Failure analysis of an attemperator in a steam line of a boiler

Spray flow attemperator is used for controlling superheater outlet steam temperature in power house. The attemperator undergoes cyclic thermal load and pressure and is prone to failures associated with thermal fatigue cracking of its components and welds. This paper presents the investigation of such a failure in a power house. The investigation consists of visual inspection, chemical analysis, characterization of microstructures, energy dispersive spectroscopy, measurement of hardness and fractography. Multiple cracks are observed on the surface as well as on the weld joint of the spray nozzle dislodged from the attemperator. Fracture surface shows dull woody appearance which reveals striations during examination under scanning electron microscope. The material is found to be nickel based Inconel as obtained by chemical analysis. Microstructural examination exhibits transgranular/intergranular cracks. Presence of chromium carbide precipitations are observed inside the grains and along the grain boundaries. The investigation reveals that the component suffered from thermal fatigue and crack growth occurred under the combination of creep–fatigue.

► Attemperators in superheater steam line of boilers are prone to failures associated with thermal fatigue cracking.
► With increasing temperature and prolonged exposure, a combination of creep and thermal fatigue occur which is potentially more deleterious.
► The investigation consists of fractography, chemical analysis, characterization of microstructures, energy dispersive spectroscopy, and measurement of hardness profile.
► Fractography shows striations and microstructures reveal transgranular/intergranular cracks along with voids.
► Analyses of the results reveal that the component failed due to combined effect of creep and thermal fatigue.