welding stainless pipe lumpy welds

[markie]

hi new member here i`m a panel beater by trade so do a fair bit of normal steel welding and with bodywork most of it gets cleaned up and covered up anyway but i can do a decent clean weld. now i`m trying to build a custom 3inch enxhaust for my car in 3inch stainless 1.5mm T304 stainless pipe and i`m having real trouble getting decent welds. i`m having to butt weld them but its either blowing holes in it or making a really tall uneven weld which are a nightmare to clean up. can anyone give me any pointers i`m using a clarke 151te mig with clarke stainless wire using argon light gas. i was told i was using the wrong gas then someone else told me only tig can do a neat weld on stainless so i thought i`d ask the experts.

thanks mark

 

[runnach]

TIG's the way to go, 1.5 thick matl is not very forgivable using mig.........

Cheers.......

Ps, yes incorrect gas too............

 

[markie]

o`k thanks for that what gas should i be using? any pointers that might help me. am i best trying to do a running weld or just doing a quick pot weld at a time and working around tack by tack.

thanks again

 

[runnach]

o`k thanks for that what gas should i be using? any pointers that might help me. am i best trying to do a running weld or just doing a quick pot weld at a time and working around tack by tack.

thanks again

Yeh you could try stop/starting till you complete joint, don't know how good it will be if working at high temps?

Gas: BOC stainshield is good to go, you can use on Stainless steels and austenitic stainless steel.

Cheers...........

 

[Stephen]

I Have Your Answer.

You have to "Purge" the pipe before welding it. Unfortunately I don't think you can accomplish this with the MIG process. I used to do a lot of sanitary welding on SS pipe and I'll share with you how to weld your exhaust properly.

Ideally you'll need:

-A TIG Welder with a "red" Tungsten Electrode

-A Bottle of 100 % Nitrogen Gas

-A Bottle of 100 % Argon Gas

-A chuck on a turntable (this would be a thing that you can clamp your pipe into and would spin it for you at a speed that you could set)

-And finally some masking tape...

If you don't have a chuck... don't worry... you can do this freehand.

Oh and if you are wondering why I didn't mention filler metal, that's because you don't need any.

First you butt up your pipe and tack weld it in 4 places 12,3,6 and 9 o'clock.
Tacking thin material with a TIG is very easy... Find the grove of the butt with your electrode and pull it back about .5 mm, then floor the pedal and immediately let off. Speed is the key here.

Second you will need to set up your Nitrogen bottle with a regulator set at about 15 psi or so and mask off both ends of your pipe with the masking tape.

At one end of the pipe you'll need to make a hole big enough to slide your Nitrogen line into. Then reinforce with more tape so it doesn't fall out.

At the other end poke a small hole in the tape. The purpose of this is to allow the Nitrogen to push the Oxygen out of the pipe. Depending on the length of pipe you'll need to wait a bit longer before starting your weld.

Then... With just your TIG torch... fuse weld the pipe. The small amount of pressure will keep you from burning through. You'll need to make a few starts and stops if you don't have a chuck to spin your pipe for you. When complete your weld should be about 3.5mm thick and sink into the pipe about .25 mm.

These welds are meant to be sanded down with an air belt sander and if done properly... you won't even know there is a weld there.

This may seem like a lot for some custom exhaust, but you can use this process for so much more.

 

[Angusdog]

I can't see why you can't do it with MIG. For example, you can purge the pipe by taking another line off your shielding gas line, which I believe needs to be argon.

I've found welding stainless more or less the same as mild steel but as you've noticed a lot more work to clean up, being so much harder.

Rather than try another discipline (TIG) and arrange the necessary equipment, I think I'd try practicing more with some scrap. Ultimately TIG gives you more control as with MIG you are somewhat committed to the weld when you pull the trigger, but it sounds to me like trying a different balance of wire speed & voltage, i.e. lower voltage and higher wire speed. Worth a shot. I'd also try sacrificing a gas shroud by trimming it down to allow the tip to stick out further for tight spots between pipes; the gas will still provide a reasonable shield for the weld.

I wouldn't have thought that a rotary positioner isn't going to be a huge amount of use on an exhaust as you can't rotate a manifold around the axis of each weld.

Since it's your car, it doesn't sound to me like you're too far from being able to make this work.