Dehydrating Heavily Water Laden Systems

[Marc O'Brien]

With new installations we would ordinarily start the pre-commissioning tests with a strength pressure test, perhaps for 30 mins, followed by a 24hr tightness. Then there is a 24hr vacuum finished off with a 30 minute vacuum rise test for moisture.

Is this similar to your procedures?

Assuming the piping system inadvertently took on say a pint of water with out you knowing. What would you expect to see on the Torr gauge after a 24 hr vacuum.

I have done a few calculations and have recently made a discovery which I'd like to share but first I ask the above to set a benchmark against which to discover what is common practice and what might become new practice.

[The King]

Yup yup except I use a micron gauge to gauge the evacuation time.

Five gallons of used vaccum pump oil and a micron gauge reading of

25000. :)

Marc I had a chiller barrel leak and it took me damn near a week to de-hyrdrate the system after I replaced the barrel and it was only a

50 ton machine.

One of my favorite things to do is put a small amount of water in a sealed glass jar and observe the process of moisture removal with an apprentice. Its fun to watch the micron gauge to see at what level things take place.

At first the water boils violently then it turns to ice then it sublimes and disappears.

[mobrien.acrtc]

My next article in the UK industry magazine I write routinely for will be on how I insist that the industry's traditional moisture checking method be changed. I believe it is flawed. I don't want to give all the details right now because I first want to be sure that no one else known to me is aware of the flaw I have identified.

In your chiller case above the best process would have been a combination of triple vac and deep vac. Triple vac does not remove water but does remove vapour contaminants by compounding percentage reductions - 4% is left in the system after the first vac and then 4% of 4% after the second and finally 4% of 4% of 4% on the third vac and so on. Only a deep vac with multiple vac oil changes can remove water. The more heat the better and the better your cold trap the less often you have to change the oil. But we cleaned a large system up pretty quick finishing yesterday after 4 days of alternate deep vac and warm nitrogen purging to about 30psi each time. The nitrogen was put into the system through a length of copper pipe heated by hand with a blow torch. The nitrogen was going in each time at about 40=B0C. Warm nitrogen is an old trick of mine I chose to do on my own as an apprentice years back.

My question everyone is really - at what point after a vacuum do you check for moisture and how is it you know you have no moisture - what instruments and what time frames do you use. This is for piping on new installations.

How much water do you use? How long does it take to sublime away? I'm assuming this is all done at room temperature and the glass jar is not sat on a heat source warmer than the room.

[Marc O'Brien - ACRTC]

I've uploaded a video of the ice we removed from one of the suction strainers on the system recently meant to be commissioned if it weren't for the water.

[The King]

I cant wait.

About a table spoon.

Its been a while since I've done it but it wasn't long. All the visible water had sublimed well before 400 microns. I think it was in the neighborhood of 1400 microns but I may be misremembering. :)

Correct.

Cool video by the way. What was that black stuff in the ice.

[The King]

I propose that you first post it here and we will pick at it so you don't end up making a industry wide fool out of yourself. Just kidding. :)

Post a link to the article when it is published, it sounds interesting.

[Marc O'Brien - ACRTC]

quoted text -

I guessed the black was a little copper oxide from a few joints the guys might have soldred without nitrogen purging.

I am just the methods consultant on this project. I have asked them to install temporary replaceable drier cores starting off with a few changes of Molecular Sieve and then to finish off with a few changes of a Activated Alumina to remove the acids that would have been generated by the oil/water reactions.

[The King]

Sounds reasonable to me. What refrigerant?

[Sanjay]

Dear sir/madam

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[Bubba]

Dear Sanjay, If Im not mistaken, It sounds like you got a "woody" going there? You should check your shorts and go clean yourself up. Bubba

[Apache -=CW=-]

How large of a system are we looking at? A pint of water in a system that is two pints in size will no doubt have a different reaction to the contamination vs a system that's 50 million pints in volume. Moisture is moisture yes, but you can't make a procedure that is all encompassing as ever job has it's own uniqueness.

However, if I were to suspect contamination were present I'd first try and determine how it entered the system rather than treat the symptom. After that, I'd remove the moisture, and then evacuate the system with a micron gauge connected, breaking the vacume at various stages with a dry compressed gas, such as nitrogen or perhaps with a trace amount of refrigerent to help scavenge the moisture, until I achieved a deep vacume that would hold. There's no time limit either, I've had systems take a few weeks to remove the water/moisture to a point where I was confident enough to walk away from the job knowing that the system was perfectly free from contamination.

You're not telling us your operating pressures (normal) so I can't comment on your pressure test. Again... a 30 pound test on a system that runs at 300 pounds would be kind of useless don't you think? But I use a 1.5 times the normal operating pressure for my tests, and then it's done for 24 hours. Any drop in pressure is absolutely unacceptable.

A New York State Journeyman :)

[Marc O'Brien - ACRTC]

Mike, I will post some of the thoughts here.

I will be posting the majority of the thinking an illustrations on