How to minimize downtime and maximize performance.
by Richard Bailey
June 6, 2018

Pumps play a major role in the processes of power generation plants, so healthy boiler feed, condensate extraction and cooling water pumps are all essential to providing an efficient and reliable service. To keep this equipment in the best condition and operating at optimum levels, a considered and cost-effective approach to maintenance and renewal is required.

Power generation plants have always relied on their pumping assets to provide reliable service, but as the equipment ages, it requires more attention in terms of maintenance. As the length of time in service increases, the magnitude of repairs can escalate. This leads to a decision of whether it is best to repair, retrofit or replace the asset. By looking at each option, it is possible to assess the most cost-effective solution for each situation.

Minimize Downtime

From the outset, the best policy is to implement a preventative maintenance strategy that will enable potential service issues to be identified and resolved within a proscribed time frame, such as an annual shutdown period. However, unexpected failures can still happen, so it is advisable to also have a contingency procedure in place for isolating and removing pumps as necessary.

Repair & Replace

During the period that the pump is being repaired or serviced off-site, either a replacement must be installed, plant outage must be sustained or the remaining assets will have to cover the duty requirement until the pump is reinstalled.

In almost every application associated with the thermal cycle, the pumps are process critical and will have to be swapped out for service. In a scheduled overhaul or nonemergency situation with proper planning, replacement wear parts should be in stock at the user’s site, pre-purchased for the planned maintenance. If the replacement wear parts are readily available or reproducible by the chosen repair partner, this allows the work to be completed within the planned maintenance time frame. This is important when a spare pump is not available and ready for exchange.

workers fixing impellerImage 1. Using the expertise of a pump manufacturer is essential for retrofit projects. (Images courtesy of Sulzer)

Repairs made as part of a standard, scheduled overhaul will usually meet user requirements for a straightforward return to service. What the user expects is a refurbishment that achieves the objective of reclaiming the original performance, replacing wear parts and resetting the clock to the next scheduled overhaul.

If an upgrade is available, then an assessment of this decision can be made using a cost benefit analysis. This looks at the total cost of any investment plus opportunity cost (downtime) against the benefit of improving the design of the pump for increased performance. When known issues are in play, then a scheduled overhaul can be used as an opportunity to retrofit improvements that have already been developed—providing they can be achieved within the time frame and budget available.

Retrofit to Maximize Performance

Proper planning is important in cases when the pump is of an age where a simple repair can become more difficult due to changes in design or poorly documented past repairs. Planning may require the assistance of a known or trusted repair partner. In most cases, employing one with pump design and manufacturing capabilities will be beneficial.

Very often, it will be possible to engineer new components that incorporate modern design and manufacturing technology to create parts that are more effective and durable. Then the simple repair begins to look more like a retrofit, where additional benefits can be included with the replacement of a series of parts. Improved performance or longevity can be achieved by addressing a design issue or simply applying new materials and designs developed during the normal product life cycle.

Many pumping assets have been in service for a considerable number of years. During that time, the technology used in designing and manufacturing components such as impellers has progressed a great deal. This means that plant owners can benefit from increased efficiency or make changes to duty cycles without having to replace complete pumps.

Modern 3D design software and computational fluid dynamics (CFD) are now integral to creating an optimum hydraulic design. Companies that frequently repair pumps from other (sometimes obsolete) manufacturers will use these tools in tandem with reverse engineering techniques to manufacture new components when required.

large pumpImage 2. Careful monitoring of large pumps will identify any drop in efficiency.

While parts can be reverse engineered using precision instruments, a professional, independent maintenance provider will also constantly review original designs looking for ways to make improvements, using their experience and knowledge to enhance the design.

Selecting the most appropriate replacement components for a power generation pump should not be a case of accepting the specification of the legacy item. Moving to modern materials for wear components is the simplest first step for gaining time between required repairs. Adopting new impeller designs, for example, is the most common way of improving performance. The application of one or more of these retrofit options can clearly improve performance and extend the life cycle of this type of equipment.