This study investigates the impact of expanding and reducing deformation ratios on the performance of L360 straight-seam welded pipes formed by the JCO process for offshore oil and gas transportation. The Split Hopkinson Pressure Bar (SHPB) experimental technique was used to examine the stress/strain relationships, yield strength, and compressive strength of the pipe materials subjected to high strain rates. The results indicated that the impact performance of the pipes significantly improves with both expansion and reduction processes, demonstrating an enhancement effect of deformation. The impact of yield strength and compressive strength increases with higher expansion ratios, reaching maximum values of 1009 MPa and 847 MPa, respectively, at an expansion ratio of 1.2%. At a reduction ratio of 0.8%, the impact yield strength increased by 64% and the compressive strength by 14%. These findings not only provide theoretical support for optimizing the expansion and reduction processes and their associated equipment but also have direct and significant practical implications for enhancing the performance and safety of offshore oil and gas transmission pipelines, thereby contributing to the advancement of the field.