Condition Based Monitoring (CBM) System - Research Paper Example

 Condition-based Monitoring (CBM) System of a Case Study 1. Background of the study The Heating, Ventilation and Air Conditioning (HVAC) system is a very important part of life for when if it is good enough; it ensures total comfort (Mathews et al., 2001). This is a report paper which in particular has something to do about maintenance of HVAC used at the Shopping City retail centre. This paper shall address the issues and concerns raised by the case in question by closely examining the history of failure as well as closer scrutiny of the reasons and impacts of failure. Thus, in order to obtain desirable results, condition-based monitoring system needs to be critically and successfully implemented so as to further come up with the needed solutions for the problems stated in the case. 2. Introduction and objective To enjoy one’s shopping experience at Shopping City retail centre, the said shopping center maintains desirable temperature inside so as to continue give its shoppers a comfortable and wonderful shopping experience. This is quite a challenge knowing the fact that the number of customers especially during holidays tends to be abundant. This simply implies more load for the HVAC system of the shopping center. Not only that, this problem seems to be aggravated further especially during summer when temperature becomes higher than the normal levels. The shopping center has glass roofs which eventually absorbed too much heat from outside increasing the task of HVAC system due to more than just enough amount of conducted heat level. At Shopping City retail center, a bank of circulation pumps serves cooling water to the wings of the shopping center generated by two pumps in which one being a redundant standby. The desired temperature inside the shopping center is 250C. In order to achieve the desired temperature, 1,000-ton chillers need to continuously work for the entire air conditioning system of the shopping center. This paper aims to introduce a condition based monitoring (CBM) system so as to constantly keep the air conditioning system at Shopping City retail center in check. This is also to help avoid any future failure through health check up of the system. The bottom line of CBM system in this case is to prevent the occurrence of any failure to ensure continuation of function of the system and just even before the problem arises; correct measures may then be justified and implemented beforehand. In line with this, the failure history of the shopping center is considered beforehand taking priority on the reasons and impacts of failures. Thus, criticality analysis, task selection and proper CBM techniques were considered in order to come up with condition based monitoring system. Fig. 1 A Simple Representation of Air Conditioning System at Shopping City retail center. Picture taken from Burbank Service Company (2010) 3. History and criticality analysis In the span of five-year operation of Shopping City, there was absolutely no catastrophic breakdown ever recorded on its AC system. However, one pump seizing was recorded leading to the increase of temperature up to 290C gaining numerous number of complaints. Even though the problem was addressed right away, problem persisted knowing that temperatures persistently remained high due to thermal lag. Due to this incident, the management decided to conduct inspection only to find out that most of the critical areas are in good exterior condition. However, leaks of the two pumps were remarkable. Knowing that the pumps play significant role in ventilation and air conditioning system of the Shopping center, the pumps therefore need more concerned. As reported, the seizing of pump may have been due to damaged bearings or damaged impeller. Vibration levels may have been higher and the cause of leakage was probably due to damaged seals caused by poor lubrication. This suggests that the pumps need to be included in the CBM just even when the report stated that the system revealed only two leaking pumps, the problem needs to be further investigated. The hypothesis is that their might be inner problems with the pumps. If these cannot be addressed, problems continue to exist, thus more financial hammering in the future. This includes but not limited to customer dissatisfaction level, costly repairs and other related expenses. The nature of the problem seems need to be addressed using the concept of vibration and debris analysis. This in detail will boil down to analysis of the damaged bearings and impellers and damaged seals. Thus in particular, more concerns are needed in lube oil analysis and vibration analysis. 