title = "Post-Weld Heat Treatment (PWHT)"

content = """
Post-weld heat treatment (PWHT) is the controlled heating and cooling of a weldment after welding is completed, performed to relieve residual stresses, improve ductility and toughness of the heat-affected zone, reduce hardness in hardenable steels, and for pressure vessels and piping, satisfy code requirements. At Ridgecrest Metalworks, PWHT is performed on pressure vessel components, heavy structural weldments requiring stress relief, and alloy steel parts subject to hydrogen cracking risk.

Stress relief PWHT heats the weldment uniformly to a temperature below the lower critical transformation temperature (Ac1), typically 1100–1200°F (590–650°C) for carbon and low-alloy steels. At this temperature, the yield strength of the steel drops to approximately 20% of its room-temperature value; residual stresses above this level relax by plastic flow. Holding at temperature for a time based on material thickness (typically 1 hour per inch of thickness, 15-minute minimum) allows stress relaxation throughout the section. Controlled slow cooling after soaking prevents re-introduction of thermal stresses.

ASME Boiler and Pressure Vessel Code Section VIII (pressure vessels) and Section I (power boilers) specify mandatory PWHT requirements based on material P-Number, thickness, and operating conditions. ASME B31.3 covers process piping PWHT requirements. When code-required, PWHT must be documented with calibrated chart recorder traces that verify compliance with temperature uniformity, ramp rate, hold time, and cooling rate requirements.

PWHT can also perform hydrogen bake-out for alloy steels: holding at 400–600°F (200–315°C) for several hours immediately after welding allows hydrogen in the HAZ to diffuse out before cracking can initiate—this is a pre-emptive measure distinct from full stress relief.

PWHT equipment includes batch furnaces (large box furnaces for complete weldments), local resistance heating (ceramic pad heaters attached to the component, enclosed with insulation—used for piping and large structures that cannot be furnace-treated), and induction heating (fast and precise for joints on large components). Thermocouple placement, quantity, and attachment method are specified to verify temperature uniformity throughout the weldment cross-section.
"""

version = "0.0.1"
