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Operators and managers often overlook the critical role played by lube-oil reservoirs that support rotating machinery, hydraulics and mechanical power transmissions. Often viewed as lifeless metal tanks and sumps, half-hidden from sight and inaccessible, reservoirs are not only treasure chests of information, but they offer a convenient stage from which to perform remedial tasks.
Hard-working lube oils travel their circuits many times depending on the quantity of oil in the system. However, every drop of oil must return to the reservoir; the time it takes the oil to return depends on the system. A reservoir is like the Indy 500 grandstand; every unit of oil passes in front of it for review. But unlike race cars, that same drop of oil decelerates as it enters the reservoir, lingering while it waits its call to make another trip around the lube-oil circuit. Reservoir residency varies, yet while within the reservoir, lube oil is conveniently accessible to operators for analytical and remedial action.
Reservoir management is the practice of monitoring, analyzing and conditioning lube oils at the reservoir. There are three fluid properties that are routinely measured: solid contaminants, moisture and chemical stability. Tests used to characterize each are ISO Contaminant Code for solids, ratio in parts per million (PPM) for moisture and acid number (AN) for general chemical health.
Practicing reservoir management (PRM) wraps many routine activities into an orderly process designed to reach and sustain cleanliness objectives. Fortunately, most organizations already have basic equipment and services including: oil analysis reports, portable filter carts, sampling devices, pump/motor/filter sets, oil dispensing equipment, coalescers and access to qualified replacement filter elements.
Therefore, getting started does not involve upfront capital spending. Off-line (kidney-loop) filters, for example, can be assembled with a pump, electric motor and simplex filter. Off-line filtration plays an important role in PRM. Innovative operators will find a way to make-do with components on hand. Upgrades come later. Filter carts should be fitted with disconnects and should accept widely available particle removal and water-absorbing filter elements.
Oil sample ports of various types are usually available from store rooms and should be installed in the correct locations in return piping upstream of the reservoir. Oil sampling procedures and cleanliness techniques need to be well-defined and understood by operators. Oil storage and handling are fundamental practices that can also negatively impact system performance. System control begins when the lubricants enter the plant. If system control is to be maintained, technicians need to have the right tools to do the right job, including closed containers, filters on storage containers, isolated fluid systems and oil-fill equipment designed to introduce only prefiltered lubricants to reservoirs.
Within 60 days, oil analysis reports will reveal marked improvements. Operators and lube technicians can demonstrate to managers that practicing reservoir management gets results. Early success also validates that PRM is the cohesive link between oil analysis, remedial filtration, fluid conditioning and equipment reliability. PRM can be initiated without spending a dime of the company’s money.
Stick to Fundamentals
While there are many important lube-oil characteristics, PRM emphasizes only three of the most important readings: particles (ISO), water (PPM) and acid number (AN). Short of major equipment breakdowns, the vast majority of reservoir-supported machinery and equipment problems can be traced to early trouble with particles, water and acid. Operators and lubrication technicians who stick with fundamentals, understand basics and pursue remedial game plans will quickly grasp the concept and mindset of reservoir management.
Green Bay Packer coach Vince Lombardi exemplified his team’s winning ways by concentrating on just a few plays, staying with fundamentals and executing each play to perfection. PRM follows the same concepts by targeting and establishing game-winning dominance over particle count, water and acid number.
New ideas often meet resistance. PRM augments programs already in place by directing the company’s existing tools and services toward specific machines where persistent PRM efforts produce maximum benefits.
Select the most important reservoir-supported machines and equipment that are critical to plant and systems reliability. Retrieve at least five of the most recent oil analysis reports. Many operators have computer access to this information. Other operators should set up a working manual for each reservoir.
Identify those machines that are a “must” priority. Oil reports contain abnormal warnings, oftentimes underlined individual readings, that are out of specification. Machines and processes demanding attention will be obvious. Focus on high particle count, high water content and high acid levels. Reservoirs on machines or processes that warrant zero outage should still be part of a priority list.
Set Cleanliness Targets
Setting targets is important to PRM as it establishes the goals and serves as a performance measure toward those goals. Fortunately, operators can draw information from independent oil analysis labs, OEM equipment makers, oil companies and operator’s experience. Operators can instruct labs to set specific alert points.
Because PRM is a reservoir-oriented process, representative samples are critical cornerstones and must include the main reservoir and return line, if possible.
Repeatability and location are critical components of proper sample collection. If the process of sample collection inserts doubt about the quality of the data, then it will be difficult to make decisions with a high degree of confidence.
Samples can be collected from return lines through a variety of methods. Drain traps and sample ports with extension tubes offer both attractive efficiencies and repeatability to the technician. Awkward locations can be reached with wand extensions or sample tubing accessed via reservoir oil-filling caps. Avoid taking samples from the reservoir drain valve. While this practice has been followed for many years, it is neither a reliable nor a consistent representation of the reservoir’s contamination profile.
