Instrumentation Commissioning in Cement, Power & Water Plants:

 

Instrumentation commissioning is one of the most critical and risky phases in any industrial project.
Most early plant failures, false trips, unstable control loops, and repeated shutdowns can be traced back to poor or incomplete instrumentation commissioning.

This guide is not a textbook explanation.
It is built around real questions asked by field engineers, commissioning teams, and plant owners during cement, power, water, and process plant projects.

1. What Must Be Completed Before Starting Instrumentation Commissioning?

Before commissioning begins, several activities must be fully completed to avoid rework and unsafe conditions:

• Instrument installation must be mechanically complete

• All cables terminated, labeled, and megger-tested

• Instrument air systems flushed and leak-free

• Power supplies and marshalling panels energized and verified

• Latest approved drawings available at site

Starting commissioning without these prerequisites almost always leads to delays and false fault finding.

2. What Is the Real Difference Between Pre-Commissioning and Commissioning?

This is one of the most misunderstood topics on site.

Pre-commissioning focuses on:

• Physical checks

• Installation verification

• Calibration and wiring integrity

Commissioning focuses on:

• System integration

• Signal verification

• Control functionality and logic validation

Pre-commissioning proves the instrument is ready.
Commissioning proves the instrument works within the control system.

3. Can Commissioning Start If Loop Folders Are Incomplete?

Technically yes — practically dangerous.

Incomplete loop folders often result in:

• Wrong signal ranges

• Incorrect termination points

• Mismatched I/O assignments

Experienced teams may proceed with partial commissioning, but only with controlled risk and strict punch list tracking.

4. What Are the Most Common Issues Found During Instrumentation Commissioning?

Across industrial plants, the most frequent problems include:

• Wrong instrument range configured in DCS

• Reversed impulse lines on pressure instruments

• Incorrect polarity on temperature sensors

• Wrong fail-safe action on control valves

• Missing or incorrect grounding

Most of these issues are not manufacturing defects — they are site execution problems.

5. How Do You Properly Verify an Instrument Loop?

A complete loop verification includes:

• Field signal simulation

• Confirmation at marshalling panel

• DCS signal verification

• Alarm and trend confirmation

• Return signal verification for final elements

Loop check is not only continuity — it is full signal integrity verification.

6. Why Do Signals Mismatch Between Field and DCS?

Signal mismatches are usually caused by:

• Wrong scaling in DCS

• Incorrect instrument range configuration

• Engineering unit mismatch

• Analog card configuration errors

This is why commissioning engineers must understand both field devices and control logic.

7. Should Instruments Be Re-Calibrated During Commissioning?

Yes  especially for critical loops.

Even if calibrated in the workshop, instruments may drift due to:

• Transportation

• Installation stress

• Environmental conditions

Field calibration during commissioning ensures real process accuracy.

8. What Are the Most Frequent Loop Check Mistakes?

Common loop check errors include:

• Checking wiring only, ignoring configuration

• Skipping return signals

• Not testing alarms

• Poor documentation of results

A loop check without records has no engineering value.

9. How Do You Deal With Incorrect or Outdated Drawings?

This is a daily site reality.

Best practice includes:

• Marking red-line drawings immediately

• Updating loop folders daily

• Coordinating changes with engineering

Never commission based on assumptions — always document deviations.

10. What Problems Appear Only During Functional Testing?

Functional testing reveals issues that loop checks cannot detect, such as:

• Logic sequencing errors

• Wrong interlock priorities

• Missing permissives

• Incorrect alarm setpoints

This phase requires strong coordination between instrumentation, control, and operations.

11. Why Do Control Valves Fail Functional Tests?

Control valve issues during commissioning are extremely common due to:

• Wrong air supply pressure

• Incorrect positioner calibration

• Wrong fail position configuration

• Feedback signal mismatch

A valve that strokes locally may still fail under control logic.

12. How Do You Verify Fail-Safe Action of Control Valves?

Fail-safe verification must include:

• Loss of air test

• Loss of signal test

• Confirmation of final position

• DCS indication verification

This step is critical for safety and process protection.

13. Why Do Instrument Signals Become Unstable During Start-Up?

Unstable signals during start-up are often caused by:

• Process disturbances

• Poor impulse line routing

• Electrical noise and grounding issues

• Incorrect filtering settings

These issues usually appear only when the process becomes live.

14. How Do Grounding and Earthing Affect Commissioning?

Improper grounding can cause:

• Signal noise

• Communication loss

• Intermittent faults

Instrumentation grounding must be verified before blaming devices or control systems.

15. What Are Typical HART Communication Problems on Site?

Common HART issues include:

• Wrong loop resistance

• Address conflicts

• Incorrect device descriptions

• Grounding problems

Successful communication confirms correct wiring and device health.

16. What Documentation Is Required Before Commissioning Sign-Off?

Minimum required documentation includes:

• Approved loop folders

• Calibration certificates

• Loop check reports

• Functional test records

• Punch list closure evidence

Without documentation, commissioning is incomplete.

17. How Do You Manage Punch Lists Without Delaying Start-Up?

Effective punch list management includes:

• Prioritizing safety and critical loops

• Clear ownership of actions

• Daily progress tracking

• Clear acceptance criteria

Not all punch items should delay start-up — but all must be tracked.

18. What Coordination Is Required Between Disciplines?

Instrumentation commissioning cannot succeed in isolation.

Strong coordination is required with:

• Electrical teams (power and grounding)

• Control engineers (logic and alarms)

• Operations (process understanding)

Poor coordination is one of the top causes of delays.

19. What Are the Main Safety Risks During Live Commissioning?

Key safety risks include:

• Working on energized loops

• Live process exposure

• Unexpected valve movements

• Bypassed interlocks

Strict permit-to-work and isolation procedures are mandatory.

20. How Do You Know Commissioning Was Done Correctly?

Proper commissioning is confirmed when:

• Loops respond correctly under process conditions

• Alarms and interlocks perform as designed

• Operators are confident with system behavior

• Early plant operation is stable

Successful commissioning reduces downtime, trips, and maintenance costs.

Conclusion

Instrumentation commissioning is not a checklist activity — it is a critical engineering process that directly affects plant reliability, safety, and performance.

Plants that invest time and expertise during commissioning experience:

• Fewer start-up problems

• Lower maintenance costs

• Improved operational stability

Poor commissioning, on the other hand, guarantees problems after start-up.