某凝析气田异种不锈钢偶对在不同NaCl溶液中的腐蚀行为

为了考察某凝析气田现场新投用的3种合金钢材316L、双相不锈钢2205以及Inconel 625在现场出现耦合后是否会发生电偶腐蚀,对Inconel 625/316L、Inconel 625/2205偶对在不同Cl~-浓度下的电偶腐蚀特性进行了电化学试验,研究了耦合前各自的开路电位随时间的变化、耦合后的耦合电流随时间的变化、耦合(闭路)电位随时间的变化、耦合电流及耦合(闭路)电位的稳定值大小。结果表明:不同影响因素(电偶、Cl~-浓度)下,电位差均为50 mV左右,电偶电流密度约为1×10~(-6)A/cm~2,由此计算出材料偶接后的均匀腐蚀速度为0.002 mm/a,按照腐蚀速度划分标准(NACE RP0775-2005),均属于轻度腐蚀,因此625/316L、625/2205异种不锈钢之间耦合不会引起明显的电偶腐蚀问题。本方法对在油气田上使用类似异种钢耦合后出现的腐蚀研究具有一定的指导意义。     

连续重整装置中三通管开裂分析

采用宏观形貌分析、扫描电镜观察、电子探针能谱分析、电极电位测定和电偶电流测定等手段,分析了某石化公司连续重整装置中氢气与石脑油混合的三通管的开裂原因。结果表明:开裂邻近三通管与变径管的焊接焊缝处,导致三通管开裂的主要原因是叠加在气蚀、氯和硫腐蚀基础上的电偶腐蚀;开裂三通管材料为Cr5Mo钢,而焊缝材料为铬镍不锈钢,两者之间的电位差高达60 mV,形成了电偶腐蚀,其中三通管因其电极电位比焊缝的更负,成为电偶对中的阳极而被加速腐蚀,从而使三通管在邻近焊缝处的壁厚不断减薄并最终开裂。     

X65管线钢在沉积物下腐蚀与缓蚀剂作用效果

通过电化学阻抗谱和动电位扫描法研究X65管线钢在含氧氯化钠溶液中沉积物对电化学参数的影响。采用电阻法(ER)结合零电阻电流计(ZRA)研究X65钢在沉积物覆盖下的电偶腐蚀行为与不同浓度有机膦缓蚀剂的作用效果。结果表明:X65钢在SiO_2沉积物覆盖时腐蚀电位负移,腐蚀速率降低。当有沉积物覆盖与无沉积物覆盖的电偶试片相连时,X65钢在沉积物下发生阳极极化,阳极电偶电流密度在18h内由120μA/cm~2衰减到50μA/cm~2并保持稳定。依次加入5×10~(-5),8×10~(-5)和3×10~(-4)浓度的PBTCA后,电偶电流在最高升至1300μA/cm~2后逐渐下降并稳定在610μA/cm~2附近,沉积物下X65钢腐蚀速率达到6.11mm/a,PBTCA加速了X65钢在含氧溶液中沉积物下的腐蚀。通过对试片表面进行观察,沉积物下X65钢表面发生了严重的局部腐蚀。     

不同液膜厚度下电偶腐蚀当量折算研究

搭建薄液膜厚度测量与控制装置,采用微距参比电极后置法组建三电极体系,测量了在3.5%(质量分数,下同)NaCl不同液膜厚度下2024铝合金和TA15钛合金极化曲线和电偶电流,得到了不同厚度液膜下两种材料的电化学动力学参数;建立了基于薄壳电流分布的Comsol腐蚀仿真模型,得出了不同液膜厚度下的电偶电流以及电偶腐蚀与无电偶腐蚀时的当量折算系数。结果表明,利用仿真模型得到的电偶电流值与试验值吻合较好,50μm液膜厚度下的电偶电流约是溶液状态的25倍,随着液膜厚度的增大,电偶电流的下降速度逐渐增大,当液膜厚度达到1 000μm时,电偶电流趋近于溶液状态;50μm和100μm液膜厚度下电偶腐蚀折算系数约为无电偶状态下的5倍,当液膜厚度超过100μm时,折算系数急剧下降,到1 000μm时无论有无电偶腐蚀其折算系数均基本趋于1。     

