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Old 08-18-2016, 05:51 PM
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Default Backpurging Stainless

I have some 4XX stainless exhaust work to do, I want to avoid corrosion issues/ sugaring on the inside of the TIG weld so backpurging should prevent this. My first problem is I only have one cylinder of 100% argon which I will be using at the time. I have a couple other common MIG mixes including a trimix, can I use any of them to purge? I contemplated capping an end filling with 100% capping the other end and going from there, will the joint leaking be a problem if I do it this way? I believe there is some sort of flux I can apply to prevent sugaring if purging will not, does that work satisfactory?
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Old 08-18-2016, 06:00 PM
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I would think it would work we used to purge with CO2. We used to dam the pipe with rice paper with a pin hole poked it it and purge from the other end. Leaking won't be a problem unless your purge pressure is to high and interferes with your argon.IMO Used this method on pipe up to 24" dia.
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Old 08-18-2016, 06:20 PM
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I have back purged with c25 before with ok results but people say it is not correct. I have also teed off of my argon hose and that worked ok as well.

A few years ago I did some welding for a shop building food processing equipment. They would spray the back side of the part being welded with wd40. I guess as it burned away it would shield the weld. I haven't tried it on exhaust tubing yet but it worked great for them.

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Old 08-18-2016, 09:15 PM
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Originally Posted by Camaro Zach View Post
I have back purged with c25 before with ok results but people say it is not correct. I have also teed off of my argon hose and that worked ok as well...
I've seen other gases used for purging non-critical stuff but if you're doing sanitary welding you should only use argon. Running a tee off the main line is common practice. For an exhaust system I wouldn't even bother.

Quote:
...A few years ago I did some welding for a shop building food processing equipment. They would spray the back side of the part being welded with wd40. I guess as it burned away it would shield the weld. I haven't tried it on exhaust tubing yet but it worked great for them...
I've heard of that but I seriously doubt that you'd get an acceptable weld out of it. Believe me, if you were doing real sanitary work and got caught pulling a stunt like that you'd be out on your ass real quick...
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Old 08-18-2016, 09:31 PM
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Quote:
Originally Posted by Camaro Zach View Post
I have back purged with c25 before with ok results but people say it is not correct. I have also teed off of my argon hose and that worked ok as well.

A few years ago I did some welding for a shop building food processing equipment. They would spray the back side of the part being welded with wd40. I guess as it burned away it would shield the weld. I haven't tried it on exhaust tubing yet but it worked great for them.

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hmmm What's that taste Marv?.... must be the WD40 purge. No worries, it will soon be rinsed off in the product....
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Old 08-18-2016, 09:57 PM
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All of my stainless welding of pipe was in a paper mill and all we used was co2 for purge. Ofcourse that was 40 years ago so maybe my memory is off. I am sure it was a cost thing.
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Old 08-19-2016, 04:31 AM
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Originally Posted by LKeithR View Post
For an exhaust system I wouldn't even bother.
The weld will be about 20" post turbo, so I have concerns about the crappy grade of stainless coupled with a weld and high heat corroding.
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Old 08-19-2016, 06:21 AM
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I'm sure you don't want to add cost to the project, but either another bottle and regulator of argon, or this little guy . Available from most LWS as well. Next best thing people are doing today to cheapen the purge is Nitrogen.

Doing so with a split flow meter provides the ability to have a lower flow rate on your purge gas so that it is not pushing through the joint and disrupting your torches shielding gas, something that can not easily be done with just putting a wye in your gas line as others suggested.
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Old 08-19-2016, 06:42 AM
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Default this works

http://www.shopfloortalk.com/forums/...8&d=1471605676
This setup worked well for me,hope this helps.
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Old 08-19-2016, 09:14 AM
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Thanks all, I think I will pick up a split regulator. I'm sure it will get used again.
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