Study of Pitting Morphology Fractal Characteristic of Corroded Surface of 304 Stainless Steel in FeCl3 Environment

Experiments were performed to study the pitting corrosion morphology of 304 stainless steel exposed to FeCl3 environments and SEM micrographs of the pitting corrosion morphology were obtained. The image processing technique combining with the fractal method was employed to analyze these pitting corrosion images and the self-similarity of pits morphology was observed. It indicates that fractal characteristics exist in pitting corrosion of 304 stainless steel. The self-similarity and complexity of the pitting morphology phenomenon were described in terms of fractal dimension which can also be an important parameter related to characterize pitting morphology qualitatively and quantitatively.     

Influence of coupled chemo-mechanical process on corrosion characteristics in reinforcing bars

We studied the corrosion characteristics of reinforcing bars in concrete under different corrosion conditions. The area-box (AB) value was used to classify the shape of pitting corrosion morphology in meso-scale, and fractographs of reinforcing bars with different corrosion morphology were discussed in micro- and macro-scales. The results show that the existence of the tensile stress affects the corrosion characteristics of reinforcing bars. The pitting morphology and fractograph of reinforcing bars exhibit a statistical fractal feature. The linear regression model fits the relationship between fractal dimensions of corrosion morphology and fractal dimension of fractograph fairly well. Using fractal dimension as the characterization parameter can not only reflect the characteristics of pitting corrosion morphology in reinforcing bars, but also reveal the fracture feature of corroded reinforcing bars.     

点蚀孔腐蚀钢构件力学性能劣化简化分析方法

点蚀是一种局部和剧烈的腐蚀形态,导致钢结构构件力学性能退化,突然之间发生事故,对结构整体造成安全隐患.本文针对具有点蚀孔腐蚀特征的钢构件,提出一种通过等效弹性模量定量评价其力学性能劣化程度的简化分析方法.依据周期喷雾复合试验数据,以锈蚀率和最大点蚀深度为基础,对点蚀孔深度、直径及分布情况作出适当假定;考虑涂层寿命的影响,以锈蚀率相等为原则建立人工加速腐蚀试验和海洋大气条件下Q235钢构件腐蚀情况的转换关系.建立考虑点蚀影响的有限元构件模型,通过轴向均布力作用下的构件变形确定海洋大气环境不同暴露时间下点蚀构件的等效弹性模量,提出点蚀构件力学性能劣化分析的实用计算方法.数值算例验证了上述采用等效弹性模量分析腐蚀构件受力性能方法的正确性;计算结果表明,在相同锈蚀率条件下,点蚀构件的等效弹性模量低于均匀腐蚀构件.     

加速腐蚀环境下钢板表面坑蚀形貌统计规律

采用光学表面测量技术对实验室加速腐蚀钢板试件进行坑蚀表面数据采集,通过建立不同龄期的锈蚀钢板表面形貌图讨论了锈蚀钢板表面点蚀特征随腐蚀时间的变化趋势。对于以局部腐蚀为主的锈蚀钢板,通过计算证明坑蚀平均深度近似等于腐蚀平均深度,且其随时间的变化趋势可以采用新型weibull函数加以描述。经过对垂直于钢板受力方向的坑蚀截面损失率进行探究,指出可以利用正态分布模型表征其随机分布规律,并建立了模型参数与坑蚀平均深度之间关系式。最后讨论了与腐蚀时间相关的钢板屈服强度退化概率模型。     

Corrosion behavior of Al-Zn-Sn-Ga alloy in NaCl solution

The corrosion behavior of Al-Zn-Sn-Ga alloy in 3.5% NaCl solution was investigated by corrosion morphology observation and electrochemical testing. The experimental results show that there exist three stages during the course of corrosion. At the initial stage, pitting occurs surrounding the precipitates, which is driven by the galvanic couple effect. At the middle stage, pitting rapidly extends toward the horizontal direction, forming the shallow circular structure caused by the deposition of Ga ions around Sn. At the final stage, the new active sites led to the continuous corrosion of the alloy.     

