As an instrumentation engineer, we’ve accumulated numerous valuable experiences in the field. Here are 60 essential tips summarized for your benefit.
Separate Signal and Power Cables: Avoid using a multi-core cable for both signal and power lines to prevent signal interference.
Oil-Free Maintenance for Oxygen Pipelines: Ensure that oxygen pipeline instruments are free from oil contamination. Do not mix oil-free transmitters and pressure gauges with standard ones.
Prevent Short Circuits During Maintenance: When disconnecting wires, always insulate the wire ends to prevent short circuits.
No Intermediate Joints in Cables: Ensure that cables are free from intermediate joints to reduce potential failure points.
Shielding Grounding on Control Room Side: Shielding grounding should typically be done on the control room side for effective grounding.
Protective Hose Below Instrument Inlet: The protective hose must be lower than the instrument inlet to prevent water ingress.
Protect Outdoor Instruments: Install protection boxes or wrap outdoor instruments in nylon bags to shield them from rain and dust.
Segregate Different Types of Cables: When laying cables in a tray, separate intrinsic safety cables, power cables, and signal cables with partitions.
Proper Compensation Wire Connection: When connecting compensation wires, avoid using lugs to prevent measurement errors due to different conductors contacting.
Follow Procedures for Instrument Issues: During production, handle instrument issues per procedures and notify operators, sometimes requiring written approval.
Surge Protection for Lightning Areas: In lightning-prone areas, connect field instruments to surge protectors before connecting to safety barriers and control systems.
Animal Prevention in Control Rooms: Implement measures to keep rodents and other small animals out of the control room to avoid equipment damage.
Thorough Instrument Testing: Complete individual testing before installation and loop testing after installation before integrating into the system.
Presence of Process Personnel During Repairs: During operation, ensure process personnel are present during instrument repairs to avoid major issues.
Coordinate Instrument Maintenance with Process Personnel: Always confirm the process status and power off the instrument before maintenance to ensure safety.
Proper Flow Meter Selection and Installation: Choose the right flow meter based on the medium, temperature, and pressure. Follow specific installation requirements.
Rain Protection for Control Room Entry: When designing instrument trays entering the control room, include bends and seal to prevent rainwater ingress.
Valve Position for Instrument Air Lines: Position valves above the centerline of the pipe to avoid debris entering the instrument valves.
Single-End Shielding Ground: Ensure the shielding layer is grounded at one end only. Protect outdoor cable conduit ends from rain and seal in explosive environments.
Alarm Device Maintenance: Keep alarm instruments and sound devices in good working condition to ensure timely alerts during process issues.
Copper-Free Zones for Ammonia: Avoid using copper and copper alloys in ammonia environments. Ensure DCS systems have dual power supplies.
Avoid Two-Wire Transmission for RTDs: For long-distance RTD temperature measurement, avoid using two-wire systems.
Cable Laying Standards: Insulation resistance of cables should exceed 5 megaohms. Bend radius should be more than 10 times the cable diameter, and fiber optics should be 15 times. Maintain appropriate spacing between instrument cables, electrical cables, equipment, and pipes.
Hydraulic Testing of Stainless Steel Pipes: Ensure chloride content in water does not exceed 25 PPM for austenitic stainless steel pipe testing. Work grounding should be less than 1 ohm, and other grounding should be less than 4 ohms.
Use Fireproof Cloth for Instrument Protection: Use fireproof (asbestos) cloth for instrument protection, not plastic bags.
Explosion Protection for Hydrogen Units: Instruments in hydrogen units must meet both explosion-proof and protection level requirements. Intrinsically safe and explosion-proof signal cables should not enter the same junction box.
Insulation Resistance and Bending Radius: Insulation resistance should be greater than 5 megaohms. Bend radius should be more than 10 times the cable diameter, and fiber optics should be 15 times. Maintain spacing between instrument and electrical cables.
Hydraulic Testing Standards for Stainless Steel Pipes: Chloride content in water should not exceed 25 PPM for austenitic stainless steel pipe testing. Grounding should be less than 1 ohm for work, and less than 4 ohms for other purposes.
Intrinsic Safety and Explosion-Proof Signal Separation: For hydrogen units, ensure intrinsically safe and explosion-proof signals do not share the same junction box.
Adding Terminators in FF Bus Design: Install terminators (resistor and capacitor in series) at the power conditioner and fieldbus junction box terminals.
