Combined Effects of Thermal Contraction and Internal Pressure on Stress Behavior of L-Shaped LNG Pipeline Elbows

This study investigates the stress behavior of the L-shaped pipeline elbows at LNG receiving terminals. A finite element model is developed to investigate the effects of internal pressure, temperature, and their coupling on the stress field at the 45° cross-section of the elbow. The numerical result is compared with experimental results to evaluate its accuracy. For internal pressure loading alone, the peak stress is governed by hoop tension and located at the intrados. In contrast, under thermal loading alone, compressive hoop stress shifts the critical location to the crown. When both loads are applied simultaneously, competition between two high-stress zones causes the peak location to jump among 0°, 57°, and 83° as the relative dominance of thermal and pressure effects varies, challenging conventional fixed-location inspection strategies. A response surface model is constructed to predict extreme stress magnitudes, and multinomial logistic regression is employed to establish quantitative classification boundaries for the peak stress location as a function of temperature and pressure. Within the investigated range, the critical pressures predicted by the logistic regression model agree well with the finite element results. These findings provide a predictive basis for risk-based inspection prioritization and failure probability assessment of cryogenic pipeline elbows under operational thermal-pressure conditions.