Cause Analysis on Fracture of Induced Draft Fan Blade of a Boiler

The blade of induced draft fan of a power plant boiler broke in service. The causes of blade fracture were analyzed by means of macroscopic observation, chemical composition analysis, tensile property test, metallographic examination and hardness test. The results show that the thick edge of the induced draft fan blade had a brittle and hard surfacing weld layer. The improper thermal spraying process on the surface of surfacing weld layer resulted in holes in the coating and the interface between the coating and the substrate, which reduced the strength and toughness of the coating and the bonding strength between the coating and the substrate. Under the action of wind pressure, scouring of fly ash and dust, vibration stress, the surface of blade coating or the interface between coating and substrate cracked, and cracks expanded to the inside of blade, resulting in the stress concentration on the thick edge notch of the blade, and the crack expanded to the thin edge of the blade, finally leading to the blade fracture.