In the pumping world today, pump efficiency and operational flexibility have become primary points of consideration in many markets. The expansion of variable frequency drives (VFDs) into the pumping market has enabled end users to better control their pumping operations within the hydraulic capacity of their equipment. Though that may be the case, what options exist when a more drastic change in performance is needed? A pump rerate might just be the solution. Typically, this entails some form of modification to the pump hydraulics to achieve the desired performance. This article will look at some reasons why an end user may wish to consider a rerate, ponder some of the challenges that might exist and review some key points that go into making a pump rerate successful.
A pump rerate is overhauling a pump to modify the pump differential pressure, flow rate (or both) or to increase pump efficiency to reduce power consumption. This can typically be done regardless of the style of pump. There are several reasons an end user may wish to change how their pump operates: improved efficiency, performance adjustments due to changes in system operation or increased rate. For example, a crude oil pipeline operator may need to increase product rates to meet a rise in commercial demand. If the rate increase is minor, say 5%, then it may be possible to address with speed or impeller trim adjustments. However, a larger rate increase, 20% for example, will likely require a change in pump hydraulics. This will ensure capacity requirements are met while still operating the pumps within the allowable operating region (AOR). Another example is a water transport pump station in a rural area where utility power costs are at a premium. New impeller hydraulics, optimized to the existing operating conditions, can provide increases to pump efficiency. This can result in increased savings in operational power costs. These are examples where adjusting existing pump performance to better align with operational requirements can provide a financial advantage to the end user. A final example may be the need for higher differential pressure. Changes to system piping and operation over time could result in a system curve that prevents the pump from running at a more favorable spot on its performance curve. By adding stages, adjusting trim or changing impeller hydraulics to produce a higher differential pressure, the pump can overcome system limitations and run closer to its best efficiency point (BEP). Discussing operational needs with an OEM is the best way to discover what can be achieved with a particular piece of equipment.
Details to Consider
Good communication is critical. Often a rerate project is a collaborative endeavor, and along with the end user and the shop doing the actual work, there may be an engineering, procurement and construction (EPC) company, contractors and other third-party vendors involved. Therefore, careful planning during the initial stages goes a long way in ensuring a successful rerate. While this is an easy statement to make, what should one consider when planning? Here are a few areas where challenges may come up during rerate projects.
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Changes in operation
It can be a common occurrence where the desired pump duty point may change between the initial concept phase and the execution phase. For example, a crude oil pipeline operator is able to secure an additional 40,000 barrels per day of crude oil for transport. During the concept phase, it is determined that a new higher specific speed impeller will work. The preliminary pump curve and associated impeller trim is approved and accepted. However, by the time the project has begun and purchase orders are in place, the operator has secured an additional 20,000 barrels per day of product to ship. At this point, the project’s success may hinge on whether additional performance margin was built into the hydraulic selection. The best way to work with a dynamic scenario like this is upfront discussion with the end user, especially if there may be other limiting factors, such as available driver horsepower. It also enables discussion about future needs and equipment flexibility. A BB1 style pump might benefit from using case nozzle inserts to maximize equipment flexibility if future capacity needs may change. A VS1 pump might be rerated with a longer pump shaft and stage inserts if the end user anticipates additional head requirements in the future. While it may be difficult to predict future needs during the concept phase, open discussion about possible future needs makes it easier to plan accordingly and ensure the end user is aware of what options are available to meet those potential needs.
2. Third-party suppliers
When turnaround time is tight, and there are contractors and riggers scheduled to be on site at a specific date, the last thing users want is a delay. Depending on the scope of the re-rate, third-party suppliers may range from a mechanical seal supplier to foundries and fabricators. While it is common for unforeseen and discovery work to happen during a rerate, some of these risks can be mitigated by good planning and collaboration upfront. Discuss timing and part criticality with third-party suppliers during the concept phase. Get their commitments and input on key project dates. Consider the use of existing spares and procuring critical items upfront. On one successful pipeline rerate, an aftermarket services company collaborated with the end user to use existing spare mechanical seals up front for three units. Those were used to rebuild three rerated units. The seals that came off the pumps were sent out for rebuild and were ready by the time the next set of pumps arrived at the shop. At the end of the rerate, the last sets of mechanical seals were rebuilt and returned for spares. The same type of planning can be done with other long-lead items, such as impellers and shafts. For rerate projects involving multiple pumps where timing is critical, build in time at the start of the project to acquire these long-lead items first so that when the pump(s) are pulled from service there are items on hand, and a delay will have less impact on the project schedule. This will require communication and partnership between the end user and repair shop, as there may be commercial options to consider to better facilitate this approach.
