低浓度含氯介质中氯离子向局部腐蚀闭塞区内的迁移规律及其对应力腐蚀破裂的影响

The enrichment of chloride anion within the occluded cell （OC） for Type 304 austenitic stainless steel in low chloride concentration solution has been investigated by means of a simulated OC. The influence of the enrichment of chloride anion on stress corrosion crack （SCC） of Type 304 stainless steel has been studied. It was observed that the amount of chloride anion migration was proportional to the charge flowing through the anode. Owning to the effects of enrichment of chloride anion, low chloride concentration solution could induce SCC for Type 304 stainless steel.     

重力下水道中混凝土的微生物诱导腐蚀及防护涂层(英文)

Microbiologically induced corrosion of concrete(MICC) and its protective coatings has a high economic impact on sewer maintenance and rehabilitation.A better understanding of the micro-organisms and the biogenic acids that are generated in the sewer is essential in controlling the corrosion of concrete pipes and protective coatings.The role of succession of micro-organisms growth in the corrosion of concrete and protective coatings was evaluated in this study.Examination of various sewer pipe materials exhibiting various extents of degradation,including concrete,cement based and epoxy based coating revealed the presence of both organic and biogenic sulphuric acids.This reflects the activity of fungi and the thiobacilli strains.Organism growth and metabolism were strongly related to the substrate pH.Fungi were found to grow and metabolise organic acids at pH from 2.0-8.0.Whilst the thiobacilli strains grew and generated sulphuric acids at pH below 3.0.The successive growth of the organisms provides an important bearing in developing improved strategies to better manage sewers.     

Wear of MgO-C Refractories in EBT Type Furnaces Experienced at lranian Mobarakeh Steel Plant

Mobarakeh steel Company produces 3 million tons of steel annually with eight 180 tons EBT furnaces.Different types of magnesia-carbon refractories have been employed at slagline during last 5 years.In the present study the wear and corrosion of MgO-C refractories of these furnaces have been studied via post-mortem analysis of used bricks and the observation of operational effects.Laboratory corrosion tests were also arranged to investigate the effect of slag chemistry and the mechanism of chemical corrosion.Characterization of different magnesia-carbon bricks clarified that the crystal size,type and chemistry of magnesia as well as graphite structure have the main influence on corrosion resistance.The CaO:SiO2 ratio in slag also plays a vital role in the wear of slagline refractories.The iron oxide content of slag also has a major role in graphite oxidation.Of metallurgical parameters,the electric power input and the contact time have great influence on refractories life.The results will be discussed with emphasis on particular operational factors in Mobarakeh steel plant.     

Corrosion performance of Al–Al_2O_3 cold sprayed coatings on mild carbon steel pipe under thermal insulation

This paper focused on the corrosion resistance of cold spray Al–Al_2O_3composite coatings used on carbon steel pipe surfaces under thermal insulation. Al–Al_2O_3coatings were produced on the carbon steel pipe surface by cold spray(CS) technology. Experimental apparatus was built to test the corrosion resistance of coatings beneath mineral wool insulation under isothermal, thermal cycling and wet/dry conditions. The results showed that when α-Al_2O_3 was added in spraying powder, the coating could obtain higher hardness and a denser microstructure. From corrosionunder-insulation(CUI) tests, Al–Al_2O_3CS coatings were proven to be efficient in protecting carbon steel pipe from CUI mainly owning to lamellar microstructures of coatings. There was no evidence to show that α-Al_2O_3 might bring any negative effect on corrosion resistance. Al–Al_2O_3CS coatings were sensitive to the chloride ion concentration. When these coatings were exposed to higher concentrations of NaC l, the coating's exhibited faster degradation.     

Synthesis,characterization and electrochemical evaluation of anticorrosion property of a tetrapolymer for carbon steel in strong acid media

A novel tetrapolymer(TP) consisting of carboxylate, sulphonate, phosphonate and sulfur dioxide based comonomers was synthesized using Butler cyclopoymerization technique. The synthesized tetrapolymer was characterized using FTIR,1 H-NMR,~(13)CNMR and elemental analysis. The performance of the tetrapolymer as a corrosion inhibitor for St37 carbon steel in 15% HCl and 15% H_2SO_4 acid media was assessed using electrochemical impedance spectroscopy(EIS), linear polarization resistance(LPR), potentiodynamic polarization(PDP) and electrochemical frequency modulation(EFM) techniques. The influence of addition of a small amount of KI on the corrosion inhibition efficiency of TP was also assessed. Results obtained showed that the tetrapolymer moderately inhibited the corrosion of St37 steel in the acid media with protection efficiency of 79.5% and 61.1% at the optimum concentration of 1000 mg·L~(-1) studied in HCl and H_2SO_4 media respectively. On addition of 5 mmol·L~(-1) KI to the optimum tetrapolymer concentration, the protection efficiency was upgraded to 90.6% and 93.5% in HCl and H_2SO_4 environment, respectively. The enhanced performance of the polymer in the presence of KI is due to synergistic action deduced from synergism parameter(S1) which was found to be greater than unity.The tetrapolymer afforded the corrosion inhibition of St37 steel in the acid media by virtue of adsorption of the polymer molecules on the steel surface which was confirmed by ATR-FTIR analysis of the adsorbed film extracted from the steel surface. TP + KI formed complex with St37 steel surface in H_2SO_4 solution but not in HCl solution.     

