The approach of detecting and analyzing sludge and varnish problems in machinery is not the same as used oil analysis. In many instances this is because the evidence is not always in the oil. The sludge and varnish should be analyzed directly, using a completely different set of tests and evaluation parameters. Still, used oil analysis plays an important diagnostic role to help reveal candidate causes as well as to rule-out others.

The conditions that commonly lead to sludge and varnish problems vary, which complicates the process of identifying the root cause analytically. There are at least 25 unique lubricant degradation mechanisms leading to sludge or varnish formation.

The post Demystifying Sludge and Varnish appeared first on Tesibis.

A wide range of fluid degradation and contamination-related issues can affect turbine lube oil systems. One serious and growing concern is the presence of sludge and varnish. This condition can occur in even the most well-maintained machines. Surprisingly, it can also happen when oils are not particularly old or contaminated. And it can occur with even the most thermally robust synthetic lubricants and hydraulic fluids.

In turbine systems, there are few failure conditions that can disrupt operation as quickly and completely as a varnished and seized-up control valve operation. This can be the cause of a tripped turbine forced outage or other production losses. So too, sludge in many circulating lube oil systems can gum up flow controls, strainers and critical oil ways. In recent years, there has been a large number of reported cases associated with varnish and sludge formation in turbine-generator applications. Explanations for these problems have varied but typically include Group II mineral oil solubility issues, additive instability, bulk oil oxidation, adiabatic compressive heating and electrostatic discharge, among others. This paper will review precursor conditions that lead to sludge formation, some of the common lubricant degradation methods and the role of oil analysis in recognizing the potential risk well ahead of failure.

The post Review of Degradation Mechanisms Leading to Sludge and Varnish in Modem Turbine Oil Formulations appeared first on Tesibis.

Hot oil has typically received the most press, even in this publication. After all, oil is not like fine wines that get better over time. In fact, even the very best wine will stress-out when exposed to too much heat. For instance, most wines will age roughly twice as fast at 77°F compared to 55°F, which is why connoisseurs and collectors prefer cellar temperature to store their liquid assets.

In 1903, Svante Arrhenius won a Nobel Prize when he figured out the relationship between temperature and most chemical reaction rates. Often called the Arrhenius Rate Rule, it relates to the fact that lubricants, once they’ve exceeded their base activation temperature, will degrade or oxidize twice as fast for every 10°C (18°F) increase in temperature.

The post The Effects of Temperature on Lubricants (Why oil is like an egg) appeared first on Tesibis.

Excessive heat is a severe contaminant. It wreaks havoc on oil (chemically and physically) and retards lubricant performance by increasing wear, corrosion and friction. Friction and wear cause more heat, which sends the machine into a cycle of despair.

Heat must be controlled within the machine’s operating limits. This varies considerably between machine types and applications. Lubricants have their own unique limits as well.

Attempting to solve heat problems by simply adding a cooler or enlarging the cooler just masks the symptom and prolongs the solution. Abnormal heat is a telegraphed S.O.S. call that commands attention and remediation.

Critical temperatures on most high-speed and high-value machines are monitored in real time, often at multiple points, such as guide and thrust bearings (typically imbedded thermal couples). A common example of bearing temperature monitoring is shown in Figure 1.

Here, a temperature excursion was noticed first before any other symptoms. After inspection, a lubrication issue (cake-lock) was found to be the root cause.

The post Be Alert to Heat as Both a Contaminant and a Symptom appeared first on Tesibis.

One of the main disadvantages of using grease over oil is the annoying tendency of grease to cake and dry out. We all know that oil has a natural tendency to drain out of the grease thickener over time. We see conspicuous evidence of this when oil puddles in unleveled grease pockets in pails of new grease. We’ve also seen the dribble of oil from stored grease cartridges and prepacked bearings on storeroom shelves.

More serious is the hardened byproduct of oil drainage that builds inside the cavities of operating bearings and gears over time. Often this takes years to develop, while in other cases the condition can reach catastrophic levels in just a few weeks. The failure can be self-propagating. As grease becomes dry, frictional forces escalate, causing concentrated heat within the bearing.

The elevated heat continues to force more rapid and complete drying of the grease. In time, the grease can reach a state of consistency ranging from hard putty to sandstone, depending on the thickener type and degradation conditions.

Frequently the most serious offending conditions leading to grease dry-out are aided by other causes working in concert. Let’s begin by reviewing the primary causes of grease dry-out. Once the causes are determined, we have the information necessary to prescribe steps to grease your bearings properly.

The post Grease Dry-out: Causes, Effects and Remedies appeared first on Tesibis.