Advice

Nearly every end consumer is familiar with the phenomenon of oil varnish and oxidation. Varnish removal filters, routine oil changes and overhauls do not offer a solution to this problem. Tanis Engineering can show you that the cause often lies with oil quality. Why does one type of oil form a lot of varnish deposits, whereas others do not? Tanis Engineering advises on the use of the right oil type with which your installation can perform optimally, making varnish and oil oxidation things of the past.

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Oxidation/ degradation

A crucial installation such as a gas or steam turbine needs constant, clean and dry oil for the right lubrication of everything ranging from bearings and the gearbox to the control hydraulics. Yet, it is often the case that the oil is (extremely) contaminated, despite the standard filters being replaced on time. How is this possible?

 

Oil ages as it is impacted by oxygen, metal, temperature, water and contamination. Here, a chemical reaction occurs in the oil, namely oxidation. These oxidation products then precipitate on metal surfaces and cause a brown deposit, also known as varnish. Varnish formation does not only cause the oil to oxidise even faster but it also accumulates on the walls of the tank and settles in the plumbing of the entire system, in the pumps and valves, and causes the existing filters to be clogged. This results in increased bearing temperatures and vibrations, deteriorating temperature regulation, poorly functioning pumps and valves, and having to replace the filters and even the oil more frequently. In extreme cases, this can even lead to unplanned downtime of machines, resulting in large production losses.

Varnish removal

Removing the brown deposits, replacing existing filters and changing the oil merely treat the symptoms. Replacing the oil is a temporary solution, since the new oil oxidises extra quickly in an already contaminated system. Varnish removal techniques, such as resin/ ionisation filters or additive boosters, seem like a definitive solution but do not address the underlying problem: the oxidation/degradation of the oil in the machine.

Solution

The best approach is to select an oil that does not produce varnish deposits while operating. But how do you do that? Every oil manufacturer describes the good properties, with regard to oxidation resistance, of their oils in practice. However, none of the oxidation tests mentioned on the brochures and data sheets actually give a good indication of this. The tests that are stated on the data sheets (i.e. TOST and RPVOT) are intended to either assess the suitability of a lubricant for use as a turbine oil or give an indication of the anticipated lifetime. These tests are thus not intended to accurately predict the varnish during use.

Tanis Engineering uses a screening test that indicates the oil's tendency to form varnish deposits. A modified version of the so-called Wolf Strip test (ex DIN 51392). This test assesses an oil's resistance to the formation of varnish deposits when exposed to high temperatures, air and catalytic metals. This screening method creates conditions comparable to those in practice and makes it possible, supplemented with data from the datasheets, to select the best oil.

Types of analysis
  • Adriaan Tanis
  • Blienkerd 1
  • 3253 CE Goedereede
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