In This Issue:

• Up Front: Hazards of Haphazard Lubricant Application

• Book Bits: Factors Influencing Oil Degradation

• Today's Tip: Critical New Bearing Inspections

• Q & A: Lube Dyes are Useful, But Use Caution
  

Up Front

Hazards of Haphazard Lubricant Application

A recent alternator pedestal bearing failure at one of our facilities was likely due to inappropriate lubricant application. Repair costs totaled $30,000. Downtime costs were estimated at $200,000.

A well-intentioned, but uninformed, maintenance engineer apparently did not have lubricant application listings handy and made an arbitrary decision to refill this system using an ISO VG 68-grade hydraulic oil at a routine oil change. The basis for this choice was that in his experience, he had encountered pedestal bearings lubricated with that type of product. The oil type recommended for this application was actually an SAE 30-grade engine oil.

Within 10 minutes of start-up it was detected that the bearing was running hot, and the eventual result was a total wipe-out of the bearing including damage to the alternator shaft.

While journal bearings in steady-state are hydrodynamically lubricated and not subject to rapid wear, immediately following start-up, boundary lubrication conditions dominate until sufficient speeds are reached to provide separation. During this transient phase, the lubricant's viscosity and anti-scuff additives help prevent excessive wear. The proper lubricant as indicated by the lubricant survey performed here was an SAE 30 oil with a viscosity of 104 cSt at 40°C vs. only 68 cSt for that actually used in this case. For that matter, this grade of lubricant may not have been sufficient even for steady-state operation.

It is also unclear if the antiwear package of the hydraulic oil was robust enough for this application. While it is not inconceivable that an ISO 68 hydraulic oil can sometimes be used to lubricate pedestal bearings, it is possible that the misapplication played a significant role in this failure.

It pays to stick to the recommended lubricant type for a given application rather than make an unsupported assumption.

(Submitted by Sandeep Banerji, Technical Manager, Shell Marine Products Limited. Thanks Sandeep!)

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Book Bits

Factors Influencing Oil Degradation

From "Machinery Failure Analysis and Troubleshooting":

A rather large number of factors influences lubricating oil degradation and, consequently, pump bearing life. If your centrifugal pumps are equipped with rolling element bearings, there is little doubt that medium viscosity turbine oils (ISO Grade 68) will perform better than the lighter oils originally specified by many pump manufacturers. But, by far, the most frequent cause of lube-oil-related failure incidents is water and dirt contamination. With only 20 ppm water in pure mineral oil, bearing surface and rolling element fatigue life is reduced by an incredible 48 percent. Although the fatigue life reduction is less pronounced with inhibited lubricants, there are always compelling reasons to exclude dirt and water from pump bearing housings. Lip seals are a poor choice for centrifugal pump installations demanding high reliability. Face seals represent superior, "hermetic" sealing and should be given serious consideration.

Click here for more information about "Machinery Failure Analysis and Troubleshooting".

Today's Tip

• Carefully inspect new bearings upon arrival for any obvious damage that may have occurred during shipping, storage or manufacture. Inspect bearings to determine if all parts are present. Bearings have been known to ship from the factory missing roller elements and other parts. Also, check for factory lubricant. Lack of lubricant from factory can cause rust. (Tip submitted by Doug Gribble, UVLM, Inc. Thanks Doug!)

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Q & A

Lube Dyes are Useful, But Use Caution

"I want to add a colorant or dye to my food-safe lubricants to ensure that there are no errors in selecting the right product in the lubricant storeroom. Is this a good idea?"

While the regulations do not call for special precautionary measures such as this, any attempts to eliminate potential error are a good idea. I know some companies that have implemented separate storage areas for food-safe lubricants and handling equipment to address this same problem, or have switched all their machines to food-safe lubricants irrespective.

However, a word of caution. In general, food-safe lubricants are, specifically colored by the supplier. If not, then discuss your request with your supplier. The concern with adding aftermarket colorants or dyes to the food-safe product is that there may be some chemical reactions which may produce toxic by-products in the lubricant. Therefore, if adding any dye, it should be retested or qualified for food safety.

Martin Williamson, Senior Technical Consultant, Noria UK Ltd.