1、 Utilization of Reliability Centered Maintenance By Allen F. Goodson Manager of Operations doing more with less, along with information over-load have placed an even larger burden on maintenance and operation management decisions. What do we need to do to become more effective and how do we get ther
2、e? The Asset Management Section, Operations and Maintenance Department, is developing an integrated program based on streamlined Reliability-Centered Maintenance (RCM) methodology that assists in cost-effectively maintaining an optimized maintenance program. Several respected industries including ai
3、rline and nuclear power have pioneered the classical RCM approach for systems reliability. Industry experience for process facilities similar to the Districts has shown that a streamlined RCM process can provide the best maintenance practices in the most cost-effective manner. The District has recog
4、nized this opportunity and is applying the RCM methodology to its infrastructure. By using a logical step-by-step approach to determine the maintenance strategy for facilities/systems, the District is able to provide a documented basis for its maintenance program, more effectively manage change to t
5、he plant maintenance program, and focus resources on doing the right task at the right time on the right equipment. Documenting the basis for the Districts maintenance program is mainly performed by use of a facilitated meeting with an RCM Resource Team. The Resource Team is comprised of representat
6、ive journeymen responsible for the maintenance and operation of the system chosen for review. The RCM facilitator along with these subject matter experts are given the authority to walk-thru the decision making process of determining the critical and non-critical assets particular to the system proc
7、ess. A comparison is made between fundamental goals of the District, Critical Evaluation Criteria, and the failure effects on a component level to determine its Criticality. This initial phase of the RCM process is known in the RCM industries as the Failure Modes and Effects Analysis (FMEA). All thi
8、ngs being equal, if component A fails to provide its function what will be the effects of the functional failure to the process? The asset name, type, failure modes, failure effects are all documented as evidence of component criticality by the RCM resource team. Essentially, the documentation of th
9、e FMEA is saying that if an effective maintenance strategy is not applied to component A, here is what will happen to the process. The forecasting of future anomalies by use of past experience and intuition is the driving force for this decision making process. Once the critical and non-critical com
10、ponents have been identified, critical components are assigned maintenance tasks that address failure causes related specifically to the equipment type. Dominant failures found for synchronous and form-wound motors are first vibration related or second - electrical related. Utilizing vibration monit
11、oring techniques and motor circuit analysis, these incipient failures can be found and addressed cost-effectively by preventing failures that would result in extended downtime and high cost of replacement. Consequently, the challenge for this type of change management will be resource allocation, tr
12、aining, investment in equipment, and buy in. RCM Effectiveness The Districts key to developing an optimized maintenance program with an RCM basis is to focus resources on doing the right task at the right time on the right equipment. The approach is to ensure that the maintenance recommendations are
13、 functionally related, applicable and effective. RCM maintenance tasks are assigned to preserve the function of the equipment or system. The RCM goal is to maintain that function not just equipment operability. Therefore, maintenance recommendations that do not contribute to the function of the equi
14、pment should be eliminated from the maintenance program. If calibration efforts are being performed on a particular instrument whose function has nothing to do with process control and operations personnel are not using it for indication then either the operational strategy or maintenance strategy i
15、s suspect. Applicability of an RCM maintenance task requires that the task address potential failure causes by either preventing the failure, delaying the failure or by mitigating the effects of the failure, which could substantially reduce the resulting secondary damage. Again, the RCM team is fore
16、casting future failure anomalies with their experience and intuition and addressing the failure causes of Critical equipment with applicable maintenance recommendations. Cleaning and inspection of a breaker cubicle will find particular failures but the hidden failures may remain with the trip circui
17、t. Without testing the trip circuit there is a potential for hidden failures when the functionality of the breaker is called upon. Testing of the trip circuit will result in a complete performance test that will let the technician know of other potential failures related to the function of the circu
