Volvo Penta Heat Exchanger corrosion poll - please help

[MagicalArmchair]

My new boat has a VP D2-55A. During her first big annual service, I removed the exhaust elbow and found the flange between the heat exchanger and the exhaust elbow had been eaten away by galvanic corrosion and was leaking toxic gas into the boat. There is no insulation between the the steel of the elbow, and the aluminium of the heat exchanger, leaving it free to eat away at the heat exchanger until critical failure. Many other owners have had these fail, so I asked Volvo for a response.

Their response has somewhat irritated me:

We have analysed the information.
There are no known quality issues with this part.
The corrosion seems purely age-related.

Yes, the engine is old, but the rest of the engine is operating fine and if maintained would go on doing so. Lazy engineering putting aluminum directly next to steel with no insultation in a marine environment, that led to toxic gases being leaked into the cabin of my youngest child seems inexcusable? Am I being unfair in this? I expected a little more from Volvo - a recognition that putting metals together in this way was a bad idea, some kind of assurance in later engine they had done away with this, and there was now an insulator in there, like a composite gasket? All I got was the above...

All of those that have had this issue, can you please reply to this post with the name of your vessel, the age of the engine at failure, and the circumstances?

 

[pvb]

There is no insulation between the the steel of the elbow, and the aluminium of the heat exchanger, leaving it free to eat away at the heat exchanger until critical failure.

The parts diagram shows a gasket between them; doesn't this insulate?

 

[MagicalArmchair]

Nope, its a (stainless I think, so even more noble) metal gasket, here it is before I prised the little sucker off:

The fix is easy, a composite gasket between the two I should think would do it.

 

[RichardS]

I'm not familiar with this engine or the specific issue but the response is typical of manufacturers, I'm afraid.

We have had hundreds of threads on here where I have explained how I do something very different to that which is in the manual and the usual response from some is that one should always follow the manual.

I always reply that, on many issues, it has become clear to me over the last 50 years that manufacturers either do not have a clue what they are doing or are simply covering their arses.

Richard

 

[pvb]

The fix is easy, a composite gasket between the two I should think would do it.

Could you fit the gasket used on later versions of the engine? It looks more complicated, so could be composite, and it's rather more expensive.

EDIT: Have you asked Volspec about it? Here's the link to the parts website showing the later gasket - https://www.volvopentashop.com/volspec/en-GB/Details/PentaPartsCatalog/7744440_035

 

[MagicalArmchair]

It's even easier than that - Parts4Engines make one (Volvo Penta D2-55 Exhaust outlet gasket kit). If people knew about it, they could save themselves whole lot of bother, cost (a new heat exchanger costs £2.5k) and danger. I'm going to write it up into an article to warn people to be on the lookout - I'm astounded by Volvos response.

 

[rogerthebodger]

It one of the problems of design here days using incompatible materials and as long as it does not give a problem inside the guarantee period all is ok for the supplier.

The same happen with GRP rudders that have a metal shaft. They will leak and thus cause corrosion issues inside.

This comes up on here time after time, yet all the people who have GRP boats with GRP rudders see no issue because they are my by professional boat builders and the are hundreds in service.

On my current boat I have a stainless steel raw water cooled exhaust with a seperate raw water / fresh water heat exchanger. It cheaper to have both ase in one piece and it will last a time but will need attending to in too short a time.

My previous boat had a similar setup

Looking at the parts4engines site this comment struck me " This type of exhaust outlet frequently suffers from internal corrosion which can cause the engine to overheat. " so why does volvo not fix it. Answer too much income cones from spares. Same concept in ink jet printer cartridges

 

[VicS]

My new boat has a VP D2-55A. During her first big annual service, I removed the exhaust elbow and found the flange between the heat exchanger and the exhaust elbow had been eaten away by galvanic corrosion and was leaking toxic gas into the boat. There is no insulation between the the steel of the elbow, and the aluminium of the heat exchanger, leaving it free to eat away at the heat exchanger until critical failure. Many other owners have had these fail, so I asked Volvo for a response.

I do not understand how galvanic corrosion can occur at this point

You have two dissimilar alloys in contact with each other but galvanic corrosion requires them them to be immersed in, or at least in contact with, an electrolyte, namely seawater.

Why is seawater even reaching this point .

 

[MagicalArmchair]

Vic, quite right, the exhaust elbow is where the water is injected - north of this point there should be only exhaust gases (note there is no corrosion between the block and the heat exchanger for just that reason).

I was hoping the engineers (Volvo) would shed some light as to why this happens in so many instances and I had directly asked how this could be avoided (running the engine hard before turning it off for instance), however, all I received was the lazy response above. Could it be some form of back pressure pushing water the wrong way towards the flange in some instances? Water condensing on and around the flange? It has corroded from the inside out, so water is reaching that area somehow. Or worse, the exhaust chamber is compromised, and water it being pushed into it from either the fresh or raw water chambers of the exchanger?

