Early detection means frequent detection. While daily one-minute visual inspections may be performed, many questions remain, including where and how to inspect, what the observed conditions mean, and how to penetrate a machines exterior without X-ray vision.
According to Jim Fitch, CEO of Noria Corp., There are three important inspection zones in common oil reservoirs and sumps. In a presentation at Lubmat in Bilbao, Spain, in June, he said, These zones have a story to tell about your oil and machine. They might be difficult to reach, but difficult does not mean impossible and certainly doesnt mean unnecessary.
Level, Foam & Deposit Zone
Machines need a sustained and adequate supply of the right lubricant. Adequate doesnt just mean dampness or the nearby presence of lubricant, Fitch related. Adequate varies somewhat from machine to machine, but is critical nonetheless.
High-speed equipment, running with a full hydrodynamic film, has the greatest lubricant appetite and is also the most punished when starved. Machines running at low speeds and loads are more forgiving when the lubricant supply is restricted. However, even these machines can fail suddenly when severe starvation occurs.
Fitch explained that there are four keys to solving starvation problems using proactive maintenance. First, identify the required lube supply or level to optimize reliability. Second, establish and deploy a means to sustain the optimum supply or level. Third, implement a monitoring program to verify that the optimum supply or level is consistently maintained. Fourth, quickly remedy noncompliant lube supplies or levels.
For noncirculating, wet-sump machines, slight changes in oil level can be catastrophic, Fitch noted. These include bath, splash, oil-ring, flinger/slinger and similar lubricant supply methods. For these machines, frequent confirmation that the correct oil level is maintained has everything to do with machine reliability. This is best done by properly mounted and frequently inspected level gauges.
Some things float; others sink. For instance, certain low-density additives can rise and form a visible film on the oils surface. Air bubbles, water vapor, natural gas and refrigerants are all buoyant. Once they get to the oils surface, they either release gases into the atmosphere or create bubbles. A stable layer of bubbles forms foam, which is disruptive for a variety of reasons. Most importantly, foam is associated with lubricant starvation.
Aeration and foam can be detected as long as you have a window, said Fitch. Sight glasses and level gauges mounted in ports that are centerline to the oil level enable observation and should be checked daily. Inspection windows allow both oil level and aeration issues to be checked simultaneously. Hatches and access ports can also facilitate early detection of abnormal foam and aeration.
Oil level sight glasses and internal tank inspections permit detection of surface deposits such as varnish and sludge. The worst deposits usually build up just above the oil level, called the splash zone, and look similar to a tar-like bathtub ring, Fitch noted.
The cooler metal surfaces above the oil level enable splashed oil to deposit insoluble suspensions (condensation) that accumulate over time. These adherent gums and resins are associated with a range of problems that require early detection, including oil oxidation, microdieseling and electrostatic discharge, he added.
Sight glasses can also be used for early detection of deposits. However, the acrylic or glass used often becomes fouled by deposits when high varnish potential conditions exist.
Bottom Sediment & Water Zone
Sooner or later, gravity drags things out of oil. On one hand, this is beneficial because sedimentation and stratification of impurities can have a moderate cleansing effect on the oil. On the other hand, sedimentation can cause a number of hazards and risks.
Most of the things you dont want in your oil are heavier than the oil, said Fitch. These include hard solids (dirt, wear debris, corrosion debris, process solids, etc.), soft solids (sludge, agglomerated oxides, microbial contaminants, dead additives, etc.) and stratified liquids (such as free water and glycol).
Low-lying impurities can be called bottom sediment and water and include:
Agglomerated sludge (resinous solids, gums, oxides and dead additives)
Stratified solids (dense zones of soft contaminants, oxides and dead additives)
Sediment (settled hard contaminants like dirt and wear debris)
Water and other settled liquid contaminants (for example, antifreeze)
Often the sludge and sediment found on the bottom of sumps and reservoirs are tightly bound by water, he continued. Most oil impurities are polar (water loving). When free and emulsified water contaminates an oil, it can act like a mop to collect and bind these impurities together. Eventually, gravity pulls the growing sludgy mass to the sump floor. Dirt and wear debris that fall by normal sedimentation can also cling to these sludge pools.