Corrosion of Alumina and Mullite Based Refractories by an Ingot Casting Steel

The corrosion of refractory crucibles by a highly corrosive steel(18CrNiMo7-6) with a high aluminum content and casting temperature of 1580℃ was investigated. The tested refractories were alumina,mullite and alumina doped with zirconia and titania( AZT). The samples were decreasingly attacked in the sequence AZT,alumina and mullite with corrosion layers of about 14,6 and 1 mm,respectively. In the alumina and AZT,compositions corresponding to manganese aluminates and subsequently manganese aluminosilicates formed with manganese and silicon from the steel. In the mullite crucible,compositions corresponding to manganese aluminosilicates formed directly with manganese from the steel giving a highly viscous interfacial melt which retarded the further corrosion.     

Multifunctional Refractory-lined Vessel: Ladle Aggregate

A ladle primarily is a container used to transport molten steel from the steelmaking unit to the casting facility.The essential requirements are heat resistant,insulative and strong enough to hold molten steel up to 300 t,with a structure of multilayered refractory lining in a steel shell vessel.When a ladle is assembled with three-phase graphite electrodes,a ladle furnace forms,starting steel refining process with/without the vacuum tank degasser and RH circulating degasser,in order to meet the growing demand on high purity and higher quality steel.The working lining is under aggressive conditions that comprise the chemical reaction with molten steel,the severe corrosion of liquid slag,the disaggregation through oxidation,and the strong stress due to the impacting of the melts and gases and the effects of thermomechanical behaviors.Magnesiacarbon brick is one of the major materials,being indispensable for the slagline of a ladle furnace.Alumina-magnesiacarbon brick has played an important role to substantially increase the service life in the metal zone,from the early lining materials of high alumina and doloma bricks.The permanent lining must assume sufficient responsibility to allow finishing the process of the engaged charge in case of a failure in the working lining.The insulation layer must be as thin as possible in order to maximize the ladle’s capacity,and reduce the shell temperature for saving energy.In this issue,several integrant refractories are reviewed or investigated in order to compile a lining overview,and to contribute a prolonged service life under aggressive working conditions of the ladle furnace.     

Slag Corrosion Resistance of MgO-ZrO2 Refractories

Slag corrosion resistance of MgO ZrO2 refractories was investigated in this work. The results indicate that in a non-oriented electric steel slag system with a high ratio of calcia to silica,the slag resistance of MgO ZrO2 refractories can be described as follows: ZrO2 reacts with CaO forming calcium zirconate compound which strengthens the material and blocks the channel of the slag infiltration; however,in an oriented electric steel slag system with a high concentration of silica and the low ratio of calcia to silica,the slag corrosion resistance of MgO ZrO2 refractories is different; ZrO2 reacts with CaO forming the calcium zirconate and simultaneously one more product C2S as well; C2S can improve corrosion resistance by blinding pore and enhancing slag viscosity; therefore,it is expected to be the major reason for the enhanced corrosion resistance observed for MgO ZrO2 refractories.     

A novel green inhibitor for C-steel corrosion in 2.0 mol·L~(-1) hydrochloric acid solution

The corrosion inhibition characteristics of aqueous extract of seeds of Melia azedarach L.(MA) have been studied as eco-friendly green inhibitor for corrosion control of C-steel in 2 mol·L~(-1) HCl solution by gravimetric and electrochemical methods. The results depict that, the extract inhibits efficiently the corrosion of carbon steel in hydrochloric acid. The efficiency of extract is increased with increasing the extract concentration but independent on the studied temperature. The adsorption of the extract components onto the steel surface was found to be spontaneous, and follows Langmuir adsorption isotherm. The surface morphology of C-steel, in the absence and presence of MA extract in 2.0 mol·L~(-1) hydrochloric acid solution, was studied using scanning electron microscopy(SEM).     

