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Old 06-22-2020, 08:30 AM   #1
CorneliusRox
 
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Welding Stainless Exhaust Piping

Looking for advice.
I made up a good deal of pie cuts. I'm going to start tacking everything in place, wipe it all down with acetone, and then start welding.

What I don't know is the whole back purge side of it. I know with stainless you've got to back purge or it'll give youi a terrible weld. I've ordered up an extra regulator for my Argon tank, but I'm curious on everyone's thoughts about how much pressure, how you made your purge exit, how long to let it saturate before welding, etc...

I was thinking of just the rubber tube for argon into tin foil to cover one end, then do the opposite end in tin foil with some holes poked through it. Not sure on flow or if gaps between non-welded pie cuts change anything.
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Old 06-22-2020, 08:44 AM   #2
Vincejax

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Wire brush with acetone all edges, fit together and hold in place with masking tape. Seal with tape/tinfoil and purge into the bottom side and put a few small pinholes in the top side. Remember argon is heavier than air and will "fill up" the inside of your tube. Regulators measure flow, not pressure. Use about 5cfm of flow and let it flow long enough that it flows cubic feet equal to the tube's volume. A simple internet volume calculator for a cylinder will work. If you purge with too much flow the argon will actually swirl and mix with air and take longer to get a good purge. Once purge is complete peal back the masking tape in the area you are going to tack and clean any residue away with wire brush and acetone. Turn the purge up to 15-20cfm and place your tack, continue this way until all tacks are placed. Leave purge in place and begin welding. Skip around and use a backstep technique. Be careful not to get the stainless too hot, overheating will cause carbon precipitation/sugaring and reduce corrosion resistance. On your torch use a gas lens and 25-30cfm argon. Amperage should be <1amp/0.001" material thickness. Hope this helps!
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Old 06-22-2020, 09:32 AM   #3
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Quote:
Originally Posted by Vincejax View Post
Wire brush with acetone all edges, fit together and hold in place with masking tape. Seal with tape/tinfoil and purge into the bottom side and put a few small pinholes in the top side. Remember argon is heavier than air and will "fill up" the inside of your tube. Regulators measure flow, not pressure. Use about 5cfm of flow and let it flow long enough that it flows cubic feet equal to the tube's volume. A simple internet volume calculator for a cylinder will work. If you purge with too much flow the argon will actually swirl and mix with air and take longer to get a good purge. Once purge is complete peal back the masking tape in the area you are going to tack and clean any residue away with wire brush and acetone. Turn the purge up to 15-20cfm and place your tack, continue this way until all tacks are placed. Leave purge in place and begin welding. Skip around and use a backstep technique. Be careful not to get the stainless too hot, overheating will cause carbon precipitation/sugaring and reduce corrosion resistance. On your torch use a gas lens and 25-30cfm argon. Amperage should be <1amp/0.001" material thickness. Hope this helps!
This is very helpful! Thank you
This will be 1mm wall thickness (not turbo diesel application). Any thoughts on how far I should do my backstepping? Maybe an inch?
I'll start at 40amp on the non-show side and see how it goes.

Thanks again!
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Old 06-22-2020, 12:23 PM   #4
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Bring it over ill cup walk that bad boy for ya...
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Old 06-22-2020, 12:36 PM   #5
Vincejax

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Quote:
Originally Posted by CorneliusRox View Post
This is very helpful! Thank you
This will be 1mm wall thickness (not turbo diesel application). Any thoughts on how far I should do my backstepping? Maybe an inch?
I'll start at 40amp on the non-show side and see how it goes.

Thanks again!
That depends on your welding skill, if you are able to use a very short arc and quick travel speed, you can weld longer without too much heat input. Try to keep your color in the silver/gold range. Purple you re getting hot, blue borderline, gray you are overheated.
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Old 06-22-2020, 03:25 PM   #6
CorneliusRox
 
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Bring it over ill cup walk that bad boy for ya...
Maybe if you were closer! I kinda like doing it on my own and getting better too.

Quote:
Originally Posted by Vincejax View Post
That depends on your welding skill, if you are able to use a very short arc and quick travel speed, you can weld longer without too much heat input. Try to keep your color in the silver/gold range. Purple you re getting hot, blue borderline, gray you are overheated.
Good to know. I can go pretty quick on a bench on plate, but I'm guessing I'll be pretty slow on 2" tube at weird angles.
Thanks again!
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