Sulzer develop the world's highest-pressure injection pump

Citation

(2003), "Sulzer develop the world's highest-pressure injection pump", Industrial Lubrication and Tribology, Vol. 55 No. 3. https://doi.org/10.1108/ilt.2003.01855cad.005

Sulzer develop the world's highest-pressure injection pump

Sulzer develop the world's highest-pressure injection pump

Keywords: Sulzer Pumps, Pumps

As oil exploration moves further offshore into deeper water, the oil reservoir pressures increase far beyond those experienced in the past. Therefore, injection pumps used to support the oil reservoir pressure need injection pressures far above the technology of existing centrifugal pump designs. Sulzer Pumps has trodden new paths – and developed the world's highest-pressure centrifugal injection pump.

The exploration of deep-water oil fields requires injection pumps with extremely high pumping heads. Oil companies have selected several pump companies to develop designs to meet their tough demands. This gives them the opportunity to participate and review the designs and manufacturing processes thoroughly, to address interfaces to the other equipment and assess risks in an early phase. Robust, reliable pump designs as well as safety of the operating personnel and production facility are of high priority.

The very high pumping head – up to 5,600 m or 580 bar – demonstrates the biggest challenge. In order to minimize risk, the pump selection criteria such as hydraulics, speed, head per stage, number of stages, and design pressure should not deviate too much from the designer's experience wherever possible.

Typically, the existing hydraulics for multistage pumps, consisting of impellers and diffusers, need a larger shaft to transmit the high power. This is a relatively small design change, but nevertheless, the altered hydraulics have to be model-tested for validation of their performance.

Speeds of rotation not higher than 6,000 rpm are common. The generated head per stage is to be limited to about 600 m, ensuring acceptable erosion rates for the super duplex stainless steel and hence achieving long operational life for the pump parts.

The combination of number of stages, type and size of the hydraulics, and speed determines the rotordynamics of the pump, which can only be analyzed after the pump rotor has been designed. A detailed rotordynamic analysis is of great importance to demonstrate that the eigenfrequencies have enough separation from the operating frequencies and that the damping is high enough, even with worn internal running clearances, hence ensuring smooth running of the pumps at all operating conditions in the field.

After the selection of the pump, a plan has to be established addressing how the features that are beyond the manufacturers experience are handled to minimize risk. One area of concern on all the ultra-high-pressure pump designs are the static seals to keep the joints of the pressure-retaining parts tight during operation and during hydrostatic pressure test. Detailed finite-element calculations have to be conducted to determine the maximum stresses and deformations. Furthermore, the static seals are to be tested in a test rig.

Sulzer Pumps offers two pump designs:

• •

  impellers arranged in-line for higher flows, and

• •

  impellers arranged back-to-back for lower flows

The in-line design is the classical concept used on most high-power multistage pumps either for injection or boiler feed services. A balance drum installed after the last stage reduces the axial hydraulic thrust to the capacity of the double acting thrust bearing. Normally, mechanical seals seal the suction pressure to atmosphere. Pressure oil feed journal and thrust bearings align the rotor to the stationary casing. The pump features a full pull-out cartridge, allowing for a quick exchange of the cartridge.

The back-to-back design balances the thrust itself to a large extent. Thus, a smaller thrust bearing can be used. The center and the throttle bushings are only subjected to half the pump pressure and act as Lomakin type bearings. This design is especially suited for ultra high pressure at low flow. All other features are the same as for the in-line design.

Components and features critical to reliability and safety have been identified for detailed investigation during the design process. Here, only two parts of the many analyzed are described.

The delivery (or discharge) cover closing the barrel casing to atmosphere is sealed with a face O-ring. This seal is only tight if full metal-to-metal contact can be maintained. To prove this, a finite-element calculation has been performed, utilizing state-of-the-art 3D modeling techniques and analyzing tools. With this analysis, it can be proven that a positive surface pressure at the inside of the bolting near the O-ring groove can be maintained, thus eliminating any possible O-ring extrusion at all operating conditions.

For safety reasons the suction casing has to be sealed to the atmosphere for the full discharge pressure if there is no pressure relief system installed in the suction pipe. Only a radially arranged sealing system is feasible by design. With rising pressure the radial extrusion gap increases. A sealing system for this purpose consists of a tough, resilient, T-shaped ring with a pressure-actuated anti-extrusion ring used in the aeronautical industry. For the first ultra-high-pressure pump a test rig which reproduced this radial gap under this high pressure was built for testing the sealing system prior to pump manufacture. The tests were successful and confirmed that the suction end sealing system was fit for purpose.

Injection pumps must be capable of handling sand, especially if produced water is pumped. The components forming the close running clearances have to be protected by using newly developed HVOF coatings or wear parts with solid tungsten carbide inserts.

For the BP Thunder Horse project in the Gulf of Mexico, Sulzer Pumps has participated in a development competition and, in 2001, was awarded the manufacturing and testing of the prototype injection pump with the highest pressure in the world. The pump had to generate a head of over 5,600 m, turned at 6,000 rpm and was driven through a gearbox with a 10 MW variable-frequency drive motor. The selected pump was of the back-to-back design and had 12 stages. The material of construction was super duplex stainless steel with high strength and corrosion resistance.

The pump was vital to the customers' project success. Since a pump with such high pressure had never been built before, a prototype pump was manufactured and extensively tested. The hydrostatic pressure test had to be conducted under severe safety precautions. The pump test assembly was set up in a pit not accessible to the test personnel. The pressure was increased incrementally up to 957 bar (65 per cent higher than the required operation pressure) and successfully held at that pressure for 30 min.

The predicted hydraulic performance was confirmed with the performance test conducted at full speed at the Sulzer Pumps test facility in Leeds (UK). The customer's requirements including the standards of API 610, 8th edition, could be met.

Rotordynamic tests were carried out running the pump at full speed and full load with two times new running clearances simulating end-of-life condition. The stiffness gained with close running clearances is reduced with large clearances, thus vibration is expected to be higher. Hardly any change of the low vibration level was detected between the tests with new and worn running clearances. Vibration levels were all within the limits set out in API 610 across the full operating range. In addition, unbalance was added to the coupling to check the rotor sensitivity. The measured vibration amplitude was below the predicted value.

All test results fulfilled the customer's requirements and demonstrated that the pump is robust even with end-of-life running clearances. The customer then released an order for three additional complete pump units.

This new and innovative development of ultra-high-pressure injection pumps allowed Sulzer Pumps to extend its range of pumps in order to meet even more challenging demands in the future.

For more information, contact: Tony Waterfield, Sulzer Pumps. E-mail: tony.waterfield@sulzer.com