welding stainless steel exhaust

[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.