Inspection Checklists

Instrumentation Inspection Checklist

(Part 2 of 7 – TEMPERATURE Instruments & Transmitters)

Note - this checklist applies only to temperature instrument specifics.

This checklist should be used in conjunction with the general checklist that applies to generic checks for all instruments.

□ Ensure sensor hookup style is correct (RTD: 3-wire, 4-wire, etc. | TC: Proper Type)

□ For RTD instruments, verify the RTD type and ‘Alpha’ value matches configuration & spec (example: a Pt100 could be a 0.385 or 0.392 ohm per degree Alpha or others…)

□ Ensure no “On Terminal” ‘jumpers’ used to change from 2-wire, 3-wire, or 4-wire (the exact wiring matters and must match the configuration of transmitter or errors will be introduced – same applies to simulations during calibrations/checks).

□ Ensure using proper RTD lookup table if using decade box for RTD simulations.

□ For transmitters with Hot Backup, be sure to verify the settings and config matches specifications and standards.

□ Verify RTD good thermal conductivity on sensor (spring pressing sensor into thermowell, clean/replace old thermal paste if applicable – thermal conductivity is critical for time response and impacts both process control/tuning and process safety)

□ For thermocouple instruments, ensure the probe and all extension wiring and TB’s are of proper type (only TC extension wire or specific type TC terminal blocks should be used between the probe and wherever the cold junction compensation is taking place).

□ Ensure the cold junction compensation is configured and installed correctly (CJC is typically applied at transmitter terminals, or at the input card if using PLC/DCS type temperature input cards.

Additional checks (if accessible / applicable):

□ Check for “green-rot” for type K Thermocouples (when accessible – only applicable on high temp applications)

□ Check baseline resistance of actual thermocouple probes and compare to recent/past values (very helpful at identifying developing problems in TC probes over time)

□ Verify thermowell not fouled or coated excessively as this can impact time response. Only applicable if access to thermowell is available.

□ Ensure no leakage or excess wear on thermowell. Only applicable if access to thermowell is available.

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Instrumentation Inspection Checklist

(Part 3 of 7 – PRESSURE Instruments & Transmitters)

Note - this checklist applies only to pressure instrument specifics.

This checklist should be used in conjunction with the general checklist (part 1) that applies to generic checks for all instruments.

□ Check impulse (sensing) lines for any pockets that could trap air or gas where it shouldn’t be.

• • All gases will have some condensation that will work downward, and all liquids have some amount of gases entrained that will vaporize out and rise upwards.
  • Impulse lines should have a taper of about 1” per foot, to allow for gases or liquids to return to process.

□ Look at installation of tubing all the way back to process to see if there is a likelihood of sludge buildup, or inline pressure snubbers (or porous filters), valves, kinks, dents, or anything else that might cause them to clog, or slow reaction times, etc.

□ Look for any ‘wet-legs’ that might not stay fully wet.

□ Look for ‘wet-legs’ whose temperature can vary considerably. Changes in wet-leg temperature can alter the DP reading due to density changes.

□ Ensure impulse lines and fittings are tight and do not leak (or show evidence of leakage). If any oddities are noticed, it may be good to apply some snoop to the fittings to look for any leaks.

□ Verify manifold valves operate smoothly and properly.

□ Some DP test procedures (SIS and others) setup to allow process gas/liquid to from the HP and LP lines to vents to ensure they are not clogged. This procedure needs to be engineered and vetted – but it can be extremely valuable, since clogging is one of the most likely dangerous-undetected failure modes for DP instruments. Actual procedures vary.

□ Factor in stabilization time (pressure and temperature) of test equipment tubing, pumps, etc. – especially with lower pressure measurements and especially with gas/air source.

□ Verify no sludge build up (or spots where it could build up). Note condition of material that comes out during any vents or when connecting/disconnecting test fittings.

□ Ensure any square root functions are properly configured and setup. (Example: DP flow square rooting is typically handled in the controller – if signal is also square rooted in the transmitter the values between 0 and 100% would be dramatically off target.

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Instrumentation Inspection Checklist

(Part 4 of 7 – LEVEL Instruments & Transmitters)

Note - this checklist applies only to Level Instrument specifics.

This checklist should be used in conjunction with the general checklist (Part 1) that applies to generic checks for all instruments.

