Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels

Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.

Numerical Simulation for Crevice Corrosion of 304 Stainless Steel in Sodium Chloride Solution

The authors presented a mechanistic model describing the chemical reactions within a corroded thin, narrow crevice. In the mathematical model, a two-dimensional steady-state was used to predict the crevice pH profile by taking into account dissolved oxygen and hydrogen ions within the crevice. It consists of six parallel electrochemical reactions： multi anodic reactions（Fe, Cr, Ni dissolution reactions） and three cathodic reactions（the oxygen reduction, the hydrogen reaction and water dissociation）. Current density distribution and oxygen concentration distribution were determined to be corresponding to the evolution of potential distribution within the crevice. The contribution of each metal reaction to the overall corrosion process was in proportion to the mole fraction, and the simulation pro vided a good agreement with published experimental results for the crevice corrosion of stainless steel in sodium chloride solution.

Corrosion products of reverse crevice corrosion of copper

Open-circuit potential measurements and Raman spectroscopy were used to investigate the reverse crevice corrosion phenomenon and its corresponding corrosion products. With the aid of these techniques, the existence of reverse-crevice corrosion in copper was verified, i.e., while the surface of a crevice was corrosion free, the outside surface of the copper was attacked. The processes associated with this phe-nomenon were classified into three phases, and different compositions of the corrosion products were determined. Raman spectra showed that copper and Cu2O were found in the crevice, while CuO, Cu2O, and CuCl2 were the corrosion products on the bold surface. Based on these findings, a hypothesis relating to the three phases of reverse crevice corrosion has been proposed.

The Relationship between Shell Morphology and Crevice Size Affecting Retreat Selection of the Keeled Box Turtle(Cuora mouhotii)

Rock crevices are important retreat sites for many reptiles.Unlike lizards and snakes,crevicedwelling turtles have rigid shells which severely limit the size and shape of crevices they are able to use.Few studies have addressed the relationship between turtle's shell morphology,behavior,and crevice size.Here,we investigate the relationship between morphology and crevice size selection in the Keeled box turtle(Cuora mouhotii).We radio tracked turtles in the field to document crevice dimensions and turtle behavior associated with crevices,and we conducted a controlled experiment in the lab to understand how a turtle's morphology influences its decision to select crevices with different dimensions.Both laboratory and field experiments demonstrate that turtles select deep and moderately wide crevices that are low enough to barely accommodate the carapace.Crevices used by turtles tend to be about 2 times as wide,1.2 times as high,and 3 times longer than the turtle's shell.Moreover,turtles tended to prefer crevices with horizontal openings in the field and position themselves head first in the crevice.We conclude that morphology,especially carapace height,influences the Keeled box turtles' decision to select specific sizes of crevice.We argue that the tendency for turtles to select crevices that come into contact with their carapace contributes to successful defense against predators,as it would be more difficult for a predator to remove a turtle when the crevice is nearly touching the turtles shell.

The Crevice Corrosion of 316<i>L SS</i>Alloy in NaCl Solution at Different Applied Potentials

316L SS alloy was tested under different applied potentials to study the susceptibility of this alloy to crevice corrosion. XPS measurements have been carried out to detect and define the products which formed on the surface of 316L SS in 3.5% NaCl at room temperature at applied potential = 200 mVSCE. The formation of Fe, Cr and Mo compounds were found, and these compounds play a great role in protecting the alloy which was found. The boundaries of the corroded area under washer teeth are in agreement with IR drop. The potentiodynamic technique is also studied to examine the overall corrosion behavior of 316L SS.

Development of a Test Program for Assessing the SCC, Pitting and Crevice Corrosion Behaviour of Selected Corrosion Resistant Alloy Liner Materials for Clad Pipe for Offshore Applications

The development of an offshore gas field involves production of oil and gas from subsea wells. Design considerations for a particular subsea system have identified the maximum temperature for operations which is greater than 130 ~C. Consequently, for large diameter flowlines, this precludes the use of duplex stainless steels as CRA＇s （corrosion resistant alloys） for service under the expected operating conditions. Attention has therefore focused on alternative CRA＇s such as austenitic stainless steels and Ni based alloys as mechanically clad or lined clad pipe for carbon steel subsea gas flowlines. One design concern is the recognized temperature limit for CRA materials, such as 316L stainless steel and similar alloys in production fluids is taken to be 120 ~C. This then raises concerns surrounding their suitability for providing sufficient corrosion resistance/stress corrosion cracking resistance in gas environments containing COz and H2S at temperatures higher than 130 ~C. It was recommended that specific testing should be completed at temperatures greater than 133 ~C to establish that candidate materials are still corrosion resistant. The focus of this study was to develop, implement and assess a testing program that would predict the suitability of a series of CPA＇s alloys for use in mechanical clad/lined subsea gas flowlines, with respect to pitting corrosion, crevice corrosion and stress corrosion cracking. This paper will present the rationale adopted for this testing program to simulate the stringent operating conditions, the results from these findings and the overall assessment/integrity of the candidate alloys selected.

