POE Organic Acid signs?

[bryan l]

Excess moisture in a POE system produces organic acid. Other than the obvious of testing the oil with a acid test kit, what are other tell tail signs that there is acid buildup?

[condenseddave]

Strange tingling sensations in the testicular region.

Hair loss, mostly ear and nose hair.

Loss of continence.

Sour taste.

But they're only a few.

Seriously, the best way to determine acidity is with acid test kits...

[wolfdog]

You had me worried.

[t527ed]

damn my acid must be high

[oogene]

Timothy Leary has/had an answer for that acid problem-no problem !!!

[RobY]

Originally posted by bryan l
Excess moisture in a POE system produces organic acid. Other than the obvious of testing the oil with a acid test kit, what are other tell tail signs that there is acid buildup?

From a system chemistry view (sorry, its the way I make my living), the organic acids from POE hydrolysis are weak and do not normally cause any metal corrosion. Also, water does not attack POE very quickly, and it normally takes a long time to generate a significant amount of acid if the only problem the system has is excess water. I've seen one guy running a large chiller with 700-1000 ppm of moisture for two years (can't take the unit down to fix the water leak because of the process it is cooling), and he changes the oil and driers when the acid number gets above 0.3. It takes about six months for the acidity to climb that high. There are no other issues with the system from the acids, but he is checking the oil condition on a regular basis.

The potential problem to be worried about is salt formation when the acids are neutralized on an active metal surface. An active metal surface is one where the protective oxide and hydrate layers are removed by wear or by high temperature, and the base metal is then in contact with the POE. The carboxylic acid salts aren't very soluble in refrigerant and will deposit at the first narrow part of the system - capillary tube inlet or TXV pins.

Filter driers will do a good job of removing the organic acids, but don't grab the salts. In my experience, the big problems with POE come from when POE is decomposed by heat at a metal surface and goes directly to salt, rather than by water where it goes to acid. Neither one is good, but a wet system with no other problems will run for a whole lot longer than a system with an excessive bearing or discharge temperature problem.

[R12rules]

Say Roby, that was a real good analysis.

Now can you break it down for us non-scientists?


Say we find a system with POE and moisture in it. And we suspect salts. What steps can we take to bring this under control?


Thanks

[RobY]

Originally posted by R12rules

Say we find a system with POE and moisture in it. And we suspect salts. What steps can we take to bring this under control?

Acid / water and salts are normally two different problems. The acid is caused by high water, and you need to control the water to remove the root cause of the problem. Once you get the system dry, change the oil and filter driers to remove the existing acid, you should have no more problems. Any residual acid will either leave with the old oil or be adsorbed onto the new filter driers. Your test kits or lab analysis should show normal acidity at that point (less than 0.2 mg KOH/g is OK. less than 0.05 is best). I haven't looked at a field test kit for POEs in over 10 years, so I don't remember where they are designed to show high acidity at. I do know what I told the guys developing the kits at the time is the same as above.

The salts are a lot more of a problem. The salts are formed when another component fails in the system, so again you first you have to fix that problem (compressor bearing failure, plugged condensor fins, bad condensor fan, high ambient temperatures, etc.) I know it's stating the obvious, but if you don't fix the root cause, then the rest of the work is pointless.

The salts don't dissolve well in any commercial flush solvents I know of (chloroform works very well in the lab, but you shouldn't use it in the field). All you can do is remove the salt by removing the parts of the equipment the salt has deposited into. Cutting off the first 6 inches of cap tube, examining / replacing the TXV, replacing the filter driers, etc. are the quickest way to get the salts out of the system. In a lot of cases, replacing the entire cap tube may make more sense. I wouldn't worry about anything downstream of the expansion device, as the salts aren't likely to move any farther.

You will want to check out the discharge line to make sure it is not filled with crud (salts as well as compressor failure debris). Replace anything that looks like it has a port wine or reddish brown colored gel in it, as that is what the iron carboxylate salts look like. The aluminum salts look more like very light gray / brown gel, and the oil normally looks gray from the fine aluminum particles suspended in it (not a good thing to see). Potassium salts look a lot like wax, but are rarely found in a system (they come from brazing flux and overheated POE). I've never seen copper, tin, lead or zinc salts so I can't describe them.

Disclaimer: Rob's rules for POE are not hard and fast, and need to be applied with some common sense. The chain of equipment failure that caused the acidity or salt formation is a key part in how to attack the POE breakdown problems. Some systems are more prone than others to generate POE breakdown, so what is OK for one application may cause problems in another.

[R12rules]

So what your saying about removing six inches of cap tube, this is due to salts which adhere themselves to the copper and not to the POE oil itself?

Or is that the same thing?

[bryan l]

I have seen some systems that have a Wax like substance plugging up TX inlet strainers and actually on the orfice itself. This was something that a bunch of us mechanics have never seen before other than on a Mineral to ALK swap over that was actually the wax you hear about from the distributors. Now the question I have about Potassium salts is how common is it to be found. High temps are the cause you say but what is high temp? the 200f disc limit or does it have to go higher into the known breakdown temps like 250f?

[RobY]

Originally posted by R12rules
So what your saying about removing six inches of cap tube, this is due to salts which adhere themselves to the copper and not to the POE oil itself?

Or is that the same thing?

Yes, the problem is the salts are sticky. The POE itself will not be in as good of shape after the salts form, and the more torn up the POE is, the more likely it is to generate more salts. You need to get the old POE out of the system if you see salts, and start with fresh oil and driers.

[RobY]

Originally posted by bryan l
I have seen some systems that have a Wax like substance plugging up TX inlet strainers and actually on the orfice itself. This was something that a bunch of us mechanics have never seen before other than on a Mineral to ALK swap over that was actually the wax you hear about from the distributors. Now the question I have about Potassium salts is how common is it to be found. High temps are the cause you say but what is high temp? the 200f disc limit or does it have to go higher into the known breakdown temps like 250f?

You may have a completely different problem than POE salts. There were several POEs that were prone to forming plugs at TXVs and filter driers that looked like wax. This was due to the way these particular POEs were chemically manufactured. In refrigerants with marginal POE solubility like R-404A and R-507, some components of the the POE would 'associate' with each other and form semisolid plugs. These plugs would go away when the system warmed up, only to reappear a week or two later. The oil can be dry, low acid number and the temperatures normal, and the system would plug up. This frustrated a lot of mechanics, which in turn frustrated a lot of engineers, which is when I heard about it.

Carlyle used to recommend Castrol SW68, but no longer does for the reason above. They now recommend Castrol SW68E, which has had the manufacturing process changed to prevent the formation of these plugs. Mobil also made some POEs that had the same problems. Other POE manufacturers like Uniqema (Emkarate) and CPI (Solest) never made products that formed plugs. I think Mobil and Castrol no longer make the problem POEs, and have replaced them with ones that are acceptable.

If any of this sounds familiar, let us know.

[DeltaT]

Rob
What is your take on the refrigeration manufacturers warning about not leaving the POE oil in any form exposed to atmosphere for longer then 15 minutes or acid can form which can do harm to the systems.

Most of us are dealing with 2 to 10 ton systems in some form with small tubing, small expansion valve plugs, cap tubes, etc that can be easily blocked or plugged.

One POE oil manufacturer wrote an article that any form of POE acid can set on the compressor winding and eat the insulation. Any experience with that?

And why has the salt formation not been introduced into this picture by the POE manufacturers to date? Any info on your part would be appreciated.

Thanks