Improving Machinery Reliability 3 Episode 12 ppt

Maintenance Cost Reduction 469 especially applicable if alignment-related failure repair is performed by a relatively small part of the workforce, and their labor data are available in breakout form. For example, in a given facility perhaps only millwrights repair rotating machin- ery, and their overtime hours go down after implementing a precision alignment pro- gram. Since there are likely to be relatively few millwrights compared to the overall maintenance workforce, the factors having an impact on their overtime can be rela- tively easy to isolate. Energy Usage There have been several papers documenting the energy savings of a precision alignment program. The savings claims vary from 3% to 12%, but there is consider- able debate about the measurement methods and validity of the data. As of 1996, there were at least two studies under way that attempted to more definitively study the issue. One is sponsored by the U.S. Department of Energy and the results of that study will eventually be made public. All of the work and proposed calculations about energy savings due to alignment have been applicable only to machinery driven by electric motors. Although one might expect any savings to apply to turbine-driven machinery, we are unaware of data to substantiate this. Our worksheets (pages 470-476) should apply equally well to any type of driver, but the illustrations will all use electric motors. Methods for evaluating energy savings realized from improved alignment funda- mentally fall into two categories: real power and apparent power. To simplify a rather technical definition, apparent power savings are calculated from changes in volts and amps. Real power, by contrast, is a sophisticated measurement involving not only volts and amps, but also power factor or phase. In most industrial facilities, real power is the basis upon which the electrical bill is computed, so it would be the better value to use. The caveat is that real power is problematical to measure with common volt and amp meters. One must use an ener- gy analyzer, such as the Dranetz Model 8000. Even with the use of an energy analyzer, measuring power consumption before and after alignment may not be enough. In most cases, the load varies considerably with respect to the expected savings. For example, an expected alignment energy savings may be 3%, but the load variation may be 10% or more. Load, or horsepower trans- mitted across the coupling, may vary with pressure, flow, speed, temperature, viscosi- ty, or almost any other process variable. It is thus necessary to ascertain that the load parameters are the same when energy consumption is measured. When the process has changed so that the load is different, it may still be possible to do an energy sav- ings calculation based on over-all drive train efficiency. This will require access to the efficiency curves for the driver and driven machines. The curves are usually available from the original equipment manufacturer for pumps, motors, and turbines. 470 Improving Machinery Reliability Quantifying Impact NmBF Savings Worksheet Any evaluation of equipment life must account for the time value of money. Although the inclusion of interest rates makes the calculations more complex, it greatly improves the va- lidity of the results. Although many methods are available, this calculation is based on pre- sent worth. Formula Where: Savings = Dollar savings per year due to MTBF improvements Re, Rn ne, nA i = Interest rate for comparison M = number of similar machines in facility = Average repair cost before and after alignment program, respectively. Can include both parts and labor, or only labor, or only parts, but be consistent. = MTBF before and after alignment, respectively. (in years) Calculations Line L1 L2 L3 L4 L5 L6 L7 L8 L9 LID L11 Parameter Interest rate per year Before precision alignment MTBF After precision alignment MTBF Before alignment average direct repair cost After alignment average direct repair costs Number of similar machines in facility (1 + LI)"L2 (1 +L1)AL3 (1 .