Welding Class 1 piping with MIG

Usually TIG welding is used for root/hot pass and SMAW for filling
/capping of pipe welding especially class 1 piping. I am exploring the
use of MIG process for increasing the production rate. Can some one
advise on what shielding gas I should be using for SS 304L and SS 316
L piping .
Various sources give different mixtures ranging from pure argon to 25%
Co2 and 75% Argon,and 2% O2 in argon. What are the relatative merits
demerits of these mixture. Which one should be used for high quality
pipe work (X-ray inspection)
FH
Reply to
Fakharul Hasan
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All the MIG guys that run hardwire at the company I work for use straight Argon....
Reply to
jessp
Although some flux core stainless steel wires do use carbon dioxide mixes generally carbaon in any form is to be avoided. I have never heard of hard wire stainless used with a carbon dioxide mix. Usually the small amount of oxygen in the argon mix is to improve arc characteristics. I would try several wires giving the sales departments concerned a chance to provide a weld procedure. Bottom line should be the wire and process that qualifies and satisfies the welders on the floor should get your business. This site may be a good place to start.
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Reply to
Randy Zimmerman
For MIG welding Stainless steel pipe? How would you get any penetration at all? I can't see how that would work.
Oxygen or Helium tri-mixes work best. C25 can work in a pinch, but you get a lot of oxides.
Reply to
Ernie Leimkuhler
They use a large gap, tack at several places and then go back to weld it out. The ones I have seen do it, do it in short weld intervals, like less than a second at a time. As you can see from the pics that it can and is done. Almost like a pulsing weld only with their mig guns. I understand how some of you may find it hard to believe, so I put up some pics at the following address so that you can view them and make up your own minds. And by the way, these welds were xrayed as they were going underground.
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Reply to
jessp

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