Analysis of a Failed Primary Superheater Tube and Life Assessment in a Coal-Fired Powerplant
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The paper presents results of failure analysis of a primary superheater tube in a steam powerplant boiler. The boiler has been in service for around 52,000 h (6 years) and failure occurred on one of the primary superheater tubes in the form of a wide-open burst with appreciable wall thinning. The location of failure was first determined by on-site visual examination. Subsequently, specimens were taken from a region near the fracture surface for chemical analysis, microstructural examination using optical microscopy, and scanning electron microscopy equipped with energy-dispersive X-ray analysis to determine the probable cause of failure; whereas the lifetime of the superheater tubes was assessed using stress rupture test. Results suggest that the cause of failure was overheating due to deposit buildup inside the superheater tube which acted as thermal barrier and wall thinning resulted from direct impingement of flue gases. The lifetime of the superheater tubes is estimated and is discussed in the present investigation.
KeywordsBoiler material Fish mouth fracture Stress rupture
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