含Cr低合金管线钢的焊接性能和耐蚀性能研究

发布时间：2018-03-30 21:37

  本文选题：CO_2腐蚀　切入点：焊接性能　出处：《北京科技大学》2016年博士论文

【摘要】：为了应对日益加剧的C02腐蚀问题带来的严峻挑战,一类新型高性价比含Cr低合金钢在近年得以开发,并受到越来越多的关注和研究。含Cr低合金钢作为目前经济性与安全性结合最为理想的抗CO2腐蚀管线钢,有望替代传统碳钢成为新一代主流集输管线材料。然而,其焊接性能的不完善和抗C02腐蚀机理的不明确,大大限制了其在油气工业领域的推广和发展。因此,本文针对焊接接头力学性能、焊接接头电偶腐蚀、高温高压C02腐蚀以及抗C02腐蚀机理对低Cr钢进行了研究,主要包括以下几个方面：首先,通过大量焊接实验及焊接接头力学性能测试和对比研究,开发出目前与3Cr管线钢匹配最为理想的焊接材料,并制定了合理的现场焊接工艺。对比商用TGS-2CML和H08Cr3MoMnA焊丝,采用自制AR01自动焊焊丝结合半自动焊焊接工艺得到的焊接接头焊缝区晶粒最为均匀细密,且焊缝区与热影响区过渡更为自然,各项力学性能也均能较好满足挪威船级社制管工艺DNV-OS-F101标准。焊接接头各区域间形成理想的“大阳极(BM)+小阴极(WZ、HAZ)"电偶组合,对管线的服役安全和使用寿命十分有利。其次,利用高温高压C02腐蚀模拟实验和电化学测试,研究了3Cr钢表面腐蚀产物膜生长过程的演变,并建立了其腐蚀产物膜生长模型。该模型指出3Cr钢表面腐蚀产物膜的生长可以分为三个阶段,即FeOH/CrOH动态吸附阶段、不完整产物膜覆盖阶段、完整产物膜稳定生长阶段。最后,通过高温高压原位电化学及pH监测手段,明确了低Cr钢区别于传统碳钢的阴极反应机制,给出了低Cr钢耐蚀性能评价的一个关键指标——自发半钝化,并进一步提出了低Cr钢完整的自发半钝化机制。低Cr钢中Cr的加入通过对阴极过程和阳极过程的共同影响来诱发基体的自发半钝化,从而大大提高其耐蚀性能。对于阳极过程,基体中Cr的加入使阳极过程附加Cr的系列反应,导致基体表面在腐蚀初期被完整致密的Cr(OH)3膜覆盖,阳极电流密度降低。对于阴极过程,基体中Cr的加入可以通过快速降低基体表面溶液pH来驱动阴极过程由HC03-的还原向H+的还原转变,从而导致混合电位的正移,进入钝化电位区间,发生自发半钝化。另外,本文发现并提出了3Cr钢表面Cr(OH)3膜的形成与苯甲酰胺缓蚀剂吸附行为的竞争机制,认为在苯甲酰胺浓度低于200 mM时,缓蚀剂的存在对3Cr钢表面Cr(OH)3膜的生成基本没有影响,此时Cr(OH)3膜的生成占据主导过程。而当苯甲酰胺浓度达到或超过600 mM时,缓蚀剂则可以快速富集并吸附于基体表面,从而对Cr(OH)3膜的生成起到完全抑制作用,影响基体的钝化行为。在介于200 mM与600 mM之间,缓蚀剂吸附与Cr(OH)3膜的生成共同发生。该竞争机制的提出对工业应用中低Cr钢缓蚀剂的匹配及浓度选择具有重要的指导和借鉴意义。
[Abstract]:In order to meet the severe challenge brought by the increasing corrosion problem of CO2, a new type of low alloy steel containing Cr with high performance and price ratio has been developed in recent years. Cr-containing low alloy steel, as the most ideal CO2 corrosion resistant pipeline steel combining economy and safety, is expected to replace traditional carbon steel as a new generation of mainstream pipeline materials. The imperfection of its welding properties and the unclear mechanism of corrosion resistance to CO2 greatly limit its popularization and development in the field of oil and gas industry. Therefore, the mechanical properties of welded joints and the galvanic corrosion of welded joints are studied in this paper. The corrosion mechanism of high temperature and high pressure CO2 and the mechanism of corrosion resistance to CO2 are studied. The main contents are as follows: firstly, through a large number of welding experiments, the mechanical properties of welded joints are tested and compared. The most ideal welding material matching with 3Cr pipeline steel is developed, and a reasonable welding process is made. Compared with commercial TGS-2CML and H08Cr3MoMnA welding wire, The grain size of weld zone obtained by self-made AR01 automatic welding wire combined with semi-automatic welding process is the most uniform and compact, and the transition between weld zone and heat affected zone is more natural. All mechanical properties can also meet the DNV-OS-F101 standard of pipe making process of Norwegian Classification Society. An ideal combination of "large anode BMM small cathode WZZHAZ)" is formed between the regions of welded joints, which is very beneficial to the service safety and service life of the pipeline. Secondly, The growth process of corrosion product film on 3Cr steel was studied by means of high temperature and high pressure corrosion simulation experiment and electrochemical test. The growth model of corrosion product film on 3Cr steel was established. The model indicates that the growth of corrosion product film on 3Cr steel can be divided into three stages: dynamic adsorption stage of FeOH/CrOH, covering stage of incomplete product film, stable growth stage of intact product film. By means of high temperature and high pressure in situ electrochemistry and pH monitoring, the cathodic reaction mechanism of low Cr steel and traditional carbon steel is clarified. A key index for evaluation of corrosion resistance of low Cr steel, spontaneous semi-passivation, is given. Furthermore, the mechanism of complete spontaneous semi-passivation of low Cr steel is put forward. The addition of Cr in low Cr steel induces spontaneous semi-passivation of matrix through the influence of cathodic process and anode process, which greatly improves the corrosion resistance of low Cr steel. The addition of Cr in the substrate results in the addition of a series of reactions of Cr to the anode process, which results in the substrate surface being covered by a complete and compact Cr(OH)3 film at the beginning of corrosion, and the anode current density decreases. The addition of Cr in the matrix can drive the cathodic process from reduction of HC03- to reduction of H by rapidly reducing the pH of the solution on the substrate surface, which leads to the positive shift of the mixed potential into the range of passivation potential and spontaneous semi-passivation. In this paper, the competitive mechanism between the formation of Cr(OH)3 film on 3Cr steel surface and the adsorption behavior of benzoamide inhibitor is proposed. It is considered that when the concentration of benzoamide is less than 200mm, the existence of inhibitor has little effect on the formation of Cr(OH)3 film on 3Cr steel surface. However, when the concentration of benzoamide reached or exceeded 600mm, the inhibitor could be rapidly enriched and adsorbed on the substrate surface, which completely inhibited the formation of Cr(OH)3 film. Affects the passivation behavior of the substrate. Between 200 mm and 600 mm, Adsorption of corrosion inhibitor and formation of Cr(OH)3 membrane occur together. This competitive mechanism has important guidance and reference significance for industrial application of medium and low Cr steel corrosion inhibitor matching and concentration selection.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG406;TG178
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本文编号：1687738