What are the exhaust manifolds and ducts made of?
I am asking because these things turn red hot in normal operation (even more so on turbo engines) and from my information it seems that the material is steel.
I was wondering if this is true and how come.
Our O200 ones are some form of stainless steel. Repairable by a suitable welder. I think non-stainless steel is used for some O200 exhausts. Much cheaper, but much shorter life.
The ones I am familiar with (Socata engines) are stainless steel, and the GT aircraft (roughly after year 2000) use inconel [ only partly – this is a lie by Socata!! ] which is an expensive and difficult to weld high temperature alloy.
Stainless exhausts last maybe the 2k hrs before they need parts remanufactured, though this seems to vary. Inconel exhausts seem to last for ever; one Socata guy said that he has never seen one fail.
Exhaust rebuilders in the USA can repair inconel ones but one high profile guy (may have been Acorn Welding) said he doesn’t like them because the material is so expensive and owners don’t want to pay for it.
Thanks guys. After investigating I can say that mine is stainless steel and this is not good enough for turbocharged engines.
The shop says that cracks and welding are normal maintenance events.
I was told by an expert today that Inconel is good for 1400 degrees C whereas stainless steel struggles at 600 which is the normal operating temp of the exhaust line. (Gases are much hotter at 800-900 C).
Exhaust rebuilders in the USA can repair inconel ones but one high profile guy (may have been Acord Welding) said he doesn’t like them because the material is so expensive and owners don’t want to pay for it.
this is a good shop in france for exhausts in inconelhttps://www.echappement-chabord.fr/
inconel is very light and incredible hard to cut (when you weld it, you should purge the tubes so the inside of the weld is flush – (in compare of lifing, when we started to use incolnel on F1 engines in the 1980s vs stainless exhausts they lasted about 3 to 4 times longer and where much lighter)
more about inconel exhausts
https://www.goodfabs.com/our-history (a former very keen aviator with helicopters)
highly recommended for repairs etc.
“Stainless” steel covers a vast range of metalurgies; austenitic, martensitic, ferritic, with different chemical compositions and properties of strength, elongation, corrosion resistance, expansion etc.
My RV uses 321 tubing and 304 flanges welded in an inert gas environment. I have had issues with cracking at the flange weld in the HAZ. That was rectified by adding additional gussets at the joint. The cracking was probably exacerbated by the slip and ball joints being partially seized not allowing compliance for engine movement during starting.
The metal itself has shown no real deterioration despite having several EGT probes burn out.
When I was getting my exhaust stubs made for my Turbulent Iooked into getting stainless steel ones and was told that they tended to fail by welds cracking rather than erosion by hot gases, so they often only lasted a little longer and cost an order of magnitude more. The ones on offer were welded by hand so perhaps something industrially produced would be more dependable. I think I paid about £60 for my whole exhaust system so the argument went that it was better simply to replace it on a regular basis as this is not a difficult job.
I wondered whether it was possible to get Titanium exhaust pipes and google shows that it is… Also wondered whether anybody has ever tried using thinner liners made out of Inconel/Titanium/whatever with relatively weldable steel outer liners. As I understand it the problem is a combination of high temperature and corrosive gases, and as this combination is only present on the inside presumably a relatively thin layer of Inconel might suffice to protect a thiner lighter steel exhaust.
I generally presume that for an application like this everything halfway sensible has already been tried, so if this is not commonly done then it must not work for some reason?
Very useful post, Peter_Paul, since Socata never revealed who they used for the GT exhausts It could well be the company you mention.
Whether that company does repairs on exhausts for Socata is a very different question though; in line with standard Socata / industry practice they may be prohibited from serving Socata owners directly.
if this is not commonly done then it must not work for some reason?
True, though the reason could also be simple laziness or stupidity Most people keep their plane a relatively short time, and sell it when too many things start to go wrong. It is not an environment which supports long term reliable solutions, especially as certification in GA is absolutely disconnected from any demonstration of reliability. And turbo owners are accustomed to throwing away cylinders (at $1000 each, plus labour) every 1000hrs or less, and throwing away bits of exhausts is “just normal” – many posts here from turbo owners saying this much.
Stainless exhausts last maybe the 2k hrs before they need parts remanufactured
Here is a pic of the L/H exhaust on the1984 Bonanza A36 that I used to own. This part failed at around 1700hrs from new and 19 years old.
About 100 hours earlier I had exchanged the engine (IO550B) for a factory new engine and cannot understand why for the little additional expense the engineers did not suggest changing both manifolds at the same time.
The warning signs were there prior to the failure, on closing the throttle there was a popping noise, much like a leaking car exhaust and I should have checked.
The hot gases from the hole burnt the area around the ‘Gills’ on the side of the front cowling and narrowly missed the fuel line which could have been catastrophic.
So the moral of the story …. dont mess with cracks in the exhaust system and any popping noises, investigate it …