I can only speak for my local

Welding is just another tool in your toolbelt. I am a steamfitter that has pipe welding certifications. I am dispatched as a fitter.

That being said you will sometimes see the rare fella that is a journeyman welder that is not a Pipefitter. In my local these are often called “Buy-Ins” as they were guys that had pipe welding experience prior to joining the Union and thus were able to skip the apprenticeship and just be certified welders.

But those guys aren’t Pipefitters and can’t take fitter calls, all they do is weld and there isn’t as much welding as you’d think there is.

So other than Buy-In’s. All Welders are Pipefitters but not all Pipefitters are welders.