welding stainless steel exhaust

[frankv11]

got some info
http://www.unisource-mfg.com/images/...Basic_Info.pdf

[The WidowMaker]

fusion welded the 304 on my 70 but dont have a motor yet. did the same for my silverado and im at a year with no issues. i agree that a few tacks were murder to take apart. not so much for a mig since its more difficult to get the heat with a tack.

[64pontiac]

I haven't seem to have had the "growing" issues as much as some of you.....I am sure at some point I will have to deal with it though.

All of our stuff runs flex joints and the "snapper" grommets that were seen in the pics a bit back. But I mount them bolted to another bracket.

Also, I have put some serious heat into the exhaust via super and turbo charging, and I have yet to have my stainless stuff get grey like the pic of Blu Ballz exhaust.....I know he tracks it, but the crossover section there is a bit back from the collectors....ours only goes gold/purple. Is this just exterior contamination like oil that makes it go overheat grey like that? Maybe that has to do with the cracking.

I have use fusion on stainless exhaust joints too, it looks amazing. I havent been experiencing the sugaring issues that much, I have only purges on header tubes, not our exhaust systems.

What tungstens are you guys using? On 16 gauge stainless I am only running 30 amps max to get a nice bead. I have never had to put 60 amp into stainless exhaust unless I am adding an 1/8 inch thick bracket or muffler/flex joint lap welds. I guess its all in the welder operator!

Good info in here. I do believe you on the exhaust growing Greg, just haven't experienced it myself.

[GregWeld]

Originally Posted by 64pontiac

Good info in here. I do believe you on the exhaust growing Greg, just haven't experienced it myself.

My little '32 doesn't have any flex joints in it... and that's the problem with that particular system. If it did -- it would have been fine.


The "old trick" I've used to figure where the crossover goes -- spray some paint on the exhaust after the collector --- from there back about 18" ---- Run the system -- and put the crossover where the paint 'boiled'. But that was before the days of "X" pipes. And is probably about as scientific as spitting.

[jst8a5.0]

geez i have built a ton of ss systems and i have only had one turbo manifold crack but it was for a ton of reasons working against the manifold itself such as wheel hop, no flex coupler, the car bottomed out a few good times, heavy turbo was hung directly off the manifold with no support, etc....

[parsonsj]

Love this discussion!

Originally Posted by funcars

Coeff of thermal expansions for those who like specs: - 304 11x10E-6 in/in/deg F, 321 11.4x10E-6, 316L 10.8x10E-6, low carbon steel 6.3x10E-6

That's the data we need. SS grows a bit less than twice as much as mild steel, and a typical SS exhaust will grow about 0.3 to 0.4 inches, given 800 degree temps at the collector, 400 at the muffler, and 200 at the tail pipe. More heat: more growth, more length: more growth, etc.

I've been fusion-welding SS exhaust since I saw the Stainless Works welders doing it. I spend a lot of time on fit-up, de-burr all weld edges, and clean the metal with acetone before welding. I use 35-40 amps on 16g, and back-purge everything.

Because SS moves so much during welding, I fully weld the exhaust tubes as I go. Tacking the whole thing and then fully welding makes it difficult to keep everything where you want it. Plus you get to do some of the early welds without having 6 feet of tube rolling around while you weld.

[toddoky]

All of the issues discussed here is why I don't use 304 for building exhaust systems; it is an un-stabilized austenitic grade of stainless that is not recommended for use in high temperature applications (850 degree F. use temp threshold). If you need increased high-temperature strength beyond what mild steel provides, 321 and 347 are the stabilized grades that can provide it by design. 304 became the poor-mans stainless exhaust material due to its availability and affordable price (relative to 321 and 347) and the fact that its the only lower-cost option most people think they have besides using 409ss. If you want to use an affordable stainless material that is designed for use in a high-temp environment with better corrosion resistance than 304 in cyclic high-temp applications (i.e. exhaust systems) look at the stabilized 2nd-generation ferritic grade 439. It has the same 18 percent chromium content that 304 has (409 has 11.5 percent)without the nickel content, which is the real price driver of the austenitic grades. I've used it to build headers and exhaust systems for 15 years without any issues and highly recommend it. Its coefficient of thermal expansion is closer to mild steel than it is to 304. The trouble with using it is in finding it in U/J-bend form but you can find them in many different tube diameters from Bassani Manufacturing in Anaheim, Ca.

[Vince@Meanstreets]

Originally Posted by toddoky

All of the issues discussed here is why I don't use 304 for building exhaust systems; it is an un-stabilized austenitic grade of stainless that is not recommended for use in high temperature applications (850 degree F. use temp threshold). If you need increased high-temperature strength beyond what mild steel provides, 321 and 347 are the stabilized grades that can provide it by design. 304 became the poor-mans stainless exhaust material due to its availability and affordable price (relative to 321 and 347) and the fact that its the only lower-cost option most people think they have besides using 409ss. If you want to use an affordable stainless material that is designed for use in a high-temp environment with better corrosion resistance than 304 in cyclic high-temp applications (i.e. exhaust systems) look at the stabilized 2nd-generation ferritic grade 439. It has the same 18 percent chromium content that 304 has (409 has 11.5 percent)without the nickel content, which is the real price driver of the austenitic grades. I've used it to build headers and exhaust systems for 15 years without any issues and highly recommend it. Its coefficient of thermal expansion is closer to mild steel than it is to 304. The trouble with using it is in finding it in U/J-bend form but you can find them in many different tube diameters from Bassani Manufacturing in Anaheim, Ca.

and because average people don't know about alternatives...its become an industry standard.

What is the cost difference and what filler is used with it?

[toddoky]

Originally Posted by Vince@MSperfab

and because average people don't know about alternatives...its become an industry standard.

What is the cost difference and what filler is used with it?

In terms of typical coil prices, it runs about 30-35% less than 304 on the market. When it comes to U-bend prices I haven't shopped 304 U-bends recently to be able to compare but was absolutely floored the last time I saw the prices for single 304 U-bends from the typical outlets...you'd think the stuff was made of gold instead of stainless steel. You could make an easy comparison by calling Bassani and asking for a price for a common U-bend size, such as 2-1/2 on a 4" radius and then shop prices for the same in 304 from the known suppliers of 304 U-bends (the list is too long to mention). Once you factor in the superior cyclic high temp corrosion properties of 439 and its much lower coefficient of thermal expansion, it's a no-brainer for me even if it was the same price as 304. The only place I wouldn't recommend it is when you need the increase in high temperature strength that the austenitic grades provide (i.e. hot side turbo plumbing on a competition vehicle), but in that case I would skip over 304 and go right to 321 or 347 as they are not subject to stress corrosion cracking like 304 is. 439 can be autogeneously welded (no filler rod) or be welded to itself with a matching 439 filler wire (if you can find it locally) or the common 308L austenitic filler wire. You can weld it to 304ss or low carbon steels by using 309L filler wire, which is the go-to stardard for dissimilar metal welds of this type.