Welding Tips and Tricks

A eutectic plate off a charter boat came in for repair with a refrigerant leak. I'm not a fan of these repairs because there is a fair bit of science in the design and construction of eutectic plates, but they always seem to be made by well meaning handy-men who have not got a clue about the science and invariably I have to fix up all the bad workmanship as well as effecting the repair which drives the price up and ends up with an unhappy customer who also does not understand the science.

Anyway here it is:
Ugly little beasty ain't it. Yup, done by a handy-man. You can tell straight away by looking at it. The s/s casing is bulged because it was not sealed and therefore no vacuum pulled to allow for expansion. What fittings are soldered to the casing has been done with inferior grade silver and has not taken. One fitting has fallen off and is not present. This is going to be fun.

So pressure testing the internal pipe coil shows a leak at the one soldered casing joint:
Someone has had a go repairing this already and failed. I know why, the leak is inside and not repairable from outside. So I must cut a piece out of the casing and take a look:
Yup, there it is. Done by a moron who kinked the pipe right where it penetrates the casing. Who would do that? (Unfortunately I nicked the pipe with my cutting disc, no probs to solder it up though.)

So the next job is to cut it out and silver solder in a new piece (gas flushed of course!)
Next step is to weld the cut-out back in, and solder the pipes to the casing and solder in a new access valve. Then pressure test the case (5-10psi will do it) to confirm it will hold a vacuum.
Nope. Here is a leak in the original edge weld. Tig that up and retest. Poof - off flies the last remaining original soldered fitting. Oh boy oh boy.
So I decide to tig in a 1/2" s/s socket which will be the fill point. Access is very poor, special equipment is needed here. Guess what I bought at the weldmongerstore as soon as it came available? I like my gadgets but never thought I would need this for a long time but I had to have it anyway.
Used a 26mm stick out (tad over 1") and welded up great. Better than the cutout weld - I had alot of trouble with all the crap coming though from the inside even though I purged. Not pretty but holds pressure and vacuum.
Repair complete. Filled it nine tenths full with 25% propylene glycol and vacuumed it to pull the sides in a little an provide freeze expansion room. Took it out to the boat and did all the fridgy stuff to install and get it going.

All good. Hope the customer does not argue the bill.

Nice work.

What does that thing do?

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weldin mike 27 wrote:What does that thing do?

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Fridgy stuff bro, can't you read?!

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Vacuum-y expandy stuff

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Eutectic plates are have an internal cooling coil and are filled with fluid that freezes at different temperatures below 0*C depending whether its a fridge or freezer box. Water ice melts at 0C so food in the ice box with be 6C or above. If your eutectic fl I don't melts at say minus 3C your food will be at 3C. Used in marine and transport while engine is running to freeze the plate fluid and when engine is off you have frozen plates to maintain food temperature.

Awesome, thanks for that

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What refrigerat do you use?

Many are suitable. this one is an R22 system.

Just one plate or several on a system? How long does a plate set last with the freeze thaw cycles?

You can have as many plates as the refrigeration system is designed for. On a typical pleasure cruiser you might find one fridge and one freezer with one plate in each. It is common to find a belt driven compressor on the main engine with a water cooled condenser. Sometimes there are two compressors, one belt drive off the main engine (donk) and an electric compressor to run off shore power or an on-board genset (auxiliary).
This particular boat is larger being a charter boat. It has two main deck bar fridges with two plates each and one galley fridge with two plates, all on the one system with a 240V air cooled compressor set. It is capable of running from shore power and an on board auxiliary. Mostly on their river ya-hoo party cruises ( which last for a 2-4hrs) they leave the compressor off and rely on the plates to continue cooling off the beer stock (and the odd bottle of lemonade or sherry for the sheilas). I think these plates can keep the fridges cold for a day.

Pull down run time varies with system design and cooling capacity, hot stock entry and door opening frequency. Typically between 1/2hr and 4hrs.