Journal Bearing Pre-Lubes During Turbine Startup - Beware the Risks

Noria Corporation
Tags: turbine lubrication

Question: What do you get when you mix half a bottle of oil, a popular aftermarket engine oil additive and water? Answer: Trouble - if that is not how the additive is supposed to be used!

One technician employed at a power company believed an aftermarket product was causing problems with his company’s turbine lubricant management program. He tested his hypothesis and proved that aftermarket additives can create problems if they are not used in the manner for which they were intended.

The technician is in charge of the oil program at his plant. Every three months, he sends a sample of the turbine oil to an off-site lab for analysis. The supplier, a major oil company, also takes samples regularly, and reports its findings to the plant. After one such testing, the results indicated borderline foaming and water separability characteristics and a high acid number. Another run of samples confirmed water separability and other issues with the fluid.

... results indicated borderline foaming and water separability characteristics and a high acid number ...

The technician suspected that product cross-contamination was occurring and began to look for the source contaminant. The engine oil additive was discussed as a potential culprit. Clearly, the additive supplier did not propose in the additive product labeling the practice of pre-lubricating the journal bearings with this material during turbine teardowns. Plant supervision was skeptical that the additive was creating the problem given the long plant history with the practice, but was willing to let the technician take a hard look.

The technician began to collect information on the suspected problem from various sources. One report said three pints of this type of additive, and/or a detergent motor oil, could destroy the surface tension characteristics of up to 10,000 gallons of turbine oil. This motivated the technician to conduct a test at the plant’s oil shop. He mixed three concoctions, and came up with the results seen in Table 1.

He put each of the three bottles in a paint shaker for a long time, then left the bottles on his desk for a couple of days. He repeated the test with new samples from the same batch, and achieved the same results.

After the initial test, the technician re-ran the tests, this time using a blender. Again, some foaming occurred. It took approximately one month for the additive/oil mixture to separate from the solution. In the mixture of straight turbine oil and water, the emulsion broke right away; there was very little time difference when shedding its water vs. a test without the heavy synthetic.

The technician called an independent manufacturer of oils and greases for a recommendation. After they discussed his requirements, the technician settled on a high-viscosity synthetic lubricant (see Table 2), which was clear and had the same consistency as the engine oil additive. The synthetic formulation is designed to provide surface wear protection and is compatible with the rust and corrosion inhibitors, antifoam and demulsibility agents used in turbine oils. The synthetic also provides tackiness qualities; the lubricant is formulated with special additives to adhere to component surfaces without interfering with demulsibility. The synthetic was not a motor oil and didn’t contain detergents and dispersants.

There was clearly a difference between how the two products reacted ...

The technician repeated the tests using the synthetic to see if there was a similar foaming problem, and found that the separation was rapid and complete. There was clearly a difference between how the two products reacted under similar circumstances. The appearance of the mixtures was compelling. The stable emulsion created with such a small amount of the additive in the turbine oil convinced supervisory personnel that there was a connection.

The manager moved to replace the engine oil additive with the high viscosity synthetic lubricant after seeing the results. Other plants within the company are now following suit.

Figure 1

Historical Perspective

Why was the additive used in the first place? Rotors are largely stationary during teardown activities. Periodically, the shaft must be turned to check alignment and do other work. The high viscosity, tacky additive tended to stay between the shaft and the bearing much better than the other oils and products that were readily available at the plant. Consequently, re-oiling the turbine bearings could be done less frequently with the engine additive than with other materials during the outage.

Approximately seven years ago, the additive was reformulated with more detergents and dispersants to clean and hold particles better in the intended application: engine lubrication. At that same time, the power company changed the oil in its turbines. It was the first change in 15 years. Shortly after the change, the oil began to fail.

It’s a common story that bearings on turbine generators are pulled apart and frequently coated with this product to facilitate rebuild.

The synthetic supplier works to provide solutions to various problems in plants, improving efficiencies within power generating plants, reducing station service costs, reducing energy consumption, and extending the life and longevity of both the equipment and the lubricant. It is challenging for smaller independent companies to compete with larger companies. The supplier’s success is based on quality and performance of products, technical expertise and service.

Editor’s Note
Information for this article was gathered through an interview and conversations with the technician of the power company, who wishes to remain anonymous.

Chevron Corporation manufactures a widely used turbine lubricant. Chevron is familiar with the problems that incidental lubricant and additive contamination of any turbine or R&O oil causes in lubricant performance. Additive competition or incompatibility is not uncommon when mixing lubricant products that are designed for different applications. It is, therefore, not particularly surprising that an additive designed for use in engine applications could create difficulties when used in a turbine oil application with a turbine oil.

According to research by Chevron, the detergent/ dispersant package in the engine oil additive is not compatible with R&O oils. The calcium in the engine oil additive reacts with acidic rust inhibitors (present in all turbine oils) to form an insoluble calcium carboxylate. These by-products are insoluble and will form deposits and/or varnish. Although Chevron hasn't directly measured the effect on foaming, it is possible that small particles (from calcium carboxylates) will act as boiling stones (more surface area) to cause more foaming.

The detergent/dispersant package in the additive also destroys water separability within typical turbine oils. Chevron studies show that as little as 500 ppm of the engine oil additive in its GST product will cause poor water separability (ASTM D1401).