Postweld

Postweld refers to operations performed after a welding process to restore or enhance a welded joint's properties, appearance, and performance. It encompasses heat treatment, surface finishing, cleaning, and inspection conducted after welding to manage residual stresses, improve corrosion resistance, and verify integrity. The term is commonly used in manufacturing, construction, and pressure-boundary applications where welded joints must meet strict standards.

Postweld heat treatment (PWHT) is a controlled heating and cooling cycle applied to welded joints. Its main purpose is to relieve residual stresses generated during welding, reduce susceptibility to hydrogen-induced cracking, and refine or normalize the microstructure and hardness of the metal. PWHT can be performed in a furnace, induction coil, or other controlled heating method, followed by a slow, controlled cool. Exact temperatures and soak times depend on material and code requirements.

Postweld cleaning and surface finishing remove flux residue, spatter, oxides, and other contaminants that can initiate corrosion or interfere with inspection. Common methods include mechanical grinding or brushing, solvent cleaning, pickling, and passivation for stainless steels. Proper cleaning helps meet corrosion resistance specifications and prepares surfaces for coating or inspection.

Postweld inspection ensures the weld meets design and code requirements after any postweld work. Visual inspection is standard, followed by nondestructive testing such as dye penetrant, magnetic particle, radiography, or ultrasonic testing as required by the applicable code. Documentation verifies conformity and supports warranty and safety assessments.

Standards for postweld procedures are provided by organizations such as ASME, AWS, and ISO. PWHT and postweld processes may affect distortion, mechanical properties, and corrosion behavior, so process verification, qualification, and adherence to procedure specifications are essential. Safety, heat-treatment equipment, and energy use are also important considerations.