土壤中尿素对Q235钢硫酸盐还原菌腐蚀影响的研究

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	土壤中尿素对Q235钢硫酸盐还原菌腐蚀影响的研究
	李喜明
学位类型	硕士
导师	王振尧 ; 孙成
	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	腐蚀科学与防护
关键词	Q235钢 Srb 尿素土壤腐蚀 Q235 Steel Srb Urea Soil Corrosion
摘要	" 随着地下管线的发展，管线钢在土壤中的腐蚀与防护受到越来越多的重视。土壤环境复杂多变，因而管线钢的腐蚀受到诸多因素的影响如土壤湿度、酸碱度、盐分组成及含量、微生物组成及含量等。但以往的研究多是在土壤模拟溶液或者自然土壤环境中，忽略了很多管道铺设在农田中。随着农业的发展，为了提高农作物产量，人们大量施用化肥，其中最常用的是氮肥-尿素。尿素可以抑制碳钢在含氯离子溶液中的腐蚀。此外尿素在含水量较大的环境中可以分解成氨气和二氧化碳，改变碳钢所处的土壤环境。腐蚀是金属与所处环境之间的相互作用，因此土壤环境的改变肯定会影响碳钢的腐蚀行为。土壤是微生物生长的天然培养基，由微生物引起的管道腐蚀受到广泛关注，其中研究最多也最为重要的是硫酸盐还原菌(SRB)。尿素作为有机物可以促进微生物生长，其对SRB生长活性影响如何尚没有报道。因此不同浓度的尿素在有菌和无菌土壤中分别对Q235钢的腐蚀产生怎么样的影响，需要进行探讨。本文将通过实验室模拟土壤环境，利用电化学、微生物、表面分析等测试技术，研究不同土壤湿度条件(10%，20%，30%)下，不同尿素浓度变化(0wt%，0.05wt%，0.1wt%，0.2wt%，0.3wt%，0.5wt%)对硫酸盐还原菌活性及Q235钢的有菌和无菌腐蚀的影响。研究结果发现：在无菌土壤中，尿素吸附在试样表面，抑制碳钢腐蚀；同时部分尿素发生分解生成氨气和二氧化碳，改变了土壤环境。不同湿度条件下，随尿素含量增加，碳钢的平均腐蚀速率降低，说明尿素抑制碳钢的无菌土壤腐蚀；且这种抑制作用随尿素浓度的增加而增强。Q235钢在湿度为20%的土壤中平均腐蚀速率远大于湿度为10%的平均腐蚀速率。当湿度进一步增加为30%时，氧含量降低，腐蚀过程的阴极反应受到抑制，腐蚀速率降低。但在低含量尿素(0.05wt%，0.1wt%)土壤中，湿度为30%的土壤中平均腐蚀速率高于湿度为20%，因为尿素在湿度较高时更易分解，此时低含量尿素对碳钢的保护作用减弱，腐蚀速率有所增大。在有菌土壤中，尿素对Q235钢腐蚀的影响比较复杂：一部分尿素仍被吸附在试样表面，抑制腐蚀进行；一部分尿素促进SRB生长，SRB促进Q235钢的腐蚀；一部分尿素发生分解，生成氨气和二氧化碳，改变碳钢所处的土壤环境。因此这三种不同影响因素相互竞争，碳钢则表现出不同的腐蚀速率。不同湿度条件下，尿素的分解程度不同，生成的氨气和二氧化碳的扩散不同，SRB的生长活性不同，碳钢的表面腐蚀产物形貌不同，则Q235钢的平均腐蚀速率也不同。不同湿度条件下Q235钢的平均腐蚀速率相比大小为：20%＞10%＞30%。湿度10%时，尿素促进SRB腐蚀：随着尿素浓度增加，Q235钢的平均腐蚀速率增大，在尿素含量为0.3wt%时有所减小；因为低含量尿素促进SRB生长，高含量尿素抑制SRB生长。湿度为20%时，尿素促进了SRB腐蚀(尿素含量0.5wt%除外)：随着尿素含量的增加，腐蚀速率减小，在尿素含量为0.5wt%时抑制了SRB腐蚀。湿度为30%时，尿素抑制了SRB腐蚀：随尿素含量增加，碳钢的平均腐蚀速率变化没有规律。"
其他摘要	" Along with the development of underground pipelines, more and more attention is paid on corrosion and protection of pipeline in soils. Since soil environment is complicated and changeful, the corrosion of pipeline steel is affected by various factoRs such as soil humidity, acidity, soil salinity and composition of microbes and so on. However, previous researches in soil corrosion have been conducted in soil simulated solution or nature soils, which ignores the situation of pipelines in farmland. With agricultural development, more fettilizers are used on farmland in order to raise crop outputs, of which nitrogenous fertilizer, urea, is the most common. Urea can decrease the corrosion rate of carbon steel in solution containing chloride ion. Besides urea can be decomposed into ammonia and carbon dioxide under wet condition, which could change soil environment. Corrosion happens between metals and its ambient environment, hence changes of soil environment would influence corrosion of pipeline steel. Microbes have been considered as one of the major causes of soil corrosion, known as Microbiological Influenced Corrosion (MIC). Sulphate-reducing bacterial is one of the key elements of MIC and also best studied. Urea can be served as energy source for microbe growth. Whether urea can promote the growth of SRB in soils has not been studied. What effects of different content of urea would produce on corrosion of Q235 steel both in sterile soil and inoculated soil with SRB is to be