Upgrading Water Injection Pumps


Courtesy of Courtesy of Sulzer

Water injection pumps that are used in oil exploration typically face extreme abrasion, chemical attack, and cavitation erosion in their daily operation. The injected water is frequently loaded with abrasive particles, such as quartz sand, which quickly erode conventional pump surfaces. Sulzer’s service teams offer solutions to increase the lifetime and the performance of water injection pumps.

Sulzer Service Centers provide support in creating solutions to optimize equipment performance through the entire life cycle of the pump. With today’s technology, it is common practice to take a ductile iron pump and supply it with upgraded materials, as well as overlay the wear parts with HVOF (high-velocity oxygen fuel) coatings. These key improvements ensure longer mean time between repairs (MTBR) and allow the cast parts to be serviceable through more repair cycles. The Los Angeles Service Center had the opportunity to upgrade a pair of pumps: a low-pressure pump that discharges into the suction of a high-pressure pump. These pumps operate in series for produced water injection service.

The customer has more than 20 water injection pumps in the field. They are VS6 (double-casing diffuser) vertical pumps. Each pump consisted of fifteen stages, generating a combined discharge pressure of 3320 psig (229 barg). Originally, these were designed by a third-party OEM; they were later retrofitted with Sulzer hydraulics. Throughout the years, Sulzer pump expertise has been applied to make improvements to these pumps to keep them in service. However, the changes were inconsistent because of the maintenance schedule and budget. It was on this particular job that the customer decided it was time to perform a complete overhaul of two pumps.

The customer was having several problems with these pumps. Mechanical-seal failures were caused by:

  • Shaft runout
  • Excessive pressure levels
  • Produced water with abrasive particles

Further issues were motor-bearing failures due to:

  • Ductile iron casting and ring clearance wear
  • Performance degradation
Comprehensive solution

In order to solve these issues, Sulzer performed the following upgrades:

  • New Duplex castings were manufactured to extend the serviceable life of the major components. Duplex material is not only resistant to abrasion and corrosion but can be repaired in the future, unlike the previous ductile iron bowls.
  • HVOF coating was applied on the wear surfaces to maintain the efficiency for an extended period.
  • The seal housing arrangement was modified to provide a better environment for the mechanical seal and increase flow to lower the pressure. The seal housing for both the high-pressure and low-pressure pump was arranged with the return line going back to the low-pressure pump suction, and the throttle bushing was sized to achieve the required pressure breakdown.
  • Vertical thrust bearing was added to reduce the runout on the pump shaft and absorb axial thrust developed from the pump.

A new flexible coupling was selected for the pump and the seal manufacturer made design changes to the seal to keep particles away from the contacting surfaces.

Thrust bearing upgrade

When selecting the vertical thrust bearing, it was important to calculate the downthrust as well as the momentary upthrust, check the deep-radial-groove-bearing upthrust capability, and check the housing footprint size. With the calculated thrust values and the known shaft size, Sulzer engineering determined that the Sulzer VTBH 4 thrust-bearing assembly would be suitable for this application. Since these pumps run in series, the second pump will see a high upthrust during startup. This was a concern because the current vertical-thrust-bearing design was designed to absorb a downthrust with the momentary upthrust taken by the deep radial groove bearing. From the thrust calculation, engineering was able to determine that the first pump would see the highest downthrust, which was used to determine the expected bearing life.

Once the bearing design had been selected, modifications to the existing discharge head had to be applied to accept a vertical thrust bearing. Sulzer limited the height of the discharge head to avoid a possible excitation of the reed frequency.

Benefits of the new thrust bearing

Since the pump thrust bearing is separate from the motor, the customer can use a lower-cost motor without sacrificing reliability. The pump thrust bearing is better designed for the varying pump thrusts and will have a longer life. Also, the presence of the bearing close to the mechanical seal reduced the shaft radial movement, which increases the seal life. A disadvantage to having the bearing housing in the discharge head is that the vertical thrust bearing must be removed in order to perform maintenance on the mechanical seal. However, due to the increase in MTBR, seal changes are less frequent.

Because of Sulzer’s technology and its in-house field engineering team, the Los Angeles Service Center was able to provide a comprehensive solution to the customer. More importantly, the service center team was able to communicate and execute the solution within a suitable time frame. Currently, the modified pumps are running well and are providing the necessary head and flow, and they have not had any reported mechanical-seal or thrust bearing issues.

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