A plant can be fully built and still be weeks from making product. The gap is commissioning: proving, system by system, that what was built works as designed, and only then putting process materials into it. Projects that rush this stage tend to pay for it at start-up, with leaks, trips, damaged equipment and, at worst, incidents.
This three-part series follows the 50,000 t/y plant from the FEED series from the end of construction to handover. This part sets out the sequence. Part 2 covers the pre-startup safety review, the last check before hazardous materials go in. Part 3 covers start-up, the punch list and the performance test.
The sequence
| Stage | What it proves | Typical activities |
|---|---|---|
| Mechanical completion | The system is built as designed and tested for integrity | Walkdown against P&IDs, pressure tests, punch list, completion certificate |
| Pre-commissioning | Each component works on its own, with no process fluids | Flushing and cleaning, instrument calibration, loop checks, motor rotation and run-in, valve stroking |
| Commissioning | Systems work together, on water, air, nitrogen or solvent | Water runs, utility start-up, control loop checks, alarm tests, safety function testing |
| Pre-startup safety review | The plant is safe to receive hazardous materials | Review against design, procedures, training, hazard study actions |
| Start-up | The plant runs on process materials | First feed at reduced rate, stepwise increase to design rate |
| Performance test | The plant meets its design and guarantees | Sustained test at design rate with measured inputs and outputs |
| Handover | Responsibility passes to operations | Documents, spares, training records, remaining punch items |
Systemization: the unit of commissioning
A plant is not commissioned all at once. It is divided into systems, each a set of equipment that can be tested together, with clear boundaries on the P&IDs. Each system gets a test pack: the drawings marked up with its boundary, the test procedures, the check sheets and the punch list. Construction hands over by system, so commissioning can start on the first systems while others are still being built.
| System | Boundary | Key commissioning tests |
|---|---|---|
| Electrical supply | Substation to motor control centres | Protection relay tests, energization, motor rotation |
| Control and safety systems | DCS, safety system, field instruments | Loop checks, alarm tests, cause and effect testing of every safety function |
| Steam and condensate | Boiler or header to E-101 and condensate return | Steam blowing to clean lines, trap checks, heat-up of E-101 on water |
| Cooling water | Pumps, tower, R-101 jacket | Flow and temperature checks at design load |
| Feed system | T-101, P-101, E-101 to R-101 inlet | Flushing, P-101 run on water or solvent, flow control, level trips on T-101 |
| Reactor | R-101 with agitator, jacket and vent | Agitator run, temperature control on solvent, emergency cooling and vent tests |
| Vent and relief | Relief valves, headers, knock-out drum, flare or scrubber | Valve set pressures certified, block valves car-sealed open, flare pilot lit |
Utilities come first, because everything else needs them. Then the control and safety systems, because nothing should be operated without its protections working. Then the process systems, in the order the process runs.
Pre-commissioning in practice
Pre-commissioning is the unglamorous work that prevents most start-up problems. For the feed system it includes:
- Flushing and cleaning. Construction debris left in pipes ends up in pump impellers, control valves and exchanger tubes. Temporary strainers protect the pumps for the first weeks.
- Leak and pressure testing. Hydrostatic tests prove the strength of the piping at the time of construction. A leak test with nitrogen before start-up finds the flanges disturbed since.
- Instrument loop checks. Each instrument is checked from the field device to the control room display, so that a high level in T-101 shows as a high level on the right screen and trips the right pump.
- Rotating equipment. Motors are run uncoupled to check rotation and vibration, then coupled and aligned. Pumps are not run dry.
Commissioning: proving the systems together
With components proven, systems are run together on safe fluids. The feed system runs on water or the plant solvent, P-101 pushing through E-101 into R-101, with flow controlled and E-101 heated on steam. Control loops are tuned. Alarms are triggered from the field. Every safety instrumented function is tested end to end, from sensor to final element, against the cause and effect diagram. The functional safety standard IEC 61511 requires the safety system to be validated before the hazards it protects against are present.
Water runs also test the people. Operators run the plant on their procedures, find the steps that are wrong or missing, and fix them before the procedures matter.
Who leads, and when
The handover points in Figure 1 are also changes of responsibility. Construction leads until mechanical completion. A commissioning team, usually a mix of the engineering contractor, vendors and the owner's future operators, leads until the plant is ready for start-up. Operations leads once process materials are in. Projects that blur these lines tend to discover, during start-up, that nobody owned a particular check.
Key points
- Commissioning proves the plant works before process materials go in, one system at a time.
- Divide the plant into systems with clear boundaries and a test pack each; start with utilities and the control and safety systems.
- Pre-commissioning (cleaning, testing, loop checks, run-in) prevents most start-up problems.
- Test every safety function end to end before the hazard is present.
- Be clear who leads each stage and what proves it is complete.
Next: Part 2, the pre-startup safety review.
The plant, schedule and numbers in this series are an illustrative example. Commissioning and start-up must follow your own procedures, the vendors' instructions and the regulations that apply where you operate.
