Post weld heat treatment/ Pre weld heat treatment

Post-Weld Heat Treatment (PWHT) Controlled heating and cooling of welded steel (typically 550–760°C, held 1–4 hours) to relieve residual stresses, improve toughness, and restore microstructure in the heat-affected zone (HAZ). Common methods: electrical resistance pads, induction coils, or temporary furnaces.

Key benefits for welding:

• Prevents hydrogen-induced cracking (HIC)

• Reduces hardness in HAZ → better ductility & fatigue life

• Ensures compliance with ASME VIII, API 650/653, EN 13445, EN 15085

• Essential for high-thickness (>25 mm), high-strength, or Cr-Mo steels

Pre-Heating Uniform heating of base metal (100–400°C) immediately before and during welding.

Key benefits for welding:

• Slows cooling rate → avoids brittle martensite

• Drives out moisture & diffusible hydrogen

• Improves weldability of alloyed or thick materials

• Mandatory for most P-No. 3–11 steels in ASME IX