Equipment inspection and condition-based maintenance

Thread Content

The main tasks of equipment operation management include equipment inspection, defect management, and equipment maintenance. It improves the rate of defect detection and the accuracy of judgment during equipment inspections, enhances the management of equipment defects, enables timely awareness of the equipment’s operating status, ensures the safe operation of the equipment, and provides a reliable basis for condition-based maintenance, striving to adhere to the principle of repairing equipment only when necessary and ensuring that repairs are done properly. I. Equipment Inspection 　　 During the operation of equipment, inspectors are required to conduct inspections in accordance with the specified standards, contents, operating parameters, and inspection intervals for each type of equipment. Under special conditions such as extreme weather (high temperatures, thunderstorms, strong winds, ice and snow), full-load operation, operations to ensure power supply continuity, operation of equipment with defects, or after major repairs, inspections of the equipment should be intensified as appropriate (special inspections). Special attention should be paid to the key aspects of equipment inspection; inspectors must be familiar with the normal operating parameter ranges and technical standards of the equipment, and they are required to keep detailed records of the inspection results. 　　 These long-term accumulated equipment inspection data serve as the basis for equipment managers to conduct comprehensive analysis, diagnosis, and assessment of the equipment’s health status; they are the prerequisite and foundation for condition-based maintenance of equipment – and this is the true core of equipment inspections. II. Development Process of Equipment Maintenance The development of equipment maintenance has gone through the following three stages: Stage 1: From the Industrial Revolution to before World War II. Due to the large design margins and simple functionality of most devices, they have high reliability and are easy to repair. Therefore, the requirement for maintenance is to repair it only after it breaks down, that is, to carry out post-maintenance, also known as emergency maintenance. 　　 Phase Two: After World War II to the 1970s. Post-maintenance repairs result in excessive downtime, affecting production efficiency; it became apparent that it was necessary to prevent equipment failures, which led to the development of the concept of planned and preventive maintenance centered around regular inspections. This maintenance approach reduces downtime due to failures, eliminates potential problems at an early stage, and decreases the randomness of some maintenance tasks. However, the economic considerations are insufficient, which may still lead to excessive or inadequate maintenance. 　　 Third phase: The 1970s to the present. As equipment becomes more complex, automated, and valuable, maintenance costs rise sharply; as a result, preventive maintenance and maintenance based on equipment reliability are increasingly adopted. Its maintenance characteristic is the implementation of reliability-centered maintenance, supplemented by predictive maintenance or condition-based maintenance. The main strategies employed for equipment maintenance are as follows: fault-based maintenance strategy, scheduled maintenance strategy, and condition-based maintenance strategy. 　　 1. Fault repair 　　 Fault repair is generally carried out after a fault occurs, that is, it is repair done retrospectively. Its greatest advantage is that it makes full use of the lifespan of components or system parts, but routine maintenance is unplanned, resulting in significant waste of remaining repair resources; at the same time, it has certain defects and shortcomings. 　　 2. Regular maintenance 　　 Regular maintenance is a time-based preventive maintenance approach in which the level of maintenance, maintenance intervals, and specific tasks to be carried out are determined in advance, based on the patterns of the equipment’s lifecycle. 　　 3. Condition-based maintenance 　　 Condition-based maintenance is a type of preventive maintenance that relies on the condition of the equipment. It utilizes state monitoring and diagnosis techniques to obtain information regarding the equipment’s condition, assess its status, and determine in advance the timing of maintenance, the level of maintenance required, as well as the specific tasks to be carried out. III. Technical requirements for condition-based maintenance of equipment 　　 The premise of condition-based maintenance is to conduct a condition analysis and assessment of the equipment, in order to determine what state the equipment is in at present, whether there are any potential faults, what the rate of change of fault-related parameters is, how long the fault development period will last, and how to predict the trend of fault development. The technologies for condition-based maintenance include condition monitoring technology, condition prediction technology, and equipment maintenance decision-making. 　　 1. Equipment condition monitoring: For various failure modes of equipment, appropriate technical methods are employed to monitor its condition information, extract data that reflects the characteristics of its status, identify existing and impending defects, and analyze and predict the timing for maintenance, thereby effectively reducing equipment damage. Equipment condition monitoring can be divided into three basic steps: data collection, data analysis and feature extraction, and fault diagnosis and evaluation. 2. Equipment condition prediction 　　 Commonly used methods in prediction include time series analysis, regression analysis, fuzzy prediction, grey prediction, artificial neural network methods, etc. 　　 3. Equipment condition assessment: A technical approach that utilizes methods to predict the development trend of equipment conditions, with the goal of improving equipment reliability and availability. The current condition of equipment is determined following an assessment; therefore, the condition assessment of equipment serves as the basis for implementing condition-based maintenance. 　　 