All welds on pressure vessels must be made by qualified welders, using qualified weld procedures. Section IX of the ASME Code specifies all the requirements for those qualifications. A weld procedure, known in the code as a Weld Procedure Specification (or WPS), gives guidance to the welder about what base materials can be used and what allowable joint types can be used. It also lists other essential variables for making a weld, such as welding current, voltage, and filler metal. The WPS informs the welder what the allowable ranges are of all required welding parameters. To qualify a weld procedure, a coupon is welded and tested according to code requirements (usually with bend and tensile tests). The record of the parameters used for welding the coupon, and the testing results, is called a Procedure Qualification Record (PQR) and is kept with the WPS to support it.
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