Parikshit Munda

Failure Investigation of Boiler Water Wall Tubes of a Thermal Power Station

AbstractFailure investigation was carried out on boiler water wall tubes of a thermal power plant through visual inspection, chemical analysis, and metallurgical analysis. Failure was in the form of thin/micro cracks along the length of the tubes which were located at the girth welding joint of tubes. Experimental results revealed that the cracking was from inward to outward of the tube thickness. Discontinuities/cavities were observed in the welded region which might have occurred due to lack of fusion of base metal and the weld metal. Cracks were initiated from the sharp corner/crack tip of the cavities/discontinuities present at the welded region under the action of hoop/thermal stress existed during the operation. Nature of the crack propagation indicates the case of typical hydrogen-induced cracking. Moreover, the presence of the cavities/discontinuities reduced the cross-sectional area of tubes resulting increased stress intensity. Increased stress beyond the flow stress of the material assisted by hydrogen-induced effect resulted the cracking of the tubes. In order to mitigate the problem, proper welding of tubes joints should be carried out followed by proper inspection after weld. Secondly, hydrogen dissolution during welding should be prevented and treatment for its removal after welding should be carried out.

Failure Analysis of SA213-T22 Re-heater Rear Tube of Thermal Power Plant

SA213-T22 steel had been widely used in petrochemical and power generation plants. But due to prolonged service exposure in various conditions, these tubes have been ageing continuously and deteriorations of the materials cannot be avoided. This paper presents a case study of SA213 type-T22 alloy steel reheater tube that failed in a boiler of a power plant. The failed tube was investigated through visual examination, mechanical properties evaluation, and microstructural analysis to find the root cause of failure. The tube was found to fail by long term over-heating due to formation of thick oxide scale formation leading to creep.

Evolution of Microstructure During Short-term Overheating Failure of a Boiler Water Wall Tube Made of Carbon Steel

This paper highlights the evolution of different microstructures during short-term overheating failure of a boiler water wall tube made of SA210 Grade C steel. Short-term overheating failure of the boiler tube caused fish mouth rupture with thin lips, along the longitudinal direction of the tube with extensive tube bulging. Microstructure examination revealed elongation of grains at the fracture signifying plastic deformation due to hoop stress becoming equal to the flow stress of the tube at the elevated temperature. Overheating caused degeneration of the initial ferrite–pearlite microstructure. Spheroidization and coalescence of carbides occurred in the ferrite matrix from the initial ferrite–pearlite microstructure of the boiler tube near the ruptured region. Moreover, the formation of bainite microstructure at the fracture fish mouth opening indicates heating above the eutectoid temperature (lower critical temperature) of the tube material.