Dear experts,

I am doing a stress analysis for existing pipe from HP stripper to pool condenser inter connecting piping. In this existing line they are provided four flanges and here the flange gets leakage and the bolts & nuts gets loosened frequently at the time of shut down and start up condition.

The plant has been installed in 2002. The service of the pipe is ammonia and carbon dioxide supply ammonia feed. The line has a design temperature of 150 deg C and pressure 220kg/cm2.g. The pipe is A312 TP316L Seamless pipe, flanges are A182 F316L, Bolts are A193 B8M & gasket is SS 316L and flange rating is 2500#.

We have checked the flange leakage for above materials, and found ok. Kindly advice me is there any other causes for flange leakage. There is no vibration in these lines during operation time.