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Calcium effect on demulsibility of turbine oil. |
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I recieved a delivery of 5000 gallons of ExxonMobil DTE 732 Turbine Oil. Sample results show the oil to contain 13PPM of calcium. I was told that just a small amount of calcium will have a drastic effect on demulsibility of the turbine oil. Is this true, and if so is there any acceptable limit for calcium?
Calcium suggests the presence of detergents in the oil. Detergents are important ingredients in some oil formulations such as motor oils, but can have devastating effects on demulsibility performance of turbine oils. A recent study by Mobil suggested that less than a 1/10th of a percent of a detergent-based cleaner can impact the oil's demulsibility characteristics. In this study, just 3ppm of calcium significantly impacted the performance of the fluid.
We suggest that you retest your sample using ICP to determine metal content. In addition, you should test the water separability characteristics of the fluid by testing D1401. If the second sample indicates the presence of calcium and you fail the demulsibility test, immediate action may be required.
If this is a steam or hydroelectric turbine application, poor water separability characteristics can put your plant at significant risk should you get a steam or water leak in your reservoir. It is important that you have access to a Membrane Technology (Fluitec UltiDri) or vacuum dehydration technology to quickly remove water from the fluid in the case of sudden moisture ingression. Note that coalescing technologies are ineffective if the water separability characteristics are poor. You should consider changing the fluid as soon as practical.
If this is a gas turbine application, you should consult with your oil supplier to evaluate the operating risk posed by running a fluid with poor water separability characteristics.
The two most common ways for detergents to get into a new charge of turbine oil is either residual flushing fluid from recent maintenance activities or by contamination in the delivery truck with another type of lubricant, most likely engine oil. It is important to attempt to find the source of the calcium contaminant to ensure that this does not happen in future oil changes. |
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Can the RULER be used to detect and monitor ZDDP (zinc dialkyldithiophosphate additives?
ZDDP is a very common additive for hydraulic oils, engine oils and a multitude of other applications where combined antiwear (AW) and antioxidant (AO) properties are desired in an economical additive component. Often ZDDP is used primarily as an antiwear agent and in oxidatively stressful environments, other antioxidants are formulated into oil. The RULER measures additive molecules which exhibit antioxidant properties (multifunctional additive), making ZDDP an easy molecule to detect and trend. Several research papers have reported excellent detection capabilities for ZDDP in hydraulic and lubricating oils, motor and gas engine oils, as well greases. By trending the ZDDP depletion, research has shown a correlation between the depletion of ZDDP and increase in water and heat in hydraulic oils.
How do I Interpret RULER results for ZDDP formulations?
As ZDDP depletes, it transitions into multiple intermediary products prior to becoming completely exhausted and precipitating out of the oil (and in non-detergent formulations, usually forming inorganic deposits in the system). Even though the original ZDDP molecule has been altered, some of these intermediary products still provide valuable antiwear and anti-oxidation protection. The RULER will only detect new ZDDP molecules and those intermediates that possess antioxidant properties.
Traditional oil analysis uses metal spectroscopy (ICP, RDE, X-ray) to measure the presence of zinc and phosphorus – the key components in a ZDDP molecule. This is misleading because as long as the zinc or phosphorus molecules are still in the oil, they will be picked up by spectroscopy, even if all of the functional properties of the ZDDP molecule have been depleted. It is only after the ZDDP components start to precipitate out of the oil (in the form of sulfates and phosphates) will an analyst detect changes in metal content, hardly making this a predictive test. RULER provides further information on ZDDP depletion by trending the antioxidant properties, providing proactive information in an oil monitoring program.
If the RULER indicates that all of the antioxidant properties of ZDDP have been depleted, this does not necessarily mean that the oil is condemned. ZDDP intermediates may still provide antiwear properties even if no antioxidant properties remain. Depending upon the application, the oil’s ability to provide AW protection may be paramount to performance. Once the AO properties are depleted, the analyst should pay careful attention to other signs of oxidation, such as increases in acid number or viscosity. Tests to measure the oil’s deposit tendency, like Membrane Patch Colorimetry also become critical when ZDDP depletes.
In order to fully understand ZDDP depletion, tests such as P-31 NMR or GCMS is required. Unfortunately, these are not feasible tests for most oil condition monitoring programs. The RULER provides a valuable link to monitor ZDDP depletion and when combined with other oil analysis tests, is an important part of an effective proactive oil analysis program. |
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