WPS vs WPDS: What's the Difference?

A plain-English guide for welders and shop supervisors

If you've spent any time in a fab shop, you've heard both terms thrown around — sometimes like they mean the same thing. They don't. A WPS and a WPDS are two different documents that do two different jobs, and mixing them up can cause real headaches when an inspector or client comes asking for paperwork.

Here's the difference in plain terms.

What is a WPS?

A WPS — Welding Procedure Specification — is the recipe for making a weld. It's a written document that tells the welder exactly how a joint is supposed to be welded so the result is sound and repeatable.

A WPS spells out the variables that matter, things like:

• The welding process (SMAW, GMAW, FCAW, GTAW, and so on)
• Base metal type and thickness range
• Filler metal and classification
• Joint design and fit-up
• Welding position
• Electrical parameters — amperage, voltage, travel speed
• Preheat and interpass temperature
• Shielding gas, if used

Follow the WPS and you should get a weld that meets the code it was written to. Think of it as the instructions everyone on the floor works from so welds come out consistent no matter who's running the bead.

What is a WPDS?

A WPDS — Welding Procedure Data Sheet — is the document that records the actual parameters used, tied to a qualified procedure. In Canadian shops working to CSA standards, the WPDS is the form that lists the specific welding data for a given joint, supporting the WPS.

Where the WPS describes how a weld should be made, the WPDS captures the detailed parameter data behind it. The two travel together: the WPS sets the approach, and the WPDS carries the specific numbers that back it up.

Why the distinction matters

It's not just paperwork pedantry. When a job gets inspected, the documentation has to line up. If a client asks for your procedure and you hand over the wrong sheet — or can't produce one at all — that's a problem that stops work and costs money.

It matters even more in Canada. Under the CSA welding standards, fabricators have to be certified, and the procedures a shop welds to generally need to be reviewed and accepted by the Canadian Welding Bureau (CWB) before they're used in production. So these aren't documents you write up casually — they're part of staying compliant and certified.

If you're studying for a CWB ticket or running a certified shop, knowing exactly which document does what isn't optional. It's the difference between passing an audit and scrambling.

A note on getting the official requirements

This article explains the concepts in plain language, but the exact requirements for what a WPS and WPDS must contain — and how they're qualified and accepted — live in the applicable CSA standards (like W47.1 and W59) and CWB program rules. Always work from your own current copies of those standards and your shop's accepted procedures. Don't treat a general guide as a substitute for the code itself.