+ L7) x L4 (1 i L8) x L5 Savings = (L9 - LIO) x L6 Example .09 3 3.5 $2,300 $2,100 200 3.31178 3.91773 694.49 536.03 $31,692.00 Actual Maintenance Cost Reducrion 471 Process Uptime Savings Worksheet If the plant can run more hours during a year it can make more product. That product can be sold, but has an offsetting incremental cost of production. To account for the various in- cremental sales factors, this calculation is based on incremental profit. Typically the incre- mental profit per unit of production is a figure available from the accounting or industrial engineering departments. In this instance, "savings" is actually increased profit Formula Savings = U x Hrs x IP Where: Savings = Dollar savings per year due to uptime improvements u = Typical unit production rate, units per hour. Hrs = Hours of increased production per year IP = Incremental profit per unit Calculations Line Parameter Example Actual L1 Production rate L2 Hours of increased production L3 Incremental profit L11 Savings = L1 x L2 x L3 1600 48 $8.00 $614,400 472 Improving Machinery Reliability Unscheduled Outages Cost Savings Worksheet In some facilities there is an unscheduled downtime cost that is readily available. Note that it generally overlaps with the increased uptime profit, so most evaluations should only claim one savings or the other, but not both. Formula Savings = D x Hrs Where: Savings = Dollar savings per year due to downtime improvements D = Unscheduled downtime costs per hour. Hrs = Hours of reduced unscheduled downtime per year Calculations L1 Unscheduled downtime costs per hour $10,000 Line Parameter Example Actual L2 Hours improvement 16 L11 Savings = L1 x L2 $160,000 Maintenance Cost Reduction 473 Simple Energy Savings Worksheet This is a simple, yet accurate, energy savings worksheet based on overall improvement in machine efficiency. It is useful when estimating savings potential given a typical improve- ment. For example, perhaps another unit or facility has proven a percentage savings that is applicable to the equipment under study. - Formula 100 100 Savings = 0.746 x HP x Hrs x Cost x Where: Savings 0.746 HP Hrs Cost eff" e43 = Dollar savings per year due to alignment = kilowatt per horsepower = Horsepower ratings of motors being aligned = Hours the motor is run per year, 330 days x 24 hr/day = 7,920 hr. = Cost of electricity in dollars per kilowatt-hour, typical = $0.078 per kWh = Efficiency afier alignment, 2% illustrative improvement = Efficiency before alignment, range for new motors at optimum (full) load is 78% to 96.5%. Plant typical 82%. Calculations Line I: Line 2 Line 3 Line 4 Line 5 Line 6 Line 7 Line 8 Line 9 Line 10 Savings Parameter Horsepower Line 1 times 0.746 Hours per year or per month Cost of electricity per kWh Line2 x Line3 x Line4 Efficiency before alignment Efficiency after alignment 100 + Line 6 100 + Line 7 Line8 - Line9 Line10 x Line5 Single Motor 200 149.2 350 x 24=8,160 $0.078 $94,962.82 82% 84% 1.2195 1.1905 0.0290 $2757.34 Entire Plant 30,000 22,380 340 x 24=8,160 $0.078 $14,244,422.40 82% 84% 1.2195 1.1905 0.0290 $413,601.11 Actual 474 Improving Machinery Reliability Measured Energy Savings Worksheet For most applications, there is no applicable and proven energy savings information avail- able. Thus, if one wants the numbers, one is forced to measure it. The following procedure has the advantage that it looks at the overall performance of a machine before and after alignment. The drawback is that it may require permanent installation or servicing of in- strumentation during a process shutdown, prior to beginning the study and well before alignment is performed. Procedure 1) Install and calibrate instrumentation to measure power output from the driveN. For most pumps, this includes pressure and flow. A data logger or strip recorder would be best, but in stable operating conditions visual monitoring is sufficient. Also prepare to measure shaft RPM in order to account for efficiency, which can vary significantly with speed. 2) Connect Dranetz or similar instrument to motor, usually at the motor control center. Program the analyzer to collect rea/power(kWh) for 2 hours. Average the data for energy accumulation over 1 hour. If driver is not an electric motor, install and calibrate the necessary instrumentation to measure power input to the driver. 3) Operate machinery train and record data as found. Two hours of steady state opera- tion would be a practical minimum time, with a printout from the Draneh every hour. Carefully note any power factor fluctuations. Only use the data if the power factor variations remain less than 0.1; ideally it would remain constant. Also collect process parameter data such as temperature (of the bearings, fluids, coupling, and ambient air), vibration (overall and spectrum), noise level, and pressure. 