How to fix exhaust corrosion?

[BaldEagle]

Morning,

Annual coming up and a handful of annoying things to take care of this year.  This is a Powerflow exhaust on a J.  What's the recommended practice for treating cosmetic corrosion?  Thought I'd ask here before reaching out to the vendor.

[N201MKTurbo]

Is it rust or baked on crud?

[Utah20Gflyer]

Is the exhaust stainless steel or a ceramic coated material?  

[Pinecone]

Call PowerFlow.

[1980Mooney]

On 12/2/2024 at 11:42 PM, Utah20Gflyer said:

Is the exhaust stainless steel or a ceramic coated material?  

Per Powerflow

”The entire system is constructed of 321 grade stainless steel”

[EricJ]

3 minutes ago, 1980Mooney said:

Per Powerflow

”The entire system is constructed of 321 grade stainless steel”

Might try just some scotch brite on it.   Worst case it's pitted a bit, and it's probably worth checking the manual or any ICA from powerflow on whether there's any limitations on pit size/depth.   If not, going nuts with some scotch brite might getting it looking decent again.   You can get various scotch brite types and shapes suitable for use with a power tool like a drill, etc.   Sorting out the appropriate pad type(s) for the material will be worthwhile, too.

 

[Utah20Gflyer]

2 hours ago, 1980Mooney said:

Per Powerflow

”The entire system is constructed of 321 grade stainless steel”

Another option other than the scotch pad is a brass brush.  Its softer than the stainless so should do much to stainless steel but is harder than rust or carbon.  
 

To me it looks like maybe it’s oil that got on the exhaust and then got cooked into some carbon deposits but hard to say from a picture.   If it is rust then I would expect power flow to do something with it since stainless shouldn’t rust like that.  My standard stainless exhaust is 20+ years old and exhibits zero corrosion that looks like that.  It has turned a brass color which is I’m sure an oxidation reaction but no “rust”.  
 

long story short I would just go at it with something that isn’t going to hurt the stainless steel and see what happens.   That’s really the only way to determine what’s going on.  

[PT20J]

My exhaust pipe hanger was installed incorrectly and the pipe was rubbing on the cowl flap causing some minor abrasion. I cleaned it up with some scotchbrite but it left a visibly discolored spot that has not improved in 300 hours. Something about stainless and heat. Maybe there's a metallurgist here that can explain it. So, I think if you want it too look good you will need to polish the whole thing uniformly - or maybe a mild acid etch - after cleaning up whatever that is.

[Slick Nick]

What's that screwed / riveted into the end of the pipe?

[Gee Bee Aeroproducts]

This is why my tailpipes are made from Titanium 

 

Made to sample 

[Pinecone]

16 hours ago, Gee Bee Aeroproducts said:

This is why my tailpipes are made from Titanium 

 

Made to sample 

 

So you going to start making Mooney tailpipes?????

[MikeOH]

4 hours ago, Pinecone said:

So you going to start making Mooney tailpipes?????

I took his comment "Made to sample" as a 'yes' he can

[Gee Bee Aeroproducts]

No , The mooney market won’t bare the cost .

Some people want quality, others want cost.

There is only one engine mfg that ships there engines with Titanium exhaust.

 

Titanium is half the weight of stainless and is covered by a lifetime warranty as I use a particular grade and we have invested in the dies to stamp the clamps that join the muffler to tailpipe, the hardware is inconel .

I designed my exhaust stacks for my tbm700 using a 3d printer before final design to the die mfg also in CP2 titanium.

Cnc the flange was the easy part.

 

 

[MB65E]

What was the TBM material from Pratt?

I thought some stacks were inconel.

I’d be interested in a set for the pT6-25c

-Matt

[Pinecone]

Hmm, I wonder ho much for a 252?  Not a complicated piece.

[1980Mooney]

On 12/2/2024 at 12:20 PM, BaldEagle said:

Morning,

Annual coming up and a handful of annoying things to take care of this year.  This is a Powerflow exhaust on a J.  What's the recommended practice for treating cosmetic corrosion?  Thought I'd ask here before reaching out to the vendor.

Have you inspected inside the pipe for internal corrosion?

Just curious - are you running LOP or ROP?

 

[A64Pilot]

A few comments, do NOT use any kind of ferrous steel, brillo pad, regular steel wire brush etc to clean stainless steel, it will imbed ferrous steel in the SS and that will rust.

Very often good grades of Stainless like 316 wire rigging on sailboats for example will appear to rust, but it’s from the steel tooling that was used that leaves steel behind that rusts.

The answer is to “passivite” the stainless, that is use an acid that removes the ferrous metal and voila the rust stops. I’ve not read tge article but think considering the source it’s probably pretty good, Most any piping is drawn through a steel die and that contaminates it, then any bending process is another way

https://www.mmsonline.com/articles/how-to-passivate-stainless-steel-parts.

I’ve had decent luck with believe it or not but Citric acid on a sailboat, but usually nitric acid is used, but that’s nasty stuff to put on parts that can’t be removed like on a boat.

The process is to remove the iron contaminate physically as much as possible, scratch brite on a die grinder is good, then passivate

Titanium isn’t as expensive as you may think, I had Allied Titanium in Washington I think make me grade 5 Titanium chain plates on my boat for not much more than the 304L ones Island Packet used.

Pic is one of eight chain plates made from Grade 5 Titanium, business card is just for scale

 

 

Edited December 6 by A64Pilot

[bigmo]

By no means a metal expert, but it looks as if the presence of the retention strap is causing or at least accelerating the rust (or whatever reaction that is). I know dissimilar metal reactions can be complex…but it looks awfully concentrated to that strap.

I have the exact Powerflow exhaust and my retention strap looks much different. Mine appears to be made from the same steel as they are both identical in how they have aged and colored with temp.

[BaldEagle]

On 12/6/2024 at 4:00 PM, bigmo said:

By no means a metal expert, but it looks as if the presence of the retention strap is causing or at least accelerating the rust (or whatever reaction that is). I know dissimilar metal reactions can be complex…but it looks awfully concentrated to that strap.

I have the exact Powerflow exhaust and my retention strap looks much different. Mine appears to be made from the same steel as they are both identical in how they have aged and colored with temp.

Interesting.  My Powerflow exhaust was installed by the previous owner, but I believe it was installed by the Powerflow folks at their facility in Fl.  I'll reach out to the vendor to see what they have to say.