Abstract
Abstract Super heater tubes and outlet headers are subjected to thermal fatigue from alternating heating and cooling during start up and shut down, causing cracks and eventually failure. Super heater tubes are subjected to a temperature of 600 °C and steam at a temperature of 540 °C and a pressure of 160 bar. In this paper, a laboratory simulation for reproducing thermal fatigue phenomena was developed to determine the number of cycles before failure occurs in a header tube to stub welded joint. For this purpose a carbon steel tube (stub) welded to a carbon steel plate which resembles a header pipe to stub welded joint was subjected to thermal cycles from 800 °C (accelerated test) to room temperature. A tungsten inert gas arc was used as a heating source and a water bath was utilized for quenching. After 300 thermal cycles, the cross-section of the header was subjected to optical microscopy. Micro fissures were observed in the header tube. This study reveals that subsequent localized heating and cooling will cause thermal fatigue, which will initiate and propagate cracks in the tubes.
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