With the quantitative growth of the petroleum industry, the pipe facilities that connect each process increased significantly and the corresponding maintenance and repair costs of the pipe facilities increased as well. The diagnosis techniques to check a pipe efficiency while in operation are few in Korea, but in the advanced countries the pipe diagnosis using gramma-ray source was on-going research since 1960's. In this study, field experiments were performed to analyze the reasons for abnormal operation of the pipe connected to a distillation tower, and the degree of abnormality was estimated using a sealed gamma-ray source (137Cs). Gamma radiation counts were measured by a detector (Nal) positioned outside the pipe-wall diametrically opposite to thte gamma source. The results showed that a gas zone section's distribution pettern was different from the pattern of nearby fluid in a pipe. Th diagnosis technique using a gamma radiation source was proved to be an effective and reliable method, offering the information on the fluid distribution in pipe.