Meaning
Thermal conditioning applied to completed weld joints reduces internal stresses and restores material ductility to baseline levels. Executing post-weld heat treatment reduces the risk of brittle fracture and stress corrosion cracking in high-strength carbon and low-alloy steels. This process governs fabricated piping and pressure vessels, ending where the metal cools to ambient temperatures.
Stress Relief
High residual stresses generated during the rapid cooling of the weld pool are relieved by controlled heating. When applying post-weld heat treatment, the temperature is raised to a specific holding point and maintained for a set duration depending on wall thickness. This thermal dwell allows the atomic lattice to rearrange and release stored energy.
It minimizes localized stress concentrations.
Metallurgical Reform
Hardness values in the heat-affected zone are reduced to improve toughness and prevent hydrogen-induced cracking. Under these elevated temperatures, the brittle martensitic microstructures are tempered into softer, more ductile phases. This reform prevents the formation of hard zones that are highly susceptible to environmental degradation.
It restores the mechanical properties of the weldment to match the base metal. The process is mandated by major pressure vessel codes.
Operational Boundary
Heating above the critical transformation temperature must be avoided to prevent modifying the properties of the base steel. Precise temperature monitoring utilizes thermocouples attached directly to the weld zone.
