In simple terms, the commissioning is a series of checks, tests and final activities that confirm a plant is fit for operation and finally prepare the plant for the start-up and continued operation at rated conditions. A complete, well-planned commissioning job is one of the important factors for reliable, efficient and long-term operation of machineries, control systems and whole the plant. The key is a standardised and systemised approach to the "commissioning".
Commissioning team should include experts with different backgrounds such as instrument engineers, process experts, control specialists, electrical engineers, machinery experts and most importantly operational specialists. The skills shortage is a sad reality in the commissioning sector, however some plants, control systems and machinery packages could be commissioned by unqualified personnel which can result in short-term and long-term problems.
Sufficient commissioning engineers, technicians, and staff should be made available to correctly implement different commissioning activities and also manage other personnel for commissioning stages.
They should make themselves familiar with all site specific regulatory, codes, specifications, procedures and work instructions. In other words, even the most experienced commissioning experts and engineers should read and understand many site specific (and machinery package specific) documents, manuals and instructions. Each commissioning engineer is actually the manager of a team of other engineers and technicians for an assigned commissioning task; the team is responsible for some packages and systems. It is difficult to give a general rule on the number of assigned systems to each commissioning team, as each commissioning engineer and his team normally can handle 4-8 systems or packages, depending on complexity, size and details of packages and systems.
Operation and maintenance staff presence at the commissioning team is always encouraged. This can help for a smooth handover to the operation team; it also helps to ensure all lessons learned through commissioning are retained by the ongoing operation team. In addition to operation teams, the plant maintenance team should be made fully aware of the nature and details of the facilities and machinery packages.
As a rough indication, commissioning cost for a plant or a facility could be around 3-4.5 per cent of the total capital cost. The commissioning budget typically includes 65-75 per cent manpower expenses; the balance is the consumable and rental equipment expenditures. Contingency for engineering of commissioning modifications is a significant factor and could be considered as 15-30 per cent of total commissioning budget. Sometimes special instruments or rental equipment could be required for the commissioning; significant costs are associated with them. Examples could be instruments required for site performance tests, equipment for cleaning services, special safety equipment, etc.
Usually a spare part package is provided as the commissioning spares which include items, consumables and replacements need at commissioning. Commissioning spares should be ready for use. Initial fill of lubrications and chemicals should also be available for the commissioning. Camera and photography are important tools in commissioning.
Safety and MOC
Safety is one of the most important aspects of any commissioning activity. Commissioning representatives should attend various safety studies such as HAZOP (Hazard and Operability Studies) and the pre-start-up safety review (PSSR). The pre-start-up safety review (PSSR) is known as the last stage to catch and solve any safety issue before the start-up. Another important safety requirement is that no equipment (no machinery) can be brought into service until its registration, documentations and safety checks have been completed.
An important skill in a commissioning team is the knowledge and experience in technical problems solving in an operational environment. There are always constrains of fast-track sub-projects in the commissioning of any plant. Many changes are usually required during the commissioning. Any hidden defect or issue of the design, manufacturing, delivery and installation stages should be resolved or corrected in the commissioning phase.
The management of change (MOC) is one of the challenges of the commissioning stage, which require a very systematic and sound procedure. Changes could present many safety and reliability issues to machinery packages, control systems and the plant if not managed properly using a robust management of change (MOC) procedure.
Scope and responsibilities
In many plants, there are actually two commissioning parties (sub-teams) which constitute the plant commissioning team and they should work together closely for a successful and seamless start-up of the plant:
- Contractor and vendor commissioning sub-team.
- Client and operator sub-team.
All pre-commissioning activities and around 60-80 per cent of commissioning tasks are usually done by the contractor and vendor commissioning sub-teams. The final stages of commissioning activities and start-up should be done by the client and operator sub-teams with help from contractor staff and machinery technical supports from vendor personnel. The scope of service varies project to project. In each project, it is important to investigate and finalise what each commissioning sub-team is responsible to deliver. It is critical that all parties are fully aware of the scope and boundaries of responsibility. One of the drivers for confusion in the commissioning is the poorly defined scope. Usually the introduction of utilities (air, water, nitrogen, and similar) is undertaken by contractor commissioning team. Most often, the steam, process medium, chemicals, fuels, and similar are introduced to packages by the operator or client commissioning team.
Different systems of a project should be properly divided between commissioning engineers in that project. Commissioning systems are identified by highlighting principally the P&IDs, clearly marking the boundaries of each commissioning entity. Electrical and control systems are typically identified by highlighting "one-line" (or "single-line") diagrams and control system architectural drawings. Clear and smart boundaries can facilitate commissioning tasks. For example, one system can be leak tested and energized whereas adjacent system is under construction or completion.
