Industrial Maintenance Solutions

By Kyle Brandenburg. Steam turbines provide an efficient means of producing electricity. Improving the corro s ion fatigue performance and damage tolerance of steam turbine blades can offer overhaul and maintenance cost savings improved reliability and reduced outages. The application of surface residual compressive stress to components can enhance fatigue strength and reduce the effects of applied tensile stresses. Shot peening has been used for decades to reduce overall operating tensile stresses in steam turbine components. However, corrosion pits, erosion, fretting, and other damage can penetrate shot peening’s shallow layer of residual compression, providing a starting point for stress corrosion cracking and fatigue failures. Instead of settling for shallow compression, the introduction of a deep layer of compressive residual stress can extend service life . To test the benefits of deep compression , high-cycle fatigue tests were done on Type 410 stainless steel ,...

In recognition of the possibility of static charge build up in condensing steam turbines, API 612 (2005) specifies that grounding brushes be installed. The electrical flow to ground through these brushes  be monitored and useful information can be extracted. This article carries excerpts from the paper, “Babbitted bearing health assessment” by John K Whalen of John Crane, Thomas D Hess of Chestnut Run, Jim Allen of Nova Chemicals and Jack Craighton of Schneider Electric. Grounding brushes take current from the rotor to ground so that a charge does not build up on the rotor to the point where it discharges to ground though the best path possible – which is usually the closest point between the rotor and stator which is usually (hopefully) the point of minimum film thickness in a bearing. Typically this point of minimum film thickness is found in the active thrust bearing (as will be shown later). Shaft grounding brushes serve two purposes. The brushes are able to transmit modest amo...