Chemical process instruments → Inspection

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In chemical plants, instruments serve as the primary means for monitoring the operating status of equipment, and their parameters are crucial for ensuring safe production and the manufacture of quality products. Therefore, the inspection of chemical process instruments is not as simple as just checking in, putting up a sign, and signing off to complete the task. The key aspects lie in identifying potential hazards, eliminating risks, and ensuring the quality of chemical products. Otherwise, in chemical plants with complex processes and equipment that operates at high speeds, leaks can occur from time to time, and various safety hazards will arise. The production of defective products will also result in significant economic losses for the company. In this issue of Inner Mongolia Chemical Industry, the editor will discuss this topic with you. What are the main tasks of instrument inspection? The main task is to detect any abnormalities in the instruments in a timely manner, thereby preventing system shutdowns, accidents, and the production of defective products. In actual chemical production, variations exist due to differences in industries and processes, but the overall requirement should be to be able to detect abnormalities in the production equipment and address them promptly to ensure stable operation. What are the main regulations for instrument inspections? 1. On-site inspections must be equipped with a three-in-one alarm device as well as other personal protective equipment ； 2. All instrument and equipment that have been inspected during routine checks must have clear, visible, and correct tag numbers ； 3. Check for any air leaks in the air supply of the pneumatic control valve; inspect the exterior of the instrument to ensure that all components are present and undamaged, and verify that the valve’s adjustment range is normal and there are no abnormal noises ； 4. Check whether the seals on the temperature transmitter cover and junction box are worn out, whether there is any ground connection in the sensing elements, whether the bolts are present and secure, and whether there are any leaks in the primary connections ； 5. Pressure transmitter: Check whether the pressure transmitter and its pressure guiding tubes are properly sealed with no leaks, and whether the insulation and heating systems are functioning correctly ； 6. Check whether the pneumatic cut-off valve operates properly when opened and closed, and whether the valve position indicator functions correctly; also verify if there is any air leakage from the air supply source and if any abnormal noises are present ； 7. Check whether the flow meter is displaying properly, and ensure that insulation and heating are in good condition (in winter), with no leaks ； 8. Check whether all the exterior components of the analyzer are present and undamaged: verify that the wiring terminals are properly secured, that the device is operating properly, and that there are no alarms ； 9. The flange connection of the level transmitter is well-sealed with no leaks ； Indicates whether normal operation, heat retention, and heating are functioning properly (in winter), with no leaks ； 10. Inspect the combustible gas alarm for complete and undamaged components; ensure its exterior is clean, check for power loss, and verify that the display is normal ； 11. Are the connections and wiring of the shaft system instruments in each unit secure? Are there any alarms, and are the trend fluctuations normal? ； 12. All instruments on site display accurate readings; the instrument equipment is clean, with no leaks or spills ； 13. In accordance with the inspection plan, carefully carry out instrument inspections on time and at the designated locations (areas) ； 14. All instruments and equipment inspected during routine checks must be kept clean and tidy. 15. During routine inspections, it is necessary to check whether instruments and equipment, especially control valves, instrument measurement wires, and instruments installed directly on pipelines, are subject to any risks such as vibration. 16. Inspections of standby equipment should be carried out daily (such as the standby main fans for catalytic units, the standby reciprocating compressors for atmospheric/ vacuum distillation/hydrogen production/continuous reforming/diesel hydrogenation/hydroprocessing units, the standby fans for sulfur recovery units, and the standby screw compressors for atmospheric/ vacuum distillation/gas holders, etc.). 17. The contents of inspections must be carried out in strict accordance with the requirements of the \"Inspection Rules,\" but are not limited to those rules. Each maintenance unit may, based on the specific operating conditions of the instruments and equipment, add more items and frequency to inspections. Special attention should be paid to key areas and instruments that suffer from frequent failures, so as to ensure that all instruments function properly and that the installation operates safely. 18. All instrument and equipment that have been inspected during routine checks should have clear, visible, and correct tag numbers, including any necessary descriptions of those tag numbers. 19. Fill in the inspection records carefully in accordance with the contents of the inspection record form and the requirements of these Inspection Rules. Specific inspection requirements for instruments and control systems:
I. Pressure and differential pressure transmitters
1. Check whether the pressure and differential pressure transmitters are in good condition.
2. Inspect the measurement wires of the instruments as well as the static sealing points to ensure there are no leaks.
3. Verify that the valves used for isolation, venting, and drainage on the measurement wires and the lines for flushing/isolating fluids are in the correct position, and that the vent caps/plugs are properly tightened.
4. Check the insulation and heating arrangements (if any) on the measurement wires of the instruments.
5. Examine the waterproofing of the pressure and differential pressure transmitters.
6. Check whether there are any hazards such as vibration affecting these transmitters.
7. Verify that the readings displayed by the transmitters match those shown by the local measuring instruments (such as pressure gauges and differential pressure gauges).

