The WPS is the recipe provided to the welder when making production welds. Initially, the WPS is nothing more than the engineer's best guess of what will produce acceptable welds. In order to ensure the WPS will produce acceptable welds, a welded sample is welded and tested.
The test coupon is welded following the untested WPS. The exercise is intended to demonstrate acceptable welds, with the necessary mechanical properties, can be obtained. What is done and how the coupon is welded is recorded on a document called a procedure qualification record (PQR). The information should be an independent verification of what was actually done to weld the test coupon as well as the results of the NDE and mechanical testing used to verify the required properties were obtained.
Based on the acceptable results of the testing performed and the data recorded by the PQR, a production WPS is developed. One would find it very expensive to qualify every combination of base metals and every combination of welding parameters, so the applicable welding standard permits a single PQR to support a combination of base metals having similar weldability and a range of welding parameters, i.e., voltage +/- 10%, amperage +/- 7%, etc. This approach reduces the number of procedures that must be qualified and it reduces the cost in terms of time and money.
The welding standard used or invoked by the customer defines the variables that must be controlled and recorded by both the WPS and the PQR. The variables are categorized as essential and nonessential variables. One can think of an essential variable as one that will have a profound affect on the mechanical properties of the completed weld. A nonessential variable can be thought of as a variable, if changed, will have little affect on the mechanical properties of the completed weld. Some welding standards (ASME Section IX) includes a group of welding variables called essential variables that only apply when notch toughness requirements are required by the construction code.
Consider there is an established WPS used in production. There is a change in production requirements. The original WPS was qualified for welding low carbon steel (C<0.3%), but now there is a need to weld low carbon steel to austenitic stainless steel. Such a combination will affect the mechanical properties of the joint. The electrode used will not be the same as that used to weld carbon steel to carbon steel. Thus both the base metal and the electrode type have to be changed. Both the (combination of) base metals and the electrode specification are essential variables. The base metal combination is different than that specified in the original WPS, thus a new test coupon must be welded and tested. The electrode specification was changed, thus a new test coupon must be welded and tested and the data collected and recorded on the PQR. The combination of base metal and electrode can be tested using a single test assemble and tested to qualify the new WPS. The test data is recorded in a new PQR.
Consider there is an established WPS used for production. The electrode diameter is listed as 1/8 inch E7018. However, because there is a need to increase production, a decision is made to increase the electrode diameter to 5/32 inch. The increased electrode diameter requires an increased in the arc voltage from 24 V to 26V, and the amperage is increased from 135 to 185 amps. The increase in electrode diameter and the associated increase in voltage and amperage has no influence on the tensile strength, yield strength, or ductility of the completed weld. Thus, the increase in diameter, voltage, and amperage are considered to be nonessential variables. The change in electrode diameter, voltage, and diameter must be listed in a revised WPS, but no additional testing is required.
Again, the welding standard provides direction about how WPSs are qualified, what information must be recorded by the PQR, and what information must be listed by the WPS. The welding standard also defines the variables (essential and nonessential) and when a WPS must be qualified by testing. The standard also listed the permitted ranges of welding parameters listed by the WPS based on the welding parameters recorded by the PQR. When the permitted ranges are exceeded, a new WPS must be qualified by testing.
Best regards - Al
Thank Al,you made my concept clear.
I read PQR qualifies WPS. If we doesn't achieve require properties how can PQR qualifies WPS,it is only recerded information during welding operations and conditions and results of mechanical and ndt testing which is just to be write on a document, am I correct? needs more clarification and answer.
And please tell me SWPS with examples as you demonstrate previously?
Furthermore, in D1.1 it prequalifies some welding processes within specific limits and condition, are these SWPS or simple WPS which welding engineer can be consider to make WPS or SWPS, what is confusion?