Post by Dr Alfred Zohrabian PhD,MBA,CEng,FIMechE

The Use of Gas Turbines and Centrifugal Compressors and the Start of Modern Natural Gas Transmission System-Europe and US 1950to1960 (Part 6-16)   This history of tilting pad bearings: (Part 7 – 2) As noted earlier, the tilting pad thrust bearing revolutionised turbomachinery primarily because of its ability to handle high loads and speeds, whereas fixed bushing bearings proved inadequate. In addition, after WWII, there was a significant boom in industrial power and naval expansion. The tilting pad thrust bearing’s major advantages were self-alignment, vibration damping, heat dissipation, long lifespan, and reduced power loss due to low friction. In 1946, Arthur Hagg recognised that a tilting pad thrust bearing could also dampen self-excited rotor vibration in journal bearing applications. In the 1950s, NASA’s engineers Anderson and Etsion developed a flexure pivot gas bearing (an oil-free tilting pad bearing) for specialised aerospace turbomachinery to address instability and thermal expansion issues associated with earlier rigid point-contact pivots in aerospace and space power applications. The advantage of flexural pivots or beams is that the bearing flexes rather than slides, thereby eliminating wear and friction. In 1952, Fred W. Ocvirk developed and validated a steady-state model for tilting-pad journal bearings at Cornell University. In 1964, Jürgen Lund, a Danish engineer and academic in the field of rotor-bearing dynamics, published his work “Spring and Damping Coefficient for Tilting-Pad Journal Bearing”, which remains a basis for modern rotor-bearing dynamic analysis. His theoretical work provided the industry with a methodology for designing and analysing tilting-pad bearings for centrifugal compressors and gas turbines. His work enables engineers to calculate bearing stiffness and damping coefficients, which in turn allow them to determine critical speeds and define the threshold at which a gas turbine or compressor becomes unstable. He also introduced an analytical method that treats each pad as a separate degree of freedom, enabling engineers to predict how the system would respond to vibrations. This enables engineers to safely push gas turbines and centrifugal compressors to higher speeds and loads. By early 1972, all compressor manufacturers had adopted tilting pad technology to prevent rotor instabilities, such as oil whip, following severe self-excited vibrations caused by inadequate bearing damping and destabilising forces in high-speed centrifugal compressors during the natural gas reinjection project at the North Sea Ekofisk field. The compressors discharged at 635 bar (considerable at the time), with a natural gas injection flow of 12.5 million cubic metres per day. Waukesha Flexure Pivot Thrust Bearing and combined journal and thrust bearings on the right (can reduce machine size)