Abstract: Puyang-Linyi Oil Transportation Pipeline was put into operation more than 20 years with total length of 261.556 km and 9 heated pump stations in the whole line. To meet the needs of gas supply to Ji'nan City of Shandong Province, the partial pipeline section of the pipeline (Puyang-Duanzhuang pipe section, 213.83 km in length) will be transformed to transmit natural gas. To fulfill this project for the purpose of safety and reliability, the stress analysis, strength and residual strength calculation on the original pipeline were made. According to the calculation result, an accumulative 11.88 km-long pipe section was displaced substituted L360 steel pipe instead of Q235-A·F steel pipe. The transformed pipeline was successfully brought to stream in 1999.