Tale of the tailpipe....

[pagirard]

Hi everyone,

I developed a crack on the straight portion of the tailpipe of our '74 Mooney M20E a few weeks ago, the crack was small so we decided to patch it with this while we figured out how to repair/replace the tailpipe.

Fast forward to today and the crack opened up a lot:

 

and an hour later the straight section of the tailpipe fell of :

 

Some research later and after a lot of discussion with a very patient sales rep name Tim at AWI-AMI, we located the replacement part : https://awi-ami.com/a630056-501-mooney-m-20e-m-20f-tailpipe-m20-200-ball-rib.html

 

My questions are:

1. Is the tailpipe just old or are we operating the plane incorrectly ? I always lean 20 to 40deg LOP in cruise cross country but since we are both working on our instrument rating, we tend to fly the plane slow, rich (think 3 approaches in 1.5hr). I checked with a magnet and the tailpipe is indeed stainless so heat should be more a factor that corrosion.

2. Can we fly for the time being with no tailpipe ? Reading a thread on this forum I read that no more tailpipe falls into the category of major airplane and power plant modification

3. When we receive the part, can I swap it myself or does it need to be done and/or signed off  by and A&P or an IA ? there is a spring coupler between the muffler and the tailpipe so it looks pretty straightforward.

 

Thanks in advance for your help

Pierre

[carusoam]

Pierre,

 

you probably already know the answer…

Start working with the OH shops and get your exhaust system up to spec…

Flying with an inferior exhaust system has its fire and CO hazards…

If it is only the tail pipe, get it replaced…

Have your mechanic show you how to log it…

What does your CO meter tell you?

when one part of the exhaust system has fallen to bits… your mechanic would be wise to give the whole thing a once over…

PP thoughts only, not a mechanic…

Best regards,

-a-

[Boilermonkey]

ROP/LOP....for exhaust it is all about EGTs (and TITs in turbos).  

Cracks happen in exhausts over time influenced by hot hot you run the exhaust, vibration, environmental conditions, age, etc.

If the happen in the wrong place they can be fatal (CO or fire) if not dealt with quickly.

Good news is that they are straight forward to fix.

 

[N201MKTurbo]

2 hours ago, Boilermonkey said:

ROP/LOP....for exhaust it is all about EGTs (and TITs in turbos).  

 

Thats not completely true. LOP produces an oxidizing exhaust and ROP produces a reducing exhaust. They probably affect the 304 SS a little bit differently. I run my turbo engine LOP most of the time and haven’t noticed any rotting of the pipes. They get coated with lead bromide when you are LOP and carbon when you are ROP. I think both tend to passivate the SS.

I wonder how moisture plays into the equation? If you live in a humid and wet place the carbon or lead bromide may get saturated with water and help corrode the SS.

[pagirard]

1 hour ago, N201MKTurbo said:

Thats not completely true. LOP produces an oxidizing exhaust and ROP produces a reducing exhaust. They probably affect the 304 SS a little bit differently. I run my turbo engine LOP most of the time and haven’t noticed any rotting of the pipes. They get coated with lead bromide when you are LOP and carbon when you are ROP. I think both tend to passivate the SS.

I wonder how moisture plays into the equation? If you live in a humid and wet place the carbon or lead bromide may get saturated with water and help corrode the SS.

Guilty as charged - home airport is in Central Florida so high humidity all the time. it looks like in temp > 70degC

https://chemiday.com/en/reaction/3-1-0-9647

I'll look if either the lead(II) hydroxide-bromide or hydrogen bromide are corrosive to a Stainless Steel 312

Of course the big unknown for me if the condition the tail pipe was when we purchased the plane, it could have very well been corroded and we didn't notice.

 

Pierre

Edited May 19, 2022 by pagirard

[LANCECASPER]

On 5/18/2022 at 3:08 PM, pagirard said:

Hi everyone,

I developed a crack on the straight portion of the tailpipe of our '74 Mooney M20E a few weeks ago, the crack was small so we decided to patch it with this while we figured out how to repair/replace the tailpipe.

Fast forward to today and the crack opened up a lot:

 

and an hour later the straight section of the tailpipe fell of :

 

Some research later and after a lot of discussion with a very patient sales rep name Tim at AWI-AMI, we located the replacement part : https://awi-ami.com/a630056-501-mooney-m-20e-m-20f-tailpipe-m20-200-ball-rib.html

 

My questions are:

1. Is the tailpipe just old or are we operating the plane incorrectly ? I always lean 20 to 40deg LOP in cruise cross country but since we are both working on our instrument rating, we tend to fly the plane slow, rich (think 3 approaches in 1.5hr). I checked with a magnet and the tailpipe is indeed stainless so heat should be more a factor that corrosion.

