Skip to main content

During routine oil analysis in Propane Refrigeration Compressor (screw & flooded Type, Howden Make), it has been observed high water content - 750 ppm and low viscosity - 113 cst @ 40 C. The Oil grade is ISO VG 150. The repeated re-tests value is also consistent.

What is the acceptable level of water content and viscosity for this type of compressor oil?

Is there any guideline which states the acceptable level of water content and viscosity? Can anyone post the copy of the guidelines or standards?

Replies sorted oldest to newest

The Howden ammonia refrigeration compressors I monitor have an acceptable water content of 0.00 ppm in the oil. Water is not acceptable at all. The thrust bearings in these things are heavily loaded, and water does not make a good lubricant. If it has degraded the viscosity down to 113 from 150, you need to change the oil, find how the water is getting in and address that issue.

Just my opinion and I could be wrong.

Dave
RM
Candy/Dave - Thanks for your reply.

The acceptable limits are not written in the manual. I am going to contact Howden.

The new oil was tested. The water content level is 218 ppm and viscosity is 153 cst @ 40 C.

I searched standards & guidelines for refrigeration compressor's oil analysis but not getting ASTM or ISO guidelines. As per my knowledge and based on many written articles about oil analysis believe we can accept up to 500 ppm for used oil for continuous operations. However, support that Iā€™m looking for ASTM or ISO guidelines.
RM
The lower the moisture content the better, but I don't see how you will ever reach Dave's acceptance criteria of 0.00 ppm (1 ppb?).

The 500 ppm for lubricating oils is a pretty good rule of thumb, but again the lower the better.

An article from Machinery Lubrication,

http://www.machinerylubricatio...compressor-lubricant

indicates that 75 - 125 ppm is a guideline for a hermtically sealed compressor. Another thing you need to be wary of is moisture ingression into the sample after it has been drawn. Anyway you slice it, 750 ppm is too much.

In regards to viscosity, the presence of refrigerant in the oil can cause low viscosity readings. Talk with your oil lab about possible fixes. I think they can pull a vacuum on the oil which causes the refrigerant to boil off, then test the viscosity.

Steve
RM
Steve

I agree lower the water content is better and it is reasonable 125 ppm.

The water was tested by Karl Fischer method and viscosity was on CSI Oil analyser.

Regarding viscosity, both used and new oil test was done in similar manner in the lab. But old is 113 and new is 153 @ 40 C. The readings are almost consistent for different samples. Anyway to confirm I am planning to send sample to outside lab.

Though everyone is agreeing here moisture content is high but to convince my Maintenance team I need some supportive standard or guidelines. The link that you provided may help me for discussion however I believe it not enough to convince.

While searching ASTM D6304, it says test method to determine water in lubricating oil. Is this standard specifies the acceptable level of water content or moisture in oil also?

Thanks
RM
Fellows, why would 0.0 PPM by Karl Fischer be unrealistic? We check it all the time for gearbox's, hydraulic systems and the compressor oil. When there is any water showing at all, we either filter with a water absorbtion filter and try to get it out (especially if we're talking a substantial quantity of expensive oil) or we change and flush.
I would't think the compressor would be any different. It should have some basic filters on the seperator, and you can put a water absorber in one of the cans. Takes some time but if the moisture is in the system and you want it out that is one solution. Talk to your filter people.
I'm wondering about the new oil too. Where in the world did you get it that has a water content of 218 ppm? Really?
Maybe I'm used to too stringent a guideline, but I don't think I have any customer that would allow water in their systems without trying to get rid of what is there and finding out how it got there in the first place and rectifying that situation.

D
RM
quote:
Originally posted by RRS_Dave:
Fellows, why would 0.0 PPM by Karl Fischer be unrealistic? We check it all the time for gearbox's, hydraulic systems and the compressor oil. When there is any water showing at all, we either filter with a water absorbtion filter and try to get it out (especially if we're talking a substantial quantity of expensive oil) or we change and flush.
I would't think the compressor would be any different. It should have some basic filters on the seperator, and you can put a water absorber in one of the cans. Takes some time but if the moisture is in the system and you want it out that is one solution. Talk to your filter people.
I'm wondering about the new oil too. Where in the world did you get it that has a water content of 218 ppm? Really?
Maybe I'm used to too stringent a guideline, but I don't think I have any customer that would allow water in their systems without trying to get rid of what is there and finding out how it got there in the first place and rectifying that situation.

D


Dave - In your initial comment, you wrote 0.00 ppm and in this comment you wrote 0.0 ppm. I was and still am dubious of those numbers. However, you did describe the actions that you undertook to drive the water content down. I don't have the ASTM documents at hand, but I'm not sure how far down in single digits that the Karl Fischer testing can get you. This link from Machinery Lubrication,

http://www.machinerylubricatio...7/water-oil-analysis

suggests reproducibility problems below 200 ppm for ASTM D1744.

