RESOLVING ISSUES AND FAILURES OF DIAPHRAGMS IN TURBINES

Diaphragms are used in steam turbines to regulate the flow of the steam to the rotating blades. The regulation or the change of flow direction is to increase the efficiency of the turbine. Though diaphragms are non- rotating parts, they may experience elevated temperature and they may also be subjected to high stress and or cyclic stresses during service. As a result, they may develop failures and other issues due to long term service. The vanes of the diaphragms may develop cracks and the diaphragms may develop dishing which is generally a result of creep deformation resulting from long term service at elevated temperature. This paper discusses different types of diaphragms and their fabrication methods first. The fabrication of the diaphragm involves casting or machining of vanes. Then these vanes or vane segments are welded to the inner and outer rings to make the rigid diaphragms. Then some of the common failures and issues these diaphragms see in their service will be discussed. These will be illustrated with some recent field examples. This will be followed by some approaches to mitigate the risk of these failures and issues.