Bridle-based Level Measurements:

□ Ensure isolation valves are open (in some cases/procedures, the valves may be manipulated such that clear flow-path through isolation valves is verified by opening/draining some amount of liquid.

□ If measurement problems arise, it may be helpful to x-ray the bridle to ensure centering tubes or top/bottom mounts are secure and rod is not bent or kinked.

□ Ensure physical indicators (mag flippers, etc.) are legible and functional

Magneto-strictive Level Transmitters:

□ Ensure float capsule travels smoothly and freely with minimal hysteresis or deadband (indicative of catching in bridle). A fast history trend can show sticky spots as stair-step changes.

□ Periodically check probe/bridle with gauss meter and clear up any magnetized areas.

□ Check float to ensure not damaged or crushed due to poor maintenance practices.

□ Ensure rod is not vibrating since this will cause errors (utilize dampeners if needed).

Echo-based (GWR, Ultrasonic, etc.):

□ Ensure config is correct and perform a ‘logic’ check of the setup. This is an extremely common problem area with echo based level measurements.

DP Based:

□ Ensure that SG matches spec and that it is properly accounted for in configuration.

□ Ensure that any capillary lines are properly factored in (use SG x Head height of capillary material).

□ Ensure that any elevation/suppression between taps and transmitter is factored in.

□ Verify that URV/LRV config seems logical. It is wise to do the math on this periodically to ensure any errors are caught (since there are SOOOO many mistakes on this).

□ Visually inspect impulse lines / capillary lines per the DP instrument checklist items.

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Instrumentation Inspection Checklist

(Part 5 of 7 – FLOW Instruments & Transmitters)

Note - this checklist applies only to FLOW Instrument Specifics.

This checklist should be used in conjunction with the general checklist (Part 1) that applies to generic checks for all instruments.

DP Based Flow Measurement

□ Ensure SQRT function is only occurring in one location (typically at controller). Sometimes DP flows are inadvertently square rooted at transmitter and at controller. When this occurs, they look right at 0 and 100%, but are way off through mid-ranges.

□ Ensure the transmitter configuration properly aligns with SPEC Sheet of primary element (orifice, etc.).

• • Often times, engineers mistakenly do a linear “prorated” change to DP flow systems (because they forget how they work). If the config doesn’t match the spec sheet or if the spec sheet hasn’t come from factor or source of the actual primary element, resolve it.

□ Ensure proper tubing lineups (no dents, kinks, pockets, traps, or sludge buildup spots).

□ Look at historical trends

• • Note DP variability over time to check for signs of sensor tube clogging, or buildup/erosion of primary element.
  • (If possible) compare DP value vs Pump speed or other variables or downstream flow measurements that directly relate to flow rate.

□ Periodically, you should inspect and gauge out the primary element (even tiny amounts of wear on orifice hole edges will cause surprisingly large errors or noise).

• • This step would be a fairly invasive procedure in most cases due to requirement to pull the element - but is often neglected for extremely long periods of time and is the real cause of many/most DP flow measurement problems.

□ Ensure that gas flows are properly density compensated – this means they need to be based on absolute pressure (I.E. Psia scale) and ABSOLUTE temperature (I.E. Kelvin or Rankine scales).

• • I often see situations where gas flow density corrections utilize PSIG configured transmitters and scaling – this could lead to a significant error in lower pressure systems, since the ambient pressure can vary considerably (0.5 psia conceivably), which would result in incorrect density factors.

Time based flow measurements (Vortex, Coriolis, Ultrasonic, etc.)

□ Verify the configuration matches the official specification sheet. It is wise to periodically do a logic check of the config specs as well, since the problem is sometimes in the original configuration.

□ For Coriolis flow meters, ensure operating density range is correct per specs.

□ For ultrasonic flow meters, ensure the interface is in good shape (you may need to reseal the transducer to pipe in some cases).

□ Note – time based measurements themselves have extremely low drift rates since they are typically based on the timing of the onboard crystal time references which are insanely accurate and consistent due to modern chip manufacturing. Most problems with these types of instruments will be in the installation, neglected specs, improper configurations, or process material parameters being outside the specified/configured ranges.

Magnetic Flow Measurements (Mag-Meters)

□ Ensure there is no gas/air buildup in the measurement part of the mag-meter. There is often a vent/burp valve that will allow one to ‘burp’ any gas buildup since this would result in a direct measurement error.

