Mechanical completion (MC) is the point at which a system or subsystem has been fully installed, inspected and tested in accordance with the drawings, specifications and applicable codes, and is ready for pre-commissioning. It is formally recorded by a mechanical completion certificate (MCC), signed by the contractor and accepted by the client, confirming that all construction-stage inspection records are complete and that no punch items remain that would prevent the next stage from starting safely.
MC is the handshake between construction and commissioning. Get it right and commissioning receives a clean, well-documented scope. Get it wrong and the commissioning team spends weeks finding construction defects the hard way.
What is mechanical completion?
Technically, mechanical completion means the physical work is done. Equipment is set and aligned, piping is erected and pressure tested, cables are pulled, terminated and insulation-resistance tested, instruments are installed and supports are complete. The system is in a "dead" or de-energised state: nothing has been run, flushed or energised for process purposes yet.
Contractually, MC is often a milestone with commercial weight. Depending on the contract, it can trigger a progress payment, start the clock on certain obligations, or mark the point at which responsibility for the work begins to move from construction towards the commissioning organisation. Contracts differ widely here, so treat the contract's own definition as the one that governs, and check it rather than assuming.
The name also varies. You will see "mechanical completion", "construction completion", "ready for pre-commissioning" and, on some projects, a separate "systems completion" stage. Some owners issue MC by discipline first and then by system. The principle is the same: evidence that construction is finished for a defined scope.
Mechanical completion by system, not by area
On industrial projects, MC is normally declared per subsystem or system, not per area or per contract package. That is because commissioning needs a coherent functional scope. A pipe rack being finished is useful to the piping contractor; the instrument air system being finished is useful to commissioning.
This is why systemisation has to be settled before MC planning starts in earnest. If the subsystem boundaries on the P&IDs and single lines keep moving, the scope of each MCC keeps moving too, and construction cannot plan its work to finish systems in the order commissioning needs them. For background on how the system hierarchy supports this, see our guide to what a completions management system is.
Mechanical completion criteria
Every project defines its own MC criteria in the completions procedure or commissioning execution plan, but a typical set looks like this.
| Criterion | What "done" looks like | Typical evidence |
|---|---|---|
| Installation complete | All tagged items in the subsystem installed to the latest approved drawings | Signed A-type ITRs for every tag |
| Pressure testing | All lines in the subsystem hydrotested or pneumatically tested and reinstated | Test pack records, reinstatement checklists |
| Electrical installation | Cables pulled, glanded, terminated and insulation-resistance tested | Cable schedules, IR test records, termination ITRs |
| Instrument installation | Instruments installed, impulse lines complete and tested, tubing tight | Instrument installation ITRs |
| Rotating equipment | Set, levelled, grouted and aligned (cold alignment) | Alignment records, grouting records |
| Supports and structures | Pipe supports, steelwork and access complete | Structural and support ITRs |
| Insulation and painting | Complete, or excluded and listed as agreed B punch | Coating and insulation ITRs |
| Punch status | No open Category A punch items | Punch list extract for the subsystem |
| Walkdown | Joint walkdown carried out and findings recorded | Walkdown record and resulting punch list |
| Documentation | Required construction records compiled for the subsystem | MC dossier or document checklist |
Two points are worth stressing. First, "all tagged items" only means something if the tag register is complete; an item missing from the register has no ITRs and will sail through MC uninspected. Second, the criteria must be agreed with the client before the first MCC is submitted, not argued over subsystem by subsystem.
Which punch items can remain open at mechanical completion?
This is where most MC disputes happen. The usual convention is:
- Category A punch must be cleared before the MCC is signed. These are items that affect safety, integrity or the ability to pre-commission: a missing pipe support, an unterminated cable, an instrument installed in the wrong orientation, a failed test.
- Category B punch can remain open at MC, provided it does not stop pre-commissioning and is tracked to close-out before a later milestone such as RFSU or handover. Examples include missing labels, minor paint damage or incomplete insulation where it does not affect the test.
- Category C punch, where used, covers minor or cosmetic items that may be carried into handover or the defects period.
Definitions differ between clients. Some make "blocks energisation" the test for Category A; others tie it to the next certificate in the chain; some add a Category D for owner or operations requests. Whatever your contract says, apply it consistently and make sure the category is set by someone with the authority to set it, not by whoever raised the item.
