Effect of flue gas constituents on boiler tube failure of a captive power plant

Water leakage was reported from one of the superheater tubes of the boiler during operation. The power plant is a part of the copper ore smelting and refining industry. It was observed, that the leakage took place through a cracked region of the tube, which was severely damaged due to a chemical attack. Damage occurred due to a reaction between the flue gas and the outer wall of the superheater tube. Inefficient treatment of flue gas resulted in the retention of metal particles, SO2 gas, and particulate within the same in substantial concentration. When the same flue gas was used in the boiler, SO2 reacted with the tube surface at elevated temperatures. The incident led to wall thinning and
deep pit formation over the tube surface. Metal particles were fused, adhered to the tube surface, and
triggered secondary cracking during operation. Gradual wall thinning, increment in pit size, and crack propagation through thickness resulted in the ultimate failure of tube material.