剥离涂层下Q235钢硫酸盐还原菌腐蚀机理研究

IMR OpenIR

	剥离涂层下Q235钢硫酸盐还原菌腐蚀机理研究
	许进
学位类型	博士
导师	张劲松 ; 王福会
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料加工工程
关键词	硫酸盐还原菌剥离涂层 Q235钢土壤浸出液微生物腐蚀 Sulfate-reducing Bacteria Disbonded Coatings Carbon Steel Q235 Soil Extract Solution Microbiologically Influenced Corrosion
摘要	"通常埋地石油及天然气管道都采用防腐涂层与阴极保护联合防护方式进行腐蚀控制。防腐涂层能够使金属构件与腐蚀介质隔离，进而防止金属腐蚀的发生，起到物理屏障的作用。而阴极保护则是通过降低金属构件的电位，使裸露金属进入免蚀区，进而减缓或消除涂层破损处金属的腐蚀，即电化学保护。然而，由于涂层本身缺陷及外部原因导致防腐涂层失去粘结力而发生剥离，一旦环境中的腐蚀性介质渗入，就会在缝隙内形成局部腐蚀微环境，从而导致剥离涂层下管道发生腐蚀。本文主要通过微生物技术、微电极技术、电化学阻抗谱及微观分析技术，对有、无硫酸盐还原菌（SRB）条件下，剥离涂层下缝隙内Q235钢局部电位和电流分布、腐蚀微环境变化及Q235钢腐蚀进行系统研究，为进一步了解剥离涂层下金属腐蚀行为，并为埋地管道腐蚀防护提供必要的理论依据。本文通过富集培养、分离及纯化从沈阳土壤中心站土壤中提取了纯的SRB菌株。革兰氏染色结果表明，该菌株为革兰氏阴性菌；产硫化氢试验表明，该菌株能够将硫酸根离子还原成为硫离子。本文通过对三种制备钨/氧化钨pH电极方法进行比较，确定采用钨丝通过电化学方法制备钨/氧化钨pH微电极，该电极具有较好的线性关系及良好的稳定性。本文采用银和铂丝分别制备了Cl离子微电极和氧化还原电位（Eh）微电极。采用上述微电极对剥离涂层下缝隙内溶液pH值、Cl离子浓度和Eh进行原位测量。本文首先对土壤浸出液中SRB与Q235钢之间的相互作用进行了研究。结果表明，试验前期SRB对Q235钢起缓蚀作用，而试验后期则加速了其腐蚀；SRB通过吸附非游离态氧以抵御游离态氧的侵害。本文分别对剥离涂层下缝隙内局部电位和电流分布、微环境变化及Q235钢腐蚀三方面进行研究。探讨了SRB对剥离涂层下缝隙内Q235钢腐蚀及微环境变化的影响。结果表明，外加电位的负移有利于阴极电流渗入到缝隙深处，但当外加电位为-1.076V时，缝隙内Q235钢极化电位发生正移。SRB能够增强外加阴极电位对缝隙深处的影响。SRB的存在降低了溶液中SO42-浓度，且增大了溶液的电导率。当外加电位正于-1.076V时，对溶液中SRB生长影响较小，而当外加电位为-1.076V时，则抑制了溶液中SRB生长。无论有菌还是无菌条件下，缝隙内Eh都呈降低的趋势。外加阴极电位导致缝隙内溶液发生碱化，且随外加电位的负移碱化程度逐渐增强。当外加电位为-0.876V时，在极化前期SRB对Q235钢起缓蚀作用，而极化后期则起加速作用。当外加电位负于-0.876V时，在整个试验过程中SRB都对Q235钢起缓蚀作用。"
其他摘要	"Buried steel pipelines of oil and natural gas usually are prevented from corroding by a combination of insulated coatings and cathodic protection. A coating, which is a physical barrier, has the basic function of letting the steel away from a corrosive environment. Cathodic protection (i.e., electrochemical protection) inhibits or prevents the corrosion of metals by reducing the potential of the metals and making bare metals into immune areas. However, the coating is disbonded because of flaws of the coating and external reasons. A local corrosive micro-environment is formed once corrosive media enter into the crevice between coatings and the steel, which leads to corrosion of steel pipelines under disbonded coatings. In this paper, potential and current distributions of cathodic protection, variation of corrosive micro-environment and corrosion of carbon steel Q235 are investigated in the crevice under the disbonded coatings with and without sulfate-reducing bacteria (SRB) by using microbiological technology, microelectrode technology, electrochemical impedance spectroscopy (EIS) and microscopic analysis, which affords a theoretical base to further studies of corrosion behaviors of the metals and protection of corrosion of buried pipelines under the disbonded coatings. A pure strain of SRB is isolated from soils of Shenyang soil central station by rich-culture, isolation and purification. The results show that the strain is negative in gram stain, and can reduce sulfate to sulfide ion. Compared with three methods of making pH electrode, a W/WO3 pH microelectrode is prepared by electrochemical method, which has a good linear relation and good stabilization. Electrodes of chloride ion and redox potential are also prepared. The pH values, Cl ion concentrations and Eh are in-situ measured in the crevice under the disbonded coating by the above microelectrodes. Interaction between SRB and carbon steel Q235 is studied in soil extract solutions (SES). The results show that SRB has an effect of inhibition on the steel in prior period of experiment, and enhance the corrosion of the steel in later period. SRB protect itself from harmful free oxygen by absorbing substances containing non-free oxygen. The effects of SRB on the potential and current distributions, micro-enviromental variation and corrosion of carbon steel Q235 are studied in the crevice under the disbonded coatings. The results show that increasing of cathodic potential is of advantage to penetration of current into the crevice, but the polarizing potentials of the steel increase in the crevice at the applied potential of -1.076V. SRB can enhance the effect of the applied potential on the electrodes in the deeper crevice. During the course of experiment, SRB consume amounts of sulfate ions, and increase conductivity of solution. When the applied potential is more positive than -1.076V, it has little influence on SRB numbers, but SRB growth is inhibited at the applied potential of -1.076V. The values of Eh decrease with time in the SES with and without SRB. Applied potentials make the solution basification in the crevice, and the degree of bascification increases with the applied potentials increasing. SRB can inhibit corrosion of steel applied potential of -0.876V in prior period, and accelerate the corrosion in later period. However, when the applied potential is more negative than -0.876V, SRB decelerate the corrosion of the steel during the whole period."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64471
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	许进. 剥离涂层下Q235钢硫酸盐还原菌腐蚀机理研究[D]. 北京. 中国科学院金属研究所,2012.