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#### xchcui

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##### stainless steel thickness for repairing exhaust hole
« on: February 04, 2019, 06:59:11 AM »

Hi.

I was suggested to use a stainless steel sheet(followed by
an high temp. exaust repair cement)to repair an hole in the exhaust pipe).
The stainless steel will experience gases tempertature of about 400°C-800°C.The stainless steel 304 has a melt point of 1400°C-1450°C,but i am pretty sure that the thickness in that task is important.
What should be the minimum thickness of the stainless steel(304)sheet that will be suitable for that task?

Thanks.
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#### Enthalpy

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##### Re: stainless steel thickness for repairing exhaust hole
« Reply #1 on: February 04, 2019, 07:38:39 AM »

Hi,

the melting point doesn't determine the operation temperature of an alloy, it's only a very far limit.

For continuous operation, 800°C would be far too much for the Aisi304. Even nickel-based superalloys stop around 750°C in non-structural applications (understand: the carter, not the turbine).

Though, exhaust pipes (you mean, at a car?) are usually built of dumb steel, and they do survive for some time, so the Aisi 304 should do it much better. Aisi 316 would be even better. Just take the same thickness as had the dumb steel that was punched through. Or take what you find.

One possible worry is that the cement may not adhere on stainless steel. To be tried.
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#### xchcui

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##### Re: stainless steel thickness for repairing exhaust hole
« Reply #2 on: February 05, 2019, 02:47:34 AM »

Yes,i meant to a car exhaust.
The thickness of the car exhaust is about 1.5mm,but while i checked the thickness of several stainless steel sheets,i found out that it is hard to work/make a bond with a stainless steel that is more than 0.1-0.2 mm for this task,since it is too strong and springy.
Will 0.1-0.2mm thickness be enough to do the job?
BTW,why did you say that it is possible that the cement may not adhere to the stainless steel?The exhaust cement,as far as i know,is designed to adhere to stainless steel/steel exhaust,isn't it?
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#### P

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##### Re: stainless steel thickness for repairing exhaust hole
« Reply #3 on: February 05, 2019, 03:27:18 AM »

The exhaust cement,as far as i know,is designed to adhere to stainless steel/steel exhaust,isn't it?

As far I know these silicate exhaust cements are a temporary fix. They will blow again after a week or so iirc. They will tide you over until you replace the section of exhaust that has blown though.   I guess you could weld it...  but I assume that would be more hassle than just getting it replaced these days surely?
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Tonight I’m going to party like it’s on sale for $19.99! - Apu Nahasapeemapetilon #### Enthalpy • Chemist • Sr. Member • Mole Snacks: +240/-54 • Offline • Posts: 2799 ##### Re: stainless steel thickness for repairing exhaust hole « Reply #4 on: February 05, 2019, 06:28:59 AM » Will 0.1-0.2mm thickness be enough to do the job? BTW,why did you say that it is possible that the cement may not adhere to the stainless steel?The exhaust cement,as far as i know,is designed to adhere to stainless steel/steel exhaust,isn't it? 0.2mm possibly Try it and observe. Predictions are about impossible. Adhere: stainless is radically different from carbon steel in that aspect. For instance concrete, zinc, paint don't adhere on stainless steel. If the cement is explicitly meant for stainless steel, nice. If not, experiment. Logged #### xchcui • Full Member • Mole Snacks: +1/-3 • Offline • Posts: 140 ##### Re: stainless steel thickness for repairing exhaust hole « Reply #5 on: February 06, 2019, 03:40:59 AM » Quote stainless is radically different from carbon steel in that aspect. For instance concrete, zinc, paint don't adhere on stainless steel. If the cement is explicitly meant for stainless steel, nice. If not, experiment. The exhaust cement data sheet says that it adhere to metals,but doesn't say which metals,so it is something to take into consideration and might take me back to my previous option. My previous option was to use a food can for my task. I saw that option in several web sites It made of a carbon steel and it is about 3mm thickness. But the food can usually doesn't smooth(it has folds for strength)and it has a kind of synthetic coating(epoxy,polyester,acrylic etc.),so i wasn't sure if this coating will have a negative effect on the bonding or a toxic odor emition from the burning coating while car operation. Also,i wasn't sure how long will this carbon steel food-can resist corrosion.So,i thought to use a stainless steel. What do you think about the carbon steel food can regard to my points? And besides that,isn't using 0.1mm stainless steel sheet better than using 0.3mm carbon steel sheet for this task? Logged #### Enthalpy • Chemist • Sr. Member • Mole Snacks: +240/-54 • Offline • Posts: 2799 ##### Re: stainless steel thickness for repairing exhaust hole « Reply #6 on: February 06, 2019, 10:11:23 AM » I expect the coating on food can to catch fire (danger!) or degrade quickly, with emission of yuk gases, yes. And once the coating is burnt away, the steel will corrode. Most car exhausts use a banal steel formulation, but at least it's thicker (you mentioned 1.5mm) and it may have some protective metallic coating. 0.3mm steel from a food can will be punched through quickly. That's practically sure, while the thin stainless steel is at lest doubtful. I'd add a steel wire around the repair, to avoid accidents if the cement doesn't hold. Logged #### xchcui • Full Member • Mole Snacks: +1/-3 • Offline • Posts: 140 ##### Re: stainless steel thickness for repairing exhaust hole « Reply #7 on: February 07, 2019, 02:27:00 AM » Yes,i assume that i have to add a steel wire around the repair due to the reason you have explained before. Thank you very much for your help. Logged #### P • Full Member • Mole Snacks: +63/-15 • Offline • Gender: • Posts: 629 • I am what I am ##### Re: stainless steel thickness for repairing exhaust hole « Reply #8 on: February 07, 2019, 05:07:34 AM » Sounds fine for a temporary fix. Logged Tonight I’m going to party like it’s on sale for$19.99!

