Failure analysis of turbo-blower blades

Twelve percent chromium martensitic stainless steel blades of the medium-pressure stage of a thermoelectric centre turbo-blower broke during use. The present work will investigate the possible causes for the premature failure of these blades and the condition of the high-pressure blades. The results indicated that at least one of the blades of the medium-pressure stage failed by a corrosion-fatigue mechanism, whose nucleation was associated with the presence of corrosion pits on its suction side. The high-pressure blades presented hardness bellow the specification and presence of corrosion pits and cracks. The softening of the microstructure (from 250 to 220 HV) could not be explained by microstructural instability during the intermittent use of the blade, indicating that either the material was initially tempered at a higher temperature or that the working temperature is higher than the predicted. A rough and conservative estimation of the residual life of the high-pressure blades indicated that the high-pressure blades should also replaced. The quality of the feed water (from the sea) used for the production of the vapour should be optimised and any action taken to improve the cleanliness and dryness of the equipment during its intermittent use may improve the life of the blades.