Water hammer effects on a gray cast iron water network after adding pumps

A numerical model was developed to simulate the propagation of pressure waves in water gray cast iron pipe systems in the presence of pumps. The pressure waves are caused by the water hammer phenomenon due to fast valve maneuvers in the pipe network. The mathematical formulation of the present model is based on a system of two partial differential equations of hyperbolic type. This system was solved by the method of characteristics. The constructed numeric algorithm permits to follow the propagation of pressure waves. It provides the damping of the water hammer waves in the network taking into account the effect of reflection and refraction phenomena to the passage of junctions, bifurcations and change of conducts characteristics. The numerical algorithm sustains the maximum pressure values and; therefore, FEM ABAQUS simulation of gray cast iron pipes with a superficial defect gives the maximum stresses in the different network pipes. The severity of a corrosion crater defect was estimated by calculating the safety factor for the stress distribution at the tip of defects. It allows the acquisition of the applied notch intensity factor. To study the effects of the geometry defects, semi-elliptical defects are deemed to exist up to half the thickness of the pipe wall. To obtain the value of the safety factor, the results were fed into the assessment procedure for the structural integrity (SINTAP) which offers a Failure Assessment Diagram (FAD). Conventionally, it is considered that the risk of failure occurs if the safety factor is less than two. The study allows concluding that the entire network, studied after the addition of pumps, does not work in the security field and, therefore, requires the installation of control and protection systems against sudden pressure variations.