II. Pressure/differential pressure switches
1. Check whether the pressure/differential pressure switches are in good condition.
2. Inspect the measurement wires of the instruments as well as the static sealing points to ensure there are no leaks.
3. Check the waterproofing of the pressure/differential pressure switches.
4. Check whether there are any hazards such as vibration affecting these switches.
5. Verify that the valves used for isolation, venting, and drainage on the measurement wires and the lines for flushing/isolating fluids are in the correct position, and that the vent caps/plugs are properly tightened. 6. Check the insulation and heating of the measurement leads (if any).
III. Temperature Transmitter
1. Check whether the temperature transmitter is in good condition.
2. Check the waterproofing of the temperature transmitter.
3. Check for any hazards such as vibration that could affect the transmitter.
4. Verify that the measurement values displayed by the temperature transmitter match those shown by local measuring instruments (such as bimetallic thermometers).
IV. Float Level/Boundary Level Transmitter
1. Check whether the float level/boundary level transmitter is in good condition.
2. Check for any leaks in the float level/boundary level transmitter.
3. Verify that the measurement values displayed by the transmitter match those shown by local indicating instruments (such as glass plate/glass tube/magnetic flap level gauges) as well as other measuring instruments at the same measurement point (such as double-flange transmitters/magnetic float transmitters). 4. Check whether the switch states of the float isolation valve and the vent/scrubbing valves are correct, and whether the vent pipe caps/plugs are tightened. 5. Check the waterproofing condition of the float level/level-sensing transmitter. 6. Check whether there are any hazards such as vibration affecting the float level/level-sensing transmitter. 7. Check the insulation/thermal protection/heating mechanism of the transmitter’s cylinder (if available).

V. Float Level/Level-Sensing Switches
1. Check whether the float level/level-sensing switches are in good condition. 2. Check for any leaks in these switches. 3. Check whether the switch states of the float isolation valve and the vent/scrubbing valves are correct, and whether the vent pipe caps/plugs are tightened. 4. Check the waterproofing condition of these switches. 5. Check the gas phase condition at the upper part of the switch’s cylinder to determine if there is a “gas accumulation” issue. 6. Check the insulation/thermal protection/heating mechanism of the switch’s cylinder (if available). 7. Check whether there are any hazards such as vibration affecting these switches.

VI. Ball Level Transmitters
1. Check whether the ball level transmitters are in good condition. 2. Check their waterproofing condition. 3. Check for any leaks in these transmitters. 4. Check the fixation of the weight slider in the ball level transmitter. 5. Check the transmission and lubrication conditions of the transmitting parts; apply high-temperature resistant lubricant as needed. VII. Mass flow meters
1. Check whether the mass flow meter is in good condition.
2. Check for any leaks in the mass flow meter.
3. Check the waterproofing of the mass flow meter.
4. Check how the mass flow meter vibrates along with the process piping.
5. Verify whether the status alarms and measurement functions of the mass flow meter are normal (e.g., whether flow rate, density, and temperature readings fall within acceptable ranges).

VIII. Pipe-type vortex flowmeters / pipe-type turbine flowmeters / pipe-type electromagnetic flowmeters / insertable electromagnetic flowmeters
1. Check whether these flowmeters are in good condition.
2. Check for any leaks in them.
3. Check their waterproofing performance.
4. Verify whether their status alarms and measurement functions are normal (e.g., whether flow rate readings are within acceptable ranges).

