Damage analysis of the forced draft fan blade in coal fired power plant

The Forced Draft Fan (FDF) blade in a 300 MW coal fired power plant that experienced catastrophic failure has been investigated. There were two main locations of the blade damage, namely damage at the root of the blade and the other one is at the third of the blade height. The FDF blade has been run for 5 years and before its failure, the FDF experienced high vibration (14 mm/s). The forced draft fan is an axial flow fan horizontally in front of the boiler and the fan is single stage. Visual inspection, metallographic analysis, chemical composition and hardness test were carried out to find the cause of the failure. It is concluded that the material of the blade is cast Al-Si alloy (A356.0) that fits the requirements for FDF blade application, the failure of the third of the blade height is owing to the external particles collide to the leading edge of the blades causing erosion and notch. That notch acted as initial crack. The failure at the root blade was caused by broken fragments of the others damaged blades entered in between casing (stator) and the blade (rotor) so they obstructed the blade rotation.