What Is WPS?
Quick Answer: A WPS (Welding Procedure Specification) is a written document that provides direction to the welder for making production welds per code requirements. It specifies all essential, supplementary essential, and non-essential welding variables; process type, base metal, filler metal, preheat, interpass temperature, electrical parameters, and technique. Every pressure weld on a piping system must be made following a qualified WPS.
WPS in the Qualification Framework
The WPS is one of three interconnected documents required by ASME Section IX (and equivalent codes like AWS D1.1 and API 1104):
| Document | Purpose | Who Prepares It |
|---|---|---|
| WPS | Written instruction for the welder | Welding engineer / fabricator |
| PQR (Procedure Qualification Record) | Proves the WPS produces acceptable welds via test results | Welding engineer (from test coupon data) |
| WPQ (Welder Performance Qualification) | Proves the welder can execute the WPS | Welder (tested by examiner) |
A WPS must be supported by at least one PQR. No production welding is permitted until both the WPS is qualified (via PQR) and the welder is qualified (via WPQ).
Essential Variables (ASME Section IX, QW-250)
| Variable Category | Examples | Effect if Changed |
|---|---|---|
| Essential | Welding process, P-number, F-number, A-number, thickness range, PWHT | WPS must be re-qualified (new PQR required) |
| Supplementary essential | Impact test requirements, toughness testing temperature | Re-qualification required only when impact testing is specified |
| Non-essential | Joint design, root spacing, electrode diameter, travel speed, technique | WPS revision permitted without re-qualification |
Typical WPS Contents
| Section | Information Documented |
|---|---|
| Joint design | Groove type, angle, root gap, backing |
| Base metal | ASME P-number and Group number (e.g., P-1 Gr.1 for A105, A234 WPB) |
| Filler metal | AWS classification, F-number, A-number (e.g., F-4, A-1 for E7018) |
| Position | 1G, 2G, 5G, 6G or combinations |
| Preheat | Minimum preheat and maximum interpass temperature |
| Electrical | Current type, polarity, amperage range, voltage range |
| Technique | Stringer or weave, single or multi-pass, contact tip distance |
| PWHT | Post-weld heat treatment temperature range and hold time |
| Shielding | Gas type and flow rate (for GTAW, GMAW, FCAW) |
WPS and Piping Codes
ASME B31.3 (Process Piping) requires all welds to be made per qualified WPS documents. The WPS number is recorded on weld maps and NDT reports, providing full traceability from the joint to its welding parameters, inspection results, and welder identity.
Leave a Comment
Have a question or feedback? Send us a message.