Up Time Magazine - December 2008/January 2009 - (Page 50) relative success makes us comfortable with the McKenna-Oliverson definition mentioned earlier. In stark contrast, we consider endless debates over more precise or limited definitions both unproductive and all too often diversionary. In this context, debates generally solve nothing, they are mere exercises in bureaucracy. Exploring the failure history of a given pump in a given service in YOUR refinery and then comparing its reliability with that of a pump in the same service at SOMEONE ELSE’S refinery is of real value. It points out the way to lasting improvement. How to Recognize a Good Pump MTBF Examining pump repair records (and the admittedly imperfect MTBF metric) is deemed useful for responsible and conscientious pump users. In view of that fact, the preface to the 2006 Pump User’s Handbook (ISBN 0-88173-517-5) alludes to pump failure statistics. Again, and for the sake of convenience, these failure statistics are often translated into MTBF. Agreeing with McKenna and Oliverson and because they wanted to avoid arguments on statistics, many of the best practices plants in the time period of the early 2000’s simply took all their installed pumps, divided this number by the number of repair incidents, and multiplied it by the time period being observed. For a wellmanaged and reasonably reliability-focused U.S. refinery with 2,400 installed pumps and 312 repair incidents in one year, the MTBF would be (2,400/312) = 7.7 years. The refinery would count as a repair incident the replacement of parts, any parts, regardless of cost. In this instance, a drain plug worth $2.90 or a casing costing $8,000 would show up the same way on the MTBF statistics. Only the replacement of lube oil, a routine maintenance task, would not be counted as a repair. Using the same bare-bones measurement strategy, and from published data and observations made in the course of performing maintenance effectiveness studies and reliability audits in the late 1990’s and early 2000’s, the mean-times-between-failures of Table 1 have been estimated. As of 2008, we have reason to believe the figures are valid within a 10% range of accuracy. It should again be emphasized that many plants are achieving these mean times before a failure occurs. Why, then, the difference between a “best-of-class” U.S. refinery and a somewhat mediocre performer? There are many reasons that account for the difference. An unsuitable seal with a lifetime of just two or three months will have a catastrophic effect on pump MTBF, as would a badly-performing coupling or bearing. A good refinery frowns upon pulling piping towards the nozzle of a fluid machine, a mediocre refinery permits these disastrous procedures to continue for decades. One refinery supports its machine baseplates with epoxy grout, another refinery not only uses an inferior grout system, but might also allow it to soak with oil, degrade, and deteriorate. It is those types of things, and in areas of lube application, bearing housing protection, mechanical seal selection, installation methods and so forth, that the “best-of-class” differ from the weak performers. What Constitutes a “Failure” Finally, we were asked what constitutes a failure. In particular, we would like to comment on the sordid implications of limiting the term 50 december/january 2009 http://www.mikroninfrared.com http://www.mikroninfrared.com
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