利用微电极阵列技术研究合金的腐蚀

随着工业水平的不断发展与提高,合金材料的使用量亦不断增大。然而合金材料的腐蚀问题在工业生产及生态环境中造成了不可估量的损失。为此,国内外学者已经开展了大量关于合金腐蚀机理与防护方面的研究,并取得了一定的进展。微电极阵列技术是一种介于宏观的经典电化学技术和微区扫描探针技术之间的新型电化学测试方法。它既能获取合金大面积电极的整体平均信息,又能探测合金局部微小区域内的电位、电流分布特征,能更加准确地测试合金局部腐蚀过程中非均一的电化学信息。随着国内外学者的不断研究与开发,现已实现微电极阵列的优化。该技术联合其他电化学测试技术和表面科学技术等方法,不断丰富了合金/腐蚀溶液界面的物理、化学及电化学信息。近几年,大量专家学者采用该微电极阵列技术与其他测试技术相结合的方法研究了常用合金在不同环境和腐蚀状态下的局部腐蚀过程及机理,并取得了重要的研究进展。其中,对异材质金属的电偶腐蚀行为及演变规律的研究取得了重大突破。此外,实时耦合的多电极阵列传感器(CMAS)探针的开发应用,对合金局部腐蚀的在线监/检测起到了举足轻重的作用。本文主要综述了微电极阵列技术在研究合金的电偶腐蚀、表面涂层失效、腐蚀环境的影响方面的进展,探讨了微电极阵列技术在表征合金局部电化学不均一性方面的优势与不足,并对其进行了总结和展望。     

不同pH值模拟混凝土孔隙液中镀锌层的阳极特性逆转

在不同pH值的混凝土中镀锌层显示有阳极逆转现象,其对基体钢的保护作用出现变化。以回填海沙导致近海陆地混凝土建筑镀锌钢管的局部腐蚀为例,模拟其实际工况,将镀锌试样置于6种不同的模拟混凝土孔隙液中,将去锌层钢基置于3.5%NaCl中性溶液中浸泡24 h,用盐桥连接电解池,测定2种试样间的电位-时间曲线和电偶电流值,并与无预浸泡的相应值对比。结果表明:(1)当镀锌层在含有Cl-的中性溶液及pH=10.0,11.0的Ca(OH)2溶液中时,对钢基体起到了牺牲阳极的保护作用;(2)当镀锌层在pH=12.0的Ca(OH)2溶液中时,无论是否预浸泡其电位均出现逆转现象,且电偶电流值为正值,反而会促进钢基体的腐蚀;(3)在pH=12.5的Ca(OH)2溶液中,无预浸泡时镀锌层对去锌层钢基有保护作用,预浸泡24 h后初始阶段具有保护作用,1 650 s后时出现逆转,不仅已失去对钢基体的保护作用,反而会加速其腐蚀。     

混凝土腐蚀监测用参比电极制作及电化学性能研究

参比电极对监测混凝土中钢筋的电位至关重要。使用凝胶作为电极内部电解质、水泥浆作为渗透层,制成Ag/AgCl凝胶参比电极。在混凝土模拟液中测试了电极电位的稳定性、电极的温度系数以及氯离子含量对电位的影响,通过动电位和恒电流极化测试了电极的抗极化性能,并在混凝土中进一步研究了电极电位的时变特性。结果表明,电极电位有良好的稳定性和可靠性,电极温度系数较小,氯离子含量对电极电位的影响可以忽略,电极抗极化性能优良。研制的电极可用于实时监测混凝土内部钢筋的腐蚀电位,为钢筋混凝土构件寿命预测提供参考。     

