Failure analysis of a steam generator superheater drain tube used in a dump

This paper analyses the failure of a superheater drain tube of a steam generator used in a dump to obtain energy from the biogas produced by organic waste. Chemical and microstructure analyses, together with microhardness measurements, have been performed in order to check any possible deviation from the material specification, finding as the only deviation significant increases in hardness in the failure section, suggesting that the failure section is located in the heat affected zone of a nearby weld. Also, the failure mechanism has been analysed by both visual and SEM inspection of the fracture surface, identifying fatigue as the major cause of the final failure, assisted by corrosion processes. The different areas found on the fracture surface suggest that fatigue processes were caused by the maintenance operation consisting of hitting (hammering) the collector tube to which the drain tube is joined. No evidence has been found in relation to any other anomalous operating conditions, such as overpressure or unexpected high temperatures. (C) 2009 Elsevier Ltd. All rights reserved.