IX. Ultrasonic flowmeters
1. Check whether the ultrasonic flowmeter is in good condition.
2. Check its waterproofing performance.
3. Ensure that the probes of the ultrasonic flowmeter are securely connected and fixed.
4. Verify whether its status alarms and measurement functions are normal (e.g., whether flow rate and velocity readings fall within acceptable ranges).

X. Ordinary control valves
1. Check whether the control valve and its accessories are intact.
2. Confirm whether the air supply pressure for the positioner/electric converter is correct, and check its waterproofing performance.
3. Look for any leaks in the air supply and signal lines; ensure all connections are tightly secured.
4. Make sure the feedback rod of the positioner is firmly attached to the valve stem, and verify that the signal air pressure corresponds to the valve opening.
5. Check for any leaks at the valve flanges or packing areas.
6. Ensure the handwheel of the control valve is positioned correctly.
7. Determine whether there are any risks such as vibration affecting the control valve and its accessories.

XI. Modulating/interlock valves
1. Check whether the modulating/interlock valve and its accessories are intact.
2. Confirm whether the air supply pressure for the positioner/electric converter is correct, and check its waterproofing performance.
3. Look for any leaks in the air supply and signal lines; ensure all connections are tightly secured.
4. Make sure the feedback rod of the positioner is firmly attached to the valve stem, and verify that the signal air pressure corresponds to the valve opening.
5. Check for any leaks at the valve flanges or packing areas.
6. Verify the installation, fixation, and waterproofing of the solenoid valves used with the modulating/interlock valve.
7. Check the connection between the position feedback switch and the valve stem, as well as its waterproofing performance.
8. Determine whether there are any risks such as vibration affecting the modulating/interlock valve.

XII. Interlock/switch valves
1. Check whether the interlock/switch valve and its accessories are intact.
2. Confirm whether the air supply pressure is correct; look for any leaks in the air supply and signal lines, and ensure all connections are tightly secured.
3. Verify that the signal air pressure corresponds to the valve opening.
4. Check for any leaks at the valve flanges or packing areas.
5. Verify the installation, fixation, and waterproofing of the solenoid valves used with the interlock/switch valve.
6. Check the connection between the position feedback switch and the valve stem, as well as its waterproofing performance.
7. Determine whether there are any risks such as vibration affecting the interlock/switch valve.

XIII. XV interlock valves for hydrotreating units
1. Check whether the XV interlock valve and its accessories are intact.
2. Confirm whether the air supply pressure is correct (for HARTMANN ball valves, the air pressure should be set to its maximum value); look for any leaks in the air supply and signal lines, and ensure all connections are tightly secured.
3. Verify that the signal air pressure corresponds to the valve opening.
4. Check for any leaks at the valve flanges or packing areas.
5. Verify the installation, fixation, and waterproofing of the solenoid valves used with the XV interlock valve.
6. Check the connection between the position feedback switch and the valve stem, as well as its waterproofing performance.

XIV. Self-acting control valves
1. Check whether the self-acting control valve is in good condition.
2. Look for any leaks in the pressure pilot lines; ensure all connections are tightly secured.
3. Check for any leaks at the valve flanges or packing areas.
4. Determine whether there are any risks such as vibration affecting the self-acting control valve.

XV. Radar level gauges
1. Check whether the radar level gauge and the tank-side indicator are intact.
2. Check their waterproofing performance.
3. Look for any leaks in the radar level gauge.
4. Verify whether the measured values displayed by both devices fall within acceptable ranges, and check for any alarm messages.

XVI. Servo level gauges
1. Check whether the servo level gauge and the tank-side indicator are intact.
2. Check their waterproofing performance.
3. Look for any leaks in the servo level gauge.
4. Verify whether the measured values displayed by both devices fall within acceptable ranges, and check for any alarm messages.

XVII. Combustible gas/toxic gas detection transmitters
1. Check whether the readings shown on the DCS operator station are abnormal.
2. Check whether the combustible gas/toxic gas detection transmitter is in good condition.
3. Check its waterproofing performance; also verify that the rain cover for the probe is intact and properly used.
4. Ensure the installation height of the probe meets the required specifications.
5. Verify whether the readings displayed by the transmitter are normal, and check for any alarm messages.

