GENERAL SESSION. "Targeted Maintenance. Presenters: Robert Aronen and George Dierssen IndustryUptime, Inc. Tuesday, November 9, :30-2 :30 p.m.

Transcription

1 GENERAL SESSION "Targeted Maintenance In Municipal Water Systems" Presenters: Robert Aronen and George Dierssen IndustryUptime, Inc. Tuesday, November 9, :30-2 :30 p.m. PUMPS & SYSTEMS EXPO 2004 BATONROUGE, LOUISIANA

2 "Understanding the Condition ofmunicipal Water Pu nps" By Robert A rim en and George DiE rssen IndustryUp tim I, Inc. Understanding The Condition Of Municipal Water Pumps By Robert Aronen and George Dierssen, IndustryUptime, Inc. The Most Common Maintenance Schemes On a basic level, there are three common maintenance schemes-run to failure, planned maintenance and predictive maintenance. (Note: Advanced schemes such as reliabilitybased maintenance and total productive maintenance are beyond the scope ofthis work.) II Run to failure is self explanatory. Operating equipment until it is destroyed results in unplanned work, excessive repair costs and potential safety incidents. Planned or "preventive maintenance" means that the plant pulls equipment on a II scheduled basis (for example, rebuilding pumps every three years). Of course, this also leads to higher-than-necessary maintenance costs, because the pulled pumps actually may be able to run for 10 years or more. I Predictive maintenance (also called "condition-based maintenance") means that maintenance activities are scheduled only when dictated by the equipment condition. The additional cost of monitoring is paid for by reducing the severity, frequency and cost of unplanned failures. II I. r Municipal water system operators, whether they're dealing with clean or dirty water, face the same challenges to reduce costs as their counterparts in other process ' industries. Experienced personnel are retiring... energy costs are rising...maintenance departments must increase reliability, availability and efficiency, while simultaneously reducing headcounts and expenses. It's especially important for these systems to have effective predictive maintenance programs in place-programs that connect maintenance activity to equipment condition. This type of program will minimize, costly emergency maintenance calls, allowing maintenance personnel to work on a planned basis to eliminate mechanical faults, rebuild worn-out pumps and replace inefficient systems. The question, though, lies in how best to determine pump condition. Vibration monitoring uses vibration, frequency and amplitude measurements to identify mechanical faults before failure occurs. Performance testing compares operational data to original design parameters, thereby identifying equipment that is "worn out" and inefficient. Both methods offer benefits, but they serve different objectives. Thus, using both methods, as consultants with IndustryUptime do, provides a more complete picture of pump condition.

3 "Understanding the Condition ofmunicipal Water Pe mps" By Robert Aronen and George Di ~rssen IndustryUptim " Inc. Vibration Monitoring Vibration monitoring is the cornerstone of most predictive maintenance programs because it identifies equipment faults before failure occurs. Vibration data is collected during machine operation, downloaded into software and analyzed to assess equipment condition. When vibration levels exceed industry-accepted standards, the equipment is said to be in "alarm," and appropriate corrective action is recommended. Any discussion of vibration monitoring inevitably starts a debate about the best way to set up a program. As numerous resources are available to address the "how to" details, this article will focus on the application of vibration monitoring, specifically to municipal water pumps. Benefits ofvibration monitoring... Vibration monitoring is considered an industry best practice because it saves money. By knowing equipment condition, plants can take corrective action before failures occur. Damage at failure is reduced, repair costs minimized and manpower used more effectively. In 2002, IndustryUptime implemented a program that helped a large western water district save over $200,000 in pump maintenance. Initial data collection noted three areas for improvement-equipment lubrication, motor electrical faults and pump wear. Over the course of a year, the water district targeted its efforts towards improving lubrication, improving motor rebuild quality and rebuilding the worn pumps. The results from 2002 to 2003 were as follows: Bearing faults dropped from 16 faults to I fault. Motor electrical faults dropped from 8 faults to I fault. Pumps in alarm dropped from 17 alarms to 6 alarms. Vibration monitoring considerations... Because municipal water systems often incorporate large populations of vertical pumps, it is important to note that the effectiveness of monitoring with handheld equipment is limited for vertical pumps. Horizontal pumps are easy to monitor, as all of the data collection points are readily available. However, with a vertical pump, vibration readings on the motor and pump housing above ground are readily available, but the entire hydraulic assembly is inaccessible. The readings above ground only provide a partial indication of the pump condition, ("the tail wagging the dog"). To fully understand pump condition, more information is needed. Figure 1 shows vibration monitoring being performed on a vertical pump. For critical equipment and very large horsepower pumps, permanently mounting probes in the hydraulic assembly is one solution that's becoming more common and more cost effective. See Figure 1 Attached. Vibration monitoring being performed on a vertical pump

