AWWA INF55776

This paper describes an American Water Works Association Research Foundation funded research project "Circumferential Failures in Grey Cast Iron Distribution Pipes" currently underway at the National Research Council Canada (NRC) to investigate circumferential failures under a wide variety of loading and soil conditions. It combines mechanical testing of pipe coupons, experimental measurements of pipes in bending using the neutron diffraction method and finite element modeling. Neutron diffraction can measure the strain distribution around a corrosion pit in a pipe that is in bending, while finite element modeling can be used to determine how changing soil and loading conditions affect pipe failures. Combining the two techniques gives the potential to produce an accurate understanding of the conditions that cause circumferential failures and to determine when a corrosion pit becomes a threat to the integrity of a water pipe. The project involves three different phases: uniaxial mechanical testing of coupons taken from pipe samples, neutron diffraction measurements on pipe samples in bending and finite element modeling. The uniaxial mechanical testing is intended to provide appropriate stress-strain curves and Poisson's ratio data for the cast iron pipe samples used in the project for use as inputs to the finite element modeling phase. Section 3 of this paper describes results from the mechanical testing phase. The neutron diffraction measurements show the strains in bent sections of pipe as well as whole pipe sections. These measurements will be used to provide a check on the validity of the finite element models and to ensure that the mechanical behavior of grey cast iron in the triaxial stress states found in bending pipes is fully undertstood. The finite element models will need to duplicate the experimentally observed behavior before modeling of pipes in soil begins. Section 4 shows some of the first neutron diffraction results from the project. Finally, future work on finite element modeling will investigate the interaction between the pipes, corrosion pits and the surrounding environmental conditions. It should provide guidance on the potential for premature pipe failure due to corrosion pits of different sizes and dimensions. Includes 15 references, figures.