The erect pipe is a dangerous one with a special double concentric pipes, in which the inner pipe and outer pipe are both corroded on the offshore platform so that a effective corrosion inspection is needed to measure the thinning to the inner pipe and outer pipe at the same time. In addition, because of the narrow space in the offshore platform, it is difficult for the digital X-ray tangential photography (DR) to be implemented during the operation because of the larger X-ray dose that is enough to threaten the personal safety according to the standards in China. Hence, a special inspection tech is demanded to obtain the wall thicknesses of erect pipe which is the most important information to the corrosion management. In this article, A new measuring tech is proposed for the concentric multi-pipe structure to dissolve the bottleneck on the inspection of the offshore erect pipeline. Through the tangential scanning and a wall boundary identifying algorithm, the tech can accurately measure the wall thicknesses of erect pipe, and the ray dose can also be decreased about to the one thousandth of traditional DR, which can guarantee the safety of a inspection and monitoring during the operation in a narrow space as the offshore platform. Besides, the low dose of ray doesn’t influence the accuracy of the measurement which can still be kept into 0.2mm according to the theoretical analysis and experimental data.