4 "Understanding the Condition ofmunicipal Water Pl4mps" By Robert Aronen and George Di Irssen IndustryUptim!, Inc. Expectations ofvibration monitoring... Managers might ask, "What am I going to do with a report on machinery vibration?" This is a valid question, as the program will be a new budget item the manager will need to justify. Therefore, it is important to understand how results will be communicated and how this information will save money. A typical method of communicating vibration monitoring results categorizes data in three levels: alarm, alert and acceptable. Alarms require immediate corrective action (e.g. remove equipment from service and overhaul as soon as possible). Alerts require corrective action on a planned basis (e.g. perform shaft alignment at next shut down). Equipment in acceptable condition does not require corrective action. This format allows maintenance resources to be efficiently scheduled and directed. Maintenance savings result when equipment in alarm is scheduled for repair before a destructive failure, such as a bearing failure, occurs. The rebuild takes place on a planned, straight-time basis, with less damage to the equipment. Additional savings are achieved when recommendations prevent failures-grease the bearings before failure occurs. Finally, the program should highlight opportunities to improve the reliability of the entire population (e.g. improve shaft alignment practices and procedures). Performance Testing For new pumps, a performance test is conducted on a test stand to create the pump curve. In this article, the focus is on field-performance testing, which measures actual operating conditions at the site. The field-performance test compares head, flow and power consumption against original design specifications. While vibration monitoring is excellent for assessing the mechanical condition of pumps, performance testing is required to generate useful information regarding hydraulic condition. In an extreme example, vibration monitoring could indicate that a certain pump is running with no mechanical faults. Performance testing, however, would indicate that this pump did not have an impeller. Simply put, the performance test shows where the pump operates relative to its best efficiency point (BEP), and whether or not it is operating per its original design. Figures 2, 3 and 4 show three common operating situations that can be highlighted by a performance test. Figure 2 shows a pump running per the original design at BEP. Figure 3 shows a pump that is worn out. The flow rate is at BEP, but internal clearances have increased, causing losses in head and efficiency. A quality overhaul ofthis pump will

5 "Understanding the Condition ofmunicipal Water P, mps" By Robert Aronen and George Di 'rssen IndustryUptim, Inc. restore the lost efficiency that can often exceed 10%. (Note: a cavitating pump will show a similar result, andfurther investigation will be required.) Figure 4 shows a pump running at a very low flow rate relative to BEP. Even it's perfonning in line with the original design, "on the curve," low-flow operation results in low efficiency, recirculation damage and poor reliability (See "Maintenance Costs Start with Design, " Pumps & Systems, April 2004). The pump or system needs to be adjusted so that the BEP occurs at the required flow condition, which will often yield efficiency increases greater than 20%. See Figure 2 Attached. A pump running per the original design at BEP. See Figure 3 Attached. A worn-out pump See Figure 4 Attached. A pump running at a very low flow rate relative to BEP Benefits ofperformance testing... Industry studies have shown that up to 20% of the energy consumed by pumping systems can be saved. For a 250 HP pump, a 20% energy reduction translates to roughly $20,000 in savings per year. For an entire water system, savings of several hundred thousand dollars per year are often within reach. The examples shown in Figures 2, 3 and 4 are illustrative of how perfonnance testing results can be used to identify these savings opportunities and focus resources on maintenance and design issues. Generating operating sequences is an immediate use for performance testing results. Many pumping stations will have fi ve or more pumps that run in parallel, and their hydraulic perfonnance may vary significantly. Consider the following example: Pump Operating Efficiency Operating Sequence A 76% 1 B 72% 3 C 75% 2 D 65% 5 E 71% 4 At this station, Pumps A and C are running per their original design efficiency and would be operated first. Pumps B and E show some wear and would be next in the sequence. Pump D is worn out; it would be last in the sequence, and should be scheduled for maintenance at the nearest opportunity. By changing the order of operation, energy consumption at this station could be reduced by up to 10% immediately. Performance testing also can highlight maintenance savings. The consultants on this water district project tested a pumping station with four 250 HP pumps. The operators were working to obtain grant money for energy savings. Perfonnance testing indicated that the

