3.Challenges to industries For any power generation facility, the turbine is considered the lifeblood of the operation. According to a 1991 study by General Electric (GE), turbines contribute on average 20 percent of all forced outages in a conventional power plant. Among this 20 percent, GE noted that 19 percent of turbine/generator problems were associated with the lube oil system. For this reason, monitoring turbine oils has become common place in the power generation industry.
4.PurposeLubricant testing is recommended for the following reasons: To study the condition (wear, and so on) of the machine being lubricated. If there is a problem with the lubricant, there is a strong possibility that the machine will need maintenance. To determine if the lubricant is meeting the specifications.
5.LUBRICANT LAB TESTS The following are laboratory tests performed on oil samples: 1. Particle count -ISO 4405, 4406) 2. Fourier transform-infrared analysis 3. Additive Package Condition 4. Viscosity testing (ASTM D445) 5. Total acid number (TAN) 6. Spectrometric analysis/emission spectroscopy 7. Crackle test/Karl Fischer water test 8. Oxidation stability test (ASTM D2272) 9. Demulsibility (ASTM D1401-96) 10. Pour point (ASTM D97) 11 .Foam test (ASTM D892-95 12. Flash point (ASTM D92)
5.1.Particle Count -ISO 4405, 4406: Particles in lube oil have long been recognized as the main cause of failure in hydraulics and rotational machinery. Particles are also a leading indicator of a machine’s condition. Because all contaminants in the oil are counted as particles, the particle count includes wear particles, soot, dirt, and other contaminates. This test provides information on lubricant cleanliness.
5.2. Fourier transform-infrared analysis The FT-IR monitors the chemical composition of the oil in certain key wavelengths. The infrared absorption spectrum of a lubricant furnishes a means of fingerprinting organic compounds and functional groups. Test results are trended and quantitative and qualitative determinations can be made. Infrared analysis is often used for identifying additives and their concentrations, reaction products, and contamination by organic materials in used lubricants. Oxidation (carboxylic acids and esters), nitrate esters, water, soot, and glycol can be quantified.
5.3. Additive Package Condition: Additives present in a lubricant improve and strengthen the performance characteristics. Chemically active additives are able to interact with metals and form a protective film with the metallic components present in the machinery. The designer of the additive package must ensure that the additives will not produce unacceptable side effects. If an additive is present in excessive levels or interacts in an unsatisfactory manner with other additives that are present, it can be detrimental to the equipment. Over time, additive packages can deplete, leaving machinery unprotected and vulnerable to failure.
5.4. Viscosity testing (ASTM D445): Viscosity is one of the most important characteristics of an oil because it ensures that the proper film strength is present to minimize metal-to-metal contact and machine wear. Viscosity is a factor in the formation of lubricating films under both thick and thin film conditions. If the viscosity is too low, the oil may not have the necessary film strength required to maintain a proper oil film. An inadequate oil film results in excessive wear. A decrease in viscosity may indicate contamination with a solvent or fuel or with lower grade viscosity oil. If the viscosity is too high, additional fluid friction is generated. This increases the operating temperature of the bearings and increases the rate of oxidation.
5.5. Total acid number (TAN) (ASTM D664 and D974) The acidity of lubricants is measured by the amount of potassium hydroxide required for neutralization (mg KOH/g), and the resultant number is called the TAN. An increase in TAN may indicate lube oxidation or contamination with an acidic product. A severely degraded lubricant indicated by a high TAN may be very corrosive.
5.6. Spectrometric Analysis/emissionspectroscopy/rotrode filter spectroscopy Elemental analysis is performed in accordance with atomic emission spectroscopy (AES). A specific volume of lubricant is energized using an electrical arc. The light frequencies and intensities are measured and reported in parts per million of various elements. The following elements are analyzed: Fe, Cr, Al, Pb, Sn, Cu, Ag, Ni, Na, V, Cd, Ti, Mo, Ca, Ba, P, Zn, B, K, Mg, and Si.
5.7. Crackle test/Karl Fischer water test(ASTM D-4928 and D1744) Water in a lubricant not only promotes corrosion and oxidation, but also it may form an emulsion having the appearance of a soft sludge. In many bearing applications, even a small amount of water can be detrimental, especially in journal-bearing applications where the oil film thickness is critical. In the crackle test, a drop of oil from an eyedropper is placed on a hot plate heated to 100°C, and monitored for the characteristic crackle that occurs as water explodes into steam.
5.8. Oxidation Stability Test(ASTM D2272): This was formerly called the rotating bomb oxidation test, and it is used to assess the remaining life of in-service lubricants.
5.9. Demulsibility (ASTM D1401-96): This test provides a guide for determining the water separation characteristics of oils subject to water contamination and turbulence.
5.10. Pour Point (ASTM D97): The pour point is the determination of the lowest temperature that a petroleum product may be used if fluidity is necessary to the application.
5.11 .Foam Test (ASTM D892-95) Foaming of the oil may result when air is picked up by the oil and is thoroughly mixed by agitation and churning. Excessive foam accumulation can result in loss of oil by overflow or seepage. High quality oil should have good resistance to excessive foaming, and the air bubbles formed on the surface should break up quickly. The foam test is the determination of the foaming characteristics of lubricating oils at specified temperatures.
