深海环境对纯镍腐蚀行为的影响Ⅱ—利用随机分析方法研究纯镍在静水压力下的点蚀行为

利用电化学测量方法测量纯镍在3.5%NaC l溶液中,静水压力为0 MPa和8 MPa条件下的点蚀击破电位和孕育时间.分析得到纯镍在不同静水压力下点蚀击破电位的理论精确值,利用随机分析方法分析纯镍在静水压力下的点蚀机制.实验结果表明静水压力对纯镍的点蚀过程有着重要的影响,在静水压力下纯镍的点蚀行为和机制发生了改变.在较高的静水压力下,纯镍点蚀产生的敏感性增强,点蚀击破电位Ecritical明显降低;纯镍点蚀诱导时间也变短,其点蚀产生的机制发生了改变;在较高静水压力下,纯镍表面的钝化膜活性增强,恶化了纯镍的耐蚀能力.     

在不同Cl-含量土壤中硫酸盐还原菌对Q235钢腐蚀的影响

利用交流阻抗测试技术、扫描电镜及表面能谱分析、失重法、微生物分析等方法，研究了在同一类型不同Cl-含量的土壤中，硫酸盐还原菌对Q235钢腐蚀的影响规律.136天的试验结果表明：随着土壤中Cl-含量的增大，Q235钢腐蚀速率也增大，当Cl-含量增大到0.5%时，腐蚀速率达到最大；随后腐蚀速率随着土壤中Cl-含量的增大而减小，当土壤中Cl-含量高于1%时，接菌土壤与灭菌土壤中Q235钢腐蚀速率相差不大.在土壤中Cl-含量低于1%时，接菌土壤中Q235钢腐蚀速率明显大于灭菌土壤的腐蚀速率；点蚀速率在不同Cl-含量的土壤中的变化规律与腐蚀速率的变化有所不同，点蚀速率基本随着土壤中Cl-含量的增加而增大.而且接菌土壤中的点蚀速率大于灭菌土壤的点蚀速率. TG174.5  硫酸盐还原菌； 含Cl-土壤； Q235钢； 微生物腐蚀 2003-01-13 2003-05-08     

热镀锌高强钢点焊的点蚀对电极寿命的影响

建立了点焊过程多物理场耦合的点蚀有限元模型,分析了点蚀对电极端面温度与应力分布的影响规律,并进行相应的试验研究.结果表明,点蚀区域产生更高的温度与应力集中,降低电极使用寿命;点蚀区域在高温高压下容易产生微裂纹,镀层金属元素沿微裂纹渗入电极内部,加速电极失效,点蚀的产生与发展加剧电极寿命下降.     

土壤中SRB及Cl-对1Cr18Ni9Ti不锈钢腐蚀的相互影响

利用交流阻抗测试技术、扫描电镜及表面能谱、失重法、微生物分析等方法 ,研究了在不同Cl-含量的土壤中 ,硫酸盐还原菌对 1Cr18Ni9Ti不锈钢腐蚀的影响规律 .13 6d的试验结果表明 ,不同Cl-含量土壤中SRB菌量在2 3 0 0 0～ 3 5 0 0 0 (个 /克土 )之间 ,Cl-的加入并没有显著影响SRB的生长 ,随着Cl-的加入土壤中SRB的菌量有增大的趋势 ;随着土壤中Cl-含量的增大 ,不锈钢腐蚀电位负偏移 ,而且在接菌土壤中的腐蚀电位比在灭菌土壤中负移幅度更大 ;不锈钢在灭菌土壤中没有发生点蚀现象 ,而在接菌土壤中发生了严重的点蚀 ,最大点蚀深度随着土壤中Cl-含量的增加而增大 ,这说明在土壤中SRB及Cl-的共同作用下 ,增大了不锈钢的点蚀敏感性 .不锈钢在灭菌土壤中的阻抗图谱表现为一个半径很大的容抗弧 ,而在接菌土壤中的阻抗图表现为两个时间常数的双容抗弧     

