Equipment inspection and condition-based maintenance

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1. Equipment inspection: During the operation of equipment, inspectors are required to conduct inspections in accordance with the specified standards, procedures, operating parameters, and inspection intervals for that equipment. Under special conditions such as extreme weather (high temperatures, thunderstorms, strong winds, ice and snow), full-load operation, operation under power maintenance requirements, operation despite mechanical 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 essence of equipment inspection. II. Development process of equipment maintenance
The development of equipment maintenance has gone through the following three stages:
First stage: From the Industrial Revolution to before World War II. Since most devices have a large design margin and simple functions, they exhibit 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 maintenance after the fact, 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 maintenance and preventive maintenance centered around regular inspections. This maintenance approach reduces unplanned downtime, nips potential failures in the bud, and minimizes the randomness associated with certain maintenance activities. However, economic considerations are not sufficient enough, which may still lead to either excessive or insufficient 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 wasted spare 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 life cycle. 　 3 Condition-based Maintenance Condition-based maintenance is a type of preventive maintenance that relies on the condition of the equipment. It utilizes condition 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 prerequisite for condition-based maintenance is to analyze and evaluate the condition of equipment. This involves determining the current state of the equipment, whether there are any potential faults, the rate of change of fault parameters, how long the fault development period will be, and how to predict the future trend of the fault. The technologies of condition-based maintenance include condition monitoring technology, condition prediction technology, and equipment maintenance decision-making, etc. 1 Equipment condition monitoring: For various failure modes of equipment, appropriate technical methods are employed to monitor the equipment’s 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 acquisition, data analysis and feature extraction, and fault diagnosis and evaluation. 2 Equipment status prediction. The commonly used methods in prediction include time series analysis, regression analysis, fuzzy prediction, grey prediction, artificial neural networks, etc. 3 Equipment condition assessment is 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 the equipment is determined after evaluation; therefore, the condition assessment of the equipment serves as the basis for carrying out 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 integrating historical equipment data and utilizing technologies such as neural networks and expert systems, it is possible to determine the health status of the equipment, make accurate assessments of its condition, and ultimately decide on appropriate maintenance actions. IV. Solutions for condition-based maintenance of equipment
1. Equipment inspections
During equipment operation, inspections must be carried out in accordance with the specified inspection contents and cycles for each type of equipment. Detailed records of these inspections must be kept. In cases of special weather conditions, full-load operation, or after major repairs when equipment is put back into service, inspections should be intensified as appropriate. Particular attention should be paid to key inspection points. Inspectors are required to be proficient in operating the equipment used during inspections and to have a clear understanding of the normal operating ranges of the equipment. This provides equipment managers with a basis for comprehensive analysis and diagnosis, enabling them to conduct routine tests or diagnostic tests. 2 Periodic adjustment of equipment status: For live testing items conducted during equipment operation, if it is confirmed that the displayed values are accurate enough to reflect the normal condition of the equipment and that the real-time data indicates that the equipment is in good condition, then regardless of whether the scheduled testing time has arrived or not, various routine tests may be postponed or waived. If abnormalities are detected during live equipment inspections 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 to include such tests in the regular maintenance schedule. In severe cases, the equipment will be overhauled; if overhulling is not feasible, it will be replaced. 3 Evaluation and handling principles for status quantities: When a status quantity reaches the caution value, it indicates that there may be or could develop some defect in the equipment. Operating equipment should be monitored and tracked, with timely reports made to equipment managers ； For equipment that has experienced a power outage, it is generally not advisable to put it into operation until it is confirmed that there are no major defects. When the status parameters exceed the warning values, power outage should be arranged as soon as possible for diagnostic tests or maintenance on the operating equipment. The equipment manager must be informed promptly; the equipment shall not be put back into service until all potential hazards have been eliminated. Under similar operating and testing conditions, the same state variable of identical equipment should not exhibit any significant differences; otherwise, it warrants attention. 4 Routine maintenance and testing plans: These plans are formulated based on the principles of equipment inspection and evaluation of operational conditions, rather than being carried out merely on a regular basis according to preset time 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 operating status: Conduct statistical analysis on the equipment status to accurately understand its condition. Currently, online monitoring technologies are not yet fully mature. It is necessary to make full use of established online and offline monitoring devices and techniques—such as infrared thermography and gas chromatography for transformers—to test equipment so as to 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: The work involved in condition-based maintenance is complex, long-term, challenging, and requires a scientific approach. It needs sound 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 equipment. Currently, the online equipment condition monitoring system still has several problems, such as a limited number of monitoring points, single-functionality, and a lack of systematicness and comprehensiveness. In particular, there is a lack of hierarchical and networked monitoring, which hinders the centralization and integration of equipment condition information. There are still many issues to be resolved regarding how to establish accurate device reliability models and develop device failure diagnosis expert systems with practical value.