This link (also from Machinery Lubrication) indicates that KF coulometric titration can be capable of measuring down to 1 ppm.

http://www.machinerylubricatio...oulometric-titration

So maybe you are getting 0 ppm of water content, I don't know. If you want to confirm your results I would suggest that you find out what KF test method the lab is using and perhaps split a sample and send to another lab for confirmation.

In regards to the 218 ppm in the "new" oil sample, I am not necessarily shocked. I would defintely look into ingression as a means of the oil/sample being contaminated. Also, talking to the supplier about water content. There's a good chance that you might get the "deer in the headlights look".

Good luck.

Steve
RM
Dear,

Lets go back to the original question by Vibrave,
Water content: 750 ppm and Oil viscosity drop to 113 cst@40 C
When I check the posted MSDS, Primeria LPG 150, is having density closed to water, around 1 kg/L, it may Synthetic PAG based.
Synthetic PAG is having polar molecule which will be detected as water in KF method. it may be the reason why water content is high

The ASTM guidedance for In-Service (Used) oil analysis acceptance criteria are:
ASTM D 6224 and ASTM D 4378
But all of them are not suitable for Refrigeration Compressor

It is a common situation that oil viscosity is drop in screw and floaded type refrigeration compressor, due to dilution of refrigerant in the lubricating oil.
More the dilution, The drop of oil viscosity will more also.
So, it is important at the begining to sellect the correct oil which compatible with the refrigerant (Propane)

1. I am advising you to send the in-service oil sample to Independent Oil Analysis Laboratory, rather than rely on "Tool Kit".
Request them to check the following properties:
- Oil Color Code (ASTM D 1500)
- Kinematic Viscosity (ASTM D 445)
- TAN (ASTM D 664)
- Water content by distillation (ASTM D 95), DO NOT USE KARL FISCHER
- Metal content ICP/AAS

2. In general, you may use the following criteria for the refrigerant compressor:
- Oil Color, Max 6
- Kinematic Viscosity MAX +10% , but MIN -50% from fresh oil.
- Water content, MAX 0.05% THE UNIT OF DISTILLATION IS IN PERCENTAGE, NOT IN PPM
- TAN, Max 1.00 mg KOH/g
- Metal Content, max 20 ppm

I hope it will help
Regards,
RM
It will depend on bearing type and loading also. If it is equipped with hydrodynamic Radial and thrust bearings, oil replacement may be required based on water content and viscosity. For anti friction bearings, some OEMs suggest maximum limit of up to 1000 ppm. But again we need to find water source in Propane circuit. Water carryover in Propane may create process problem. It is unheard for me to find 0 ppm in this kind of application. For Ammonia compressor, may be Ammonia is reacting with water..
RM
Thanks to all. Thanks to Nurudin for guideline.

There is no water content detail specified in the oil specification sheet. However, similar oil of other grade (Chilled Water Compressor) it has mentioned < 100 ppm for new oil. Refer attachment. Enquiry had sent to OEM for more details also collecting oil sample to send outside lab for analysis.

My concern is on running compressor it has 750 pmm of water and 113 cst @ 40 C. Iā€™m also following the same guideline that is posted by Nurudin but it is not enough to convince the Maintenance team and need standards.
I am looking below ASTM standard and like to know what the acceptable limits written in these standards

ASTM D7669 : Standard Guide for Practical Lubricant Condition Data Trend Analysis
ASTM D7720 : Standard Guide for Statistically Evaluating Measurand Alarm Limits when Using Oil Analysis to Monitor Equipment and Oil for Fitness and Contamination
ASTM D6224 : Standard Practice for In-Service Monitoring of Lubricating Oil for Auxiliary Power Plant Equipment
ASTM D4378 : Practice for In-Service Monitoring of Mineral Turbine Oils for Steam and Gas Turbines

Not only Iā€™m facing moisture issue in Propane Compressor also having high moisture content issue in Chilled Water Compressor (Howden make, Screw Type and Freon 134 refrigerant). This compressor oil contains about 1497 ppm of moisture. The specification sheet of Chilled water compressor has attached for reference.

Both these compressors are unable to stop for oil replacement or inspection and without the standards, not easy to convince for corrective plan on these compressors.

Attachments

RM
I'm going to throw in some thoughts. My experience is with gearbox lubes of similar viscosity.

- The ppm limit of every oil is different. Many oils won't hold 200ppm at room temp, much less 500ppm. Try to find free water too.

- That said, the saturation point of the oil is certainly the highest possible limit for use in PdM, since a higher limit will never work. The approx saturation limit of the oil can be obtained by a phone call to the lubricant manufacturer.
RM

Add Reply

×
×
×
×
Link copied to your clipboard.
×