Application of Reliability Based Design and Assessment to Seismic Evaluations

The application of reliability based design and assessment (RBDA) as a basis for seismic evaluations of natural gas pipelines is explored through analysis of a number of representative pipeline examples. To accomplish this, a simplified approach was developed to generate a representative probability distribution of permanent ground deformations due to soil liquefaction. An idealized pipeline alignment through a liquefiable layer under a river was defined, and a number of cases representing NPS12 and NPS36 pipelines in classes 1, 2 and 3 were analyzed using a finite element model. The probability of exceeding the strain limits for pipe body and girth weld were calculated and compared to the reliability targets. The results were used to identify diameter and class combinations that can meet the reliability targets, and to make preliminary conclusions regarding the viability of using RBDA for seismic evaluations.