Ovation Muffler durability/lifespan

[Mark89114]

So when I bought my Ovation 9 years ago from a gentleman in Canada, it had a fresh inspection, brought it down to the US for yet another inspection and DER signoff.  No major issues.

Approximately 4 months into ownership, brought to my local mechanic to show me how to change oil on an IO-550, during the oil change, he looked over the whole engine and found the left exhaust manifold was worn through, pulled it off and was inspecting the muffler and I guess the screens inside were loose, sent them off for repair.  (details are foggy, going on memory as I haven't dug up paperwork yet).   Little bit irked went through 2 annual inspections in 2 months and no exhaust damage was notated, but that is in the past.

Here I am at annual and we find the right manifold worn through, dutifully pull it off for repair and we peek inside the muffler and the screens are clearly all out of whack, should have taken a picture, but I didn't.  Attached is picture of exhaust manifold, thinking it is 25 years old.  Again will check the logbooks. 

My question is....what is life of a muffler?  I have had backfires vary rarely on some conditions where I can't see what I did to cause but I am guessing it caused the damage?  Or are these things just fragile?

 

[PT20J]

No idea if this is the issue with the exhaust pipe wearing out, but they can get stressed by thermal expansion if you don’t keep the slip joints lubed and free. 

The “screens” within the muffler are usually called flame tubes or flame cones and they don’t seem to last long. Mine were completely gone on my J after about 500 hrs. As long as they are not restricting the exhaust flow, many mechanics just ignore them.

[hypertech]

I'm struggling to visualize what we are looking at but that doesn't look normal to me.  Why is colors and textured like that?  Are those repairs or paint or something?

My oviation is a 2000.  Last year we noted exhaust leaking from the slip joints No cracks.  No pitting.  Certainly no worn through holes like that.  Just generally worn and not sealing tightly anymore.  Replaced the whole thing with an overhaul from AWI.

[A64Pilot]

Life is often maybe 2,000 hours on many, some less. I think how they are run often is part of it, I suspicion running LOP or peak shortens life as it’s higher temp.

Aircraft exhausts live a hard life, first they are designed to be lightweight above all, secondly we run at high power levels all the time when compared to Autos for example.

They are most often 300 Series SS.

Many do ignore flame tubes, those that do I believe are foolish, once the flame tube is gone nothing prevents the flame from impinging on the wall of the muffler possibly burning through and causing fires or putting high levels of CO in the cockpit. Replacing the tubes saves the muffler in my opinion, they lasted maybe 500 hours in my Maule but likely less, but Maule sold repair kits amounting to the muffler cap end and the flame tube, easy repair. I assume you have to fabricate them for a Mooney?

Exhaust systems in general are wear items like tires, they don’t last forever, seems Turbo aircraft are even harder on exhausts

[A64Pilot]

On 1/16/2025 at 11:00 AM, hypertech said:

I'm struggling to visualize what we are looking at but that doesn't look normal to me.  Why is colors and textured like that?  Are those repairs or paint or something?

My oviation is a 2000.  Last year we noted exhaust leaking from the slip joints No cracks.  No pitting.  Certainly no worn through holes like that.  Just generally worn and not sealing tightly anymore.  Replaced the whole thing with an overhaul from AWI.

Exhausts literally wear out, the pipes etc get thinner over time from flame erosion and when they get thin enough and hot enough the steel gets plastic and deforms and holes form, it’s not like modern autos who’s exhausts last the life of the car, what you are seeing is not uncommon and of course is a safety concern

[A64Pilot]

Twin Cessna. unsure of which one, but just normal cruise, look at the exhaust under the vents. This is not abnormal

 

Edited January 22 by A64Pilot

[Mark89114]

On 1/16/2025 at 10:00 AM, hypertech said:

I'm struggling to visualize what we are looking at but that doesn't look normal to me.  Why is colors and textured like that?  Are those repairs or paint or something?

My oviation is a 2000.  Last year we noted exhaust leaking from the slip joints No cracks.  No pitting.  Certainly no worn through holes like that.  Just generally worn and not sealing tightly anymore.  Replaced the whole thing with an overhaul from AWI.

This is the right hand exhaust manifold, the 90 degree turn heads directly into muffler.  I don't know how they bend these, but I suspect this is where the material is thinner as it was stretched on the outside radius.  I bend tube and we get wrinkles, our parts are no structural, non cosmetic so we don't worry about it.  

My question as just curiosity more than anything.  A64pilot just provided some more data points.  

[philiplane]

Many manufacturers list 1000 hours as the service life of a muffler. 

In reality, it can be much less depending on how the pilot manages EGT. Operating at or near peak reduces the metal's corrosion resistance.

 

"One of the key properties of any stainless steel alloy is its resistance to oxidation. High temperatures can compromise the the oxidation resistance of steel alloys, leading them to become rusted and weakening their structural integrity.

As stated by AZO Materials, grade 304 stainless steel possesses “good oxidation resistance in intermittent service to 870 °C and in continuous service to 925 °C.” However, they warn that “continuous use of 304 in the 425-860 °C range is not recommended if subsequent aqueous corrosion resistance is important.”

In other words, you can expose grade 304 alloy steel to temperatures of up to 1,598 °F for short periods of time without ill effect, and for extended periods of time in temperatures of up to 1,697 °F. However, this can compromise the corrosion resistance of the metal, making it more susceptible to corrosion damage from exposure to moisture.

As noted in an AK Steel data sheet on 304 stainless steel, the alloy reaches its melting point at the 2,550 °F – 2,650 °F (1399 °C – 1454 °C) range. Naturally, the closer the steel is to its melting point, the more tensile strength it loses."