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2016 04 baboo NFL Causes and prevention for steam turbine blade scaling & fouling

Although several factors influence the formation of deposits on turbine components, the general effect is the same no matter what the cause. Adherent deposits form in the steam passage, distorting the original shape of turbine nozzles and blades. These deposits, often rough or uneven at the surface, increase resistance to the flow of steam. Distortion of steam passages alters steam velocities and pressure drops, reducing the capacity and efficiency of the turbine. Where conditions are severe, deposits can cause excessive rotor thrust. Uneven deposition can unbalance the turbine rotor, causing vibration problems. When a turbine becomes fouled with water-soluble salts as a result of boiler water carryover or attemperating water contamination, turbine capacity can often be restored by water washing. Because it can cause severe turbine damage, water washing should be supervised carefully and the recommendations of the turbine vendor should be followed. When the turbine becomes fouled with compounds that are not water-soluble (including silica), water washing rarely restores capacity. Out-of-service cleaning by blasting with aluminum oxide or other soft grit material is required to remove these deposits. This paper is about major steam turbine problems causes and effects.

 

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