阀控式铅酸蓄电池负极汇流排的腐蚀成因及防护对策

阀控式铅酸蓄电池负极汇流排的腐蚀及脱落是造成电池早期失效的一个重要原因。对早期失效电池负极汇流排的腐蚀形态进行了宏微观分析,对其不同部位(极柱、极群和焊接区)进行了电化学测试。结果表明:在电池浮充条件下负极汇流排处于贫液富氧环境和缺乏足够的阴极保护,形成了汇流排腐蚀的环境;汇流排焊接区的冷却速度与极柱和极群存在显著差异,使焊接区材料的晶粒变为粗大的柱状晶,从而导致其电化学反应活性高于极柱和极群区域,造成其焊接区严重的晶间腐蚀。对此,从3个方面提出了相应的防护对策。     

316L不锈钢焊缝腐蚀微电池的形成机理

为了探究316L不锈钢焊缝腐蚀微电池的形成机理,通过微观组织观察及电化学试验进行了分析。采用扫描电镜(SEM)对焊件三区(焊缝区、热影响区、母材区)的形貌及元素组成进行了观察分析,采用金相显微镜观察微观组织,并确定晶粒度及非金属夹杂物及其分布。结果表明:316L不锈钢焊缝形成腐蚀微电池的倾向与元素组成、非金属夹杂物和晶粒度大小等因素紧密相关;焊缝三区腐蚀电位、腐蚀电流不同,耐蚀性能差异较大,因而腐蚀电位最低的热影响区与腐蚀电位最高的母材区在电解液中比较容易形成腐蚀微电池,且热影响区可视为此微电池的阳极,腐蚀进程较快。     

柴油加氢装置高压换热器管束断裂原因与防护

对热高分气与混氢换热器断裂管束进行了失效原因分析。结果表明,氯化物应力腐蚀开裂是管束失效的主要原因,氢的存在及管板与管束在溶液环境组成的腐蚀电池加快了该腐蚀的速度。针对腐蚀原因采取了优化设计和制造、安装和操作等腐蚀防护措施,效果良好。     

冷凝器中的镍白铜管泄漏分析

对镍白铜管的材质、显微组织及其腐蚀产物进行了分析，结果表明，由于管内壁粘附有一层碳膜，并与基体形成了微电池，在浓缩的长江水中，促进了腐蚀作用，导致冷凝器管早期泄漏。提出了改进措施后，避免了冷凝管的早期失效。     

锅炉再热器管腐蚀失效及防止措施

介绍了某电厂锅炉高温再热器发生失效的基本情况，通过化学元素分析，机械性能试验，宏观检查，金相分析和电子探针微区成分分析等试验表明，管子外表面存在较明显的结垢现象，氧化物下的金属金相组织出现深2～3个晶粒的沿晶腐蚀裂纹，沿晶腐蚀产物中存在S元素，综合分析认为，其失效类型为高温硫腐蚀，并提出了预防措施。     

某注水井P110油管外腐蚀穿孔原因分析

通过对注水井腐蚀穿孔油管进行宏观形貌、材质性能及腐蚀产物成分的分析,结合服役工况调研和油管中性点计算,对注水井P110油管外腐蚀穿孔原因进行了探讨.研究结果表明:全井深油管仅腐蚀穿孔P110油管出现明显局部腐蚀,且失效油管腐蚀形貌呈"溃疡状",同时该失效油管位于中性点以下,处于正弦屈曲状态;穿孔油管材质性能符合标准API SPEC 5CT-2011对P110钢的要求,油管外壁腐蚀产物主要为FeOOH和CaCO3.因此,P110油管在屈曲状态下与套管接触形成缝隙,而后发生缝隙腐蚀失效.腐蚀类型为吸氧腐蚀,腐蚀主控因素为缝隙效应和溶解氧含量,腐蚀机理为闭塞电池的酸化自催化效应.     

宏电池腐蚀阴极保护不足的危害

对地下管线上作用强度最大的氧浓差宏电池腐蚀进行了阴极保护研究，发现对宏电池腐蚀阴极保护不足时，不能抑制腐蚀，反而会加速腐蚀，这与对微电池腐蚀阴极保护不足时的效果不同。认为用电位值低于０．８５Ｖ的电位进行阴极保护，称为对氧浓差宏电池阴极保护不足，只有达到完全保护时，才能起到阴极保护作用。这对阴极保护现场施工具有重要的指导意义。     

