Abstract Free span along a buried gas pipeline is inevitable since the buried gas pipeline is constantly exposed to the complex surrounding environment. A free span is commonly identified by manual inspection, sonar technology, or a remote robot. The main disadvantage of these identification methods is that the detection process is significantly interfered with by pipeline surrounding environment. In this paper, free-span identification of a buried gas pipeline subjected to a sine sweep load inside the pipe is experimentally studied. Two critical parameters, the sine sweep rate of an excitation signal and the moving speed of a free span detector, are experimentally researched in order to explore their impact on free-span identification results. The frequency response characteristics and the weighted response signal energy are adopted as evaluation indexes to analyze the location and length of a free span. Both static and moving experiments were carried out to verify the capability of detecting a free span under the moving state of a free span detector, the reliability of the two evaluation indexes. The experimental results show that location and length of a free span along a buried gas pipe can be identified.