Preliminary Welding Procedure Specification
A draft welding instruction used as the basis for welding a test piece during procedure qualification. It outlines the initial parameters that need to be verified during the test.
The preliminary welding procedure specifies how you weld the joint so the heat input is right. The cooling time determines whether the structure in the heat-affected zone turns out good or you get hard, crack-prone spots. If you cool too fast, you get hardness cracks; if you cool too slowly, the grain coarsens and the material loses toughness. You have to keep preheat and interpass temperature in mind to avoid hydrogen cracking. You write the procedure before the procedure qualification test, document all important settings, and stick to it exactly during the test – then it becomes the binding welding procedure specification.