包铝层对铝合金腐蚀行为的影响

对LC4CS、LY12CZ、LF6M三种铝合金在厦门海域全浸区有、无包铝层的条件下的腐蚀行为及腐蚀数据进行了对比研究。同时,通过自腐蚀电位和电偶电流的测量,对LF6M（包铝）在厦门海域潮差区的反常腐蚀行为进行了分析。     

Crevice Corrosion Behaviors Between CFRP and Stainless Steel 316L for Automotive Applications

Carbon fiber reinforced plastics(CFRP) are promising lightweight materials for vehicle applications. 316 L is one of the most widely used types of austenite stainless steels and applied in lots of automotive applications. The existence of crevices will result in galvanic corrosion and crevice corrosion when CFRPs and 316 L are directly connected. A crevice former for the galvanic system was therefore designed and applied to evaluate the crevice corrosion behaviors and study the mechanism of galvanic crevice corrosion through several electrochemical techniques in this research. The results showed that the crevice corrosion of galvanic systems grew from crevice mouth to the inside crevice and could be divided into four steps, metastable pitting corrosion at the crevice mouth, initiating step of crevice corrosion, propagating step and ending step of crevice corrosion. Because of the influences of the galvanic system, electrode reaction rates were speeded up and the passivation region was shortened at the initiating stage of crevice corrosion. Corrosion rate was observed to be higher in the galvanic system than that in normal crevice systems.     

某核电站上充泵转轴的腐蚀原因

某电站上充泵马氏体不锈钢转轴在化学清洗后表面出现局部腐蚀,为了查明局部腐蚀发生的原因,开展了现场检查和模拟试验。结果表明:在操作不当的情况下,马氏体不锈钢的表面易发生缝隙腐蚀;在模拟酸性溶液中,马氏体不锈钢的自腐蚀电位远远低于奥氏体不锈钢的,存在严重的电偶腐蚀倾向。在缝隙腐蚀和电偶腐蚀的共同作用下,马氏体不锈钢的泵轴出现了局部腐蚀。     

乏燃料贮存环境中Al-B4C复合材料的腐蚀行为研究

通过实验室环境模拟沸水堆(BWR)和压水堆(PWR)乏燃料的贮存环境对不同表面处理试样开展全浸腐蚀实验。采用SEM和EDS观测腐蚀微观形貌和分析腐蚀产物,采用XRD测试腐蚀试样的物相,并通过测试试样干重得到腐蚀动力学曲线。结果表明,材料中的Al和微量元素Mg,Fe是引起腐蚀的主要因素;抛光处理试样在PWR贮存液中时,因Fe的影响出现4种微观腐蚀形貌,耐蚀性较差,而在BWR贮存液中时生成Al(OH)₃保护膜,耐蚀性较好;阳极氧化处理试样在PWR和BWR贮存液中均腐蚀增重,腐蚀产物能封闭氧化膜孔洞,抗腐蚀性能最好。     

Effect of chlorination on stainless steels in seawater

The effect of chlorination on the corrosion resistance of different stainless steels in North Sea water has been studied, the sea-water exposures being performed at two Norwegian seawater laboratories. In one laboratory test specimens, simulating various components used in a seawater cooling system, were immersed in the water. In the other laboratory a pipe system containing real components was studied. Seawater temperature, chlorine concentration and chlorination procedure have been varied at both laboratories. The steels investigated include highly alloyed grades like UNS S31254 (AVESTA 254 SMO), UNS S44635 (Avesta Monit) and UNS NO8028 (Sandvik Sanicro 28). The investigation shows that continuously chlorinated seawater is considerably more aggressive than unchlorinated or intermittently chlorinated seawater and that high temperature increases the risks of localized corrosion at the same chlorine concentration. The highest alloyed steel grades were very resistant to crevice corrosion even in continuously chlorinated water but certain kinds of metal-metal crevices have to be avoided. When welded, duplex UNS S31803 was sensitive to pitting corrosion in chlorinated water. Contrary to crevice corrosion, the risk for galvanic corrosion decreases considerably if the seawater is chlorinated.     