热镀锌高强钢电阻点焊的点蚀对熔核形成的影响

热镀锌高强钢由于高强度特性以及良好的抗腐蚀性,可满足汽车轻量化与安全性需要,在车身制造中逐渐得到广泛应用.但热镀锌高强钢点焊的电极磨损严重,点蚀磨损特征变化明显,对熔核形成产生较大影响.建立点焊过程的点蚀有限元模型,采用数值分析与试验方法研究点蚀对熔核形成影响.结果表明,点蚀的产生与发展增加了工件之间的实际接触面积,使电流密度降低,熔核直径减小;同边缘位置点蚀相比,电极中心位置点蚀由于对熔核区域的电流分流作用,更加不利于熔核的形成.随着点蚀面积的增大,形成环状熔核几率增加.     

用随机分析方法研究磁场对纯镁点蚀过程的影响机理

通过恒电位的方法测量了在有无磁场条件下纯镁的电流-时间响应曲线,并用随机的方法对结果进行分析,研究了磁场对纯镁点蚀产生过程和点蚀成长概率的影响。磁场通过洛仑兹力产生磁流体动力学效应（Magnetohydrodynamic）,显著地增加了纯Mg的点蚀敏感性：对于点蚀的产生过程,磁场的存在改变了纯镁的点蚀产生机制。在无磁场作用的条件下,纯镁的点蚀产生过程都遵循“生死异地”的B1机制;在有磁场作用的条件下,纯镁的点蚀产生过程都遵循“相同点蚀并联”的A3机制。磁场不仅增大了点蚀产生速度,而且降低了点蚀的再钝化速度。对于点蚀的成长过程,磁场提高了稳态点蚀的成长概率,更容易成长为较大的点蚀坑。     

热镀锌钢板点焊的点蚀对电极使用寿命的影响

热镀锌钢板点焊时电极磨损严重,点蚀特征变化明显.建立点焊过程中的电极端面接触电阻模型与接触热阻模型,分析点蚀变化对电极使用寿命的影响,并进行相应试验验证.结果表明.点蚀的产生与发展使电极端面接触电阻与接触热阻增大,导致电极端面温度升高、电极使用寿命降低.试验研究表明,热镀锌钢板点焊的点蚀区域在高温高压下容易产生微裂纹,镀锌层金属元素沿微裂纹渗八电极的内部,加速了电极失效.     

在NaHCO3-NaCI体系中阴离子对低碳钢点蚀的抑制作用

采用动电位和恒电位技术研究了低碳钢在NaHCO3-NaCl体系中的点蚀电位和再钝化电位的分布以及5种阴离子对它们的影响.结果表明,点蚀电位和再钝化电位均服从正态分布;在5种阴离子中,NO2-和MoO2-4能够抑制点蚀的发生和发展,而SO2-4、NO-3在低浓度时降低点蚀电位和再钝化电位,促进点蚀的发生,在高浓度时能够破坏自钝化;Cr2O2-7能显著抑制点蚀的发生,然而点蚀一旦产生后它却能加速点蚀的发展.     

X100管线钢在水饱和酸性土壤中的电化学阻抗谱特征

利用电化学阻抗谱(EIS)研究X100管线钢在水饱和酸性土壤中短期的电化学腐蚀行为。结果表明,X100管线钢在鹰潭水饱和土壤中浸泡104 h后已产生点蚀。腐蚀过程的EIS谱具有两个时间常数特征,高频区为代表反应的容抗弧,低频区为代表吸附或点蚀形核期产生的感抗弧。腐蚀初期(1 h～33 h),由于水饱和土壤介质电导率较低,电极反应过程受扩散控制;腐蚀产物在电极表面积累对反应离子扩散有阻碍作用,使阻抗增大;腐蚀产物膜疏松多孔,形成局部活化区域,使阻抗减小;Cl~-对腐蚀产物膜有破坏作用且在膜内局部地区浓缩,诱发点蚀,使阻抗减小,出现感抗特征。     

在NaHCO3-NaCl体系中阴离子对低碳钢点蚀的抑制作用

采用动电位和恒电位技术研究了低碳钢在NaHCO3-N aCl体系中的点蚀电位和再钝化电位的分布以及5种阴离子对它们的影响.结果表明,点蚀电 位和再钝化电位均服从正态分布;在5种阴离子中,NO-2和MoO2-4能够抑制点 蚀的发生和发展,而SO2-4、NO-3在低浓度时降低点蚀电位和再钝化电位,促 进点蚀的发生,在高浓度时能够破坏自钝化;Cr2O2-7能显著抑制点蚀的发生, 然而点蚀一旦产生后它却能加速点蚀的发展.     

