Brown, Norman
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Publication Slow Crack Growth-Notches-Pressurized Polyethylene Pipes(2007-11-01) Brown, NormanA general method for predicting the life time of a polyethylene structure that fails by slow crack growth was applied to the case of externally notched pressurized pipes. An analysis of experimental data indicated that the residual stress must be taken into account. The critical notch depths associated with a given life time were calculated as a function of pipe size, PENT value of the resin and temperature. The results were tabulated to serve as practical guide lines for deciding whether a pipe should be discarded if the notch is too deep. The current 10% of the thickness rule now used by industry was found to be invalid.Publication Intrinsic Lifetime of Polyethylene Pipelines(2007-04-01) Brown, NormanAn equation was developed for calculating the time to failure by slow crack growth (SCG) failure in any polyethylene structure. The equation requires the following experimental inputs: (1) the resistance to SCG as measured by the PENT test (ASTM F1473), (2) the stress intensity of the defect from which failure originates, and (3) the temperature. A simple experiment for determining the stress intensity is presented. The equation was applied to SCG failures that are associated with the inherent random defects that occur in the wall of all pipes. The size of the inherent random defect that exists in commercial gas pipes was found to be 0.14 mm.