Fail-Safe Solenoid Valves: Use fail-safe solenoid valves that are energized under normal conditions and de-energized during interlocks.
Temperature Instrument Installation on Small Pipes: For pipes below DN80, use temperature gauge expanders to increase the pipe size to DN80 for installation.
Flow Measurement Elements Exclusion: Flow measurement elements should not participate in plant water pressure testing.
Condensing Pots Installation Height: For steam flow measurement, ensure the same installation height for both condensing pots.
Cold Bending for Instrument Pressure Tubes: Use cold bending for instrument pressure tubes and avoid using gas welding for bending.
Flash Evaporation Consideration in Control Valves: During design and selection of control valves, consider flash evaporation and take measures such as:
Increasing material hardness.
Reducing fluid velocity.
Selecting suitable control valve types and flow directions.
Implementing multi-stage pressure reduction.
Cavitation Reduction Methods: Methods to reduce cavitation include:
Controlling pressure drops to prevent cavitation, such as using multi-stage pressure reduction.
Reducing cavitation impact by increasing material hardness and reducing flow velocity.
Properly distributing pipeline pressure to increase downstream pressure.
Cable Entry to Control Room: Ensure cables and wires entering the control room have a fixed support point to prevent stress due to climate changes. Provide a slope (greater than 1/100) towards the outside to prevent rainwater ingress. Seal wall penetrations to prevent entry of rodents and insects.
Local Pressure Gauge Selection: Choose the correct local pressure gauge based on the nature of the pressure source, whether it is an impact load or general pressure.
Safety Measures for Live Equipment: Do not disassemble live equipment. Always carry a test pen to prevent electric shock hazards.
Anti-Static Measures for DCS: Implement anti-static measures for DCS systems to prevent accidents caused by static electricity.
Forced Action for Interlock Equipment Maintenance: During interlock equipment maintenance, forced action must be applied through DCS.
Solenoid Valve Coil Maintenance: Do not remove the solenoid valve coil while energized to avoid burning the coil.
Flow Meter Installation: Ensure that rotor and turbine flow meters are installed vertically with the fluid flowing from bottom to top.
Regulating Valve Air Line Maintenance: After installing a regulating valve, vent the air line before connecting it to the valve positioner to prevent oil from entering and damaging the positioner.
Instrument Selection for Acetylene: For acetylene applications, use copper-free instruments and ensure explosion-proof rating is met. Check for “Not Suitable for Acetylene” markings on devices.
Isolation Between DCS and Electrical Systems: Use isolators between DCS and electrical systems to prevent interference and ensure proper communication.
Steam Tracing Line Selection: For steam tracing of instrument lines, use pipes with a minimum O.D. of 12 mm to ensure effective tracing over longer distances.
Safety Barriers for Intrinsic Safety Systems: Safety barriers should be used only for intrinsically safe explosion-proof systems. Ensure:
Field instruments are intrinsically safe.
Safety barriers are installed on the control room side.
Cables are intrinsically safe signal cables.
Signal Isolation for Enhanced Safety and Explosion-Proof Instruments: Use isolators for signal isolation where necessary for enhanced and explosion-proof instruments.
Zener Barrier Grounding: Pay attention to grounding requirements for Zener barriers to ensure safety.
Integration of Instrumentation and Process: Instrumentation and process are closely linked. Online maintenance should minimize interference with the process.
Flow Meter Selection Based on Conductivity: Do not use electromagnetic flow meters for low-conductivity media. For high-accuracy measurements at the plant level, use mass flow meters.
Pressure Measurement for High-Temperature Media: When the medium temperature exceeds 60°C, add a cooling tube or siphon to the pressure measurement setup.
Pneumatic Control Valve Setting: Ensure the correct setting of air-to-open and air-to-close valves in the DCS to avoid operational errors.
Fault Diagnosis for Temperature Instruments: A sudden maximum or minimum reading typically indicates a system fault, such as a broken thermocouple, RTD, or faulty transmitter amplifier.
Proper Labeling of Instrument Wires: Label instrument wires correctly during installation to avoid future maintenance issues.
Temperature Sensor Installation: Install temperature sensors against the flow direction if installed at pipe bends or inclined positions.
Relative Position of Pressure and Temperature Points: On the same pipe, place the pressure point upstream of the temperature point.
Rotameter Installation: Install rotameters vertically on pipes with the medium flowing from bottom to top.
