Uncertainty analyses for calculated failure probabilities of piping welds

The objective of this paper is to quantify the uncertainties associated with inputs to probabilistic fracture mechanics calculations and with the resulting uncertainties in the calculated values of piping failure probabilities. All calculations used the pc-PRAISE computer code to address both leak and break probabilities. The first step was a sensitivity study which identified the uncertainties that have the greatest effect on the pc-PRAISE results. The second step was a quantitative uncertainty analysis that addressed the most critical parameters so identified. The failure mechanisms addressed were mechanical and thermal fatigue of stainless steel piping due to the presence of fabrication defects. Distributions of calculated failure probabilities are summarized in a format usable as input to higher level uncertainty analyses that combine the uncertainties in failure probabilities with uncertainties from probabilistic risk assessments that address the consequences of piping failures.