Hard Foulers Induced Crevice Corrosion of HSLA Steel in the Coastal Waters of the Gulf of Mannar (Bay of Bengal), India

In the present study an attempt has been made to investigate the relationship between the variations in the fouling assemblage and corrosion behaviour of HSLA steel at three coastal locations in the Gulf of Mannar, India, over a period of 24 months. Oyster fouling was dominant in the Tuticorin open sea, while barnacles were the major foulants in the Tuticorin harbour and Mandapam. The fouling load in the Tuticorin waters was higher when compared to the Mandapam waters. The corrosion rates decreased progressively with the immersion time at all three test locations. In the Tuticorin open sea, the corrosion rates were higher when compared to the other two locations throughout the study period. The surface of the coupons was characterized by crevices beneath the hard foulers in the Tuticorin harbour and Mandapam, whereas in the Tuticorin open sea, the coupons experienced crevices of a tunneling nature. The percentage of the loss of the tensile strength increased with time at all the test locations.

Optimal Placement of Reclosers to Minimize Power Losses during Non-Load Bearing Disturbances in a Power Distribution Using Firefly Algorithm

The research reported in this paper focuses on non-technical power loss reduction for power distribution systems. Such reduction of costs of energy not served (ENS.COST), is intelligently evaluated and optimized using a firefly algorithm, from where savings of 43.3% on energy not served are achieved.

Q235碳钢在中性模拟土壤溶液中的缝隙腐蚀行为

[目的]碳钢构件在中性土壤环境中的缝隙腐蚀行为值得探究。[方法]将Q235钢单一缝隙试样浸泡在模拟土壤溶液中,分析了腐蚀不同时间后试样的腐蚀速率、腐蚀形貌及腐蚀产物。[结果]Q235钢在中性模拟土壤溶液中的腐蚀存在缝隙加速现象,初期在缝隙口发生明显的沿缝腐蚀,后期则在缝隙内发生点蚀。缝隙内外区域的主要腐蚀产物都是Fe_(3)O_(4)和FeOOH,且不受腐蚀时间影响。[结论]Q235钢在中性模拟土壤溶液中会发生明显的缝隙腐蚀,其腐蚀过程可分为初期均匀腐蚀、中期氧浓差电池引发缝隙腐蚀和后期闭塞电池自催化3个阶段。为确保碳钢结构在中性土壤环境中的服役安全性,需对钢结构的缝隙腐蚀采取必要的控制措施。

20钢输气管道穿孔原因

某油田现场输气管道发生穿孔现象。采用宏观观察、壁厚测量、化学成分分析、金相检验、力学性能测试、扫描电镜及能谱分析等方法研究了管道穿孔的原因。结果表明:焊缝穿孔泄漏的原因是天然气夹带的固体颗粒沉积后与未焊透焊缝内表面构成缝隙,在含水酸性介质的作用下,管道发生缝隙腐蚀,焊缝阳极溶解,最终导致管道发生腐蚀穿孔。

6A01-T5铝合金/304不锈钢的缝隙腐蚀行为研究

目的 研究6A01-T5铝合金和304不锈钢异种金属间的缝隙腐蚀行为规律。方法 采用常温常压浸泡腐蚀方法,结合SEM、EDS、XRD和白光干涉检测,对6A01-T5铝合金/304不锈钢缝隙结构在碱性Na Cl溶液中的腐蚀行为进行研究。结果 6A01-T5铝合金/304不锈钢缝隙腐蚀表现为在缝口处产生沿缝口方向的凹陷渠,在缝内,以局部减薄和腐蚀坑为主,并随着腐蚀时间的延长,腐蚀程度逐渐加重。不同区域腐蚀产物的形貌和成分组成不尽相同,缝外暴露区的腐蚀产物表现为晶体颗粒状,主要成分为Ca CO3和Al(OH)3等铝的腐蚀产物。缝口附近沿缝口方向形成一层有明显界线的腐蚀产物覆盖层,缝隙内部的腐蚀产物相对较少,表现为尺寸相对较小的结块,主要成分为Al(OH)3等铝的腐蚀产物。结论 在6A01-T5铝合金与304不锈钢非电连接情况下,6A01-T5铝合金/304不锈钢缝隙内2种金属分别独立发生缝隙腐蚀,因2种金属在腐蚀过程中争夺O2,使得304不锈钢对6A01-T5铝合金的缝隙腐蚀起到抑制作用。

