Should we consider friction on the very first piping support from the nozzle while analyzing a rotating system(Like pump suction & Discharge line)?.

Our project specification says we can ignore friction on the very first support.In my opinion, this may be because vibration can overcome friction very quickly.Or should we use teflon pad on the very first support to reduce frictional load on the nozzle?.

Saneh Gupta
Piping Stress Engineer
Fluor India,New Delhi

Saneh,

I too, ignore friction and the first pump support unless the load is heavy and the movement significant. Friction is a transient condition that occurs only while the pipe heats up and while it cools down.

Let me advise of a commom mis-understanding about pump analysis using friction. A lot of wannabe stress engineers think pump analysis that includes friction is conservative and if the pumps qualify with friction then it's OK. Make sure you analyse your pumps both WITH and WITHOUT friction. While friction will increase the forces on the pump nozzles, it will also many times decrease the moments at the nozzles as well. The moments are the killers, so qualify the pump loads both ways.

Good Luck,

Agree 110% with Mr. Monroe!!! Well said!!!! This is easily accomplished at the load case level....