18.1 The Process of Developing a WPS
David Colameco, M.Ed.
This section will introduce you to the general steps of developing a WPS so you are aware of the general process, however there are many details of WPS development that are beyond the scope of this chapter. It is important to note that this discussion is intended to be generic and not exact since different welding codes and fabrications have different requirements that will make those processes look different, however the basic process will be common to what is presented here.
Going back to the cooking examples, imagine you are hungry and want to make a meal, but you want to use the ingredients available to you at home. If you haven’t done this yourself before, you may have had friends or someone who loves to cook do this in front of you. First, a look at the ingredients that are available is done and ideas form as what to make. Inside their mind they are thinking through what they can cook, how best to cook it, and details about spices or processes such as on the stovetop, oven, or grill.
With welding a similar process occurs for code welds, where a fabrication is made to the requirements of a welding code. An engineer or senior certified welding inspector, depending upon the complexity of the build and familiarity with the type of fabrication will develop an initial educated guess as to what welding process, machine settings, and technique will create a successful weld. This information is written down on a preliminary WPS or pWPS, and a welder or welding operator will try it out while someone records the essential variables such as the important settings and characteristics of the weld on a Procedure Qualification Record (PQR). The sample weld is then visually inspected and mechanically tested. If it passes all of the requirements of visual and mechanical testing and the PQR is reviewed and accepted in accordance with the company procedures and the quality program, then the PQR is qualified.
Let’s look at each of these closer:
Preliminary Welding Procedure Specification
The preliminary welding procedure specification, or pWPS, is an initial educated guess at what the welding essential variables are, based upon the code being used, manufacturer’s recommendations and experience welding the same or similar material. If the material or process is not one that is often used by the company, a welding engineer will very likely research the joint design and setting needed to create a successful weld.
This information is then used by the welding or welding operator to create a weld. The PQR is then used to record the settings used.
Procedure Qualification Record
A pWPS provides a range for the essential variables that the welder or welding operator uses to create the weld. For example, if welding with SMAW, a range could be 90 to 110 amps. The welder would use a value within that range to perform the weld. As the welder is welding, another person would write down all of the essential information on a procedure qualification record, or PQR, to record the inputs used. A single value is typically written down for each essential variable, such as an average current used. This single value is important because welding codes will provide ranges of +/- X% (plus or minus the percentage) so a range can be listed on a WPS.
As a welder you may be asked to weld for the development of a PQR. It is common for companies to ask a relatively new welder to do the welding for a PQR because a newer welder will typically listen more and follow directions more easily than a welder that has been welding for a long time. If you weld for a PQR and it passes visual and mechanical testing, the welding codes typically make you a qualified welder for that weld. It is worth asking if your welding in support of the PQR has qualified you as a welder, as this could be mistakenly overlooked by those asking you to weld.
Welding Procedure Specification
The PQR is then used to create a Welding Procedure Specification (WPS). A single PQR can be used to create many WPSs depending upon the rules of the welding code being used. There are various reasons for creating multiple WPSs from one PQR. One reason is that different alloys might be welded, and creating many WPSs might make the WPS easier to read rather than containing many options. This will depend upon the company preferences. Another reason would be finer control of the welder’s machine settings. The ranges that are developed from the PQR come from single values. If a welder uses the low end of voltage range for GMAW, and the high end of the range for wire feed speed, the welder is technically within the WPS; however those settings are likely not the best for success. A certain level of common welding sense that is learned by the welder is assumed.
Standard Welding Procedure Specification
Developing a PQR for a WPS is a time consuming and expensive process. The American Welding Society, American Society of Mechanical Engineers, and others have welding codes that allow for Standard Welding Procedure Specifications (SWPS) which are developed for common welding configurations of geometry, welding processes, base materials, and filler materials. A company will purchase an SWPS for an application that they wish to create WPSs for. The SWPS has the advantage of having the backing of the various welding codes and societies that allow them. This reduces liability of the company if something were not 100% with their PQR.
a weld made to the specifications of a welding code
variables identified by a welding code that are vital to a successful weld