The burst failure and the structural reliability of ultra-high strength (X-100 to X-120) steel pipelines is investigated analytically based on their elastic-plastic collapse behaviour. Structural models for high strength pipes and codes are adopted from literature and their key features are discussed. The models are verified by burst test data for ultra-high-grade steel pipelines. Two statistical measures are used to compare the accuracy of models for ultra-high strength steel pipes. The most accurate theoretical model for ultra-high strength pipes is identified. Limit state functions are formulated based on the strength models for reliability analysis of ultra-high-grade steel pipelines under operational conditions. Probabilistic models are applied to the basic variables of limit state functions. A First-Order Reliability Method is used to assess the reliability for this category of pipelines followed by a sensitivity analysis that identifies the most significant limit state variables. The results of this study can provide vital measures for design and maintenance planning of ultra-high-grade steel pipelines.

This paper assesses the uncertainty in the collapse strength of sandwich pipelines under external pressure predicted by various strength models in three categories based on interlayer adhesion conditions. First, the validity of the strength models is verified by comparing their predictions with sandwich pipeline collapse test data and the corresponding model uncertainty factors are derived. Then, a parametric analysis of deterministic collapse strength predictions by models is conducted, illustrating insights of models’ behaviour for a wide range of design configurations. Furthermore, the uncertainty among different model predictions is perceived at different configurations of outer and inner pipes and core thicknesses. A case study of a realistic sandwich pipeline is developed, and probabilistic models are defined to basic design parameters. Uncertainty propagation of models’ predictions is assessed by the Monte Carlo simulation method. Finally, the strength model predictions of sandwich pipelines are compared to that of an equivalent single walled pipe.