In-situ predictive maintenance by vibration analysis for Cryogenic Pilot Plant for Tritium and Deuterium Separation

Transcription

1 In-situ predictive maintenance by vibration analysis for Cryogenic Pilot Plant for Tritium and Deuterium Separation SORIN GHERGHINESCU 1, GHEORGHE POPESCU 1 1 National R&D Institute for Cryogenics and Isotopic Technologies (ICIT) code Rm. Valcea, Uzinei street no.4, CP7 Riureni, Valcea, ROMANIA, phone: , fax: , sorin@.icsi.ro ; sorin70g@yahoo.com; Abstract: Maintenance is the assembly of all technical and organizational measures, which are linked in order to keep the equipment availability to perform their specific functions. Predictive maintenance and inspections performed during operation can eliminate a crash event by taking necessary measures to avoid such a situation. Thus, stopping the machine for intervention is planned according the predictions. Predictive maintenance can become a mandatory requirement for operation of an international standard. Predictive Maintenance can be applied to any equipment, whether; physical parameters like vibration, temperature, pressure, current and resistance can be measured. Engineering limits for the measurement of physical parameters must be established if the problem is detected before excessive damage occurs. Correcting the problem at the roots is the purpose of all predictive efforts. The research done in this paper highlights the importance of applying a predictive maintenance program. Keywords: Predictive maintenance, optimal availability of equipment, intervention program, vibration analysis. 1. Introduction The role of maintenance strategy is to obtain and maintain following: - Optimal availability of equipment/systems and auxiliary production systems to maintain production capacity at the company's performance targets; - Optimal operating conditions for the main production equipment/systems or auxiliary/support production systems; - Efficient use of resources and maintenance capacity; - Extending the life time of equipment/systems; - Fast reaction in case of failure; 2. Theoretical approach Maintenance Concepts: - Reactive - Corrective - Preventive - Predictive Reactive Maintenance - It occurs on the machine/equipment only when the fault occurs. - The work focuses on repairing without looking for the cause. Features: - Poor planning - Incomplete repair Corrective Maintenance - The work focuses on the tasks planned at regular intervals to ensure that the optimal operation of is maintain. - Efficient maintenance program shall be judged according to the critical machines/systems life cycle cost and not depending on how fast the equipment/system is reinstated. Features: - Well established intervention program - Accurate and complete repair Preventive Maintenance - Define a maintenance program aimed at eliminating or preventing corrective and/or reactive maintenance. - A preventive maintenance program consist in the periodic evaluation of equipment/machinery/critical systems to detect potential problems and interventions required to ISBN:

2 immediately prevent any deterioration of operating conditions. Predictive maintenance - It is a mean to improve and increase productivity, product quality and overall efficiency of manufacturing and production systems. - It is based on scheduling parameters/indicators of the actual operation of equipment/machine/system. dv( a( = = 2 π f v dt = a sin(2 π f t+ sin(2 π f t+ (3) To develop a predictive maintenance program it is mandatory the: - Training of staff to have main goal the maintenance policy development and implementation. - Involvement of all departments of R&D, purchasing, production, sales, maintenance. Techniques used: - Vibration Analysis - Analysis of lubricating fluid - Ultrasonic noise detection - Infrared thermography - Specific methods to electrical systems a. Measurement of complex impedance b. Insulation resistance measurement c. Analysis of the harmonic spectrum of phase current Figure 1. Graphical representation of displacement functions, speed and acceleration. Figure 3. Graphical representation of amplitude function with different frequency. Vibration description X( t ) = Asin( 2πft +φ ) (1) A-Amplitude f-frequency, number of complete oscillations per unit time φ - phase defines the position of the body in relation one to another at a given time Period t in the oscillatory motion mean an oscillation time, namely the equilibrium position: - High position - position of equilibrium - bottom position velocity Figure 4. Graphical representation of amplitude function with high frequency. dx ( v( = = 2 π f A cos(2 π dt = v cos(2 π f t+ acceleration f t+ (2) Figure 5. Waveform containing all the frequencies ISBN:

