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Old 03-01-2021, 12:49 PM   #1
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Heat Exchanger Tube Repair?

I had my heat exchangers pulled this year for a pressure check. There had been some increased coolant usage on one engine over the other on end of year cruise in 2020.

When tested, one HX was fine and one had a hole in a tube (1 of 15 tubes). I was presented with options to have a new HX fabricated (engines are DD 8.2T's and parts not easy to find) or to have the offending tube plugged. The new fabrication cost was 4.5X the repair.

Plugging the tube will leave me with 14/15 tubes (a loss of 6.7% heat transfer efficiency?). I am deciding to do the repair based on the following assumptions... 1) The HX could have been designed without some factor of safety for heat transfer efficiency. 2) I boat exclusively in the PNW and the raw water is much colder than in other climates (probably 20-30 degF delta T from FL?) that I assume they need to design boat systems to be able to handle.

Am I way off base with my thinking or should this be fine as long as I keep an eye on the running temperatures?
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Old 03-01-2021, 02:05 PM   #2
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Your thinking is reasonable (I am a retired ChemE). But I am surprised that you can't find a replacement at a reasonable price. Often they were generics made by Sen-Dure, Lenco and Mr Cool. Buy the ones with cupro nickel tubes which last much longer than copper.

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Old 03-01-2021, 02:36 PM   #3
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Originally Posted by RentonRiggos View Post
I had my heat exchangers pulled this year for a pressure check. There had been some increased coolant usage on one engine over the other on end of year cruise in 2020.

When tested, one HX was fine and one had a hole in a tube (1 of 15 tubes). I was presented with options to have a new HX fabricated (engines are DD 8.2T's and parts not easy to find) or to have the offending tube plugged. The new fabrication cost was 4.5X the repair.

Plugging the tube will leave me with 14/15 tubes (a loss of 6.7% heat transfer efficiency?). I am deciding to do the repair based on the following assumptions... 1) The HX could have been designed without some factor of safety for heat transfer efficiency. 2) I boat exclusively in the PNW and the raw water is much colder than in other climates (probably 20-30 degF delta T from FL?) that I assume they need to design boat systems to be able to handle.

Am I way off base with my thinking or should this be fine as long as I keep an eye on the running temperatures?
I think you are relatively safe.

Most HXs are built with 10% overcapacity at design parameters.

Your inlet temperature is, as you say, probably lower than design temperature.

Would it not be possible to cut out and stab in a new tube?

Just an idea.

I have written dozens of repair procedures, plugging procedures, and created a database for required plugs and mapped plugged heat exchangers at my workplace.

But honestly, it has little relevance to our teeny tiny unregulated heat exchangers on our boats cooling systems.
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Old 03-01-2021, 03:21 PM   #4
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Plug it and forget it.
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Old 03-01-2021, 03:22 PM   #5
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If I bought a new one I was going to go cupro-nickel. The initial quote was for almost $2000 for the heat exchanger. I was a little surprised at the plugging costs but At least that includes the testing, cleaning and etc. as well. If both had leaked I would have figured an age related issue (26 years) and probably replaced them both (ouch). Given it was just one of them that was leaking, I was hoping to get by with the repair. I am glad my reasoning is standing up so far.
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Old 03-01-2021, 03:41 PM   #6
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My question is what caused the hole and how close are any of the other tubes to having holes or leaking? Depending on intended length of ownership or till repower, might impact my decision. I would probably plug it also, but not knowing if and when the next one might fail, would nag at me.

Ted
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Old 03-01-2021, 03:50 PM   #7
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Try orcamarine.com in Bellingham. Should have them.
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Old 03-01-2021, 05:25 PM   #8
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Try orcamarine.com in Bellingham. Should have them.
Thank you for the information. They have a item # for the HX for my engines and I have reached out to them to see what the pricing is.

On an unrelated note... Is that a Great Harbour in your profile pic? I have wondered how the hull shape and windage do specifically in the PNW.
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Old 03-01-2021, 06:14 PM   #9
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Plugging will buy you several more years, maybe. Mr Cool lists CuNi exchanger at $1267 plus shipping. Put one in your capital improvement list.
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Old 03-01-2021, 06:57 PM   #10
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My question is what caused the hole and how close are any of the other tubes to having holes or leaking? Depending on intended length of ownership or till repower, might impact my decision. I would probably plug it also, but not knowing if and when the next one might fail, would nag at me.
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My guess is the other tubes aren't far behind.
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Old 03-01-2021, 07:27 PM   #11
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My guess is the other tubes aren't far behind.
My experience is that consistent degradation across a heat exchanger is the exception, not the rule.

Although if galvanic corrosion is the failure mechanism, you may very well be correct.
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Old 03-01-2021, 07:37 PM   #12
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Buy a new one if you are going to keep the boat. I take it the engines are most likely older. So with that all of the heat exchanger tubes may have have several hours on them.
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Old 03-01-2021, 10:30 PM   #13
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My question is what caused the hole and how close are any of the other tubes to having holes or leaking? Depending on intended length of ownership or till repower, might impact my decision. I would probably plug it also, but not knowing if and when the next one might fail, would nag at me.

Ted
Definitely wondering what caused the one hole. Plugging the tube will cause a nagging concern but the cost of the replacement (so far) has exceeded the opportunity cost of the nagging concern.
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Old 03-01-2021, 10:38 PM   #14
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Buy a new one if you are going to keep the boat. I take it the engines are most likely older. So with that all of the heat exchanger tubes may have have several hours on them.
I am planning on keeping the boat for a few years at least. The engines are old but not many hours (26 years and 1200ish hours) so the HX are newer than their calendar age. For 23 of the 26 years it has been docked in freshwater so there has been even less saltwater aging than normal as it gets as good flush between cruises.

If another tube goes (especially in other HX) I would probably replace both HX.
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Old 03-01-2021, 10:48 PM   #15
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Thanks. I had not seen that one. Significantly better than the pricing so far... HX are definitely on the capital improvement list. Just not sure of the timing yet.
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Old 03-02-2021, 08:51 AM   #16
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Plug it and forget it.

This. I would not fret about any loss of efficiency at this point. I would just monitor for additional problems in the future.
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Old 03-02-2021, 10:05 AM   #17
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Plugging should be easy. There isnt much pressure maybe 15 psi depending on cap.

Squire it full of 5200 or epoxy after a thorough inside cleaning. But as Lepke said above dont be surprised on other tubes fail.
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Old 03-02-2021, 10:47 AM   #18
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My guess is the other tubes aren't far behind.
This ^
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Old 03-02-2021, 10:51 AM   #19
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Plugging should be easy. There isnt much pressure maybe 15 psi depending on cap.

Squire it full of 5200 or epoxy after a thorough inside cleaning. But as Lepke said above dont be surprised on other tubes fail.
Wondering if you could straight thread tap both ends and put in screws, maybe with a little sealant.

Ted
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Old 03-02-2021, 11:08 AM   #20
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What does it look like? Is it hanging off the engine or incorporated like an aftercooler? Lots of options for heat exchangers, don't be afraid to look at alternative solutions like plate coolers?
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