Stainless steel grades and suitability

[1.8T]

I am fabricating a stainless steel exhaust downpipe, or should i say i will cut out all the components, tack (or maybe tape) together then have someone purge and tig weld it, until looking into whether 304 can be used alongside 316 i had never really given the grades of stainless steel much thought, this exhaust downpipe will be used on a turbo petrol engine, which grade of stainless steel will be most suited to the heat, offer the best corrosion resistance and offer the best resistance to cracking, lastly i think i will struggle to get certain components (v band clamps, flexible joints etc) in the same grade will this matter? i would appreciate the imput of those in the know thanks

 

[Hitch]

321 is probaly the best, but i believe most are 304. Clips etc should be easily got in 304 i expect.....I think 316 will be a bit wasted on an exhaust tbh.

A few that do these things all the time will no doubt be allong to give some more info very soon.

 

[tigler]

Most aftermarket manifolds and exhausts are 304 and are fine. For the ultimate durability 321 or 316 would be the choice and is easily available from hygienic stainless suppliers. V bands and clamps are also available in 316 and 321 but not so necessary as the pipe itself. Cracking is only a problem on manifolds, proper support is the way to avoid cracking. The ultimate for exhausts is Inconel, but the cost is astronomic !

 

[1.8T]

Been doing some more thinking since i started this thread, main questions then, can 304 be welded to 316 / 316L too without adverse effects, if there are adverse effects what are they and to what extent, i think 316L is about the best i will be able to do without having stuff custom made, i know 316L is meant to be better than 316 for corrosion resistance once welded but it is any better or worse off for heat and crack resistance? i can get bends, transitions and pipe in 316L but i doubt i would get it in 321

 

[TechnicAl]

Exhaust fumes contain sulphur. Sulphur attacks the Nickel in the 3 series stainless steels so the best steel for exhausts is 409 which is usually welded with 309 (which contains nickel). However, they are also attacked from the outside (road salt / acid rain etc) so its a toss up really. Some will tell you one grade, some another.

In this instance you can weld 304L to 316L without a problem using either as a filler.

Here they say 409
http://www.stainless-steel-tube.org/Stainless-Steel-Grade-Characteristics-Usage-025.htm

 

[1.8T]

The more i read the more confused i become im not going to worry about the sulphur as there really is no point, i dont think i can really cover all eventualites, i have run an off the shelf stainless exhaust on one of my cars since 2003 and its still going strong and thats 304, salt and acid rain not an issue given intended use, my main issue is of the parts i need not all are available in the same grade of stainless (hence i started to look into joining different grades) you didnt mention in your post technicAL 304, can 304 be joined without adverse effects to 316 and 316L ? i found this a bit odd http://www.zorstec.net/mandrel_bending_flash.htm

 

[tigler]

Look at this way, the majority of OEM vehicle exhausts are carbon steel, plated to varying extent with anti corrosive treatments, and these systems can last for a surprising amount of time. Recently I had to replace the original back box on my Cit Xantia, it was the original and over 10 years old, and a diesel where sulphur would be a big issue !!!
Any stainless you use on an exhaust component for a car will outlast carbon steel by a substantial margin, certainly by more than you will ever need to worry about !
Welding 304 to 316 or 321 in this application will not be an issue practically speaking, there are universal welding wires and rods for this purpose.

 

[penfold]

Look at this way, the majority of OEM vehicle exhausts are carbon steel, plated to varying extent with anti corrosive treatments, and these systems can last for a surprising amount of time. Recently I had to replace the original back box on my Cit Xantia, it was the original and over 10 years old, and a diesel where sulphur would be a big issue !!!
Any stainless you use on an exhaust component for a car will outlast carbon steel by a substantial margin, certainly by more than you will ever need to worry about !
Welding 304 to 316 or 321 in this application will not be an issue practically speaking, there are universal welding wires and rods for this purpose.

DERV has had most sulphur removed; it's been below 50ppm since 2005, and I think the level was lowered to 10ppm in 2009. Prior to that, sulphur was mostly uncontrolled unless made from very sour crude as the BS upper limit was 3000ppm(I think).

 

[hotrodder]

304 and 316 are the same with regards to heat resistance. 316 has better corrosion resistance in some atmospheres that don't really apply to a car exhaust. Dual designation 304/304L isn't uncommon. 321 deals with high temps and heat cycling better, is much harder to get hold of and silly money in comparison as it's not generally available- companies that make exhaust components from the stuff are rolling their own tube from sheet. All 3 are very similar with just slight differences to optomise properties for different environments

Ignoring 321 welding wire will be one of the L grades, as Al said for this application can use 308L or 316L wire regardless of whether the exhaust is a mix of 304 and 316, all 304 etc.

Generally speaking 304 is cheaper but when buying mandrel bends 'hygienic bends' (316L) from a stainless stockholder will be cheaper than 304 bends from an exhaust company. Hygienic bends aren't available in as wide a range though- 1/2" increments on diameter only and generally less choice with bend angles

V-band clamp quality varies a lot, some of the cheaper ones are shockingly bad. Other than that it's down pipe, don't worry about it too much

Has the sulphur content of exhaust gases ever been high enough to cause problems with 3xx series? http://www.bssa.org.uk/topics.php?article=37.

 

[1.8T]

The only bits im yet to find a source of in 316L is a couple of tight radius 2.5" 90 degree bends and some plate for making the flange from, been able to find the other bits even the transition, having a v band clamp isnt essential it just makes working on the exhaust easier and removes the need to take things off to work on the exhaust, if i really want to be fussy and keep the exhaust downpipe to nothing but 316L i could try and find a v band in that grade, or should they not be available just have two new rings machined up for mine from 316L

 

[langy]

I think you maybe over thinking this, I've been using 304 & 316 for exhausts for about 35 years and i've never had a problem, I use 316 rods for every thing.

 

[1.8T]

Your probably right langy, i should never have looked at whether i can combine different grades thats what prompted all this and now it just doesnt sit right for some reason not doing it all in the same grade, on that note anyone know where i can get 2.5" od 1.5mm wall tight radius 90 degree bends in 316L? langy can you supply these? (saw your site)

 

[langy]

I only keep the 2D bends in stock as we don't usually use any tighter, The bends are available in 1D, 1.5D. 2D & 3D
The way its measured is the radius in a 2D for example is 2 x the diameter.
I can get the other radius bends in a couple of days usually.

Virtually all the bends i use are 316L but for some reason the 1.75" bends are always in 304L, they weld in fine although they are 304L, nothing to worry about.

Your probably right langy, i should never have looked at whether i can combine different grades thats what prompted all this and now it just doesnt sit right for some reason not doing it all in the same grade, on that note anyone know where i can get 2.5" od 1.5mm wall tight radius 90 degree bends in 316L? langy can you supply these? (saw your site)

 

[1.8T]

Thanks langy, out of interest what radius are standard 2.5" bends as i dont think most suppliers say

 

[langy]

2D i believe, can't check as not in workshop today.

Thanks langy, out of interest what radius are standard 2.5" bends as i dont think most suppliers say

 

[1.8T]

Thanks, btw what do you use to cut your tubing? i was wondering whether my tube cutter (an old record 203) would be up to stainless what with it being harder than mild steel, will drop you a pm at some point about prices etc

 

[langy]

I use thin cutting discs in a 5" grinder, nothing complicated, I also have a large disc sander for getting perfect joints.

Thanks, btw what do you use to cut your tubing? i was wondering whether my tube cutter (an old record 203) would be up to stainless what with it being harder than mild steel, will drop you a pm at some point about prices etc