The WPS must be exactly within the essential variables qualified by the PQR. Change a filler metal classification? That requires a new PQR. 3. Welder Performance Qualification (WPQ) A welder cannot use a qualified WPS until they demonstrate skill. During a WPQ test, the welder deposits a test coupon that is visually inspected and then subjected to bend tests or radiography. The welder receives a performance qualification that limits them to certain processes, positions, and thickness ranges. Essential Variables: What Changes Require Re-Qualification? One of the most misunderstood aspects of the welding standard ASME is the concept of essential variables . These are changes in the WPS that are so significant they invalidate the original PQR.
The Authorized Inspector rejected the welds. The PQR only tested a ½” coupon; Section IX limits the qualified thickness to 2X the test coupon thickness, i.e., 1 inch. The vessel had to be scrapped, costing $50,000. welding standard asme
| Aspect | ASME (Section IX) | AWS (e.g., D1.1) | | :--- | :--- | :--- | | | Pressure vessels, boilers, nuclear piping | Structural steel (buildings, bridges, cranes) | | Qualification philosophy | Performance-based; PQR proves mechanical properties | Often prequalified WPSs allowed | | Who enforces | Authorized Inspector (AI) from ASME | Owner's engineer or building code official | | Toughness testing | Typically required for many services | Only if specified by contract | The WPS must be exactly within the essential