Strange phenomena

[Peter_1]

http://www.coolandcomfortforum.be/viewtopic.php?t=53 hope this links works.
What can be the reason of this.
The holes you see is in the aluminum that is and expand fin over the copper tube.

[NoNickName]

Internal helically grooved pipe. Too much grooved and later bursted.

[Argus]

.

He might be right.....


.

[chillin out]

I have seen this loads of times, its only moisture getting under the coating , freezing and then bursting the coating (which is very thin anyway).

Copper pipes underneath remain intact.

Chillin

[lana]

I did not find anything in the link above. Just saw the picture by NoNickName.
I am in coil business but I have not seen anything like this before
Are the fins aluminum? or they are steel and dip galvanized.
If they are aluminum then after tube expansion there is no way that the moisture can get between fin collars and the tubes.
As Chilling Out said, if it is the coating then it is possible.

Cheers

[Peter_1]

I have seen this loads of times, its only moisture getting under the coating , freezing and then bursting the coating (which is very thin anyway).

Copper pipes underneath remain intact.

Chillin

Maybe right, but why then all at once?

[Peter_1]

Here are the pictures for those wgo can't open the link

[Peter_1]

Chillin, also the copper is leaking
Fins are aluminum
They hang there for several years
Brand Friga Bohn France (=Heatcraft)

[lana]

Dear Peter-1,

You are completely right to call it "Strange phenomena".

I have not seen anything like this. If moisture gets there and freezes then the rupture will not be like this.
What comes to my mind is :
1- This is like corrosion or something at certain points.
2- The alloy of the aluminum is not good.
3- The coating problem.

Cheers

[Peter_1]

Al the pinholes came at once, that's what's so strange.
This is of course the first time that this happens.

[Lowrider]

You wrote it's also in the copper pipes? Is it possible that the copper is not strong enough to withstand the pressure/temperature combination?

[lana]

You wrote it's also in the copper pipes? Is it possible that the copper is not strong enough to withstand the pressure/temperature combination?

I think it's imposible. Tubes can stand a lot of pressure.
Cheers

[Lowrider]

I think it's imposible. Tubes can stand a lot of pressure.
Cheers

That's like saying apples taste good!

If the walls are to thin and the temperature is low enough a little pressure is all it will take!

I've seen copper pipes burst under 1 bar of pressure!

[lana]

Hi Sanderth,

Copper tubes used in coil industry (Fin-tube) is usually 3/8" , 1/2 " , 5/8 " OD. The thinesst tube I have seen is 0.45mm thickness. You can see that they can stand a lot of pressure.
These tubes are used to make condenser coils which usually operate in the range of 16 to 22 bar (or more).
If you had a tube which ruptured under 1bar then, I think there was another problem which caused it NOT the pressure.
Cheers

[momo]

Was the evaporator (?) treated with inappropriate chemicals that by capillary action flowed under the aluminium to copper joint, then salt formation, water absorbtion, freeze and pop, pop, pop... even if cleaned off with water afterwards.
I think you mentioned the copper leaked and simultaneity of the occurance. I'm not a chemist but the first to go will be the aluminium (locally we suffer salty dust/spray a lot, but that usually first rots away the Al - even Daikin coatings suffer particle impact damage!)
A similarity could be: steel car rust, once the oxidisation action starts it spreads ramifications like a cancer under the paint (later sunlight holes appear in you van's roof! ) here it went radially between the materials then causing pin points AL-Cu weakening the pressure resistance.
Looking at the geometry the holes: the gentleman from Merate could also be right as to weaker points in the structure.

[The MG Pony]

I seen this tons of times it isn't strange or seldom. Stuff forming under the Alu, wether salt or moisture or Alu oxide the result is the same. With the coastal air I see it more on evaps but I do at times see it on condencers.

Iana, Rule one nothing is perect or 100% sealed, rule two see rule one. No matter what they decay and die, this is fact, so the name of the game is getting it to live as long as possible, so no shame in seing it happen to a coil no matter who made them.

[US Iceman]

I have been trying to look at these pictures Peter and have some problems trying to see what may have happened.

NoNickName has an interesting reason as the failure seems to have occurred over most of the tubes. Is this a DX evaporator?

