交流电作用下X80钢在高pH值溶液中的应力腐蚀开裂行为及机理研究

发布时间：2018-02-01 07:04

本文关键词： AC 应力腐蚀开裂 X80管线钢高pH　出处：《北京科技大学》2015年博士论文　论文类型：学位论文

【摘要】：近年来,随着高压交流输电线路及交流电气化铁路的快速建设,使得埋地钢质管道遭受交流干扰的风险日益增加。交流干扰导致管道发生交流腐蚀,加速管道的腐蚀,严重威胁管道的正常运营。目前,国内外学者对交流腐蚀进行了大量的研究,但未有交流电对管线钢的SCC行为及机理影响的相关文献报道。因此,本文采用极化曲线、开路电位测试、EIS测试、Mott-Schottky曲线测试、浸泡实验、SSRT实验、U形弯实验及裂纹扩展实验系统研究了交流电作用下X80钢在高pH值溶液中的腐蚀行为,尤其是重点研究了交流电对X80钢在高pH值溶液中的SCC行为及机理的影响。主要结论如下：电化学测试结果表明：AC作用下X80钢的开路电位负移,开路电位负移程度随交流电流密度的增加而增加。低频率交流电作用下(30-300Hz),开路电位负移明显；高频率交流电作用下(300-1000Hz),X80钢的开路电位负移程度较小。不同波形交流电作用下X80钢的开路电位负移程度由小到大依次为：正弦波、三角波、方波。交流电作用导致X80钢在高pH值溶液的钝性下降,低交流电流密度对钝化膜的破坏作用较小,随交流电流密度的增加,钝化区明显变窄,临界点蚀电位负移,维钝电流密度增大,钝化膜内的施主密度ND增大。低频率交流电对X80钢的钝性有明显的破坏,高频AC对钝化膜的破坏较小。不同波形交流电作用下试样的钝性均明显下降。浸泡实验结果表明：低交流电流密度作用下X80钢主要以轻微的均匀腐蚀为主,高交流电流密度下试样的局部腐蚀特征明显；高频交流电作用下试样产生轻微的均匀腐蚀,低频交流电作用下,腐蚀加剧,点蚀明显；方波作用下局部腐蚀最明显,其次为三角波,正弦波作用下局部腐蚀较轻微。AC作用增加了X80钢的腐蚀速率,腐蚀速率随交流电流密度的增加而增加。低频交流电作用下X80钢的腐蚀速率随频率的增大而快速减小,而高频交流电作用下腐蚀速率缓慢减小。不同波形交流电作用下腐蚀速率由小到大依次为：正弦波、三角波、方波。预加交流电作用下,AC诱发的局部腐蚀促进了SCC裂纹的萌生与扩展,导致SCC敏感性增加。预加交流电X80钢在高pH值溶液中的的裂纹扩展方式均为沿晶扩展,SCC机理均为阳极溶解,这与IGSCC一致。当iAC大于30A/m2时,SCC敏感性随交流电流密度的增加而增加。高频交流电对SCC敏感性影响很小,随频率的减小SCC敏感性有所增加,30Hz作用下SCC敏感性明显增加。交流电波形对SCC敏感性影响由大到小依次为方波、三角波、正弦波。在SSRT进行过程中施加交流电,观察发现X80钢的SCC裂纹密集度很高,裂纹宽且深,裂纹穿晶扩展,呈现出明显的脆性断裂特征,SCC机理为阳极溶解+氢脆作用；无交流电作用下,裂纹窄且浅,裂纹沿晶扩展,SCC机理为阳极溶解。X80钢SCC敏感性随施加的交流电流密度的增加而增加,当iAC大于100A/m2时,SCC敏感性较高。不同波形交流电作用SCC敏感性由小到大依次为正弦波、方波、三角波。SCC敏感性随频率的减小而增加,低频AC作用下SCC敏感性较高。 U形弯实验结果亦表明：交流电的施加加速了X80钢的腐蚀,诱发了点蚀的产生,有利于SCC裂纹的萌生。裂纹扩展实验结果表明：有无AC作用X80钢的裂纹扩展行为差异明显。有无交流电作用X80钢的平均裂纹扩展速率分别为5.645×10-3mm/cycle(7.056×10-6mm/s),5.99×10-4mm/cycle(7.48×10-7mm/s),交流电的施加加快了X80钢裂纹的扩展。 AC和C1-发生了协同作用,导致X80钢的电化学活性增大,开路电位的负移幅度明显,钝化膜破坏严重,腐蚀速率大幅增加,局部腐蚀特征明显,SCC敏感性增加,呈明显的脆性断裂,SCC机理为阳极溶解+氢脆作用。
[Abstract]:In recent years, with the rapid development of UHV AC transmission line and AC electrified railway, the risk of buried steel pipelines subjected to AC interference increasing. AC interference caused pipeline AC corrosion, corrosion of the pipeline, a serious threat to the normal operation of pipeline. At present, the domestic and foreign scholars have conducted a lot of research on the AC corrosion. But the reported effects of SCC behavior and mechanism of no alternating current on the pipeline steel. Therefore, this paper uses the polarization curve, open circuit potential test, EIS test, Mott-Schottky curve test, immersion test, SSRT test, studied under the action of alternating current corrosion behaviors of X80 steel in solution of high pH value expansion experiment system and crack bending experiment the shape of U, especially focusing on the alternating current of X80 steel in high pH value SCC behavior and mechanism in solution. The main conclusions are as follows:
The electrochemical results show that the open circuit potential of X80 steel AC under the effect of negative shift, open circuit potential negative increases with the increase of AC current density shift. Under the action of low frequency alternating current (30-300Hz), open circuit potential negative shift significantly; under the action of high frequency alternating current (300-1000Hz), open circuit potential negative shift of X80 steel is lesser. The open circuit potential of X80 steel in different degree under the action of alternating current waveform negative shift in order was: sine wave, triangle wave, square wave alternating current. Due to blunt solution drop of X80 steel in high pH value, low AC current density damage on the passivation film is small, with the increase of AC current density, the passivation region becomes narrow. The critical pitting potential shifted negatively, passive current density increased and the donor density ND in passive film increases. Low frequency alternating current blunt on X80 steel has obvious damage to the passivation film with less damage. Different frequency AC waveform The passivity of the specimen decreased obviously under the action of alternating current.