Method for Calculating the Ultimate Strength of Pitting Corrosion Ship Structural Plates Under Combined Loads

联合载荷作用下点蚀船体板的极限强度计算方法研究

滑林^1,2,吴梵^1,2,牟金磊^1,2,马晓龙¹

（1. 海军工程大学 舰船与海洋学院,武汉 430033;

2. 海军舰艇技术鉴定船体结构强度校核中心, 武汉 430033）

创新点说明：

1）结合实船（舰艇）点蚀勘验数据,提出了点蚀矩阵的概念,建立了点蚀分布的数学模型,为全面开展点蚀相关研究提供了新的途径;

2）采用新的灵敏度计算方法开展了点蚀特征（分布,点蚀深度及蚀坑半径等）对船体板极限强度的贡献值计算;

3）提出了刚度缩减因子的概念,并拟合出了点蚀损伤船体板极限强度的计算评估公式。

关键词：船体结构;点蚀损伤;极限强度;联合载荷;灵敏度分析

     

分维方法对碳钢土壤腐蚀行为的表征

碳钢土壤腐蚀规律涉及埋地管道的安全运行,受到高度重视。根据大量的碳钢土壤腐蚀数据样本,用分形理论研究平均腐蚀速度、点蚀深度、腐蚀坑深分布和坑直径分布等参数特征,比较它们的分维和无标度区。研究表明,在足够的平行试样、足够的腐蚀发展量及腐蚀发展时间下,相应腐蚀速度标准偏差分维、腐蚀坑深分布分维和腐蚀坑直径分布分维具有稳定性。分维值提供衡量腐蚀随机复杂程度的定量指标,如平行腐蚀试验和区域腐蚀试验的平均偏差分维分别等于1.34和1.4 9。并且经分维修正后的变异系数、点蚀系数成为衡量腐蚀特性的更通用参数。通过分维和它们自相似性(无标度区间)特性的研究,为揭示腐蚀机理及发展过程提供了参考。     

Pitting and galvanic corrosion behavior of stainless steel with weld in wet-dry environment containing CI

Accelerated corrosion test of stainless steel with weld was carried out to investigate the corrosion behavior under the wetdry cyclic condition in the atmosphere containing Cl-. In the surface morphology, corrosion products were analyzed by metallographic observation, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the damage to stainless steel with weld in the atmosphere containing Cl- is due to localized corrosion, especially pitting and galvanic corrosion.Weld acts as the anode, whereas matrix acts as the cathode in the corrosion process. The pitting corrosion, including the nucleation and growth of a stable pit, is promoted by the presence of wet-dry cycles, especially during the drying stage. Pits centralizing in weld are found to be grouped together like colonies, with a number of smaller pits surrounding a larger pit. The composition of the corrosion products is Fe2O3, Cr2O3, Fe3O4, NiCrO4, etc.     

Fractal Characteristic of Pits Distribution on 304 Stainless Steel Corroded Surface and Its Application in Corrosion Diagnosis

Electrochemical techniques and fractal theory were employed to study the corrosion behaviors and pits distribution characteristics on the corroded surfaces of 304 stainless steel exposed in FeCl3 solution. Fractal features of pits distribution over the corroded surfaces were observed and described by the fractal dimension. A 5-8-2 back-propagation （BP） artificial neural network model for the diagnoses of the pitting corrosion rate and pits deepness of 304 stainless steel under various conditions was developed by considering the fractal dimension as a key parameter for describing the pitting corrosion characteristics. The predicted results are well in agreement with the experimental data of pitting corrosion rate and pit deepness. The max relative errors between their experimental and simulation data are 6.69% and 4.62%, respectively.     

Pitting and galvanic corrosion behavior of stainless steel with weld in wet-dry environment containing Cl~-

Accelerated corrosion test of stainless steel with weld was carried out to investigate the corrosion behavior under the wet-dry cyclic condition in the atmosphere containing Cl?. In the surface morphology, corrosion products were analyzed by metal- lographic observation, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the damage to stainless steel with weld in the atmosphere containing Cl? is due to localized corrosion, especially pitting and galvanic corrosion. Weld acts as the anode, whereas matrix acts as the cathode in the corrosion process. The pitting corrosion, including the nucleation and growth of a stable pit, is promoted by the presence of wet-dry cycles, especially during the drying stage. Pits centralizing in weld are found to be grouped together like colonies, with a number of smaller pits surrounding a larger pit. The composition of the corro- sion products is Fe2O3, Cr2O3, Fe3O4, NiCrO4, etc.     