□ Occasionally, the electrodes of the Mag-Meter should be checks. Some newer mag-meters have great onboard diagnostics and analytics and the new electrodes tend to last much longer than earlier Mag-Meters.

□ Ensure the grounding is correct. There are many ways to ground a Mag-Meter depending on piping material, fluid, etc. And it must be done correctly per vendor references or problems and errors will occur. Take the time to study the vendor references (or talk to them) and be sure that any grounding wires, bonding bars/straps, etc. are installed properly.

Rotary/Pulse Based Flow Meters (Turbine, Paddlewheel, and Positive Displacement Flow Meters)

□ Ensure the connection is tight and sensor is secure and sensor cable is in good shape.

□ Ensure sensor spacing and mounting is correct.

□ Ensure no magnetic fields or parasitic/relic magnetism exists near sensors.

□ Verify the pickup amplifier is operating properly (as applicable).

□ Also refer to vendor specific inspection and installation recommendations as they vary.

□ Occasionally, it is good to look at the waveform on o-scope and compare to a base reference of the instrument when working well/new. You should keep a record of the waveforms in material history files or equivalent. (it is also wise to list the o-scope type and settings for the waveform record).

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Instrumentation Inspection Checklist

(Part 6 – Control Valves)

Note - this checklist applies only to I&C Control Valve specifics.

This checklist should be used in conjunction with the general checklist (part 1) that applies to generic checks for all instruments.

Air/hydraulic supply system checks (perform as separate check, monthly or quarterly at minimum).

□ Ensure compressor, receiver tank, pressure is appropriate.

□ Ensure air system moisture removal systems are operating properly.

□ Ensure compressor filtration and moisture separation system functioning properly.

□ Check air receiver system filters. Note any substantial particulate buildup and ensure rust is not developing (especially on non-stainless systems).

□ Verify hydraulic pump system pressure is appropriate, and main system tubing and components seem in good repair with no leakage, or physical damage/corrosion/etc.

□ Listen to air compressor (and/or Hydraulic Pumps and recycle/relief valves) and note any changes or abnormalities.

□ Pull up historical trend of air (and/or Hydraulic) pressure cycles and compare to specs. Identify and resolve any ‘low pressure’ situations that have occurred since last check.

Local valve supply checks (for control and/or isolation valves)

□ Check air lines for kinks, dents, damage, or possible leakage/clogs.

□ Verify appropriate air/hydraulic operating pressure at valve.

□ Inspect clean/change valve local filters & drain any water from water separators.

□ Note coloration of any water in water traps (rust color is bad and should be resolved).

□ Verify integrity of position switches and/or sensors. Note – on any linkage based position sensors, note and correct any corrosion or buildup, and look for any gaps or slack in the linkage mechanisms, as this will lead to problems.

Actuators and positioners (for control and/or isolation valves)

□ Observe positioner for excess hunting or slow/sticky response.

□ Observe supply, and valve pressure gauges for any signs of problems.

• • For SMART positioners, look for alert/warning indicators if available, or connect communicator to check for alerts.
  • With proper design, this check can be very quick and easy – and is probably the single most helpful indicator in the entire I&C field. If you are not checking the built in alerts of your smart positioners, you are losing money you shouldn’t be losing and lowering your safety margins.
  • SMART positioners will see the problem and could alert you to it BEFORE it costs money, or causes trips or accidents.

□ Verify valve stems are clean and shiny (for sliding stem type valves) – be sure to remedy any corrosion buildup (emery cloth, etc. – per your specific maintenance specs).

• • Buildup on control valve stems is an extremely common cause of problems in many plants. This is entirely preventable – but often goes unresolved until plant trips or downtime causes a replacement of the actuator.

□ Verify gears of rotary actuators are clean and/or properly lubricated (as applicable).

□ Check any motor operated valves for alerts or odd noises.

Control Valves

□ Historical - Pull up trend of (PV vs Valve Position) and of (Valve Position vs Valve Command) over time. It may be helpful to also plot any major process load variables that impact these relationships.

• • Changes in position for same PV and process ‘load conditions’ may indicate valve body or plug changes/problems.
  • Mismatches between Command and Actual position may indicate actuator problems, position sensor problems, etc. Any deviations should be identified and resolved.
  • Note any difference between valve opening vs closing rates.

• • • Differences could be indicative of inadequate valve ‘stiffness’ factors (I.E. You may need a larger or more powerful actuator if the valve struggles to open/close against process pressure)

• • Control valves should operate in the mid-range (~25-75%). If they get out of this range, you risk running into numerous control problems such as Reset Windup.

