Severe fracture of impeller had successively occurred in slurry-recirculating pumps equipped for the Absorption tower of lime-stone/gypsum wet flue gas desulphurization(FGD) system for boilers of 600 MW units NO.1 and NO.2 in Shanwei Power Plant.Through metallographic examination

chemical composition analysis

and hardness test etc.

it is believed that the cause leading to base corrosion of impeller blades is the low pH value of slurry from the Absorption tower

reducing the strength of impeller.In addition

the abrasion of slurry further accelerates the fracture of impeller.For this

it is recommented to control the pH value of slurry from the Absorption tower

eliminating cavitation phenomenon in the pumps

selecting materials with high strength

high toughness

and strong corrosion-resisting property for manufacturing the impeller

as well as the rotational speed of pumps should be designed within 450~530 r/min.