Consulting Services/Expertise

Surge And Water Hammer Analysis

While often used interchangeably, water hammer and surge are not exactly the same. Water hammer relates to a sudden momentum change in the piping. Surge on the other hand is the slow-motion mass oscillation that results from a water hammer event or cavitation collapse caused by e.g. sudden valve closure. This pressure surge is accompanied by large pressure surges (waves) traveling through the piping system. Correct timing of valves, start-up of pumps, or other actions are necessary to keep the pressures in a piping system within the acceptable range.

Pipe rupture due to surge-related overpressure is a common failure mechanism for piping. The traveling surge pressures also generate shaking forces on the piping. Proper support is required to ensure that the piping can accommodate the shaking forces. During a transient event, the pressure may drop below atmospheric pressure. 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 as determined in consultation with the client. At DRG surge analyses are performed using our in-house developed, state-of-the-art, software solution BOSfluids. Examples of transient events that may cause pressure surges are control valve operation, the start or trip of a pump, failure of equipment, and the rapid opening of fire hydrants, sprinklers, or monitors.

After presenting the surge analysis results to the client, realistic mitigations will be proposed to improve the system’s reliability, and safety or to improve the system’s performance. Typical mitigations include careful timing of valve operation and implementing re-routes or pressure suppression devices like surge vessels or air valves. 

With our expertise, decades of experience, and high-end software solutions we partner up with our clients to prevent issues related to surge and water hammer in piping. If water hammer or surge problems have already occurred, we help solve those issues in the least invasive way possible.


State-of-the-art software

DRG is the developer of the state-of-the-art software solution BOSfluids. The surge analysis tool of choice.

+35 years of experience

Dynaflow has 35 years of experience doing water hammer and surge analyses and is a respected surge analysis training provider.


Loading lines are especially susceptible to water hammer due to the PERC or Powered Emergency Release Coupling and high flow rate. The PERC is located at the loading arm and allows the loading arm to quickly detach from the ship in case of excessive ship movement. To limit the amount of fluid lost, the PERC closes in the order of seconds.

The fast closure causes a sudden stoppage of fluid transport with a subsequent pressure surge. The fluid flow is now halted which requires the pumps to be tripped. Pressure increases at the loading arms may cause flow reversal and cavitation at the loading arms. The pressure wave, now at the location of the pumps, causes another flow reversal that may cause implosion of the cavitation bubbles at the loading arms. The implosion of cavitation bubbles typically generates larger pressure surges than valve closure.

With the surge analysis tool of choice, BOSfluids, the described scenarios can be captured in detail. We develop a 3D model of the loading system with the applicable pumps, valves, and other equipment. The exact scenarios are determined in close consultation with the client.

Possible outcomes of the analysis include large pressure surges with accompanying shaking forces. The primary pressure peak may cause pipe rupture whereas the traveling pressure wave causes shaking forces between elbow pairs. Excessive shaking forces may cause restraint failure, nozzle failure, or pipe failure.

Typical mitigation measures include surge vessels, vacuum breakers, air valves, changing valve closure or opening times or even re-routing the piping layout. 

Resultant shaking forces are then assessed in the piping analysis software, Caesar II, to verify that they can be accommodated by the piping and support arrangement.

surge analysis, LNG loading line, water hammer

Discover how we can support your Surge and Water Hammer Analysis related projects

Software Solutions For Surge And Water Hammer Analysis

Caesar II

DRG conducts piping flexibility assessments using the software Caesar II from Hexagon. Caesar II is used for both static and dynamic piping analyses. We have a thorough understanding of the software and are also an official Caesar II training provider for Hexagon. Caesar II is considered the industry standard for pipe stress analysis.


Our inhouse developed professional software solution BOSfluids is an interactive and visual software package for the simulation and analysis of fluid flow to determine the flow rates, pressures and unbalanced forces in piping systems. It is an effective tool to study the steady state and transient flow conditions and help you perform coupled fluid-structure analyses.

Learn more about BOSfluids