What Is Commissioning?

Quick Answer

Commissioning (also called cold commissioning) is the systematic process of verifying that every system in a facility functions as designed, using utilities (water, air, nitrogen, electricity) rather than process fluids. Commissioning follows pre-commissioning and precedes hot commissioning. It confirms that instruments read correctly, control loops respond as intended, safety systems trip at the right setpoints, and rotating equipment operates within specifications.

Commissioning vs Pre-Commissioning vs Hot Commissioning

Phase	Medium Used	Focus	Output
Pre-commissioning	Water, air, nitrogen	Physical integrity (leaks, cleanliness, pressure)	Clean, pressure-tested system
Commissioning (cold)	Utilities (air, water, nitrogen, electricity)	Functional performance (controls, interlocks, alarms)	Verified, functionally tested system
Hot commissioning	Process fluids (hydrocarbons, chemicals, steam)	Process performance under real operating conditions	Operating system at design capacity

Commissioning Activities by Discipline

Discipline	Key Activities
Piping	Final reinstatement verification, valve operation checks, line walk-down
Instrumentation	Loop checks, instrument calibration verification, control loop tuning
Electrical	Motor no-load run, protection relay verification, busbar energization
Rotating equipment	Pump/compressor solo run on water or air, vibration monitoring, alignment verification
Safety systems	ESD logic testing, F&G detector function test, PSV verification, cause-and-effect validation
DCS/control	HMI verification, alarm management, sequence testing, batch logic

Commissioning Sequence

Step	Activity	Prerequisites
1	Energize electrical systems (MCC, switchgear)	Megger tests passed, cable termination complete
2	Instrument loop checks (field to DCS)	Cables terminated, instrument air available
3	Control valve stroking	Air supply available, DCS operational
4	Motor solo run (uncoupled)	Electrical protection set, rotation confirmed
5	Pump test run on water	Piping flushed, mechanical seal set, motor tested
6	Safety system functional test	ESD and F&G systems powered, field devices connected
7	Interlock and cause-and-effect validation	All related systems commissioned
8	Integrated system test	All sub-systems operational on utilities
9	RFSU declaration	All commissioning tests passed, documentation complete

Common Commissioning Issues

Issue	Frequency	Impact	Resolution
Instrument loop errors	High	Wrong signal at DCS; incorrect readings	Re-check termination, marshalling, DCS configuration
Control valve hunting	Medium	Unstable process control	PID retuning, check valve sizing, actuator adjustment
Motor tripping on overload	Medium	Equipment cannot operate	Verify protection settings, check mechanical alignment
ESD logic mismatch	Low-Medium	Safety system does not respond correctly	Review cause-and-effect matrix, update DCS logic
Missing utilities	Medium	Cannot perform tests	Prioritize utility system commissioning first
Documentation gaps	High	Commissioning delayed pending paperwork	Track vendor documentation submission in VDR

Common Mistake

Starting commissioning activities before utility systems are complete and stable. Instrument air, cooling water, and electrical power must be available before any functional testing begins. Attempting to commission a control valve without stable instrument air supply produces false test results and wasted effort. Always commission utility systems first, then process systems.

Commissioning Documentation

Document	Purpose
Commissioning procedures	Step-by-step test protocols per system
Loop check sheets	Record of each instrument loop verified from field to DCS
Functional test reports	Results of valve, motor, pump, and safety system tests
Punch list updates	New deficiencies found during commissioning
System status log	Daily tracking of commissioning progress per system
RFSU certificate	Final sign-off that the system is ready for start-up

Commissioning Team Structure

Role	Responsibility
Commissioning manager	Overall commissioning planning and execution
System completion engineer	Tracks MC, pre-commissioning, and commissioning status per system
Discipline leads	Piping, E&I, mechanical, process—each leads discipline-specific activities
Vendor representatives	On-site support for packaged equipment, DCS, specialty items
Operations representatives	Participate in testing, prepare for handover

Commissioning transforms a constructed facility into a verified, functional plant. The quality of procurement and construction directly determines commissioning duration. Material defects, incorrect installations, and incomplete hydrostatic testing all surface during commissioning as rework.

Read the full guide to pipe classes and specifications