18、it breaker. Tasks that fail to meet the applicability criterion, such as this example of cleaning and inspecting the breaker cubicle vs. functional trip test, should be discarded. The effectiveness of the task is also a consideration in developing the RCM maintenance recommendations. Greasing a bear
19、ing or performing thermographic inspection on breakers and switchgear are measures to either preventing degradation or failure of the equipment. What is the cost if there is no lubrication performed on the motor or abnormal hot spots are not located in switchgear? The maintenance value must be great
20、er than the cost of failure or the effectiveness criterion must be discarded as an applicable recommendation. Hierarchy of Maintenance The hierarchy of maintenance tasks involves a spectrum of approaches mainly dependent on the importance (Criticality) of the equipment. These approaches vary from pr
21、edictive maintenance, condition directed to time-directed maintenance to having little or no maintenance requirements. Predictive maintenance can effectively warn of incipient failures to equipment long before the problem comes into awareness by operations or maintenance personnel. This expands the
22、window of time allowed for planning, scheduling and parts ordering prior to placing the equipment out of service for repairs. Condition directed tasks are essentially self-evident failure warnings accomplished only when the condition of the monitored equipment indicates that a maintenance action is
23、needed to prevent imminent failure. Indications of rising bearing temperatures or abnormal low flows through a heat exchanger could be warnings of necessary maintenance activity. Time directed tasks are of less value and should be less desirable than the foremost predictive and condition directed ta
24、sks. Predictive technologies and condition directed tasks are meant to examine the current state of the equipment while time-directed tasks take into account no detailed information regarding real-time equipment performance or degradation. We assume that the time-directed task is needed. If a condit
25、ion-monitoring task cannot be assigned when warranted then time-directed tasks may be the only alternative. Failure finding tasks are part of the time-directed realm since these types of failures are not self-evident. Critical back up and safety equipment often fall into this category. Case Study: S
26、obrante Ozone System Review of an existing Ozonation Plant demonstrated the value that the RCM process can bring to improvement to many underlying areas; reliability, spare parts inventory alignment, safety issues, documentation and design improvement. The Sobrante Water Treatment Plant (WTP) Ozone
27、System boundaries for the RCM study include all equipment, piping, valves, monitoring equipment, instrumentation and controls necessary to produce and feed ozone, as well as eliminate excess ozone. This includes the power supply breakers for the compressors, cooling pumps and Ozone generators. The c
28、ooling waterside includes those cooling water pumps and instrumentation specific to the function of supplying cooling water to Ozone system components for cooling. Existing Preventive Maintenance Man-hours Existing PM hours listed in the electronic work order system, MAXIMO, were annualized and veri
29、fied by maintenance personnel. The purpose of gathering the data was for comparison study of the resulting RCM PM hours. Maintenance Machinists: 39 hrs Instrument Technician: 259 hrs Electrician: 0 hrs Predictive Maintenance: 18 hrs (Vibration Monitoring) Total 316 hrs/yr Avg Hourly Cost $60/hr Annu
30、al PM Cost $18,960 New Preventive Maintenance Man-hours Maintenance personnel underwent an extensive review for job plan development with the new RCM recommendations. With their field experience new PM hours were estimated as follows: Maintenance Machinists: 60 hrs Instrument Technician: 25 hrs Elec
31、trician: 30 hrs Predictive Maintenance: 18 hrs (Vibration Monitoring Total 133 hrs/yr Avg Hourly Cost $60/hr Annual PM Cost $7,980 Direct labor cost savings $10,980 % Annual manpower reduction 57.9% RCM: Examples of Costly Asset Failures in Ozone System Compressor rotor damage Check valve failures r
32、esulted in multiple compressor rotor damage due to backflow leakage to the compressor rotors. Total cost of repair including parts and labor was estimated at $35,000. The RCM analysis results recommended a visual inspection of the check valves every 18 months. Inverter choke cooling system leaks The
33、re is a history of inverter cooling coil failures for each of the three power supply units, 2 3 times, since its original installation due to corrosion. It is recommended that eddy current testing be evaluated for use on the cooling water piping within each Power Supply Unit. Eddy current testing us
