Commissioning generally consists of four stages: pre-commissioning, core commissioning, start-up and post-commissioning. Pre-commissioning efforts overlap with construction activities. Post-commissioning includes troubleshooting during commercial operation, handover to the normal operating team, closeout and other final-stage activities.
Pre-commissioning starts during the final steps of construction and installation, with the aim of making the unit or plant ready for commissioning and start-up (Figure 1). In other words, the main objective of pre-commissioning is achieving the orderly handover from the construction team to the commissioning team and, subsequently, to the normal operating team. This involves a set of inspections, tests and checks as well as troubleshooting and addressing any issues identified.
Many steps within each stage of pre-commissioning and commissioning usually overlap and, potentially, run in parallel to each other. The keys to ensuring a successful pre-commissioning and commissioning are thorough studies and evaluations of the unit or plant, as well as excellent planning and preparation, a high-quality team and proper methodologies.
This article focuses on practical pointers and guidelines on pre-commissioning.
The Timing
Pre-commissioning starts when a unit or plant nears mechanical completion. In today’s fast track projects, construction often advances area by area. Generally, by the time erection and installation progress exceeds around 85%, it’s time to begin turning over systems from construction to pre-commissioning in line with the project’s integrated critical path schedule.
Usually, a system can undergo pre-commissioning while a neighboring one still is under construction; the two are isolated from each other by system boundaries and use of a robust package-turnover protocol. A number of tools, databases and software offerings can aid in the timely and efficient management of activities and tasks for completion and pre-commissioning. It’s important to carefully coordinate all completion and pre-commissioning tasks, clearly define priorities, and properly allocate resources and personnel.
Site inspections and verifications are key parts of pre-commissioning. Typical activities include: thoroughly examining all items and components, cleaning, leak testing, and performing equipment run-in and control-system action checks. Confirming complete assembly and installation of all parts and equipment as well as thoroughly inspecting all bits and pieces are important. Common issues include missing gaskets, damaged equipment, malfunctioning valves, among others. It’s also crucial to check for conformance with the intended design and operational requirements as well as code compliance. Defects, missing or incomplete items, and nonconformance issues should appear on pending-action lists that should guide problem-solving and completion efforts.
After this stage, a thorough cleaning should take place. This often starts with a caustic wash or similar to remove oil, grease and other contaminants, followed by chemical cleaning, most often acid cleaning.
The need for a chemical cleaning can provoke debate. Many contractors suggest other cleaning methods such as extensive conventional cleaning, all sorts of mechanical cleaning, etc., of piping and much other equipment (e.g., boilers and some vessels) at a site. However, many operators still consider chemical cleaning as the best (or even only) option for a thorough cleaning. Challenging this belief or perception often is difficult and not worthwhile.
Passivation and preservation should follow cleaning.
Important Documents
Each unit or plant is unique and, therefore, presents a unique set of tasks and challenges for pre-commissioning. This mandates a thorough review of key documents and extensive discussion of issues and concerns by the parties involved, such as contractors, client, operators, etc., to determine specific needs and requirements.
Documenting the completion of pre-commissioning tasks such as checking out equipment being installed, cleaning, leak testing, etc., is essential to confirm the unit or plant is fit for commissioning. Because a large portion of pre-commissioning and commissioning activities depend on checking and counterchecking, a set of properly developed checklists can help; this may require creation of some customized checklists.
Pre-commissioning planning and procedures need great care. The procedures should clearly spell out the details and sequence of what should be done.
Many contractor pre-commissioning/commissioning teams claim they know how to do their job and don’t need documents. Don’t accept that. Pre-commissioning is a challenging and hectic stage of site work. Many things can go wrong. Different people can offer disparate views and suggestions on how to resolve an issue or complete a task. Therefore, the procedures should thoroughly detail how to pre-commission and subsequently commission each unit or system. They should contain all useful information collected during the design and construction along with safety precautions.
Too often, pre-commissioning teams don’t use key plant documents such as piping and instrumentation diagrams, layout drawings, etc., to the extent they should. These documents, of course, should get updated based on changes and modifications during construction and completion. Properly sorted, they can form the foundation for an intelligent database.
