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What is Water Hammer?
Water hammer (also commonly spelled as waterhammer) is a pressure surge or wave, which results from the fluid changing momentum (i.e., the fluid is forced to stop or change direction). The system response is acoustic in nature, rather than an inertial response, and therefore much more rapid (milliseconds to seconds rather than seconds to tens of seconds in duration). The pressure surge or wave propagates throughout the entire piping network, including through valves, orifices, and might cause hydrodynamic loads (forces) that result in supports damage. The transient might be dynamic enough to also damage system components, e.g. relief valves, check valves, pumps, filters, and even the piping itself. Water hammer is a common phenomenon that could occur in any industry which deals with flowing or pressurized fluids, including municipal water systems, power generating plants, and oil, gas, and chemical systems. As an example, a fire water system might undergo a water hammer when the fire water pump is started to fill a voided system to deliver suppression. Should the system be started inadvertently with an isolated path, the accelerating fluid might then be rapidly brought to rest thus resulting in a water hammer. Another common example is the closure of a valve in an extensive piping network that extends hundreds or thousands of feet. The closure of the valve brings the system to rest, and if the valve closure time is shorter than the system‘s acoustic response time, water hammer will likely result on both the downstream and upstream sides of the valve. The downstream side will experience column separation and rejoining, and the upstream side will undergo column stagnation. In the nuclear industry, the US Nuclear Regulatory Commission (NRC) stressed the importance of water hammer by issuing Generic Letters 96-06 and 08-01, which require the US nuclear power plants to evaluate their systems for potential steam and non-condensable gas water hammers, respectively.
Why is it important?
Another acoustic event for a piping system is a postulated pipe break. It is assumed that the pipe ruptures by either fully separating (commonly referred to as a guillotine break) or a large opening forming on the side of the pipe, e.g. fish mouth type of opening. This type of transient is less likely compared to a water hammer, but important to consider in a system’s design. If a pipe rupture occurs, a decompression wave is generated inside the piping system. As this wave propagates inside the system at the speed of sound, it generates hydrodynamic loads that act on the piping. Such an event is especially important for industries that support power generation, such as the oil and gas suppliers, or the power plants themselves. A ruptured pipe would result in a disruption in the fuel supply and a loss in power generation, thus resulting in heavy financial losses. A rupture at a power plant would also result in a power generation disruption, which is a credible scenario for any power plant. In the nuclear industry, this even is commonly referred to as a LOCA (Loss-of-Coolant Accident). Thus, it is important to design systems that will undergo minimal damage should such an event occur.
JENSEN HUGHES has provided water hammer services to many domestic and international power plant utilities, municipal water distribution system suppliers, water filter manufacturers, and oil, gas, and petroleum companies. These services included the evaluation of potential or existing water hammer events, including unique solutions to reduce the effects of water hammer.
JENSEN HUGHES is dedicated to providing an engineered, performance-based approach towards water hammer and fluid decompression problems. Our team is built with top experts in the subjects of thermal-hydraulics and structural engineering. Our engineers can analyze the fluid and structural transient responses of your system and design mitigation solutions or identify the limited window of operation.
- Generate hydrodynamic loads as a consequence of water hammer or fluid decompression events
- Evaluate piping and supports with respect to applicable structural codes
- Design solutions to mitigate the water hammer events, or identify operating limitations