Method for preventing cracks of runner blade of mixed-flow water turbine

Abstract

The invention discloses a method for preventing cracks of a runner blade of a mixed-flow water turbine. The method includes the following steps: A, for different dynamic stress conditions of surface opening defects and internal defects, drawing a relation curve of maximum allowable equivalent defect size and static stress; B, according to the stress level, dividing the water outlet edge of the runner blade into several different areas, and searching the maximum allowable equivalent defect size in the relation curve in the step A according to maximum static stress and dynamic stress; C, performing nondestructive inspection on each area of the water outlet edge of the runner blade, finding out the surface opening defects or internal defects larger than the maximum allowable equivalent defect size of each area, and repairing the defects. By the method, the size of the allowable defects of key areas of the blade is determined according to fracture mechanics and failure analysis and based on combination of working stress of a target runner, so that quality requirements of the key areas are guaranteed effectively, and cracks are avoided during operation of the runner blade of the mixed-flow water turbine.

Description

technical field [0001] The invention relates to the technical field of water turbines, in particular to a method for avoiding cracks in the running process of runner blades of a Francis water turbine due to defects in key areas. Background technique [0002] In the same industry at home and abroad, the current inspection standards for runner castings (including upper crowns, lower rings, and blades) are mainly implemented in accordance with CCH70-3 inspection specifications for steel castings for hydraulic machinery. The specification proposes a concept of "Quality Inspection Sheet (QS means Quality Sheet)". In QS, components are divided into different areas according to the stress level and importance, and different levels of non-destructive testing measures are implemented for different areas. However, the specification has too loose requirements on the inspection of the runner blades, especially for the critical area where the outlet edge of the runner blades is located,...

AI Technical Summary

Problems solved by technology

However, the standard has too loose requirements for the inspection of the runner blades, especially for the key areas where the runner blades are located at the water edge, and even does not require ultrasonic testing (UT)

Practice has shown that even if you choose a higher level of acceptance in this specification, you still cannot guarantee the quality requirements of the blades, and cracks will still appear in the blades that pass the inspection during operation.

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