Rusting exhaust bend?

[bbilly]

Hello,
The "exhaust bend" (where the exhaust fumes are mixed with sea water to cool) shows some external rust and corrosion right on the bend. When the mechanics looked over the engine they indicated that this was due to "galvanic corrosion" and estimated €800-900 to change the part! I went along to Volvo Penta and spoke to them and they said it was due to the heat and just needed cleaning up and painting. The engine is 7 years old but has only 100-200 hours (indicated by the mechanics), it's a VP TAMD22P (turbo charged diesel). Seems strange to me that this is galvanic corrosion as there are no other tell tales (anodes don't look much corroded) and the rest of the engine looks like new. Any opinions?

Thanks in advance

Will

<hr width=100% size=1>"Life is too important to take seriously."

 

[itsonlymoney]

Yeah it's called a "job creation scheme" /forums/images/icons/wink.gif
Ian

<hr width=100% size=1>Play the best game you can with the cards you've been dealt ! ! !

 

[ArthurWood]

I had a similar experience on an exhaust part on a petrol genset - I thought the rust was from the outside, but when it fell off, I realised it was from the inside. If I were you, I would remove and thoroughly inspect the part on the inside too.

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[robind]

I have a pair of Volvos and I am told that this is a common fault. In my case there was no support to the elbows and the threaded end nearest the Turbo flange ( in fact its fitted/ threaded into its own flange which apes the Turbos one, for mating ) has had the metal reduced so much by the thread cut that it causes a stress line and thus a weakness. With the vibration from the lack of support, the stress caused creep and then failure. Having now supported and replaced both elbows, and upon investigation of the old ones, I found a lot of corrosion adjacent to the weld where the inner is mated with the outer once again in the area of the threaded connection. It looks very much like it could be a design fault!

Regards

Rob



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[Deleted User YDKXO]

Hello Billy. Had the samething last year on a 6yr old Cat engine also on a boat in the Med. The exhaust elbow developed a crack in a corroded weld area causing the engine bay to fill with smoke. Bit worrying at the time. Actually, I was told, in my case, that the exhaust elbows are not supplied by the engine manufacturer but by the boat builder so maybe not fair to blame Volvo
I agree with Robind in that, at least in my case, the exhaust elbow was virtually unsupported which I'm sure cant help their longevity

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[gonfishing]

I agree with all that's been said, It sounds like good old fashioned corrosion, and design error and certainly not Galvanic corrosion which, as far as I am aware that only occurs below the water line, if I am wrong I know doubt I will be corrected!!

Julian

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[Nauti Fox]

Had that on mine and got a plate welded over the elbow for about £30..00.It had cracked all around the weld due to internal rust.The rusted part was a joint between mild steel and stainless.
Al

<hr width=100% size=1>No dear,the water goes in the other one.

 

[bbilly]

Thanks to everybody on the follow-up. The "elbow" is cast iron I think and the corrosion is right on the bend, there are no welds and no cracks (at least visibly). Also don't think it is being stressed by vibes as there is big rubber tube after the elbow so it has room to move. How come it is corroding in this specific point on the outside? The corrossion is a gorge 50mm long by 2 mm wide by 1mm deep in the casting following the flow of the exhaust? It doesn't leak so I can't figure out why the rust is there. Could the rust be caused by the effect of the heat being concentrated on this point internally which causes rust on the outside! It's also very close to the turbo, maybe the turbo also ejects some gasses into this part. As I said before the engine has had very little use and I am concerned that a failure at this point could fill up the engine compartment with hot seawater and fumes, however knowing VP spares costs and the "honesty" of the Italian mechanics (galvanic corrosion!!!!) I'll probably try and strip it down :-( and have a look on the inside. Is it worth repairng these bits like patching them up with a weld or should it be part of NORMAL maintenance as this has come up after such a short use of the engine?

Thanks a thou to everybody...and if you turn up in Rome we can go for a spin..

Regards

Will

<hr width=100% size=1>"Life is too important to take seriously."

 

[capsco]

I do not think you will gain anything by stripping it down, they are double skinned [water on outside, exaust gasses inside] so nothing will be visible.
price will be severall hundred pounds so a patch will do no harm to try

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