应变和氯离子浓度对304不锈钢点蚀敏感性的影响

The effects of strain and chloride concentration on pitting susceptibility for type 304 stainless steel were studied in situ using the electrochemical technology under constant strain. The impact factor fc was brought forward to value the effect of strain on pitting. The pitting behaviors of type 304 stainless steel in various chloride concentrations under the strain levels 0%, 10%, and 30% were investigated. Potentiostatic polarization technology was used to study how the chloride concentration affected corrosion current density. The results indicated that fc increased substantially and pitting potential varied remarkably when chloride concentration was over 90 mg.L . Under the three levels of strain mentioned above, when chloride concentration was below 463 mg.L^-1,121 mg.L^-1, and 98 mg.L^-1 respectively, the pitting potential shifted towards positivity and, the passive film became more stable. When the strain was below 10%, the pitting susceptibility of type 304 stainless steel varied greatly as strain increased, whereas the susceptibility only changed a little when the strain was over 10%.     

不同杀菌剂对硫酸盐还原菌杀菌能力评价

采用静态培养法考察NaClO、1227和异噻唑啉酮3种杀菌剂对循环水中硫酸盐还原菌（SRB）的杀菌效果,并利用扫描电镜（SEM）观察SRB细胞形态结构变化和SS316L不锈钢试件的腐蚀形貌.结果表明,NaClO在投药12h时杀菌效果最佳,早于1227和异噻唑啉酮的24 h; NaClO抑菌持续时间较短,仅为24 h,抑制细菌生长时间最长的杀菌剂为1227,可持续1周左右;在最佳条件下,NaClO、1227、异噻唑啉酮的最大杀菌率分别为86.71％、89.70％、79.70％;随着杀菌时间的延长,SRB细胞结构由局部分解开始,7h后细胞完全解体.在接种SRB的循环冷却水中SS316L表面会生成一层分布不均的生物膜,其对SS316L的腐蚀以点蚀为主.     

The influence of bacteria on the passive film stability of 304 stainless steel

The stability of stainless steel 304 in the presence of aerobic and anaerobic bacteria was investigated in a continuous flow system using electrochemical impedance spectroscopy and scanning electron microscopy (SEM) examinations. The results show that the open circuit potential (OCP) of stainless steel was ennobled (shifted in the electropositive direction) by about +150 mV in the presence of the aerobic bacteria. The observed change of OCP in the electropositive direction can be explained by an increase in the rate of the cathodic reaction. Also the presence of an aerobic biofilm led to a decrease in the polarization resistance of stainless steel is not only due to the growth of micropits, as shown from SEM micrographs, but also due to thinning of the passive film. In the presence of only Pseudomonas fragi, the electrochemical impedance response showed a capacitive behavior with RP on the order of 500 kΩ. The addition of anaerobic sulfate reducing bacteria (SRB) to the test medium decreased RP to 12 kΩ due to an increase in localized corrosion, as indicated by SEM examination.     

Accelerated low water corrosion of carbon steel in the presence of a biofilm harbouring sulphate-reducing and sulphur-oxidising bacteria recovered from a marine sediment

Investigations were undertaken to elucidate causes of accelerated low water corrosion (ALWC) of steel piling in a harbour in Southern England. Visual inspection revealed features characteristic of ALWC such as the presence of poorly adherent, thick corrosion products of varying morphology, often seen as large blisters randomly located on sections of the structure at the low water mark. Upon the removal of blisters, a bright surface covered with shallow pits was exposed. Representative samples of the corrosion products were collected from the structure and water and sediment specimens were retrieved from selected areas in the harbour for microbiological, chemical and microscopy testing. In the laboratory, field samples were enriched to detect and enumerate communities of sulphur-oxidising bacteria (SOB) and sulphate-reducing bacteria (SRB). Biofilms, comprising SRB and SOB populations isolated from a sediment sample were grown under static conditions on surfaces of electrodes manufactured from steel piling material. Linear polarisation resistance (LPR) measurements revealed that the corrosion rate of steel with biofilms (0.518 mm y⁻¹) was higher than that recorded in sterile seawater alone (0.054 mm y⁻¹) and in sterile seawater to which nutrient was added (0.218 mm y⁻¹). Scanning electron microscopy (SEM) imaging demonstrated enhanced pitting under biofilms. The results of our investigation revealed for the first time that the attack on steel piling in the presence of sediment SRB and SOB populations was characteristic of ALWC.     

脱氮硫杆菌生长特性及其对碳钢SRB腐蚀的防护作用研究

将脱氮硫杆菌(TDN)作用于被硫酸盐还原菌(SRB)微生物腐蚀的碳钢,研究了SRB和TDN生长特性及最适生长条件.利用静态挂片法研究SRB在不同环境下的腐蚀行为,以及TDN的防护效果;并借助扫描电子显微镜、X-射线能谱仪等研究了腐蚀后钢片的形貌及腐蚀产物.结果表明,SRB和TDN生存条件相似并可共存于同一环境;SRB可加速对X70钢的腐蚀,若有TDN共存时腐蚀程度明显降低,且TDN可消耗SRB代谢的具有腐蚀性的硫化物从而减轻SRB对钢基体的腐蚀.     