4. Literature Review This section tries to discuss information about vibration and wear debris analysis and lubricant oil analysis based on available related studies conducted on these areas. These are all related information discussed in this report. Lubricant oil and vibration monitoring analysis Lubricating oil reduces friction and wear, cool working surfaces and helps remove other contaminants. The bottom line of lubricant oil analysis is to scrutinize the health of lubricating oil and machine. It is therefore important to consider the following parameters (Sinha, 2009-2010): viscosity, oxidation, concentration of additives, acidity, dilution, debris content and microbial growth. In order to find out the undesirable properties in oil including but not limited to foaming indicating excess churning or passage through opening, it is important to measure the above mentioned parameters. Debris in fact, can tell the wear mechanisms, wear modes, wear phases occurring inside the machine. Therefore, a wear debris analysis is a very essential assessment that can be used to find out machine condition. In particular, in the wear debris analysis one needs to understand further portable oil diagnostic system (PODS) so as to successfully implement the whole idea about lubricant analysis. More so, PODS will be able to measure the three oil parameters. Particle concentration (from which cleanliness classes based on several standards are derived) Oil Temperature Oil Viscosity On the other hand, vibration analysis sees to it that the system is remarkably checked if it has already reached to the fullest. Reaching to the maximum level of vibration of the system causes stress which is widely known as fatigue stress that is capable of giving remarkable failures. Studies Related to Vibration and wear debris analysis According to Peng and Kessissoglou (2003), for machinery maintenance and fault diagnosis, the two major condition monitoring techniques are vibration and wear debris analysis. Peng (2002) explained that wear debris as an outcome from two moving surfaces inside a machine is considered production of machine that is in operation. According to Peng, the study of debris can tell the wear mechanisms, wear modes, wear phases occurring inside the machine. Therefore, Peng concluded that a wear debris analysis is a very essential assessment that can be used to find out machine condition. However, Peng argued that the present techniques used for individual analysis can be costly and time consuming because of the requirements needed by the analyst just to perform the following: particle inspection, morphology characterization and data interpretation. It is therefore implied that the limitation stands as barrier for the successful implementation of the method. Thus, according to Peng, it is necessary to create effective, reliable and cost-efficient techniques in order to carry out wear debris analysis especially for industrial applications. Peng and Kessissoglou added that most of the time in actual practice, vibration and wear debris analysis are conducted separately resulting to about only 30% to 40% diagnosis of faults. Peng and Kessissoglou explained that latest evidence can tell that using vibration and wear debris analysis together can give greater and more reliable information which is the bottom line; a program for effective maintenance and large cost benefits to industry. Peng and Kessissoglou actually were able to conduct a study that was able to investigate the correlation of vibration analysis and wear debris analysis. They were able to conduct an experiment with the aid of rig with a worm gearbox operated by an electric motor. This was to ensure to measure the correlation of vibration and wear debris analysis under different wear conditions. There were three tests conducted falling under conditions such as (a) lack of proper lubrication, (b) normal operation and (c) with the presence of contaminant particles mixed to the lubricating oil. There was a regular collection of oil samples and vibration data. In the wear debris analysis, Peng and Kessissoglou included the study of particle number and size distribution, the examination of particle morphology and types in order to determine the probable wear mechanisms and the analysis of chemical compositions so as to assess sources of wear. On the other hand, Peng and Kessissoglou also were able to compare the fault detection in the vibration signature with the particle analysis. The results of the study of Peng and Kessissoglou gave more meaningful understanding on the dependent and independent roles of vibration and wear debris analyses during machine condition monitoring and fault diagnosis. Ebersbach et al. (2006) also conducted a study in order to investigate the effectiveness of the combination of vibration analysis and wear debris analysis using an integrated machine condition monitoring maintenance program. In line with this, there were series of studies conducted on a spur gearbox testing. The moment test underlying normal condition was conducted to achieve baseline information of the test rig, the next step was the introduction of machine with different defect conditions in a controlled operating conditions matching to constant overload conditions and cyclic load conditions. Ebersbach together with the group was able to compare the data provided by wear debris analysis with vibration analysis spectra so as to get the quantitative measure of effectiveness of both vibration analysis and wear debris analysis in line with predicting and diagnosing machine failures. Ebersbach and company discussed the numerical approach for wear debris analysis that was made possible with the aid of a laser scanning confocal microscope (LSCM) allowing them to discuss the correlation between wear debris and vibration analysis techniques. Not only that, they were also able to evaluate the numerical descriptors for wear debris analysis. Peng et al (2005) practically believed that integrating vibration and wear debris analyses can really provide greater and more reliable information in machine condition monitoring in which the bottom line