Welding Tips and Tricks

Tomorrow morning I have a test on 6 inch schedule 80 stainless steel pipe. I've welded a lot of stainless but mainly thinwall like schedule 5 and 10. I've done a lot of tig on carbon too. I'm just asking if there is anything different from schedule 80 carbon to schedule 80 stainless besides having a good purge and letting it cool between passes
Also should I leave my purge on for the entire weld or can I shut it off after several passes
Thanks

Ask the CWI about purge. The welding procedure should have limitations on this and he will tell you what they are.

jde120,
First welcome to the forum! The person to help you with this question it Otto Nobedder aka Steve. He is well experienced in SS. I agree, you need to follow the WPS, that will answer most of your questions. The best of luck to you!

http://forum.weldingtipsandtricks.com/v ... f=3&t=4328
Look at the video link in this thread, Jody did a videos "Close" to what your up against.
Hope this helps,
John

Welcome to the forum jde120.

jde120 wrote:Tomorrow morning I have a test on 6 inch schedule 80 stainless steel pipe. I've welded a lot of stainless but mainly thinwall like schedule 5 and 10. I've done a lot of tig on carbon too. I'm just asking if there is anything different from schedule 80 carbon to schedule 80 stainless besides having a good purge and letting it cool between passes
Also should I leave my purge on for the entire weld or can I shut it off after several passes
Thanks

I'd say the biggest difference between mild and stainless steels is in the "plastic" temperature range. You know from your carbon steel experience that there is a temperature where steel goes "soft" and a higher temperature where steel drips out on you, or folds into a huge hole. In the middle of that, the steel is kind-of "plastic", holding its shape as you work it. Stainless steel has a much narrower range between solid and liquid, and you'll need to watch the puddle very closely as you first experiment with it.

Second, the heat travels away from the weld slower than with carbon steel. You'll find a need to back off the heat (if you have a remote) or move faster (if your current is fixed), more than with carbon.

Third, stainless shrinks considerably more when it cools, compared to mild steel. Expect your first weld between tacks to put a dog-leg in the pipe. The second weld will even it out (mostly), but you'll see your gap shrinking on the remaining welds.

Anything else I can say would fit in one of these categories.

As for your back-purge question, I leave it on until the weld is finished, regardless of the material thickness or number of passes. If I were buying the gas, I might reconsider...

Steve S

jde120 wrote:Tomorrow morning I have a test on 6 inch schedule 80 stainless steel pipe. I've welded a lot of stainless but mainly thinwall like schedule 5 and 10. I've done a lot of tig on carbon too. I'm just asking if there is anything different from schedule 80 carbon to schedule 80 stainless besides having a good purge and letting it cool between passes
Also should I leave my purge on for the entire weld or can I shut it off after several passes
Thanks

It just occurred to me, the "tomorrow" you mentioned in that post was actually today, and my reply was a bit late...

Did you test? How did it go?

Steve S