Project Start-up, Commissioning, and Loop Checking
Project Start-up, Commissioning, and Loop Checking covers the path from mechanical completion to operations accepting a loop. Level III expects you to plan a loop-check programme, execute point-to-point verification, prove fail-safe action, and hand over with signed, traceable documentation.
The sequence
- Pre-commissioning: P&ID walkdown, tag verification, continuity and insulation-resistance checks, grounding, instrument air quality (dew point, oil-free, correct pressure), and confirmation that each instrument has a current as-left calibration record.
- Point-to-point loop check: inject a known signal at the field terminals and confirm the DCS or PLC reads the correct engineering value under the correct tag.
- Stroke test: drive the output through 0, 25, 50, 75 and 100 % and verify travel, direction, position feedback and stroking time.
- Prove the fail action: remove the signal or air and confirm the valve reaches its specified fail-safe position.
- Verify alarms, trips and interlocks against the cause-and-effect matrix, then close punch-list items and file the signed loop folder.
Worked example
For a fail-closed level control valve: inject 4, 12 and 20 mA at the transmitter terminals and confirm the DCS reads 0, 50 and 100 %. Drive the analogue output from 0 to 100 % and confirm the valve strokes in the correct direction with matching position feedback. Cut instrument air and confirm the valve closes fully. Raise the simulated level to the high-alarm setpoint and confirm the alarm appears in the DCS event list.
Traps
- Leaving a mA simulator or jumper installed after the check.
- Doing a soft check at the DCS input only, never proving the field wiring.
- Bypassing an interlock without a logged bypass permit and removal date.
- Presenting a loop check as a calibration record; they are different documents.