Page 393 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

368 Surge Pressure Calculations
The critical time is the maximum flow stoppage time that will The designer must consider the effective closure time as
still allow the maximum surge pressure. Flow stoppage times opposed to the actual closure time.
that are higher than this value produce smaller surge pressures. Pressure surges may be caused by valve closures, pumps
This critical time is dependent on the piping configuration starting or stopping, the sudden meeting of fluid columns mov-
because the reflection time from the initiating event governs the ing at different velocities, or other phenomena that abruptly
calculation. change the velocity of the pipe fluid. Many design options are
It is important to note that, in the case of valve closures, the available that allow for pressure surge effects including relief
flow stopping is not necessarily proportional to the actual valves, surge tanks, valve closure controls, pump bypasses, and
amount ofclosure. A gate valve, for instance, may cause 90% of use of stronger pipe at critical sections.
the flow stoppage within the last 10 to 50% of the gate travel.