Stress Analysis and Crack Formation Mechanism of Cryogenic LNG Pipeline

Natural gas plays a critical supporting role in the energy transition, and LNG storage tanks, as key storage facilities, face the risk of fracture failure in their inlet pipelines under complex loads. Using the finite element method (FEM), this study establishes a temperature field calculation model and a stress calculation model for the inlet pipeline of LNG storage tanks. Based on real operational parameters from an LNG terminal, the pipeline temperature distribution is calculated and applied as an initial loading condition in the stress calculation model to compute the axial and hoop stress distribution characteristics of the pipeline. Uniaxial tensile and strain-controlled low-cycle fatigue tests were conducted on 304/304L stainless steel, which is commonly used in LNG pipelines, under both room and cryogenic temperatures to assess the material’s performance in service environments. By combining the stress analysis of the LNG inlet pipeline with the material test results, the causes of crack formation in the pipeline were analyzed. The results indicate that uneven temperature distribution during operation induces significant axial and circumferential stresses at the 6 o’clock position on the pipeline’s inner surface. The cyclic loads caused by repeated liquid injection do not lead to fatigue cracks. However, insufficient precooling or excessive insulation temperature of the LNG pipeline can result in a large temperature gradient between the inner and outer walls, generating significant thermal stresses in both axial and circumferential directions, potentially leading to crack formation.