Multiphase pumps for crude oil are truly multitalented. They reliably pump mixtures of crude oil, formation water and natural gas in vastly differing concentrations and compositions. The pump’s sensitive components include the mechanical seals. These are generally equipped with complicated purging and lubricating systems to allow them to work without interruption, despite the multiphase mixture. This overcomes problems such as overheating due to dry running or erosion of the sliding surfaces by abrasive media.
DiamondFace mechanical seals for booster pumps also make things easier, as EagleBurgmann has demonstrated with its seals that are in use under extreme conditions in the Panacocha oilfield in Ecuador’s Amazon region.
The customer and development partner for this mechanical seal is the German pump manufacturer Bornemann. With its screw spindle pumps, typically displacement pumps, Bornemann is one of the biggest names in multiphase and subsea technology. This traditional company was established in 1853, making it the oldest player in the German pump industry. It is one of the world’s first ports of call for oil pumping and processing applications.
Ecuador is the fourth largest crude oil-producing countries in South America. In 2009, Bornemann received the go-ahead from the state-run Petroamazonas EP Company to supply three powerful multiphase pumps. These were to be used deep in the primeval Amazonian rainforest. In the Panacocha project, which was linked into the network in October 2010 and is ultimately designed for 16 boreholes and a daily output of 25,000 barrels of crude oil, the booster pumps were needed to transport the pumped multiphase mixture at high pressure through the 310 mi (500 km) long pipeline to the Esmeraldas refinery on the Pacific coast.
In the past, the heterogeneous mixture of crude oil, gas, water, and various solids from the oilfield was separated and then transported via separate pipelines. Today, a single multiphase pipeline is sufficient. This has already proved to be a significant advantage in environmentally-sensitive projects.
Bornemann needed a seal that demanded little to no servicing and would work under harsh operating conditions (inadequate lubrication, high temperatures and exposure to abrasive solids), even without external liquid lubrication. For this demanding challenge, EagleBurgmann presented DiamondFace to a meeting of all the project partners. This groundbreaking coating technology for sliding surfaces was introduced by EagleBurgmann in 2007 and since then has really proven its worth in over 2,000 mechanical seal applications under extreme conditions.
The DiamondFace method was developed together with the Fraunhofer Institute for Surface Engineering and Thin Films in Braunschweig/Germany, and includes the silicon carbide sliding surfaces being coated with a closed layer of polycrystalline diamond. The up to 10um thick diamond layer, which is applied under vacuum and at temperatures of 2,192°F (1,200°C), is characterized by its extreme hardness, high wear resistance, excellent thermal conductivity, chemical resistance and low friction, which explains why the project managers decided to use DiamondFace in the Panacocha project.
Maintenance-Free and Robust
Less is more. This is true for pipelines and pump stations, but it also applies to the design of the mechanical seals in the pressure booster pumps for the Panacocha project. Bornemann, which has collaborated closely with EagleBurgmann for decades, needed extremely simple and reliable single seals for the multiphase pumps installed deep in the Amazon. The specification demanded a mechanical seal that was as maintenance-free as possible, but still robust so that it could be used in an unmanned station.
The seals for Panacocha were intentionally not based on the API Plan 32 method. Plan 32 involves supplying a clean fluid, generally water, from an external source upstream of the seal and is the standard for many multiphase applications. The supply of liquid provides a constant lubricating film in the sealing gap between the sliding surfaces and offers effective protection against inadequate lubrication. This is important if gas is pumped for long periods, and the risk of overheating and dry running are particularly great. Another plus point is the permanent purging and keeping of the solids-contaminated pumping medium away from the sliding surfaces. This prevents the early wear and leaks that could be caused by abrasion.
The main disadvantage of API Plan 32 when used a long way from civilization is the cost of logistics and monitoring, which is why this method was not a practical option for the Ecuador project.
Optimized Service Life
Even though DiamondFace was undisputedly the ideal solution to handle the difficult conditions at Panacocha, there were still a few details that needed to be ironed out. All the metal components of the preassembled cartridge were made from super-duplex steel (G4) due to the high chloride content in the formation water, the water that is pumped up from the ground together with the oil/gas mixture.
To optimize the service life of the mechanical seal, EagleBurgmann opted for an unpressurized quench for the Panacocha solution. This involved providing an unpressurised oil quench (ISO VG32) from the atmosphere side as per API Plan 62. This is distributed on the back of the sliding surface via milled hydrodynamic oil grooves or pockets, thus providing a slight cooling effect. At the end of the day, it is these detailed and highly-precisioned additional measures that allow the DiamondFace system to perform for maximum effect.
A Cost-Effective Solution
Many years’ experience and excellent cooperation with the pump manufacturer meant that the DiamondFace sealing solution could be integrated into the Bornemann pump without great expense. As the sealing concept was already proven, it took only a few steps to supply a DiamondFace seal that met the requirements. The finished product, which is known as the DF-HSHJ4S1, is characterized by its cartridge design, balanced principle, springs that are protected from the product, and suitable secondary seals that can handle the various challenges associated with pressure, temperature and medium composition.
By diamond-facing both bearing ring and stationary seat, it was possible to ensure that the sliding surfaces can withstand dry running for several minutes without damage and even handle temperatures in the sealing gap of up to 572°F (300°C) without problems—all without using the complicated methods based on API Plan 32 systems. The DiamondFace mechanical seal is ideally equipped to cope with abrupt fluctuations in the media content in the pumped product mixture commonly found in multiphase applications. The spectrum ranges from pure gas to water or oil with differing solids contents.
EagleBurgmann consulting engineers in Ecuador were able to see for themselves how the DiamondFace Panacocha seals (four of which are installed in each booster pump) work perfectly in practice. Despite operating continuously, there are no signs whatsoever of any fault in the seals. The service life should greatly exceed the guaranteed warranty period of one year. So far, it is all running as though lubricated, even without constant liquid lubrication.
For more information on DiamondFace technology, contact us at firstname.lastname@example.org.