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early car idiot driver
 
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Stainless vs. Hardened Steel

For all you metallurgist out there. What are the differences, benefits, etc. between hardened steel and stainless steel, as it relates to an exhaust pipe? Bypass pipe to be exact.

Thanks in advance!
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Old 03-21-2005, 09:38 AM
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I'm no metallurgist, but the primary (and usually only) advantage of using stainless is corrosion resistance. It sucks in alot of other ways in comparison to other steels.

Are you considering making a bypass pipe out of Custom 455? :>)

Mike
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Old 03-21-2005, 09:52 AM
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The main advantage of using stainless in an application like that is corrosion resistance. I don't really see the reason for using hardened steel for an exhaust pipe, it is generally more brittle and would be more likely to crack when bent into shape, also the heat cycles when operating would probably anneal the metal anyway causing it to lose some of its hardened microstructure. I'd stick with the stainless. I believe F1 teams use Inconel and other nickel based alloys for their headers, there was a cool article in Racetech or Racecar Engineering a couple of years ago about a UK outfit that fabricates F1 exhaust, they were using very thin walled nickel base tubing for low weight and corrosion resistance at elavated temperatures.
Old 03-21-2005, 09:52 AM
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There are several grades of stainless to consider as well. Lower grades of stainless can still oxidize.

Sherwood
Old 03-21-2005, 10:13 AM
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For example: Ruf makes a bypass pipe made out of hardened steel and Dansk makes a bypass pipe out of stainless steel, which is better? That is my delimma.
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Old 03-21-2005, 10:31 AM
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Do you still have the old CAT? Or are you keeping that for street use?
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Old 03-21-2005, 10:49 AM
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Quote:
Originally posted by Scooter92
For example: Ruf makes a bypass pipe made out of hardened steel and Dansk makes a bypass pipe out of stainless steel, which is better? That is my delimma.
Better in what respect?

Corrosion? Probably the Dansk.

Does a catpipe need to be SS? I don't think so.

Heat cycles? Probably the Ruf.

Made a decision on those RS door panels yet?
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Old 03-21-2005, 10:55 AM
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Quote:
Originally posted by Drago
Better in what respect?

Corrosion? Probably the Dansk.

Does a catpipe need to be SS? I don't think so.

Heat cycles? Probably the Ruf.

Made a decision on those RS door panels yet?
No decision on the door panels yet, but leaning toward keeping and using them.

I am not talking about a cat bypass pipe here, I am talking about a primary muffler bypass pipe. For those of you unfamilir with a 3.6, there are two mufflers. I am replacing one with a bypass pipe.

Being in the Pacific Northwest, I am of course concerned with corrosion. Yes, I will drive my car in the rain.
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Old 03-21-2005, 11:33 AM
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Re: Stainless vs. Hardened Steel

Quote:
Originally posted by Scooter92
For all you metallurgist out there. What are the differences, benefits, etc. between hardened steel and stainless steel, as it relates to an exhaust pipe?
I think the better question is to ask the difference between carbon steel and stainless steel. "Hardened" implies a heat treatment process more than a "type" of steel.

There are many different types (alloys) of both carbon and stainless steels; the primary reason to use a stainless steel (a steel alloyed with chromium and nickel) is for corrosion resistance. The other big issue is expense.

In construction uses most stainless steels cost around 8 times more than carbon steel; the fabrication expense/replacement expense/life expectancy estimates all come into play when choosing stainless or carbon steel (in construction you usually have the option of galvanized too).

Right now with auto parts (particularly exhaust), I'd say there is a "marketing" factor too; parts makers are both creating and responding to consumer demands for more stainless steels.
Old 03-21-2005, 11:55 AM
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Stainless steels also (generally) have a lower thermal conductivity, meaning that hot exhaust gases stay hot and therefore keep up their velocity. You loose less heat energy into the exhaust piping. Slowing the exhaust gases is not optimal and should be avoided/lessened if it can be.
Old 03-21-2005, 12:01 PM
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Quote:
Originally posted by Scooter92
Being in the Pacific Northwest, I am of course concerned with corrosion. Yes, I will drive my car in the rain.
Actually most issues with exhaust corrosion have to do with corrosion from the inside-out. One of your primary waste products from combustion is water; not only can condensation be an issue (especially if you take a short trip then park for an extended period of time), but the water as steam can attack steel.
Old 03-21-2005, 12:02 PM
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Quote:
Originally posted by Scooter92
...Ruf makes a bypass pipe made out of hardened steel and Dansk makes a bypass pipe out of stainless steel, which is better?
The one that weighs less!
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Old 03-21-2005, 12:18 PM
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Re: Thermal conductivity of various stainless ( and carbon) steels:

http://www.outokumpu.com/pages/Page____5764.aspx

- Wil
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Old 03-21-2005, 12:31 PM
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Carbon steel and most stainless steels are not that good for elevated temps, over 1000F. Chromemoly steel, 321, 347, 410, and 422SS are better. As for exhaust material 321 is available but most off the shelf exhaust manufacturers don't use it.

Check out: www.burnsstainless.com
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Old 03-21-2005, 02:42 PM
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Whoa, you guys are way ahead of me. I have no idea what type, thermal conductivity, etc. I just want a bypass pipe. I knew when I posted this that I would get some great knowledgeable answers, but I also knew they would be over my head. Excellent stuff, but let's dumb it down to my level...which one should I buy?
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Old 03-21-2005, 03:10 PM
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Quote:
Originally posted by Scooter92
...which one should I buy?
The one that doesn't work with the RS door panels...

Seriously, all this for what? Pick one and get over it.
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Old 03-21-2005, 03:34 PM
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Stainless. After a few years it won't look as good as the better grades but it will last longer than alloy steel.
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Old 03-21-2005, 03:56 PM
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Old 03-21-2005, 03:56 PM
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