- Apu Nahasapeemapetilon

#### xchcui

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##### Re: stainless steel thickness for repairing exhaust hole
« Reply #9 on: February 08, 2019, 01:25:09 AM »

Hi,P.

Why did you mention,that it is a temporary fix?
Do you mean,that even if the hole(which is applied around with cement)will be covered and
secured with stainless steel sheet and a wire,it won't last long?why?
Do you refer to the ability of the exhaust cement to keep
its features for extended time,like cracking and crumbling?
Do you familiar with other type of adhesive/cement that can handle the high exhaust gas temperature?

As far as i know,the exhaust cement contains sodium silicates and organic fibers(though i don't know which organic substance it is)and it is used for repairing exhaust holes for many years.I didn't find any other formula for that task.I used before the epoxy putty,but even though it repaired the hole,it emit a very stink and probably toxic
gasses forever.(since it doesn't resist so high temp.)
Of course that the best solution is to replace the exhaust section or weld a patch to the pipe etc.but in this case i am interest in the other solution.
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#### Enthalpy

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##### Re: stainless steel thickness for repairing exhaust hole
« Reply #10 on: February 08, 2019, 03:20:26 AM »

I don't expect the repaired exhaust to last as long as a new one neither. If corrosion punched one location through, other places way well be weakened. But if you gain a year, it can be worth the effort.
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#### xchcui

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##### Re: stainless steel thickness for repairing exhaust hole
« Reply #11 on: February 08, 2019, 10:23:38 PM »

I don't expect the repaired exhaust to last as long as a new one neither. If corrosion punched one location through, other places way well be weakened. But if you gain a year, it can be worth the effort.
Yes,the rust will spread over the rest of the pipe soon or later and i am aware of that,but since P mentioned that the repair will be temporary and won't last(even after a week)due to the exhaust cement rather than the corrosion spearding issue.So my points in my questions refered to the features of the exhaust cement over time,
P said:
Quote
As far I know these silicate exhaust cements are a temporary fix. They will blow again after a week or so iirc...
So,is there any concern with the features of those exhaust cement(sodium silicates based)that make them
fail over time(like to crack,crumble etc)?or it is not exactly accurate what he said and the only issue,in my task,is the spreading corrosion on rest of the pipe over time?
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