In the commissioning/start-up of water pumps and water pumping systems, sufficient time should be allotted for planning and preparation. The commissioning/start-up team’s skill level, early planning and proper preparation are keys for success. Commissioning/start-up is the most critical and the busiest phase of a project. Design flaws, hidden manufacturing problems and construction/installation errors will show themselves at this stage. Modifications and corrections should be implemented during commissioning activities. Practical notes for commissioning/start-up of water pumps and water pumping systems are discussed in this article.
The following factors are important for commissioning/start-up:
- A correct/realistic plan for commissioning/start-up
- A correct mixture of various start-up engineers, including pump, mechanical, piping, electrical, instrument and other engineers, is required on the commissioning/start-up team
- Properly empowering each commissioning/start-up team member to implement his/her responsibilities.
There are always engineering/construction contractors interested in the commissioning, start-up and operation jobs who argue that because they can design/build water pumping facilities and procure/install water pumps, they should also be able to commission, start-up and operate these pumps and facilities. The commissioning and the start-up of water pumps and water pumping facilities involve very special types of work and requires very specific skills. These skills are normally retained within operating companies and specialized commissioning/start-up agencies (and often some water pump vendors). To the maximum extent possible, the construction/installation team and the commissioning/start-up team should not be blended.
For proper commissioning/start-up of water pumping systems, modifications are often required. Common problems/modifications could include:
- Undersized or oversized control valves, actuators and equipment
- Incorrectly-configured instrumentation and control systems
- Piping re-configuration/modification.
The lack of spare-parts is another well-known problem that can cause considerable delay during the commissioning/start-up phase. Many completion/commissioning activities, including last minute corrections, modifications in water pumping facilities/systems, changes in piping and any activities that cause a load on a pump nozzle, can change water pump alignment, requiring re-alignment. The proper amount of time should be allotted for the re-alignment of water pumps. Time for re-alignment is often neglected in a commissioning plan.
The re-commissioning of water pumps is also often forgotten in a commissioning plan. If a water pumping system has been commissioned, this system should be re-commissioned when the water pumping system is integrated with all other systems. Only after the integration can a water pumping system be tested in a situation that resembles the actual working full-load condition. Proper time/resource allowances should be respected for re-commissioning activities for water pump packages.
The time required for oil flushing of oil/bearings systems in water pumps is nearly always under-estimated. For special/complex lubrication oil systems, a complete/high-quality oil flushing could take two to five days, depending on the details of the water pump’s oil system.
Correct time frames should be allotted for cleaning checks and internal inspections, including boroscoping for very large and complex water pumps or electric motors. Water pumping systems handed over from construction to commissioning should be properly inspected for cleanliness. Usually, water pumps are not as clean as required during the handover. Water pump train machines should be inspected for cleanliness using modern methods, including boroscoping.
Temporary facilities are usually required for commissioning. For example, in some modern plants, the electrical power is generated in the plant. At the start of the commissioning, the electrical load is usually not enough to adequately perform the power generation unit testing and support the commissioning of other facilities, packages and systems simultaneously. In this regard, details such as the number of independent generators or the variable load capability (minimum load capability) of the power generation unit are important. For some plants, temporary power generators should be used for the start of the commissioning. These temporary generators are required for the commissioning of enough facilities to support a sufficient electrical load for a permanent generator working at the minimum load.
For many plants, the air, nitrogen or other utilities may be commissioned late because of a problem, a delay or an issue. These utilities should be provided by temporary packages to facilitate the commissioning of water pumping systems. These temporary units are expensive rental equipment and special care is required to be sure about the correct timing.
The identification of commissioning packages (or take-over packages) is an important step in commissioning preparation. Each commissioning package should be an operable entity or a system that the operation team can take over and actually run. In other words, the commissioning package should be big enough for the operation to take over and operate it. For each commissioning package, a dedicated drawing should be prepared. There should be no confusion about the commissioning package scope.
