MIG welding SS

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Nov 30, 2021, 12:11:19 AM11/30/21

I'm getting a start on fabbing a new exhaust for my truck (currently
down for an engine rebuild/hopup) . This morning I set my Lincoln
Weldpak 100 up to run a couple of beads on the header collector adapters
, and it wasn't at all pretty . The wire is .023 ER309L , shield gas is
argon at varying flow rates , electrode negative . First thing I noticed
is that this wire sure seems to burn a lot faster than ER70S6 , so I
bumped the feed speed up . Still ain't right , so I drop the amps a
notch (this machine has 4 settings for current) and it's a bit better
but still too hot . Drop it another notch and the wire isn't burning
back so fast but there's zero penetration and the bead is very narrow
and tall . Drop the wire feed and it's still too cold .
I'm totally lost here , I was hoping MIG welding the joints would be
fast and easy but ... I ended up using the TIG to flow the welds and got
things looking less like pigeons crapped on my weld seam , but that has
problems too . I have no means (yet) to purge the back side of welds in
tube . I did get the inside cleaned up with die grinders and flap wheels
, but that ain't going to work on a 6 or 7 foot long piece of exhaust
tube !
I sure could use some tips on MIG welding SS ! I hesitate to use
ER70S6 or flux core since the tubing is stainless , but it may come down
to that to get a decent weld .
Let's Go Brandon !

Richard Smith

Nov 30, 2021, 12:26:59 AM11/30/21
You say the torch / gun is on DCEN.
With MIG you need to be on DCEP?
I never got an explanation, but while for TIG DCEN is super
penetrative, you can damn' well see for stick/SMAW that DCEP is more
penetrative. Never had a chance to try MIG on DCEN - never had the
time on a machine which offers means to change polarity (rare).

'nother thing. I have tried Stainless MIG with pure Argon - "TIG
gas". There is 2/10's of not-a-lot of penetration.
MIG stainless - you have to add a smidgeon of oxygen to give it any
"bite" / penno. As I have heard. Only MIG stainless I met was
testing out making road sweepers. They had Ar / He / O2 mix. As good
as you get. Pity their welding wasn't. They did pause in their
telling us nonsensical weld practices they demanded when, seeing the
way things were going - to the door - I put in a small neat spray bead
which did the job so much better. Really really looked the part.
I've repeatedly ensured you know how little experience I have of this.
Hope what I've mentioned helps.

Cydrome Leader

Nov 30, 2021, 1:25:36 AM11/30/21
Here's some basic stuff on SS


stainless behaves quite differently from plain steel. It's a terrible heat
conductor and it burns up easier. I always marvel at a well done stainless
weld job, no matter what the process is.

Jim Wilkins

Nov 30, 2021, 7:28:45 AM11/30/21
"Snag" wrote in message news:so4bph$5e8$1...@dont-email.me...

On the welding salesman's recommendation I used 312 rod to stick weld 1/16"
sheet stainless into the bucket on the front end loader I made for my Sears
garden tractor. Although the weld area is discolored the stitched beads were
neat and strong enough to survive years of ramming into snow, ice and
occasionally rocks and trees. Road salt didn't seem to affect the unshielded
back side of the welds.


Nov 30, 2021, 12:46:02 PM11/30/21
My thanks to all who responded . I think I'll just figure out a way
to shield the back side of my welds and TIG it all together . I'll have
the bed off the truck for an axle gearing change , that might make it
easier . Or I could just MIG it with ER70S2 ...
Now hold on thar ! I just discovered (browsing a car forum) a product
called Solar Flux . Paint it on the back side of your weld area and it
forms a shield as it gets melted by the weld heat . Just exactly what I
needed , considering the forums I was browsing are pretty emphatic about
NOT using ER70 to weld SS exhaust tube . The recommended filler is
ER308L , which I happen to have on hand . I was concerned about sugaring
causing flow problems ... this has been an exhausting discussion !

Bob La Londe

Nov 30, 2021, 1:17:25 PM11/30/21
Paint on flux is a new one on me, but it makes perfect sense. I was
just going to comment that if you plug the ends with just a small weep
hole you really do not use that much gas in a piece of pipe the size you
mention. The weep hole is two fold. To allow you to actually purge the
air, and to make sure you do not pop your plugs out when the gas inside
the tube starts to expand from heat.