镁/钢激光-电弧复合焊接接头的腐蚀行为

采用激光-电弧复合填丝对接焊方法获得了成形及力学性能良好的AZ31B镁合金/Q235钢板焊接接头;利用金相显微镜和电子探针观察焊接接头组织和元素分布状态,通过浸泡腐蚀试验和电化学试验研究了焊接接头不同区域(镁母材、焊缝、钢母材)的腐蚀行为。结果表明:AZ31B母材存在各向异性的腐蚀现象;焊缝与钢母材之间发生电偶腐蚀,邻近界面处的焊缝腐蚀严重,而界面处富集Al、Mn元素,腐蚀倾向较小;焊缝中存在较多钢飞溅,钢飞溅周围的区域比焊缝其他位置的腐蚀更为严重,焊接过程中产生的钢飞溅对焊缝的耐蚀性是不利的;焊缝中的β相一方面作为屏障层阻碍基体的腐蚀,另一方面作为电偶腐蚀中的阴极增加焊缝基体的腐蚀敏感性。     

飞机多金属耦合在溶液状态与大气状态下的腐蚀行为对比及当量折算研究

本研究改进了薄液膜测厚装置与电化学测量装置,搭建了溶液电化学测量平台,得到了飞机材料体系中7050铝合金、Aermet100高强钢、1Cr18Ni9Ti不锈钢和QA110-4-4铜合金极化曲线及由它们构成的四电极体系中各电极表面的电偶电流;分别构建基于二次电流分布和壳电流分布的Comsol仿真模型,得到了溶液状态下和100μm液膜下四电极体系的电位和电流密度分布;将四种金属放入溶液状态和大气状态下得到的腐蚀形貌与仿真得到的电位分布进行了对比分析,并对四电极体系中各电极表面进行局部电流密度的面积分,计算得到各电极表面的电偶电流,与测试得到的电流值进行了比较。结果表明:四电极体系中各电极表面电偶电流仿真值与测量值误差在10%以内,液膜状态下多电极表面电位分布区间要远远大于溶液状态下,对比分析腐蚀形貌与仿真电位分布,可以看出仿真得到的表面电位分布高于自腐蚀电位的电极且均出现不同程度的腐蚀损伤,而对低于自腐蚀电位的电极表面腐蚀不明显,证明了模型对电位分布预测的准确性;Aermet100钢在溶液和100μm液膜下出现极性反转现象,在液膜状态下Aermet100钢与7050铝合金作为多电极体系阳极,存在一定竞争关系,使得液膜状态下铝合金腐蚀坑数量和表面电偶电流要小于溶液状态下,铜合金和不锈钢在四电极体系中无论液膜状态还是溶液状态均充当阴极,极性不发生改变。根据腐蚀损伤等效原则,分别计算了溶液状态和液膜状态下不同面积比7050铝合金和Aermet100高强钢的折算系数,这对飞机环境适应性考核广泛采用的加速环境谱中折算系数的选取有一定的参考价值。     

哈氏C-276合金与16MnR钢在盐酸中的电偶腐蚀行为

石化厂急冷塔中的哈氏C-276合金和16MnR钢易形成电偶对,在塔中HCl气氛下发生腐蚀。测定了哈氏C-276合金与16MnR钢在10%盐酸中的自腐蚀速率、电偶腐蚀速率和稳态极化曲线,探讨了偶接时间、阴阳极面积比、环境温度及腐蚀液流速对阳极电流密度的影响。结果表明:2种金属偶接后,阴极哈氏C-276合金腐蚀速率得到抑制,阳极16MnR钢腐蚀速率急剧增大;2种金属自腐蚀电位相差超过200 mV,电偶电位接近16MnR钢的自腐蚀电位;随偶接时间延长,电偶电流不断衰减,24 h后趋于稳定;阳极电流密度随阴阳极面积比增大、温度升高而增大,但呈非线性增长,一定程度后增长趋势变缓;流动的腐蚀液中的阳极电流密度大于静止腐蚀液中的。     

