Welding procedure specification (WPS)

A welding procedure specification, WPS, is the document that turns a qualified welding procedure into instructions a welder or welding operator can actually follow: base and filler materials, process, joint design, position, preheat and interpass requirements, and the range of parameters — current, voltage, travel speed, and where relevant heat input — inside which the weld stays qualified. It is the reference a welder consults during production, and the document an inspector checks a completed weld against. ISO 15609-1 sets what an arc-welding WPS document must contain; equivalent content requirements exist under other codes, including ASME Section IX.

A WPS does not stand alone. It is written from, and only as good as, the PQR — the record that demonstrated a weld made under those same conditions actually meets the required mechanical and soundness properties. Move a variable in the WPS far enough, in a way the governing code calls an essential variable, and the qualification no longer covers it: a new qualification test, or a formal extension of the existing one, is required before the WPS can be revised to include it. Which variables count as essential, and how far they may move before requalification is triggered, is set by the applicable code and differs by process and material.

Following a WPS is only half the traceability chain. The other half is confirming the person executing it holds a current welder qualification that covers the joint being made, because a correct WPS run by an unqualified welder, or run outside that welder’s qualified range, produces a weld the paperwork does not actually support. A production weld that leaves the WPS’s parameter range is outside the qualification regardless of how the finished bead looks, which is the practical reason digital records capture the measured parameters rather than the ones written on the sheet.