Rusted Megan Racing SS DP

[Oldsid]

While changing my clutch, I removed the DP and to my surprise it was all "rusted" and it lost a lot of metal (black powder) under the wrapping (see pictures). The wrapping was good quality Cool-it-Thermotec sprayed with high temperature DEI high temperature silicone. I wrapped the DP because it was very close to the oil pan and the alternator.
I know that the wrapping and the road salt probably caused the rust. however, I still want to wrap the DP but to protect it, I want to spray it with high temperature header spray that is good to 2000 deg. F.
I am hoping that by spraying the DP, it will be protected from the elements and will not rust. Do I need a primer before spraying? If so what primer can I use for high temperature like this? has anyone had this problem with SS wrapped pipe?

 

[Bud92gsx]

Its semi pitted.But it looks more black to me like carbon buildup.

 

[g4ebguy90]

Yea that header wrap really kinda is a win/lose item. I like it though. Id say the way id do it, is sand blast it, make sure shes all good and then put the paint on, prime if you want. It will eventually probaly come off to.

 

[Oldsid]

I cleaned it and it is pitted uniformly and a lot wherever it was wrapped as you can see from the pictures. The bend is the worst place and you can see the black powder which is really metal sulfidation. At this rate it will be full of holes soon.

 

[99gst_racer]

If Megan realy does use stainless steel, it's probably some low grade like 409 that does rust. It's a cheap, junk material but it affords them the opportunity to use the term "stainless steel" to help sell their products.

If you really want to use a header wrap, then you really should seal the outside of the wrap with something like this: Thermo-Tec : Hi-Heat Coating

 

[Oldsid]

Yea that header wrap really kinda is a win/lose item. I like it though. Id say the way id do it, is sand blast it, make sure shes all good and then put the paint on, prime if you want. It will eventually probaly come off to.

I am not sandblasting it because shops here charge an arm and a leg for any little thing. I used a 3M paint/rust removing wheel and have already removed most of the rust. But because of the pitting, there is a little left so I soaked the DP in rust remover and I am hoping it will remove everything. I read somewhere that for SS we should use "Galvanized metal etching spray primer" but I do not know what the hell is that and no auto part store had any idea of what it is!
If I can't remove all the rust properly, I will just take it to a shop and have it sandblasted.

 

[Oldsid]

If Megan realy does use stainless steel, it's probably some low grade like 409 that does rust. It's a cheap, junk material but it affords them the opportunity to use the term "stainless steel" to help sell their products.

If you really want to use a header wrap, then you really should seal the outside of the wrap with something like this: Thermo-Tec : Hi-Heat Coating

According to Extremepsi Website, MR DP is made out of 304 SS. I have seen this kind of problem on the inside of SS piping exposed to high temperature and and hydrogen sulfide but I was not expecting to see that on a DP. Another possibility is that the wrapping material used may be incompatible with stainless steel especially if it contains chloride.
I did use DEI high temperature coating to seal the wrapping and made sure that I sprayed many layers especially at the beginning of the wraps where most leak occurs. However, it did not seem to help especially in the harsh salty environment we have in the winter. I think the best way to protect the DP would be to paint it and then wrap it. That way, even if the spray coating breaks, there is still a barrier between to protect the DP.
I am planning to coat he DP and cure it first then remove it and apply the wrapping with the coating.

 

[99gst_racer]

It will probably eventually corode completely with enough time. When it does, upgrade to something made of 304 stainless and you won't have to worry about it happening again.

 

[Oldsid]

It will probably eventually corode completely with enough time. When it does, upgrade to something made of 304 stainless and you won't have to worry about it happening again.

MR DP is made of 304 SS and it still rusted. As I said in my previous post, it may be that the wrapping is incompatible with SS and that is why I am coating it. The other option is not to wrap but that will probably cause a hot spot on the oil pan and that is what I was trying to avoid by wrapping.

 

[Spyder FX]

I would love to see that cheap steel sent to a real Metallurgy lab...