炭纤维环氧复合材料腐蚀行为的研究

采用电化学测试、腐蚀失重测量和SEM表面微观分析等试验方法,研究了炭纤维环氧复合材料浸泡在腐蚀介质中,由于腐蚀介质的存在和作用,对炭纤维环氧复合材料腐蚀行为的影响;同时对偶接了LY12CZ铝合金的炭纤维环氧复合材料也进行了腐蚀浸泡对比试验.结果表明,炭纤维环氧复合材料在3.5%NaCl腐蚀介质中,由于氧扩散的作用,开路电位需要近10h才能达到平衡,其腐蚀电位较正,树脂及树脂与纤维界面对腐蚀介质的吸湿,导致复合材料本身腐蚀增重.浸泡1464h后炭纤维环氧复合材料的表面微观形貌变化不大;在同样的浸泡条件下,偶接了LY12CZ铝合金对炭纤维环氧复合材料的腐蚀行为基本没有影响.     

复合材料表面防护对LY12CZ铝合金电偶腐蚀的影响

应用电化学测量、ＡＳＴＭ ５％盐雾试验、周浸腐蚀和大气暴露试验，研究不同表面处理的复合材料对ＬＹ１２ＣＺ铝合金电偶腐蚀的影响。     

Corrosion behavior of SiC p /6061 Al metal matrix composites in chloride solutions

The corrosion behavior of silicon carbide particulates-aluminum metal matrix composites was studied in chloride solution by means of electrochemical techniques, scanning electron microscope (SEM), transmission electron microscope (TEM) and optical microscope. The materials under investigation were compocasting processed 6061 Al reinforced with increasing amounts of SiC particulates. Electrochemical tests such as potentiostatic polarization were done in 0.1 kmol·m^–3 NaCl solutions that were aerated and deaerated to observe overall corrosion behavior. In addition, pit morphology was observed after immersion tests. It was seen that the pitting potentials did not vary greatly or show definite trends in relation to the amounts of SiC _p reinforcement. However, the degree of corrosion increased with increasing SiC _p content; probably mainly due to galvanic couple. No intermetallics layer was found at the SiC _p /Al interface. Based on pitting potentials of Al-Si alloys, a pitting process around SiC particulate was proposed.Abbreviations SiC _p (silicon carbide particulates) - SiC _f (silicon carbide fibers) - SiC _w (silicon carbide whiskers) - E_pit (pitting potential) - E_prot (protection potential) - E _corr (corrosion potential) - i _galv (galvanic current density) - E _galv (galvanic potential)     

7B04铝合金-CFRP300在模拟海洋大气环境下的电偶腐蚀行为

为了有效地从腐蚀防护角度为飞机异种金属选材提供指导,针对飞机特定的服役环境,通过有限元仿真和腐蚀实验研究飞机典型搭接结构的腐蚀行为。对铝合金、复合材料及搭接件进行了实验室的周浸实验,然后通过极化曲线测量实验、宏微观形貌的观察、疲劳测试、XRD等表征手段研究7B04铝合金与CCF300/QY9511复合材料搭接件的电偶腐蚀规律,并以极化曲线测得的电化学参数为边界条件,建立了搭接件的腐蚀仿真模型。结果表明,在周浸实验0周期和10周期后,铝合金的自腐蚀电位和自腐蚀电流密度分别为-802 mV和2.357×10^-7 A/cm²,-872 mV和1.477×10^-6 A/cm²,复合材料则分别为-240 mV和6.217×10^-7 A/cm²,-98 mV和2.286×10^-7 A/cm²,随着腐蚀周期的延长7B04铝合金材料呈现自腐蚀速率加快、自腐蚀电位负移的变化趋势,而复合材料呈现自腐蚀电位正移、自腐蚀速率缓慢增大的变化趋势;搭接件腐蚀产物逐渐增多,腐蚀程度越来越严重;疲劳寿命随着腐蚀周期的延长而降低;随着腐蚀周期延长,腐蚀坑深度逐渐增大;腐蚀的产物包括Al（OH）₃,Al₂O₃,AlCl₃;搭接件仿真结果与加速腐蚀实验后的结果具有良好的一致性。该研究给出了飞机典型搭接结构的易腐蚀部位,揭示了电偶腐蚀规律,为飞机结构的腐蚀防护指明了方向。     

