The Stages of Commissioning
Each phase of commissioning varies with its focus and activities. Each phase also varies with the equipment involved. The three phases of commissioning are described further below with the intention of focusing on the required outcomes.
Pre-Commissioning
Pre-commissioning includes all testing and inspection activities to confirm that the Project and Works have been constructed as required by the various contracts. This stage is equipment orientated and generally involves the handing over checks performed to complete the contracts for the supply and installation of the various plant sections. At a minimum it includes:
- Bump starting all drives, disconnected from their equipment, to check motor direction.
- No load starts of all motors connected to Variable Speed Drives (VSD) to ensure minimum/maximum speed settings and speed up/slow down parameters are correct.
- Emergency stop switches are convenient and not hidden.
- Connection and tension/alignment tests of drives.
- Lubricants are in place and at the correct quantities.
- Stroking of all valves to ensure directional signals are consistent.
- Manual trips of all alarms to ensure correct readings.
- Pressure testing of piping and/or vessels.
At the conclusion of pre-commissioning, the contractors will have achieved mechanical and electrical completion, if not practical completion, of their contracts. The equipment will be identified with a blue commissioning tag as being handed over to the project by the contractor.
This blue tag designates that the tagged equipment and/or system is in commissioning progress. It is used on equipment such as circuit breaker handles, control switches, equipment valves, etc. Any system and equipment bearing blue tags will be energised, started, and operated solely by Commissioning personnel. Contractors’ and Clients must not touch or work on any equipment or systems bearing blue tags unless authorised.
The equipment in the section under consideration and the requirements for the contractor must be completed prior to hand over of the equipment. A checklist for each item will be completed and signed off by the contractor.
Cold Commissioning
Wet commissioning (sometimes called “cold” commissioning) includes simulation of plant operation using an inert material (usually water), to test equipment, piping, electrical interlocks, alarms, instrumentation, control systems, and sequence stops and starts, to the maximum extent possible.
The purpose of this operation is to check that the equipment functions together and leakages and/or misalignments are discovered. This can be a hazardous time and extra care should be taken. Planning is critical and adherence to those plans is vital.
There are some conditions that are unique to wet commissioning. They include, but are not limited to:
- Excessive spillage is common as leaks and incomplete flanges are discovered. The need for quick shut off from the flows is required.
- Water hammer is a common problem found at this time. Communication is very important to allow for quick shutdowns, specifically in cases where this cannot be solved by a simple valve adjustment.
- Filling up pipes can be made dangerous by people not realising that for water to get into a pipe, the same volume of air must be removed from that pipe. Facilities for the safe removal of this air must be made.
- When enthusiasm for projects rise, the site team can try save time by commissioning a section of the plant prior to another being made available. This can have detrimental effects on the project so the process must be well managed.
This stage of the process is usually undertaken by the commissioning teams with local responsibility, in contact with the central management function in the control room.
It is normal for a number of wet commissioning runs to be made, so it is important for the facility to print or copy the check sheets. If multiple runs are performed, each day’s checks need to be dated correctly.
The shutting down time for each of these runs is a good time to check the safety interlocks of vital shut down operations. These interlocks can be identified and listed in the manual.
Some orifice plates may need to be inserted into some flanges to ensure back pressure in the pipelines and so the equipment can run stably.
The performance of each item of equipment should be monitored and checks on items like hot bearings and/or electrical boxes, pressure surges, unusual noises, and evidence of burning should be reported as a matter of urgency to the maintenance staff. Such items must also be noted on the check sheets.
At the end of wet commissioning, the section should be seen to work in a safe manner with all alarms, sensors and meters being checked for correct indication and the no-load power draw recorded for each drive. These no-load power draws should be checked to ensure that the correct transducers are installed.
These measurements should be recorded on the check sheets, both hard copy and electronically, so they can be signed off by the Client’s representatives. The original copy of the check list is to be filed in the commissioning file and a copy provided to the Client.
At the conclusion of Wet Commissioning, the equipment will be identified with a green commissioning tag to indicate that the equipment is ready to accept process flows and is under the process of Ore Commissioning.
Hot-Commissioning
Ore-commissioning (sometimes called “hot” commissioning) is undertaken under the operational direction and technical control of the Owner to bring the Project into service and to prove the plant.
Ore commissioning is done following safe and successful water runs, which is usually a continuation of the final water run. Items such as orifice plates, that simulated performance on the slurry, should be removed from the pipelines.
Ore commissioning is normally completed by ramping up the feed tonnages in a few short stages. The plant is usually shut down between each stage and then brought back through previously achieved feed rates, prior to increasing the feed rate to design.
The initial feed rate should be significant so that the plant will show the effects of the slurry, not simply dirty water. At least 50 per cent of the design rate is normal. Given good plant performance, it is common for management to go directly for 80 per cent the next day, and 100 per cent the following day. If these proceed well, then the plant is generally kept on line for as long as possible.
If the plant does not perform well, the ramp up can be much slower and its speed and duration is determined by spillages, blockages and/or equipment failure. It is vital that these times are recorded so they can start the trouble shooting knowledge base for the plant.
At each feed rate, the performance of each item of equipment should be monitored. Checks on items like hot bearings and/or electrical boxes, pressure surges, unusual noises, or evidence of burning, should be reported as a matter of urgency for inspection by the maintenance staff and recorded in the manual. Motor loads should consistently be checked to ensure the various transducers are functioning as required.
At the end of ore commissioning, the section should be seen to work productively and safely. All alarms, sensors, and meters should have been checked for correct indication and the loaded power draw recorded for each drive.
The green tags will normally remain in place as the equipment remains under the direction of the Client.