4) Perform the alignment 5) Repeat step 3. Maintenance Cost Reduction 415 Formula and Theory 100 100 Savings= Pxhrsxcostx Where: Savings = P hPdriveN = - - hPdriveR = Hrs = Cost = effA = effB = Dollar savings per year due to alignment Power measured before alignment, kWh Horsepower calculated from output parameters of driveN Horsepower measured or calculated for driveR (typically from power ana- lyzer) Hours the motor is run per year Cost of electricity, dollars per kilowatt-hour Measured efficiency after alignment Measured efficiency before alignment For a pump, the output horsepower can be computed as follows: Q x y x H - GPIW,~,,~, x PSI - hp ww = 550 9126 In the case where the speed, flow, or pressure changes signifcantly, then the pump hy- draulic efficiency curve should be checked and the shaff horsepower used. Changes in load parameters could make the pump operate at a more inefficient place on its curve and thereby offset or even augment gains due to alignment. Since the goal is to quantify align- ment benefits, the method used must account for changes in efficiency due to changed operating conditions. Q x y x H - GPM,,,,,,, x PSI - hp 5b/r = 5 5 Q x e,, 9126 x e,, Where: Calculated hydraulic, or output, horsepower Calculated shaft, or input, horsepower Flow of fluid, cubic feet per second Density of fluid, pounds per cubic foot Pressure, feet of head Flow of water, gallons per minute Pressure, pounds per square inch Hydraulic efficiency 476 Improving Machinery Reliability Calculations Line Ll L2 L3 L4 L5 L6 L7 L8 L9 L10 L11 L12 L13 Ll4 L15 L16 L17 L18 L19 L20 L21 L22 L23 Parameter Initial motor power, kWh Hours per year or per month Cost of electricity per kWh L1 x L2 x L3 motor hp = L1 x 1.340 Initial flow of Water, ft3/sec Initial density of fluid, Ib/ft3 Initial pressure, ft of head Initial efficiency from pump curve pump hp = (L6 x L7 x L8) + (550 x L9) effe = (L10 + L5) x 100 Final motor power, kWh Final motor hp = LIZ x 1.340 Final flow of Water, ft3/sec Final density of fluid, lb/ft3 Final pressure, ft of head Final efficiency from pump curve hp = (L14 x L15 x L16) + (550 x L17) effA = (L18 + L13) x 100 100 + L11 100 +. L19 L8 - L9 Savings = L22 x L3 Single Motor 150 350 x 24=8,160 $0.078 $95,472 201 10.5 62.4 115 .72 190.3 94.66 147 196.98 10.5 62.4 115 .72 190.3 96.61 1.0564 1.035 0.0213 $2035.74 Actual Maintenance Cost Reduction 471 Why and How to Monitor Centrifugal Pump Condition It is not unusual to find 1,200 centrifugal pumps installed in a good-sized petro- chemical plant, with approximately 600 of these running at a given time. If only 400 of them require shop repairs during the course of a year, the plant has a better than average repair record.1° Not counting product losses or fire damage caused by approximately one event per 1,000 pump failures, the average pump repair costs $9,800. These are valid 1998 accounting figures that include field removal, installa- tion, failure analysis, and burden. It is easy to visualize how pump failure reductions may save the average petrochemical plant a very sizable amount of money every year. The desired reduction in failure incidents or failure severities can be achieved by monitoring the condition of centrifugal pumps and initiating corrective action at the right time. Let us look at it from another vantage point. A survey of “condition monitoring” in British industry” estimated that industries already using condition monitoring could readily increase their savings at least six-fold if available instrumentation were applied more widely. The same survey estimates that approximately 180 industries could benefit from condition surveillance; however, only ten industries are presently utilizing these cost-saving techniques. Finally, if improved surveillance techniques and their proper management could be implemented in these 180 industries, British industry is thought to be able to realize annual net savings in excess of $1 billion, or about 40 times the amount presently saved by the limited application of machinery surveillance in only ten industries. Centrifugal pumps and their drivers probably represent a large portion of this total. From the point of view of condition monitoring, they are simple machines, and much data are available which allow reliable determination of component integrity. Condition Monitoring Defined The concept