腐蚀产物晶体结构及离子选择性对P110S低合金钢在H2S/CO2环境中腐蚀行为的影响

目的研究P110S低合金钢在H2S/CO2环境中的腐蚀行为及腐蚀产物对其影响机理。方法通过P110S低合金钢在不同温度下的腐蚀失重实验、微观SEM形貌观察、XRD分析和离子选择性实验,探究腐蚀产物的晶体结构以及离子选择性对腐蚀行为的影响。腐蚀实验环境为模拟我国西北某油田现场不同井深的腐蚀工况,其中CO2与H2S的分压比为2.5。结果温度低于100℃时,腐蚀产物主要为马基诺矿型FeS,其为阳离子选择性,能够阻碍阴离子与基体接触,起到抑制腐蚀的作用,因此腐蚀速率较低,约为0.15 mm/a,且随温度升高基本保持不变,试样表面的腐蚀产物膜平整未脱落;温度达到120℃后,腐蚀速率急剧增大,部分腐蚀产物由马基诺矿转变为磁黄铁矿,腐蚀产物膜因下层腐蚀产物挤压而发生破裂脱落,试样发生局部腐蚀;温度高于160℃时,腐蚀产物全部为磁黄铁矿型FeS,其为阴离子选择性,无法阻碍阴离子穿过腐蚀产物膜与基体接触,因此随着温度的升高,腐蚀速率逐渐增大并趋于平缓,达到3.6 mm/a。结论H2S/CO2环境中低合金钢腐蚀行为与腐蚀产物晶体构型及离子选择性密切相关,若腐蚀产物为马基诺矿型FeS时,其具有阳离子选择性,能够抑制金属基体腐蚀溶解;而若腐蚀产物为磁黄铁矿型FeS时,因其具有阴离子选择性,则不能抑制金属基体发生腐蚀溶解。

Effect of Crystal Structure and Ion Selectivity of Corrosion Products on Corrosion Behavior of P110S Low Alloy Steel in H2S/CO2 Environment

The corrosion behavior of P110S low alloy steel in H2S/CO2 environment and the effect mechanism of corrosion products on it were studied.In this paper,the effect of P110S low-alloy steel on corrosion weightlessness experiment at different temperatures,microscopic SEM morphology observation,XRD,and ion selectivity experiments to explore the crystal structure of corrosion products and the effect of ion selectivity on corrosion behavior.The environment of the corrosion experiment is to simulate the corrosion conditions of different well depths in the field of an oil field in Northwest China.The partial pressure ratio of CO2 and H2S remains basically unchanged at 2.5.When the temperature is lower than 100℃,the corrosion product is mainly mackinawite type FeS,which is cation selective,can prevent anions from contacting the substrate,and plays a role in inhibiting corrosion.Therefore,the corrosion rate is low,about 0.15 mm/a.And it basically keeps unchanged with the increase of temperature,the corrosion product film on the sample surface is flat and does not fall.After the temperature reached 120℃,the corrosion rate increased sharply,and some corrosion products were transformed from mackinawite to pyrrhotite.The corrosion product film was cracked and peeled off due to the extrusion of the underlying corrosion product,and the sample was locally corroded.When the temperature is higher than 160℃,the corrosion products are all pyrrhotite type FeS,which is anion selective and cannot prevent the anions from contacting the substrate through the corrosion product film.Therefore,as the temperature increases,the corrosion rate gradually increases and becomes flat,reaching 3.6 mm/a.The corrosion behavior of low alloy steel in H2S/CO2 environment is closely related to the crystal structure and ion selectivity of the corrosion product.If the corrosion product is mackinawite type FeS,it has cation selectivity and can inhibit the corrosion and dissolution of the metal matrix.However,if the corrosion product is pyrrhotite type FeS,because of its anion selectivity,the corrosion and dissolution of the metal matrix cannot be suppressed.