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Bob La Londe

Nov 30, 2021, 1:44:51 PM11/30/21
Oh, yeah, and I have to ask. Is exhaust using an pipe expander so the
joints can slide together totally out of vogue now?


Nov 30, 2021, 4:56:57 PM11/30/21
I recently figured out the reason the expander I have doesn't work . The
threads are stripped . It was a gift , so I can't complain too much .
One of these days I'll make new parts for it and see how it works . Maybe .

Clare Snyder

Nov 30, 2021, 5:24:40 PM11/30/21
Tig it and back gas with dry ice - a lot easier than flowing welding
gas just tape up the "bottom" and throw in a few chunks of dry ice -
it will back purge perfectly and no clinkers inside the pipe.

Bob La Londe

Nov 30, 2021, 6:09:48 PM11/30/21
That is clever. I was not aware pure C02 was good for shielding stainless.

Jim Wilkins

Nov 30, 2021, 6:14:22 PM11/30/21
"Snag" wrote in message news:so66n4$jlt$1...@dont-email.me...

I recently figured out the reason the expander I have doesn't work . The
threads are stripped . It was a gift , so I can't complain too much .
One of these days I'll make new parts for it and see how it works . Maybe .

I recently reduced the diameter of a tailpipe expander from the 1970's (not
a recent import) and found that the plain cone under the head was
case-hardened and needed carbide but the bars and the internally threaded,
faceted cone cut easily with HSS.

Perhaps you could machine a harder faceted cone from an impact socket and a
grade 8 nut. You could anneal the socket if necessary without softening the

Jim Wilkins

Nov 30, 2021, 6:33:15 PM11/30/21
"Bob La Londe" wrote in message news:so6avl$1nfn$1...@gioia.aioe.org...

That is clever. I was not aware pure C02 was good for shielding stainless.


I wanted to suggest using CO2 if you have a tank of it for steel, but a
fairly brief Google search only returned advice not to, without describing
bad experiences.

David Billington

Nov 30, 2021, 7:37:42 PM11/30/21
IIRC CO2 isn't recommended as a shielding gas for stainless as it can
compromise the corrosion resistance, as a purge gas it may be fine as
it's not exposed to the arc. I've known people that have used it for
steel body repairs and had good results but it's not as nice a weld and
more spatter apparently but has the advantage of better penetration, all
those I know who have used CO2 had mates down the pub that could get
bottles pinched as necessary at the time. The UK pub suppliers have
apparently clamped down on that as they can match CO2 consumption to the
drinks requiring it and flag up inconsistencies. The only time I have
tried Argon for steel MIG it didn't work well, the depot had no BOC
Argoshield light at the time and they thought Argon would do it OK but
didn't so later in the day they had Argoshield light back in stock and
swapped the bottle FOC and all was good again. I've MIG  welded
stainless with 0.6mm and 1.0mm wire with the Argoshield light and all
went well. Argoshield light is apparently 93% Argon with 5% CO2 and 2%
O2, maybe not the best for stainless but it's what I have.

Clare Snyder

Nov 30, 2021, 8:52:38 PM11/30/21
On Tue, 30 Nov 2021 16:09:42 -0700, Bob La Londe <no...@none.com99>
100% effective at eliminating oxygen from the hot joint. Maybee niot
as good as tri-mix - ot ideally Argon but better than plain atmosphere
at stopping "sugaring". You can't use co2 as sheilding gas but I've
seen it used as a back purge. (Wouldn't use it on a Nuke installation,
but it's better than a mild steel MIG weld on exhaust pipes - and I;ve
seen a LOT of that!!!


Nov 30, 2021, 9:37:43 PM11/30/21
I've seen lots of pictures of what it looks like down the road ...
which is why I want to do it with SS filler . Too bad the MIG experiment
didn't work out for me , but I gots TIG and plenty of 308L filler . Also
got some of that Solar Flux coming - the dry ice idea is intriguing ,
but I'm not aware of any place near here to get some . I do have a
bottle of CO2 for the MIG , but wasn't sure if it was suitable for a
back purge .
Now I know !

Bob La Londe

Dec 1, 2021, 12:17:16 PM12/1/21
I think some grocery stores have dry ice... or used to. We used to get
it at Thrifty Drug back in the day (40+ years ago.)
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