Mechanical Completion, MC and RFSU.
Mechanical completion, MC is the milestone at which a system has been installed and inspected in line with the drawings and specifications, with construction punch items recorded, ready to hand from construction to commissioning. RFSU, ready for start-up, is the later milestone at which the system has been commissioned and is ready to be started up and introduced to process. Outstanding work is recorded on the punch list and sorted into categories: category A must be cleared before mechanical completion is declared, category B before the system is handed for commissioning, and category C may be closed out during or after commissioning.
What Mechanical Completion, MC and RFSU means.
Completion runs as a ladder, system by system rather than across the whole plant at once. Construction finishes a system and presents it for mechanical completion, where it is walked down against the P&IDs, line lists, and instrument index, and any outstanding items are logged as punch points. From there the system passes through pre-commissioning and commissioning, where loops are checked, functions are tested, and the control system is proven against the I/O list and the cause-and-effect matrix. Ready for start-up is the assertion that this work is done and the system can safely be energised, pressured, or charged. Punch items are graded so that category A points, the ones that prevent safe commissioning, are cleared first, while category B points can be carried and closed before final handover. The instrument register and the loop folder are what the loop checks between mechanical completion and RFSU are run against.
The completion milestone ladder
Construction hands a system to mechanical completion, then pre-commissioning, then commissioning, then ready for start-up, then start-up and the performance or acceptance test. Each step has entry and exit criteria, and each is certified per system or subsystem rather than for the plant as a whole.
Mechanical completion and the punch list
At mechanical completion the system is walked down against the drawings and specifications and remaining work is recorded on a punch list. Category A items must be cleared before the system can be energised or commissioned. Category B items can be carried and closed before final handover. The signed MC certificate marks the transfer from construction to commissioning.
From MC to RFSU
Between mechanical completion and ready for start-up the system is pre-commissioned and commissioned. Loops are checked end to end, instruments are verified, functions and interlocks are tested against the cause-and-effect matrix, and the control logic is proven. RFSU asserts that this is complete and the system can be started up safely.
Systems and subsystems
Completion is managed by system and subsystem, defined on a system limit or boundary diagram, not for the whole plant at once. This lets commissioning begin on early-completed systems while construction continues elsewhere, which is why a clear per-system instrument and loop register matters so much during this phase.
Punch list categories
The three categories most projects use, keyed to the gate each one blocks. Project procedures define the exact wording, but the ordering is consistent: A blocks the mechanical completion declaration, B blocks the start of commissioning, C is closed out around it.
| Category | Blocks | Typical content |
|---|---|---|
| A | Mechanical completion declaration | Work that stops the system being declared complete. Missing or wrongly installed equipment, failed inspection, safety-critical defects. |
| B | Ready for commissioning, RFC | Work that does not stop the MC declaration but must clear before the system is energised or introduced to process. |
| C | Commissioning completion certificate | Cosmetic and non-essential items. Painting, insulation finishing, labelling that can be closed during or after commissioning. |
Common questions
What is the difference between mechanical completion and RFSU.
What are punch list categories A and B.
What happens between MC and RFSU.
Is mechanical completion plant-wide or system-by-system.
What does RFSU stand for.
Get the loop check sheet.
The per-loop check record commissioning signs against, keyed to the I/O list the system was built from.