Commissioning and the punch list: from mechanical completion to handover, with a template
The stages from mechanical completion through pre-commissioning and commissioning to the performance test and handover, the gate at the end of each, why commissioning runs by system and not by discipline, how the punch list is run and categorised, what the pre-startup safety review holds, and what handover has to include. With a free punch list template.
Key takeaways
- Commissioning is the staged proof that a built plant does what it was designed to do, from mechanical completion through pre-commissioning and commissioning to the performance test and handover.
- Each stage ends at a gate, and the gate is a decision with evidence: the records complete, the tests passed, the punch items of the right category closed.
- The punch list is the one register of everything found wrong, from a missing guard to a paint scratch, categorised by what it must be closed before. It is run by system, not by discipline.
- A items close before the gate they were found at. B items close before start-up. C items close after handover by an agreed date. The letters are a convention; the discipline is that nothing passes a gate with an A open.
- Handover is the transfer of care, custody and control to operations, and it is accepted only when operations have what they need to run and maintain the plant.
Commissioning is where a project's promises are tested. The plant has been designed and built, and now it has to be proved, system by system, to do what the design said, before people depend on it. Done well it is a staged, evidenced process with a gate at the end of each stage. Done badly it is a rush to a start-up date with a list of things to fix later that is never finished.
The punch list is the instrument of that process. It is the one register of everything found wrong, from a missing guard to a paint scratch, with a category that says what each item must be closed before. A clean punch list is the evidence a gate is passed on, and an honest one is the project's best defence against the start-up that reveals what was skipped.
This guide sets out the stages and their gates, how the plant is broken into systems so that commissioning can be staged at all, what each stage tests, how the punch list is run and categorised, what the pre-startup safety review holds, what handover has to include, and the mistakes that are common enough to plan against. A punch list template comes with it. The operational readiness guide covers the owner's side of the same period, which is getting the organisation ready to receive the plant.
Free download
Punch list template
A punch list laid out by system with category, owner, due date, status and separate close and verify columns, a summary of open items by system and category worked out from what you enter, and the stages and gates on a sheet of their own.
The stages and their gates
The stages are a sequence of proofs, each resting on the one before. Construction complete says it was built to the drawings. Mechanical completion is the gate: walked down, the records signed, the A items closed. Pre-commissioning tests each system cold, with no process material: flushing and pressure tests, loop checks, instrument calibration, motor solo runs, interlock and trip tests. Commissioning introduces process material and tests the system doing its job: sequences, control tuning, alarms and trips under real conditions. The performance test runs the plant at rate against the guarantees. Handover transfers care, custody and control.
A gate is a decision with evidence, and the evidence is the inspection and test records for the system and the punch list for it. The names of the stages and the exact gates vary by industry and contract. IEC 62337 gives the phases and milestones for electrical, instrumentation and control systems in the process industry, and most commissioning procedures follow its shape across disciplines.
1Construction complete
Built to the drawings, by system and subsystem, with the inspection and test records signed for each
Gate
Mechanical completion: the walkdown done, the records complete, the A items closed
Punch closed: Category A
2Pre-commissioning
Static and energised checks with no process material: flushing, pressure tests, loop checks, motor solo runs, instrument calibration, interlock tests
Gate
Ready for commissioning: every system tested cold, the B items closed or scheduled
Punch closed: Category B on the system
3Commissioning
Process material introduced, by system: functional tests, sequences, control tuning, alarm and trip tests under real conditions
Gate
Ready for start-up: the pre-startup safety review held, the operators trained, the maintenance plans live
Punch closed: Every A and B
4Performance test
Run at rate against the guarantees: throughput, quality, availability and consumption over the agreed period
Gate
Performance accepted, or the shortfalls listed with who owns each
Punch closed: C items scheduled
5Handover
Care, custody and control pass to operations, with the documents, the spares, the data and the open items
Gate
Acceptance: operations sign that they have what they need to run and maintain it
Punch closed: C items by agreed dates
→ Care, custody and control move right. Nothing passes a gate with an A item open
| Stage | What it does | The gate | Punch closed |
|---|---|---|---|
| Construction complete | Built to the drawings, by system and subsystem, with the inspection and test records signed for each | Mechanical completion: the walkdown done, the records complete, the A items closed | Category A |
| Pre-commissioning | Static and energised checks with no process material: flushing, pressure tests, loop checks, motor solo runs, instrument calibration, interlock tests | Ready for commissioning: every system tested cold, the B items closed or scheduled | Category B on the system |
| Commissioning | Process material introduced, by system: functional tests, sequences, control tuning, alarm and trip tests under real conditions | Ready for start-up: the pre-startup safety review held, the operators trained, the maintenance plans live | Every A and B |
| Performance test | Run at rate against the guarantees: throughput, quality, availability and consumption over the agreed period | Performance accepted, or the shortfalls listed with who owns each | C items scheduled |
| Handover | Care, custody and control pass to operations, with the documents, the spares, the data and the open items | Acceptance: operations sign that they have what they need to run and maintain it | C items by agreed dates |
Systems, not disciplines
Commissioning can only be staged if the plant is broken into systems and subsystems that can each be completed, tested and handed over on their own: a conveyor with its drive, its protection and its control; a lubrication system; a substation; a water supply. The breakdown is made early, numbered, and used by everyone from construction completion through to the CMMS, so that a system can reach mechanical completion while the one beside it is still being built.
