原油长输管道阴极保护有效性评价分析

Effectiveness Evaluation Analysis on Cathodic Protection of Crude Oil Long-distance Pipeline

目的 探究原油长输管道阴极保护失效的原因。方法 通过管道通/断电电位测试、集输末站内外电位测试和绝缘法兰测试等方法,判断集输管线是否处于有效的保护状态,站内外阴极保护是否存在直流干扰情况,以及绝缘法兰的工作情况。结果 1~#集气站-1~#阀室管道通电电位为-850~1200 mV,断电电位为-773~788 mV,不满足比-850 mV更负的准则。站外管线通/断电电位虽然随着站内阴保电流的增大而增大,但是在电流为6、18 A时,其断电电位分别为-880 mV和-1198 mV,在保护电位范围之内（-850~1200 mV）,没有产生过保护,符合国标的要求。站内外阴极保护干扰是客观存在的,可以通过调节及平衡站内外的输出,使站内外管道的保护电位在规定的电位区间之内（-850~1200 mV）。集输末站处的绝缘法兰性能良好,但是锌接地电池基本耗尽。结论 管道断电电位没有达到要求,且集输末站内外阴极保护存在相互干扰,是该长输管道阴极保护失效的主要原因。

Objective To explore the reasons for the failure of cathodic protection （CP） of long-distance pipeline. Methods The pipe on/off-potential test, potential distribution measurement and insulated flange test were adopted to investigate the protection status of the gathering pipelines, the direct current effects on the cathodic protection and the operation status of the insulated flange. Results The on-potential values of pipelines of 1# gas gathering station-1^# valve chamber met the national standard within the range from -850 mV to -1200 mV. However, the off-potential values were in the range of-773-788 mV, which conflicted with the principle that requested the value to be lower than -850 mV. Although the on/off-potential of outside station increased with the increasing cathodic current in the inside station, the off-potential was still in the protection range of -850-1200 mV with the values of-880 mV and -1198 mV, respectively. As a result, overprotection was not observed and the national standard was strictly kept. The interference of CP was supposed to exist both inside and outside of the gathering station.We could adjust and balance the output inside and outside the station to make the protective potential of the pipeline reach the standard value within the range from -850 mV to -1200 mV, such as decreasing the output current of anode close to pipe outside the station, increasing the output of anode far from pipe of the station. Insulation flange performed well in the terminal station, but the grounding zinc battery was depleted. Conclusion The CP off-potential in the terminal station didn＇t meet the requirements. The interference of cathodic protection systems between the inside and outside of the terminal station was the main reason for the failure of the cathodic protection of the long-distance pipeline.