Condition-based maintenance encompasses three meanings: equipment condition monitoring, equipment condition prediction, and equipment condition assessment. Equipment condition monitoring is the foundation of condition-based maintenance. Equipment condition prediction relies on this monitoring; by combining historical data on the equipment and using techniques such as neural networks and expert systems, it is possible to assess the health status of the equipment, make an accurate evaluation of its condition, and ultimately determine the appropriate maintenance actions. IV. Solutions for Condition-Based Maintenance of Equipment 1. Equipment Inspection 　　 During the operation of equipment, inspections are carried out in accordance with the specified inspection contents and intervals for different types of equipment. Detailed records of these inspections are kept. Inspections are intensified as appropriate in cases of adverse weather conditions, during full-load operation, or after major repairs when the equipment is put back into service. Special attention is paid to the key aspects of equipment inspection; inspectors are required to be proficient in using the equipment used for inspections and to know the normal operating ranges of the equipment. This provides equipment managers with a basis for comprehensive analysis and diagnosis, as well as for conducting routine or diagnostic tests. 　　 2. Periodic adjustment of equipment status 　　 For the live testing items carried out while the equipment is in operation, if it is confirmed that the accuracy of the displayed values is sufficient to reflect the normal condition of the equipment and that the real-time data indicate good equipment status, then routine tests can be extended or waived, regardless of whether the scheduled inspection time has arrived. If abnormalities are detected during live equipment inspection or routine checks, or if the equipment has been exposed to severe adverse operating conditions that could threaten its safe operation, the equipment manager will decide whether it is necessary to shut down the equipment for diagnostic tests or include such tests in the regular maintenance schedule. In severe cases, the equipment will be overhauled; if overhauling is not feasible, it will be replaced. 　　 3. Principles for evaluating and handling status quantities 　　 When a status quantity reaches the warning value, it indicates that the equipment may have or develop some kind of defect. Devices that are in operation should be monitored continuously, and the device managers should be informed promptly ； For equipment that has been shut down, it is generally not advisable to put it back into operation until it is confirmed that there are no major defects. When the status value exceeds the warning limit, it is necessary to arrange for the equipment to be shut down as soon as possible in order to conduct diagnostic tests or maintenance, and the equipment manager should be informed promptly; the equipment must not be put back into operation until the potential hazards have been eliminated. Under similar operating and testing conditions, the same state parameters of identical equipment should not show significant differences; otherwise, it should be a matter of concern. 　　 4. Routine maintenance and testing plans 　　 Routine maintenance and testing plans are formulated based on the principles of equipment inspection and evaluation of operational conditions, rather than simply being carried out at fixed intervals. Regularly prepare plans for maintenance and testing as well as conduct equipment analysis; whenever there is an opportunity for a power outage, make full use of that time to carry out maintenance and testing on the equipment. 　　 5. Statistical analysis of equipment operation status 　　 Conduct statistical analysis on the equipment’s status to accurately understand its condition. Currently, online monitoring technologies are not yet mature enough. It is necessary to make full use of established online and offline monitoring devices and technologies, such as infrared thermal imaging and gas chromatography testing for transformers, in order to test the equipment and analyze its condition. V. Conclusion 　　 1. An objective evaluation of condition-based maintenance 　　 The core of condition-based maintenance management lies in formulating economical and reasonable maintenance and testing plans based on the results of equipment condition assessments. The purpose of equipment maintenance is to eliminate defects in the equipment through maintenance, ensuring its stable and reliable operation throughout the maintenance period. Condition-based maintenance can reduce the randomness of maintenance work, significantly cut down maintenance time, and improve equipment availability. 　　 2. A correct understanding of condition-based maintenance 　　 Condition-based maintenance is a complex, long-term, challenging, and scientific process; it requires scientific management to support it as well as appropriate testing and inspection techniques to ensure its effectiveness. However, there are still many weaknesses in current production technology management; basic management fails to provide complete equipment records as well as records of operation, maintenance, and testing. 　　 3. Key issues to be addressed 　　 The application of condition-based maintenance must be based on comprehensive condition monitoring of the equipment. Currently, the online monitoring systems for equipment status still have some issues, such as a limited number of monitoring points, single functions, a lack of systematicness and comprehensiveness, and especially a lack of hierarchical and networked monitoring, which hinders the consolidation and integration of equipment status information. There are still many problems to be solved regarding how to establish accurate equipment reliability models and develop practically useful expert systems for equipment fault diagnosis.