of condition monitoring encompasses the detection of mechanical defects as well as fluid-flow disturbances. Typical mechanical defects include bear- ing flaws, mechanical-seal defects, coupling malfunctions, rotor unbalance, erosion, corrosion, and wear. Fluid-flow disturbances include inadequate NPSH, insufficient flow, and gas entrainment or cavitation. Abnormal flow conditions can lead to mechanical defects and vice versa. Also, abnormal flow conditions may or may not manifest themselves in pump vibration. Similarly, mechanical defects may or may not manifest themselves in pump vibration. True condition monitoring should not be confined to mere vibration data logging, because measureable vibration increases are sometimes occurring only after irreversible mechanical damage has taken place. Condition monitoring should, therefore, be defined as the detection of any abnormal parameters which must be corrected if pump damage is to be avoided. 478 Improving Machinery Reliability How Abnormal Parameters Can Be Detected A number of diagnostic means are usually available to determine the condition of centrifugal pumps. Fluid-flow disturbances are best measured by pressure devia- tions, or changes in flow patterns and, sometimes, temperatures. Mechanical distress, both existing or potential, can manifest itself as changes in lube-oil temperature, lube-oil particulate contamination, bearing noise, and, of course, pump vibration. All of these parameters can be measured with available techniques. However, the deter- mination of mechanical distress by continuous lube-oil analysis, bearing surface con- tact roughness measurements, etc., is not presently considered practical for centrifu- gal pumps in the petrochemical industry.I2 On the other hand, the determination of machinery distress by measuring increases in vibration levels has achieved widespread acceptance. Monitoring vibration levels of operating machinery through the point of failure has shown that 90% of the time this indicator moves up sharply prior to actual fai1~re.I~ Consequently, machinery conditioning monitoring is often confined to vibration monitoring andlor vibration analysis. However, state-of-the-art condition monitoring methods go beyond vibra- tion monitoring. As will be seen later, these up-to-date methods attempt to capture incipient failure events by monitoring stress waves andlor shock pulses which can precede machinery vibration by days or sometimes weeks. Conventional (low-frequency) vibration monitoring. Excessive vibration of cen- trifugal pumps can lead to internal rubbing, overstressing of pipe flanges and hold- down bolts, grout failures, mechanical-seal leakage, bearing damage, coupling wear, and a host of other difficulties. Vibration detection and remedial action are necessary if equipment life and safety of personnel are to be ensured. Vibration detection and monitoring are commonly used to determine existence and severity of the problem, while vibration analysis is needed to define the cause of deviations from normal equipment behavior. With the exception of spring-operated, hand-held vibrographs, conventional vibration instrumentation makes use of transducers which change mechanical energy into electrical energy. Transducers can embody one or both of the following principles: 1. Proximity measuring techniques employing non-contacting, eddy-current probes to determine distance or change in distance to a conductive material. Proximity measurements are indispensable for the surveillance of large turbo- machinery. Centrifugal pump applications include nuclear reactor coolant circu- lators and large boiler feedwater pumps.14 Figure 11-26 shows a typical pump installation incorporating proximity probes. 2. Velocity transducer techniques operating on the inertial mass, moving-case principle. The inertial mass consists of a copper wire coil suspended inside the pickup case. The pickup case incorporates a permanent magnet. Machine vibra- tion induces a current in the coil. Within frequencies ranging from approximate- ly 10 Hz to 2kHz, the induced current is proportional to the velocity of vibra- tion.I5 A centrifugal pump equipped with a velocity transducer is shown in Figure 1 1-27. [...]... analysis of machinery are encouraged to look at R C Eisenmann’s Machinery Malfunction Diagnosis and Correction-Vibration Analysis for the Process Industries, Prentice PTR, Upper Saddle River, New Jersey; 1997 ISBN 0- 13- 240946-1 Written by an expert father-and-son engineering team, the Eisenmann book deals with many different types of process machinery vibration case histories 484 Improving Machinery Reliability. .. of oil purification were viewed prirnarily as reducing oil consumption and improving machinery reliability, thereby contributing to plant operating cost reductions -~- - _ - *Adapted from Bloch, Allen, Russo presentation at 5th International Turbomachinery Maintenance Congress, Singapore, 1991 492 Improving Machinery Reliability While these benefits are self-evident, it is becoming increasingly... finally cor- 4 WATER IN OIL SOLUBILITY CHART - 3 1 Mineral Lube Oil (No Additives) 2 2 IS0 32 Mineral Oil with Additives - 3 Commercial EP Gear Oils I (.001%) -O F 68 20 "C l l 1 % 40 I I l l I I l l 1 s 174 2 2 24a "F 60 80 100 120 °C Temperature, "FPC Figure 12- 4 Water in oil solubility chart / 494 Improving Machinery Reliability roding the surface Emulsified water and dissolved water may vaporize due to... and 482 Improving Machinery Reliability ,- Bearing condition development over time Figure 11 -30 Broadband measurements monitor bearing condition (Courtesy of PmeltechnikAG, 0-85 730 Ismaning, Germany.) Good bearing condition: LOW Carpet V D l W Low mailmum ualw Poor lubrlcatlon: EleuaWd c a r p i valua Low mah'lmum value Baarlno damnee: Elevatedcarp.( ualua V a v hlqh madmumvalue Figure 11 -31 Shock... separating the turbine bearings from the adjacent casing This is accomplished by bleeding small volumes (1 4m3/hr or 50 scfh) of shop or instrument air into the annulus formed between sets of labyrinth teeth, as shown in Figure 12- 2 Most of the air escapes 488 Improving Machinery Reliability Figure 12- 2 Air-purged bearing housing labyrinth for large steam turbines toward the turbine exterior, and in doing... centrifuges 496 Improving Machinery Reliability OPERATING LEVEL PURlFlEt OIL RETURN e A -GATE VALVES FOR TO lAGE TO PURIFIER TOWbRDS OIL RESWfOIR Figure 12- 6 Typical centrifugal separator installation (Courtesy of De Lava/ Separator Company, Poughkeepsie, New York.) Figure 12- 7 Cutaway view of oil purifier bowl (Courtesy of De Lava/ Separator Company, Poughkeepsie, New York.) Lubrication and Reliability. .. (once per 10 years) 3 0.1 Annual liters of oil saved: Line 1 x (Line 2 - Line 3) 4 800 Costlliter of oil 5 $1.50 Annual value of oil saved 6 $1,200 Labor charge to change oil (30 manhours @ $20/hr including overhead) 7 $600 Annual value of labor saved: Line 7 x (Line 2 - Line 3) 8 $240 Subtotal (Line 6 + Line 8) 9 $1,440 Annual number of filter changes WITHOUT purifier (3 per year) 10 3 Annual number of... explains the fact that even motor-driven turbomachinery experiences lube-oil contamination The potential problems are compounded on steam-turbine-driven machinery Figure 12- 1 illustrates a typical mechanical drive steam turbine Steam leakage past the Lubrication and Reliability 487 LP END +TO MEDIUM PRESSURE STEAM TO MAIN CONDENSER TO GLAND CONDENSER Figure 12- 1 Labyrinth seals of mechanical drive steam... Mitchell, John S., An Introduction to Machinery Analysis and Monitoring, Mitchell Turbomachinery Consulting, San Juan Capistrano, California (Seminar Textbook) 15 Kinne, H W., “Selection Guide for Vibration Monitoring,” Metrix Instrument Company, Houston, Texas (Undated Sales Literature) Chapter 12 lubrication and Reliability The importance of properly lubricating process machinery is so obvious that little... continuously to avoid long-term machinery distress RELIEF V LE AV- VENT 1 O-RING - SEPARATOR CARTRIDGES COALESCER CARTRIDGES LIQUID LEVEL GAUGE CONNECTIONS CARTRIDGE e MOUNTING PLATE INLET COMPARTME DRAIN ' DRAIN CONNECTION OUTLET MPARTMENT DRAIN Figure 12- 8 Cross section of typical vertical two-stage coalescer (Courtesy of Special Fluid Products, Inc.) 498 Improving Machinery Reliability The moment they . LI)"L2 (1 +L1)AL3 (1 .+ L7) x L4 (1 i L8) x L5 Savings = (L9 - LIO) x L6 Example .09 3 3. 5 $2 ,30 0 $2,100 200 3. 31178 3. 917 73 694.49 536 . 03 $31 ,692.00 Actual Maintenance. 1.1905 0.0290 $2757 .34 Entire Plant 30 ,000 22 ,38 0 34 0 x 24=8,160 $0.078 $14,244,422.40 82% 84% 1.2195 1.1905 0.0290 $4 13, 601.11 Actual 474 Improving Machinery Reliability Measured. efficiency 476 Improving Machinery Reliability Calculations Line Ll L2 L3 L4 L5 L6 L7 L8 L9 L10 L11 L12 L 13 Ll4 L15 L16 L17 L18 L19 L20 L21 L22 L 23 Parameter Initial