流速对L360管线钢在H2S/CO2环境中腐蚀行为的影响

目的为选取合适的流速来输送油气,降低流速对管线钢腐蚀造成的危害。方法以L360管线钢为实验用钢,流速(0、3、5 m/s)为变量,利用高压釜研究L360钢在含Cl-的H_2S/CO_2酸性环境中的腐蚀行为,采用极化曲线及交流阻抗研究L360钢的腐蚀电化学行为,利用SEM、EDS分析腐蚀后试样的微观形貌、结构特征以及腐蚀产物成分。结果失重法测定L360钢的腐蚀速率时,在实验条件完全相同的情况下,流速为5 m/s时的腐蚀速率(0.4824 mm/a)大于0 m/s时的腐蚀速率(0.3696 mm/a)。电化学测试中,3种状态对应的实验条件完全相同,可以发现流速为3 m/s时钢被腐蚀的难易程度位于0 m/s和5 m/s之间。随着流速的增加,试样表面腐蚀产物膜的破裂程度加剧。腐蚀产物以Fe的硫化物为主,流速为0 m/s时,有少量Fe CO3和Fe C3生成,流速为3 m/s时形成了四方硫铁和硫复铁矿晶体。随着流速从0 m/s增加到5 m/s,试样的腐蚀电位负移,腐蚀电流密度增大,在5 m/s时的腐蚀电位最负,此时自腐蚀电流密度最大,容抗弧半径最小,最易被腐蚀。结论结合腐蚀失重实验和电化学实验,发现流速在0~5 m/s范围内,流速越小,对L360管线钢造成的腐蚀作用越小,在不影响油气正常输送的情况下,尽可能选取小的流速,以保证管线钢的安全使用,提高管线钢的使用寿命。

Effect of Flow Velocity on Corrosion Behavior of L360 Pipeline Steel in H2S/CO2 Environment

The work aims to select appropriate flow velocity for oil and gas transmission, and reduce harm of flow velocity to corrosion of pipeline steel. With L360 steel as experimental steel and flow velocity as variable, corrosion behavior of the L360 steel in H2S/CO2 acidic environment containing Cl- was investigated with autoclave, corrosion electrochemical behavior of the L360 steel was studied based upon polarization curves and AC impedance, microstructure, structural characteristics and corrosion product constituents of the sample were analyzed with SEM and EDS. Corrosion rate of the L360 steel was determined in weight-loss method. Provided experiment conditions were identical, corrosion rate at flow velocity of 5 m/s (0.4824 mm/a) was higher than that at 0 m/s (0.3696 mm/a). In electrochemical tests, experimental conditions corresponding to 3 states were identical, the corrosion degree of steel ranged from 0 m/s to 5 m/s at the flow velocity of 3 m/s. As the flow velocity increased, the corrosion product film was increasingly fractured on the surface of the sample. The main corrosion product was FeS. At the flow velocity of 0 m/s, a small amount of FeCO3 and FeC3 was generated, and at the flow velocity of 3 m/s, tetragonal iron and greigite were generated. As the flow velocity increased from 0 m/s to 5 m/s, the corrosion potential shifted negatively and corrosion current density increased. At the flow velocity of 5 m/s, the corrosion potential was the most negative, self-corrosion current density was the maximum, radius of capacitive reactance arc was the minimum, and the steel was most susceptible to corrosion. According to corrosion weight loss experiment and electrochemical experiment, as flow rate ranges within 0~5 m/s, the lower the flow velocity is, the less corrosive effect on L360 pipeline steel will be. In order to ensure safe use of pipeline steel and improve its service life, low flow velocity should be selected as far as possible provided that normal transmission of oil and gas is not affected.