Safety Evaluation of Branch Pipe in Hydropower Station Using Elastic Modulus Reduction Method

The high pressure branch pipe in hydropower station (BPHS) is usually composed by different materials in different parts and has complicated geometric configurations. The accurate and efficient methods for safety evaluation of the BPHS are still desirable. By introducing the element bearing ratio (EBR), generalized yield criterion as well as the reference volume concept, the elastic modulus reduction method (EMRM) is improved and applied to determine both the upper and lower bounds on limit loads of the BPHS. The global safety factor (GSF) is defined as the ratio of limit load to design load. The safety performance of the BPHS is assessed by comparing the GSF resulted from the EMRM with its allowable value specified in code. The efficiency and precision of the proposed method for safety evaluation of the BPHS are demonstrated through numerical examples in this paper. The results show that the proposed method is more suitable for safety evaluation and design optimization of the BPHS, compared with the elastic stress analysis method (ESAM) based on stress categorization which might underestimate the safety performance of the BPHS.