Abstract: For detecting and locating leaks on buried pipelines, a leak--detection techniqueand related instruments have been developed. Some quantity of fluid mixedwith a radioactive tracer is injected. After the pipeline is cleaned, a leak-detector is put into and moves along the pipeline to monitor the leaked radioacti-vity and record both the radioactive signal and the time signal on a magnetic tape.From the signal curves, it can be judged whether there are any leaks on thepipeline and,if any, where they are.