Mechanical properties of an exhumed cast iron pipe material

Ali, Ismail (2017) Mechanical properties of an exhumed cast iron pipe material. Masters thesis, Memorial University of Newfoundland.

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Abstract

Cast iron is one of the most commonly used materials for municipal water mains. Although cast iron pipes are no longer used for new water mains, a significant portion of existing water mains are still cast iron. These aged cast iron pipes are undergoing deterioration and are susceptible to leakage and breakage. In this thesis, a deteriorating cast water main is investigated to understand the failure mechanism and to determine the mechanical properties of the material as a tool for the structural integrity assessment of existing pipes. A better understanding of pipe failure mechanisms can lead to a realistic evaluation of the strength of the pipes in the system, and hence of their current level of safety. A pipe segment exhumed after failure from the city of Mount Pearl in the province of Newfoundland and Labrador is investigated. The failure is apparently due to subcritical corrosion fatigue crack growth. Localized defects were observed over the pipe wall thickness through which water could penetrate, providing an environment conducive to stress corrosion cracking. Tensile tests were conducted at different rates of loading to examine the effects of loading rate. The ultimate tensile strengths of the specimens varied from around 150 MPa to around 200 MPa, which are independent of the rate of loading. However, the stress strain responses are dependent on the rate of loading. The Poisson’s ratio of the material is determined through the measurement of longitudinal and lateral strains. Single Edge Notch Beam (SENB) tests are conducted to examine the mechanical properties in bending and to determine the fracture toughness. Numerical analyses using the finite element method (FEM) conducted to evaluate the performance of determined mechanical parameters in simulating the test conditions.

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