From "The Lubrication Field Test and Inspection Guide"

Our sense of touch is not a good oil analysis instrument. In fact, it is difficult to detect even highly contaminated oils with your fingers. Most particles that are large enough to be felt have very short life in the oil. They become filtered, crushed, or simply settle to the bottom of tanks and sumps.

Therefore, in order to feel these contaminants, to get a sense of the consistency, hardness and size, it is best to go to the places where they accumulate. These places include the bottom of the sample bottle, a tank/sump BS&W sample, sediment from centrifugal separators, and debris on the surface of a used filter.

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Recently, Lube-Tips provided advice regarding a coating method that is useful for protecting carbon steel against rust and corrosion in lubrication and hydraulic reservoirs. For in-service conditions, the material proposed does offer relief. There is a large volume of corroded storage tanks and active circulation and hydraulic reservoirs that are severely rusted and degraded due to years of contact with moisture from the air and from the production environment itself.

The proposed material, Glyptol 1201, is reported to provide excellent long-term protection providing the surfaces are not exposed to sunlight.

For the reliability manager who is intent on 'best practice', particularly as it applies to new construction, it is best to specify stainless-steel construction for lube storage tanks and active oil and hydraulic reservoirs, for a handful of reasons associated with rust and corrosion control.

1. Lower lifecycle cost. Carbon steel will require maintenance (surface reconditioning and sealing) eventually, particularly in high humidity environments. The cost differential between carbon and stainless is generally not significant for new equipment (skid mount-type installation), but may be for in-situ retrofits. API Standard 611, Section 6.10 specifies the use of stainless steel for lube oil reservoirs and piping as a general requirement to minimize risk and achieve optimum long-term lifecycle cost. Additional advice is given for the use of stainless components and piping throughout the 611 standard. (The API standards also provide a machine builder with other practical advice derived from years of hands-on experience building refinery machinery that can endure punishing service.)

2. Rusting reservoirs add collectively to a variety of lubrication-related cost penalties. Particles released by rusting surfaces increase the cost of filtration.

3. The catalytic effect of rust accelerates lubricant degradation, which in turn may accelerate the rate of corrosion.

Given the minimal difference between stainless and carbon steel for new equipment installations, it is difficult to imagine a persuasive argument for the use of carbon steel if any consideration is given to lifecycle cost measurement during the design process.

Mike Johnson, CMRP, Noria Corporation

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