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西南油气田天然气输气干线两付线自1979年9月建成投产至今国内外腐蚀造成的管道事故86起。为评价水下及埋地管线的腐蚀状况，1998年4－5月地全线260.7km进行有重点的密集性开挖，208个探坑反映出石油沥青涂层一部分老化明显。1999年3月输气处利用世界银行贷款项目，对两付线中的榕山至佛荫段管线进行了（漏磁）清管智能检测，发现的外腐蚀点比采用腐蚀探坑调查时增多。由于智能检测器的外定标为2km左右一个，尽管检测出有较多、较严重的外腐蚀点，但却难以定位开挖处理。借助最新产品RD400－PCM电流梯度探测仪，对水下及埋地管线严重外腐蚀管段进行检测定位，定位准确率达到98％，减小了不必要的开挖及费用。本文介绍利用RD－PCM检测水下管线外腐蚀和腐蚀定位，以及检测涂层破损和CP故障。

New Corrosion-detecting Technique for Underwater and Underground Pipelines

??Eighty-six cases of accident caused by internal and external corrosion have occurred since Liang-Fu main gas line of Southwest Oil and Gas Field Branch was put in operation in September 1979.In order to evaluate the corrosion state of the underwater and underground pipeline,the complete pipeline of 260.7 km length has been selectively excavated in April to May 1998 208 trail holes show that a part of asphaltic coating has obviously aged.The section from Rongshan to Fuying of Liang-Fu pipline was detected and the found external corroded points are more than those found by trail holes.Because the scale of the instrumented pig is about two kilometers,though more and grievous external corroded points have been detected out,it was difficult to locate,excavate and remedy.The section with grievous external corrosion of the underwater and underground pipeline was detected and located with the aid of the newest product??RD 400-PCM current gradient detection instrument which locating accuracy can reach 98%,reducing the unnecessary expenses in excavation.In this paper,using RD-PCD to detect the external corrosion and locate the corroded points as well as to detect the coating damage and cathodic protection accident is presented.