□ Observation/inspection - if/when possible, stroke valve as far as process conditions allow.

• • Ideally, start with small up and down bumps (~5%) and then increase magnitude of bumps. Operate through as much of the range as allowable per process conditions at the time. Watch for any sticky points or speed variations as this would cause process control problems.

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Instrumentation Inspection Checklist

(Part 7 – Isolation Valves)

Note - this checklist applies only to I&C Isolation Valve specifics.

This checklist should be used in conjunction with the general checklist (part 1) that applies to generic checks for all instruments.

Air/hydraulic Supply System Checks (perform as separate check, monthly or quarterly at minimum).

□ Ensure compressor, receiver tank, pressure is appropriate.

□ Ensure air system moisture removal systems are operating properly.

□ Ensure compressor filtration and moisture separation system functioning properly.

□ Check air receiver system filters. Note any substantial particulate buildup and ensure rust is not developing (especially on non-stainless systems).

□ Verify hydraulic pump system pressure is appropriate, and main system tubing and components seem in good repair with no leakage, or physical damage/corrosion/etc.

□ Listen to air compressor (and/or hydraulic pumps and recycle/relief valves) and note any changes or abnormalities.

□ Pull up historical trend of air (and/or Hydraulic) pressure cycles and compare to specs. Identify and resolve any ‘low pressure’ situations that have occurred since last check.

Local Valve Supply Checks (for control and/or isolation valves)

□ Check air lines for kinks, dents, damage, or possible leakage/clogs.

□ Verify appropriate air/hydraulic operating pressure at valve.

□ Inspect clean/change valve local filters & drain any water from water separators.

□ Note coloration of any water in water traps (rust color is bad and should be resolved).

□ Verify integrity of position switches and/or sensors. Note – on any linkage based position sensors, note and correct any corrosion or buildup, and look for any gaps or slack in the linkage mechanisms, as this will lead to problems.

Actuators and Positioners (for Control and/or Isolation Valves)

□ Observe positioner for excess hunting or slow/sticky response.

□ Observe supply, and valve pressure gauges for any signs of problems.

• • For SMART positioners, look for alert/warning indicators if available, or connect communicator to check for alerts.
  • With proper design, this check can be very quick and easy – and is probably the single most helpful indicator in the entire I&C field. If you are not checking the built in alerts of your smart positioners, you are losing money you shouldn’t be losing and lowering your safety margins.
  • Smart positioners will see the problem and COULD alert you to it BEFORE it costs money, or causes trips or accidents.

□ Verify valve stems are clean and shiny (for sliding stem type valves) – be sure to remedy any corrosion buildup (emery cloth, etc. – per your specific maintenance specs).

• • Buildup on control valve stems is an extremely common cause of problems in many plants. This is entirely preventable – but often goes unresolved until plant trips or downtime causes a replacement of the actuator.

□ Verify gears of rotary actuators is clean and/or properly lubricated (as applicable).

□ Check any motor operated valves for alerts or odd noises.

Isolation Valves (Shutdown Valves, ESD Valves, Blowdown Valves, etc.)

□ Historical - pull up trend of Valve Command vs Valve Position. Note the typical time for opening and closing. Ideally record this for posterity and review each check for any changes. Changes in opening/closing time may be indicative of developing problems.

• • Changes in position for same PV may indicate valve body or plug changes/problems.
  • Mismatches between Command and Actual position may indicate actuator problems, position sensor problems, etc. Any deviations should be identified and resolved.
  • Control valves should operate in the mid-range (~25-75%). If they get out of this range, you risk running into numerous control problems such as Reset Windup.
  • In case you are wondering… yes – this could and probably should be digitized into your control system… it’s so easy to do, yet very few sites do it.

□ Observation/Inspection - if/when possible, stroke valve as far as process conditions allow. Possibly do this during downtime or turnarounds to allow maximum test range.

• • Watch for any sticky points or speed variations as this would cause process control problems. Compare command position to actual position in 5-25% increments going up and then down. A variation or difference in upscale and downscale readings indicates a problem (hysteresis, stiction, etc.).
  • Also watch behavior of positioner during command changes. Ensure it does not hunt or is not excessively slow or sticky. Watching valve actuator pressure during these changes can be incredibly insightful to a well-trained eye.

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