Due to geographical restrictions, it is often necessary to lay two pipelines in the same ditch during pipeline construction. However, as developments in natural gas pipelines increasingly incorporate higher grades of steel, larger diameters, and higher pressures, the consequences of an accident caused by leakage, explosion, or ignition become progressively more severe. The explosion occurred in one pipe would affect the other pipe laid in the same ditch, resulting in subsequent explosion. In this study, a full-scale explosion test was conducted on two X80 steel pipes with diameters of 1422 mm and 1219 mm, laid in one ditch and set up in parallel arrangement, with a spacing of 36 m between one another, and a burying depth of 1.5 m. Some X80 steel samples were selected to assess materials performance in different areas of a given pipe in the same ditch by deploying selective explosions. The mechanical performance tests on a number of points including tensile strength, impact, and hardness were executed by the Mechanical Testing and Sensing (MTS) universal testing machine. Drop-Weight Tear Test (DWTT) of the selected samples were executed by the DWTT pendulum test machine. Metallography and microstructure analysis of the steel samples was performed by the MEF4M metallographic microscope and image analysis system. Results indicate that limited effects of jet fire on the macroscopic tensile properties and impact toughness of the pipelines, but a more obvious softening effect on the steel surface material. Drop-Weight Tear Test and microscopic observation revealed that jet fire can significantly reduce crack propagation resistance on the surface of the pipeline, pointing to deformation behavior and other concerns that could impact pipeline safety and efficacy. The results of this experimentation can help to improve pipeline construction, resulting in better safety.

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