1. Why the boundaries matter
Every completions milestone is a transfer of risk. When mechanical completion is issued, the constructing contractor is asserting that the plant is built to drawing. When ready for start-up is issued, someone is asserting it is safe to put hydrocarbons, current or product into it. Those are very different claims, and each is backed by a different set of records.
When teams blur the boundaries, two failures follow. The first is premature: a milestone is issued because the schedule demanded it, and the missing evidence surfaces at the next gate. The second is duplicated effort: the same check is performed twice under two different names because nobody agreed which stage owned it.
2. Mechanical completion (MC)
Mechanical completion is a construction statement. It says the subsystem has been installed in accordance with the design and specification, that static inspection is complete, and that nothing physically outstanding prevents the next phase.
Typical evidence at MC:
- A-ITRs signed — the static inspection and test records: installation checks, dimensional checks, torque records, pressure tests, continuity and insulation resistance.
- Walkdown complete — a structured physical inspection against the subsystem boundary, normally attended by the client.
- Category A punch cleared — items that block progression are corrected; Category B items are carried forward with visibility.
- As-built markups captured — deviations from drawing recorded rather than remembered.
MC is issued per subsystem, not per area or discipline. That distinction is the reason the systems and subsystems breakdown has to be right before construction finishes.
Put a number on it
What is this costing your project right now?
Estimate the hours and cost lost to transcription, register consolidation and dossier assembly — with editable assumptions and the maths shown.
3. Pre-commissioning
Pre-commissioning covers everything done to prepare a mechanically complete subsystem for energisation, without yet putting it into service. It is the least well-defined of the four stages and the one most often absorbed into either MC or commissioning depending on the contract.
Work typically in scope:
- Cleaning, flushing, air blowing and drying of piping systems.
- Chemical cleaning and passivation where specified.
- Instrument calibration and loop checks.
- Motor solo runs and rotation checks.
- Function checks on control logic without process medium.
The practical rule: pre-commissioning is anything that proves the system will work when energised, done before it is energised. Read the contract — where pre-commissioning sits determines who pays for it.
4. Commissioning
Commissioning is the stage where systems are energised and function-tested under controlled procedures. This is where B-ITRs — the dynamic records — are raised, and where commissioning procedures govern the sequence step by step.
The defining characteristic is that the system is live. That changes the safety regime, the permit requirements and the authority needed to sign. A commissioning signature usually requires a higher role than a construction inspection signature, which is why role-based signing rights matter here more than anywhere else in the sequence.
5. RFSU and final handover
Ready for start-up (RFSU) declares that a subsystem is proven safe and ready to be put into service. On most projects care, custody and control transfer at RFSU, which is why the operator scrutinises it hardest.
Final handover comes later, after start-up and performance testing, when the complete documentation dossier is issued and remaining punch items are closed. See handover and RFSU explained for how the two differ contractually.
6. The four stages at a glance
| Stage | Claim being made | Primary evidence |
|---|---|---|
| Mechanical completion | Built to design, statically inspected. | A-ITRs, walkdown, Category A punch cleared. |
| Pre-commissioning | Prepared and ready to energise. | Flushing, cleaning, calibration and loop check records. |
| Commissioning | Energised and functioning as designed. | B-ITRs, commissioning procedures, function test results. |
| RFSU | Safe and ready for service. | Complete record set per subsystem, punch status, certificate chain. |
7. How to avoid the usual disputes
- Write the gate criteria down before construction finishes. Define, per stage, exactly which record types must be signed and which punch categories block. Agree it with the client early, not at the first certificate meeting.
- Make the criteria machine-checkable. If the prerequisite list lives in a procedure document, it gets interpreted. If it is enforced by the system that issues the certificate, it gets applied consistently.
- Keep one subsystem definition. The same subsystem boundary must apply to ITRs, punch, walkdowns and certificates, or the stages will never reconcile.
- Do not let categories inflate. If everything becomes Category A, the gate stops discriminating. See punch list categories.
This is the core of what commissioning software is for: turning stage criteria from a document people interpret into a rule the system applies.
Check your own process
Score your handover readiness in eight questions
A structured self-assessment of register control, evidence capture, sign-off and gate logic — with a specific recommendation for every gap.
