In This Issue:

• Up Front: Source of Leak is a Mystery

• Book Bits: Wear Debris Reflects Condition of the System

• Today's Tip: Pay Attention to that Oil Level Indicator!

• Q & A: Filter Quality and Oil Analysis
  

Up Front

Source of Leak is a Mystery

While working onboard a cargo ship, the crew encountered a challenge in the engine room. We were confused as to why the main propulsion engine leaked lube oil from the crankcase doors and relief valve seals at will.

There were times when no leaks were visible. Other times, from out of the blue, oil would seep from even the tiniest cracks in the casing.

Eventually we discovered that one of the engine crew members was leaving the engine room entrance door open. This amazingly caused the leak!

We made it a practice to keep our engine spaces under positive air pressure to ensure the turbochargers were never starved of air. This provided higher pressure outside the engine casing than inside. Leaving the door open caused a severe drop in engine room air pressure.

Additionally, the buildup of crankcase pressure increased through partial leakage past the piston rings (blowby). This resulted in the lube oil on the inside walls of the casing being forced out of the narrow openings.

This problem helped us to identify the leaks in the casing and take corrective actions quickly! (Submitted by Sujit Mukherjee. Thanks Sujit!)

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Book Bits

Wear Debris Reflects Condition of the System

From "Wear Debris Analysis":

The whole concept of Wear Debris Analysis (WDA) is based on the idea that debris released from a system conveys the condition of that system. Take a simple example: if a hose is flexed and no debris is generated from it, then the hose is probably in excellent condition and likely to last a long time. However, if bits of hose are coming off the surface (either within the hose or on the outside), then the likelihood is that fracture will occur soon.

More information about "Wear Debris Analysis".

Today's Tip

• When rolling element bearings are lubricated from oil held in a sump, attention to the oil sump level indicator will not only bring savings in terms of extended bearing life, but also will lead to reduced bearing temperatures due to churning and metal-to-metal contact resulting from possible oil starvation. As a general rule, the lowest rolling element should be half covered with the oil, when the bearing is stationary. This may seem like a simple rule to observe but it is suprising how often it is completely overlooked! (Submitted by Derek Peasley, FAG Bearings. Thanks Derek!)

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Q & A

Filter Quality and Oil Analysis

"How does the quality of a filter impact oil analysis results (contamination and ferrous wear)? Is it correct to say that using filters with different beta ratios in same equipment will result in different analysis results? Is there any correlation in setting alarm levels and filter beta ratio?" - Erwin Sadhoe, Alcoa

The quality of the filter is directly proportional to the cleanliness and wear rate of the system. The higher the beta for the same micron pore size will result in a faster cleanup rate; thus, it is better able to control ingression of solids in the system. The main system ingression sources typically are seals, breathers and oil top-ups, and wear debris. When catalytic wear metals are removed from the oil, the lubricant will experience longer oxidative life.

Therefore, expect to see better cleanliness results on the hard particle measurements, as well as lower levels of wear debris in the system, assuming that the oil is in good condition and there are no other problems like water ingress or misalignment or imbalance.

In terms of setting alarm levels, the first step is to set the alarm levels to achieve a reasonable and realistic gain in lubricant and machine life. Using any of several methods, this can be done to optimize your requirements based on financial, safety, environmental and reliability goals.

On that basis, the appropriate filter can be selected. Most filter manufacturers have methods to determine the required element size and pore rating to not only meet the cleanliness target, but also to match the lubricant viscosities at operating temperature that would affect the flow rate. Most companies have established a beta ratio of 200 for their quoted pore size, although recent changes mean that they must also quote a beta value for a number of size ranges to establish performance. (See this article for more information.)

Over the life of the machine, a better-quality filter (generally more expensive) will prove to be more cost-effective than a cheaper filter owing to the relationship between filter performance and the system wear rates. To add value to that, many high-performance filters offer an associated improved dirt- holding capacity.

Martin Williamson, Senior Technical Consultant, Noria UK Ltd.

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