Modification to Nanni N2.14 Exhaust Elbow

[BabaYaga]

It's possible that a plastic hosetail would suffice, though the very idea makes me rather nervous.

Trudesign fittings have a safe working temperature of up to 110 degrees C. Marine cooling water hose (at least the one I am using) has 120 degrees C. So I think plastic should be OK, especially if you have an exhaust temperature alarm, giving early warning.
On my 20 hp Beta I have monitored the temp on the elbow just after the injection point – around 30 degrees while the engine is running, rising to about 40 some minutes after engine shut down.

 

[JumbleDuck]

Update from the boat. Elbow now installed and seems to work well. I haven't applied Duralac yet, so for now it has PTFE take sealing and maybe insulating it a bit. She comes out next week for the winter so I'll review then.

Is it possible that the anode works in the damp environment of the elbow when the engine isn't running? Which is probably 99% of the time.
Or does the elbow dry out completely when the engine isn't running?
Is that different when the engine has been at its operating temperature verses a 10 minute idle?

Good questions. I don't think much will happen in damp air, because it doesn't conduct as well as liquid, but it would be interesting to know how much it dries in the residual heat. It seems that Nanni redesigned the elbow with the anode, so I presume - though nothing Tranona's comments - that they had some plan in mind.

Is it in good order internally? How long did it go before the failure? No reason, just curious to compare how ally compares to the life of my stainless Beta effort.

It looks Ok. I can't find my inspection camera, so I haven't checked in detail, but everything I can see or feel days fine. I would very much prefer stainless, though, and will look into having something fabricated in the future.

By the way, another oddity of the design is that clearance for the bottom fixing nuts is so absurdly tight that they use 11mm AF nuts on M8. One these had been replaced with 13mm AF, which couldn't be done up tight, so I have replaced the lot with 11mm brass - the originals are mild steel. Air-cooled VW specialists sell brass nuts that size, because that's what hold the carbs down. I had a camper van

My memory at fault. However, I do recall that the heat exchanger body is not aluminium like the Beta, which was one of the selling points of the Nanni. I don't think that anode does anything. The failure of your original spigot seems to have been dezincification which an anode won't prevent.

Seems to me the folks who design heat exchangers and elbows don't have a grasp of the issues involved. Volvos use aluminium for the exchanger bodies, but seem to be able to isolate the tube stack so don't have an anode. Then they spoil it all by using cast iron for the elbow with an integral spigot for the water injection. The iron inevitably corrodes and blocks with deposits from poor combustion and saltwater and the next thing is the mating face of the aluminium to iron corrodes. Sometimes can be repaired by welding, but otherwise £3k for a new HE!. Stainless elbow and an isolating gasket is the current fix, although not seen any reports on long term success.

There seems to be a curious reluctance in parts of the marine industry to use good materials. Bronze is not that more expensive than brass, and only a small part of the overall cost. Using bronze or even stainless for the original injection spigot might have added a quid to the first of a £3.5k engine ...

Trudesign fittings have a safe working temperature of up to 110 degrees C. Marine cooling water hose (at least the one I am using) has 120 degrees C. So I think plastic should be OK, especially if you have an exhaust temperature alarm, giving early warning.
On my 20 hp Beta I have monitored the temp on the elbow just after the injection point – around 30 degrees while the engine is running, rising to about 40 some minutes after engine shut down.

I'm thinking of fitting a flow indicator to the elbow inlet. Visual, probably, but an audible no flow or high temperature warning would be good too.

 

[JohnGC]

Good questions. I don't think much will happen in damp air, because it doesn't conduct as well as liquid, but it would be interesting to know how much it dries in the residual heat. It seems that Nanni redesigned the elbow with the anode, so I presume - though nothing Tranona's comments - that they had some plan in mind.

I was thinking of a film of liquid water on the surfaces rather than damp gas. But now you've got me wondering if the combustion products dissolve in the water and so create a more conductive solution than salt water. Note: my chemistry knowledge is best described as dreadful.

 

[Wing Mark]

I was thinking of a film of liquid water on the surfaces rather than damp gas. But now you've got me wondering if the combustion products dissolve in the water and so create a more conductive solution than salt water. Note: my chemistry knowledge is best described as dreadful.

I'd imagine as the salt water evaporates from the warm surface, it leaves a highly concentrated salt solution for a while?
There will also be other stuff in the seawater, calcium etc.
Maybe the ideal is a plating of some metal which bonds with the calcium to provide a useful coating?

Maybe what works well is more about years of industry knowledge than a bit of schoolboy chemistry?

 

[JumbleDuck]

For completeness, here is the best photo my phone can manage of the remains of the original spigot. The wall thickness of the section between hose tail and screw thread is 0.6mm.