Multiple leaks on capillary tube and suction lines

[keepmecool]

Hi Forum

We are a domestic fridge manufacturer and we have experienced a strange problem on a model of our chest freezer.

The capillary tube and the suction line (also copper) are foamed-in with heat shrink around to keep the pipes in contact (for heat exchange). In this section (under the heat shrink tube), there have appeared many leaks in both the capillary tube as well as the copper suction line. The leaks become worse with time until it is not possible to re-charge the system.

Can you suggest the cause of this?

[Clk320_Greg]

You shouldnt be rechargeing a system with any leaks, however small.

[desA]

Galvanic corrosion?
Chemical, pitting corrosion - accelerated under wrap?
Poor copper tube.

Go & see my friend at Copper Tube Africa - Dave Machet - he'll see you right with good copper, I'm sure.

[keepmecool]

Thanks desA (and Greg)

The service technicians have reported that they are not able to charge the system, not us.

desA, I also suspected Galvanic corrosion, but between copper and copper?

[Brian_UK]

The question must be - "How clean was the pipework before it was shrink wrapped?"

Any form of dirt in there will create problems.

[Peter_1]

You shouldnt be rechargeing a system with any leaks, however small.

This isn't an answer to the question

[Peter_1]

What brand of copper do you use? Copper is not always copper.

[keepmecool]

Peter and Brian

The copper is as clean as it comes from the coil, handled by human hands that may or may not be clean after touching food, dirty, etc. We don't assemble wearing gloves nor do we do any pre-cleaning of our copper tubing (is this bad practice not to pre-clean?). So I guess it is moderately clean but I wouldn't put my tounge anywhere near it! Why? Could dirt aggrivate the problem/cause the problem.

Peter, I am not exactly sure on Brand? I presume you are referring to the grade of copper? I am interested in what you say 'copper not always copper'. Could you expand on this?

[Peter_1]

I've seen copper evaporators which rusted, so there must be some sort of steel in it.
The heatshrink you use, is this with glue in it? Perhaps this is reacting with it although I use this practice very often myself.

Rubbing against each other is almost impossible.
All the causes given by DesA are possible.

In such a case - I have one for the moment - I'm sending these pieces to the corrosion lab of the University of Gent not so far from me.
In attachment a Stainless vessel 316 with pure water in it, heated t o+/- 35°C, installed 11 months ago.! (in BW, color file is too big) IN most cases, they can find the cause but it cost of course something.

Most cap tubes I've seen were welded together with the suction with tin-alloy. Perhaps this tin acts as a sacrifying anode

Anyhow, you must find the cause of this problem because your reputation will fall with this. Did you had this problems never in the past? Is this a new product? Have you changed recently from copper supplier?

[monkey spanners]

Peter, do they use hypochlorite anywhere near that stainless vessel?

Does it look a bit like the stainless has got woodworm?

[desA]

To the OP:
Check for contamination in your assembly system.
As mentioned - chemicals in the wrap / poor grade copper (use oxygen-free);
Be careful of tin-copper solders - they can eat copper.
***Stray electrical current, passing through the assembly - earthing strap is where?***
Do you wrap the assembly in cork tape?



[I think that Peter's problem lies in poor fabrication practice. The stainless shop has mild steel (carbon steel) somewhere in their system. Perhaps the grinder disc, wire brush. It's on the weld stop/starts - from the look of it.
What about chlorides? Stress-corrosion - but, this would generally show up as porosity, or surface cracks]

[Peter_1]

Peter, do they use hypochlorite anywhere near that stainless vessel?

Does it look a bit like the stainless has got woodworm?

No water was tested for several elements and chlorides were teh most important tested.

[keepmecool]

desA

We don't wrap in cork tape. I have not heard of this. Where / When is it common to use and for what reason?

I am going to investigate electrical current. I know that it can have a big effect if the materials have a significant potential difference (e.g. copper and aluminum), but I am still puzzled how this can be the case with copper to copper contact!? Plus the fact that this section is inside the foam so there is hardly moisture for galvanic effect to take place?

I also will look at what chemicals are in the heat shrink tube and maybe this is the culprit.

[Peter_1]

Can you make some close-up pictures of the problem area? I can show those perhaps once to the Professor and ask his opinion. Try also to find the specs of the heatshrink.
I doubt galvanic corrosion because you used copper on copper although like I said, even in copper you can have differences in material.

This is a little bit the same problem http://www.refrigeration-engineer.co...ead.php?t=7555
http://www.refrigeration-engineer.co...3&d=1175680488

[desA]

desA
We don't wrap in cork tape. I have not heard of this. Where / When is it common to use and for what reason?