储热式热水器不锈钢水箱腐蚀漏水原因分析

采用材料显微分析方法,对某品牌储热式热水器的水箱漏水原因进行了分析.结果表明:厂家采用的304不锈钢储热式热水器水箱在使用过程中位于搭接焊处发生了严重的腐蚀深沟导致了漏水,其主要原因是搭接焊方式形成了狭窄的缝隙,造成了缝隙内的介质处于滞流状态,使得与腐蚀有关的物质迁移困难从而引起了缝隙腐蚀.同时,当缝隙内溶液中的氧耗竭...     

环境因素诱导入井管具的腐蚀

对于同一口油井来说,腐蚀介质基本一致,但是井下油井管各部位的腐蚀差异却较大,这主要是环境因素造成的.本文讨论环境因素引起的杂散电流腐蚀、缝隙腐蚀、电偶腐蚀和应力腐蚀.这些腐蚀现象在油气田开发过程普遍存在.入井管具较多,因材质存在一定的差异,电位差较大的局部区域出现较严重的电偶腐蚀.在其连接处可能发生缝隙腐蚀,钻杆加厚过渡带的残余应力将诱发应力腐蚀.希望本文的讨论为油田开发的相关设计和决策提供一定的参考依据.     

350 MW燃气轮机组煤气加热器螺栓断裂失效分析

采用宏观和微观分析法对350 MW燃气轮机组煤气加热器盲板螺栓断裂进行了系统的表征分析.结果表明,螺栓的断裂是由于材质和加工质量不合格、螺栓紧固力不当以及环境介质的交互作用所产生的电偶腐蚀、缝隙腐蚀和随后的应力腐蚀开裂而引起的,并提出了防止螺栓断裂重复发生的相应对策.     

缝隙腐蚀研究进展及核电材料的缝隙腐蚀问题

综述了缝隙腐蚀的主要机理、模拟研究技术及影响因素,介绍了核电材料在实际服役过程中的缝隙腐蚀问题,讨论了高温高压水环境下缝隙腐蚀研究存在的主要问题以及进一步的研究方向。     

Transport processes in steam generator crevices: III. Experimental results

Corrosion within the tube/support plate crevices of pressurized water reactor steam generators (SGs) has proven to be an important operating problem in the nuclear power industry. In order to explore the electrochemical nature of SG crevice corrosion, and to evaluate our previously published theoretical models (Parts I and II), a SG simulator was developed to perform selected experiments. These experiments involved three different bulk solution environments (acidic, neutral, and alkaline), a bulk water temperature of 200°C at a pressure of 21 kg cm⁻², and experimental times of up to 15 days. The crevice was divided into four different components: an alloy 600 tube within the crevice, an alloy 600 tube external to the crevice, an AISI 4140 steel support plate within the crevice, and an AISI 4140 steel external surface, with each component being electrically isolated from the others. The coupling currents flowing between the components were measured using zero resistance ammeters and maps of galvanic activity have been derived. Under heat transfer conditions, it was found that the crevice is inverted, with positive current flowing from the external environment into the crevice. This inversion was predicted theoretically in Part I of this series. Finally, the general corrosion rate of each component has been estimated, and the inversion of the crevice has been explained in terms of the effect of thermohydraulic processes on the crevice chemistry.     

Moiré based method for real‐time crevice corrosion monitoring

A novel real‐time technique was developed to monitor localized corrosion occurring over a metal surface. It is an optical method based on the Moiré technique that has undergone further improvements and fine tuning for more accurate measurements. Upon testing, good agreements were obtained with the microscopically determined penetration depth. Application for this technique was demonstrated through real‐time monitoring of crevice corrosion activity occurring on the surface of AISI 316 (UNS S31600) stainless steel immersed in 3% NaCl at 60 °C. The crevice was an artificial clear glass/metal crevice with a gap thickness of 5 μm. Based on the findings of these results it was shown that this method can effectively and accurately be used to monitor crevice corrosion.     

