creating significant constraints on many fabrication processes. Appropriate heat treatment can reduce this delay time by accelerating hydrogen diffusion. While a coherent procedure for determining suitable post heating parameters is lacking. In response to this gap, a method for reducing the delay time based on hydrogen removal heat treatment and equivalent holding time has been developed and incorporated into the NORSOK M-101 standard. The approach replaces a fixed delay time with a temperature-dependent equivalent holding time, defined as the duration of heat treatment required to achieve the same degree of hydrogen removal as a specified reference delay time at ambient conditions. This work presents the methodology for calculating equivalent holding time. The approach does not require explicit determination of hydrogen concentrations or hydrogen removal efficiency. Rather, equivalence is established relative to a selected reference condition assumed to provide an acceptable degree of hydrogen removal. Equivalent holding times corresponding to the standard 48-h delay at 20 °C are derived for carbon and low-alloy steels and presented in tabulated form for temperatures between 50 and 400 °C, allowing for direct application of the method in welding and inspection. The results demonstrate that moderate heat treatment can substantially reduce the required delay time prior to non-destructive testing. The proposed method provides a practical and quantitative basis for selecting heat treatment parameters, enabling reduced delay times while adhering to current standards and requirements.