The programs may be used to simulate steady state and transient (unsteady) operations of liquid-carrying systems of pipes, valves, pumps, reservoirs, and surge control devices, some of which are discussed in the following section. With the advancement of computational efficiency and time, the models are capable of providing solutions in a reasonable time. Many computer models utilize this method to calculate transient pressure in a system. The most widely used technique for solving transient flow equations is the method of characteristics. The basis for any computer model to analyze a transient event in a fluid-carrying system is the numerical solution of the equations describing the conservation of mass and momentum. These one-dimensional models provide sectional average flow variables along the pipe length. Transient modeling softwares are commercially available for assessing the risk of transient pressure in a system. Provision of surge-control devices should be considered to mitigate the transient events. Therefore, a hydraulic transient analysis covering the possible operational scenarios is a critical component in finalizing a pipeline design. For example, it can be initiated by poor system operation such as rapid closure or opening of a system valve, can be caused during pump startup, or by pipe breaks, earthquakes, or wear and tear of system components. However, there are many incidents that can generate transient pressure in pipelines. Power trip is typically considered the most critical transient event that can occur in a pumping system. Many authors (e.g., Boulos et al., 2005 Chaudhry, 2014) have reported catastrophic failure of pipelines resulting from accidental transient events. However, the collapse of vapor cavities or rejoining of separated water columns can produce excessive high pressures leading to failure of pipes. The pipes are typically designed to withstand the full vacuum condition. Depending on the size of the leak, the volume of intrusion can range from a few gallons to hundreds of gallons. Depending on the magnitude, the negative pressure may reach the vacuum pressure, which has significant pipeline structural and water quality implications, as low pressure can rupture the pipe material and cause intrusion of contaminated surface water or groundwater into the pipe at a leaky joint or break (Thorley, 2004). As a result, the hydraulic grade line (HGL) of the pipeline drops from its initial position and at some locations may reach below the pipe centerline, thus creating negative pressure in the system. This creates a sudden drop in pressure downstream of the pumps, and the pressure wave propagates in the pipeline back and forth until it reaches a steady state. If a power outage happens, the pumps stop instantaneously, resulting in zero flow with the check valve closure. As shown, pumps are withdrawing water from a reservoir and conveying it through a pipeline to a reservoir at a higher elevation. These events occur in a very short period of time but have the potential to cause significant damage to pipelines.Ĭonsider the example of a pumping system presented in Figure 1. Sudden change in flow at a point in a system creates a corresponding change in water pressure, commonly termed as hydraulic transients or water hammer. Is water hammer pounding your pipeline infrastructure into submission? Here are some tips for avoiding issues associated with hydraulic transients.įlow conditions in a pipeline can be disrupted by many reasons, such as operational mistakes, poor maintenance, faulty instruments, emergency situations, etc.
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