Varnish has been used as a catch all phrase within the industry. Typically, any degradation found within a lube system is automatically called varnish. As you may expect, there are many different types of varnish. In the industry, there’s an ongoing debate which states that Sludge can be described as wipe-able deposits while Varnish is likened to the material that sticks to the surfaces and cannot be easily removed. This gives varnish the image of only being deposits but that is not true when we think about varnish from a chemical perspective.
Within the industry, the question of whether to flush between oil changes has been asked numerous times. “Is it cost effective, does it really make a difference to the system?” are also asked in tandem. Flushing is recommended in systems that have experienced varnish and in systems that have accumulated some form of contamination. Two examples are given where it would have been a wise decision to flush between oil changes.
Do you work in the fertilizer industry? If you do, then you know how critical it is for your compressors to be fully functional! Typically, we’ve seen compression gases such as ammonia, nitrogen, carbon dioxide, oxygen or even nitrogen migrate through the seals and find their way into the lube system! The effects are usually disastrous! Additionally, there has been the demand for compressors to be more compact and efficient. This results in higher thermal and mechanical stress on the lubricant as it has to perform at higher temperatures in small capacity systems for longer periods of time and in the presence of contaminants!
Within the industry, we’ve always heard that “flushing” should be done or there are particular conditions required to do a flush but what exactly is a flush? Is there one standard definition? As per ASTM D6349 (Standard guide for Cleaning, Flushing and Purification of Steam, Gas and Hydroelectric Turbine Lubrication Systems), flushing is defined as, “circulation of liquid through the lubrication system or a component, when the turbine is not operating to remove contaminant”. While this may constitute the standardized definition of a turbine flush, we’ve realized that within the industry, a flush can mean many different things. Typically, these are categorized into Mechanical, Chemical or Solubility Enhanced System Cleaning.
Oxidation is one of the most prevalent forms of lubrication degradation which takes place in almost all lubricants. One method of combatting oxidation is through the use of antioxidants. While antioxidants are sacrificial in nature, their presence (or absence) is typically used as an indicator for oxidation. Hence, tests have been formulated to track different aspects of antioxidants but do these measures really add value?
Developing an oil analysis strategy for any component involves a lot of variables. When we think about Wind Turbine Gearboxes, this also holds true. Before we begin thinking about the strategy for oil analysis, we need to understand the manner in which the fluid and equipment components degrade during service. This must then be matched to appropriate oil analysis tests and frequencies to predict fluid and component failures. Typically, oil analysis can be used as a predictive tool to monitor three key aspects; lubricant health, equipment health and contaminant ingression.
Varnish exists in all shapes and sizes. Typically, when we think about varnish, our thoughts move towards large pieces of equipment. However, due to the nature of varnish, it usually affects the smaller (or tighter) component clearances first which in turn cause the entire machine to fail. One such component is Hydrogen seals usually found in turbines, generators and lots of other equipment.
The turbine oils of today undergo various stress factors. They are responsible for performing their functions in extremely harsh conditions. In some instances, the turbine oil is also used in the turbine bearings, generator bearings, load gears and servo valves in the hydraulic system. The oil can have a bulk reservoir temperature of 135°F (57°C) with a reservoir residence time of 5.8 mins. However, this can be exposed to temperatures in excess of 500°F (260°C). This is typically experienced in Class E gas turbine models. Additionally, the environmental conditions of the location of the unit, its duty cycle and the plant’s maintenance practices all have integral roles regarding the stress experienced by a turbine oil.
During the life of a lubricant, it usually undergoes aging and depletion of its additives. If a lubricant is subjected to particular environmental and operational conditions then it can start to degrade and produce deposits. Traditionally, if deposits start appearing or the antioxidants get depleted, the lubricant is rendered as failed and is disposed. This leads to a new charge of oil being ordered, flushing procedure carried out and the scheduling of all the logistics required to have the system returned to functionality. What if we didn’t have to dispose of the lubricant in the first place? Perhaps, we could have used some method of eliminating the deposits formed and even rebalancing the antioxidants in the lubricant? Does such a product exist?
Varnish occurs in many types of equipment ranging from hydraulics, turbines, compressors or even pumps. However, the only common factor amongst these types of equipment is the occurrence of these degradation deposits. The type of deposits produced varies significantly and is typically characterized as being either organic and soluble or inorganic and insoluble. These degradation products are usually quite complex and can have very unique physical characteristics.
Gearboxes require different types of oils based on the rotational speed of the gears, the type of the gears and the environment in which they are working. When we begin thinking about wind turbine gearboxes, there are a lot more factors to consider than these traditional ones for industrial gearboxes. Wind turbine gear oils have to perform in quite challenging environments and as such particular attention is paid to conditions such as wear, EP protection, water separation, air separation, detergency and oxidation.
There are instances where the MPC reading may prove to be ineffective. These cases can be characterized into non-traditional deposits or the system condition not being reflected in the oil condition. For non-traditional deposits such as chemical degradation, non-oxidation derived deposits and compatibility issues, the MPC readings do not accurately reflect the amount of soft contaminants present. PAGs and Phosphate Ester fluids are incompatible and can form immiscible droplets which can impact on the MPC rating. On the other hand, a recent oil change may not reflect varnish which is already in the system. Similarly, if a system has remained cooled for an extended time its condition will not be accurately reflected in the MPC rating.