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Surge pressures, line-pack and pack-in all cause high pressure problems on pipelines and can also impose forces that can lead to failure. These transient changes are frequently caused by valves but can also be caused by pump start-up and shutdown.
Less commonly, surge pressures are caused by NRV or air valve/vents. The analysis of these transient events is stipulated on most industry standards.
Problems are common on liquid pipelines, but can also occur on multi-phase and gas pipelines as well.
These pressure changes cannot be studied by standard (steady-state) methods and programs, so specialist simulation and surge programs are needed to quantify the maximum and minimum pressures that can occur due to start-up and shutdown.
Many remedial techniques can be used to surpass surge pressures and to control line-pack and pack-in. Each of these remedial techniques can be specified using the surge analysis programs and considerable cost saving can be achieved by this type of specification process.
Statistically, high pressures cause more frequent problems on pipelines. But Start-up and shutdown can also cause low pressures (down to the vapour pressure of the fluid being transported) and this can also cause structural problems and can collapse some pipes.
Start-up into a low pressure system is one cause of a major problem that is called ‘vapour collapse’ which creates high transient pressures and forces that invariably cause problems.
On operating system the frequency of shutdown, the frequency of damage to equipment and noticeable signs of pipe movement are all strong indication of sure/transient pressure problems.
