At Noria we often speak of specification drift that occurs when lubricant specifications are based upon specific products from specific blenders. While in many situations this approach works and does little to compromise machine reliability, in other cases, critical mistakes can be made. Consider the following:
I previously worked as a rotating equipment engineer at a lubricants refinery. Because we produced lubricants, there was strong pressure from management to use our own products wherever possible. However, repeated failures of variable speed drives prompted me to investigate the choice of lubricant in use, with some surprising results. While the lubricant seemed similar to the lubricant recommended by the OEM, familiarity with other blenders’ products lead me to question the selection. After some digging, I discovered that the product we were using was very different from the OEM recommendation - even though the recommendation was in our own product line!
The reason, I discovered this was that at some point, the company I was working for had changed the naming system for its line of lubricants, years after the original printing of the OEM manual. As a result, what used to be the trade name for an ISO 460 compounded gear oil was now an ISO 150 sulfur-phosphorous EP gear oil.
The OEM never reevaluated or updated the lubricant recommendations in the manual, which were based on a name-brand specification, nor had anyone at our facility thoroughly evaluated the lubricant specifications provided by the OEM. Instead, the brand-specific recommendations were applied blindly, without thought as to whether this name-brand met the required design specifications for the application.
The result of this oversight was costly. Mean-time-between-failure for these expensive, mission-critical units, was less than a year. The problem was that because they were heavily loaded with high sliding velocities, operating at elevated temperatures, with a great number of load-bearing copper components, they required a higher viscosity; ISO 460 instead of ISO 150, and an additive package that was designed for sliding friction between copper components; a compounded oil, rather than an active sulfur phosphorus EP additive.
This problem could have been avoided simply by specifying a lubricant based on its physical properties, most importantly, its ISO viscosity grade, and its chemical properties, particularly the ability to prevent mechanical wear under sliding friction, without reacting chemically with the fundamental metallurgy of the copper components. However, by blindly following a written name-brand specification - after all, the OEM couldn’t have gotten it wrong: right? - we were victims of specification drift, which in this case, proved to be a costly killer!