XVIII. Online analyzers
1. Check whether the online analyzer is in good condition.
2. Check its waterproofing performance.
3. Look for any leaks in sample gas lines, calibration gas lines, and purge gas lines.
4. Verify whether parameters such as sample gas flow rate and pressure meet the required specifications.
5. Check whether insulation and heating measures (if any) for the sampling lines/pre-treatment units are functioning properly.
6. Verify whether the readings displayed by the analyzer fall within acceptable ranges, and check for any alarm messages.
7. Ensure that standard calibration gases and solutions are readily available (if applicable).

XIX. RTU
1. Check whether the input/output ports of the RTU cabinet are properly sealed.
2. Verify whether the RTU system is operating normally, and check for any alarm messages.
3. Ensure the RTU cabinet provides adequate protection against weather, high temperatures, and sunlight.

XX. Equipment in the control room/cabinet room
(A) DC regulated power supplies
1. Check whether the status indicator lights of the DC regulated power supplies are functioning normally.
2. Check whether the fans (if present) are operating normally.

(B) Power switches
1. Verify whether the switches and circuit breakers inside the cabinets are in proper working condition.
2. Check whether the status indicator lights of terminal-type power switches are functioning normally.

(C) Isolated safety barriers / MTA boards
1. Check whether the status indicator lights of isolated safety barriers are functioning normally.
2. Verify whether the dual-power supply indicator lights on the MTA board are functioning normally.

(D) BN3500 series shaft monitoring instruments
1. Check whether the status indicator lights on each channel board are functioning normally; all “OK” lights should be illuminated.

(E) Cabinets/control consoles
1. Determine whether the filter elements/filters in the cabinets/control consoles need cleaning.
2. Check whether the fans are operating normally.
3. Ensure that wire ducts and covers inside the cabinets/control consoles are intact.
4. Check for any debris inside; ensure the overall cleanliness of the area.
5. Verify whether the status indicator lights on each channel of the terminal boards are functioning normally.
6. Check whether the status indicators of DCS, SIS, ITCC, PLC, and other system cards are functioning normally.

(F) Miscellaneous
1. Inspect mouse traps installed in the cabinet room.
2. Check the operation of air conditioners in the cabinet room (including operating mode, set temperature, actual temperature, set humidity, actual humidity, and alarm messages).
3. Ensure the cabinet room remains clean and tidy.

XXI. Field junction boxes
1. Check whether the junction box is intact and clearly labeled with identification numbers.
2. Check its waterproofing performance (e.g., whether all screws securing the lid are present and tightened).
3. Ensure all unused entry/exit ports on the junction box are properly sealed.

XXII. Barrier fluid/high-pressure oil injection systems
1. Verify whether the barrier fluid pump is operating normally.
2. Check whether the liquid level in the barrier fluid storage tank is normal.
4. Verify whether the high-pressure oil injection pump is operating normally.
5. Check whether the liquid level in the high-pressure oil injection system’s tank is normal.
6. Look for any loose connections or leaks in the high-pressure oil injection pipelines.

