| A certain airport jet fuel pipeline in service was founded in 2003, total length of about 50 km. The distribution of branch pipeline in pipe network is very complicated, and there are more metallic structures underground. Thus, serious interference and shielding effect between each other, causing the original cathodic protection system fall short of protective effect. It needs to rectify and reform cathodic protection system. In addition, the rectification cathodic protection system in normal operation after a year, appear the phenomenon of abnormal fluctuations in protection potential, which is due to the metro stray current interference. So, the cathodic protection system invalidation, which lead to the operation of pipeline exist hidden dangers. In this paper, we aimed at the cathodic protection system defects of a jet fuel in service pipeline to carry on the field monitoring and testing, and put forward the additional retrofit scheme of pipeline cathodic protection. For the situation of the metro stray current interference to the pipe network, the field monitoring and analysis was carried out to determine the type of the stray current interference, interference sources and interference degree. Then, the corresponding drainage measures of metro stray current interference were adopted. Drainage effect was good, and the cathodic protection system of pipeline was running normally. Main conclusions are as follows:(1) Initial cathodic protection system test results of airport pipe network showed that the pipeline protection potential could not meet the protection requirements(negative to 0.85 V); The protection current distribution of pipe network was not uniform; The whole pipe network electric connectivity was good; A single cathodic protection station was not enough to protect the whole pipe network; The original cathodic protection equipments couldn’t work normally.(2) Considering the pipeline is an in service pipeline, which is running a busy airport area and not having the excavation construction conditions of large area. Therefore, the impressed current cathodic protection was selected, and the MMO tubular anode was used for auxiliary anode.(3) In view of the pipe network is relatively complex, considering the auxiliary anode bed may cause interference to other underground steel structures and covers an area of condition, the design of deep well anode ground bed was selected.(4) A reasonable regional impressed current cathodic protection system was designed by feeding test. On the basis of the original cathodic protection system, two new cathodic protection stations were set up, and the original cathodic protection system was rectified. The debugging for the completely installed cathodic protection system was carried out, which showed that all cathodic protection equipments can effective output. Three different systems have protection point and can complement each other. Each test point protection potential can satisfy the requirements of protection, and the pipeline effectively protected.(5) The effective testing was carried out for the stray current interference of pipe network, which determined the subway stray current interference of pipeline. A strong stand row add to grounding row flow joint drainage measures was taken, and the pipeline protection potential basic returned to normal range. |
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