A failure analysis of exhaust systems for naval gas turbines. Part I: Fatigue life assessment

Cracks nucleated and propagated through the wall thickness of naval gas turbine's exhaust systems. Each exhaust system was manufactured with AISI 316L stainless steel grade type, supplied in the annealed condition and rolled in plates with 3.8 mm thickness, which were bent and welded by MIG/MAG weld process. The main cracks propagated, along the circumferential direction, from the weld toe of some butt and fillet welded joints located near the lower supporting ring, where the measured temperature was about 350 degrees C. The exhaust system studied has more than 8 m height and the cross sections dimensions vary from 1.5 x 1 m at the inlet section to 2.5 x 2 m at the outlet section, approximately. Its typical service temperatures ranges from 500 degrees C at the inlet section to nearly 200 degrees C at the exit. Based on the stress spectra measured in service and on the fatigue crack growth rates of the material, the paper presents a fatigue life assessment for the exhaust systems studied. The likelihood to occur instantaneous and unstable fracture was also studied and is included in the paper. (C) 2008 Elsevier Ltd. All rights reserved.