studied. In the present paper, the effects of different content of urea (0wt%，0.05wt%，0.1wt%，0.2wt%，0.3wt%，0.5wt%) on the corrosion of carbon steel Q235 both in sterile and inoculated soil with SRB have been investigated at different soil moisture (10%, 20%, 30%) by using electrochemical methods, microbiological test methods, surface analysis methods and so on. In sterile soil, urea is adsorbed on carbon steel surface, which prevents its corrosion; some of urea has been decomposed into ammonia and carbon dioxide, which have changed soil environment. In different soil moisture, average corrosion rate of Q235 steel deceases along with increasing urea content, which shows urea prevents corrosion of Q235 steel in sterile soil and this influence has been strengthened with increasing urea content. Corrosion rate of Q235 steel in soil moisture of 20% is much larger than that in moisture of 10%. When in soil moisture of 30%, there is few dissolve oxygen, which prevents the cathodal reaction, the corrosion rate down. However in soils containing low urea concentration(0.05wt% and 0.1wt%), corrosion rate in soil with the moisture of 30% is larger than that in moisture of 20%, because urea can be decomposed easier in higher soil moisture. Then low content of urea cannot protect the carbon steel so well, and corrosion rate increases. In inoculated soil with SRB, effects of urea on corrosion of Q235 steel have been complicated: some urea can be adsorbed on the steel surface to protect it from corrosion; some urea promotes SRB growth and SRB can induce corrosion of carbon steel; some can be decomposed to ammonia and carbon dioxide. Hence these three different kinds of effects compete with each other, which make different corrosion behavior of Q235 steel in inoculated soil. Meanwhile at the different soil moisture, there are different in the decomposition level of urea, the confusion level of ammonia and carbon dioxide, SRB growth and corrosion products morphology on the steel surface, consequently the average corrosion rate of Q235 steel. When compared in different soil moisture, the average corrosion rate of Q235 steel varies in the order of 20%＞10%＞30%. In soil with the moisture of 10%, urea promotes SRB corrosion: average corrosion rate increases with increasing urea concentration, but decreases in soil containing 0.3wt% urea. Because low concentration of urea can promote SRB growth, and high concentration of urea can prevent SRB growth. In soil with the moisture of 20%, urea also promotes SRB corrosion (0.5wt% excluded) but in different level: corrosion rate decreases with increasing urea content; in soil containing 0.5wt% urea corrosion rate being lower than that in soil without urea. In soil with the moisture of 30%, urea prevents SRB corrosion: along with increasing urea content, there is no constant distinct regularity in average corrosion rates."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64522
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	李喜明. 土壤中尿素对Q235钢硫酸盐还原菌腐蚀影响的研究[D]. 北京. 中国科学院金属研究所,2012.