RESTORING PLANTS QUICKLY AND SAFELY Managing turnarounds on time and on budget can present many challenges. Cudd Energy Services helps you meet WKHVHFKDOOHQJHVKHDGRQ2XUÀHHWRISXPSLQJWUDQVSRUW DQGVWRUDJHYHVVHOVDFFRPPRGDWHVDZLGHUDQJHRIÀRZ UDWHVIRU+3+7RSHQÀDPHHQYLURQPHQWVWKDWJHW\RXEDFN RQOLQHVDIHO\DQGHI¿FLHQWO\
:LWKDPLOOLRQVFIFDSDFLW\WKHTXHHQVWRUDJHYHVVHO WDQN UHGXFHV IUHTXHQW GHOLYHULHV WKDW FDXVH FRQJHVWLRQ DQGFDQEHVDIHO\UHSOHQLVKHGZLWKRXWLQWHUUXSWLQJSXPSLQJ RSHUDWLRQV VDYLQJ \RX WLPH DQG PRQH\ (TXLSSHG ZLWK HPHUJHQF\VKXWGRZQGHYLFHVWKHGXDOPRGHSXPSIHDWXUHV DKHDWUHFRYHU\V\VWHPWKDWUHGXFHVIXHOFRVWVDQGLWV(3$ 7LHU&$5%HPLVVLRQUDWLQJKHOSVUHGXFHHPLVVLRQV )RUPRUHLQIRUPDWLRQDERXWRXULQGXVWULDOQLWURJHQVROXWLRQV YLVLWXVDWZZZFXGGFRPRUFDOOXVDW
2. Measure the actual efficiency of the motor. If the motor
is inefficient, consider replacing it with a modern high- efficiency motor, using oil-mist lubrication in line with the mentioned recommendations. This will allow capturing all benefits, and it will yield a greatly enhanced ROI.
3. Evaluate if the capacity of the motor is the most suitable for the application. “Most suitable” typically
implies driven loads that represent 75% to 95% of nominal motor capacity. Result: Operation conditions are at the best efficiency.
Note: Converting an overloaded, hot-running electric motor
to an oil-mist lubrication system will only provide marginal im- provement at best.
Oil-mist systems. The required volume of oil mist is often ex- pressed in bearing-inches (BIs). A BI is the volume of oil mist needed to satisfy the demand of a row of rolling elements in a 1-in. (25-mm) bore diameter bearing. One BI assumes a rate of mist containing 0.01 fl oz, or 0.3 ml, of oil per hour. Other factors must be considered to determine the necessary oil-mist flow, and these are known to oil-mist system providers and bear- ing manufacturers. The various factors are also extensively doc- umented in several references; they are readily summarized as:
• Type of bearing. The different internal geometries
include different types of contact (point contact at ball bearings and linear contacts at roller bearings), amount of sliding contacts (between rolling elements
and raceways, cages, flanges or guide rings), angle of contact between rolling elements and raceways, and prevailing load on rolling elements. The most common bearing types in electrical motors are deep-groove ball bearings, cylindrical roller bearings and angular contact ball bearings.
• Number of rows of rolling elements. Multiple row
bearing or paired bearing arrangements require a simple multiplier to quantify the volume of mist flow.
• Size of the bearings. It is related to the shaft diameter
and is inherently expressed in Bls.
• Rotating speed. The influence of the rotating speed
should not be considered as a linear function. It can be linear for a certain intermediate speed range, but, at lower and higher speeds, the oil requirements in the contact regions may differ from straight linearity. • Bearing load conditions. It includes the preload,
minimum or even less-than-minimum load, heavy axial loads and more.
• Cage design. Different cage designs may affect mist
flow in different ways. It has been reasoned that stamped (pressed) metal cages, polyamide cages or machined metal cages can create different degrees of turbulence. While different rates of turbulence may cause varying amounts of oil to “plate out” on the various bearing components, the concern vanishes when oil mist is applied in the through-flow mode.
62MAY 2015 | HydrocarbonProcessing.com
Maintenance and Reliability
Using the right bearing and proper installation methods.
Very significant increases in bearing life and overall electric motor reliability have been documented. Oil mist cannot eliminate basic bearing problems. However, it can provide a reliable means of lubricant application. Bearings must be:
• Adequate for the application, i.e., deep-groove ball bearings for coupled drives, cylindrical roller bearings to support high radial loads in certain belt drives or angular contact ball bearings to support the axial (constant) loads in vertical motor applications • Incorporating the correct bearing-internal clearances • Mounted with correct shaft and housing fits
• Installed carefully and handled correctly, using the proper tools to avoid damaging the bearings • Correctly assembled and fitted to the motor caps,
thus carefully avoiding misalignment or skewing • Part of a correctly installed motor, avoiding shaft
misalignment and soft foot, or bearing damage incurred while mounting either the coupling or drive pulley • Subjected to a vibration spectrum analysis. This will
indicate the lubrication condition (lubricating film), bearing condition (possible bearing damage) and general equipment condition, including misalignment, lack of support (soft foot), unbalance and more.
Sealing to avoid stray mist releases to the environment.
Closed systems and oil-mist-lubricated electric motors give
reliability-focused users several important advantages: • Compliance with environmental regulations • Proof that oil-mist lubrication will benefit electric
motors and the maintenance budget
• Technical and economic justifications to use high- performance synthetic oils.
Modern additives technology has further strengthened wear protection. They offer reduced energy consumption with other synthetic base oils. All are worthy considerations.
LITERATURE CITED
1 Morrison, F. R., J. Zielinsky and R. James, “Effects of synthetic fluids on ball
bearing performance,” Transactions of the ASME, Journal of Energy Resource,
Technology, Vol. 104, pp. 174–181, 1982.
2 Pinkus, O., O. Decker and D. F. Wilcock, “How to save 5% of our energy,”
Mechanical Engineering, September 1997.
3 Bloch, H. P., Practical Lubrication for Industrial Facilities, 2nd Ed., The Fairmont
Press, Lilburn, Georgia, 2009.
4 Bloch, H. P., “Statistics to think about,” Hydrocarbon Processing, July 2006, pg. 9. 5 Bloch, H. P., Pump Wisdom: Problem Solving for Operators and Specialists, John
Wiley & Sons, Hoboken, New Jersey, 2011.
HEINZ P. BLOCH resides in Westminster, Colorado. His professional career began in 1962 and included long-term assignments as Exxon Chemical’s regional machinery specialist for the US. He has authored over 600 publications, among them 19 comprehensive books on practical machinery management, failure analysis, failure avoidance, compressors, steam turbines, pumps, oil-mist lubrication and practical lubrication for industry. Mr. Bloch holds BS and MS degrees in mechanical engineering and is an ASME Life Fellow.