The Different Types of WPSs

Every CWI and SCWI knows the welder should follow a welding procedure specification (WPS) if he or she is working to a welding code such as AWS D1.1, Structural Welding Code — Steel, or the ASME Boiler and Pressure Vessel Code. Many welders are unaware of what a WPS is and how it influences their work. Maybe we should include manufacturers and contractors in that last sentence because there are more than a few who have little to no understanding of what WPSs are or why they exist.
The first step in our journey to a better understanding of the WPS is to provide a working definition of what it is. Simply put, it is a recipe for making a weld that meets the requirements of a welding code or standard.
It is a written document that provides the welder with information needed to make a weld with the mechanical properties required to meet “code” in a consistent manner.
Those who make their living creating welds have their own opinion of what information should be contained in a WPS. A welder who uses the WPS may have an opinion that differs substantially from what an engineer believes the WPS needs to include.
Everyone involved with welding has an opinion of what belongs in a WPS.

The Different Types of WPSs

There are several types of welding procedure specifications. The first type are those WPSs that have been validated by testing.
That is, the WPS has been put to the test by welding a sample, then subjecting that sample to a regimen of tests to verify it is free of defects and the mechanical properties meet the minimum requirements of the applicable code or standard. The third article in this series presents more details on how the WPS is qualified by testing.
The second type of WPS is one that is prequalified by the applicable code. This type of procedure has to meet certain limitations and requirements listed in the code. They are based on acceptable historic use. For instance, they have to utilize base metals that have a history of good weldability and utilize a listed welding process that has a history of successful use.

 The filler metals must have matching mechanical and chemical properties, and the joint details have to be selected from the approved joint details, etc. A WPS that meets prequalification status is exempt from testing and can save the contractor or fabricator substantial time and money.

 A few are recognized by welding codes such as the ASME Boiler and Pressure Vessel Code. These WPSs are supported through tests performed by various contractors and fabricators. The use of a SWPS minimizes the costs associated with doing a complete welding procedure qualification, but there are limits on their application.
When the application is very specialized and it is nearly impossible to qualify the WPS in the normal manner, a mock-up might suffice. The mock-up would be subjected to different tests than required for a normal WPS. The specifics of the testing regimen is usually agreed upon by the manufacturer/fabricator and the customer/owner.