The pre-commissioning activities (and subsequently the commissioning activities) should begin at the correct time. If they begin too early, the commissioning team’s involvement in the construction job could create inefficiencies and sometimes problems. All engineering and installation changes should be implemented before the pre-commissioning activities begin to avoid re-works. The pre-commissioning checking cannot begin early, since changes and modifications in water pumping facilities may mandate re-checking. On the other hand, the commissioning team should be involved in final completion activities, tests, cleaning/flushing jobs and end-stage controlling/inspections. As an indication, the commissioning team should begin their involvement in construction/installation activities when 80 percent of the construction/installation job is completed with a full presence at around 90-95 percent completion.
The commissioning punch-listing is one of the most critical and important steps in any project. A well-prepared, properly-detailed punch-list is a good indication of a high-quality commissioning. The commissioning punch-list is a team activity. Where possible, instrument engineer(s), the electrical team and other engineers should accompany water pump/machinery engineers for the punch-listing. Usually one or two member(s) check items in a facility (for example, water pump components, lubrication systems in water pumps, gasket presence, bolt tightening, piping supports, instruments, valve installation, access and labeling) and other member(s) record status and defects in the punch-list. A missing gasket in water piping (or in a water pump) is a common punch-list item; if left unchecked it could surface as a leak in the leak test during the actual commissioning activities, which could result in delays. A primary punch-list should be completed at around 85-95 percent of the construction/installation job.
The water pumping facility leak test is one of the first commissioning activities after the completion of punch-listing (this leak test should not be confused with the construction pressure test). The commissioning leak test indicates all potential leak paths within a complete water pumping facility. Common leak points could be water pump seals, pipe or equipment joints/gaskets, valve stem/packing/bonnet-gaskets, etc. As an indication, the commissioning leak test pressure can be around 1.1 times the normal operating pressure. The hold points could be at 25 percent and 65 percent (in addition to 100 percent) of the leak test pressure, which allow for an inspection to check for a major leakage.
Prototype equipment and machineries are always discouraged; however, it is sometimes required to use a new design for the first time. Prototype systems could be used in areas with modern requirements or developing technologies such as advanced high-pressure water systems. The commissioning schedule for prototype systems should be planned carefully, with suitable allowances added.
The uniform bolt tensioning and torqueing procedure can be an issue for water pumping facilities. Many water pumps require re-tensioning the bolts at start-up (especially piping-pump bolting connections). Isolation valves/devices are sometimes not removed for commissioning/start-up which can cause serious damages. Hydraulic systems could offer some difficulties in machinery package start-up. The hydraulic lines and valves may not be sized properly (often the hydraulic return lines are undersized) which could result in some problems.
Lubricant-related bearing issues are common at the start-up. A well-known reason could be the lack of lubrication. Considering the lubrication, the following factors are very important:
- The lubricant properties (for example, viscosity)
- The quality of the lubricant and the lubrication oil system
- The lubricating system operating conditions (for example, pressure, temperature, flow, etc.).
Insufficient lubrication could cause bearing surface damages. These damages can progress quickly to a failure. If there is insufficient lubrication flow, there will be inadequate heat removal from the bearing, which could result in discoloration (black color on bearing components) and mechanical strength reduction. It is necessary to ensure that any water pump receives proper lubrication during the start-up.
Large, critical water pumps always receive a lot of attention, while small- and medium-size pumps will often not receive the necessary attention. Ball-bearings and roller-bearings are usually used in small and medium water pumps, which usually do not reach their life expectancies because of poor installation, improper commissioning, careless start-up or poor operation. Some rolling-element bearings even fail during the start-up. The major reason for early failures of rolling-element bearings are: mechanical damage (sometimes due to misalignment), lubrication and material defects.
Some rolling-element bearings can tolerate only very limited amounts of misalignment. Correct alignment is a critical point in a proper commissioning/start-up. For example, a deep-groove ball-bearing can generate complex and destructive patterns of load zones as the result of misalignment. Cylindrical roller-bearings, tapered-roller bearings and the angular-contact ball-bearings could not tolerate the misalignment.
Foreign matter (for example, as the result of unclean lubrication oil, an improper flushing at pre-commissioning or insufficient bearing seals) can result in high rates of wear. Particularly, the bearing’s life expectancy can be considerably reduced. Impact damage during delivery, installation or start-up can result in small defects which could develop into large defects in a very short time.