Stainless Steel Exhaust - why has it got paint ?

[Neil W]

Another question which I have been thinking about - this Stainless Steel Exhaust System is for sale on an auction site - mine has the same greyish colour ( paint ?) on my SS System.
My old TR7 SS Exhaust was shiney the complete length - why is the Stags 'part painted / coated' ?

What is the coating ?

http://www.ebay.co.uk/itm/TRIUMPH-STAG-EXHAUST-SYSTEM-/351497326870?hash=item51d6df9116

Neil

[stagwingnut]

I've never seen coated stainless exhaust for a stag before , I'd say the seller has painted them to improve the overall look ,for selling purposes! Graham

[Delayed Steve]

I've had m exhaust fitted for a long time . It's not painted with anything. I've never seen a stainless system painted before
Steve

[jleyton]

I fitted a Stainless steel system that I got from a fellow forumite, several years ago. It had only been used for a short time and was in 'as new' condition.

Only a couple of yers later the two 'link tubes', near the rear axle, were showing quite considerable corrosion

Apparently the cheaper stainless steels can, in fact, rust. I cleaned them up and painted them with silver exhaust paint, although the rust is beginning to show through again. The rest of the system has remained corrosion free.

Cheers

Julian

[Mike Stevens]

I had to replace the two pipes that Julian refers to earlier this year due to rust holes appearing in the stainless! However, only in the link pipes - the rest of the system seems to be OK. A bit much after only 27 years....

Cheers,
Mike.

[Neil W]

Hi - I went through my car's history file & found a receipt from Falcon Exhausts with a life time Guarantee - bought new in 10th March 1984 so that is 31 years ago - so a bit of exhaust paint is something I can live with

Get out clause it had to be with original purchaser to claim & had to be inspected yearly ( record on back of leaflet ) - still not bad going for an exhaust, now Mike I expect mine to get a rust hole anytime now !

Neil

[HersnotHis]

There are 2 basic distinct types of stainless steel Austenitic and Ferritic. The former is basically an alloy of Iron, Chromium, and Nickel (18/8 Cr/Ni being a common type). Ferritic Stainless is cheaper as its basis is an alloy of just Iron and Nickel , whilst it is far more corrosion resistant than mild steel it is less so than Austenic types but this depends on operating environment.

You can tell the difference by using a magnet. Austenitic grades are non magnetic but Ferritic grades are * . Checking the stainless exhaust systems on both my Stag and Daimler I found that most of the systems are magnetic and therefore ferritic but in both cases the tail pipes are non magnetic i.e. Austenitic

HTH

H

* As an experiment test your stainless steel cutlery. Most good quality cutlery will be non magnetic except the knives as Austenitic stainless will not mantain a cutting edge . The best stainless cutlery will have knife blades that are magnetic but handles that are nonmagnetic with an imperceptible interface between the two!

[Staggard]

There are 2 basic distinct types of stainless steel Austenitic and Ferritic. The former is basically an alloy of Iron, Chromium, and Nickel (18/8 Cr/Ni being a common type). Ferritic Stainless is cheaper as its basis is an alloy of just Iron and Nickel , whilst it is far more corrosion resistant than mild steel it is less so than Austenic types but this depends on operating environment.

You can tell the difference by using a magnet. Austenitic grades are non magnetic but Ferritic grades are * . Checking the stainless exhaust systems on both my Stag and Daimler I found that most of the systems are magnetic and therefore ferritic but in both cases the tail pipes are non magnetic i.e. Austenitic

HTH

H

* As an experiment test your stainless steel cutlery. Most good quality cutlery will be non magnetic except the knives as Austenitic stainless will not mantain a cutting edge . The best stainless cutlery will have knife blades that are magnetic but handles that are nonmagnetic with an imperceptible interface between the two!

The short version is 316 stainless is more resistant to corrosion than 304 but does not hold a sharp edge, most stainless exhausts are made from 304 which will hold a better edge, so when your exhaust has had its day you can always use part of it to carve the Sunday roast

[marshman]

The system on my Stag and the system on my Landy are both stainless. Both systems have nice shiney silencers, but on both systems the pipe work is very dirty looking with obvious rust in places. I suspect the pipes are made from a different grade (304 to use Grahams reference). The system on the Landy I fitted about 18 years ago. I bought it from Rimmers with a lifetime guarantee. Still have the receipt and the Land Rover, I suspect I will make a claim one day not too far away as the tail pipe is starting to get a bit tatty. It will be interesting to see what hoops I have to jump through to get them to honour the guarantee!

Also interesting what H says as I know that the local scrap yard will not accept stainless that is magnetic, (it gets classified as light iron) - they check it all with a big magnet.

Roger

[HersnotHis]

The short version is 316 stainless is more resistant to corrosion than 304 but does not hold a sharp edge, most stainless exhausts are made from 304 which will hold a better edge, so when your exhaust has had its day you can always use part of it to carve the Sunday roast

Whilst there are many other variants to both types, thanks for putting the practical end of my reply.

H

(believe it or not)

BSc Metallurgy (Via 5 yr part time/evening classes - before OU)

Although apart from some fundamentals ( as we are discussing) it might as well be BA History!!

H

[Paul Roberts]

I believe the "link-pipe" may suffer from the close proximity of the welds. Welding stainless causes metallurgical changes to the properties (ductility, hardness, and most importantly, corrosion resistance.)

I'm dredging my memory cells here (forty odd years have passed me by since having to study metallurgy and such things) and I'm sure that welding technology has progressed significantly since then.... , but I think it was something to do with dendritic formations or some such.

I trust H or others will qualify or correct my claim.

I was told, by a bloke who knew a thing or two, that stainless steel was a great material - as long as you didn't actually want to make anything out of it.... .

That said; thirty years for an exhaust ain't all bad - so maybe my old mentor didn't know quite as much as they told me he did....

[HersnotHis]

I believe the "link-pipe" may suffer from the close proximity of the welds. Welding stainless causes metallurgical changes to the properties (ductility, hardness, and most importantly, corrosion resistance.)

I'm dredging my memory cells here (forty odd years have passed me by since having to study metallurgy and such things) and I'm sure that welding technology has progressed significantly since then.... , but I think it was something to do with dendritic formations or some such.

I trust H or others will qualify or correct my claim.

I was told, by a bloke who knew a thing or two, that stainless steel was a great material - as long as you didn't actually want to make anything out of it.... .

That said; thirty years for an exhaust ain't all bad - so maybe my old mentor didn't know quite as much as they told me he did....

As said my metallurgy is now also history but what you say does ring at least a vague bell

As with any metal heating/cooling history is very important. I was alarmed to see that on a recent repeat of wheeler/dealers that in order to rectify a slightly bent cross member on a Volvo P1800 it was heated up with a blow torch to enable it to be easily re-bent to shape! The original was probably a hot pressing which will enduce a structure of strength- heating it up and letting it cool down naturally will reduce this strength .

H

[Princejohny]

Fascinating thread...
Wife is now asking why I'm not in the garage welding but instead testing the cutlery with a magnet...
So far every knife, fork and spoon is magnetic.
The pizza cutter wheel isn't but the handle is. The spiral point of the corkscrew is, but not the metal handle. The kettle is not.
I've just been told I'm not allowed to do any further blowtorch testing and go back outside...
Johny

[Paul Roberts]

I can ask nurse to post you some of my new multi-coloured tablets, Johny, if your wife thinks they might help.... .

[Princejohny]

Well thank you Paul. They'll go well with the plastic cutlery that I usually use. I wasn't supposed to be touching the sharp magnetic stuff, anyway... Johny