I agree with someone else, that you can get different grades of stainless steel that are magnetic.

Of course, if a magnet will stick to it, then it will rust (regardless of whether or not it's stainless steel).

Later, Steve

 

Magnets will stick to most common grades of stainless (sergical grade 304 for sure). Thinner tubing has less steel concentrated in the area that the magnet is touching. The greater the thickness the more likely a strong magnet will stick to stainless.

 

without getting complicated, and Im no expert at this, the rule of thumb is that if a magnet sticks to metal , like on a exhaust part, its not stainless... I checked OEM exhaust flange and it does not stick.. nor rust... thus I would only assume high end after market exhausts would do at least the same ...

 

I'm no expert either- but I had a "SS" Stromung exhaust on an Audi- and a magnet would stick to it.

Never rusted, despite a couple of winters in the NE.

 

I was curious so I did some reading. 400 series stainless is ferretic (magnetic) and the 300 series is austenitic (not magnetic). Both are not supposed to rust though. So either way those flanges are a no no. Dis-similar metals also promote corrosion. Aircraft have the issues fairly often. It bothers me to see a vendor that deals with mods with such a prestigious marque of car providing a product that they are selling under the assumption of it "what you pay for". If were the owner I would post the maker of the exhaust. I get aggrevated with the assumption that because we own porsches we should get charged a ridiculous rate whether the quality is good or not.

 

I just wanted to point out that not all are equal... some are poorly made.. others use cheap connections and leak, and the rest are probably made in underdeveloped countries... I get hit up by prospective clients often saying why mine is more money vs this one or that one... I just wanted to point out that it comes down to details.. and this is one of them... Ironically that exhaust has the best cats on the market..

 

I was always under the impression that mild steel flanges were used because they are less likely to crack and/or warp.

The exhaust manifold flange on my evo was mild steel and I never had any issues even after driving it through a winter. Didn't look all that pretty, but held up great.

 

good stuff and I must say those bailey diverter valves really are crap. Over the years I've had to remove them so many times!

 

LOL the last two sets that were on clients car leaked from the small little hex screws... plus the cheap plastic fitting on top leaks too... even if you screw it tight... odd...

 

VAGscum has it right. The 300-series (austenitic) stainless steels contain Cr and Ni, and are non-magnetic. The 400-series (ferritic) stainless steels contain Cr, but no Ni, and are magnetic. The 400-series alloys transform around 700C (dull red) to austenite, accompanied by a fairly large volume change. That would make them a very poor choice for an exhaust flange. Probably the flange Markski found was just plain steel.

The 300-series alloys are susceptible to corrosion when welded. There are lower carbon grades 304-L and 321-L that were developed to eliminate this problem. I believe that the cost is almost the same for the lower carbon grades. Might be worthwhile to switch.

Jon

 

Yep... amazing indeed eh?!?! I used them on my car back in 2002 and then pulled the plug on ever selling those darn things. The nipples are a big POS too and leak/break.

 

If you want a Shock, go and get the wife best Stainless Steel cutlery and put a Magnet on it. You will find it sticks to it. That's food grade SS

ps the OEM muffler is supposed to be SS but when I took mine off there were patches of corrosion just starting to blister.

 

Mild steel gets a bad rap a lot of places, but in my experience the above comments hold true. I run a high performance mild steel exhaust on my daily driver. It's been on there since 2005 and has been through 6 Colorado Winters. The HPC coating that was on it when new peeled off after the 2nd winter. It's got some surface corrosion, but I inspect it a couple of times a year and it's got plenty of life left in it and is in no danger of rusting through.

 

I know any good welder would know to use 309 instead of 308 on stainless to steel. No?

 

I would be interested in knowing what manuafacturers actually make their own exhaust. I know that it is not un-heard of to outsource the exhaust manufacturing. Maybe even to china for all I know. If you request a chinese manufacturer to make you 1000 exhaust setups using german cats they probably would. Then you have a cheap chinese made exhaust with fancy cats. In the end it is difficult to find an aftermarket 996TT exhaust that looks like the quality that ~$3k-4k suggests. And yours is one of the few.

"I know any good welder would know to use 309 instead of 308 on stainless to steel. No? "

I am not an expert with metalurgy or welding so I wouldn't know what 309 or 308 stainless is much less their attributes in this application. I am sure somebody like Markski or another fabber could answer this. I would expect that if they were going to use a particular metal type if would be best to use nothing but that metal type so that the weld joints are not weakened by the dis-similar metals. But I wouldn't be suprised if a good welder has trick to make it work.