Weld Procedure Specification (WPS)

A weld procedure specification is the written recipe that every welder must follow precisely: it specifies the exact base metal type and thickness, filler metal composition, shielding gas mixture and flow rate, preheat temperature, heat input parameters, and the positions and sequence in which weld passes must be deposited. The WPS is qualified by creating test coupons that are welded using the documented procedure and then mechanically tested to confirm that tensile strength, yield strength, and impact toughness meet or exceed code requirements.

Deviations from the approved WPS, even seemingly minor ones like a 10-amp increase in arc current, can produce welds that fall below specification, so workers must measure and record actual welding parameters and demonstrate that they remain within the approved WPS bands. Modern fabrication shops maintain electronic copies of approved WPS documents at welding stations, with regular audits ensuring that field practice aligns with engineering specifications and certification standards.