Priority and Schedule
The commissioning priorities should specifically be enforced from around 85 per cent of construction progress to let vital section completed, tested and commissioned which can help for timely start-up of whole plant. Priority should be given to units and items that when completed and commissioned add value and can be utilized for commissioning other systems or can be handed-over to operation. It is important that the construction team follow the commissioning plans and priorities.
Natural flow of commissioning works based on "backwards" concept should be established whereas any system being completed and commissioned helps for an efficient plant start-up and hand-over to the operation. Priority is a significant factor in any commissioning; it shows how the commissioning team plans to approach the commissioning and start-up. It should be clearly discussed and documented that how the plant and facilities under construction is going to be commissioned.
A simple example of required priorities is noted as follows. In many plants and facilities, the lighting system has been one of the latter systems delivered by installation team probably because of low progress associated to it or a miscalculation by the installation team that this simple system might not be so important. This is not a good and safe practice. It is extremely important that all lighting systems be ready and operational as soon as possible. They can offer great benefits and safety for whole commissioning and start-up activities. Working at dark or using temporary lighting (with long exposed cables, etc) can offer hazards and risks.
Great care is needed for commissioning time schedules. For commissioning and start-up schedules, all steps should be predicted and proper time should be allocated for each step and activity. Cleaning services (such as chemical cleaning, pigging, etc) are time consuming processes; they are usually responsible for delays.
Control and Instrumentation
An important step related to control commissioning is the control and instrument loop tests. The loop test is usually an installation group task and the commissioning team is expected only to witness it. However, ensuring instrument and control loops operate effectively and to design intent it is important that the commissioning team carefully witness these tests and make themselves fully familiar with these control and instrument loops to avoid any issue or malfunction during commissioning time.
The initial power-up of electrical and control hardware is important, since usually sections of electrical and control systems are completed by different engineers. Proper co-ordination is the key to ensure all systems are ready for the power-up. Any problem in this significant task could result in damage of sensitive electrical or control items whereas some of them could be long-lead items.
Machinery commissioning team should become familiar with machinery control systems. Usual exercises in any machinery commissioning task are fine tuning of control loops, re-checking and redefining control parameters; most important ones alarm and trip settings.
Special attention should be given to complicated control systems such as gas turbine control systems, large steam turbine control systems and variable-speed drive (VSD) control systems. For example, VSD control systems should be correctly set-up both within the individual motor control cabinet and also within the corresponding loop (within the control system). In many plants and packages, at the first try for a motor start-up, the motor was not started when required and no failure alarm was also activated. Based on author's experiences, often the motor did not start because of wrong wiring terminations (for example, on a control block) and control system was not configured properly (no failure alarm).
Proper considerations should be made of how alarms are to be tested. Injecting false signals to field devices should be considered as the last solution. Other solutions to thoroughly test whole the system should be identified and planned. For example alarms on low and high temperatures should be tested using fluids with low and high temperatures; it should be planned carefully.
Start-up protocols are procedures to provide guidance and instructions for bringing packages, control systems and installations online starting from empty non-operational systems and packages (usually installed, completed and pre-commissioned facilities).
Start-up procedures and different shutdown procedures (normal shutdown, emergency shutdown, etc.) should also be prepared, checked and verified. After all these tasks and the final check of the HAZOP and the pre-start-up safety review (PSSR), machinery packages should be commissioned with job medium (machinery wet commissioning). Start-up and initial operation period are critical time for any machinery package and any control system. The machinery package should meet the defined acceptable criteria (such as sustained operation at the rated conditions, etc.), before the handover from the commissioning team to the operation team.
Handover to operation and closeout
Handover of the all commissioning documents (known as "as-commissioned") to the operation team should be done in a very organised way, usually in a series of one-to-one and team meetings. Training of the operation team (and also maintenance team) should also be completed. Re-training of operation team and final checks and confirmations are the last stages of the commissioning close-out.
Three sets of critical documents should be prepared by the commissioning team as follows:
1. Training materials for operation and maintenance teams.
2. Operating procedures.
3. Handover procedures.
Sometimes the commissioning team should continue their work and their activities for weeks (or a few months) until the 100 per cent rated capacity can be achieved (and stabilised) by the machinery packages and the plant. The handover to the operation team is very important task. Proper handover is the basis of long reliable and high-performance operation of a plant.