6 "Understanding tlte Condition ofmunicipal Water PI mps" By Robert Aronen and George Di rssen IndustryUptim e, Inc. pumps were all cavitating. Further research showed annual maintenance costs for the pump station were more than $120,000. In this case, maintenance costs were far greater than the potential energy savings. Furthermore, because the real problem was a system design issue, rebuilding the pumps would not deliver the efficiency gain. Consequently, the water district created an engineering project to renew the pump station and eliminate the cavitation. The results will be greater reliability and lower maintenance costs, plus a gain in efficiency. Performance testing considerations... Performance testing requires accurate measurement of pump head, flow and amperage. Although performance tests can be performed using permanently installed hardware, adequate instrumentation is rarely available at water stations. For this reason, most performance tests are conducted with portable equipment. The two most conunon systems are the ultrasonic method and the thermodynamic method. Both systems can be used effectively, but the methodology is significantly different. The ultrasonic method uses externally-mounted transducers measuring the speed of fluid traveling in a pipe of known size, which translates into a flow measurement. This flow reading is combined with the pump differential pressure and amperage to determine the operating point. One difficulty with this system is that flow measurements are only accurate to within 2% and often require long straight runs of piping. Efficiency is calculated based on flow, pressure and amperage readings, and is only as accurate as the measurements used. The thermodynamic method uses pump differential temperature and pressure to directly and accurately measure pump efficiency. The efficiency is combined with motor amperage to determine flow. Long straight runs of piping are not required; however, one consideration is that with vertical pumps, the suction pressure and temperature transducer must be fed into the sump near the inlet to the pump. Figure 5 Attached. Typical set-up of ultrasonic flow-measurement equipment. Expectations ofperformance testing... Again, management will need justification for a performance testing program. A well formatted report should provide four extremely valuable items: list of pumps for overhaul, operating sequences, engineering reconunendations and estimated savings. Where pumps demonstrate excessive performance degradation, the report should identify these pumps for overhaul. Worn pumps waste energy and are at risk of severe failure modes, including broken shafts or bearing seizure. The performance study also should create an operating sequence for each pumping station so the operators can inunediately benefit through energy savings.

7 Robert Aronen, has 12 years of experience in improving pump reliability, including time spent working for several refineries and a mechanical seal manufacturer. Since cofounding Benicia, CA-based IndustryUptime, Inc., in 2000, he has helped implement more than $2 million in pump reliability improvements. He also provides rotating- equipment applications support to Dupont Corporation for its non-metallic material for pump wear components. Aronen received his BSMEfrom Rose-Hulman Institute oftechnology. "Understanding the Condition ofmunicipal Water PImps" By Robert Aronen and George D. erssen IndustryUptini e, Inc. Where design problems exist, the report should provide recommendations for engineered improvements. Again, pumps that operate far off their design flow will waste a great deal of energy, be unreliable, and often have excessive damage at failure. Finally, performance testing results should be related to the savings available. Overhauling worn-out pumps, changing operating sequences and correcting severe design issues can result in energy savings of 20% for the entire water system. Conclusion "Predictive maintenance," based on equipment condition, will increasingly replace "run to failure" maintenance practices in municipal water systems. Increasing energy prices, demands for greater pump reliability and loss of experienced personnel are driving this transition. The use of both vibration monitoring and performance testing provides a clear picture of both the mechanical and hydraulic condition of pumps. Applying these proven practices will dramatically reduce pump operating costs and Improve pump reliability.<p&s> George Dierssen, a co-founder of Industry Uptime, has been working with rotating equipment for more than 20 years. His comprehensive knowledge of machinery systems stems from having spent six years with a large pump OEM and eight years as a Project Engineer and Senior Reliability Engineer at two California refineries. Dierssen has an extensive background in improving pump reliability and efficiency, as well as in meeting modern emissions requirements with mechanical seals. He received his BSME from California State University, Sacramento.

8 "Understanding the Condition ofmunicipal Water Pur. ps" By Robert Aronen and George Diel ssen IndustryUptime, Inc. Figure 1. Vibration monitoring being performed on a vertical pump

9 "Understanding the Condition ofmunicipal Water Pumps" By Robert Aronen and George Die, ssen IlIdustryUptime, Illc. Best Efficiency Point,... +oj <U... <U -"C,,-... C\3 <U I 0~... > U c:.~ u E w Flow (GPM) Figure 2. A pump running per the original design at BEP

10 "Understanding the Condition ofmunicipal Water PUMPS" By Robert A ron en and George Diel ssen IndustryUptime, Inc. Actual Operation Actual Efficiency > u c.~ u if w Flow (GPM) Figure 3. A worn-out pump

11 "Understanding tlte Condition o/municipal Water Pu nps" By Robert Aronen and George Ditrssen IndustryUptim, Inc. / Actual Operation ~ ~... ~ Actual Efficiency \ f Potential Efficiency Gain > o c.~ o IE IJ.J Flow (GPM) Figure 4. A pump running at a very low flow rate relative to BEP

12 "Understanding the Condition ofmunicipal Water p" tnps" By Robert A ron en and George Dil rssen IndustryUptimt, Inc. Figure 5. Typical set-up of ultrasonic flow measurement equipment