Fluid film bearings are often designed as a sacrificial component in rotating machines. The primary characteristics of a bearing material are compatibility, conformability and embeddability. These qualities reduce the likelihood of damage to the shaft during start-up and shutdown, or from upset conditions, misalignments or occasional ingestion of contaminants. A bearing material must also have adequate compressive strength, temperature capability, and corrosion and wear resistance for the given use.
To meet the widening range of application requirements and operating conditions for high-performing rotating equipment, advances in fluid film bearing materials give differing emphasis to these ideal characteristics, sometimes requiring trade-offs.
In the February 2017 issue of International Oil & Gas Engineer, Senior Development Engineer Sriram Venkatesan outlines differentiating characteristics of fluid film bearing material options, including tin-based alloys (babbitt), bronze, aluminium-tin, engineered polymers, ceramics (and cermets) and super-hard materials such as polycrystalline diamond (PCD).
Shafts of high-performing rotating equipment experience a certain mass unbalance distribution resulting from manufacturing tolerances, component assembly and material nonhomogeneities. The residual unbalance generates uneven forces on the rotor as it spins, resulting in vibrations and the transfer of dynamic loads to the bearings and supporting structure.
To limit the negative effects of rotor vibration, ISO and API standards set balancing criteria and acceptance levels for residual rotor unbalance. Whether magnetic or fluid film bearings are used in the machine, there is a prerequisite for spinning a rotor to its rated speed. The rotor must be balanced to meet an acceptable residual unbalance level.
The ability of an active magnetic bearing (AMB) system to tolerate high levels of unbalance on the rotor by applying unbalance force rejection control algorithms does not alter the balancing requirements. Rotors supported by AMBs and rotors supported by fluid film bearings are subject to the same balancing requirements.
In the June 2016 issue of COMPRESSORtech2, Andrea Masala of Waukesha Magnetic Bearings discusses the options and considerations in performing low- and high-speed balancing of active magnetic bearing-supported rotors. Two case studies are also discussed.
By Barry Blair, Waukesha Bearings
Published in Processing magazine, May 2016
Bearings are a critical component in equipment reliability, efficiency and life. The majority of rotating process equipment today relies on rolling element bearings or fluid film bearings to counteract gravity and other forces in the equipment and allow the shaft to rotate freely. Selecting the right bearing for the equipment and application is essential to the successful operation of that equipment.
A key difference between rolling element bearings and fluid film bearings when it comes to process equipment maintenance is the expected life of the bearings. Rolling element bearings typically have a predictable life based on the operating conditions. When properly designed and maintained, fluid film bearings can operate for decades.
The proper selection of materials and mechanical design is the foundation for a fluid film bearing’s long life. Typical factors that affect material selection include load, speed, operating temperature, insulation requirements, and lubricant type and cleanliness. Depending on the requirements, material options include babbitt (also known as whitemetal), bronze, aluminum tin, polymer, ceramic, cermet and diamond.
For the mechanical design, the fluid film bearing designer must not only consider the proper sizing of the bearing to handle the loads and minimize the power loss but also incorporate features to optimize the formation of film and tune the dynamic characteristics of the bearing. Tuning the bearing’s characteristics improves the performance of the process equipment.
For more detail about material selection and bearing design factors, continue reading the article in the May 2016 issue of Processing magazine or online at www.processingmagazine.com.
By Richard Shultz, Waukesha Magnetic Bearings
Published in Fluid Handling, January/February 2016
Groningen, Europe’s largest natural gas field, was discovered in 1959. Production began in 1963, and by the end of the decade nearly 50% of the field’s reserves were depleted with free-flow operation. Nederlandse Aardolie Maatschappij (NAM), a joint venture between Royal Dutch Shell and ExxonMobil, was created in the mid-1990s to find the most cost-effective way to extract gas from the field and extend the life of its reserves.
By upgrading the field’s equipment, including installation of motors and compressors, the field could supply gas to all of the Netherlands, Germany, and Belgium for an additional 40 years. The challenge was to achieve at least 87% availability and a low total cost of ownership.
Magnetic bearings are a proven technology for large standalone motor compressor strings, like the ones at Groningen, to provide both high availability and a low total cost of ownership, as well as lower power consumption (due to decreased rotating losses), lower maintenance costs, and lower CAPEX costs compared to conventional bearings.
Read the article in the January/February 2016 issue of Fluid Handling, or download it below, for more about the operating principles of magnetic bearings, system design considerations, and the application of the technology at Groningen.
Damping decreases vibrations by removing energy through resistance to motion. For rotating equipment, damping is necessary to control vibrations and prevent them from damaging the rotor, bearings or other components in the machine.
Using an engineered damper can increase stability, reduce rotor response, increase the separation margin between operating speed and critical speeds, reduce forces transmitted from rotor to ground, reduce pedestal vibrations, reduce bearing wear, and decrease sensitivity to changes to the rotor, such as material buildup on a rotating component.
To learn about the particular benefits of ISFD® technology – the integral squeeze film damper – read the article on engineerlive.com.
By Barry Blair, Chief Engineer, Waukesha Bearings
Published in Modern Pumping Today, February 2015
The pump industry, like many others in today’s economic landscape, is striving to extend equipment operating life while putting greater demands on that equipment. Developments toward longer life and increased productivity are creating a chain reaction of demands, innovations and improvements.
As the industry continues to push the limits for greater efficiency, the pumps require higher quality bearings with a greater operating range.
Read about recent bearing developments for electric submersible pumps, subsea pumps and traditional oil-lubricated pumps in the February 2015 issue of Modern Pumping Today.
By Jong Kim, Waukesha Bearings
Published in POWER magazine, March 2015
For one of its power generation customers in Scandinavia, Doosan Škoda Power engineered a 46 MW steam turbine as part of a combined cycle system for generation of electricity as well as heat recovery. During the initial commissioning, the turbine experienced rotor instability that prevented the drive train from operating at full load. High subsynchronous vibrations forced a trip in turbine operation at just 27 MW versus the rated 46 MW.
Changes to the bearing clearances and configurations mitigated the vibrations but were not able to eliminate them completely. Doosan Škoda Power decided to contact Bearings Plus, a Waukesha Bearings business, for a damper solution.
Learn how ISFD technology maximized the damping ratio and eliminated the subsynchronous vibrations spikes in the March 2015 issue of POWER magazine or online at www.powermag.com.
In 2002, a leading oil and gas customer approached Waukesha Magnetic Bearings with the challenge of developing a bearing for a hermetically sealed integral motor compressor. Availability and reliability were the customer’s primary objectives. The end user could achieve a significant cap-ex savings on the installation if the motor compressor could be located outdoors, with no building or enclosure required.
The sealed characteristic the Waukesha bearings and electrical connectors delivered in the end did eliminate the requirement for a costly enclosure for the motor compressor and the end user realized a significant project cap-ex savings.
Read the complete article in the September/October 2014 issue of Oil & Gas Product News, read it online, or download the PDF below.