When a steady-state fluid flow is at rest all the forces in a piping system at equilibrium and there will be no net forces moving the pipe. Transients that disturb the flow induced by valve operation, pump trips or failure of equipment cause changes in the system pressure and velocity. One consequence may be excessive surge pressures. Without careful timing of valves surge pressures can easily reach ten’s of bars. For fiberglass systems such overpressure may cause the pipe to fail, especially joints and flanges are sensitive for overpressure. During a transient event low pressures may also occur. Large diameter fiberglass systems are especially sensitive to low or sub-atmospheric pressures as they may buckle. Possible mitigation measures for non-vacuum resistant piping are changes to how the system is operated or the introduction of adequately sized buckling rings.
Another sometimes overlooked consequence of transients is that the changes in pressure will move through the system causing unbalanced forces, also known as water hammer. Proper supporting must be in place to minimize the effect of the water hammer forces.