2. Can we fly for the time being with no tailpipe ? Reading a thread on this forum I read that no more tailpipe falls into the category of major airplane and power plant modification

3. When we receive the part, can I swap it myself or does it need to be done and/or signed off  by and A&P or an IA ? there is a spring coupler between the muffler and the tailpipe so it looks pretty straightforward.

 

Thanks in advance for your help

Pierre

I'm glad you're ok. If the entire exhaust system hasn't been inspected I would do it now. If it's the same age, is it just as thin in places as this was?  Fire and CO poisoning are nothing to fool around with. I would be very suspect of the IA who signed off on the "repair" shown in that picture. This isn't a car and you can't pull over to the side of the road and call AAA if you have a problem. On your question #2, I wouldn’t think about flying it until the entire exhaust system has been carefully inspected by a qualified IA, let alone flying it without a necessary part of the exhaust system. You’ve chosen an amazing hobby, but also one of the most unforgiving if everything isn’t just right. Reading through NTSB accident reports is sobering and reminds me that every “i” needs to be dotted. The vast majority of these accidents are preventable.  When I decide I don’t want to pay so much attention to detail or I  can’t afford to have the airplane I fly maintained properly I’ll give up flying.

[DXB]

The tailpipe for some reason seems to be a common first point of failure - at least it was for me- way better that than a riser or the muffler.  Exhaust systems definitely have a finite lifespan - mine was long in the tooth (>20 years) when the tail pipe started to disintegrate. If the exhaust is old, I'd treat the tail pipe failure as a sentinel event and overhaul/replace the whole thing.  I replaced with a Powerflow, which uses heavier steel and supposedly has a longer service life when maintained correctly - then again it costs twice as much.

[Shadrach]

23 hours ago, Boilermonkey said:

ROP/LOP....for exhaust it is all about EGTs (and TITs in turbos).  

Cracks happen in exhausts over time influenced by hot hot you run the exhaust, vibration, environmental conditions, age, etc.

If the happen in the wrong place they can be fatal (CO or fire) if not dealt with quickly.

Good news is that they are straight forward to fix.

 

1) This has nothing to do with engine settings.

2) That section of the exhaust is far downstream and is significantly cooler than any of the exhaust pieces in the muffler…Again regardless of engine setting.

3) Agree that exhaust wear out overtime due to temperature and vibration.

[Shadrach]

That pipe should have never been wrapped, especially without stop drilling the crack first. That wouldn’t have made it any less “unairworthy” but it would’ve been better.  If there was not enough meat to weld the crack, the plane should’ve been grounded.  With the pipe complete, it could’ve been sent off to any number of exhaust shops to be duplicated. I agree with others that you should fully inspect the exhaust at this point

Edited May 21, 2022 by Shadrach

[EricJ]

I would suggest not flying it until you get the part replaced.   If nothing else, the CO flow will be a lot different and if more of it goes in the cabin it's not a great thing.

+1 that the wrap may have accelerated the failure.   Wraps keep heat in which has some benefits in some applications but the downside is usually accelerated wear and corrosion.   If there was an existing crack, it probably didn't do much to prevent that from propagating.

Kudos for finding a replacement part that is available.   That's a big hurdle right there.

That repair does not fall under owner maintenance, but if your A&P/IA is amenable to the idea you may be able to install it "supervised" and have them sign it off.

[Fly Boomer]

16 hours ago, Shadrach said:

Agree that exhaust wear out overtime due to temperature and vibration.

And possibly chemical erosion.

[Shadrach]

23 hours ago, Fly Boomer said:

And possibly chemical erosion.

Without question. I had the same piece fail about 18 years ago. It did not crack, it manifested as a hole on the outside of the radius. The failure was entirely due to corrosion and erosion. 

Edited May 21, 2022 by Shadrach

[slowflyin]

Airplanes tend to tell us what they need in soft whispers.  Yours seems to be yelling.     In all seriousness, inspect the entire exhaust system.  If all is well, you will have peace of mind.  If not, you could be avoiding a serious situation.  

[Guest]

Weakened old metal, the small crack was really quite large but missed and covered over. Then it fell off.

Clarence