4 Types of Welding Procedure Specifications
By Ken Fields, CET, CWI
Welding Procedure Specifications (WPS) are the parameters and variables a welder must follow to consistently produce sound welds. In the profession, WPS can also go by Preliminary WPS, prequalified WPS, Standard WPS, or simply a WPS. In the end, Welding Procedure Specifications are simply Welding Procedure Specifications. Below is a brief description of the four types of specifications and how they come into play when developing the end product—otherwise known as a qualified WPS—after completing all the required testing.
1. Preliminary-Welding Procedure Specifications
A Preliminary-WPS is written by the entity contracted to do the work before welding a Procedure Qualification Record (PQR) test coupon. Welders use the Preliminary-WPS as a starting point when welding PQR test coupons. The PQR weld coupon is formed by two pieces of steel that are cut and beveled to the dimensions specified by the governing code and then welded. Then sections of the welded coupon are cut at code-specified locations and undergo destructive testing to determine the soundness of the welds produced using the parameters of the WPS.
Use Cases for Preliminary-WPS
When a fabricator needs to develop a WPS, the person responsible for developing the WPS will review the project specifications, types of metal used, filler metal, types of joints, essential and non-essential variables, and supplementary essential variables (if Charpy V-Notch testing is required), and any additional requirements that the WPS needs to address.
Once the fabricator understands all the project needs, they will fill out a Pre-WPS form based on the welding required for the selected process and the range of the parameters that will provide the best results. The Pre-WPS will provide the welder with a starting point that shows the parameters needed to weld the PQR coupon.
Writing a Pre-WPS can speed up the PQR testing process and decrease fabricator costs while developing a qualified WPS.
A Prequalified-WPS bases its welding variables on the history of welds and variables used in previous industrial projects. No testing is required if the variables have been maintained within the parameters set forth by the code.
Use Cases for Prequalified-WPS
The D.1.1 Structural Steel Code has a clause dedicated to the preparation of a Prequalified WPS. This clause outlines all requirements for base metals, pre-heat and interpass temperatures, filler metals, joint geometry, and essential variables and weld parameters. When the Prequalified WPS adheres to the code, it will produce welds with correct mechanical and metallurgical properties, therefore preparing a PQR is not required.
3. Standard-WPS (SWPS)
A Standard-WPS (SWPS) is developed and sold by the American Welding Society (AWS). AWS has a welding procedure committee that examines and develops SWPS from PQRs submitted by industrial and government agencies.
Use Cases for Standard-WPS
Fabricators can use a SWPS when a prequalified WPS is not acceptable to the code or the process, or if the fabricator does not want (or have time and resources) to develop a WPS through the qualification method. SWPSs are inexpensive and have the testing data required to develop a WPS for a variety of welding processes and applications.
A WPS is a procedure used and created by a fabricator when Prequalified and Standard WPSs do not apply to the project specifications or welding process. When using a WPS, fabricators need to test and develop a PQR to validate and support the WPS data.
Use Cases for WPS
If the required code on your project does not allow a Prequalified WPS, there is no SWPS that meets the welding requirements, or the fabricator wants to tailor the WPS to a specific set of parameters, then a WPS is your best option. In any of these instances, the fabricator will run a test coupon, record the testing data in a PQR, and qualify the WPS based on the test results.
We Can Help
Developing and reviewing WPS can be difficult and complicated even in the best circumstances. Our team of CWIs and engineers at Morrison-Maierle is more than willing to assist you during this process. Please contact us to see how we may help with your welding projects.