高温高酸性环境下镍基合金718与异种金属偶接的电偶腐蚀行为

高温/高压高酸性腐蚀环境中镍基合金718常作为可靠的材料使用,但不可避免会与其他金属偶接使用,易产生电偶腐蚀。模拟150℃,H_2S分压1.0 MPa,CO2分压1.5 MPa,Cl~-浓度200 000 mg/L的高温高酸性腐蚀环境,采用高温高压电化学测试技术和浸泡腐蚀模拟试验,研究了镍基合金718分别与低合金钢35Cr Mo、C110和不锈钢13Cr偶接后的电偶腐蚀行为。结果表明:在模拟高温高酸性环境下,3种金属分别与718合金偶接后,均发生了一定程度的电偶腐蚀,其中C110电偶腐蚀速率最大,而不锈钢13Cr的电偶腐蚀速率最小。电偶腐蚀的驱动力是2种金属的自腐蚀电位差,异种金属偶接后的电偶效应与两偶接材料的电位差成正比,而阳极材料自身的极化特性决定了其与耐蚀合金偶接后的电偶腐蚀程度。     

Incoloy 825/L360复合管焊接接头耐蚀性研究

目的研究Incoloy 825/L360复合管焊后的焊缝耐蚀性能。方法以Incoloy 825/L360复合管为研究对象,选用Inconel625焊材进行了镍基合金焊缝的焊接,并对焊缝和Incoloy 825母材在质量分数为3.5%的NaCl溶液、6%的FeCl_3溶液中进行电化学试验,并对其耐蚀性进行了对比分析。结果在质量分数为3.5%的NaCl溶液中,不同温度下母材自腐蚀电位均高于焊缝,自腐蚀电流密度均小于焊缝,随着温度的升高,母材的自腐蚀电位和焊缝的自腐蚀电流密度均增加,母材的自腐蚀电流密度变化不明显;在质量分数为6%的FeCl_3溶液中,母材与焊缝的自腐蚀电位整体较高,母材的自腐蚀电流密度高于焊缝,不同温度下焊缝极化曲线均存在明显的钝化平台。结论 Incoloy 825母材和焊缝在两种溶液中的耐蚀性存在一定差异;在质量分数为3.5%的NaCl溶液中,母材腐蚀对温度不敏感,焊缝的腐蚀敏感倾向性随着温度的升高而增大,腐蚀敏感性高于母材;在质量分数为6%的FeCl_3溶液中,不同温度下的焊缝极化曲线均存在明显的钝化平台,腐蚀敏感性低于母材。     

Corrosion behaviour of hot dip zinc and zinc-aluminium coatings on steel in seawater

A comparative investigation of hot dip Zn-25Al alloy, Zn-55Al-Si and Zn coatings on steel was performed with attention to their corrosion performance in seawater. The results of 2-year exposure testing of these at Zhoushan test site are reported here. In tidal and immersion environments, Zn-25Al alloy coating is several times more durable than zinc coating of double thickness. At long exposure times, corrosion rate for the Zn-25Al alloy coating remains indistinguishable from that for the Zn-55Al-Si coating of similar thickness in tidal zone, and is two to three times lower than the latter in immersion zone. The decrease in tensile strength suggested that galvanized and Zn-55Al-Si coated steel suffer intense pitting corrosion in immersion zone. The electrochemical tests showed that all these coatings provide cathodic protection to the substrate metal; the galvanic potentials are equal to −1,050, −1,025 and −880 mV (SCE) for zinc, Zn-25Al alloy and Zn-55Al-Si coating, respectively, which are adequate to keep the steel inside the immunity region. It is believed that the superior performance of the Zn-25Al alloy coating is due to its optimal combination of the uniform corrosion resistance and pitting corrosion resistance. The inferior corrosion performance by comparison of the Zn coating mainly results from its larger dissolution rate, while the failure of the Zn-55Al-Si coating is probably related to its higher susceptibility to pitting corrosion in seawater.     

