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Predictive maintenance is based on the status monitoring of instruments and control systems as well as intelligent inspections; it analyzes the results of equipment condition monitoring to identify defects, guides repair activities, and determines appropriate maintenance intervals. Through the monitoring of the status of instruments and control systems, the detection results are analyzed and evaluated, and any abnormalities identified are incorporated into the equipment defect management process. The condition monitoring platform should have automatic analysis functions such as defect detection and fault diagnosis, which can directly guide enterprises in carrying out inspection and maintenance work. Establish a unified status monitoring platform to manage the equipment status monitoring data from various enterprises in a centralized manner. 1. Online Monitoring (1) The control system self-diagnosis and alarm monitoring function automatically collects system alarm events such as controller alarms, card and channel status alarms, communication alarms, grounding alarms, power module alarms, and fan alarms from the self-diagnosis data of control systems like DCS, SIS, CCS, and PLC, and transfers them to the status monitoring platform. These alarms can be sent to managers and maintenance personnel in a hierarchical manner via text messages, enabling timely handling of any abnormalities in the control systems. (2) Fixed combustible and toxic gas alarms for monitoring: These alarms transmit zero-drift and fault alarm signals to the status monitoring platform, and can deliver these signals to managers and maintenance personnel in a hierarchical manner via text messages. (3) Interlock operation status monitoring introduces the operation status signals of interlock circuits into the status monitoring platform, enabling real-time supervision of their operation status; these signals can also be sent to managers in a hierarchical manner via text messages. (4) Interlock instrument alarm monitoring: In the safety instrumented system, logic for detecting deviations, open circuits, and short circuits in redundant interlock instruments is established; these alarm signals are transmitted to the status monitoring platform, and can be sent to managers and maintenance personnel in a hierarchical manner via text messages. (5) Monitoring of control valve actuation time: For control valves that require a specific actuation time and are equipped with valve feedback devices, it is advisable to monitor their actuation time within the control system and set up timeout alarms; such alarms should be transmitted to the status monitoring platform. (6) Instrument power status monitoring: For AC power supplies such as 110VAC and 220VAC, as well as DC power supplies such as 100VDC and 24VDC, voltage transformers and current transformers should be installed on the feed side of the main air switch within the instrument power cabinet. The current and voltage values are then sent to the DCS in the form of standard signals ranging from 4mA to 20mA, and from there to the status monitoring platform. Connect the fault alarm of the 24VDC DC switching power supply for the instrument to the DCS, and transmit it to the status monitoring platform. (7) Temperature and humidity monitoring in the cabinet room: A temperature and humidity meter with a 4mA–20mA standard signal output should be installed in the cabinet room. The temperature and humidity signals are fed into the DCS system as well as sent to the status monitoring platform, with alarms set up for abnormal conditions. The temperature in the cabinet rooms and engineer’s rooms is 20°C ± 2°C in winter and 26°C ± 2°C in summer, with a relative humidity of 40% to 60%. (8) The instrument heating monitoring system collects the temperature of the transmitter diaphragm box through protocols such as HART and fieldbus, or monitors the heating condition of the instruments by using thermal resistors, etc.; it then transmits this data to the status monitoring platform and sets up alarms. (9) The intelligent instrument management system enables online configuration, debugging, calibration, status monitoring, and alarm management of HART or fieldbus instruments such as intelligent transmitters, flow meters, and level gauges. Valve management software is used to control intelligent valve positioners, and functions such as automatic testing, fault diagnosis, diagnosis of valve operating characteristics, and friction analysis are employed to enable monitoring of the status of control valves and predict maintenance needs. 2. Offline inspection: (1) For the electronic devices located in cabinets such as power supply cabinets, system cabinets, terminal cabinets, safety barrier cabinets, and network cabinets, infrared imaging inspection should be carried out at least once a month. For solenoid valves such as those operating at 220VAC and 100VDC that have reached 80% of their designed service life, infrared temperature testing should be conducted at least once per quarter. (2) For the measurement of ground resistance, portable ground loop resistance testers are used; the ground resistance of the working ground busbars and protective ground busbars in the control system cabinets should be checked at least once a year, with the value not exceeding 4Ω. (3) For the instrument air system, which serves as the power source for pneumatic actuators, it is advisable to use a portable dew point detector to conduct offline testing of the dew point of the instrument air. (4) Use a HART handheld terminal or debugging software for monitoring the status of mass flow meters; once per quarter, check operational parameters such as the baseline zero point, drive gain, detection coil voltage, and vibration frequency of those mass flow meters used for trade transfer as well as for measuring energy and materials. Analyze their stability by comparing these values with historical trends. 3. Condition assessment: Status information of instruments and control systems is collected through online monitoring and offline testing, including parameters such as intensity, value magnitude, and trends in changes. Various methods are employed for condition assessment and analysis; by drawing on analyses of similar devices, a comprehensive judgment is made to identify any abnormalities in the equipment, which are then recorded in defect management ； At the same time, a database and a condition monitoring platform for equipment condition assessment are established. 4. Service life management: (1) Principles for determining service life – To ensure both the reliability and economic viability of equipment, the recommended service life for different types of equipment is determined by taking into account factors such as equipment classification management, information provided in equipment selection manuals, mean time between failures (MTBF), service life requirements specified in technical documents, and results of equipment reliability assessments. (2) Service life assessment: Establish a dynamic evaluation mechanism for the service life of instruments and control systems. By referring to the recommended service life and taking into account factors such as the equipment’s operating conditions, operating environment, condition monitoring, and historical failure statistics, the performance of these instruments and control systems is assessed. This serves as a basis for deciding whether to replace them ahead of schedule or allow them to continue in use beyond their intended lifespan, and it also guides the implementation of preventive maintenance tasks for such instruments and control systems. When the operating conditions of the instrumentation and control systems are poor, or when they deviate for extended periods from the designed operational parameters and range, the impact of operating conditions such as temperature, pressure, and corrosion on the equipment’s service life should be taken into consideration during evaluation. When instruments and control systems operate in harsh environments such as high temperature and humidity, lightning, dirt, and strong radiation, or when the operating conditions exceed the allowable range over a long period of time, the impact of these operating conditions on the equipment’s service life should be taken into consideration during evaluation. Based on the scope of impact in the event of a failure in the instrumentation and control systems, the service life of the instrumentation and control systems for critical and important circuits is recommended. Among them, the critical circuits are those interlock circuits and important control circuits that can cause unplanned shutdowns of the equipment, or lead to safety, environmental, or quality-related incidents ； Important circuits are the interlock circuits that can cause unplanned shutdown of the unit, and the main control circuits. The recommended service life is listed in point 7.