34、es alternating current from a test coil to induce eddy currents in electrically conducting, metallic objects. Flaws and other material properties affect the current flow. This method can be used to locate defects of many types, including cracks, voids, inclusions, and weld defects, as well as to fin
35、d changes in composition, structure, hardness, and porosity. Costs of failures are unknown but the results of a failure such as a cooling water leak in a 14 kV system are dangerous to equipment and personnel. Identification of reliability improvements Consider alternative disinfection strategies for
36、 ozone. Energy costs for the ozone system are approximately $183,000 per year. This does not include maintenance and operating costs. It may not be necessary to operate the ozone system year-round if water quality is acceptable and if alternative disinfection strategies can be determined. Update dra
37、wings based on as-built conditions. Updated as-built drawings are required for the refrigerated dryers which were replaced within the past few years and for the desiccant dryers. Electrical modifications were made to the desiccant dryers that need to be documented. Order necessary spare parts for cr
38、itical components. Based on the RCM analysis, it is recommended the following spare parts be ordered. These spare parts shall be located at Sobrante WTP for quick access for repair. Ozone generator pressure relief valves. Choke cooling coil. Complete Ozone Cooling Water System Modifications. A desig
39、n was completed for modifications to the ozone cooling water system. The modifications consist of adding a second conductivity meter, flushing connections, and valves. The purpose of these modifications was to address corrosion problems in the cooling water piping within the Power Supply Units assoc
40、iated with each ozone generator (this piping has failed 2 3 times since its original installation). Investigate feasibility of predictive maintenance on cooling water piping within Power Supply Unit. The cooling water piping has failed 2 3 times since its original installation due to corrosion. It i
41、s recommended that eddy current testing be evaluated for use on the cooling water piping within each Power Supply Unit. Eddy current testing uses alternating current from a test coil to induce eddy currents in electrically conducting, metallic objects. Flaws and other material properties affect the
42、current flow. This method can be used to locate defects of many types, including cracks, voids, inclusions, and weld defects, as well as to find changes in composition, structure, hardness, and porosity. A work order will be generated to evaluate and conduct eddy testing. Replace piping on ozone gen
43、erator pressure relief lines. A Maintenance Machinist replaced the relief valve on one ozone generator when it failed. At that time, the steel piping from the relief valve on the generator up through the roof of the generator building was severely corroded. The piping associated with that relief val
44、ve was replaced at that time with stainless steel piping, but the piping for the remaining two ozone generator relief lines have not been replaced. It is anticipated similar corrosion issues exist with these two lines. A work order will be generated to replace the remaining two relief valves and ass
45、ociated piping. Note that the ozone generator relief valves are critical for regulatory reasons. Add additional control capabilities for ozone destruction. There is one controller that regulates the amount of airflow through all three ozone destruct units via a flow valve (only one destruct unit is
46、operational now, two more will be operational shortly). This configuration causes operational problems when more than one destruct unit is operating. An ESR will be generated to install three outputs on the one controller (or adding two more controllers) so that each motorized valve between the dest
47、ruct unit and the blower can be controlled individually. Add isolation valve to test air separator outlet pressure relief valve. It is not possible to test the air separator outlet pressure relief valve as the system is currently configured. Testing this valve was recommended during the RCM analysis
48、 to ensure reliability of the relief valve. A work order will be generated to add a piping tee with a pressure gauge and a valve for a hose connection for testing. Add sample pump alarm on ambient ozone analyzers. The ambient ozone analyzers have a small sample pump that must be working in order for
49、 the analyzers to be functioning. Currently, the only way to ascertain if the sample pump is working or not is to open the analyzer and look at it. However, the purpose of these analyzers is to alert personnel if there is an ozone leak before entry into the generator or destruct rooms. A work order will be issued to add an alarm sent to AIMAX when the sample pumps are not working. Purchase equipment and conduct training for thermography. The RCM analysis recommended several thermography PM tasks. Thermography, a type of predictive maintenance, uses infrar
