Leaking Plate Condenser

[sshep]

A leak check on an internal plate condenser showed several plates to be leaking. These exchangers have tempered water between plates as cooling medium. Open channels between the tempered water containing plates are exposed to the tower for condensing- in this respect the plate condenser differs from a typical plate exchanger which would have the process fluid also contained in channels. It is intended that the header boxes will be cut open and the leaking plates taken out of service by sealing them off.

This is the problem: water runs out between the plates, but the leak itself cannot actually be seen. Is there anyway to determine if the leak is on the left or right side plate? We are in a shutdown and the fastest alternative that has been suggested is to close off both plates, but this will result in double the area loss. Any quick suggestions are appreciated.

If this were a conventional plate exchanger where both sides were contained, it would be possible to cut open the header boxes of the water side and tape up the plates to isolate then. A leak check could be performed by systematically poking holes in the tape, pulling vacuum on the process side, and testing with shaving cream or smoke.

Note: I have considered it it would be possible to seal off the condensing side channel but really need to seal it on the water side.

best wishes,
sshep

 

[GL431]

Can the vendor/manufacturer suggest something? Without a sketch it is difficult for us to picture the situation.

 

[StoneCold]

Sshep

Can you pressure up the cooling water side (outide of the plates) and see which plate has water leaking into it after you open the water box header?

 

[sshep]

Thanks gentlemen,

This is the situation now. The header boxes have been cut open at top and bottom. The plates will be isolated at the bottom with a sealing plate. A fitting has been built to try and pressurize each plate individually with water from the topside. This fitting relies on an elastomer seal- we will see how this works.

Stonecold, unfortunately there is only one enclosed side to this exchanger, the other side is open to the column (internal condenser). If both sides were enclosed, we would have more options. Now that the water side header box is cut open, there is no way to apply a differential pressure across the plates (except using the testing device that maint has devised- hoping it works). Worst case we close off every plate that is suspect, but this is exactly what we wanted to avoid.

I'll let you know how this turned out. As plate type heat exchange equipment becomes more popular, I am sure more engineers will encounter these situations. Hopefully the vendors will also be addressing these issues as part of the construction and testing procedures. Even now we have found a second tower with a leaking plate condenser. At present if the exchanger must be replaced the column head must be cut off. We just did this on several towers and it is major work- some of these towers are over 100m high.

At least this post may give others some data for whether or not to go with this style internal plate condenser technology. At one time I thought it was a good idea, but now I am rethinking.

best wishes,
sshep

 

[GL431]

Dear sshep

Sorry I cannot contribute with real tips to handle your situation. You seem to have all the support you need on site. I will take up your offer in your last paragraph and ask some questions to satisfy my own interest.

What service do your internal plate type condensers work in? You say tempered water on the cooling side. What is on the condensing side?

What is the metallurgy of the condenser header and plates? CS, SS, alu?

What do you think the weak points of this construction type are, which led to the leaks? Plate to header soldering joints, vibration of the plates leading to fatigue at those joints? Differential temperature expansion?

Could the tempered water ever have boiled at some stage? (perhaps on too high a temperature on the condensing side). I have experienced failures in plate exchangers, but they all involved getting steam inadvertently or erroneously into the channels.

Interesting to see how this integral "maintenance free" equipment is being trouble shooted (trouble shot?).

 

[Shimasu]

Have you tried with a tracer, perhaps you could add it on your water stream (colorant maybe) and then run your HX normally then you would have a clearer idea where the water is coming from

 

[ApC2Kp]

sshep,

Some plumbers formerly had a product called "Liquid Glass" for sealing leaks from small porosity or hair line cracks.

The story was of an apartment complex's copper tubing water system that had been solderd with the wrong flux. Corrosion left the joints leaking like a sieve in the hydrotest. After a plumber was called in for the "Liquid Glass" seal repair of the system, there were no leaks.

Since ductile iron water pipe usually has a cement lining, maybe the "Liquid Glass" could have been a portland cement slurry solution circulated through the piping system? Any one else ever hear of "Liquid Glass?" Maybe it is not compatible with the fluids in your tower and condenser, but cooling water service would not seem severe or extreme temperature. Too thick of a cement lining would decrease heat transfer, but an application of some sealing compound to fill cracks and porosity, followed by a wash of the plates, might leave plates clean for good heat transfer performance.

from Google, possibly a source
Liquid Glass
Jackson, TN 38301
(731) 424-9530

or,

http://www.tillwite.com/prodDetail.asp?partno=C000728

Or maybe the product is some polyester or acrylic resin?

 

[DYV1973]

If a plate is cracked, you should replace it. Cracks can be found with dye penetrant testing. Plate condensors sometimes have very thick gaskets, in which it might be difficult to see if they seal correctly at higher temperatures. What type of plate condensor is it (manufacturer?).

Rgds,
DYV

 

[sshep]

Gentlemen,

Now that the repairs have played out I feel I owe an update. The initial repairs involved opening the header boxes and sealing off the suspected plates with weld metal. The header boxes were reattached with a root pass and the plate pack was re-hydrotested. The result was at least two leaking plates. The total leaks were 3 drips per minute.

It was decided to try again. This time the header box piping was also replaced due to cutting open too many times. By the time this repair was complete we had extended the shutdown by 10 days. It was reported that the hydrotest passed, but when the equipment was brought on line we started losing tempered water again.

A report was issued by the licensor (who visited during the repairs) blaming chloride induced stress corrosion cracking, although I am still skeptical as there was little or no analytical supporting data- the primary proof seemed to be the color of a rust found in the header box which the author identified as some sort of ferro-chloride material based on experience. The report noted mechanical damage at the expansion joints and supporting shroud, but the author dismissed this as coincidence. It was further noted that these repairs are difficult due to the possibility of damaging adjacent plates- the manufacturer had no detailed repair methodology. Now I have serious objections to this technology and also the report which was submitted about the failure cause and repairs.

The net of all this experience is that will never again trust the proposal of internal plate condensers in any future design. We use alot of these in new plants on this site and more than half have failed within 5 years. In all cases repairs have been a problem, the exchangers ultimately required replacement. Replacement requires the removal of column heads for removal and reinstallation- very costly in resources, money, and downtime.

Thanks for your attention and assistance. Best wishes always,

sshep