Valve-Induced Piping Vibration

Abstract

While going through the startup process of a 600MMSCFD Gas Processing Plant, the piping downstream of a gas expander bypass valve and supporting structure was observed to be shaking abnormally. The shaking was significant enough that plant personnel limited the valve flow rate to well under the design capacity and at a level that limited the plant startup. The initial assumption was that the piping or the piping supports had been improperly designed. An investigation revealed no unusual looseness in the piping supports and no significant piping natural frequency at the observed vibration frequency. Further investigation revealed that the root cause of the problem was a flow-generated pulsation in the discharge of the bypass valve that excited the piping and structural supports. Changing the valve flow path and applied valve opening limits provided a temporary work-around that allowed the plant to operate at sufficient flow rates to complete the startup. Subsequent replacement of the valve with one using the same trim but with different gas flow path characteristics proved to be the ultimate solution to the problem.