Pipe insulating Everseal - Cork Tape - Eastern Polymer Industry Co., Ltd, Thailand.

Must be a copy of someone's product out there. Seen it on Galantz a/c outdoor units - capillary.

I am going to investigate electrical current. I know that it can have a big effect if the materials have a significant potential difference (e.g. copper and aluminum), but I am still puzzled how this can be the case with copper to copper contact!? Plus the fact that this section is inside the foam so there is hardly moisture for galvanic effect to take place?

There are two types of electrical corrosion to consider:
1. Galvanic corrosion:
Local corrosion cell, in the presence of water. Slight material differences may be enough to make one sacrificial to the other.
2. Stray electrical current:
Small leakage current from compressor, or wiring, through the troubled area, towards the earth, or some other electrical sink/drain whatever.

Number 2 is a difficult one to locate. Find your power sources, & locate your earths - what lies roughly in-between?
Try attaching an earthing strap to each line to bleed off stray current - if it exists - observe the effect.

I also will look at what chemicals are in the heat shrink tube and maybe this is the culprit.

Will be interesting.

Could very well be dud copper tube, all along. Porous.

[oldesky]

Has anyone thought about the possibility of the porosity being caused from the inside as in the internal system such as system acidity? Or the possibility of galvanic corrosion being caused by this combined with poor quality copper,Aluminium deposits from such thinks as con rods etc. Moisture plus heat plus poe oil a good catylist for acidification.

[Peter_1]

....Or the possibility of galvanic corrosion being caused by this ....

Then you have chemical corrosion but not galvanic. Galvanic can only exist with 2 different materials.

[keepmecool]

Thank you for all your relevant and helpful replies.

I will try to put some photographs up of the leaky copper pipe and capillary.

The electrical corrosion is going to be a difficult one to diagnose. I will make an investigation and revert back to the forum soon.

Oldesky: The internal corrosion was very much considered but we eliminated that due to the fact that it would most likely be in parts of the system outside of the heat shrink area.

My main focus now will be on what else might be in the copper that can cause this corrosion which might be compounded with stray electrical currents.

[desA]

Send samples to Natal University (old name), Mechanical Eng dept. Let them have a go.

Alternatively CSIR.

[oldesky]

I was refering to either or, when I was refering to electrically or chemically induced corrosion. I thought it was clear but obviously not. I think, however, it would be better to concentrate on the problem rather than making pedantic corrections on something so obvious.

[Peter_1]

... I thought it was clear but obviously not. ...

Indeed, if I re-read your phrase, it still remains confusing for me but English is also not my mother tongue you know.

Blijkbaar is hier iemand serieus op zijn tenen getrapt is much clearer for me but because it's written in Dutch.
But we're all focusing here on the problem, we just have to avoid misunderstandings.

[desA]

Help nie op 'n mens se toone te trap nie...

[Peter_1]

Da Sudafrikaans is tog so scoone vo leeze.

[desA]

^

[keepmecool]

Copper brand is Feinrohren. Peter_1: I am battling to get some close up photographs because a digital camera with 12x zoom cannot magnify it sufficiently. I need to get it photographed under a microscope and as soon as I find a place to get this done I will indeed post the pictures. Watch this space...

des_A: I am also trying the university of KZN via the mech. eng dept...

[desA]

des_A: I am also trying the university of KZN via the mech. eng dept...

Good one.

Also have a chat to Copper Tubes Africa - Dave Machet - in Jhb. He may also be able to direct you to good corrosion chemists.

Tell him the yarpie from Laos sent you...

[et0]

In such a case - I have one for the moment - I'm sending these pieces to the corrosion lab of the University of Gent not so far from me.
In attachment a Stainless vessel 316 with pure water in it, heated t o+/- 35°C, installed 11 months ago.!

By "pure" do you mean distilled or deionised water? It's well known that this will eat stainless, especially at elevated temperatures!

[Peter_1]

No, drinkable water flowing to every house here. Water is strict independent controlled different times/day.

[keepmecool]

Just an update for all interested...As it turns out, the heatshrink has bromine added as a flame retardant agent which tends to become dissassociated with heat or with time (maybe both) and forms bromic acid with condensation and this pits the copper tubes (both suction and cap tubes)...who would have thought!!

[desA]

Thanks for the feedback.

I think that Brian was on that train of thought.

Glad you've got it sorted out. Always simple, in the end.

[Peter_1]

This is a real valuable feedback for all of us and it rarely happens someone comes back here with the solution of the problem.
Thanks, we're again a little bit wiser.