A “Post Weld Heat Treatment” (PWHT) is a thermal process where a welded component is reheated to a controlled temperature below its critical transformation temperature, held for a specific amount of time, and then slowly cooled to relieve residual stresses introduced during welding, thereby improving the overall mechanical properties of the welded joint and preventing potential issues like stress cracking or brittle fracture, essentially, it’s a way to “relax” the stresses built up during welding by applying heat after the welding process is complete.