海洋环境下X52管线钢的腐蚀行为研究

海洋环境下的油气管道（X52管线钢）极易受到腐蚀的影响。采用电化学测试技术,并通过观察腐蚀形貌的方法,分析了海洋环境下溶解氧质量浓度、pH、静水压力对X52管线钢腐蚀行为的影响。结果表明,随着环境pH的升高,X52管线钢腐蚀减缓;随着溶解氧质量浓度和静水压力的升高,X52管线钢腐蚀加剧。在不同条件下,X52管线钢的腐蚀行为受阳极活化溶解控制,并且出现局部点蚀现象。     

A3F和X70钢在H2S环境下腐蚀行为研究

采用动电位极化曲线与交流阻抗技术,针对辽河油田H2S含量对A3F与X70管线钢的腐蚀情况进行研究,并使用金相显微镜对腐蚀形貌进行了观察.结果表明,两种管线钢在电极过程中均呈现典型的活化控制;X70管线钢的耐腐蚀情况要明显优于A3F管线钢,腐蚀形态均为伴随着点蚀的局部腐蚀.     

金属油气管道点蚀缺陷安全评估及预警系统研究

在油气输送过程中,因为载荷和腐蚀介质等因素的影响,油气金属管道很容易萌生缺陷而引发重大安全事故.点蚀与多点蚀缺陷是存在周期最长、最普遍、最有可能产生穿孔的高危缺陷,因此对金属管道工作过程中的在线检测与安全评估一直是油气输送技术领域研究的重点和热点.作者考虑了多个点蚀及点蚀之间的相互作用,根据美国石油协会的API–579...     

Generation reason and corrosion characteristic of cavity of tinplate alloy layer

The surface morphology of alloy layer of tinplate was studied by means of scanning electron microscopy.By using the layer on layer debonding technology of glow discharge spectrum, the contents of C and O at the boundary of alloy layer and black plate were analyzed. And the corrosion characteristic of cavity of tinplate alloy layer was studied on-line and in-situ by means of electrochemical atomic force microscope. The corrosion depth of cavity of alloy layer in-situ after different corrosion time was measured. The results show that the cavity of alloy layer is a critical factor causing rapid decline of corrosion resistance of tinplate, and the formation of cavity of alloy layer is due to incorrect pretreatment of black plate before electrotinning. The cavity of alloy layer is the internal factor causing pitting corrosion of tinplate when the tinplate is applied to food packaging material. And the dynamic equation of pitting corrosion generated in the cavity of alloy layer conforms to logarithm law.     

Cl^-浓度和pH值对AZ31镁合金腐蚀行为的影响

研究了AZ31镁合金在不同Cl^-浓度和pH值的NaCI溶液中的腐蚀行为,从腐蚀形貌和腐蚀速率等方面对其进行了定性和定量描述。并对其腐蚀机理进行了探讨。经NaCl溶液腐蚀的AZ31镁合金呈现出明显的点蚀特征。随着Cl^-浓度的增大,金属的阳极溶解和局部腐蚀加剧,AZ31镁合金的腐蚀速率也急剧增加,腐蚀程度加重。同时,溶液pH值的增大有利于AZ31铁合金表面形成更稳定的Mg（OH）2钝化膜。于是,随着溶液pH值从7增大到12,AZ31镁合金的腐蚀速率减小,耐腐蚀性能增强。     

低温多效海水淡化装置中HAl77-2铜管腐蚀失效分析

通过腐蚀电化学测试和腐蚀形貌检测,借助表面物相结构和元素成分分析,对某电厂2.5×10~4t/d的4号M ED海水淡化装置HAl77-2铜合金热交换管进行失效分析.结果表明,管板或隔板与铜合金管之间出现横向开裂的主要诱因在于机组振动导致铜管的磨损,继而产生缝隙腐蚀,同时管子受到外力剪切,引起腐蚀疲劳发生开裂.麻坑腐蚀属于脱锌腐蚀,其原因与铜管表面不均匀、不致密的结垢层有关.     

