What grade stainless ?

[S2central.net]

Question for the metal experts - is stainless 303 suitable for an exhaust application ?

My understanding is that it is easier to machine than the normal 304 grade but that 303 is less resistant to corrosion. If the latter is true then I suppose a good high temp coating would maybe be wise.

[Flat on my back]

.

304 myself.

This gives you a good idea on the reasons.

http://www.stainlesssteel303.co.uk/

http://www.stainlesssteel304.co.uk/

[S2central.net]

Thanks for that... kinda confirms my findings so far, but tell me this - is there an easy way to determine if a lump of stainless steel is 303 or 304 without taking it for expensive lab tests ?

[Flat on my back]

.

Not that i know of, unfortunately, unless you have it delivered with a C of C.

[magarv]

After what I can see 304 is a better choise for elevated tempereatures than 303 due to the higher sulphur content in 303.
From www.westyorkssteel.com: The higher sulphure content of 303 stainless steel gives the grade poor weldability and reduced formability compared with other austenitic stainless specifications.

I know it is not a part of your question but, 321 (and 316Ti) is the preferd material if you ask me due to that it is titanium stabilised. The titanium is stabilizing the material structure at elevated temperatures.
To comparison:
304: Heat tensile strenght (500oC):Rp0,2 = 105 N/mm2 Rp1,0 = 130 N/mm2
304L: Heat tensile strenght (500oC):Rp0,2 = 94 N/mm2 Rp1,0 = 119 N/mm2
321: Heat tensile strenght (500oC):Rp0,2 = 124 N/mm2 Rp1,0 = 159 N/mm2

I couldnt find any specifications regarding 303, but as you can see the 321 keeps the material properties much better at higher temperatures compared to 304.

You can read a little bit about the materials here: http://www.westyorkssteel.com/stainless_steel.html

My favorite site when it comes to exhaust materials delivery: www.burnsstainless.com

[S2central.net]

OK - I got offered an offcut pipe from someone who believes it to be 303 so I dunno if its really suitable - unless all I need to do is paint it ???

What sort of wall thickness is considered minimum for an exhaust pipe ?

[S2central.net]

I don't need to weld this section - it will just form a straight link pipe / CAT bypass - so it is not going to be superheated either - as opposed to a downpipe.

I have read that 316 and 321 are superior materials but they are also more expensive - and thats not good for me right now - trying to do this on a tight budget.

[Audi Parts Guru]

Paul,

These guys in my opinion produce the finest exhaust systems in the world. They make exhaust systems for most of the F1 teams along with some of the top Rally teams. The quality of their work is superb

Lots of good info on their website

http://www.goodfabs.com/Default.aspx

[magarv]

Thanks for that... kinda confirms my findings so far, but tell me this - is there an easy way to determine if a lump of stainless steel is 303 or 304 without taking it for expensive lab tests ?

If you know some one in the industry it is not necessary with any expensive lab tests anymore. The have "guns" that can identify materials and chemical compositions within seconds. http://www.niton.com/metal-and-alloy...aspx?sflang=en

But expensive equipment, and as I said you need to know someone I think...

[magarv]

I don't need to weld this section - it will just form a straight link pipe / CAT bypass - so it is not going to be superheated either - as opposed to a downpipe.

I have read that 316 and 321 are superior materials but they are also more expensive - and thats not good for me right now - trying to do this on a tight budget.

Sorry I was thinking exhaust manifolds etc right away... And 316 are not superior to 304 in exhaust, it has to be 316Ti. Regular 316/316L cracks more easily than 304 etc when used at high temperatures

[S2central.net]

I was being lazy with '316' - I realise the metalgurus need all the codes...

So will this 303 pipe (wall thickness is 1.5mm) serve me well as a CAT bypass ?

[magarv]

So will this 303 pipe (wall thickness is 1.5mm) serve me well as a CAT bypass ?

Yes, I believe so.

[JP]

I chopped the whole centre portion out of my exhaust from the downpipe and using a 2m length of 6082 1.6mm wall thickness aluminum. It's part reduced the drone on the motorway, quieter pootling around town, hasn't restricted flow and more importantly reduced the weight drastically. All I need to do is replace it every 3years at a cost of £25

[Rusty]

Aye, Paul, might not be a permanent solution but as a cheap option to get the exhaust sorted for now, seems like a winner.

[benjo]

So will this 303 pipe (wall thickness is 1.5mm) serve me well as a CAT bypass ?

basically, yes