Paper Title
Predicting Crack Initiation Time in Cast Iron Pump Casing with Finite Element Analysis

Cast iron pump casings are hydro pressure tested, to check leakage in the casing through casting defects; to ensure leak proof function of other components, before going for performance tests. The same pressure test is continued further to estimate the burst pressure for the casing. The damage accumulated in the pressure test is a kind of local phenomenon and plays a major role in estimating burst pressure strength. Available pump standards are specifying hydro test at 1.5 times the maximum allowable working pressure; but, no standard has indicated the rate of pressure application. In this paper, authors highlighted that the pressure gradient, with respect to time, is a key factor in initiating micro-cracks in the pump casing. We stipulated the theoretical relationship of pressure gradient and energy dissipation (product of stress and strain) and suggested the equation for time to crack initiation. We postulated the theoretical factor of safety based on energy dissipation. Practically, it is not possible to test every casing in the regular production. Hence, alternative method is required to assess reliability of casing. In this paper, Finite Element Analysis approach is used to predict and calculate crack initiation time. We obtained localised stress and strain and carried out calculations for total dissipated energy (σ*ε). Location of crack initiation predicted from Finite Element Analysis is matching with the crack initiation location in burst test conducted on pump casing. The crack propagation path is in line with the stress concentration pattern in the casing. Keywords- Dissipation energy, pressure Gradient, Stress Gradient, Strain Gradient, Factor of safety, crack initiation time, Finite Element Analysis