Influence of activated carbon on crevice corrosion in adsorption tower of advanced liquid processing system

ABSTRACT

The adsorption tower made of type 316L stainless steel (SS) in Multi-nuclide Removal Equipment (Advanced Liquid Processing System) which uses Ag-impregnated activated carbon (Ag AC) as an adsorbent experienced crevice corrosion. The influence of Ag AC on the crevice corrosion susceptibility and E_sp of 316L SS was investigated by performing electrochemical experiments. Crevice corrosion was observed in the specimen in contact with the Ag AC. On the other hand, there was no crevice corrosion without the Ag AC in both pH 7.4 and pH 12 solutions. Clear ennoblement of spontaneous potential (E_sp) by in contact with activated carbon was observed and that was clearly higher than the repassivation potential for crevice corrosion (E_R,CREV). Thus, the presence of the AC notably increased E_sp of 316L SS and this resulted in increased crevice corrosion susceptibility by the galvanic effect.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

On-line corrosion monitoring in geothermal district heating systems. II. Localized corrosion

Corrosion monitoring in district heating systems has traditionally been performed by using off-line methods, such as weight loss. The disadvantage is that the method is very slow, especially in low-corrosive environments, and that it only provides information about the past corrosion (accumulated over period of time). The purpose of the work is to test on-line monitoring methods in geothermal hot water in the district heating system in Reykjavik, Iceland. Geothermal water poses certain problems with regards to corrosion monitoring due to low conductivity, high pH and the presence of sulphide. These conditions make the geothermal environment low corrosive. However, a quality control is needed, especially since the sulphide causes the steel pipes to be more vulnerable towards localized corrosion. The methods used in this study were: linear polarization resistance (LPR), harmonic analysis (HA), electrochemical noise (EN) and zero resistance ammetry (ZRA). The Pitting Factor was measured with EN and showed promising results for measuring-localized corrosion on-line. A crevice corrosion cell also gave good results but had a low lifetime. However, the results of a galvanic corrosion cell (Fe/Cu) proved more difficult to interpret since they were dependent both on the dissolved oxygen and the sulphide level.     

316L不锈钢焊接头耐蚀性能研究

分别采用扫描电镜(SEM)、X射线衍射(XRD)、动电位极化技术及零内阻安培表方法研究爆炸焊接316L不锈钢接头的显微组织形貌、物相、点蚀及电偶腐蚀行为。结果表明,316L不锈钢侧焊缝金属存在严重的组织形变和金属间化合物相,且相对于基体试样,316L不锈钢侧焊缝和熔合区产生了更多的δ铁素体相,这些因素导致焊接后的316L不锈钢耐点蚀和电偶腐蚀性能降低。     

超临界水冷堆燃料包壳候选材料的耐腐蚀性能

介绍了超临界水冷堆候选材料的相关腐蚀实验结果,并且讨论了每种候选材料在超临界水环境中的耐腐蚀性能。根据当前研究结果可知,高Cr含量的奥氏体不锈钢在超临界水中具有良好的抗腐蚀性能,因此其最有可能成为超临界水冷堆燃料包壳材料。     

The corrosion behavior of one-fifth scale lid models of transport cask submerged in sea bottom

Corrosion tests have been performed for one-fifth scale lid models of typical transport cask for radioactive materials and for other crevice corrosion test specimens at a sea bottom for maximum 6 years. The effect of corrosion on the performance of the cask was evaluated based on the test results. The dissolved oxygen (DO) value measured at the test site was about 5-14 mg/l. These values were higher than DO values at the sea bottom of 200 m to 3000 m depth in the shipping route, and hence the corrosive condition was more severe than that for the actual cask. No leak was found for models with rubber gasket after immersion at the sea bottom for about 6 years. The crevice between cask body and cask lid was unchanged after immersion for about 700 days, that is, 1.4-2.8 μm. Therefore, even if the rubber gasket were deteriorated, the crevice seemed to be narrower than 10 μm, that have been regarded as the safety opening for sunken transport cask assumed in the environmental impact assessment. The maximum penetration depth at contact surfaces of lid models after immersion for 700 days was about 200 μm which was significantly lower than that of creviced specimens of type 316 stainless steel. This might be due to galvanic effect of carbon steel bolts on the corrosion of stainless steel body.     