船舶冷却系统铜镍合金管腐蚀穿孔原因

采用体视显微镜、金相显微镜、电子探针等分析测试方法对腐蚀穿孔失效的BFe10-1.6-1铜镍合金管进行失效分析。结果表明：失效管的内壁存在不同程度的划痕，且腐蚀坑内壁显微组织呈现“波纹”状，符合海水冲刷腐蚀的特征；腐蚀区的显微组织呈现“冰糖块”状，符合晶间腐蚀的特征；腐蚀坑内的泥沙沉积致使管道发生点蚀。结合船用铜镍合金管的使用工况，确认该失效管腐蚀穿孔失效的主要原因是海水冲刷腐蚀、晶间腐蚀及点蚀。     

304不锈钢和铁素体不锈钢晶粒显示的新腐蚀方法

304不锈钢和铁素体不锈钢的耐腐蚀性能较好，导致材料的晶粒度评级比较困难。将高锰酸钾硫酸溶液作为腐蚀剂，水浴加热后对304不锈钢进行腐蚀，可获得清晰、完整的奥氏体晶粒，且不显示晶粒内孪晶界；采用放置约3 a的王水作为腐蚀剂对铁素体不锈钢进行腐蚀，可获得清晰的晶粒形貌，实现其晶粒度级别的准确评定。     

腐蚀失效分析方法及展望

概述了腐蚀失效分析的意义,根据实际腐蚀失效分析工作,从现场调查、实验室分析两个方面阐述了腐蚀失效分析的思路,并综合一些典型的腐蚀失效案例对常用的腐蚀失效分析方法进行了简单的归纳。对腐蚀失效分析工作进行了展望。     

Failure analysis of IEU drill pipe wash out

Many 127.0×9.19 mm IEU G105 drill pipe failures of wash out occurred after 2367 h of pure drilling time and 8726 m of penetration footage. This paper gives a detailed investigation on these failures and a systematic analysis is carried out on service and loading conditions of the drill pipes. Measurement and inspection were performed on configuration dimensions, chemical composition, mechanical performance, metallography, macro-fractography, micro-fractography, and corrosion products. Configuration stresses at the crack positions of the drill pipe were calculated by FEA. Crack extending velocity of the drill pipe material under corrosion medium was also measured. It is thought from test and analysis results that the drill pipe wash out or fracture accidents were premature corrosion fatigue failure accident. The failure courses were as the following: corrosion pits occurred first on the internal surface at the stress concentrating area of the drill pipe, and then fatigue cracks initiated in pit bottoms, and washed out or fractured subsequently as cracks penetrated through the wall thickness of the drill pipe. The reasons of drill pipe wash out were related to configuration, material quality, and load condition of the drill pipe string.     

Fatigue behavior of surface cracked filament wound pipes with high tangential strength in corrosive environment

The aim of this study is to examine the corrosion fatigue behavior of filament wound composite pipes with a surface crack under alternating internal pressure. The filament wound pipes are composed of multi-layered E-glass/epoxy composites with a [±75°]₃ lay-up. The surface notches were formed on the outer surface of the pipe along the pipe axis. Dilute (0.6 M) HCl acid was applied to the surface crack region by a corrosion cell mounted on the outer surface of the pipe. The results of an experimental investigation into the corrosion fatigue tests are conducted to observe the oil leakage failure and the crack propagation of the composite pipe subjected internal pressure loading with an open ended condition in which the pipe can be deformed freely in the axial direction. The internal pressure was generated by conventional hydraulic oil for fatigue loading. The fatigue tests are performed at 0.42 Hz frequency and a stress ratio of R = 0.05 in accordance with ASTM D-2992 standard. The oil leakage from the crack tip was observed after the crack propagation reached to the critical stress intensity level. The fatigue crack propagation behavior with the environment exposure was strongly dependent on the crack parameters such as crack-depth ratio and crack-aspect ratio. The micro structure of the fracture surface with the effect of environment and the fatigue loading were also observed.     

Characterization of corrosion products formed on mild steel in deoxygenated water by Raman spectroscopy and energy dispersive X-ray spectrometry

The corrosion of steel parts of heating systems is nowadays not commonly observed failure because of the lack of oxygen in circulated media. In rare cases corrosion rapidly initiates and propagates due to various, mostly unexplained mechanisms. A voluminous corrosion product that was found in the vicinity of a perforation to a pipe wall was investigated in order to understand the reasons for the observed rapid corrosion processes. Raman spectroscopy and energy dispersive X-ray microanalysis were used to examine this corrosion product across the whole cross-section of the pipe. It was observed that the inner part of the corrosion product at the contact with the pipe's inner surface mostly consisted of magnetite. The outer part of the corrosion product, which was in contact with the water in the pipe, was mostly goethite. These findings confirmed the hypothesis that the magnetite sediments on the surface of the new pipe caused oxygen concentration cell formation, which triggered corrosion dissolution of the pipe wall and led to a rapid perforation.     