 

[3kgt2nv]

no way that is 304. i had a 304 full exhaust on my 3000gt vr4 for 7 years and with constant abuse and salty ny winters it just turned a nice yellowish color. that is strait rust on that. i bet they use a 304 ss flex section and then say the whole exhaust is stainless.

 

[99gst_racer]

The thing is, 304 will not corrode like that. So whether or not they truely claim it is 304, we know it isn't. And it's definitely not the fault of the wrap either. I've wrapped a few 304 exhaust parts that I've built and they all continue to look fresh and clean underneath the wrap.

The Thermal R&D catback that I had on my old Talon was made of 304 and it continued to look great throughout our salty MI winters.

 

[silvreclips]

I built my DP out of 304 SS and had it wrapped for over year. After removing the wrap it looked just as good as before. Quality SS wont rust or corrode. My cheap catback exhaust also claims 304 SS and it is rusting away after 2 years or so.

 

[rEclipserGST]

With the air passing under the car and "cooling" the exhaust, do you really have to worry about a "hot spot" on the oil pan?

I've considered wrapping the downpipe, all my other hot pipes are wrapped. Mine is ebay. Has held up fine for at least 3 years. I just recently painted it with black high temp silicone paint I doubt I'll be wrapping it, just so I can just spray it down at the car wash during winters.

 

[99gst_racer]

I just noticed on Megans website that they carefully word a statement about materials. It says 304 stainless "is found in all of our exhaust products". They're careful to not say the exhausts systems are comprised entirely of 304 stainless. So, they could use a 304 flex section and galvanized 409 or 1010 for the rest of the exhaust, and their statement on the website would still hold true.

With the air passing under the car and "cooling" the exhaust, do you really have to worry about a "hot spot" on the oil pan?

Definitely not.

 

[wkmitsu]

I think it would be good to put a little information out there about this topic. Corrosion in stainless steel could occur because of a number of different things. The first could be some type of pitting corrosion. Pitting corrosion in stainless steels can happen for several different reasons. Any stainless steel will pit eventually in an environment with heightened concentrations of Cl-, Br-, and S2O3--. The steel in question is an austenitic stainless type 304. Type 304 has 8-10.5% Nickel. The more Ni your austenitic stainless contains the likelihood of pitting is reduced. But, pitting generally only occurs at locations where there has been damage to the passive layer in the steel. There is a chromium oxide film layer that overlays the active base metal, if it gets damaged pitting corrosion can occur. So, if you put a huge gouge in your 304 stainless downpipe for example, pitting corrosion can begin at that location. This particular brand of rusting will typically penetrate deeper into the steel rather than across the surface.

The next type is called intergranular corrosion. This effects austenitic stainless when they are improperly heat treated. In this scenario if a stainless steel is heated to the range of 800-1600 F, chromium carbides are precipitated at the grain boundaries. Put simply, because of this the adjacent regions to the grain boundary will become anodic and begin to rust if the steel is placed in a corrosive environment.

If you have a stainless that is under higher stress, then stress corrosion cracking can occur. For an austenitic steel if it's exposed to chlorides, caustic solutions, or sulfurous acids.

Preventing corrosion at the welds in a stainless is also a challenge. Carbon pick up needs to be prevented, sources of carbon include, grease, hydrocarbon base cleaners and degreasers, or excessive CO2 in a CO2 shielding gas mixture.

Galvanic corrosion can occur if the filler metal used for welding is not cathodic compared to the base metal. If the base metal, which generally has a much larger surface area than a cathodic weld deposit, can be anodic it will only need to supply very few electrons to the cathode and corrosion of the base metal will be minimal. On the other hand if the weld deposit is anodic it must supply a much larger number of electrons to the cathodic base metal and the weld will rust mush more quickly. To alleviate this condition it's important to use a filler metal that has at least 2% more chromium than than the base metal. So for a 304 stainless a 308 electrode composition should be used. 308 contains ~2% more Cr and 1% more Ni than 304.