is significant cost benefits to industry. They believed that vibration and wear debris analyses are conditions monitoring techniques for machinery maintenance and fault diagnosis of machinery. Just like to what Peng pointed out, Peng et al. argued that when only a portion of vibration and wear debris analyses is conducted independently, only a portion of machine faults is then diagnosed. In the study of Peng et al. the same procedure was done and the bottom line was again to find for any significant correlation or direct relationship between vibration analysis and wear debris analysis. The study of Peng et al. was again able to give more meaningful understanding on the dependent and independent roles of vibration and wear debris analyses in predicting and diagnosing machine faults. However this time, they were more particular on finding the effect of contaminant particles in lubricants using wear debris and vibration condition monitoring techniques. 5. Discussion This section discusses in particular the CBM system involved in the analysis and at the later part, the discussion is concluded accordingly. Jardine et al. (2006) defined condition-based maintenance (CBM) as a maintenance program that tries to recommend decision underlying information collected through constant monitoring. According to them, there are three steps involved in this maintenance program: data acquisition, data processing and maintenance decision-making. Jardine et al. pointed out that the two most important aspects of CBM program are diagnostic and prognostics. The fact that hundreds of academic papers in this field those that include theory and practical applications created every year (Jardine et al., (2006) is a clear indication of significance of the subject matter. Lube Analysis Cost affectivity of the CBM system is one of the most primary concerns. Thus, portability is important considering that in most of the time, CBM instrumentation and the devices included are more costly than the usual failure that needs to be prevented. Leaking pumps was one of the observed failures in air conditioning system as stated earlier which was caused by damaged seals because of poor lubrication. Therefore, it is clear enough that the lube analysis must be initiated using the following steps. 1. Sampling of the bearing is necessary and it has to be done clean enough to prevent unnecessary contamination. 2. Vacuum type sampling pump must be used in collecting samples. 3. Samples must be marked accordingly with the detail of pump being checked and the date and time of taking the sample. 4. Analysis of the samples is then initiated. Of all the above mentioned steps, the analysis of the samples is very crucial. It has to be conducted efficiently to save money and time. In order for it to be fast and efficient, portable diagnostic system is necessary. The analysis with this system is ensured fast and efficient while the pumping system is in its continuous operation and working condition. Considering the above situation, the parameters that have to be closely taken into consideration are concentration of additives, oxidation, soot and debris content which can all be monitored through the use of spectroscopy, a method that is quick, accurate and inexpensive. This will enable identification of problems with lubricant as wear particle concentration tries to go beyond the standard. Vibration Analysis Vibration analysis without question can tell bearing failure and other related problems. For the past five years, there was just only one recorded incident of pump seizing. However external condition of the pump system was remarkably good, the exact problem must be coming from within where failure can be significantly observed. In the long run, this will only provide further costs if not properly taken care of. Thus, it is of important consideration to introduce a vibration monitoring system. Thus a Portable-hard wired system is needed with the following necessary parts. 1. Accelerometer. This part of the system ensures correct reading of vibration since sensors and studs must be fixed with it. 2. Short run cabling 3. Portable data collector to be connected to sensors 4. Computer for the analysis of signals and corresponding failures or fault The vibration level is the parameter in this analysis which can be of clear value for proper interpretation when converted into charge or voltage. Condition monitoring of chillers On the other hand, it is also of concern to check the flow rate and pressure of chillers using hand held sensors and probes as far as accuracy, cost-effectivity and ease of usage are concerned. Using non-intrusive flow detectors, the water flow rate as the measured parameter of flow rate will be obtained. The differential pressure is measured across chiller evaporator and condenser sections. No significant instrumentation is further required since measured values will be compared to acceptable values during necessary repairs. Measurement interval At this point, it is important to consider the measurement interval. Failure does not occur instantaneously. In line with this, the measurement interval is based on expected P-F interval or the moment when the item is in between potential failure and functional failure. The interval determination may be secured from the manufacturer, history of the system or any information on CBM. The measurement interval should be based on the average