Welding Tips and Tricks

I've been doing quite a bit of research and I understand using a helium tri-mix is ideal for welding stainless steel with the GMAW process, however I've called every supplier in the state and none sell tri-mix in small bottles. This is a one time job so I can't really bring my self to dropping $300 on a new tank and gas that I'll most likely never use again.

From what I've been reading welding stainless with C25% can be done, although not ideal. I'll do some practice runs and see if I can get it fine tuned for the the real thing to get the best results with what I've got.

What wire should I run? Seems like ER308L is the go to wire for welding SS, however I was reading the description of ER309L and it looks to be for welding SS to mild steel. I'm thinking perhaps this wire can handle the carbon contamination from the CO2 better? Will purging the pipes make a significant difference? Any tips on how to approach this would be appreciated!

You’re right, trimix is the correct gas to use.
308L is the correct wire to use for 304 exhausts.

For your situation c25 will work. The weld will come out grey and funny lookin but for exhausts no-one will care unless you’re making a show rod in which case it would be tigged anyway.
Strength will be ok.
No need to purge.


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Some suppliers will just charge you for the gas and a small rental fee for the tank if you return it in a few weeks.

With respect to what Coleman posted, I differ regarding a purge while welding SS exhausts. True, many manufacturers don’t, but you always shuold. It makes for a stronger weld, eliminates the backside contamination, and insures full penetration. Your weld will last longer too.

Since you’re already using a C25 mix, purging will only improve your outcome. But it won’t be the end of the world if you don’t...

https://www.millerwelds.com/resources/a ... oductivity

Great article, talks about mig purging and not purging. A slight gap in the prep allows mig gas to flow through the joint and shield the backside. No purge required.
Purging can’t hurt and will certainly improve results but may be overkill in this situation particularly if good results can be had by attention to prep.


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Unless fluid dynamics has changed since I was in school, a slight gap isn't going to help shield the back side of a weld, especially on tube. Maybe if you have a narrow gap created from another piece of material inside, but I don't see how a slight gap will shield the back side of the weld puddle.

Demented wrote:Unless fluid dynamics has changed since I was in school, a slight gap isn't going to help shield the back side of a weld, especially on tube. Maybe if you have a narrow gap created from another piece of material inside, but I don't see how a slight gap will shield the back side of the weld puddle.

The point is having a gap allows some amount of the shielding gas from the nozzle to infiltrate the backside of the tube while you led it shut. It’s not as effective as a full purge, but it does help. Exhaust systems aren’t very effected by fluid dynamics in terms of flow as fluid filled structures are, so it’s a moot point. Dents, creases, impressions have virtually no effect to an exhaust pipes effectiveness.

The biggest reason I purge stainless exhausts is to insure full penetration and the absence of contamination, no other. Stainless is a good material for exhausts due to its corrosion resistance, but it’s far more susceptible to cracking over time due to the heat cycles versus mild steel. Yet mild steel is more prone to corrosion failure within the same time frame. So what’s a guy to do...? I choose stainless and live with its small shortcomings.

cj737 wrote:

Demented wrote:Unless fluid dynamics has changed since I was in school, a slight gap isn't going to help shield the back side of a weld, especially on tube. Maybe if you have a narrow gap created from another piece of material inside, but I don't see how a slight gap will shield the back side of the weld puddle.

The point is having a gap allows some amount of the shielding gas from the nozzle to infiltrate the backside of the tube while you led it shut. It’s not as effective as a full purge, but it does help. Exhaust systems aren’t very effected by fluid dynamics in terms of flow as fluid filled structures are, so it’s a moot point. Dents, creases, impressions have virtually no effect to an exhaust pipes effectiveness.

The biggest reason I purge stainless exhausts is to insure full penetration and the absence of contamination, no other. Stainless is a good material for exhausts due to its corrosion resistance, but it’s far more susceptible to cracking over time due to the heat cycles versus mild steel. Yet mild steel is more prone to corrosion failure within the same time frame. So what’s a guy to do...? I choose stainless and live with its small shortcomings.

When I mentioned fluid dynamics I was talking about how the shielding gas would flow through the joint and shield the backside.

Been doing more research, what's everyone's thoughts on using Argon-Oxygen blend, or an Argon-CO2-Nitrogen blend for MIG welding austenitic metals?

I believe that that will work for SS. Is it mixed at a 98%arg and 2%oxy ?

Dents do affect fluid flow! That’s why the put dents on golf balls.

Poland308 wrote:I believe that that will work for SS. Is it mixed at a 98%arg and 2%oxy ?

Dents do affect fluid flow! That’s why the put dents on golf balls.

they have virtually no effect on exhaust pipes was my statement.

cj737 wrote:

Poland308 wrote:I believe that that will work for SS. Is it mixed at a 98%arg and 2%oxy ?

Dents do affect fluid flow! That’s why the put dents on golf balls.

they have virtually no effect on exhaust pipes was my statement.

The show Engine Masters from Hot Rod mag did something testing that by smashing headers with a hammer. Engines only care about the length of the exhaust tubes.

Yes the dents in a golf ball only apply to constant or laminar flow. But are mostly negligible for turbulent flow over runs as short (linear feet) as what car exhaust runs. However if you start to get longer like say 20 ft or more it would be measurable.

I’ve got dents in my head.


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Poland308 wrote:Yes the dents in a golf ball only apply to constant or laminar flow. But are mostly negligible for turbulent flow over runs as short (linear feet) as what car exhaust runs. However if you start to get longer like say 20 ft or more it would be measurable.

The dimple pattern on a golf ball is about managing surface tension for the ball that is moving through the air, not about managing the flow of air across it (as if it were static). Comparing a golf ball’s use of dimples and an exhaust’s flow is akin to giraffes and elephants.

The dimple pattern on a golf ball is about managing surface tension for the ball that is moving through the air, not about managing the flow of air across it (as if it were static). Comparing a golf ball’s use of dimples and an exhaust’s flow is akin to giraffes and elephants.[/quote]

Air is a fluid. The same principles are used when a vapor is pushed through a tube as when a vapor flows over an object. You need to study a bit more.

The last couple of stainless exhausts I did was with an electrode( 312) and a hi frequency rig on AC. You could do it with oxy-acet too, if you have room