Also, if you want to check and see if a product you buy is actually a 304 (or any type of austenitic) stainless, then just check to see if it's magnetic. Austenitic steels have a face centered cubic structure which is not ferromagnetic.

So there is a number of conditions that need to be met for an austenitic stainless to be high quality, especially for something like an exhaust system. Odds are Megan doesn't do everything 100% or they get their steel from not the best supplier, who knows? And yeah this ended up being longer than I meant, but I spent the time on it so I'll post all of it.

 

[FIBA M - EC17PSE]

So why dont you just add some gold reflective stuff on the bottom of the oil pan to reflect the heat away? Or will this then trap the heat in the oil pan from the already hot oil?? Seems like it would work if you dont want to wrap your DP again

 

[jmartinez1228]

Never found any issues with my downpipes being close to the pan that led me to want to wrap it or put any spray on it. If i were you i'd just sand blast it and get some legit high temp coating. Call it a day.

But if that pipe is cheap like some people are saying the get a new one. I have the apexi n1 dp and never had an issue. although it comes with its own coating.

 

[turbolarry]

By coinincidence I unwrapped my downpipe yesterday. Holy s#!t!
It's scrap now. Yes, it's high quality stainless from reputable manufacturer. You can see the difference looking at the testpipe. One was heat wrapped with DEI. One wasn't. They were both put on at the exact same time, exact same roads, exact same conditions. I don't know technical metalurgy mumbo jumbo, but I know I'll never wrap an exhaust part ever again. I think road junk just gets in there and has a free lunch

 

[99gst_racer]

^^^ So both pieces are of the same material and from the same manufacturer? And the only difference was that one was wrapped and one wasn't? Who is the manufacturer btw? (just curious)

 

[snowborder714]

Oddly enough, I had my Megan Racing downpipe just crack on me on the way home from the Shootout just below the weld at the o2 flange. It was wrapped and sprayed with silicone spray before it was installed. I'm interested to see what mine looks like once I take the wrapping off.

Either way, it'll have to be replaced as it won't be worth it to have the weld fixed.

 

[FIBA M - EC17PSE]

it is the same as sanding mild steel and then using that same sanding to sand aluminum it will still rust due to the mild steel deposits! stainless still rusts just like aluminum can oxide if you leave anything with water or salt trapped inside then it more then likely will eat away at it, it would not go like that if it was 316 or even 321, thats why 1 pipe is like new and the other is corroded,

 

[turbolarry]

^^^ So both pieces are of the same material and from the same manufacturer? And the only difference was that one was wrapped and one wasn't? Who is the manufacturer btw? (just curious)

Yes, same manufacturer, XS Engineering. The real XS Engineering that was here in Southern California. They had nothing to do with XS Power Chinese crap, but of corse like a lot of other good manufactures, the Chinese crap cut too much into their business and they've gone away.
Yes, the only difference was the heat wrap. The down pipe was wrapped to the flange. No wrap on the test pipe.
I can't say for certain that they used the "exact" same stock for both pieces, but I can't imagine they deviated too much.
http://www.motoiq.com/magazine_articles/id/1096/categoryid/84/xs-power--no-not-xs-engineering.aspx

 

[kchaazz]

After a lenghthy discussion with one of our vendors about wraps vs high temp coatings some time ago, I was told that wraps almost always cause cracking and corrosion because the wraps allow moisture, amongst other things to be trapped between the metal and the wrap, which causes some type of thermal ### I dont understand enough about to explain. I went ahead and got my manifold, O2 housing and turbine housing coated inside and out and couldnt be happier with the results. Its somewhat expensive, especially compared to the cost of wrap and silicone spray sealer, but the possibility of having to replace expensive exhaust parts definitely outweighs the cost, and the coating I got even looks better.

 

[evileagleawd]

I never rapped my megan racing down pipe and its all rusted. Its just cheap material! The flanges arent even ss. I can hang a magnet from them. Whats that old saying? "You get what you pay for"