Root Cause Analysis of Steam Turbine Blade Failure

In a 110 MW unit of a fossil fuel power plant operated in western part of India, low pressure turbine 3A stage blades failed prematurely. The blades are made of X20Cr13 (tempered martensitic stainless steel) material. Since they failed prematurely, root cause analysis was sought. Failure investigation was carried out using various techniques such as visual examination, stereo microscopy, metallographic examination, Field Emission Scanning Electron Microscopic (FESEM) examination, etc., for identifying the root cause. It was observed that there was no evidence of degradation of blade material. The fracture took place at the profile region, 100 mm from the blade root. During stereomicroscopic and FESEM examination, several pits/grooves were found on the edge of the blade and chlorine was detected in these pits. The crack was originated from one of these pits on the thinner trailing section and then propagated towards the leading edge. Corrosion fatigue could be the primary reason for this failure. Detailed investigation is given in this work.