A useful discipline is to review every Category B item at MC and ask one question: will this stop anyone flushing, loop-checking or solo-running the equipment? If the answer is yes, it is really a Category A.
How the mechanical completion certificate is issued
The MCC process is usually a sequence of checks and signatures rather than a single form.
- Construction declares readiness. The contractor confirms that A-type ITRs for the subsystem are complete and that its own punch is cleared.
- Completions verifies the records. The completions team checks ITR status in the completions database, confirms every tag has its required records, and pulls the open punch list.
- Joint walkdown. Construction, completions, commissioning and often the client and operations walk the subsystem against marked-up drawings. New punch is raised and categorised on the spot.
- Category A close-out. Category A items from the walkdown are cleared and verified.
- MCC prepared. The certificate is compiled with its attachments: the list of tags in scope, ITR status summary, open Category B and C punch list, and any agreed exceptions.
- Signatures. Typically the contractor's construction manager and completions lead sign first, followed by the client's commissioning or completions representative accepting it.
- Handover to pre-commissioning. Once signed, the subsystem moves into pre-commissioning, and control of work on it usually becomes subject to the commissioning permit regime.
Some projects precede the MCC with discipline-level acceptance certificates, so that electrical, mechanical and instrument scopes are each accepted before the subsystem certificate is signed. Others require a separate mechanical completion check record listing each item verified. Your completions procedure will say which applies.
Mechanical completion versus what comes next
MC is not the end of construction-stage involvement. Construction often stays engaged through pre-commissioning to clear B punch and support tests. The key difference is the energy state and the type of activity: MC confirms a dead, installed and statically tested system; pre-commissioning starts cleaning, flushing, loop checking and running individual items. We compare those stages in detail in pre-commissioning vs commissioning.
Common mechanical completion failure modes
- Declaring MC by percentage. "The subsystem is 98% complete" is not MC. The remaining 2% may be the critical valve.
- Paper that does not match the plant. ITRs signed from the office without the item being inspected. The walkdown exists to catch this; do not skip it.
- Scope creep across boundaries. Items that sit on a subsystem boundary, such as tie-in valves, get missed by both sides. Assign them explicitly.
- Reclassifying punch to hit a date. Downgrading Category A to B to get a certificate signed moves the problem into commissioning, where it costs more and carries more risk.
- Late documentation. Test packs and vendor records that turn up weeks after MC hold up the dossier and, eventually, handover.
Managing mechanical completion in Accord
Accord ties each MCC to the subsystem it covers and the records beneath it. Tags sit in a Project → System → Sub-system → Equipment/Tag hierarchy, 'A' mechanical-completion ITRs are executed with witnessing and sign-off, and punch items carry Category A/B/C criticality with stage-gate blocking, so a certificate cannot be issued while its prerequisites are open. The certificate dependency chain, including MCCR, DAC and MCC ahead of the commissioning certificates, is enforced as a directed graph, and every approval is recorded in an audit trail. Readiness and completion dashboards show which subsystems are genuinely close to MC.
Frequently asked questions
Who signs the mechanical completion certificate?
Usually the contractor's construction or completions lead signs to declare the subsystem complete, and the client's commissioning or completions representative signs to accept it. Some projects add discipline engineers, QA/QC or operations as signatories. The completions procedure should list the required signatories for each certificate.
Is mechanical completion the same as practical completion?
No. Mechanical completion is an industrial completions milestone that confirms a system is installed and ready for pre-commissioning. Practical completion is a contractual term used mainly in UK building contracts to mark when works are complete enough to be taken over. The two can coexist on a project but mean different things, and the contract defines each.
Can mechanical completion be issued with open punch items?
Yes, but normally only Category B and C items that do not prevent pre-commissioning. All Category A items should be cleared first. The open items are listed on or attached to the MCC so that responsibility for clearing them is clear.
What is the difference between an MCC and an RFC certificate?
The MCC confirms the system is installed and statically tested. A ready for commissioning (RFC) certificate, used on many projects, confirms that pre-commissioning is also complete and the system can be commissioned with process fluids or energy. The names and exact split vary between clients and methodologies.
How long before start-up should mechanical completion happen?
There is no universal figure; it depends on the complexity of pre-commissioning and commissioning for each system. What matters is that MC is sequenced in the order commissioning needs systems, starting with utilities such as power, instrument air and water, rather than in the order construction happens to finish areas.