While performing reliability audits decades ago, pump-failure statistics were made available or could be recovered with relative ease. But even then, the sources were usually kept confidential because fire incidents are stressful, to say the least (Fig. 1). In 1974, it was known that, for every 1,000 pump repairs, there was a pump-related fire incident. More recently and in a facility with approximately 2,000 installed pumps, the acknowledged meantime between repairs (MTBR) was six years. This would allow us to calculate that approximately 333 pumps underwent repair each year. Since that particular plant experienced five pump-related near-disasters over a 14-year period, doing the simple math tells us that its rate of major pump issues tracked the 1 fire per 1,000 repairs within 6% accuracy.
Fig. 1. Assets and human lives are at stake
when there are pump fires in refineries.
Failure statistics tell the story. An airplane has about 4 million parts; an automobile has approximately 10,000 parts and a centrifugal process pump has about 200 parts. Its fair to say that if a machine is made up of a large number of parts, more parts could malfunction. However, this does not mean that more parts will, in fact, malfunction during an operational cycle. So, whats the point of this reminder?
As we think about the reasons why the average process pump requires a repair after approximately six years, we realize that not all of its components are designed, fabricated, assembled, maintained, operated or perhaps installed with the same diligence as aircraft components.
It doesnt have to be that way. Alloys can be upgraded, and better components are sold to owner-purchasers who insist on such upgrades. Advanced computer-based and reasonably priced design tools are available for the pump hydraulic assembly. It has been shown that computational fluid dynamics (CFD) can be used to define the improvement potential of impellers and stationary passages within pumps; Fig. 2 certainly attests to that.
Fig. 2. Relative velocity plot of an optimized
vertical pump stage (Source: Pump Design,
Development & Diagnostics;
But the mechanical assembly (drive end) of some pumps also deserves attention, especially since this portion of the pump has been neglected in some brands or models. Fortunately, expert advice is available for the specification and selection of better drive-end geometries for process pumps.1
Thoughtful specification and selection used to be par for the course at best-of-class companies, and there is really no reason why that thinking should have undergone change. What we see lacking today is an awareness of the precise steps that are needed for such specifying and selecting. Management has fallen prey to consultant-conceived generalities, including lean and mean and other similar, catchy utterances. HP
1 Bloch, H. P., Pump WisdomProblem Solving for Operators and Specialists, John Wiley & Sons, 2011.
|The author |
Heinz P. Bloch is Hydrocarbon Processings Reliability/Equipment Editor. A practicing consulting engineer with almost 50 years of applicable experience, he advises process plants worldwide on failure analysis, reliability improvement and maintenance cost avoidance topics. He has authored or co-authored 18 textbooks on machinery reliability improvement and close to 500 papers or articles dealing with related subjects.