Project Start-up, Commissioning and Loop Checking
This domain covers the transition from construction to operation: pre-commissioning, commissioning, loop checks and start-up. Level II tests whether you can prove that a loop is correct from field device to HMI, that alarms and fail-safe actions work, and that every check is documented and signed off.
Core rules
- The sequence is mechanical completion, pre-commissioning, commissioning and start-up. Loop checks belong in commissioning, before process fluids are introduced.
- A cold loop check is performed without process; a hot loop check is performed with process or simulated process conditions.
- Check point-to-point continuity, insulation resistance, polarity, shielding and grounding before energizing.
- Simulate the input at the field device with a loop calibrator, then verify the DCS reading in engineering units, the alarm setpoints and the trend.
- Drive the output to the final element and verify stroke, direction, travel and fail-safe action. Confirm that the valve goes to its safe position on signal loss and air failure.
- Use the current loop drawing, I/O list and P&ID revision. Record every bypass, remove it after testing, and obtain sign-off.
Worked example
A flow loop reads 0 at the DCS even though 12 mA is being injected at the field terminals. First confirm the calibrator is in source mode and the leads are correct. Measure voltage at the input-card terminals: if 1-5 VDC is present, the card or its configuration is suspect; if not, the wiring is open or the channel assignment is wrong. Cross-check the tag and channel against the I/O list before changing card configuration. The reasoning is to prove where the signal stops, not to assume the DCS is faulty.
Traps
Checking only the input and never stroking the valve; leaving a loop in manual or bypass after the test; using a superseded loop drawing; failing to verify alarm and interlock actions; and signing a loop folder without the as-left values.