Welding 304 S/S exhaust

[Ben88]

I've been asked to weld up a 304 grade stainless steel exhaust system for a car he has all the parts ready to go. I've got a lot of welding & fab exp just never done exhausts, he knows this by the way i've been praticing on some scrap material an feel good to go. I was told by an old timer at work to use 316 filler as it has better corrosion properties does any one else agree with that or is 304 filler good enough. An Purging do i need to do this? He says you don't need that much penetration, but will this not cause sugaring on the inside of the weld? thanks for reading

 

[Richard.]

308 or 316 will both be perfectly fine for that.
316 is slightly better corrosion resistant but on an exhaust it doesn't matter. As soon as that engine gets a fist full of revs the exhaust is gonna be covered in heat tint which will quickly become surface rusted any way. I would however recommend you purge the inside. Much sounder welds that way and less resistant to cracking.

 

[Ben88]

Would it be okay to use one of them disposable argon gas bottles for the purging gas? or is there any way of a 2 way regulater from my single gas bottle? cheers Richard

 

[Richard.]

Would it be okay to use one of them disposable argon gas bottles for the purging gas? or is there any way of a 2 way regulater from my single gas bottle? cheers Richard

Use your bottle and T off with a Y peace. 2 lines on 2 valves. I personally would purge it. It improves the joint by 10 times.

 

[Ben88]

cheers pal yeah i'll purge it i want to do a good quality job i'll have a look at geeting the parts to be able to do it. Any advise on distortion you can give me im planning on putting the car on the ramps (as in the garage ones) so that i can tack it all in place 1st then take it down to my bench to weld up i've got plenty of clamps to keep it in place (thinking of using some angle iron on the straights an clamping to it to keep it straight). I'll weld each joint in four stages to keep distortion down an take my time so it doesnt get to hot, maybe weld 1 side then do a weld on the opposite side

 

[Brad93]

There is, if I remember correctly, a reason why you shouldn't use 316 on 304 exhausts ill see if I can find the article.

 

[Chris Stevens]

I've been asked to weld up a 304 grade stainless steel exhaust system for a car he has all the parts ready to go. I've got a lot of welding & fab exp just never done exhausts, he knows this by the way i've been praticing on some scrap material an feel good to go. I was told by an old timer at work to use 316 filler as it has better corrosion properties does any one else agree with that or is 304 filler good enough. An Purging do i need to do this? He says you don't need that much penetration, but will this not cause sugaring on the inside of the weld? thanks for reading

Most commercially produced stainless exhausts use 304 tube, which is welded to silencer boxes with MIG using MS wire. If you intend to use TIG and purge inside tubes, I would guess you would be wanting 3 times as much money as doing the job with MIG?

 

[Ben88]

He has asked for it to be tiged through out an is willing to pay for the gas so it might take longer to do it but the experience for me is invaluable so I just agreed on £ per hour he pays for consumables + its his garage his electric

 

[Chris Stevens]

Fine if customer is willing to pay, but purging a full exhaust system will take a fair amount of gas, and the job will take quite a time to do to a high standard.

 

[Richard.]

I'll second above. Depending on exactly how big and how much of it your welding it will use a fair amount of argon to purge. The amount of filler used will be minimal. I personally would not opt for the ms joints but that's me I like to do things with correct consumable. Saying that most off the shelfys are done like that with ms filler. I've welded quite a few and 308 is what I've used.
Brad 316 is an expectable filler for 304 exhaust it's just a bit stronger and less ductile so unpurged joints. Are far more likely to crack but I believe @langy only uses this filler for his exhausts and he's done more than I have with no issues.

 

[Chris Stevens]

Unless the car exhaust is going on is something pretty exotic, purging the weld joints and Tig welding with SS filler seems a bit of a waste of time to me.

 

[Richard.]

Each to there own. Customers budget obviously is the driver here but if it was for myself it would be done with stainless consumables. I'm a stickler for the details and perfection which is the reason why. As widely accepted as it might be, to me using mild steel for a stainless joint is like buying a ck torch and fitting it with cheap lenses. It's gonna work but could be so much better.

 

[backpurge]

Agree with Richard above, also if you don't purge the stainless TIG welds there is a good chance they will fail from the inside over time

 

[Chris Stevens]

Better provide all this informed advice to those who have been manufacturing SS exhausts for many years.............they seem to making major errors......................lol

Seriously though while I know that those making SS exhausts for more run of the mill stuff dont want to add maybe 30% to the unit cost by purged Tig welding, it would be interesting to know if top end stuff is purged?

I know someone who makes SS exhausts and manifolds for Ferrari, and will ask him the question.......................I would guess they probably are purged.

 

[Richard.]

...........they seem to making major errors

Not at all.
I've made my self pretty clear I think. I know how they are productively manufactured I've seen it going on and it's as you say ms wire through a robot knocking them out by the truck load. It's not a error or a wrong way of doing it but it's not the best way either. The bike exhaust manufacturers are better examples because they generally are tig welded. Yoshimura, akrapovic, arrow etc while there top grade stuff is Ti they also build a middle level out of stainless which is never welded from ms nor are they gmaw either. Pricey systems God are they but that's a price you pay for stuff that's not blasted with a robot. Like I say it's not wrong it's just not the best way.

 

[eSCHEn]

Plus, if you're gonna do the job why not do it in a way that'll result in the best finish and longest life of the part?

Anyway; purging is just plain cool

 

[backpurge]

Better provide all this informed advice to those who have been manufacturing SS exhausts for many years.............they seem to making major errors......................lol

Someone asked a question and I gave an answer based on what was asked.

If the guy had said, I am wanting to manufacture 20,000 exhaust systems a month for Toyota my reply would have been totally different, only trying to help

 

[Richard.]

Plus, if you're gonna do the job why not do it in a way that'll result in the best finish and longest life of the part?

Anyway; purging is just plain cool

It gets expensive too. 25% of my argon use is shoved down a purge line and I don't do loads of SS. like you say mate. If you've got the gear and it's in the price then it's the way to go for sure.

 

[TechnicAl]

Most SS exhausts are welded using this MIG wire.............http://www.ugitech.com/fileadmin/us.../TREFILES/Soudure/Exhaust_F1/ExhaustF1_UK.pdf

but they arent 304 or 304L

Im not 100% certain what they use these days but they use this wire to weld it

 

[RichardM]

I would purge it but mine are bike exhausts for hobby and not costed for production purposes. Makes full pen welds nice and clean internally, no sugar ring messing flow up. To cut down on gas use some aluminium (insulation lagging) tape internally in the pipe so the argon is just around the piece of pipe the weld is on and not filling the whole tube. Pin prick at the top to let the air out. Alternatively if you do not want to purge get some copper sheet (flatten some 22mm pipe ) bend it so it fits the internal diameter nicely and use that to seal the back of the weld when welding - stops air getting to the back of the weld - make it in two halves (180 deg) easier to get out afterwards.