|
During Oil Sampling
|
||||||||||||||||||
| In the micro-world of oil analysis, the ability to extract and distill useful information from a small sample of oil depends greatly on the quality of this raw unprocessed data captured within. On the surface, this would seem like a straight-forward task, but practical experience has taught us that there are obstacles to overcome. The technology of oil sampling specifically addresses the old saying "garbage in, garbage out." | ||||||||||||||||||
| From a practical standpoint, optimal performance in oil sampling depends directly on succeeding in three areas: (1) maximizing data density while, minimizing (2) data disturbance and (3) data contamination. The challenge lies in the fact that the imbedded data in the oil sample is invisible to the human eye, a fact that is equally true for the many factors that disturb and contaminate the data. Therefore, without a well-planned course to follow, the oil sampling activity is analogous to "flying in the dark." The following is an overview of some of the essential precepts to attaining high quality oil samples. | ||||||||||||||||||
 |
||||||||||||||||||
| Maximizing Data Density. | ||||||||||||||||||
| Real estate agents are often fond of telling us that the three most important considerations in selecting a property are location, location, and location. The same factors hold true for oil sampling. In circulating oil systems, the best location is a live zone of the system upstream of filters where particles from ingression and wear debris are the most concentrated. Usually this means sampling on fluid return or drain lines. | ||||||||||||||||||
| In some cases where oil drains back to sumps without being directed through a line (e.g., diesel engine), the pressure line downstream of the pump (before the filter) must be used. Always avoid sampling from dead zones such as static tanks and reservoirs. Splash, slinger ring, and flood lubricated components are best sampled from drain plugs after considerable flushing or preferably, using a portable circulating off-line sampler. | ||||||||||||||||||
| Minimizing Data Disturbance. | ||||||||||||||||||
| Once a sampling point is properly selected and validated, a sample must be extracted without disturbing the integrity of the data. When a sample is pulled from turbulent zones such as at an elbow, it has been proven that particles, moisture, and other contaminants enter the bottle at representative concentrations. In contrast, it is well-known that sampling from ports positioned at right angles to the path of the fluid flow in high velocity, low viscosity fluids causes particle fly-by. In such cases, the higher density particles follow a forward trajectory and fail to enter the sampling pathway (sampling port). This condition can reduce particle counts by more than ten-fold. | ||||||||||||||||||
| Moreover, machines should always be sampled in their typical work environment, ideally while they are running with the lubricant at normal operating temperature. Likewise, during (or just prior to) sampling, machines should be run at normal loads, speeds, and work cycles. This insures that the wear debris that is typically generated in the usual work environment is present in the fluid sample. Similarly, it is important that particle and moisture ingestion from the atmosphere, due to ineffective seals and breathers, be at representative levels. Such contaminants and wear particles typically settle to tank bottoms and pipe walls when systems are cold and inactive. | ||||||||||||||||||
| Minimizing Data Contamination. | ||||||||||||||||||
| As previously stressed, an important objective in oil analysis is the routine monitoring of oil contamination. The same kinds of contaminants found in the oil are also found in the atmospheric work environment. Therefore, considerable care must be taken to avoid the risk of "contaminating the contaminant" in the sample. Once atmospheric contamination is allowed to contact the oil sample it cannot be distinguished from the original contamination. | ||||||||||||||||||
| There are many techniques to minimizing sample contamination. These include certified bottle cleanliness, probe-tube bottle attachments (so that bottle caps are never removed), ample sampling valve flushing, and frequent cleaning/flushing of portable sampling devices (e.g., drop-tube vacuum samplers). What might generally seem like a minor corruption of these important measures can, in fact, greatly compromise the very integrity of an oil analysis program. | ||||||||||||||||||
| Experts believe that the time and money spent on insuring the quality of an oil sample in the bottle will pay multiples when the benefits of oil analysis are totaled. This is best accomplished through properly training all those involved in oil sampling activities. | ||||||||||||||||||
|
|
||||||||||||||||||
|
|
||||||||||||||||||
|
