Fluid film bearings provide critical support for the rotors in gas turbines, steam turbines, generators, exciters and other machines through the generation and support of a hydrodynamic film. Industrial bearings are lined with a babbitt material which serves as a sacrificial element during operation and may need to be refurbished depending on the past operating and maintenance history. After inspection, engineering judgment is typically used during a machine overhaul to determine whether a bearing requires refurbishment. This engineering judgment is developed through an understanding of the principals of bearing design, machine operation, machine monitoring and babbitt wear / damage characteristics. This paper describes the criteria to serve as a basis for a decision support tool relative to the refurbishment of a babbitted, fluid-film bearing. Those criteria start with key descriptors of any damage to the bearing and evaluate the remaining load capacity, repairability, bearing support, rotordynamics influence, journal conditions and pivot conditions. The descriptors focus on visual examinations of the condition of the babbitt and seek to be intuitive, yet remaining comprehensive; to this end a graphical interface is used where feasible.
Evaluations include specific load capacity calculations, determination of damage factors for the principal modes of babbitt damage and data from lookup tables whose input is based on experience. These evaluations are combined to provide the basis for the refurbishment decision. Scaling efforts are incorporated into the evaluations to allow their combination into a single bearing condition index. Initial experience suggests that discrete ranges of the bearing condition index are preferable to numerical value.
One goal of the tool is to allow use by inexperienced engineers as a support to their technical development. Another goal is to better document the decision process for particular bearings. The preliminary tool was applied to a cylindrical, radial bearing in a horizontal orientation and to a bumper thrust bearing. Initial results have confirmed the general strategy employed and have suggested areas requiring refinement.
