Abstract

Increasing global demand and domestic production of liquefied natural gas (LNG) is leading to development of new LNG projects using modern materials and construction practices globally. This study evaluated the structural response of representative LNG piping systems subjected to rapid temperature drops from unintended exposure to cryogenic liquids of less than −243°F (−153°C) temperature. Finite Element (FE) models were developed of pressurized austenitic stainless steel jacketed pipe-in-pipe systems and large diameter insulated piping in various bend configurations. FE models were subjected to rapid temperature changes to represent potential unintended loading scenarios, such as an LNG leak or abnormal start-up or shutdown creating large temperature gradients across the pipe cross-section. FE model parameters such as geometry and boundary conditions were varied to assess the impact on the thermal-mechanical response. The FE analysis stress results were used as inputs to American Petroleum Institute (API) 579-1 fitness-for-service (FFS) assessments with assumed flaws in the pipe body and welds in multiple orientations to develop failure assessment diagrams (FADs). FFS flaw sizes were selected based on probability of detection with common nondestructive testing (NDT) methods, such as visual inspection, magnetic particle inspection (MPI), and ultrasonic testing (UT). The assessment results provide bounds on acceptable piping configurations, boundary conditions, and assumed crack sizes, along with the propensity for brittle fracture, ductile plastic collapse, or intermediate failure modes for the selected sudden temperature drop exposure scenarios. These findings are used to develop recommendations for appropriate NDT methods for identifying maximum allowable flaw sizes in system components, piping flexibility to accommodate thermally induced movement, and prioritization of components for inspection and assessment. The study is intended to provide guidelines to industry practitioners and regulators to better understand the response of austenitic stainless steel piping subjected to rapid temperature drops from LNG exposure and the associated impact on demands and safety.