applied fracture mechanics

350Applied Fracture MechanicsFigure 7. Cumulative Leak Probability over 40 Years as a Function of the Stress-Corrosion DamageParameter for Various Temperatures, Oxygen Contents and degrees of sensitization5.2. Improvement factorsThe individual data points for improvement factors exhibited some data scatter, which wasaddressed by using a regression analysis to establish best fit curves (second orderpolynomial) in terms of improvement factors versus the logarithm (base 10) of Dsigma and thecorresponding leak probabilities. For clarity, the plots below show only the best-fit curvesrather than the individual data points. Figs. (8-12) show calculated improvement factors(over a 40-year design life).Figs. (8-10) each addresses a specific inspection method (POD curve) with the individualcurves corresponding to different inspection intervals ranging from 1 to 10 years. Figs. (10-12) have rearranged the curves to maintain a common inspection interval for each plot, withthe individual curves corresponding to different POD capabilities. In general, it appears thata given inspection strategy (combination of POD curve and inspection interval) givessomewhat greater improvement factors.