WPS in welding: what it contains and when it is required

A WPS, or Welding Procedure Specification, is the work instruction that tells the welder exactly how a particular weld must be made. It fixes material, process, filler, gas, joint design, position and welding parameters, so every weld is made the way it was tested.

This article explains what a WPS contains, what it must rest on and when you need one. Want one drafted? See WPS drafting.

1. What does a WPS contain?

A WPS for arc welding follows the format of ISO 15609-1 and contains all the data that determine the quality of the weld. These are the variables the welder needs at the workplace, with their permitted ranges.

• Parent material (material group) and thickness range
• Welding process, for example 135 (MAG), 141 (TIG) or 111 (MMA)
• Filler material and shielding gas
• Joint design, welding position and run sequence
• Current, voltage, travel speed and heat input
• Preheat and interpass temperature, and any heat treatment

2. What must a WPS be based on?

A WPS is only worth something if the procedure behind it demonstrably works, and that proof is called a qualification. The most common route is a welding procedure qualification to ISO 15614-1: weld a test piece, examine and test it, recorded in a WPQR. ISO 15607 also lists other routes, such as a standard welding procedure or previous experience. Which route is allowed depends on the application standard, the execution class and the material. The difference between the two documents is explained in WPS vs WPQR: what is the difference?

3. When is a WPS required?

A WPS is required as soon as a standard or client demands qualified welding, for example for steel structures under EN 1090, pressure equipment under the PED, rail vehicles under EN 15085 or work to ISO 3834. Even without a hard requirement a WPS is sensible: it makes the work repeatable, whoever does it. Working to American codes, a prequalified WPS to AWS D1.1 may be an option.

4. Who drafts the WPS?

The WPS is drafted by or under the responsibility of the welding coordinator of the company that welds. Before testing there is a preliminary version, the pWPS; after a successful qualification the final WPS follows within the range of the WPQR. Which changes require a new qualification is covered in the essential variables of a WPS.

5. Common mistakes

The most common mistake is a WPS that falls outside the range of the underlying WPQR, for example a greater thickness or a different filler. Other classics are a WPS that is not at the welder's station, parameters that do not match practice, and a copy from another manufacturer without its own qualification.

• WPS outside the range of the WPQR
• WPS not at the workplace
• Parameters differ from what is actually welded
• WPS adopted without its own basis

6. Our advice

Build a clear WPS file that covers exactly your products, with as few qualifications as possible giving as wide a range as possible. That saves test pieces and therefore money. We draft your WPS or review an existing WPS remotely.