Root cause analysis for 316L stainless steel tube leakages

Perforation of ASTM A270 TP316L stainless steel tube, used for transportation of ozonated high purity water in a pharmaceutical plant, was discovered after 3 months in actual service. The current investigation was conducted in order to explore the root causes of failure. Various techniques including on-site investigation, emission spectroscopy, ion chromatography, radioscopy, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and intergranular corrosion testing were implemented for failure analysis of the tube components. The results revealed that the perforation of tube was initiated from the outer wall and extended to the inner wall by pitting corrosion. The stagnant state of chloride-containing water was the main reason for inducing such corrosion attack. The weld metal was the most susceptible to corrosion attack leading to perforation of the wall thickness, although initiation sites of pitting corrosion were also observed in the base metal. The dimensions of each pit mouth are very small, but enlarged subsurface cavities were observed. The selective dissolution of material due to galvanic effects between delta-ferrite and the austenite matrix occurred in the weld zone. It is suggested that failure prevention could be achieved by controlling the quality of the insulation system. In addition, careful control of welding conditions must be implemented during fabrication.     

A new method to determine the synergistic effects of area ratio and microstructure on the galvanic corrosion of LAS A508/309 L/308 L SS dissimilar metals weld

The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld(DMW)are studied by a multi-analytical approach.It was demonstrated that decreasing the anode/cathode surface area ratio obviously enhances the corrosion rate of A508,both locally and globally.Deeper analyses of the AFM results enabled quantitative comparison of the corrosion behaviour of the different surface constituents.It was revealed that in the galvanic interaction of the DMW,the grain refined region corrodes most,followed by the partial grain refined region and base metal matrix of the A508,respectively.The electrochemical localization index(LI)estimation method and AFM analysis both confirmed the presence of a mixed(localized and uniform)corrosion phenomenon occurring on the surface of the A508 anode metal in the galvanic interaction of the dissimilar metals.Finally,the degree of synergism equation was utilized to describe the synergistic effects of anode/cathode area ratio and the microstructure of the samples on the galvanic corrosion of LAS A508/309L/308L SS DMW.     

Study on periodic immersion and infrared aging corrosion behavior of bridge weathering steel Q420qNH welded joint and plate in NaHSO3 solution

The periodic immersion corrosion behavior and corrosion mechanism of Q420qNH steel weld, heat-affected zone and plate sample in simulated industrial atmospheric medium were studied. The corrosion type of the three samples is the non-uniform total corrosion, and the corrosion products at different stages are different. Ferric oxide and lepidocrocite (γ-FeOOH) are generated in the immersion stage and the initial stage of infrared drying, respectively. However, lepidocrocite (γ-FeOOH), ferrosoferric oxide (Fe₃O₄) and goethite (α-FeOOH) generated in the later stage of infrared drying. The infrared drying process is conducive to the formation of goethite (α-FeOOH). The corrosion rate of weld is always lower than that of plate, and the I_α-FeOOH/I_γ-FeOOH ratio of the weld is always higher than that of plate and heat-affected zone sample. In the later stage of corrosion, the self-corrosion current density of the three samples from small to large is weld, heat-affected zone and plate, and self-corrosion potential from large to small is weld, heat-affected zone and plate. The resistance of the rust layer of the weld and heat-affected zone sample is 1.81 times, 1.29 times of that of the plate, respectively. This is because the weld is composed of a large number of small angular grain boundary structures dominated by tiny acicular ferrite in the original austenite grain, which is conducive to the improvement of corrosion resistance. In addition, the higher chromium/carbon (Cr/C), copper and nickel elements of the weld can promote the conversion from lepidocrocite (γ-FeOOH) to goethite (α-FeOOH), and improve the density and stability of weld rust layer.