球墨铸铁煤气管道泄漏原因分析

通过宏观和微观分析等手段,对某QT400-18球墨铸铁煤气管道泄漏原因进行了分析。由宏观分析可知管道腐蚀泄漏是由局部腐蚀穿孔所致,腐蚀从内壁开始,由内向外直至穿孔泄漏;微观分析没有观察到微裂纹等缺陷,成分分析可知管道内壁腐蚀产物中含有大量硫元素,说明管道腐蚀泄漏的产生与管内介质中含有硫元素有关。综合分析结果表明:由于所输送煤气中含硫杂质超标,与管内壁冷凝水共同作用产生局部电化学腐蚀,从而导致了煤气管道的局部穿孔泄漏。建议在生产中将煤气中的有害杂质和水分含量控制在工艺要求范围内。     

舰船高温排烟管腐蚀机理分析及高温腐蚀研究

目前国内外使用的舰船排烟管材料大多为20钢，20Mn、16Mn钢，15CrMo钢，奥氏体合金钢等，海水对高温排烟管腐蚀严重。对舰船高温排烟管腐蚀机理进行了详细分析，研究了几种不同级别的材料在高温和海水交替作用下的腐蚀机理。     

Analysis of steel structure corrosion of drinking water distribution system in family indoor environment

In this paper, corrosion investigation and analysis of steel structure of drinking water distribution system in a family kitchen have been carried out. Results indicate that galvanized corrosion and condensation corrosion under thin water layer have been found the main corrosion type. XRD analysis shows that the rust layer is composed of α‐FeOOH, γ‐FeOOH and Fe₃O₄. For preventing galvanic corrosion, using non‐conductive materials between metals of different electropotential, i.e. electrically insulating the two metals from each other has been recommended. For preventing condensation corrosion under thin water layer, cleaning the pipe external surface to minimize the condensation corrosion is necessary and a good epoxy coating on the pipe external surface may also work. The selection of PVC pipe with better quality and no leaching of inorganic pollutants into water is also a good choice, however, in this condition strong hitting to the PVC pipe should be avoided.     

外丝直接头断裂失效原因分析

某新建小区住宅楼给水管道发生断裂.采用宏、微观检验、材质化学成分分析、力学性能比较及扫描电镜、能谱仪测定等方法对断裂件进行分析.结果表明,因用材错误,在水介质作用下,金属发生晶界腐蚀及显微组织变化,最终引起性能恶化而断裂失效.     

Investigation on corrosion failure of Cr–Mo P11 grade pipe in primary section of a superheated steam generation system

This paper presents failure analysis of corroded steam pipes (Cr–Mo, P11 grade) at ammonia production plant. The corrosion and deposition morphologies are characterized using scanning electron microscopy. In addition, elemental composition analysis of deposited corrosion products is carried out using energy dispersive X-ray. This study clearly indicates the sensitivity of P11 grade steel pipe to intensive oxygen corrosion in steam generation systems with improper implementation of deoxygenating processes. Furthermore, this pipe grade and oxide layer on its surface are susceptible to cracking at the presence of high-level thermal stresses.     

45Mn2钢管的"亮线"缺陷分析

在车削加工45Mn2钢管时,发现管壁中存在类似裂纹状的有金属光泽的"亮线"线务,通过宏观和微观形貌分析、力学性能测试、压扁试验和腐蚀试验等方法分析了钢管"亮线"的形成原因.结果表明:"亮线"的微观形貌由贝氏体组织构成,是异于钢管基体的成分偏析带,来源于连铸坯;这种"亮线"是一种不允许存在的缺陷,建议炼钢厂采取措施,提高...     

Failure analysis of a leak-off oil pipe from injection valves of an off-shore operating diesel engine

The failure analysis of a four-stroke 3000 kW off-shore operating diesel engine is presented. The failure occurred during engine normal operation period in the leak-off oil pipe from the injection valves, which experienced a fracture through the pipe wall and a diesel engine fire as a result. A detailed analysis of all elements which had an influence on the failure initiation was carried out, namely leak-off oil pipe vibration level, pipe stress level, presence of corrosion pits on the pipe external surface under the zinc coating and engine components temperature distribution in the failure zone. It was found that the crack initiation and propagation of the leak-off oil pipe from injection valves was driven by a fatigue mechanism, which was facilitated by loose pipe supports (excessive pipe vibration) and corrosion pits on the pipe surface that acted as stress concentrators. The contact of leak-off atomized oil due to the pipe through wall fracture with the hot engine exhaust muff (390 °C approximately) caused local fire of the diesel engine.