Bear in mind that PRM does not exclude other sampling procedures in the system utilizing pumps, actuators, servos circuits, gearboxes and bearing housings. In due course, oil analysis reports will display marked improvement for components as well as the main reservoir lube oil.
Practicing reservoir management relies on best practices in sample drawing techniques. Essential sample points are located at the reservoir’s lower center and just ahead of the return-line entry point. If this location is not available, use wand extensions, sample hoses, or install permanent pilot tubes to reach the reservoir’s midsection. As already noted, avoid taking samples from the reservoir’s drain because drain samples are rarely representative of system condition.
Remedial Tools and Techniques
Lube-oil reservoirs are highly individual; no two are alike. Lube oils and hydraulic fluids display a chameleon-like personality - never the same from one day to the next. However, remedial tools are readily available to control dirt, water and fluid health which keeps in line with the PRM concept. Consider the following:
Airborne particles and moisture penetrate reservoirs via every unprotected passageway. Up to 70 percent of component damage is traceable to particles and moisture, most of which enters the system via unprotected reservoirs. The fix is simple. In many cases, changing from the old, automotive, bayonet-type twist-on caps to a desiccant breather eliminates a major airborne invasion route. The change can be made in less than five minutes. Other openings (bad seals, open filler caps, access openings, etc.) must be protected from airborne contamination.
Off-Loop Filter Systems
Suction and return-line filters protect hydraulic and lube oil system components. However, system filters are always a compromise between flow rates, linear velocity, viscosity, contamination, system pressure, pressure drop, dirt-holding capacity, physical size, accessibility and cost.
Off-loop filters are not governed by system requirements as they operate independently from the system. Therefore, operators have many options for filters, media and micron ratings.
Filters should be reservoir-dedicated and run continuously. Periodic filtering with portable filter carts may not fit the PRM concept, depending on the rate of ingression. Removal of filter carts is an invitation to contamination.
Water invades lube-oil systems via heat exchanger leaks, unprotected reservoir openings, water-laden new oils, seal by-pass and careless dispensing. Water and oil hold great attraction for each other. Small amounts of water may not seriously damage components, but high water content will.
Operators should know when an oil has reached its 100-percent saturation point. Beyond this saturation point, additional water roams as free water, which poses the greatest threat to machinery and equipment. Relative humidity (RH) measurements within the reservoir correlate with the percent of an oil’s water saturation point through monitors that continuously record RH percent readings. Real-time water-monitoring devices create warning signals that indicate when 70 percent water saturation has been reached.
Early warning of water invasion is vital information operators need in order to avoid serious bearing damage to key rotating equipment.
Above the reservoir’s oil level and beneath the top of the same reservoir lies the headspace. Every reservoir reflects different conditions within its headspace as the contents of oil mist and water vapor vary considerably. Headspace water vapor and water within the lube-oil continuously seek equilibrium. By removing headspace water vapor via compression, water residing within the oil moves out of the oil and into to the headspace, thereby reducing the water content (PPM) of the lube oil.
Such early warning of danger ahead might have changed history if, on April 12, 1912, the Titanic had radar mounted on its main mast. In one sense, monitoring rising water saturation in lube oils is a form of radar. With advanced water warnings, operators can steer clear of reservoir icebergs by temporarily installing portable carts, coalescing separators, centrifuges, or by sweetening the oil as a temporary measure.
The continuous process is called headspace dehumidification. It is a filterless process designed to keep water in lube oils within safe limits.
Vent Mist Eliminators
Hardworking reservoirs create oil mists that vacate the system. Mists and stray vapors often escape through open ports and poorly sealed covers and hatches. While simple discharge to atmosphere has been common for many years, environmental and safety considerations changed the practice. Vent mist eliminators (VME) eliminate the plumes rising from gas or steam turbines and discharge from reciprocating engine crankcases.
Mist control means oil savings because coalesced oil mist can be returned to the main reservoir. Small and large reservoirs are sources of unwanted oil mist in work areas and walkways. For operating personnel, it is undesirable, unsafe and unhealthy and should be corrected.
Ferris density, ferrography and wear debris analyzers enable operators of lube-oil systems to conduct detective work on the equipment to determine possible causes of potential component failure. Chip detectors may also play a useful role for minimizing the effects of catastrophic failure of one component on other system components. Chip detectors are particularly useful for fairly large wear debris particles. New technology includes two chip detectors within one duplex housing, wherein one oil flow path can be isolated for inspection while the opposite side sustains uninterrupted oil flow. In this type of configuration, the chip detectors can be removed for lab analysis and inspection.
Visual checks and debris analysis at the site may present conclusive evidence of bearing failure, perhaps in time to take action.
For many years, filter carts have been the main tool for emergency remedial action in contaminated lube oils and hydraulic fluids. Far too many operators, however, are misled by the cart’s importance as a permanent improvement in system cleanliness and reliability. Once disconnected from any system, the portable filter cart’s mission is over.
Portable filter carts should be used for emergencies and assigned additional tasks including: new-oil filtering, transferring, dispensing and barrel recycling of contaminated spilled oils.