Leakage occurred in multiple electric gate valve flanges within a short time after the heating pipes were put into service in a power plant.The leakage still occurred frequently although some measures were taken

like pressure seal and flange replacement.To solve this problem

the CAESARⅡ2011software were applied to establish the stress calculation model for the heating pipes.Moreover

the equivalent stress and bending moment of the flange were calculated by the equivalent stress method and critical bending moment method.The results show the maximum primary and secondary stress of the pipeline were all within the permissible range

while the equivalent stress and bending moment of the flange exceeded the allowable value.On the basis of calculation and analysis

we can draw the conclusion that oversize axial force and external bending moment on the flange of piping layout were the ultimate reason for flanges leakage.After some measures were taken to increase the flexibility of the piping

such as adding the stopper support

modifying position of the fixed hanging bracket and changing the stopper support with no gap into with gap

the axial force and external bending moment were reduced

and no leakage occurred after one year's operation.