I looked for a picture to describe what I think NoNickName was describing. (see below)


If the holes popped up in the tubing grooves, the holes would have followed the helix angle of the grooves. This is also the thinnest part of the tube.

I have seen coating failure before and it did not look like the pictures. This looks like some type of failure mechanism due to a sudden high pressure such as a hydrostatic pressure. Although I'm not sure what would have caused it.

Has anyone cut the tube apart to see where the small holes formed?

[nh3simman]

Hi Folks, I see you have been busy here.

If it was a pressure burst, there would be tears from the hoop stress.

If there was corrosion inside the copper tube and this caused a weakening, then the pressure would cause rupture at the stress point. But, once the pipe bursts, the pressure is gone and it cannot burst in so many sites at once.

Freeze damage can cause multiple breaks but the holes don't look like a freeze burst. These would look more like tears.

Frozen moisture under the coating would not cause the copper tubes to rupture.

I think that the damage is caused by surface corrosion on the outside. The only problem with this is the outward splayed out shape of the hole. Could be caused by escaping fluid under pressure.

[US Iceman]

Could be caused by escaping fluid under pressure.

That is similar to what I'm thinking may be the cause.

If the coil were liquid locked with cold refrigerant and isolated, then a very slight rise in temperature would generate a lot of pressure/stress extremely quickly and UNIFORMLY across the tube internal surfaces.

That would cause the miniature holes to splay outwards. The distribution of the holes around the helix may be due to manufacturing imperfections.

[Peter_1]

It's a colleague of mine who gave me this pictures.
It's indeed a DX evaporator
This is the one
http://www.friga-bohn.com/literature/gb/MR.pdf
It's also very strange for me. Al the ruptures seems to happen at once.
I notice that they have indeed an internal grooved structure.
So this can point us in the right direction.
Peter

[nh3simman]

If the coil were liquid locked with cold refrigerant and isolated, then a very slight rise in temperature would generate a lot of pressure/stress extremely quickly and UNIFORMLY across the tube internal surfaces.

That would cause the miniature holes to splay outwards. The distribution of the holes around the helix may be due to manufacturing imperfections.

But if it was isolated and the temperature rise caused an increase in pressure, then the pressure would have been relieved as soon as the first hole ruptured. Also, a pressure burst would be a slit in the same direction as the tube since this is the maximum stress line.

These are a lot of outward holes that must have happened at the same time. It must have been pressure because of the outward splays.

If there was a chemical treatment that was left on the coils and this corroded the tubes. The splinters from the copper could have been like bullets perforating the fin in an outward direction.

Indeed a tricky one.

[expat]

Could this be electrolosis between the aluminium, copper and salt from seawater air offering perfect conditions for pitting on the copper surface and when one hole blew they all blew (clutching at straws here)?

[The MG Pony]

The coils are still perfectly good with no leaks, I vote electrolisys as this makes perfect sense. Like I said I see it all to often on the coast.

[US Iceman]

If there was a chemical treatment that was left on the coils and this corroded the tubes. The splinters from the copper could have been like bullets perforating the fin in an outward direction.

As you say a very tricky problem. If it was corrosion, why would the holes tend to follow the helix angle? Corrosion affects would be seen from an external reference, not internal.

I still think the culprit is pressure and the helix angle and surface enhancements have something to do with it. What, I don't know now.

Those holes in a pattern are trying to tell us something...

[nh3simman]

Those holes in a pattern are trying to tell us something...

I missed the spiral pattern. You're right, this does seem to imply that the internal grooves are a factor.

[Lowrider]

Hi Sanderth,

Copper tubes used in coil industry (Fin-tube) is usually 3/8" , 1/2 " , 5/8 " OD. The thinesst tube I have seen is 0.45mm thickness. You can see that they can stand a lot of pressure.
These tubes are used to make condenser coils which usually operate in the range of 16 to 22 bar (or more).
If you had a tube which ruptured under 1bar then, I think there was another problem which caused it NOT the pressure.
Cheers

That's why I asked, 'cause I've seen a coil or two (or more) that where made from even thinner copper tubes and the combination of pressure (even only 1 bar) and the low temperature caused it to blow!

[US Iceman]

If the root thickness is very thin and any possible manufacturing imperfections exist that coul dbe the cause. The holes seem to occur in somewhat of a regular spacing which leads me to believe problems with tooling when the grooves are formed.