REDUCING SOLID PARTICLE EROSION ON STEAM TURBINE STAGES

Solid Particle Erosion (SPE) damage can be found on steam turbine stages. These solid particles are caused by the exfoliation of iron oxides formed on the inner surfaces of both boiler tubes and steam pipes which are exposed to elevated temperature. They can damage both fixed and Moving Blades, as well as both outer extension ring and tip seals. Severe SPE damages can be expensive for the utility industry due to reduced efficiency and lost power generation, as well as increased costs of repair or replacement of eroded components. Thus it is very important to understand this phenomenon and propose cost effective solutions to reduce the damage. This study investigates the effects of SPE damage using particle trajectory calculations. This investigation confirms that "Bounce Back" is the dominant cause for the SPE damage on both Fixed Blade trailing edge and Moving Blade leading edge. The particles do not accelerate at same speed as steam, therefore they travel much slower when they hit the Moving Blade leading edge. Then they are thrown back towards the Fixed Blade to hit the trailing edge. Due to strong centrifugal forces, the particles are also thrown radically outwards and damage both outer extension ring and tip seals. Based on these enhanced understandings, a practical solution is proposed to reduce SPE damage. It is predicted to have negligible impact on the stage performance. Evidence from the latest inspection demonstrates that this solution is very effective in reducing SPE damage to the Fixed Blade trailing edge.