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Sunday, 24 May 2015

Advantages Of Synthetic Turbine Oil.

There are numerous advantages of synthetic turbine oil over mineral lubricants.

Although petroleum-based mineral oils function very well as lubricants in many turbine applications, the advantages of synthetic turbine oil under severe conditions is undeniable.

Limitations of mineral lubricants where the advantages of synthetic turbine oil are indisputable.

While mineral oils are cost-effective and provide a reasonable service life if used properly they have some limitations, depending upon the specific type of base stock used, the refining technology, the type and level of additives blended, and the operating conditions encountered. The main service difficulties within mineral oils are:

  1. The presence of waxes, which can result in poor flow properties at low temperature. 
  2. Poor oxidation stability at continuously high temperatures, which can lead to sludge and acid buildup.
  3. The significant change in viscosity as the temperature changes, which can cause the base oil to thin excessively at high temperature. 
  4. A practical maximum high-temperature application limit of about 125 degrees C above which the base oil oxidizes very rapidly. It is desired to keep mineral based turbine oil within the operating range of 40 to 65 degrees C. 
In steam turbines, lubricants using synthetic PAO may provide:

  • Exceptional chemical stability 
  • Outstanding resistance to oxidation 
  • Excellent demulsibility 
  • Protection against rust and deposits 
These lubricants can also survive hydrolytic attack under the wet conditions in a steam turbine.

When early gas turbine engines came into use in the 1940's, mineral oils were used as lubrication. These mineral oils quickly reached the limits of their capability, which lead to extensive research in the late '40s and early '50s. The result was gas turbine lubricants technology.

Turbine manufacturers develop lubricants to embrace the advantages of synthetic turbine oil.

Early research, primarily by the military, lead to the Mil-L-7808 specification and oils known as Type I or 3 centistoke (the viscosity at 99C) jet oils. Type I oils are fully synthetic (ester)-based oils. These Type I oils worked well at first but were stressed beyond their limits by the late '50s and early '60s by the newer more powerful — hotter running jet engines. Engines using Type I oils exhibited heavy oil deposits (coking) which required early maintenance action and required the Type I oils to be on fixed drain intervals.

This lead to the development of the Mil-L-23699 specification in the early '60s and the Type II (5 centistoke viscosity at 99C) oils. These Type II oil were also called "2nd generation" jet oils (Type I being "1st generation") by the industry.

Seeking to further develop the advantages of synthetic turbine oil Type II oils,ester-based synthetics, used today by virtually all turbine powered aircraft worldwide were developed. These have proven to be the most technically and commercially successful and long-lived oils developed for aviation.

However the advantages of synthetic turbine oil is due to the improved esters they use, with enhanced additive packages to attain about a 38C improvement in the high temperature serviceable limit, when compared to Type I oils, which eliminates the need for oil drains in most jet engines.

Esters boost the advantages of synthetic turbine oil.

An ester is the reaction product of an alcohol and fatty organic acids; which forms a very stable base stock (base oil) both at low temperature and high temperatures (above 250C). The ester is made in a chemical reactor and the finished oil in a blending tank.

The source of the raw materials is mostly non petroleum-based — meaning the fatty acids are obtained from sources such as palm and coconut oils, etc. The additives used are typically antioxidants, metal passivators, antifoamants, anti-wear and possibly load carrying or corrosion inhibitor additives.

In gas turbines, synthetic lubricants using quality synthetic base stocks, such as those used by Habot Oil, can provide superior rust protection, low-temperature fluidity and high-temperature oxidative stability. The advantages of synthetic turbine oil means that they can be used as circulating oils for the lubrication of land-based gas turbines, particularly units under 3,000 horsepower used as standby power units, and in some types of total energy systems.