make (drill) backpurge tubes for stainless welding

I have made dozens of purging widgets. Perforated copper tube works well for dealing with curved welds like the ends of pressure vessels.

Piping and pressure vessels are purged in simple fashion, by filling them with argon. I haven't spent my life in a vessel shop (so maybe I'm missing something) but I have welded on and to a lot of vessels and have yet to see a situation where a "perforated copper tube" could be used. I suppose on a vessel large enought that a man can crawl in thru one of the openings, then you could place objects behind the welds for purge. But then you have to stop all welding on the vessel, and evacuate the vessel every time you need to reposition one of your devices, test the atmosphere inside and use confined entry techniques to go in, re rig your "widgets", get out, start the purge and continue welding. That sounds a lot harder than just purging the thing and welding away. Especially since a vessel that big is going to have several welders working at the same time.

JTMcC.

Copper is good as it's easy to form, drill, etc... brass could be used & aluminum also. As long as the fixture doesn't contaminate the base metal, like copper on cobalt

Richard

Actually I was refering to smaller vessels, where you have only atttached one end.

Think of a 5 gallon bucket and trying to weld on the bottom. By placing a ring of copper tube around the inside of that seam you can purge it without using as much argon.

I realize that for big shops very large volumes of argon are used for purging, but for small shops being frugal with your argon can save a few bucks.

What you describe will use more purge gas, not less. You still have to purge the entire vessel when welding the other end, so now you purge one end to make a weld, then purge the whole vessel to make the other end, plus all other fittings. Welding one end on a vessel at a time is a recipe for distortion, and almost guarantees the second end will either not fit, or will require a lot more work to fit.

Argon is expensive and a small welding operation can easily use hundreds of dollars worth per day. But the method you describe calls for more gas, not less. Unless I am really missing something here.

JTMcC.

If you don't want to use a purge or can't purge Solar Flux my help you. Solar Flux works with stainless & high-nickel alloys. I have made hundreds of stainless & high-nickel type pipe & tube welds useing Solar Flux. All welds were pressure welds & all were x-ray tested. The draw back of solar flux is you get one chance to get the root in correctly.

I would not use it for food or USP gas systems unless the weld could be cleaned.

Solar Flux web page.