某含硫油田20G集输干线内腐蚀穿孔原因分析

Cause Analysis of Inner Corrosion Perforation of 20G Gathering Pipeline of a Sour Oilfield

为了探究某含硫油田20G集输干线内腐蚀穿孔原因,通过宏观形貌观察、尺寸测量、化学成分分析、金相检验、力学性能测试及腐蚀形貌观察和腐蚀产物分析等方法,并结合该管段的生产标准和现场服役工况进行了分析。结果显示:该20G集输干线材质无异常,符合相关标准要求;失效管段的腐蚀产物化学成分为C、O和Fe,还有少量的Cl和S。分析表明:该管线的输送介质流速过低,致使管道底部长期积水,使得介质中的CO2、H2S和少量溶解氧对管线底部产生腐蚀,其中采出水中高浓度的Cl-促进了点蚀的形核和发展,最终导致穿孔。针对此类低压、低流速、高腐蚀性含水原油管道,建议排查管道的输送路径,防止带入空气,如改进工艺流程和采用除氧后的水清管等,并且适当提高流速,减少管线积液。

In order to explore the cause of inner corrosion perforation in 20G gathering pipeline of a sour oilfield,and the macro-morphology observation,size measurement,chemical composition analysis,metallographic examination,mechanical property test,corrosion morphology observation and corrosion products analysis were carried out combined with the production standard and field service conditions of the pipe section.The results show that the material of the 20G gathering pipeline is normal and meets the requirements of relevant standards.The chemical composition of corrosion products in the failure section is C,O,Fe,and a small amount of Cl and S.The analysis shows that the too low flow rate of the medium in the pipeline leads to long-term water accumulation at the bottom of the pipeline,resulting in the corrosion of CO2,H2S and a small amount of dissolved oxygen in the medium on the bottom of the pipeline.The high concentration of Cl-in the produced water promotes the nucleation and development of pitting corrosion,and finally leads to perforation.For this kind of low-pressure,low-velocity and high-corrosive water-bearing crude oil pipeline,it is suggested to check the delivery path of the pipeline to prevent air entry,such as improving the technological process and using deoxygenated water to clean the pipeline,and appropriately increase the flow race to reduce the pipeline liquid accumulation.