The Team
Pre-commissioning/commissioning of units and plants is a complex and sophisticated technical specialty. It usually is considered a specific and independent engineering discipline on par in importance with the more-traditional engineering disciplines such as chemical, mechanical, electrical, etc. However, no formal education or university degree currently addresses such skills. Various training courses designed for qualified engineers are available, though. Some people with a background in a traditional engineering discipline but also a combination of training and experience in commissioning are termed “commissioning engineers.”
A commissioning manager should lead a team that includes the required commissioning experts from different backgrounds such as “process commissioning engineer,” “mechanical commissioning engineer,” “electrical commissioning engineer,” “instrument commissioning engineer,” etc. Because the commissioning and start-up of any unit or plant invariably present a number of challenges, having team members with knowledge and previous experiences — especially of similar units or plants — is important.
A commissioning team should have a broad base of knowhow related to equipment design, installation and operation. Understanding how a piece of equipment or other item should function in a specific unit or plant fosters proper checking and more-effective problem-solving.
Common Challenges
A number of issues regularly arise during pre-commissioning. So, let’s look at some common ones.
Tube failures, especially at welds, occur in equipment such as heat exchangers and boilers. Some stem from errors in manufacturing or welding procedures. Tubes used elsewhere, e.g., in instrumentation and hydraulic systems, also are vulnerable components; they particularly are weak at connection or weld points. Plastic tubes, rubber hoses, flexible joints, slip joints and similar items are sources of leaks and problems, particularly if not selected properly, as often is the case.
Many different systems suffer from over-heating or under-heating. In general, a heating, cooling or refrigeration system could perform differently than the design intension, leading to a temperature higher or lower than desired. So, it’s good to incorporate operational flexibility. For example, giving a refrigeration system 10–20% extra margin over rated capacity is sensible to ensure ample capacity is available. At the same time, you should provide a proper capacity-control and turndown system to make adjustments possible.
High noise or vibration is a common complaint. A properly tuned, balanced and aligned machine should work properly with low noise and vibration; extra noise or vibration indicates an issue. In severe cases, hold-down bolts can fail and nuts become loose. Therefore, any high noise or vibration during pre-commissioning or commissioning demands serious investigation to find the root causes, which you then must properly address. Sometimes a machinery foundation vibrates; in such a case, first record the vibration and determine the major frequencies and patterns that cause trouble. This helps to find the root cause of the issue. In rare cases, you may need to take steps such as adding extra stiffening steelwork.
Corrosion often is a problem. Incorrect material selection can prompt corrosion by an aggressive job fluid within days.
Instruments problems are fairly common and occur for many different reasons. The issue might relate to a poor choice of device, e.g., one with insufficient range, inappropriate materials, etc. Installation or hook-up errors also cause problems. For example, some cases of incorrect instrument readings stem from bad location of the instrument or its tap. The sad reality is that many such issues often only get discovered during pre-commissioning, not before it.
Wiring and hardware faults frequently afflict control systems. Many new units and plants rely on state-of-the-art control systems but that doesn’t mean easier pre-commissioning. You still must thoroughly check hardware, including wiring, to ensure that equipment, particularly electric motors and actuators, start and operate from the correct control center through the right sequences. After this step, you must check the software; verify that each electric motor, control component and actuator responds from the correct icon on the display. In addition, check the power supply and functionality of all equipment and machinery, verifying proper operation and control. For instance, you must confirm safety and software interlock sequences. You also should check and, if necessary, tune control loops, such as those for temperature, pressure, flow, etc.
Any defects found must get corrected before pre-commissioning is deemed complete. So, troubleshooting is a major task. Preparing troubleshooting guides for machinery, equipment and other items can help in identifying and correcting any malfunctions that might occur.
An Essential Preliminary
Proper pre-commissioning plays an important role in ensuring successful start-up of a unit or plant. By uncovering and addressing issues at an earlier stage, it eases subsequent commissioning and start-up activities.
AMIN ALMASI is a mechanical consultant based in Sydney, Australia. Email him at [email protected].