Disciplines build; systems commission. A piping contractor finishes pipework across the whole plant, but a system is only ready when its pipework, its electrical, its instruments and its controls are all complete, and that is the unit the punch list and the records are organised by. The system breakdown also becomes the start of the asset hierarchy, which is one reason to get it right.
A plant is built by discipline and commissioned by system. The punch list follows the system, or nobody can say what is ready.
The punch list
Every item found wrong goes on one list. Not a list per contractor, which hides items at the boundaries, and not a list per discipline, which cannot say whether a system is ready. One list, organised by system, with every item categorised, owned, dated and tracked to verified closure. The walkdowns that build it are done by the people who will own the plant, with the contractor present, because the owner's team sees what the contractor's team has stopped seeing.
The categories say what an item must be closed before, which is the only thing that matters about it at a gate. The letters below are the common convention; sites rename them, and some add a fourth for items that are disputed or belong to a change. The discipline is the same under any naming: nothing passes a gate with an A open, and a B is scheduled with a date before the system starts up.
| Category | Closed before | Examples |
|---|---|---|
| A | Must be closed before the gate it was found at. Safety, a defect that stops the test, or anything that would be hidden by the next stage | A missing guard, a relief valve not fitted, a loop wired to the wrong input |
| B | Must be closed before start-up on that system, but the next stage can proceed | A leaking flange on a water line, a missing tag plate, a trip not yet tested under load |
| C | Does not affect safety or operation. Closed after handover by an agreed date | Paint touch-up, a label the wrong way round, a cable tray lid missing |
Running the list
The columns in the template are the ones a list needs to be run rather than merely kept. The two that are most often missing are the separate close and verify columns, because an item closed by the contractor who raised the work is an item nobody has checked, and the evidence column, because a photograph or a test record is what settles a dispute at the gate.
The list is reviewed at a fixed meeting, by system, with the open A items first. Items are never deleted: a disputed item is marked disputed and resolved, a duplicate is closed as a duplicate with the number it duplicates. The count of open items by system and category, which the template works out, is the number the commissioning manager reads every morning, and it is how the project knows which systems are near a gate and which are not.
| Column | What goes in it |
|---|---|
| Item | A running number, never reused |
| System | The system or subsystem the item belongs to, from the commissioning breakdown |
| Tag | The equipment or location tag |
| Discipline | As it says |
| Description | What is wrong, in enough words that someone else could find it and fix it |
| Category | A before the gate, B before start-up, C after handover |
| Raised by | As it says |
| Date raised | As it says |
| Stage found | As it says |
| Owner | The contractor or party responsible for closing it |
| Due | As it says |
| Status | As it says |
| Closed by, date | Who did the work and when |
| Verified by, date | Who checked it was done, which is never the person who closed it |
| Evidence | Photo, test record or certificate reference |
The pre-startup safety review
Between commissioning and the introduction of process material at rate sits the pre-startup safety review, a formal hold point that confirms the plant is safe to start. It checks that the construction matches the design, that the safety systems have been tested and the results recorded, that the hazard study actions are closed, that the operating procedures exist and the operators are trained on them, that the emergency arrangements are in place, and that every punch item that could affect safety is closed. It is chaired by someone with the authority to say no, and start-up waits for it.
