Vibration of the recycle piping system on the Main Oil Line (MOL) Export Pumps from a platform in the North Sea raised concern about pipe breakage due to fatigue. Failures had already occurred in associated small bore piping and the instrument air supply lines and control accessories on the recycle flow control valves. Concern also existed due to the vibration of non-flowing pipe work and systems such as the deck structure, cable trays and other instrumentation, which included fire and gas detection systems. Many changes involving bracing of small bore attachments, stiffening of supports, adding supports and stiffing the deck structure were implemented without resolving the problem. The vibration was finally solved by adding enough pressure stages to assure the valve trim exit velcoities and energy levels were reduced to levels demonstrated historically as needed in severe service applications. This vibration energy reduction was more than 16 times. This was achieved by reducing the valve trim exit velocity from peaks of 74 m/s to 12 m/s (240 ft/s to 40 ft/s).

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