P-F interval and it should not be set beyond this level. In the case of lack of information about the P-F interval, it is recommended to do measurements at least once within 6-month period and less frequent after availability of records. Cost Issue Knowing the case, its history and specific concerns in particular, the cost issue cannot be clearly determined at this point. This boils down to the fact that there was no past experience that can be traced as far as the implementation of CBM system in the past is concerned. The £500 is relatively not a high price which was the price set for each pump in the case. However, even if there is no mention about the chiller’s price, it must be a little expensive because of the requirements stated for the demand of air conditioning system. In order to obtain a low pump price, it requires portability of the system just prior to implementation of CBM techniques all through out to pumps, chillers and piping. In this regard, it is recommended to go for permanent fixed installations excluding the necessary wiring for vibration monitoring system. It can be clearly observed that the likelihood of obtaining high price for the total CBM system which includes vibration analysis, pressure and flow rate measurements will be relatively high and cannot be justified at some point. This is surely be the case, but the recommended portability of the system will ensure cost effectivity while it will necessarily prevent costly failures and ensure good return of investment. 6. Conclusion The case in particular needs more understanding on the following analysis: wear debris analysis and vibration analysis after knowing that the problem lies on the idea of damaged bearings and impellers and damaged seals. There are actually three important things needed to be understood so as to understand the problem in this case. The problems may therefore be due to lack of proper lubrication, normal operation which might have caused more stress and the presence of contaminant particles mixed to the lubricating oil. These are just some of the most essential information obtained from CBM system. CBM combines the advantages of the strategies, with the following benefits: Better planning of repairs is possible, i.e. out of production time. Inconvenient breakdowns and expensive consequential damage are avoided. The failure rate is reduced, thus improving plant availability and reliability. Reduced spares inventory. Unnecessary work is avoided. CBM has the ability to make the system work to avoid failure by detecting early deterioration and it initiates maintenance when deterioration in machine condition occurs. After all what have been discussed, with CBM system it all boils down to cost savings, less failures and more success in the days to come. The case suggests that the proposed CBM techniques should be able to see expected defects in the future to prevent any system failure. Future cannot be predicted more so with the occurrence of failure in the system. This makes preventive time based maintenance not so effective at some point considering that failures mostly are occurring randomly. Failures follow pattern of deterioration period and this fact alone clearly suggests for CBM. For instance, in the case, it can be clearly analysed that the pumps might had failed due to problems in line with lubrication and bearing and which further caused leakage, impeller, defects, seizing of pumps, affected flow rates just to name a few. However, it was simply presented that the vibration analysis and lube oil analysis as integral parts of CBM technique can have the necessary strength to measure areas that require actions so as to prevent any development of faults and ensure maximum working condition of both systems and equipments. Overall, the proposed CBM system have the chance to become successful investment and its underlying clear high cost will ensure important benefits such as reduced costs in the future considering that preventive measures for failures in the future is what the system does. This suggests that prevention is better than cure. References Burbank Service Company (2010) ‘Duct Cleaning’. [Online] Available at: http://www.burbankservicecompany.com/images/dust1.jpg (Accessed: 11 May 2010). Ebersbach, S., Peng, Z. and Kessissoglou, N. J. (2006) ‘The investigation of the condition and faults of a spur gearbox using vibration and wear debris analysis techniques’. Wear, Vol. 260 (1-2): 16-24. Jardine, A. K. S., Lin, D. and Banjevic, D. (2006) ‘A review on machinery diagnostics and prognostics implementing condition-based maintenance’. Mechanical Systems and Signal Processing, Vol. 20 (7): 1483-1510. Mathews, E. H., Botha, C. P., Arndt, D. C. and Malan, A. (2001) ‘HVAC control strategies to enhance comfort and minimise energy usage’. Energy and Buildings, Vol. 33 (8): 853-863. Peng, Z. (2002) ‘An integrated intelligence system for wear debris analysis’. Wear, Vol. 252 (9-10): 730-743. Peng, Z. and Kessissoglou, N. (2003) ‘An integrated approach to fault diagnosis of machinery using wear debris and vibration analysis’. Wear, Vol. 255 (7-12): 1221-1232. Peng, Z., Kessissoglou, N. J. and Cox, M. (2005) ‘A study of the effect of contaminant particles in lubricants using wear debris and vibration condition monitoring techniques’. Wear, Vol. 258 (11-12): 1651-1662. Sinha, J. (2009-2010) Lube oil analysis. Condition Bases Maintenance Notes. Read More