结构缝隙宽度对6A01-T5铝合金腐蚀行为的影响

目的研究6A01-T5铝合金缝隙腐蚀行为规律,为6A01-T5铝合金缝隙腐蚀的防治提供理论依据。方法采用常温常压浸泡法对缝隙深度恒定、缝隙宽度不同的6A01-T5铝合金缝隙腐蚀试样在碱性Na Cl溶液中进行不同时间的腐蚀试验,采用数码相机、扫描电子显微镜(SEM)和X射线衍射仪(XRD)检测分析腐蚀后试片宏观形貌、腐蚀产物形貌和成分,采用白光干涉仪检测试片表面微观轮廓和腐蚀坑深度,采用电子天平检测腐蚀失重。结果缝隙宽度为0.15mm和0.3mm的试片沿缝口产生腐蚀沟,并在缝内产生局部腐蚀坑,浸泡45 d后腐蚀沟宽度和最深腐蚀坑深度分别约为2500μm、60μm,和1200μm、80μm。而缝隙宽度为0.5 mm的试片在缝口处并未检测到明显的腐蚀沟,腐蚀45 d后最深腐蚀坑深度约40μm;试片腐蚀失重随腐蚀时间的延长呈上升趋势,且在腐蚀过程中均表现为缝隙宽度为0.3 mm的试片腐蚀失重最大,缝隙宽度为0.15 mm的试片次之,缝隙宽度为0.5 mm的试片最小。结论在碱性Na Cl溶液中,6A01-T5铝合金缝隙腐蚀程度随缝隙宽度的增加呈先增大后减小的趋势,并随腐蚀时间的延长腐蚀程度逐渐上升;缝隙腐蚀会在缝口处产生沿缝口方向的腐蚀沟,并随着缝隙宽度的增加腐蚀沟孕育周期延长,腐蚀沟宽度减小,当缝隙宽度达到0.5 mm时,不再产生明显的腐蚀沟。

某核电厂发电机定子水冷却器盲板缝隙腐蚀原因分析及解决措施

某核电站大修时的腐蚀检查,发现发电机定子水冷却器的盲板存在腐蚀问题。本文从腐蚀形貌和耐蚀性能两个方面对盲板的腐蚀原因进行了分析,得出结论是由于发电机定子水冷却器盲板的材质为304不锈钢,而304不锈钢在海水环境下,耐腐蚀性能不佳,导致盲板发生了缝隙腐蚀。针对盲板缝隙腐蚀问题,本文提出了相应的解决措施,以有效解决问题并确保设备的正常运行,为核电站发电设备的维护和管理提供了参考。

增材制造Ti6Al4V合金的闪速等离子体电解氧化与在生理介质中的电化学行为

研究激光粉末床熔融增材制造(AM)(又称直接金属激光烧结)技术制备的Ti6Al4V合金等离子体电解氧化(PEO)处理及其电化学行为。通过短时间(<120 s)PEO处理(也称闪速PEO),在AM合金和传统合金表面制备了3~10μm厚、含Ca和P的涂层。然后在改良的α-MEM溶液中,通过动电位极化曲线和电化学阻抗谱(EIS)评估了合金的电化学行为。与传统合金相比,AM合金中形成了细小的层片状α显微组织和层间小尺寸的β相颗粒,这促使了火花的产生,从而促进了PEO涂层的生长。闪速PEO涂层提高了传统合金和AM合金的耐腐蚀性,最薄的涂层(<3μm)提供了高达3倍的保护。AM Ti6Al4V由于其高的晶界密度,易受局部缝隙腐蚀的影响。而即使短至35 s的闪速PEO处理也足以成功避免这种情况。

Investigation of high rate mechanical flow followed by ignition for high-energy propellant under dynamic extrusion loading