3 3. Application example The analysis in this paper was made on a cooling system (type chiller) fully automated. Running time was 380 days. In the time of operation the bearings of the pump ware broken with antifreeze mixture. Predictive Maintenance is a process driven by measurement data. It is about collecting and analyzing data to determine what corrective procedures to be done. The key is to make sure that the team analyzes the data with accuracy and according the predictive maintenance program. Unfortunately, many companies spend much time looking at useless data, because data collection was done wrong from the outset. So, collected information can not identify equipment problems. Therefore setting the database predictive maintenance technology is such a big step. Made properly, these databases allow you to trust in alarms in place to detect problems encountered. Then we can follow up the exception reports: see the alarm and analyze the equipment. Example: A proper database. Vibration analyst can collect and analyze information on equipment parts per month. Without this database, analysis efficiency may decrease with 50% (up to equipment parts per month). With proper database, it has a direct impact on productivity and the program is successful. Predictive maintenance program: 1. Intern. Predictive maintenance program is headed by the maintenance engineer: data interpretation, analysis and recommendations. 2. By contract. The predictive maintenance program is made by other firms from outside the company. 3. Hybrid. Some measurements are made by our engineers, and some are made by specialised companies. Figure 6. The process control for the vibration in Pilot Plant. 4. Parameter study Predictive maintenance cycle: Once a new piece of equipment was added to the program, enter the predictive maintenance cycle (see figure 8). The set of the parameters are measured periodically (weekly, every two weeks, monthly) [Jannie Jessen Nielsen 2011]. If the measurement need exceeds the technical capacity, then additional measurements should be planned. Analysis can take many forms. For example, the vibration can be taken by turning on/off the equipment. A well trained analyst can verify the vibration signature for common problems such as irregularity and instability, and not very common problems such as resonance. Once the cause is determined, the best repair activity can be chosen. A predictive maintenance research work usually starts with the beginning of the analyzed process. Correcting the problem at the root level allows the unit to revert to the regular monitoring program. Table 1. The spectrum of predicted maintenance Nr SPECTRUM OF PREDICTED MAINTENANCE Category The type Mode Cause of of of the of the equipment equipment Fall Fall Rotating machinery electric equipment exchangers Tanks and transfer equipment pumps, motors, compressors Electric motors, cables, transformers exchangers of compressors Tanks, reactors excessive vibration Insulation defect Dirt lubrication shortage Heat, moisture Sediment Corrosion chemical attack Detection mode vibration and lubrication analysis Resistance tests. Scan and analysis transfer calculations Check the thickness of corrosion. Sound Liability Scientists for better safety equipment, recognize that a group of machines is the probability of failure behavior. This behavior occurs when equipment is used constantly. Form of failure probability curve looks like a bath type. Equipment that survived from the beginning of his life, will continue to go along the way encountering a few drops. However, while failures begin to increase until the last group fails. ISBN:

4 Many companies, including Rolem start a predictive maintenance program by choosing one of the most common technologies that is vibration analysis [Jorn Vatn 2011]. After having gained some experience, start to apply the technology of their most critical equipment, the largest operating problems. Almost all machines give early warning signals, such as temperature changes, vibration, sound, before failing. These alarm signals can be detected with precise tracking technology. The problem is that one or two technologies alone can not detect the majority of alarm signals from your plan. As a result, a single predictive maintenance technology program will lose more than catch mistakes [Laura Swanson 2001]. So the key to a successful maintenance program is to make sure that it is extremely sensitive to failure modes of the machine. We therefore have applied several technologies to be able to detect most of the modes of failure of the plan. Failure modes of the machine tell you what technology to apply, not vice-versa. Figure 10. Variation of the vibration for cooling system in time. Figure 11. Defects observed in the bearings balls. 5. Experimental results Experiments were done on a cooling system (chiller) fully automated operated over a 380 days period. It was found one event where the antifreeze fluid pump bearings have failed. The results are presented below. Figure 12. Defects observed in the inner ring of bearings. Figure 8. Warning and alarm level of fluid pump Figure 9. Measurement of vibration levels for all cooling system components. Figure 13. Defects observed in the outer ring of bearings. ISBN:

5 6. Conclusions By applying a complete and functional predictive maintenance can be obtained the following results: depreciation with more than 10 times of the investment cost decrease between 25 and 30% of the total maintenance costs for monitored equipment. reducing the stationary time between 35 and 45% This type of maintenance, in addition to cost saving, improve the availability equipment facilitates the production schedule of the time, decreases during the stationary parts of the plant systems in case of scheduled surgery, facilitates the application of working procedures. It requires, however, investment in equipment and software that are recovered quickly and specialized personnel by attending courses, seminars and conferences. Funding Acknowledgement: This publication was made possible by Project PN II/2008 number 22139, from the National Authority for Scientific Research (ANCS). References [1]Radhoui Mehdi, Rezg Nidhal, Chelbi Anis, April 2010, Integrated maintenance and control policy based on quality control Computers & Industrial Engineering, Volume 58, Issue 3, Pages [2]Jannie Jessen Nielsen, John Dalsgaard Sørensen, January 2011, On risk-based operation and maintenance of offshore wind turbine. Reliability Engineering & System Safety, Volume 96, Issue 1, Pages [3]Jorn Vatn, Terje Aven, January 2010, An approach to maintenance optimization where safety issues are important, Reliability Engineering & System Safety, Volume 95, Issue 1, Pages [4]Laura Swanson, April 2001, Linking maintenance strategies to performance, International Journal of Production Economics, Volume 70, Issue 3, 18 Pages ISBN: