Corrision in evap

Once again an NH3 guy in trouble!

This plant has a 25,000 square foot processing area doing fruits and vegetables. We have a total of twelve upblast coils, Krack BTRC-316-DXF. (Copper) Refrigerant is 404a at forty-seven lbs suction. Room temp is thirty-six to-thirty-eight F. Three in a finished product cooler, three in a raw product cooler, and six in a process area. The coils in the FPC were replaced last year due to corrosion on the fins. Two others were replaced in production because of the epoxy electrofin coating coming off. None have been known to leak before.
Last week we had a leak which we traced down to a coil in production. After a long search we found a leak in a bottom tube. We lost three hundred of thirteen hundred pounds.
We valued the coil off and removed it this morning. When we got it down we discovered two leaks. The second was much worse than the first. I do not understand how we could have missed it.
To my knowledge none of the coils has leaked before. This one had two places where very small spots had corroded. Just a little crater with a pinhole at the bottom.
These two holes were on two tubes on the same circuit parallel to each other, three feet apart.
Because of the fins we cannot see the tubes but I see little bits of green in between the fins. We have repaired the tubes and will let it sit under pressure over the weekend.
I am surprised that both leaks occurred close together in the same circuit and at the same time. Could a stray electrical current be causing this? Any ideas would be welcome.

Hi NH3LVR.
Sounds like an expensive problem. Generally if cathodic corrosion, you will get pitting holes, possible started due acidic atmosphere from fruit and veg., With the green bits would point to chemical reaction as in copper oxide. Maybe the coil manufacturer has used re-cycled / resourced copper based tubing. With impurities that have reacted to atmospheric conditions.
Just thinking out load. magoo

Hi again NH3LVR.
as a check, try collecting some condensate water from the drain tray and check with a PH test meter. That will point you in what ever direction. For cathodic or chemical.
Magoo

Hi NH3LVR
You could also do some spot electrical checks for electrolysis with a DC Volt meter at say each end of the coil and to the aluminium then to earth. Also check for induced stray AC voltages. Then compare with another coil. These checks should be done whilst it is running with refrigerant flowing as high velocity fluid also generates electrical charge differential.

You may be on the correct path but just a thought while your still looking...I'm guessing that this is a wet wash room because you said it was a production room. If so take a look at the MSDS for your cleaning agents.. Many are great to use with stainless or galvi but hate copper..Just something to look at in room where caustic cleaners are used in food plants. Also check and see if ripping gases are used, same thing can happen...Good luck

Two things here. What is being stored in the room? Some salad makings are death on coils.

Next, if the coils are being washed down, what is the agent used for wash down.

I would get back with the folks at Krack with the information on the product stored and any wash down.

Ken

Lots of things near this. Green Vegetables, Onions, etc. They go over a scale right under the coil. We wash down with a coil cleaner and rinse. I do not recall the exact name of what we are using. But it is difficult to do often enough. The coils do develop a lot of condensate which washes the coil.

I wonder if a sacrificial anode would help like in some water heaters?