5.12. Flash Point (ASTM D92): Flash point indicates the presence of highly volatile and flammable materials in a relatively nonvolatile or nonflammable material. The lubricant sample temperature is raised at a constant rate as the flash point is approached. The flash point is the lowest temperature at which the application of the test flame causes the vapors above the surface of the liquid to ignite
5.13. Cone penetration of lubricatinggrease (ASTM D 217) This test measures the consistency of grease. The cone is dropped into the grease sample from a specified height and at a specific time. The measured amount that the cone penetrates into the grease is the cone penetration
5.14.Percent Sediment in Lubricating Oils This test is an excellent determination of sediments suspended in lubricating oil. Excessive amounts of sediments can impede oil capability and can clog filters.
6.Sample Recommendations for taking samples are: Take the sample when the system is stabilized, not before or just after makeup lubricant has been added. Take the sample ahead of filters so that contaminants are still in the lubricant. Put the oil sample in a suitable, clean, well-labeled container. Take the sample using a consistent method. Take the sample from the same location and under the same operating condition.
7.Machines Cover Under LubricantsTesting Program in thermal power plants Mill, Air preheater, Turbine , Boiler feed pump, F D Fan, ID Fan, PA Fan, Compressor,
8.Deterioration of lube Oil inService Oxidative Degradation -This occurs as the result of chemical changes brought about by oxygen in the atmosphere. Thermal/Oxidative Degradation -This may occur at hot spots in turbines. At elevated temperatures, hydrocarbons are subject to thermal cracking to form unstable compounds. Water Accumulation in the System Accumulated water promotes oil degradation . Loss 0f Additives -This can result in more rapid oxidation and premature rusting. Influx 0f Contaminants -Contaminants arising within the system (corrosion and wear products) or from fly ash/ dirt, fluids cause wear problems.
9.Turbine oil monitoring The key to efficient turbine maintenance is routine monitoring of the oil, which ensures that decisions involving the turbine, including scheduling of oil changes and other maintenance, are based on what is actually happening inside the unit, instead of the number of hours, days or years of operation. Routine and in-depth monitoring can provide warning signs early enough to take corrective action.
9.1.DAILY AND WEEKLY TEST, INSPECTION OF LUBRICANT – STEAM TURBINE LUBE OIL : DAILY-Visual Test for Change in Appearance to Indicate Excessive Water or Solid Contamination WEEKLY-Visual Test of Oil Color to Detect Deterioration (Reference ASTM Test Method D 1500-82)
9.2.QUARTERLY TEST, INSPECTION OFLUBRICANT –STEAM TURBINE LUBE OIL: Laboratory Test for Viscosity to Indicate Oil Contamination or Deterioration (Ref ASTM Test D 445- 82) Laboratory Test for Total Acid Number to Indicate Antioxidant Depletion (Ref ASTM Tests D 974-80, D 664- 81, D 3339-80/DIN 51587) Laboratory Test for Water Content to Indicate Water Contamination (Ref ASTM Tests D 95-70, D 1744-64) Laboratory Test for Cleanliness to Indicate Particle Contamination (Ref ASTM Tests F 311-78, F 312-69, F 313-78/ISO 4406).
9.3.YEARLY TEST, INSPECTION OF LUBRICANT –STEAM TURBINE LUBE OIL: Lab Test for Anti-Rust Protection Capability to Show Depletion of Rust Inhibitor (Ref ASTM Test D 665-82) Lab Test for Oxidation Stability to Reveal Anti-Oxidant Depletion and Oil Deterioration (Ref ASTM Tests D 943- 81 for New Oil and D 2272-67 for Used Oil). Any other test/frequency of test ,recommended by Turbine Manufacturers Lubrication Group/lubricant Supplier /ASTM Standard Practice/Company Technical Expert.
10. Analysis of Lubricant of Fan / pump /Mill Particle count Viscosity Total acid measure Condition of oil additives Sediment in Lubricating Oils Any other test recommended by OEM/ lubricant Supplier
11.1.Oil Analysis( Pulverizer Gearbox ) Wear Debris AnalysisThe elements found in the gearbox oil analysis are indications of the condition of the gearbox components. • Copper comes from thrust washers, bronze gears, bearing cages, and other bronze or brass components. • Iron comes from gears, bearings, worm shaft, and piping. The iron may appear as rust. • Lead in an oil sample indicates excessive babbitt bearing wear and possible failure. • Chromium and nickel in an oil sample may indicate abnormal wear of rolling element bearings. • The ISO 4406 Solid Contaminant Code is used to quantify contaminants in the oil.
12.Oil Specification-KWU –BHEL Turbine 500 MW Oil of viscosity OIL SUPPLIER BRAND class ISO VG 46 IOC SERVO PRIME 46 shall be used. The oil shall be a GULF OIL INDIA LTD GULF CREST 46 petroleum product CALTEX REGEL R&O 46 with or without additives to meet CASTROL Castrol prefecto t- 46 super clean the requirement of Indo mobil ltd Mobil DTE this standard. medium/DTE 798