XXIII. Instrumentation system for main blowers (three-unit assembly) in catalytic units
1. Check whether the pressure and temperature readings of the lubricating oil system are normal. 2. Check whether the bearing shell temperature, shaft vibration, shaft displacement, fan speed, and main air flow indication are normal. 3. Check whether the smoke extractor cut-off butterfly valve, adjustment butterfly valve, anti-surge vent valve of the main fan [to ensure that the signal air pressure matches the valve opening], and the stator actuator are functioning properly. 4. Check whether there are any alarms from the flue gas exhaust valve cut-off butterfly valve and the controller for the flue gas exhaust valve adjustment butterfly valve. 5. Check the CCS operation station alarm records for any alarms related to important parameters. 6. Check whether there are any abnormalities in the trends of key unit parameters. 7. Check for any leakage issues at the connections of the on-site instruments. 24. Instrumentation System for the Standby Main Fan in Catalytic Process 1. Check whether the pressures and temperatures of the lubricating oil system are within normal ranges. 2. Check whether the bearing bush temperature, shaft vibration, shaft displacement, and main air flow indication are normal. 3. Check the fan anti-surge valve [to ensure that the signal air pressure corresponds to the valve opening] and whether the stator actuator is functioning properly. 4. Check the CCS operation station alarm records for any alarms related to important parameters. 5. Check whether there are any abnormalities in the trends of key unit parameters. 6. Check for leaks at the connections of the on-site instruments. 25. Instrumentation systems for catalytic compressors/coking compressors/cyclic hydrogen compressors/hydrogen boosters: 1. Check whether the pressures and temperatures indicated by the lubricating oil system are normal. 2. Check whether the bearing shell temperature, shaft vibration, shaft displacement, as well as the turbine speed indication and control are normal. 3. Check whether the inlet and outlet flow rates and the inlet and outlet pressures of the compressor’s first and second stages are normal. 4. Check whether the control and operation of the compressor anti-surge valve are normal [whether the signal air pressure corresponds to the valve opening]. 5. Check the CCS operation station alarm records for any alarms related to important parameters. 6. Check whether there are any abnormalities in the trends of key unit parameters. 7. Check for leaks at the connections of the on-site instruments. 26. Instrumentation systems for reciprocating compressors in atmospheric and vacuum distillation/hydrogen production/naphtha reforming/hydrofining/hydroprocessing: 1. Check whether the connector tubes for instrument measurement at the inlet and outlet buffer tanks of each stage of the compressor are loose Are there any hazards such as vibration? 2. Check whether the readings of the pressure transmitters on the inlet and outlet buffer tanks at each stage of the compressor match the pressure readings at those same locations. 3. Inspect the air connections of the load control solenoid valves for any looseness or leaks. 4. Verify that the liquid level readings from the liquid separation tank in the machine room correspond to the readings from the local instruments (glass gauges, magnetic level indicators, etc.). 5. Check the CCS/DCS operation station alarm records for any alarms related to important parameters. 6. Check whether there are any abnormalities in the trends of parameters of critical units. 7. Check for any leaks at the connections of the measurement wires of the instruments on site. 27. Atmospheric and Vacuum / Gas Holder Screw Compressor Instrumentation System 1. Check whether the connector tubes for instrument measurement at the inlet and outlet buffer tanks of each stage of the compressor are loose Are there any hazards such as vibration? 2. Check whether the readings of the pressure transmitters on the inlet and outlet pipelines at each stage of the compressor match the pressure readings at those same locations. 3. Verify that the liquid level readings from the liquid separation tank in the machine room correspond to the readings from the local instruments (glass gauges, magnetic level indicators, etc.). 4. Check the DCS operation station’s alarm records to see if there are any alarms related to important parameters. 5. Check whether there are any abnormalities in the trends of key unit parameters. 6. Check for leaks at the connections of the on-site instruments. 28. Catalytic Electro-hydraulic Sliding Valve Servo Control System 1. Check whether the input signals and valve position signals on the display panel of the local cabinet for the electro-hydraulic sliding valve servo control system are normal, including (valve position travel indicator, amplifier travel indicator, DCS travel indicator); also check whether the deviation signal and system power supply indicator are normal. 2. Check whether there are any alarm indications on the display of the electro-hydraulic slide valve servo control system. 3. Check whether the wiring boxes of the on-site instruments and the connectors of those instruments in the electro-hydraulic slide valve servo control system are properly sealed. 4. Check whether the protective measures for the slide valve signal cables, as well as the measures to prevent exposure to high temperatures, are adequate. Raw material automatic backwash filter control system (diesel hydrogenation, hydroprocessing units): 1. Check whether the display on the local control panel of the automatic backwash filter control system is functioning properly, and whether the doors at the front, back, top, and bottom of the control panel are properly closed and sealed. Also, verify that the waterproof sealing of the display on the control panel is adequate. 2. Check whether the intermediate junction box of the automatic backwash filter is properly sealed and waterproof. 3. Check for any leaks in the air supply and signal pipelines connected to the various control ball valves of the automatic backwash filter