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Resolving and preventing water hammer issues
With our expertise, decades of experience and high-end software solutions we partner up with our clients to prevent issues related to water hammer in piping. If water hammer problems have already occurred, we help solve those issues in the least invasive way possible.
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A pressure surge is an abrupt change of the pressure in a piping system, caused by a transient event such as a pump trip or a sudden valve opening / closure. Correct timing of valves, start-up of pumps or other measures are necessary to keep the pressure in a piping system in the acceptable range.
Overpressuring is a common mechanism for pipe failure. Surge pressures also generate shaking forces on the piping, proper supporting is required to ensure that the shaking forces can be accommodated by the piping. During a transient event low (vacuum) pressures may also occur. Large diameter, thin walled systems are prone to buckling, making them especially sensitive to sub-atmospheric pressures. This can happen to both metal piping and plastic or fiber reinforced plastic piping.
In a typical surge analysis study, we perform steady state and transient calculations for the most critical scenarios. Following discussion with the client the water hamer scenarios critical for the piping system be selected by our water hammer engineers.
Typical transient events that cause pressure surges are:
valve operations (closing or opening control valves),
tripping or starting a pump (including impact of check valves),
failure of equipment (heat exchangers),
the rapid opening of fire hydrant or monitors.
After presenting the surge analysis results with the client, realistic mitigations will be proposed to improve the systems reliability, safety or to improve the systems performance. Typical mitigations include careful timing of valve operation but also the implementation of re-routes or pressure suppression devices (i.e. surge vessels or air valves).
There are several issues that can arise in the piping system due to pressure surges. These include:
High pressures can cause permanent deformation or rupture of the pipeline.
Low pressures could cause the total collapse (buckling) of the pipeline or leakage at joints and seals.
Cavitation and column separation. When the pressure drops below the vapor pressure, cavitation and column separation can cause high pressure peaks.
Reverse flow can be the result of surge pressures and lead to damaging the pump seals and brush gear on motors. This could also lead to draining of storage tanks and reservoirs.
Low flow velocity is a realistic problem that occurs in slurry lines, causing settlement of entrained solids and line blockage.
Large unbalanced loads are the result of the travelling surge pressure. These excessive loads could cause issues on flanges and nozzle connections, i.e. pumps, tanks, equipment.
Vibrations and pipeline movement of the mechanical structures can cause high cycle fatigue issues with pipe supports or the pipe itself.
Should the outcome of the surge analysis reveal potential risks to the operation of the system, DRG helps to develop measures to mitigate these risks. This in close cooperation with the clients to ensure safe operation of the respective piping system, using realistic and implementable measures to reduce the impact of pressure surge and water hammer to an acceptable level. The mitigations include the implementation of surge vessels, vacuum breakers, air valves, changing valve closure or opening times or even re-routing the piping layout. In close cooperation with the client, the mitigations will be evaluated within the time and cost constraints imposed.