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i h o 1994, Jack Lambley, an intern at Imperial Chemical Industries’ (ICI) Rocksavage site in the United Kingdom,, was quanti ying the eect o misaligned process Kingdom pumps on power consumption. He arranged to have a surplus pump overhauled and tted with new bearings. He then had the pump installed in a suitably instrumented closedclosedloop arrangement operating on water. Prüechnik loaned Lambley a la ser-op ser-optic tic alignment a lignment instrument. As an undergraduate student, Lambley had learned that misalignment aects bearing load and t hat excessive bearing load causes exponential exponential decreases i n bearing lie. His supervisor, Steve Moore, had asked Lambley to read the engineering sections o SKF’s general catalog, which stated that a 25% increase in bearing load cut its rated lie in hal. Lambley investigated investigated alignment al ignment accuracy and methods the plant was using at the time. He ound that straightedge methods were inappropriate or renery pumps. Rim-andace alignment was too difcult and generally unreliable. Properly executed, reverse-dial-indicator methods required consideration o bracket sag, which would take more time. Still, rom data available at Rocksavage, he calculated that typical misa lignment was 0.02-in. vertical and horizontal osets and 0.002 in./in. vertical and horizontal horizontal angularity. a ngularity. In 1994, lasers were already known to be inherently more accurate than the best competing techniques. Lambley believed them to be 10 times more accurate. Te graphs and tabulations Lambley constructed are reproduced here, duly acknowledging ICI’s role. Te recommendations coming out o the study suggested aligning machinery to within 0.005-in. sha oset and limiting deviations in hub gap to 0.0005 in./in. o hub diameter. Lambley urt her documented documented that adhering to these recommendations could reduce ICI’s power consumption by about 1%. He conrmed that laser alignment was ast and accurate. He ound that laser-alignment technology was bottomline cost-eective. He deserves credit or establishing acts instead o repeating the opinions o others. Average annual electrical demand or pump motors in a typical mid-sized renery is $23,652,000/yr (27 kW/pump x 8,760 hrs/yr x $0.10/kWh x 1,000 pumps). Te ability to save 1% o this total represents a gross annual savings o $236,520 (Figure1 and Figure2). It ignores the cost o laser alignment instruments and appropriate training. Also, it’s reasonable to assume 7 labor-hours o time-saving credit per alignment
job. Alignment work usua lly involves two craspe cr aspeople ople and a ew hours o operators’ and supervisor’s time. Including the overhead contributions o operating and supervisory personnel, the total job typically consumes 15 man-hours with dial indicator methods and brackets, or which one needs to determine and take into account bracket sag. In contrast, it is reasonable to assume that laser-alignment by a two-person crew, including the inevitable participation o supervi-
in your reliABility imProvement endeAvors, endeAvor s, never let someBody’s oPinion get in tHe wAy of sound sCienCe And fACts. sory and operating personnel, takes perhaps 8 man-hours. Tat would explain the 7-hour savings, which could also be expressed as a roughly 40% reduction in total man-hours or laser-alignmentt tasks. laser-alignmen For even more inormation, learn about thermography and inrared monitoring techniques. Tese technologies quantiy beyond any doubt the temperature increase in a coupling located between misaligned pump and driver shas. You might compare the energy wasted by a hot coupling to the energy loss Lambley described. You’ll nd that, regardless o calculation method, laser al ignment is or the reliability-ocused plant proessionals and can result in surprisingly rapid payback. Last, but not least, in your reliability improvement endeavors, never let somebody’s opinion get in the way o sound science and acts. I have seen many uninormed opinions expressed in trade journals on subjects including oil mist, alignment al ignment accuracy requirments, grease application, bearing housing protector protector seals, and one-type-serves-all lubricants. Tese opinions come rom people with credentials credential s ranging rom junior mechanic to Ph.D and are all aimed at using unskilled labor to the maximum extent. Te assumption is that this wil l keep cost down. In most instances, “cost” reers to contractor billing rates. I call them opinions because they don’t take into account the ramications on component lie (bearing load) and increased ailure risk. Tey lose sight o the act that our role is reliability improvement; cheap and sloppy work will not get us there. www.PLANTSE RVICES.Com
JuLy 2011
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YOUR SPACE
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Figure 1. Effect of parallel offset on power consumption of a pin coupling at 3,000 rpm. MISALIGNMENT COST
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Gardner Denver. Since 1859. Compressed Air Solutions l l
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Figure 2. Effect of angular misalignment on power consumption of a pin coupling at 3,000 rpm.
Self-promoting “noisemakers” with very little practical industrial experience, but with a resumé of 58 dierent employers in 25 years, tend to get more exposure than real eld-wise experts. e reasons are many, but it’s a fact that experts at major petrochemical companies have neither the time nor the incentive to write. Aer all, they are gainfully employed by best-ofclass companies and aren’t in need of drumming up business for themselves. Moreover, their legal departments believe that sharing factual experience on the merits of using best-available technology is to be discouraged. e legal departments believe technical articles are either giving away a competitive advantage or consume time that would be put to better use in doing reliability-focused work inside the plant, or both. Heinz P. Bloch, P.E., owns Pro cess Machinery Consulting, in West Des Moines, Iowa. Contact him at
[email protected] and (515) 225-0668.
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JULY 2011
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