某油田长输管线套管的腐蚀情况分析

Analysis on Inside Pipe Casing Corrosion of Oil FieldLong Distance Transmission Pipeline

长输管线在设计之初,常采用固定支墩对管线的穿跨越处或沿线进行锚固。随着我国长输管线的不断发展,输送距离的不断增加,管线上固定支墩处的腐蚀问题随之出现。固定支墩处一般采用外套管进行保护,然而对施加了阴极保护的管线来说,套管处容易产生电流屏蔽效应,增加了管线的腐蚀风险。分析油田现场腐蚀案例后发现腐蚀情况往往发生在套管边缘处。通过对各类防腐技术进行综合比较,分析套管对阴极保护电流产生屏蔽及管线发生腐蚀的原因,并采取一系列腐蚀防护措施来延长其使用寿命。整改措施分两种,一种是在环形空间充填电解质或绝缘材质,并做好套管处的密封工作,另一种是在套管处增加牺牲阳极保护,并严格把控现场施工材料中的氯离子含量,目前这两种方式对减缓套管内管线的腐蚀具有一定的作用。

Since the early days of oil and gas development,the design of long distance transmission pipeline often made use of fixed docking block to anchor pipeline along the route and on pipeline crossings.As a result of further development of oil and gas production in China,more transmission pipelines were installed and the issue of pipeline corrosion at the fixed docking block location began to surface.On the docking block,the pipeline is usually protected by a pipe casing.However,for pipeline with cathodic protection,the pipe casing could shield the cathodic protection current and increase pipeline corrosion risk.Based on corrosion analysis of the pipeline corrosion cases on site,it was concluded that the corrosion occurred at the edge of the casing.A survey of corrosion protection technologies development in China and internationally showed that a series of corrosion management and mitigation measures had been developed to extend pipeline operating life.These mitigation measures took into account the effect of cathodic current shielding of pipe casing on pipeline corrosion and could be grouped into mainly 2 categories;one of them is to fill-up the pipe casing annular space with electrolyte,the other being to provide sacrificial anode protection at casing with exactly controlled chloride ion content in construction material.So far,these two categories of mitigation measures are found to be effective in slowing down pipeline corrosion inside pipe casing.