Understanding Welding Quality Documents: WPS, PQR & WPQ Under ASME Section IX
In regulated industrial piping, no production welding can occur without certified engineering procedures and qualified personnel. The entire quality framework of ASME Section IX and ISO 15614 rests upon three interconnected documents: the WPS, the PQR, and the WPQ. This article demystifies the relationship between these documents and explains how they are audited on Qatar industrial sites.
1. The Welding Qualification Hierarchy
The relationship between these three documents follows a rigorous engineering progression:
- The PQR (Procedure Qualification Record): The foundational physical proof that a specific combination of base metal, filler metal, and welding parameters produces mechanically acceptable joints.
- The WPS (Welding Procedure Specification): The written operating instruction sheet issued to production welders, derived directly from the qualified ranges established by the PQR.
- The WPQ (Welder Performance Qualification): The individual welder’s practical certification proving their personal manual ability to deposit sound weld metal adhering to a qualified WPS.
2. Anatomy of a Procedure Qualification Record (PQR)
To establish a PQR under ASME Section IX, an experienced welder welds a test coupon under witness by an authorized third-party inspection agency (e.g. Bureau Veritas, TUV, Lloyd's). All actual variables are recorded: base metal heat numbers, exact voltage, amperage, travel speed, preheat temperature, and gas flow rates.
The welded coupon is then sent to an accredited metallurgical laboratory for mandatory destructive testing:
- Tensile Tests (2 specimens): Must exhibit tensile strength equal to or exceeding the minimum specified tensile strength of the base metal.
- Guided Bend Tests (4 specimens - Root/Face or Side Bends): Bent 180° around a mandrel. No open defects exceeding 3.2mm (1/8 in) are permitted.
- Charpy V-Notch Impact Tests (where notch toughness applies): Verifies absorbed energy (Joules) at low design temperatures (e.g. -45°C for LTCS or -196°C for cryogenic service).
- Hardness Testing (for sour service per NACE MR0175): Confirms weld metal and heat-affected zone (HAZ) hardness does not exceed 22 HRC (248 HV).
3. Developing the Welding Procedure Specification (WPS)
Once the PQR passes all lab tests, the welding engineer creates the WPS. The WPS translates the single test coupon variables into qualified operating ranges based on ASME Section IX QW-250 rules:
| Variable Category | Definition | Example Impact |
|---|---|---|
| Essential Variables | Parameters that directly affect the mechanical properties (tensile/impact) of the weld. | A change in P-Number (base metal), F-Number (filler wire), or PWHT invalidates the WPS and requires a new PQR. |
| Supplementary Essential Variables | Parameters that affect impact toughness. | Max heat input (kJ/mm), interpass temp limit, preheat decrease > 55°C. |
| Non-Essential Variables | Parameters affecting arc stability or bead shape, but not fundamental strength. | Change from stringer to weave bead; electrode diameter change. Can be revised on the WPS without re-qualifying the PQR. |
4. Welder Performance Qualification (WPQ)
Even with an approved WPS, individual welders must prove their skill. The welder welds a pipe coupon in the 6G position (pipe fixed at 45°). Passing the 6G test qualifies the welder for all positions (1G, 2G, 5G, 6G) across diameter and thickness ranges defined by ASME Section IX Table QW-452.1(b).
Welders must maintain their qualification by continuous activity: if a welder does not weld using that specific process for more than 6 months, their WPQ expires and must be renewed.