The operation of high pressure pipeline pumps poses great challenges to end users. Strict environmental standards must be met, and the cost effectiveness and availability of the numerous pump stations must be assured. Product leakages must be prevented by all means necessary. As a result, the pump shafts are sealed with dual seals with unpressurized buffer or pressurized barrier systems.
The current trend of many oil pipeline end users is to reduce investment and operating costs by deploying simple, universally installable sealing systems while still having to guarantee the safety of their pumping systems and components, which can be difficult.
A well-known Canadian end user approached EagleBurgmann for that reason and submitted a specification sheet for the development of an economic and safe single mechanical seal for their crude oil pumps, whose performance needed to match that of a dual seal. The main requirement was the prevention of leakage to the environment, even in the event of total seal failure, meaning that it must be equipped with the safety concept of a dual seal.
For the team of EagleBurgmann engineers, this was an interesting project not just in terms of the high technical safety requirements, but also because of the ambitious operating parameters: the large pressure range to be sealed, the partially large shaft diameters, and in addition, the objective to seal all existing pumps of a pump station with just one seal type.
Shaft diameter: d = 4.53” – 6.10” (115-155mm)
Suction pressure: p = 36-1,436 psi (2.5 – 99 bar)
Outlet pressure: max. 2,001 psi (138 bar)
Temperature: t = +50˚F - +158˚F (+10˚C - +70˚C)
Speed of rotation: n = 720 – 1,980 min-1
Medium: Crude oil with diluted bitumen contents
The Sealing Solution: EagleBurgmann SHVI
For many years, EagleBurgmann has been supplying its very successful SHV series seals for pipeline applications. Their application in crude oil pumps and MOL pumps of all types have been proven worldwide. The high pressure SHVI variant designed for the Canadian customer has a loosely inserted stationary spring loaded seal face that cannot tilt. It is also distortion resistant, robust and designed for extreme pressures and temperatures, as well as cyclic conditions.
A special grade of the silicon carbide, Buka 30, is used as the face material to ensure increased emergency running properties or dry running tolerance of the seal faces. In addition, high-precision grooves were introduced in the sliding faces to assure trouble-free lift off in lower pressure ranges and contribute to stable operation over a wide pressure range.
Safety: API Plan 66A with Special Execution
The only thing lacking was a reliable safety concept in the event of total loss of the sealing function of the single seal. Plan 66A, introduced in the 4th edition of API 682, was selected to prevent the oil from spilling into the environment.
The plan principally provides for two throttle bushings on the atmosphere side in the sealing housing. Seal failure is indicated when the pressure rises in the space between the seal faces and the first bushing. This space is connected to a pressure transmitter to inform the operator of potential troubles.
The EagleBurgmann team optimized this principle for high pressure applications. After all, pressures up to 99 bar (1,440 PSI) must be contained in this application. A special inner floating throttle (made of solid material with a shrink-fit collar) enables the system to withstand the entire product pressure. At the same time, an alarm is triggered due to the pressure change while a small amount of low pressure leakage is carried away via the drainage connection to a central collection sump in the pumping station.
Test and Acceptance
The EagleBurgmann solution SHVI and the Plan 66A were subjected to several dynamic and static test cycles in the R&D test facilities in Germany. The constant and reliable sealing performance in all operating states and the safe function of Plan 66A in the event of a fault provided impressive results. The required system safety was guaranteed at all times. The EagleBurgmann SHVI with Plan 66A was accepted by the customer, and the imposed safety requirements were fulfilled.
The EagleBurgmann Solution in Operation
Several SHVI seals were delivered. They are already operating successfully in production and have been deployed for several thousand operating hours in MOL pumps of Nuovo Pignone.
After the final release by the end user, additional pumps will be retrofitted. The new single seal concept EagleBurgmann SHVI with the Plan 66A serves as cost efficient, modularly deployable and reliable in operation - with the safety of a double seal.
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