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Wednesday, 1 August 2012

Flushing a Turbine Oil System

Flushing a turbine oil system is a specialised procedure best carried out by specialists.

When flushing a turbine oil system it’s always advisable to bear in mind the value of the equipment, and not take any short cuts; or skimp on costs!

Up-front planning and meetings with construction, start-up, oil supplier and the end user should be scheduled in advance to build consensus on the turbine flushing procedures.

Conduct this test prior to flushing a turbine oil system.

Taking a 5 lt. sample from the supply tank, and a second 5lt. sample from the turbine reservoir. Conduct the following tests on these samples:
  • Suitability for Continued Use (Annual) 
  • Viscosity ASTM D445 
  • RPVOT ASTM D2272 
  • Water by Karl Fischer Titration ASTM D1744 
  • Acid Number ASTM D664 • ISO Cleanliness Code 4406 
  • Rust ASTM D665 A 
  • Demulsibility ASTM D1401 
  • Foam ASTM D892 Sequence 2 
  • ICP Metals

The two most used procedures for flushing a turbine oil system.

When flushing a turbine oil system, the system as a whole needs to be considered. Lubrication system flushing could either be a displacement flush after a drain and fill, or a high velocity flush for initial turbine oil fills. A displacement flush is performed concurrently during turbine oil replacement and a high velocity turbine flush is designed to remove contaminants entering from transport and commissioning a new turbine.

For a high velocity flush all restrictions to flow are removed, and then (using an external flush pump and filter) oil is flushed through the system at approximately 3-6 times its normal flow rate. This high volume of oil will remove scale and particulate from the piping and flush it back to the main oil reservoir where it will be filtered.

Displacement turbine oil flushes using a separate flush oil, are done to remove residual oil oxidation product that is not removed by draining or vacuum evacuation. This method of flushing a turbine oil system is conducted by utilizing lubrication system circulation pumps without the normal oil circulation flow paths being modified, except maybe for potential kidney loop filtration.

This is typically done based on a time interval vs. cleanliness (particle levels) to facilitate the removal of soluble and insoluble contaminants that would not typically be removed by system filters.

Most turbine OEMs offer high velocity turbine flushing and filtering guidelines. Some contractors and oil suppliers also offer flushing and filtering guidelines.

Often during turbine commissioning, these guidelines are scaled back to reduce cost and time. As a result, there are some procedural concerns that arise, and these should be addressed on a risk vs. reward basis.

When flushing a turbine oil system with high-velocity flushing the following is advisable:

  • Supply and storage tanks should be clean, dry and odor-free. Diesel flushing is not acceptable. 
  • Two to three times normal fluid velocity achieved with external high-volume pumps or by sequential segmentation flushing through bearing jumpers. 
  • Removal of oil after flush is completed to inspect and manually clean (lint-free rags) turbine lube oil system internal surfaces. 
  • High-efficiency by-pass system hydraulics to eliminate the risk of fine particle damage. 
The following are supplemental or alternative elements while flushing a turbine oil system
  • Use of a separate flush oil to remove oil soluble contaminants that can impact foam, demulsibility and oxidation stability  
  • Need to filter the initial oil charge at a level consistent with the filtration specification 
  • Thermal cycling of oil while flushing a turbine oil system 
  • Pipe line vibrators and the use of rubber mallets at pipe elbows  
  • Installing special cleanliness test strainers and sampling ports 
  • Desired cleanliness criteria for flush buy-off 
  • Lab ISO 17/16/14 to 16/14/11 acceptable particulate range 
  • Use of on-site optical particle counters 
  • 100-mesh strainer, no particles detectable by naked eye 
  • Millipore patch test
Selecting a lube after flushing a turbine oil system.
Turbine OEM recommendations, past experience, customer testimonials and oil supplier reputation are key elements to be considered in the selection of a turbine oil. The correct selection of turbine oil and continued condition-based maintenance should set the stage for years of trouble-free service.

When faced with flushing a turbine oil system, you’ll probably appreciate a turbine oil with superior performance characteristics and an oil supplier with extensive technical support: That’s why knowledgeable operators turn to Habot Synthetic Lubricants. We can supply the right synthetic oil as well as advise on the best methods to follow when flushing a turbine oil system.