In an ideal world, you wouldnt allow bottom sediment and water to accumulate, and oil changes wouldnt be necessary Fitch related. However, nobody lives in an ideal world. While you cant eradicate bottom sediment and water in the real world, you can control its accumulation and resuspension by following a few guidelines.
First, use a bottom sediment and water bowl to monitor and purge these contaminants periodically. This will prevent hazardous accumulations and help track the source and rate of generation.
Second, after an oil drain, use a discharge wand from a filter cart to rinse out remaining sediment and water from the tank and sump bottoms before refilling with new fluid. Inspect to confirm that the rinse was successful.
Third, after adding new oil, circulate the fluid through a filter at the highest flow rate possible before the machine is started and put under load. Use a filter cart, if necessary. Allow the total oil volume to turn over no less than five times. Do a simple patch test or particle count to confirm cleanliness, especially for critical equipment.
Fitch explained that bottom sediment and water are symptomatic of a host of issues related to the oil and machine. Failed and degraded oil, environmental contaminants (e.g., dirt and water), active machine wear and corrosion all produce sediment and water. To find the cause, analyze drain port samples periodically, and sample the sump bottom using a drop-tube vacuum sampler.
The seriousness of bottom sediment and water goes far beyond machine problems that produce sediment and water, Fitch cautioned. They can lead directly to sudden machine failure. He noted that disturbing the sediment in oil lubrication systems can produce what is called the fishbowl effect where even slight agitation causes the oil to become murky with sediment, which is then circulated to the machine parts.
Color & Clarity Zone
Transitions in oil color and clarity are common precursors to bottom sediment, sludge, varnish, emulsified water, entrained air and stable foam conditions, said Fitch. For this reason, its important to know when color and clarity change because the oil is trying to tell you where it hurts. Simple and routine visual inspections can help track color and clarity.
Color transitions are caused by changes in oil chemistry that produce contaminants. The observed oil color is typically compared to new oil or previously sampled oil. Color bodies (called chromophoric compounds) alert inspectors to additive or base oil degradation, as well as the presence a host of contaminants that possess unique color markers.
Clarity transitions are generally caused by suspended insolubles, entrained air and emulsions. They can range from a slight haze in the oil to cloudy/murky conditions. Advanced conditions result in the oil becoming completely opaque (pitch black). Good lighting is required during inspection, including the optional use of a strong laser light source.
Fitch explained that color and clarity conditions and are less influenced by gravity and stratification. Still, these transitions can be seen when inspecting low-lying oil (tank drains and bottom sediment and water bowls). They can also be seen in oil level gauges or inline sight glasses. You can even examine the oils color and clarity in a bottle during routine sampling, he said.
Color and clarity correlate to the transmission and spectral absorption of light by oil. Examples of conditions and contaminants that produce color and clarity transitions are shown in the table.
What Isnt Happening
Fitch continued, While condition monitoring is about knowing what is happening to your oil and machine, it is also about what is not happening. For example, what can you conclude if you visually inspect the oil and machine in all three zones, and observe excellent, healthy conditions? He identified about 25 things that could go wrong but do not because the zone inspections have passing marks. Among the multitude of things not occurring are listed in the sidebar.
Fitch added, It is worth emphasizing that zone inspections are not a substitute for routine oil analysis. Also, samples that are analyzed routinely by laboratories should not be taken from the bottom of sumps and reservoirs. Rather, they should be extracted from live, turbulent fluid zones,
using the proper methods and tools.
Lubrication-enabled reliability comes from paying close attention to what he termed the Big Four, those critical attributes that individually and collectively influence the state of lubrication and are largely controllable by machinery maintainence. They are:
Stable lubricant health
Adequate and sustained lubricant level/supply
The last three can be largely examined and confirmed by employing a rigorous zone inspection program, Fitch concluded. Early detection means frequent detection. Its within your control.
Passing zone inspections means the following
things are not happening…
Base oil oxidation
Additive stratification (dropout)
Free or emulsified water contamination
Heavy sediment from a failed filter
Heavy sediment from contaminantingression
Advanced machine wear (certain cases)
Depletion of several important additives