Exhaust water injection system - copper anti-siphon vent?

[Poignard]

Easy, and very cheap, to make one up from soldered copper pipe fittings.

But is it likely to last long when exposed to warm salt water?

 

[Twister_Ken]

Salt water + copper = green gunge.

 

[pete]

Well I used a gas combi boiler water heat exchanger (Worcester) to convert my 1GM10 to fresh water cooling, the raw water went through the copper side of the heat exchanger and collected the engines heat from from the fresh water (with antifreeze) side that was steel.
Didn't have a problem for the 10 years before I sold the boat.

 

[RichardS]

Salt water + copper = green gunge.

Didn't they used to "copper bottom" boats in the old days. That suggests a reasonable life.

Richard

 

[Twister_Ken]

Didn't they used to "copper bottom" boats in the old days. That suggests a reasonable life.

Richard

Yes, and it turned green.

 

[scottie]

What are the lovely polished pipes on the salt water side of larger marine engines traditionally may of ?

Copper

 

[Deleted member 36384]

Personally I would not use copper for this purpose. Last winter I replaced copper fresh water pipes and a copper gas line. Both were green with large chunks of flaking copper pealing off, the remainder of the copper pipe was brittle at the corroded areas. The pipes were in areas that had been dark and occasionally wet but more importantly, the areas got warmed by the engine; perhaps this had an effect on corroding the copper. There are probably better materials available to make the anti syphon pipe with.

 

[RichardS]

Yes, and it turned green.

and then lasted a 100 years rather than turning into "gunge"?

Richard

 

[Twister_Ken]

and then lasted a 100 years rather than turning into "gunge"?

Richard

No, they were infamous for corroding and then coming loose from their fixings and falling off leaving the wood exposed to gribble and stuff. Might have been electrolytic action between the copper and the fixings, though?

 

[vyv_cox]

My calorifier was totally made from copper with soldered fittings, with a seawater cooled engine circulating through it. It lasted about 20 years and was still going strong but I couldn't undo the fitting for an immersion heater, so I replaced it. I cut the old one open, everything looked good including the salt water coil.

 

[Poignard]

Thanks.

I suppose I might as well make a proper job of it and assemble it using silver solder.

 

[Pasarell]

No, they were infamous for corroding and then coming loose from their fixings and falling off leaving the wood exposed to gribble and stuff. Might have been electrolytic action between the copper and the fixings, though?

Copper sheeting used to come loose when it was fixed with iron nails. Most definitely not electrolytic action but galvanic as they were a little short of electricity at the time. When they used copper nails the problem largely went away.

Heat exchanger tubes on marine engines are usually made from marine grade copper nickel. That's 70:30 alloy with a couple of other small scale ingredients. It is very durable and resistant to hot salt water. Not sure how it would fare with the hot exhaust gases mixed in. Not very well I suspect!
70:30 copper nickel will erode about 20 microns in the first 2 years of immersion in flowing salt water but dropping to less than 3 microns per year subsequently. Elevated temperatures increase that a little but not too much, and in a boat engine the water only flows for a small amount of time
When immersed in salt water the "green gunge" is a very thin surface film. The gunge only forms with atmospheric exposure