Control of local corrosion and fracture of metals in optical models of narrow crevices,gaps and cracks using ellipsometry techniques

The method of laser polarization and optical monitoring is described for model studies of distributed and localized corrosion processes in optical models of gaps and cracks. It allows studying localized corrosion fracture of a surface (crevice corrosion; pitting; corrosion cracking; galvanic, selective, intercrystallite, or microbiological corrosion; etc.) in cases in which the process is nonuniformly distributed over the surface and is inaccessible for studies using the standard corrosion–electrochemical methods.     

409型不锈钢在冷凝液中的缝隙腐蚀行为

运用冷凝液循环蒸发方法模拟汽车消声器内部腐蚀环境,对比研究了在有/无缝隙条件下409型不锈钢在冷凝液中的腐蚀行为。结果表明:与无缝隙试样相比,有缝隙试样在循环试验过程中表现出相对较低的自腐蚀电位;20次循环试验后,腐蚀阻力较低,腐蚀深度较大;缝隙导致不锈钢局部腐蚀速率约增大2.4倍,这主要是由缝隙内部在蒸发过程中更容易保持电解液腐蚀环境、并不断酸化导致的。     

Kühlwasserseitige Korrosionsbeständigkeit von metallischen Werkstoffen zur Handhabung von Schwefelsäure

Cooling water side corrosion resistance of high alloyed materials for handling of process side sulfuric acid The approved materials for use in sulfuric acid alloy 825 (German material No. 2.4858) and alloy 20 (German mater. No. 2.4660) have only a low resistance against localized corrosion in chloride containing water and are unsuitable for handling of sulfuric acid. The newly developed austenitic Cr-base alloy, alloy 33, (X1CrNiMoCuN 33-32-1, German mater. No. 1.4591) with 33 % Cr, 31 % Ni, 0,6 % Mo and 0.4 % N should have an excellent resistance against pitting and crevice corrosion additional to its high sulfuric acid resistance, too, because its Pitting Resistance Equivalent No. calculated according to PREN = %Cr + 3,3 · %Mo + 30%N runs to 50. Pitting and crevice corrosion properties of the alloy 33 are tested in comparison to those of reference materials in high chloride containing solutions (1M NaCl, artificial and modified sea water, 10% FeCl₃ · 6H₂O; 500 g/l CaCl₂ ). Pitting potentials and potentials of repassivation of pitting, critical temperatures of localized corrosion (FeCl₃-test, CaCl₂-test, artificial sea water), potentials of repassivation of crevice corrosion as well as depassivation pH values of crevice corrosion following Crolet have been determined. The results confirm that the localized corrosion behaviour of the alloy 33 corresponds to its PREN. With regard to pitting corrosion alloy 33 is comparable with the special stainless steel alloy 31 (mater. No. 1.4562), with regard to crevice corrosion it is comparable with alloy 926 (German mater. No. 1.4529).     

Mechanism of a MIC probe

Interaction of bacterial biofilms with stainless steel is expected to alter electrochemical behaviour compared with that obtained under sterile conditions and under non-biological deposits. In principle, electrochemical signals can monitor biofilm formation and microbial activity. In this study, attempts were made to understand the mechanism by which an electrochemical sensor using periodic mutual polarisation of two similar stainless steel electrodes responds to biofilm formation. This probe is believed by others to respond to cathodic depolarisation by the biofilm, but the present study using natural fresh water showed that an increase in the galvanic and applied currents of two similar, coupled AISI Type 304 SS electrodes took place only after biofilms had initiated corrosion on the anodically polarised electrode. Comparison of electrodes with natural biofilms and deposited rust layers showed that both the films showed evidence of crevice action, but with a lower ionic resistance than a conventional crevice, therefore permitting rapid propagation of localized corrosion even in dilute chloride media.