3. Strategic spares
Often, the idea of strategic spares may be overlooked in a rerate. However, keep in mind that a major rerate on a pump could involve design changes that could make existing spares unusable. For instance, a rerate to a larger impeller may require a larger shaft, depending on horsepower requirements. Considering a BB3 style pump as an example, this will likely require a new center bushing, throttle bushing, case rings, etc. As an end user, consider what strategic spares are kept in stock, and bring this into the initial conversation with the repair shop. What spares are available, and what will be needed at the end of the project? These strategic spares can be further leveraged for upfront rerate parts. On the crude oil mainline pump example, the end user kept several spare rotors in storage for the pipeline as part of their strategic spares program. Once the pumps were rerated, the spare rotors would no longer be able to perform as new impeller hydraulics were required. By considering the need for strategic spares up front, the aftermarket services company was able to take the existing spare rotors and rebuild them ahead of time, so when the first set of pumps was pulled from service, all that was needed was a rotor swap. Then, when the last set of pumps was rebuilt, the extra rotors were rebuilt, and the spare rotors returned to their spares inventory. This approach may change based on the type of rerate required, but keeping strategic spares in consideration at the front of a project will help ensure there are no surprises at the end and may help improve turnaround time on more complex projects.
One additional consideration with a rerate is the opportunity to standardize on spares. This is especially true if multiple pumps of different vintages are going to be rerated. An end user may take this opportunity to standardize where possible. Mechanical seals, wear parts and bearing components are all good items to review and discuss with a repair facility. While it may add some extra work into the rerate, it can provide the benefit of common spares in a system where multiple pumps are used. On another field example, a BB3 pump was originally installed to handle produced water. As the field has expanded, a second, similar BB3 pump was added to accommodate the extra capacity. The original pump had a ball-ball bearing setup. The second pump added had a sleeve-ball bearing arrangement. The operator wanted to rerate both pumps so that it had one 100% unit and one installed spare. With some planning upfront, during the rerate build, the ball-ball bearing arrangement was upgraded to match the sleeve-ball arrangement. Now, both units have the same bearing hardware and can use the same spare parts. This not only helps streamline on-site spare parts but also allows for process standardization for preventive maintenance and parts replacement.
4. Component upgrades
Component upgrades are another area that can often be overlooked when considering rerates. Often, pump materials and other components not part of a rerate could fall under the “If it’s not broke, don’t fix it” adage. Some discovery work can shed light on potential material upgrades: excessive wear on wear components, unexpected shaft wear, localized pitting corrosion, etc. However, what about thrust bearings, journal bearings or mechanical seals? Have the right people on the end user’s side been consulted to see if there are additional operational issues that could be addressed? On capital projects, there can be a disconnect between what operators and technicians in the field see daily compared to those issues that a project manager or EPC firm might know about. As an end user, make sure to get feedback from site personnel on any other potential issues that can be addressed during a rerate. Have bearing temperatures been trending up? Are seal failures becoming more common? Are there other quality of life issues that could be addressed? Take advantage of having the unit(s) out of service to address any other potential items that could improve equipment reliability.
5. Project scheduling
Despite all the technical details that can go into a pump rerate, project scheduling can be one of the more stressful and impactful parts of a successful rerate project. Often, minor technical issues at site during installation of the rerated equipment get quickly forgotten. However, a project where the equipment installation is six weeks late is often remembered long after the project is finished. To maximize the success of a rerate project, both the end user and repair facility need to communicate openly about their project challenges and expectations. On the crude oil pipeline example, the repair facility doing the work needs to be aware and focused on the fact that the end user has commercial commitments to meet and likely has contractors scheduled to perform necessary site work. While a repair facility may not consider a week’s delay a big deal, for an end user, it could have larger commercial impacts. Similarly, end users need to consider all the moving pieces required to get that equipment rebuilt and on site. Conflicts and unnecessary cost escalations can be mitigated by considering these items previously mentioned. Additionally, things such as discovery work, long-lead items and supplier issues can lead to delays. So, while a repair facility should be cautious of adding too much extra time into its delivery commitments, an end user needs to be aware that some scheduling contingency may be necessary in order to ensure that small delays can be absorbed in the overall schedule to ensure the equipment is ready and on site when needed and can be coordinated with the other on-site activities. Again, communication here is key, particularly on large projects affecting multiple pumps. Be open about the challenges and risks, along with the potential impacts of scheduling issues and delays.
Pump rerates offer end users the opportunity to address multiple aspects of their equipment. These include improving efficiency and meeting new operational requirements, as well as addressing other operational issues. Good communication is vital to a successful rerate project. Understand that a knowledge gap between a repair facility and an end user will exist. Just as an end user may not fully understand why a rerate requires a change in impeller specific speed, the repair facility may not grasp the multiple operating modes that may be required of the equipment. The challenges and issues presented here represent a good start to having these conversations. Be open to discussing the challenges on both sides so that the best options and optimum solutions can be achieved together.