本文關(guān)鍵詞： AC 應(yīng)力腐蝕開裂 X80管線鋼 高pH　出處：《北京科技大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：近年來,隨著高壓交流輸電線路及交流電氣化鐵路的快速建設(shè),使得埋地鋼質(zhì)管道遭受交流干擾的風(fēng)險(xiǎn)日益增加。交流干擾導(dǎo)致管道發(fā)生交流腐蝕,加速管道的腐蝕,嚴(yán)重威脅管道的正常運(yùn)營。目前,國內(nèi)外學(xué)者對(duì)交流腐蝕進(jìn)行了大量的研究,但未有交流電對(duì)管線鋼的SCC行為及機(jī)理影響的相關(guān)文獻(xiàn)報(bào)道。因此,本文采用極化曲線、開路電位測試、EIS測試、Mott-Schottky曲線測試、浸泡實(shí)驗(yàn)、SSRT實(shí)驗(yàn)、U形彎實(shí)驗(yàn)及裂紋擴(kuò)展實(shí)驗(yàn)系統(tǒng)研究了交流電作用下X80鋼在高pH值溶液中的腐蝕行為,尤其是重點(diǎn)研究了交流電對(duì)X80鋼在高pH值溶液中的SCC行為及機(jī)理的影響。主要結(jié)論如下： 電化學(xué)測試結(jié)果表明：AC作用下X80鋼的開路電位負(fù)移,開路電位負(fù)移程度隨交流電流密度的增加而增加。低頻率交流電作用下(30-300Hz),開路電位負(fù)移明顯；高頻率交流電作用下(300-1000Hz),X80鋼的開路電位負(fù)移程度較小。不同波形交流電作用下X80鋼的開路電位負(fù)移程度由小到大依次為：正弦波、三角波、方波。交流電作用導(dǎo)致X80鋼在高pH值溶液的鈍性下降,低交流電流密度對(duì)鈍化膜的破壞作用較小,隨交流電流密度的增加,鈍化區(qū)明顯變窄,臨界點(diǎn)蝕電位負(fù)移,維鈍電流密度增大,鈍化膜內(nèi)的施主密度ND增大。低頻率交流電對(duì)X80鋼的鈍性有明顯的破壞,高頻AC對(duì)鈍化膜的破壞較小。不同波形交流電作用下試樣的鈍性均明顯下降。 浸泡實(shí)驗(yàn)結(jié)果表明：低交流電流密度作用下X80鋼主要以輕微的均勻腐蝕為主,高交流電流密度下試樣的局部腐蝕特征明顯；高頻交流電作用下試樣產(chǎn)生輕微的均勻腐蝕,低頻交流電作用下,腐蝕加劇,點(diǎn)蝕明顯；方波作用下局部腐蝕最明顯,其次為三角波,正弦波作用下局部腐蝕較輕微。AC作用增加了X80鋼的腐蝕速率,腐蝕速率隨交流電流密度的增加而增加。低頻交流電作用下X80鋼的腐蝕速率隨頻率的增大而快速減小,而高頻交流電作用下腐蝕速率緩慢減小。不同波形交流電作用下腐蝕速率由小到大依次為：正弦波、三角波、方波。 預(yù)加交流電作用下,AC誘發(fā)的局部腐蝕促進(jìn)了SCC裂紋的萌生與擴(kuò)展,導(dǎo)致SCC敏感性增加。預(yù)加交流電X80鋼在高pH值溶液中的的裂紋擴(kuò)展方式均為沿晶擴(kuò)展,SCC機(jī)理均為陽極溶解,這與IGSCC一致。當(dāng)iAC大于30A/m2時(shí),SCC敏感性隨交流電流密度的增加而增加。高頻交流電對(duì)SCC敏感性影響很小,隨頻率的減小SCC敏感性有所增加,30Hz作用下SCC敏感性明顯增加。交流電波形對(duì)SCC敏感性影響由大到小依次為方波、三角波、正弦波。 在SSRT進(jìn)行過程中施加交流電,觀察發(fā)現(xiàn)X80鋼的SCC裂紋密集度很高,裂紋寬且深,裂紋穿晶擴(kuò)展,呈現(xiàn)出明顯的脆性斷裂特征,SCC機(jī)理為陽極溶解+氫脆作用；無交流電作用下,裂紋窄且淺,裂紋沿晶擴(kuò)展,SCC機(jī)理為陽極溶解。X80鋼SCC敏感性隨施加的交流電流密度的增加而增加,當(dāng)iAC大于100A/m2時(shí),SCC敏感性較高。不同波形交流電作用SCC敏感性由小到大依次為正弦波、方波、三角波。SCC敏感性隨頻率的減小而增加,低頻AC作用下SCC敏感性較高。 U形彎實(shí)驗(yàn)結(jié)果亦表明：交流電的施加加速了X80鋼的腐蝕,誘發(fā)了點(diǎn)蝕的產(chǎn)生,有利于SCC裂紋的萌生。裂紋擴(kuò)展實(shí)驗(yàn)結(jié)果表明：有無AC作用X80鋼的裂紋擴(kuò)展行為差異明顯。有無交流電作用X80鋼的平均裂紋擴(kuò)展速率分別為5.645×10-3mm/cycle(7.056×10-6mm/s),5.99×10-4mm/cycle(7.48×10-7mm/s),交流電的施加加快了X80鋼裂紋的擴(kuò)展。 AC和C1-發(fā)生了協(xié)同作用,導(dǎo)致X80鋼的電化學(xué)活性增大,開路電位的負(fù)移幅度明顯,鈍化膜破壞嚴(yán)重,腐蝕速率大幅增加,局部腐蝕特征明顯,SCC敏感性增加,呈明顯的脆性斷裂,SCC機(jī)理為陽極溶解+氫脆作用。
[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.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG172

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本文編號(hào)：1481252