Single but twice as safe at high pressure

Extreme geological and climatic conditions characterise the global network of pipelines. Differences in altitude and long distances between pump stations as well as limited access to the plants for servicing, maintenance and repair place high demands on the technical equipment. When it comes to sealing aggressive and abrasive crude oil, reliability and extended servicing intervals are vital. The harsh environments challenge the design limits of the sealing and supply systems, with frequent starting and stopping as well as occasional pressure reversals or reverse pump rotation. Pressures up to 160 bar, ambient temperatures from -55 to +60 °C, sliding velocities of up to 60 m/s and high vibration loads must be compensated.

To meet this broad range of special demands, Eagleburgmann leverages proven sealing concepts that are adapted to individual application requirements in close collaboration with plant engineers, pump manufacturers and operators. The mechanical seals in the SH and HJ4 series, for example, have become the standard for crude oil pumps.

Seals for high pressure solutions

The sealing solution for the Canadian oil pipeline operator needed to be suitable for a pressure range from 2.5 to 99 bar as well as for shaft diameters from 115 to 155 mm. Since the pump stations are operated unmanned, the seal must manage without an additional supply system. However, to protect the environment and personnel, the seal housing must not leak if the seal fails unexpectedly. These requirements were best met by the SHV series, which has proven itself thousands of times over in crude and main oil line (MOL) pumps of all types worldwide for many years. Eagleburgmann developed the SHVI variant with a loosely inserted seal face specifically for the high pressure range stipulated by the Canadian customer. The face is designed such that it always forms a parallel sealing gap with the stationary seat. The deformation behaviour of the seal face was optimised for use in crude oil pumps, so that the seal operates reliably even at very high pressures, sliding velocities and temperatures or in case of pressure and temperature fluctuations. A special quality of silicon carbide was selected for the pipeline operator’s pumps, providing the seal face with particularly good emergency running properties and partial dry running tolerance. In addition, the sliding faces have precisely ground grooves which allow the seal face to be lifted quickly, even at low pressure, and contribute to stable operation over a wide pressure range.

Optimised API Plan 66A

Plan 66A, which has been available since the introduction of API 682 4th Edition, was the obvious choice for the safety concept. Accordingly, the seal housing contains two throttles and the seal chamber is connected to a pressure transmitter. Eagleburgmann optimised the plan and used a special inner, floating throttle, which can withstand product pressure of 99 bar in an emergency. The pressure transmitter detects pressure changes in the seal chamber and triggers an alarm if certain values are exceeded. At the same time, the seal leakage at low pressure is discharged to a central collection system in the pump station.

Safely sealed

The SHVI seal and the optimised Plan 66A were subjected to dynamic and static tests, both individually and together, on Eagleburgmann test benches. The constant and failsafe sealing performance in all operating states and the reliable functioning of Plan 66A in the event of a fault were very impressive. The required system safety was ensured at all times. There are plans to upgrade more of the pipeline operator’s pumps in the same way. The combination of a SHVI single seal and optimised Plan 66A is economical, modular, dependable and as safe as a double seal. This seal type has since additionally proven itself with several thousand hours of operation in the MOL pumps of other customers.

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Autor: Andreas Pehl

Senior Expert Application Engineering,

Eagleburgmann Germany