For the experimental results show that the low AC current density under the action of X80 steel is mainly to light uniform corrosion, local corrosion characteristics of high AC current density of specimens under high frequency alternating current effect is obvious; the specimen under uniform light corrosion, low frequency alternating current under the action of corrosion, pitting is obvious; effect of square wave under local corrosion is the most obvious followed by the triangular wave, sine wave under the action of local corrosion of mild.AC increased the corrosion rate of X80 steel, the corrosion rate increases with the increase of AC current density increases. The corrosion rate of X80 steel under low frequency alternating current with frequency decreases rapidly, and the rate of corrosion under high frequency alternating current decreases slowly. Different alternating current waveform under the effect of corrosion rate in order was: sine wave, triangle wave, square wave.
Pre AC under local corrosion induced by AC promoted SCC crack initiation and expansion, resulting in increased susceptibility to SCC. The pre AC X80 steel in high pH value of the solution crack extension is transgranular, SCC mechanism are anodic dissolution, this is consistent with the IGSCC. When the iAC is greater than 30A/m2 SCC, the sensitivity increased with the increase of current density. The effect of high frequency AC AC susceptibility of SCC is very small, decreases with frequency increase the sensitivity of SCC, 30Hz under SCC sensitivity increased significantly. Effect of alternating current waveform sensitivity to SCC followed by Fang Bo, triangle wave, sine wave.
In the process of applying AC current in SSRT, observed that X80 steel SCC crack density is very high, the crack width and depth, crack transgranular brittle fracture, showing obvious characteristics of SCC, mechanism of anodic dissolution + hydrogen embrittlement; no crack under the action of alternating current, narrow and shallow cracks along the grain boundaries, the mechanism of SCC for the anodic dissolution of.X80 steel increased with the increase of AC SCC sensitivity of applied current density increases when iAC is greater than 100A/m2, the sensitivity of SCC is higher. The different effects of SCC alternating current waveform sensitivity in order was sine wave, square wave, triangle wave.SCC sensitivity increases with frequency decreases, low frequency AC SCC under the action of high sensitivity.
The experimental results also showed that the U shaped bend: alternating current applied accelerates the corrosion of X80 steel, induced the generation of pitting initiation, there is conducive to SCC crack. The crack propagation experimental results showed that the crack propagation behavior of AC X80 steel significantly. There is no AC effect of average crack growth rate of X80 steel was 5.645 * 10-3mm/cycle (7.056 * 10-6mm/s), 5.99 * 10-4mm/cycle (7.48 * 10-7mm/s), alternating current applied to accelerate the crack propagation of X80 steel.
The synergistic effect of AC and C1-, resulting in the increase of the electrochemical activity of X80 steel, the open circuit potential negative shift significantly, passivation film damage, the corrosion rate increased significantly, the local corrosion characteristics, the sensitivity of SCC was significantly increased, the brittle fracture mechanism, SCC solution + hydrogen embrittlement role for Yang Jirong.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG172

【参考文献】