渗锌钢在4种典型土壤环境中的腐蚀行为

在我国大港、鹰潭、格尔木、克拉玛依4个典型土壤中,将渗锌钢片埋藏2 a,观察试样的宏观形貌和微观形貌,用XRD物相结构检测分析了锈层的主要成分,计算渗锌钢在各试验站的腐蚀速率,并采用电化学测试分析了锈层对腐蚀介质的阻挡能力。结果表明,渗锌钢在4个土壤实验站的腐蚀速率均比较大,2 a后在鹰潭土壤中腐蚀速率最大,土壤的理化性能影响着渗锌钢腐蚀产物成分和相对含量。     

接地极Q235碳钢材料在上海土壤环境中的腐蚀行为

通过电化学阻抗 (EIS)、极化曲线、扫描电镜 (SEM)、能谱分析 (EDS) 和X射线衍射 (XRD) 等技术对接地极Q235碳钢材料在含不同盐分的上海地区土壤中的腐蚀行为进行了研究。结果表明,在不同盐分土壤条件下,Q235碳钢的阻抗均随着浸泡时间的延长出现先升高后平稳的趋势,腐蚀速率随盐分含量增大而增大。由于沿海土壤的侵蚀性阴离子含量较高,使得所产生的锈层失去保护性。Q235碳钢腐蚀主要以全面腐蚀为主,还伴有微生物腐蚀现象,腐蚀产物膜主要由Fe₂O₃组成。根据耐腐蚀性能评价标准,接地极碳钢材料在上海土壤环境中的耐腐蚀性能为良。     

Characterization of stress corrosion cracking in carbon steel using nonlinear Rayleigh surface waves

This research uses nonlinear Rayleigh surface waves to characterize stress corrosion cracking (SCC) damage in carbon steel. Cold rolled carbon steel is widely used for buried fuel pipelines; the environment surrounding these pipelines creates a mildly corrosive environment, which, in combination with an applied stress, can cause SCC. To ensure the safe operation of these structures, it is crucial that damage due to SCC be detected before their structural integrity is reduced by large cracks. In the early stages of SCC, microstructural changes such as dislocation formation and microcrack initiation occur, which have shown to considerably increase the acoustic nonlinearity of a material. These microstructural changes distort and generate higher harmonics in an initially monochromatic ultrasonic wave. This research considers four different levels of SCC induced in four separate 1018 steel specimens, a material which has a similar susceptibility to SCC as steel used for buried fuel pipelines. Then nonlinear ultrasonic measurements are performed before and after the SCC damage is induced. Nonlinear Rayleigh surface waves are utilized to detect the SCC damage that is concentrated near the material surface. The amplitudes of the fundamental and second harmonic waves are measured with contact wedge transducers at varying propagation distances to obtain the acoustic nonlinearity of the specimens as a function of SCC damage. The results show an increase in the measured acoustic nonlinearity in the early stages of SCC, indicating the feasibility of using this nonlinear ultrasonic method to detect the initiation of SCC in carbon steels.     

Influence of irradiation on water-saturated corrosion of carbon steels at 80°C

Two grades of carbon steel were exposed between 3 and 18 months at 80°C, with and without irradiation (maximum: 20 Gy/hr), in 100% humid atmosphere but some specimens were also half or totally immersed in a caustic solution. The main observations are:

• (1) No significant differences regarding the corrosion behavior between the two carbon steel grades were observed.
• (2) Generalized but nonuniform corrosion was observed in all the test conditions.
• (3) There was a large degree of scattering in the corrosion damage in a 100% humid atmosphere and this is attributed to the heterogeneity of atmospheric corrosion initiation.
• (4) Corroded areas neighboring noncorroded areas were observed on the fully immersed and semi-immersed specimens.
• (5) No major differences between the specimens exposed to irradiation and those that were not irradiated were observed; except for immersed specimens, the maximum corrosion depths were obtained under irradiations.

