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Different severe corrosions are found at the damaged point of anticorrosive coating on natural gas pipelines, even though the cathodic protection (CP) potential is between −0.85 and −1.15 V. Therefore, there are totally 168 buried steel specimens (BSSs) and 28 soil samples at 28 buried points that are taken out in situ and then analyzed in the lab to assess the CP effectiveness. First, the CP status is simulated by BSSs at the damaged points, and the corrosion products on BSSs are analyzed microscopically. Second, the corrosion rates of the testing BSSs are calculated by the weight‐loss method to perform the quantitative assessment. Third, the specific reasons for external corrosion are explored via analyzing the CP potential attenuation tendency and the corrosiveness of soil. The corrosion growth trend is also investigated by comparing the test results among three test cycles within 8 years. Finally, the control measures for external corrosion of pipelines are put forward. The study is beneficial to evaluate the CP system and determine the causes of external corrosion of pipelines, thereby formulating corresponding protective measures.

A transient flow model for heated oil transportation pipeline is built with application of continuity, momentum and energy conservation equations of pipe flow. The transient friction term of the model incorporates both of the steady and unsteady friction and the Brunone-Vitkovsky model is selected to compute unsteady flow friction in pipeline. The method of characteristic, finite-difference scheme and Newton-Raphson method are utilized to solve the model and the computer simulation software is developed on the base of investigation. Ultimately, the hydraulic transient behavior along a heated oil transportation pipeline in the condition of an interim pump station stoppage is simulated. The results show consider the unsteady flow friction is useful to improve the accuracy of water hammer simulation.

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