A welding procedure is the guidelines that you follow to perform a weld. They provide a record of the welding variables used, and the inspection results obtained during the procedure qualification test. They also provide the instructions for the welder to use in order to produce acceptable welds. Usually welding procedures are developed in accordance with a welding code or standard, and with few exceptions, require that physical weld samples be produced, inspected, and tested to establish qualification. Welding procedures are usually divided into two categories, the Procedure Qualification Record (PQR) and the Welding Procedure Specification (WPS).
Procedure Qualification Records (PQRs) are the established and recorded values used during the actual welding test, and all the inspection and test results obtained from the actual test samples.
Welding Procedure Specifications (WPSs) are the documented work instructions that can be used by the welder to conduct welding operations, and are based on, but not necessarily the same as, the parameters used for the Procedure Qualification Record.
Qualification testing of a welding procedure usually requires documentation to show all the variables used during the welding test, the documented inspection, and the test results. The variables required to be documented are typically such items as: the welding process used, size, type and classification of filler metal, type and thickness of base material to be welded, welding position, type and polarity of welding current, amps, and volts, travel speed during welding, type and dimensions of joint design, preheating temperature, inter-pass temperature, post weld heat treatment details, and others. In addition to the recording of all the welding parameters used during the test, the details of the inspection, and test results must also be recorded, in order to qualify a welding procedure, The records must show that the inspection, and testing has proven that the weld samples have met, or exceeded the specified standard requirement. The typical types of inspection and testing for welding procedure qualification are:
Inspection and Testing for Fillet Welds (Tee Joints) – involves the visual inspection of the completed weld, followed by two macro etches, and one fillet weld break test. The welded sample is first inspected for any visual discontinuities and then sectioned, and two small samples removed at predetermined locations. The small samples are then polished across their cross-section, and etched using some type of mild acid mixture, dependent on the base material used. The remaining welded sample is used as the fillet weld break test, that is broken against the weld to reveal the internal structure of the weld for inspection.
Inspection and Testing for Groove Welds (Butt Joints) – is a visual inspection, followed by two tensile tests, two root bend tests and two face bend tests. (These tests are typical but may differ dependent on material thickness, type and standard requirements. Different and/or additional testing, such as side bends, all weld tensile tests, impact testing or other testing may be required.) The completed weld coupon, after visual inspection, is divided into predetermined small sections. Each section is prepared, usually by machining, to specific dimensions as prescribed by the standard. Each sample is then tested mechanically to determine its characteristics.The samples are then inspected to determine their acceptability, against specified acceptance criteria, as laid down by the applicable code or standard.Typically the standard will provide the maximum size and location of various weld discontinuities, and values such as minimum tensile strengths or minimum desired impact properties.
Welds that are found not to have discontinuities that exceed these specified limits, and that meet or exceed the minimum values as specified in the standard, will be acceptable, and the welding procedure will be qualified.
The welding procedure is an important part of the overall welding quality control system, that provides documented evidence that inspection and testing has been performed to ensure that welding can be conducted to meet the established standard.
Written by Brian Chalmers
