IEC 62364-2019 pdf free.Hydraulic machines – Guidelines for dealing with hydro-abrasive erosion in kaplan,francis, and pelton turbines.
The following guidelines explain some recommended methods to minimize hydro-abrasiveerosion and the effects thereof, by modifying the design for clean water.
lt should be understood that every design of a hydro powerplant is a compromise betweenseveral requirements. While it is possible to design a unit to be more resistant against hydro-abrasive erosion this may adversely affect other aspects of the turbine.Some examples are:
thicker runner blades may result in decreased efficiency and increased risk of vibrations from von Karmn vortices;
fewer runner blades (in order to improve the access to the blade surfaces for thermalspray surface treatment) may result in reduced cavitation performance;
coatings against hydro-abrasive erosion may initially result in increased surfaceroughness,which may reduce the efficiency. The initially increased surface roughnessmay be reduced due to the polishing effect of operating with particle laden water. Ofcourse,over time the coated turbine will maintain a higher efficiency compared to theuncoated turbine;
reduced runner blade overhang may result in reduced cavitation performance, which inturn may reduce the output that can be achieved for a turbine upgrade;
many design features to reduce the impact of a high particle concentration will increasethe total cost of the power house.
The optimum combination of design features to reduce the impact of a high particleconcentration should be considered and selected for each site based on its specificconditions, taking the economic impact for the lifetime of the powerplant into account.
As a general rule for the design, the area exposed to the abrasive water should be as smallas possible.Discontinuities and sharp transitions or direction change of the flow should alsobe avoided.
4.2 Selection of materials with high resistance to hydro-abrasive erosion and coating
The selection of materials and possible coatings with high resistance to hydro-abrasiveerosion is important.See also Clause 6.
Because corrosion would increase the hydro-abrasive erosion rate,stainless steel is thepreferred selection.Weldable stainless steel materials are preferred.
ln case coatings resistant to hydro-abrasive erosion are not applied in the beginning, it isrecommended to make a hydraulic and mechanical component design where such coatingscan easily be applied at a later stage.
Labyrinth seals made of aluminium bronze have in general lower resistance against hydro-abrasive erosion than stainless steel.There are also examples with relative good behaviour oflabyrinth seals made of aluminium bronze.
4.3 Stainless steel overlays
Stainless steel welded overlays with sufficient thickness may be used instead of solidstainless steel components, if the cost of the overlay welding is lower than the cost of solidstainless steel components.IEC 62364 pdf download.