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topic 10209

Thermal blemish / discoloration on stainless steel

A discussion started in 2001 but continuing through 2019


Q. I am not sure if my question falls within the scope of this forum, but I am hoping that someone would have experience with this problem.

I have a high grade stainless steel exhaust system on my motorcycle. The tubing is approximately 1mm thick, and runs the entire length from the engine manifold through to the muffler.

The problem which I am experiencing is that the surface becomes black, not reflective and pitted where the temperatures are highest. At present, I sand the tubes with progressively finer Sandpaper [linked by editor to product info at Rockler] about once every 3 months, and then polish them, but this also removes the reflective colored bits (blue and purple near the engine, gold further back), which I like and want.


Is there any way I can coat the tubes with something after I have polished them up to prevent the matte black spots from appearing, while still allowing the reflective coloration to show through? Also, is there an easier way to remove the blemishes? I live on the coast, and have rather humid and salty air conditions. I am told that the manifold headers can get anything up to around 400 to 500 °C for however long I ride. Any help would be greatly appreciated.

Philip Kloppers
- Umtentweni, KZN, South Africa

A. Hi Philip. I don't have a good answer for you, but thread 27714 and thread 14857 concern the 'golding' and 'bluing' and might help.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
Striving to live "Aloha"

SS Color Change of Exhaust Headers


Q. I have an entire exhaust system on my car made of stainless steel (type unknown). I have polished it to a chrome finish. After several minutes of run time @ high temps the stainless will turn a gold color and finally blue. I am currently looking for a coating/fix to solve this problem. With an infrared heat gun I have measured the temp to be in excess of 600 °F. I have even seen the steel get hot enough to glow red. I have heard that coating the SS with Nickel will protect the System and that the Nickel will not change color (even at 700-800 °F). Also, what color will Nickel change to & at what temp?

Any Feedback would be appreciated before I ruin a $3000 exhaust system with a coating that doesn't solve my problem.

Thank You,

Robert Knuckey
- Peoria, Arizona, USA

A. Hi Robert. We have several long discussions about nickel or chrome plating of exhaust systems; topic 37758 is a good starting point and will probably be interesting to you. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
Striving to live "Aloha"

Polishing Stainless Steel - Buffs and Compounds


Q. Hello there,

I am currently using the following combination to polish steel (some is stainless) on an exhaust manifold.

- Stitched Sisal (very firm thick fibers) with tripoli [link to product info at Amazon by ed.]
- Loose-leaf Calico with 'Josco' SSX Compound (light green bar, contains aluminium oxide according to Josco website).

I'm achieving reasonable good results but still can not obtain a mirror shine.

The above tools/compounds are based on a few hours of internet research and it seems that perhaps I may have purchased the wrong buffs and compounds.

Here is the manifold in question:

I am also having trouble removing pitting from 12 years of rust and decay.

My question is .. - What would be a better steel polishing combination ? - What method could be used to remove the minor pitting in the steel's surface ? I have tried 80 grit paper and a wire-brush attached to an angle grinder.

Please note that the rear of the exhaust appears to be stainless and has polished up quite well and my greatest concern is with the front of the pipes. Both metals are visible in the following picture:

Thanks gang :)

Matt Kay
- Sydney, NSW, Australia


Q. I am about to start polishing stainless steel headers & exhausts with no idea of what tools to get and what method to use any advice will be good advice.

Richard Gray
- Busselton, West Australia

A. Hi Matt, hi Richard. A basic point about polishing anything, but especially stainless steel, is that it is not possible to do it in one or two steps ...

ABy way of example, you don't dig the foundation for a skyscraper with teaspoons because it would take forever; and you don't use a bulldozer to place seedlings in its flower pots.

Similarly, you'll never get the necessary rough polishing done with fine abrasives, but you can never get to a mirror shine with rough abrasives. 4 or more steps are required. Thread 45366 and thread 0246 address this. Although thread 0800 is actually about polishing motorcycle aluminum it has some great hints. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey
Striving to live "Aloha"

Electropolished stainless, will it stand up to high heat?


Q. My company designs and fabricates twin turbo systems for high performance automotive applications. We are using all stainless headers and exhaust hot parts. When we get these parts, they look like crap.

I'd like some way to make these pieces look much better. I've been reading about electropolishing on here and was wanting to know how it stands up to heat and what the finished product looks like? Our systems are expensive and we want them to look the absolute best they can. Other than these pieces, everything else is polished, anodized or powdercoated, this is the only area that is missing in the eye-candy area.

I'd like to have some type of a nice finish for these parts and trying to find the best method, what do you recommend? It must stand up to heat 1600-2000 degrees. If some type of electroplating won't work, is there any other way I can clean up the surface to look nicer (manual polishing) and if so will it last? Can you anodize stainless? Would it last?


Rad Craig
- Chouteau, Oklahoma


A. If your parts are standing up to this kind of heat now, I don't see any reason why EP would change that. It would be helpful to know what alloy you are using. EP will definitely improve the looks and corrosion performance. Happy to do some samples for you.

Dan Weaver
- Toccoa, Georgia


A. I would be most surprised if any coating withstood 1600-2000 degrees without some sort of change taking place. At these temperatures the stainless steel will start to turn all sorts of colours and if it isn't in an inert atmosphere, it will start to corrode. I would definitely not expect electropolishing to withstand these conditions for very long. Sorry to be so negative.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


A. I agree with Trevor that you probably cannot expect stainless steel to stand up at these temperatures without discoloration. If aesthetics is critical, EP is the best way to go, if the alloy stands up.

lee kremer
kremer signature
Lee Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
stellar solutions banner

304 stainless exhaust header pipe turns brown

March 15, 2019

Q. I have a Ducati with a low grade stainless steel header pipe
I think its probably 304 how best to clean this?
I have blasted it clean and polished it in the past but it soon goes brown again.
Any treatment to help with this?

Steve Bailey
- wiltshire united kingdom

March 2019

A. Hi Steve. I don't think there is any coating you can apply yourself that will help. You could have the pipes ceramic coated, which would probably be the most durable, and cost probably in the $300 range in the USA (don't know about the UK) --but they wouldn't be quite metallic anymore, although there are some reasonably shiny ceramic coatings available. Or you could have them nickel-chrome plated which would be better than stainless, but there still might be some "golding" or "bluing" that you don't like, and it would probably cost twice as much as ceramic coating or so.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

March 16, 2019

thumbs up sign  Hello,
thanks for the reply.
I wonder if I contaminated the stainless blasting if in a cabinet used for ferrous material?
will look at cleaning/pasivation.
Thanks again.
Great site can lose hours here.

steve bailey [returning]
- wiltshire united kingdom

stellar solutions banner

March 2019

A. Hi Steve. Thanks. You can certainly try citric acid passivation before the polishing.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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