Measuring impurity content in pipelines by positron annihilation

Abstract

γ photon pairs produced by positron annihilation can penetrate metals well; thus, they can be used for nondestructive detection of the inner state of metal pipelines. An experimental device is designed to simulate the working state of lube oil pipelines and inject nuclide into it. A symmetrical structure and a ratio algorithm are proposed considering the effects of various factors. Two sensors with good consistency are used to record the number of γ photon events in liquids with and without impurities. The ratio of the recorded events of reference and impurity sensors is taken as the test result of impurity content. The advantage of the method proposed in this paper is that it can eliminate the environmental error and inconsistency of the sensors by using ratio calculation and improve the measurement accuracy. Experimental results show that the proposed detection scheme and algorithm can well detect impurity content, including metal, in various pipelines. The detection accuracy of matched sensors can exceed 2%. Detected impurities are not limited to metal particles. Thus, the proposed method can be applied to in situ and online detection of impurities in oil piping systems equipped with engines.