低铬油套管CO2/H2S腐蚀研究进展

Research Progress of CO_2/H_2S Corrosion on Tubing and Casing Containing with Low Cr Content

介绍了低Cr油套管开发的工程背景。综述了低Cr油套管的耐CO_2/H2S腐蚀性能,详述了多种因素(如Cr含量、温度、p H值、流速等)对低Cr油套管在含甜性气体(仅含CO_2)环境中的腐蚀行为和腐蚀产物膜表面特征的影响,以及低Cr油套管在含酸性气体(H2S)环境中的腐蚀行为及其抗硫化物应力开裂(SSC)的性能。探寻了低Cr钢的抗CO_2腐蚀机理和H2S腐蚀机理。研究发现,低Cr钢因Cr元素能在产物膜中富集,形成非晶体化合物Cr(OH)3,腐蚀产物膜因此具有阳离子选择性,降低了腐蚀产物膜与金属基体界面处的阴离子浓度,抑制了阳极反应,进而提高了低Cr钢耐CO_2/H2S均匀腐蚀性能,同时也减少了Cl-在界面处团聚、形核的可能性,抑制了局部腐蚀,尤其是点蚀的发生。但是要想消除点蚀,钢基体中Cr元素的质量分数不应低于3%。另外,Cr元素在晶界及晶内以粒状碳化物析出并弥散分布,进一步增强了其抗SSC性能。简述了低Cr油套管的应用现状,最后对其发展前景进行了展望,利用钢的化学成分-工艺-组织-性能"四位一体"法得到的"经济型"低Cr抗CO_2/H2S腐蚀的油套管,是未来发展趋势的代表。

The engineering background of the development of low Cr tubing and casing was presented in this paper. The resistance of low Cr tubing and casing against CO2/H28 corrosion was summarized. The effects of various factors, such as Cr content, pH value, temperature, flow velocity, etc., on corrosion behavior of low Cr steel and surface characteristics of corrosion scales in the environment containing sweet gas （only CO2） were reviewed in details. Besides, the corrosion characteristics in the environment containing acidic gas （H2S） and the resistance performance on sulfide stress cracking （SSC） of low Cr steel were also elaborated. And the CO2 corrosion mechanism and HzS corrosion mechanism of low Cr steel were also discussed respectively. The studies found that low Cr steel had good resistance against CO2/H2S uniform corrosion owing to the enrichment of Cr element in corrosion scales, the amorphous Cr（OH）3 formed in the corrosion scales, so corrosion scale had the permselectivity towards cations, reducing anion concentrations at the interface between corrosion scales and metal substrate. And at the same time, the local corrosion was suppressed, especially pitting corrosion, owing to the decreasing possibility of Cl^- reunion and nucleation at the interfaces. However, the mass percent of Cr element in the matrix should be not lower than 3% to further suppress or eliminate pitting corrosion. The resistance against SSC was further enhanced owing to the precipitation and diffuse distribution of Cr element in the form of granular carbides in the grain boundary and inside the grains. Meanwhile, the application status of low Cr tubing and casing in oil ＆ gas fields was mentioned. At last, the potential development was prospected. Economical low Cr tubing and casing against CO2/H2S corrosion represents the future development trend, which will be obtained from the quaternity method of chemical composition, technology, structure, and performance of steel.