Chapter 24 TENSILE STRAIN CAPACITY MODEL, FULL-SCALE TESTING, SAFETY FACTOR DERIVATION, AND BENCHMARK EXAMPLE CALCULATIONS Available to Purchase

This paper describes a tensile strain capacity (TSC) prediction model and how ~ 100 full-scale pipe strain capacity tests were used to derive a safety factor for use in either pipeline design or strain-based engineering critical assessment (SBECA). The safety factor accounts for the difference between model predictions and test results thus providing a quantifiable degree of reliability. The safety factor is generated from a 95% upper confidence limit on the ratio of predicted-to-measured TSC. The practical meaning of this is that if either TSC or tolerable defect size is calculated using the model, then the probability of being non-conservative is estimated to be 5%.

The model is used to estimate TSC for a variety of hypothetical pipeline design cases. These scenarios cover a range of pipe geometries, pipe and weld physical properties, and high-low weld misalignment. Using the model as a design tool is discussed and the model is used to create flaw assessment diagrams showing trends in defect tolerance as a function of variables like weld strength overmatch and high-low misalignment. It is the intent of this paper to (1) show the utility of the model in assessing the influence of variables that affect girth weld performance in SBD scenarios, and (2) provide these calculations as benchmark cases to ensure that other users have accurately programmed their spreadsheets.