Fundamentals of Pressure Surge

An important consideration in the design of single-liquid-phase pipelines is pressure surge, also known as water hammer. Typical surge events in a pipeline or piping system are generally caused by a pump shutdown or a valve closure. The kinetic energy of flow is converted to pressure energy. The velocity of the pressure wave propagation is determined by fluid and pipeline characteristics.

Typical propagation velocities range from 1100 ft/s for propane/butane pipelines to 3300 ft/s for crude oil pipelines and up to 4200 ft/s for heavy-wall steel water pipelines. A rough estimate of the total transient pressure in a pipeline/piping

system following a surge event can be obtained from the following equations:
Typical propagation velocities range
The surge pressure wave travels upstream and is reflected downstream, oscillating back and forth until its energy is dissipated in pipe wall friction. The amplitude of the surge wave, or the magnitude of the pressure surge Psurge, is a function of the change in velocity and the steepness of the wave front and is the inverse of the time it took to generate the wave:
Function fo the change in velocity and the steepness

Pressure Surge Analysis

Surge analysis should be performed during a project’s early design and planning phases. This analysis will help to ensure the achievement of an integrated and economical design. Surge analysis provides assurance that the selected pumps/compressors, drivers, control valves, sensors, and piping can function as an integrated system in accordance with a suitable control system philosophy. A surge analysis becomes mandatory when one repairs a ruptured pipeline/piping system to determine the source of the problem.

All long pipelines/piping systems designed for high flow velocities should be checked for possible surge pressures that could exceed the maximum allowable surge pressure (MASP) of the system piping or components. A long pipeline/piping system is defined as one that can experience significant changes in flow velocity within the critical period. By this definition, a long pipeline/piping system may be 1500 ft long or 800 miles long.

A steady-state design cannot properly reflect system operation during a surge event. On one project in which a loading hose at a tanker loading system in the North Sea normally operated at 25 to 50 psig, a motoroperated valve at the tanker manifold malfunctioned and closed during tanker loading. The loading hose, which had a pressure rating of 225 psig, ruptured. Surge pressure simulation showed that the hydraulic transient pressure exceeded 550 psig. Severe surge problems can be mitigated through the use of quick-acting relief valves, tanks, and gas-filled surge bottles, but these facilities are expensive single-purpose devices.

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