Deformed copper pipe

[alpha]

Hi, would anyone know why a copper tube would cave in on itself? We just looked at a blast chiller not working and after allot of head scratching and poking we have just found that part of the suction tube (5/8) out of the evaporator has, imploded, caved in on itself blocking flow. I have seen this once before on a transport fridge where all the u tubes caved in on themselves on the evaporator and wondered what caused it, and just having come across it again in 12years or so I though it time to find some causes perhaps.

The only thing I can put it down to, or think of is heavy ice formation squashing bits of tube, any further thoughts?

[taz24]

The only thing I can put it down to, or think of is heavy ice formation squashing bits of tube, any further thoughts?

I have seen it damaged (it damages easily) and also I have seen it crushed. When it was crushed it was allways in the area of the evap and I always put it down to ice build up causeing the damage.

Cheers taz

[Argus]

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It’s almost certainly the expansion of ice.

You will come across it on shell and tube water chillers where the evaporator tube is exposed to prolonged operation at temperatures close to freezing point, though it often goes unnoticed because you have to dismantle the tube plates to expose it. It’s less common on air side evaporators because the ice formation is gradual, but not impossibility.

Additionally, your evaporator is definitely suspect in terms of pressure strength due to pipe distortion – you should consider changing it after finding a fix for the freezing and crushing problems.

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[US Iceman]

I have seen this before on chillers. It's caused by ice formation. Every case I have seen the tubes look like they have been hit repeatedly by a ball peen hammer (the round end).

[Dan]

Yes, it is ice. But not simply ice. Most commonly the result of incomplete defrosting, the interior ice nearest the tube melts, filling the volume once held by the less dense ice and refreezing during refrigeration. Over and over again, this compresses the tubing. What I notice most is the tube becoming a u-shape with the compression occurring at the top. I have seen this in gas defrost systems only, although I imagine it is possible in other applications.

[Argus]

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It looks as if the consensus is ice. So, apart from looking closely at the defrost regime of this machine and as I notice you are in the UK, may I also suggest a safety evaluation of this evaporator or pipe and the whole system?

The reason is this; it is almost certainly weakened at this point and possibly at other points within the evaporator that you may not be able to see. You don’t mention the size of this machine, but if it within the remit of the PED, it will certainly fail an evaluation given this scenario. (PED is a legal requirement in the UK and the EU for pressure equipment). Next, it will be a requirement of your customer’s insurance that the equipment is good order from a safety aspect.

Even if it is not covered by the PED, due to the size limits of its pressure/volume containment, clearly you have identified a problem. The very least you can do is to carry out a written safety assessment and if you have any doubts, recommend that the entire coil is replaced.
Some organisations would insist that it is now taken out of service and isolated until it is repaired in any case.

This may sound drastic and your customer may not like it, but it’s the correct course of action. Even at low pressures there are now burst hazards and you have a duty of care to alert your customer.

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[monkey spanners]

Also with a circuit resticted by the squashed pipe there may not be enough gas velocity to bring the oil back and over time the compressor level may drop too low. Have had this happen on a couple of milk cooling tanks.

Jon

[Brian_UK]

Just like to add that this problem can also occur with heat pump external coils.

I have had occasions where the pipe has been concaved due to incomplete defrosting of the bottom section of the coil. Also, I suppose, if the drain off is poor then a pool of water remains surrounding the bottom tubes of the coil which then freeze up after the defrost cycle.

[Dan]

I have had occasions where the pipe has been concaved due to incomplete defrosting of the bottom section of the coil. Also, I suppose, if the Drain off is poor then a pool of water remains surrounding the bottom tubes of the coil which then freeze up after the Defrost cycle.

That's exactly where I have seen it as well, Brian. It was common on large industrial Krack coils years ago. Wish I could remember the solution the manufacturer came up with.

[US Iceman]

It was common on large industrial Krack coils years ago. Wish I could remember the solution the manufacturer came up with.

Part of this may have been due to the coil circuiting. If the circuits cannot drain during defrost some of the condensate lays in the lower tubes. The liquid tends to insulate the tubes which prevents heating, and subsequently lack of defrost.

Another case would be if the defrost time is too short. Then it does exactly what you were saying before Dan.