The engineers are pressure testing both the raw and fresh water sides, so that will answer that question at least.

 

[rogerthebodger]

In your setup no raw water is surrounding the exhaust manifold it's only freshwater.

I would also be very surprised if any raw water injected into the exhaust elbow could blow back into the manifold unless the exhaust water filled up the water trap to an extent that when you stopped the engine it rose up the injection elbow to reach the manifold.

 

[MagicalArmchair]

To make sure this, is, indeed, galvanic corrosion (which in turn means water must be getting to this point of the elbow). Vic, you are a master of metals in general, would you agree the below is galvanic corrosion?

On taking off the elbow, we were left with this metal gasket:

On prising this away, I was left with this:

A quick attack with a wirebrush, left me with the remaining surface.

In my research I have seen many corroded in the same way - many much much worse.

 

[Bobc]

I believe that there is supposed to be a gasket there (not

I do not understand how galvanic corrosion can occur at this point

You have two dissimilar alloys in contact with each other but galvanic corrosion requires them them to be immersed in, or at least in contact with, an electrolyte, namely seawater.

Why is seawater even reaching this point .

Usually seawater vapour coming back up the exhaust due to lack of riser.

 

[rogerthebodger]

This looks like the head manifold interface and also looks like burning of the casting (aluminium) rather than corrosion as such.

 

[Beneteau381]

Vic, quite right, the exhaust elbow is where the water is injected - north of this point there should be only exhaust gases (note there is no corrosion between the block and the heat exchanger for just that reason).

I was hoping the engineers (Volvo) would shed some light as to why this happens in so many instances and I had directly asked how this could be avoided (running the engine hard before turning it off for instance), however, all I received was the lazy response above. Could it be some form of back pressure pushing water the wrong way towards the flange in some instances? Water condensing on and around the flange? It has corroded from the inside out, so water is reaching that area somehow. Or worse, the exhaust chamber is compromised, and water it being pushed into it from either the fresh or raw water chambers of the exchanger?

The engineers are pressure testing both the raw and fresh water sides, so that will answer that question at least.

Ive answered many questions about seawater getting back to the engine (or generator) The area affected is on the bottom of the flange where it could collect. Think about this, warm seawater sitting in the water trap, not to far away from that area. Engine shut down, a nice warm salty moist environment waiting to condense there. So why does it affect some and not others? Perhaps a look at the total exhaust system. Is it possible for sea water to splash back/ condense? Vetus do a good diagram in their catalogue showing best practice. Perhaps also the elbow should be part of a planned preventative maintenance program?

 

[MagicalArmchair]

Are we content this IS galvanic corrosion and not some other form of wear @Beneteau381, @pvb, @VicS ? @Rogershaw I would be surprised if it is 'burning of the casting' as that would not be the hottest part of that casting?

@Beneteau381 - your condensation theory I think is the most likely?

 

[Cantata]

Looks to me as though somehow a mix of seawater and exhaust acids has been sitting there.

 

[MagicalArmchair]

Vetus do a good diagram in their catalogue showing best practice. Perhaps also the elbow should be part of a planned preventative maintenance program?

Here it is: Wide collection Boat Exhaust systems at VETUS boat parts

The flange that corrodes away is this one here circled in green, and my Bavs set up is identical to the below:

So, hot engine, turned off, hot water vapour travels back up the exhaust, into the Heat Exchanger and condenses?

Two dissimilar metals, and now we have an electrolyte to complete the destructive equation?

Leading to:

Do we agree this is what's happening to cause this corrosion? If this is the case, what can be done to prevent it? I feel an email to Vetus coming on...

 

[rogerthebodger]

What puzzles me is that it it is condensation from the steam rising up the exhaust. The resultant condensate would mainly be fresh water and would be trapped and collect at the lowest point. So no corrosion at the top

Is there only condensation at the lowest point or is it at the top and sides as well.

If the water lock filled up to the point that sea water cane up to the flange that would cause galvanic corrosion.

The aluminium corrosion I had on my heat exchanger was due to sea water leaking out of the ra water tube stack the aluminum casing and was a white powderly material.

 

[lustyd]

Surely with the airvent so high the water will flow back up the exhast as is being discussed? This diagram will effectively create a water level inside the system 40cm higher than the heat exchanger. Unless I'm missing some other drain somewhere...

 

[pvb]

Surely with the airvent so high the water will flow back up the exhast as is being discussed? This diagram will effectively create a water level inside the system 40cm higher than the heat exchanger. Unless I'm missing some other drain somewhere...

No, the water in the injection line will flow down into the waterlock.