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西南油气田的输气干线有１８１０km，新建管线还在不断增加，正在使用和新建管线全部采用埋地方式，管线外防腐采用石油沥青涂层和制电流的阴极保护。目前沥青涂层开始出现龟裂、破损、剥离、老化、甚至一些管段涂层已粉化失去保护作用。管线漏电点增多，阴极保护（ＣＰ）的负荷加大，一些管段电位难以达到最低标准。由于保护不足造成管线阳极溶解严重。油气田管线沥青涂层大部分已使用２０年以上，现面临的难题是涂层缺陷检测和查清真实的ＣＰ极化电位分布及腐蚀状况，只有当涂层缺陷被检出并修复后，ＣＰ的电位才能满足标准要求，外腐蚀才可能抑制，因此需要一种能满足工种使用的检测技术，文章通过腐蚀检测技术的现场应用优选，推荐采用清管理智能检测和电流绘系统ＲＤ－ＰＣＭ技术，附带介绍其它涂层缺陷检测技术优缺点。

Industrial-scale Production of Low-permeability Coal-bed Gas Reservoirs in China Must be Realized as soon as Possible

The main gas pipeline of southwest oil and gas field is 1810 km long and the newly laid pipeline increases continuously.The active pipeline and newly laid pipeline were all buried underground.The external corrosion prevention was realized by adopting asphaltic coating and impressed current cathodic protection.At present,the crocodile,rupture,exfoliation and aging appear on the asphaltic coating and some pipeline sections coating has effloresced and lost its protection effect.Because the current leakage points increase and the load of cathodic protection is raised,the electric potential of some pipeline sections is difficult to reach the minimum criterion,which causes a serious dissolution of the cathodic coating.The majority of the pipeline's asphaltic coating in Southwest Oil and Gas Field has been used over 20 years.The difficult problem faced at present is to detect the coating flaw and to find out the real polarization potential distribution and corrosion degree.Only the coating flaw is detected and repaired can the cathodic protection potential satisfy the criterion requirement and can the external corrosion be inhibited. Thus, a detection technique which can satisfy engineering use is necessary.In this paper,through optimizing the corrosion detection techniques adopted at worksite,the instrument pig and RD PCM technique are recommended to be used and the advantages and shortages of other coating flaw detection techniques are introduced in passing.