On a brownfield modification the review is the same, scaled to the change. It is the point most often skipped when a small change is made under time pressure, and it is the point the incident investigation afterwards always finds.
Handover and acceptance
Handover is the transfer of care, custody and control from the project to operations, and acceptance is operations signing that they have what they need to run and maintain the plant. That list is longer than a project under pressure wants it to be: as-built drawings and documents, the control system and HMI backups, the operating and maintenance manuals, the spares identified and the critical ones stocked, the maintenance plans live in the CMMS and generating work, baseline readings taken at commissioning, the training records, and the punch list with every open item owned and dated.
The temptation at handover is to accept a plant with a long C list and a few Bs on the promise they will be closed. The promise is kept only if the list stays open, owned and reviewed after the project team has gone, which is why the owner's commissioning team, not the contractor's, holds the list from the first walkdown. The asset lifecycle guide explains what it costs when the handover information is missing, and the readiness guide what the organisation needs to have done on its side.
A plant is handed over when operations can run and maintain it, not when the project runs out of time.
Where it goes wrong
- No system breakdown, so nothing can be declared complete until everything is.
- A punch list per contractor, with the items at the boundaries on nobody's.
- Items closed by the person who did the work and never verified.
- A items recategorised as B to pass a gate on the date.
- Pre-commissioning skipped on a brownfield change because the system was running before.
- The pre-startup safety review held after start-up, as a record rather than a hold point.
- Handover accepted without the backups, the spares or the maintenance plans, which are then rebuilt by maintenance over the following year.
- The C list handed to operations with no owner and no dates, and still open two years later.
Common questions
What is commissioning?
The staged process of proving that a built plant or system does what it was designed to do, before it is handed to operations. It runs from mechanical completion, through pre-commissioning with no process material, commissioning with process material introduced, a performance test against the guarantees, and handover. IEC 62337 sets out the phases and milestones for electrical, instrumentation and control systems in the process industry, and the same shape is used across disciplines.
What is a punch list?
The register of every defect, omission and outstanding item found during construction, commissioning and handover, each with a category that says what it must be closed before, an owner, a due date and a status. It is also called a snag list or a deficiency list. One list per project, organised by system, with items that are closed by the owner and verified by someone else.
What are punch list categories A, B and C?
A convention for what an item must be closed before. Category A items affect safety or stop the next test and must be closed before the gate at which they were found, mechanical completion or energisation for example. Category B items must be closed before the system starts up but do not stop the next stage. Category C items are cosmetic or minor and are closed after handover by an agreed date. Sites use different letters or numbers; the three tiers are what matter.
What is the difference between mechanical completion and commissioning?
Mechanical completion is the point at which a system has been built to the drawings and its inspection and test records are complete: the construction is finished and the A items are closed. Commissioning is what follows, proving the system works, first cold with no process material in pre-commissioning, then with process material introduced. Mechanical completion is a construction milestone; commissioning is an engineering and operations activity.
What is a pre-startup safety review?
A formal review held before process material is introduced to new or modified plant, confirming that the construction matches the design, the safety systems are tested, the procedures and training are in place, the hazard studies' actions are closed and the punch items that could affect safety are closed. It is the gate between commissioning and start-up, and it is a hold point: start-up waits for it.
What does handover to operations include?
The transfer of care, custody and control of the plant from the project to operations, with the things operations need to run and maintain it: as-built drawings and documents, the control system backup, the operating and maintenance manuals, the spares identified and stocked, the maintenance plans live in the CMMS, baseline condition readings, the training records, and the punch list with every open item owned and dated. Operations sign that they have those, which is what acceptance means.
Key terms
Plain-language definitions from our glossary for the concepts this article leans on.
Standards and further reading
- IEC 62337:2012 Commissioning of electrical, instrumentation and control systems in the process industry (IEC)
- Guidelines for performing effective pre-startup safety reviews (CCPS, AIChE)
- ISO 55001:2024 Asset management system requirements (ISO)
- ISO 14224:2016 Collection and exchange of reliability and maintenance data for equipment (ISO)
- Best practices, metrics and guidelines for maintenance and reliability (SMRP)
Related case studies and tools
- Operational readiness for a new plant asset (case study)
- Shutdown coordination platform (case study)
Related reading
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