Investigating the ignition response of nitrate ester plasticized polyether(NEPE) propellant under dynamic extrusion loading is of great significant at least for two cases. Firstly, it helps to understand the mechanism and conditions of unwanted ignition inside charged propellant under accident stimulus.Secondly, evaluates the risk of a shell crevice in a solid rocket motor(SRM) under a falling or overturning scene. In the present study, an innovative visual crevice extrusion experiment is designed using a dropweight apparatus. The dynamic responses of NEPE propellant during extrusion loading, including compaction and compression, rapid shear flow into the crevice, stress concentration, and ignition reaction, have been firstly observed using a high-performance high-speed camera. The ignition reaction is observed in the triangular region of the NEPE propellant sample above the crevice when the drop weight velocity was 1.90 m/s. Based on the user material subroutine interface UMAT provided by finite element software LS-DYNA, a viscoelastic-plastic model and dual ignition criterion related to plastic shear dissipation are developed and applied to the local ignition response analysis under crevice extrusion conditions. The stress concentration occurs in the crevice location of the propellant sample, the shear stress is relatively large, the effective plastic work is relatively large, and the ignition reaction is easy to occur. When the sample thickness decreases from 5 mm to 2.5 mm, the shear stress increases from 22.3 MPa to 28.6 MPa, the critical value of effective plastic work required for ignition is shortened from 1280 μs to 730 μs, and the triangular area is easily triggering an ignition reaction. The propellant sample with a small thickness is more likely to stress concentration, resulting in large shear stress and effective work, triggering an ignition reaction.

钢轨轨底上表面缝隙腐蚀研究现状

在潮湿的环境中,铁路系统中的轨底上表面和绝缘轨距块之间容易发生缝隙腐蚀,这种现象导致轨底逐渐变薄,造成严重的安全隐患。目前缝隙腐蚀研究主要涉及螺栓螺母、边缘板等异形结构,而对轨底上表面与绝缘轨距块之间的缝隙腐蚀的研究报道较少。对轨底上表面的缝隙腐蚀现象进行深入分析,探讨了现阶段轨底上表面缝隙腐蚀的产生和机械辅助缝隙腐蚀机制、相关的检测技术和方法以及防护措施的研究现状。

保温铝板表面变色原因分析及防护

铝合金具有较好的加工性能及耐蚀性能,且具有质量轻及强度高等优点,在各个领域被广泛应用。但在炼油化工装置使用过程中,腐蚀性介质的存在会造成铝合金发生腐蚀失效,给装置的发展造成严重的影响。中国石油某炼油三部罐区下雨后,保温铝板有部分颜色发黑发黄现象(距离安装完成约5天),给装置安全平稳运行造成严重影响。通过对保温铝板进行宏观及低倍分析、材质分析、扫描电镜及能谱分析、X射线衍射分析等检测发现:铝板的材质不是3003铝合金,而是纯铝1050,其表面变色的原因是因为发生了缝隙腐蚀,外部环境中的水汽及腐蚀性元素(Cl、S、O)是造成铝板发生缝隙腐蚀的主要因素。

脱硫塔圆锥体断裂原因分析

利用金相、扫描电镜和X射线衍射等分析手段,对原料烧结厂脱硫塔圆锥体脱落的原因进行了分析,结果表明,由于脱硫灰附着在脱硫塔圆锥体内壁上,烟气中的水汽在圆锥体内壁形成冷凝水,烟气中或烟气经ClO_(2)气体氧化后反应生成的腐蚀成分溶入冷凝水,形成电解质,渗入脱硫灰中,使脱硫塔圆锥体钢板内壁产生电化学腐蚀;由于脱硫塔圆锥体材质为Q235普碳钢,不具有耐蚀性,导致在钢板内壁形成较厚的腐蚀产物,与脱硫灰附着物在脱硫塔内壁形成结垢,进一步发生缝隙腐蚀,烟气与氧化剂ClO_(2)气体反应生成的Cl^(-),与烟气中自带的Cl^(-)一起,加速了脱硫塔腐蚀进程。最终使得圆锥体钢板不断腐蚀减薄,导致其承重能力下降,当承重能力低于圆锥体自身重量时,圆锥体断裂并脱落。

电真空器件隙缝腔零件微细加工技术工艺研究

针对G波段分布作用速调管中关键零件隙缝腔零件的高精度设计要求开展微细加工技术研究。基于现有加工经验及加工设备条件,通过创新性的工艺设计、结合大量工艺试验探索,突破了微小尺寸、超高精度零件的精密加工技术,满足了毫米波及太赫兹电真空器件中关键零部件的制造需求,提升了高频段电真空器件制造技术水平。

缝隙腐蚀对化工设备装置的影响及控制途径

腐蚀形式主要发生在设备的微小缝隙中,如法兰连接、焊缝附近和覆盖层下。这种局部腐蚀的过程不仅会影响设备的正常运行,还可能导致设备的突然失效,存在巨大的安全隐患,也会给企业和个人带来巨大的经济损失和不可逆的危害。