一种基于场指纹法的金属管道小腐蚀坑的求解方法

针对场指纹法(FSM)对小腐蚀坑检测精度偏低的问题,根据小腐蚀坑会对被测管道的电流分布产生影响的现象,提出一种细分的电阻链网络模型,利用主辅电压和细分电阻网络的特定关系来准确求解小腐蚀坑,并且分析发现不同位置、不同深度和不同直径的小腐蚀坑对主辅电压有着特定的影响,进而提出了一种利用主辅电压来准确求解小腐蚀坑的方法.该方法的本质在于引入了多个已知参量,从而可以求解出多参量的小腐蚀坑.理论分析和实验表明,提出的求解小腐蚀坑的方法能够有效提高小腐蚀坑的检测精度,发展并完善了FSM方法.     

锈损冷弯薄壁型钢材料力学性能试验

为研究锈蚀对冷弯薄壁型钢材料力学性能的影响,通过对工业环境下服役9 a的冷弯薄壁C型檩条进行拉伸试验,探讨锈蚀程度、类型对其材料力学性能的影响.研究了钢材断口形态、应力-应变曲线、力学性能指标与其锈损程度、类型之间的关系,建立了锈损冷弯薄壁型钢材料本构模型.在此基础上,运用有限元方法分析比较了锈蚀对不同材料属性、不同厚度钢板力学性能的影响.结果表明:点蚀试件断口为单一的平断形式,而全面锈蚀试件断口则呈现为斜断、圆弧断或阶梯断;点蚀试件均表现为屈服平台、颈缩段消失,而全面锈蚀仅当锈蚀率达到36.14%时,屈服平台才消失;试件屈服强度、极限强度、伸长率、极限应变、弹性模量均随锈蚀程度增大而减小,当锈蚀率为36%时,强度下降36.66%,伸长率下降约70%.点蚀对延性的影响要高于全面锈蚀,锈蚀对冷弯薄壁型钢材料性能的影响要高于热轧型钢.     

Susceptibility of two types of low-alloy hull steels to pit initiation

Four low-alloy hull steels with different alloy elements were selected. Their susceptibility to pitting corrosion was compared by means of electrochemical polarization test. The inclusions in the steels and their pitting corrosion characteristics were studied by an electron probe micro-analyzer (EPMA). The results indicate that some inclusions are the main sources of pitting corrosion. The susceptibility of nickel-chromium steel to pit initiation is less than that of manganese steel. Under the same conditions, nickelchromium steel is easier to passivate than manganese steel, and the passive films on nickel-chromium steel surface are more stable than that on manganese steel. In low-alloy steels, the higher the contents of nickel and chromium, the lower the critical passive pH value. In the same kind of steel, multi-phase inclusions containing sulfide are easier to initiate pitting corrosion than other inclusions.     

高温高压含O2溴盐完井液中13Cr不锈钢的腐蚀行为研究

随着越来越复杂开发工艺的应用,油气田现场服役环境也变得更加复杂苛刻,一些现场操作环节（如井下回注CO2、回注采出水、药剂加注、环空注氮、管道试压、维修操作等）不可避免会将O2引入井下环境。O2的混入会导致井下管材发生不可预期的腐蚀风险,尤其对以13Cr不锈钢为代表的耐蚀油套管材,潜在局部腐蚀风险很高。针对溴盐完井液中O2混入导致井下管材腐蚀风险加剧的问题,本文采用高温高压腐蚀模拟实验,结合扫描电镜、能谱分析等微观表征手段,研究了高温高压含O2环境下不同浓度溴盐完井液中普通13Cr和超级13Cr两种典型不锈钢油套管材的腐蚀行为及机理。结果表明：在高温高压含O2溴盐完井液环境下,两种13Cr不锈钢的腐蚀速率均较高,尤其局部腐蚀速率;参照NACE PR-0775标准,普通13Cr在1.01 g?cm-3浓度的溴盐溶液中就已经属于严重腐蚀,并且随着溴盐质量浓度的升高,腐蚀程度不断加剧,在1.10 g?cm-3达到极严重腐蚀;当溴盐质量浓度达到1.40 g?cm-3时,两种材料的最大局部腐蚀速率均已超过5 mm?a-1;微观形貌分析结果表明,溴盐完井液中O2混入对13Cr不锈钢管材的耐蚀性能具有显著影响,这主要是由于O2混入降低了材料表面钝化膜的稳定性,点蚀萌生于材料基体表面致密富Cr钝化膜的破损处,向基体深部发展,蚀坑周边区域有大量腐蚀产物堆积,蚀坑与周边区域存在局部的电偶效应,进一步加速蚀坑的发展。