     

Corrosion resistance of stainless steel pipes in soil

To be able to give safe recommendations concerning the choice of suitable stainless steel grades for pipelines to be buried in various soil environments, a large research programme, including field exposures of test specimens buried in soil in Sweden and in France, has been performed. Resistance against external corrosion of austenitic, super austenitic, lean duplex, duplex and super duplex steel grades in soil has been investigated by laboratory tests and field exposures. The grades included have been screened according to their critical pitting‐corrosion temperature and according to their time‐to‐re‐passivation after the passive layer has been destroyed locally by scratching. The field exposures programme, being the core of the investigation, uses large specimens: 2 m pipes and plates, of different grades. The exposure has been performed to reveal effects of aeration cells, deposits or confined areas, welds and burial depth. Additionally, investigations of the tendency of stainless steel to corrode under the influence of alternating current (AC) have been performed, both in the laboratory and in the field. Recommendations for use of stainless steels under different soil conditions are given based on experimental results and on operating experiences of existing stainless steel pipelines in soil.     

碳钢在宝浪油田土壤中的腐蚀及影响因素的研究

通过室内自然腐蚀埋片试验和电化学极化测量,得出各种土壤的相对腐蚀性,同时,选取一种土壤,进行正交试验,正交分析的结果表明土壤中的含水量Ｃｌ＾－含量和Ｃａ＾２＋含量是碳钢在宝浪油田土壤中腐蚀的主要影响因素。     

Carbon steel corrosion in clay-rich environment

We investigated the carbon steel corrosion in carbon dioxide clay-rich environment to understand its behavior under geological conditions. The results show the formation of magnetite as the main corrosion product in the first step of the corrosion process, followed by the formation of different corrosion products with complex mixtures of iron-oxide, hydroxycarbonate, hydroxychloride and sulfide phases. These results strongly contrast with similar experiments conducted under H₂ atmosphere where the major corrosion products consisted of iron sulfides. It appears then important to consider all the geochemical parameters including gas composition to better study corrosion of steel buried in geological formations.     

CORROSION OF 1Cr13 STAINLESS STEEL IN SOILS

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Study of corrosion evolution of carbon steel exposed to an industrial atmosphere

ABSTRACT

The corrosion evolution of carbon steel exposed to an actual industrial atmosphere was investigated. The characteristics of the rust that formed on the steel were analysed by mass-loss measurement, X-ray diffraction, scanning electron microscopy and electrochemical techniques. Mass-loss results showed that the long-term corrosion kinetics of carbon steel can be divided into four stages, and that the corrosion rate varies during the different corrosion stages. This corrosion-rate fluctuation is attributed to the increase in the ambient temperature and the change in the composition of the rust layer formed on the steel surface. The reciprocal of charge transfer resistance (R_ct) can be used to represent the corrosion rate. The backward-facing specimens were found to be more suitable as the objects to investigate the corrosion evolution. The evolution of the rust layer that formed on the steel is also discussed.     

25钢在热带海洋环境下海水中的微生物腐蚀及其对力学性能的影响

通过对比25钢在热带海洋环境下自然海水和无菌海水中的平均腐蚀深度,研究微生物对碳钢腐蚀行为的影响。结果表明,海水中微生物的存在显著影响碳钢的平均腐蚀深度。浸泡时间为365 d时,在自然海水中的腐蚀深度为无菌海水中的2.6倍,产生了明显的局部腐蚀。无菌海水和自然海水腐蚀都会造成材料抗拉强度的下降,对比发现腐蚀时间较长时自然海水中材料抗拉强度下降更大,说明微生物腐蚀对材料抗拉强度有一定影响。微生物腐蚀对材料抗拉强度的影响作用,主要在于微生物的存在使材料的平均腐蚀深度增大,引起材料横截面积的减小。微生物腐蚀并不会降低退火25钢的延伸率和夏比冲击功,实验过程中未发现微生物作用下材料的氢脆现象。