Steel Specialist (exhaust tech question)

[mattjk]

Can someone who knows a bit about mild steel/stainless exhaust systems give me some info on the below.


With a stainless system water just sits on the surface and congregates, when the hot exhaust gases pass over it evaporates producing the fine white mist that you see.

Mild steel is a lot more porous and water isn’t retained “as much” hence my point about full stainless systems.

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The above correct?

Thanks

 

[BenR]

Pardon?

The majority of the steam you see when running is due to the cat.

 

[Fred@BTM]

not quite, from memory there's only 1 grade of stainless that DOES NOT corrode (316, which is marine grade)

full stainless system is all well and good, but this is why i bang on about quality etc (welding especially) its a bit like dating Lucy Pinder and dressing her in overalls, nice but not as good as it could be

MIG welds on stainless i hate for this reason, fin will tell you more

 

[Fred@BTM]

mild steel isn't porous, it just reacts more to the atnosphere

 

[mattjk]

I was having an argument/debate with someone, this was his response when I questioned his reply in the first post..

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Yes Cat's do, but general rule of thumb a full stainless e.g. from the manifold back generally have a decat (Jap Stuff) it's all to do with the way stainless heats up and cools down, it condensates a lot more than mild steel.

Disagree if you want, makes no odds to me.

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Sorry to elborate the conversation started off by saying the vehicle was producing a lot of steam his reponse was it just have a full stainless fitted which causes it. I didnt believe him

 

[BenR]

The only moisture your going to get is that which passes through the engine. Water is a by product, especially with a cat on.

This is pretty pointless, there would have to be a large store of water in your exhasut for it to continue steaming out simply due to evaporation.

This is so stupid.

 

[mattjk]

Ben - It wasnt me that suggested it. I challenged what he said and i got shot in the foot. thats why I put a post so I could go back to him with some mroe info


I did suggest that the cat produces most of the condensation.

 

[BenR]

just put your finger to your mouth and go 'shhhhhhhhhhhhhhhhhh'.

If he wants to be a moron, in the words of the beatles.......let it be.

 

[mattjk]

Thanks kindly for clarification. I will point him In direction of this thread if need be.

 

[mattjk]

Does this make any sense? Paying particular attention to the last paragraph. I know its b****cks but its quite an interesting debate unfortunately its got beyond my knowledge. Although logically thinking about it I think hes chatting more s**t.

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Condensation is caused by a temperature difference between the hot exhaust and the cooler metal surface, cooler because it is exposed on the outside to ambient temperature, so when the hot gas comes into contact with the metal it gets cooled and some of the steam in the gas turns into water.

Stainless steel expands and contracts at approximately the same rate as carbon steel and I don’t think this has anything to do with it.

Carbon steel is magnetic, stainless usually is non magnetic.

Carbon steel oxidises on the surface, stainless does not oxidise, maybe this has something to do with it but I can’t figure out why.

 

[BenR]

What on earth is he going on about?

Technically if the water is present as steam, then it is already visible and come out the exhaust AS steam. Water is usually exhausted in the form of vapour after combustion.

And exhausts heat up pretty darn quick, to the point where condensation cannot occur, no matter the temp differential.

Forget it, why do I care.....maybe its the earths magenetic poles effects on the exidation of steel alloys and their contributary effect on condensation rates.

 

[mattjk]

God only knows mate. I just wanted a pro's opinion.

It sounded like bull from the 1st post, thanks for your time.

 

[ditz]

someone clear something up for me,, i thought stainless steel was just a higher carbon content than mild steel ??

 

[Fred@BTM]

http://en.wikipedia.org/wiki/Stainless_steel

 

[mattjk]

So I went out with a couple of people last night & this topic popped up again. (someone else made a point that chromium which is added to stainless steel males the water sit on the surface) But I still didnt believe him & stuck to what I said.

Anyway after much debating my mate has this AQA number on his phone 63336. (bloody awesome it is) So we text it asking the question it came back with

AQA: Stainless steel exhaust systems do not cause more steam than normal exhaust. However if the system was longer more steam maybe produced.

Result haha

 

[Neomagic]

Lol well done Matthew, I bet you felt proud of yourself when you posted this.

I still think the topic is open for debate, despite all valid and sensible opinions.

 

[mattjk]

It's not a matter of being proud or not lol, I just knew you were talking out your ass & wanted a pro's opinions which is what I got!

 

[Neomagic]

Define talking out of my ass?

Passing judgement on a subject, knowingly or unknowingly isn’t considered talking from your ass.

Passing judgment when you knowingly are in the wrong just to make yourself appear superior or what have you, is considered to be talking out of your ass.

All I did was vent my opinion from personal experiences, and that anomaly still remains unsolved in my books as it seems from a general consensus that your average Joe has noticed this as well.

Whilst you have proven to me that the grade of metal itself makes no difference and I agree with what you have presented I still see cars with stainless exhausts producing steam for longer and more of it in all weathers than an OEM system for example.

 

[mattjk]

Whilst you have proven to me that the grade of metal itself makes no difference and I agree with what you have presented I still see cars with stainless exhausts producing steam for longer and more of it in all weathers than an OEM system for example.

I'm going to ignore all the other crap your spurted as it bears no relevance. However the above paragraph makes perfect sense, I thought we clarified this the other day?

Obviously the design of the system is going to impact on how the exhaust gases/vapours are distributed. The systems you have seen have been prone to hold moisture for longer than an OEM system Due to the design/length of them, not of what they are made out of!

 

[Neomagic]

I think that wraps it up nicely.