Corrosion of 2205 duplex stainless steel in chloride medium containing sulfate-reducing bacteria

Sulfate-reducing bacteria (SRB) play significant role in the corrosion of stainless steels exposed to marine and soil environment. Sulfate reduction by bacterial species results in the production of H₂S, which can significantly influence the anodic and cathodic processes and ultimately enhances the corrosion of materials. In the present study, 2205 type duplex stainless steel (DSS) coupons in solution-annealed condition were exposed to chloride medium containing SRB species, Desulfovibrio desulfuricans, for 40 days and examined by microscopy. Etching of the duplex structure, pitting as well as crevice attack were noticed. Similar results were obtained by microscopic studies with coupons exposed for 14 days in medium containing SRB followed by anodic polarization. SEM studies, of crevices observed after anodic polarization, indicated that the attack was initiated at the grain boundaries and slowly encroached into austenite grains. The initiation of attack was also evident from AFM studies of coupon exposed under freely corroding conditions for 7 days. ESCA studies reveal that under anaerobic conditions of SRB growth sulfidation of passive film occurs. The modified passive film found to depolarize the cathodic reactions. The nature and mechanism of SRB attack on DSS and possibility of detection at early stages were discussed.     

Effects of sulfate-reducing bacteria on the corrosion behavior of carbon steel

The influences of the growing process of sulfate-reducing bacteria (SRB) in seawater system on the medium state and corrosion behavior of carbon steel were studied by detecting solution state parameters and using corrosion electrochemical methods. The growing process of SRB in the seawater shows the three stages of growing, death and residual phases. The solution state parameters of the concentration of sulfide, the pH value and the redox potential changed during the three stages of the SRB growing process. And the corrosion rate of D36 carbon steel was accelerated during the growing phase and stable during the death and residual phases. The results indicate that the medium state and the corrosion rate of the steel do not depend on the number of active SRB, but depend on the accumulation of the metabolism products of SRB.     

硫酸盐还原菌诱导腐蚀的电化学噪声分析

基于电化学噪声(EN)和信号处理研究硫酸盐还原菌(SRB)对304不锈钢诱导的腐蚀。将304不锈钢电极分别置于硫酸盐还原菌接种前后的培养基中,利用电化学工作站分别对2种试样的腐蚀进程进行电化学噪声测量,将测得的噪声数据去除直流漂移,再对这些数据进行时域、频域和小波分析。结果表明:通过时域分析得到的标准偏差和噪声电阻可表征腐蚀速率,局部因子则可以区分腐蚀类型。通过频域分析得到的功率谱密度曲线,能表征304不锈钢腐蚀的程度。小波分析则能从不同尺度下分解信号,更加直观、清晰地表征腐蚀进程。利用电化学噪声技术能很好地监测SRB对不锈钢的腐蚀影响,根据不同的需求采用不同的分析方法进行电化学噪声数据分析,才能准确表征腐蚀类型、腐蚀速率以及腐蚀程度。     

Pitting corrosion studies of super austenitic stainless steels in natural sea water using dynamic electrochemical impedance spectroscopy

Potentiodynamic anodic polarisation and dynamic electrochemical impedance spectroscopic (DEIS) measurements were carried out on type 316L stainless steel (SS), alloys 33 and 24 in natural sea water environment in order to assess pitting corrosion resistance. The results revealed that the pitting corrosion resistance was higher in the case of alloys 33 and 24 than 316L SS; due to the higher contents of nitrogen, chromium and molybdenum. DEIS measurements were performed over a wide range of potentials covering the corrosion potential, passive region, breakdown region and dissolution region. It was shown that the impedance measurements in potentiodynamic conditions allow simultaneous investigation of changes in passive layer structure. The impedance spectra of various potential regions were also discussed. The Nyquist plots were fitted using non-linear least-square (NLSS) method for different potential regions.     

衣康酸介质中杂质离子对两种不锈钢腐蚀行为的影响

针对发酵法生产衣康酸过程中的腐蚀问题研究了两种不锈钢在衣康酸工况介质（发酵液）中的腐蚀行为,探讨了介质中杂质离子Ｃｌ－、Ｆｅ３＋、ＳＯ２－４等对腐蚀的影响。结果表明,随衣康酸介质中Ｃｌ－含量增加,不锈钢的腐蚀速率也增大,而其点蚀电位则随Ｃｌ－浓度的对数值增加呈线性下降;Ｆｅ３＋浓度的增大可使不锈钢／发酵液由活化体系转变成活化 钝化体系;ＳＯ２－４对不锈钢稍有缓蚀作用;在含杂质的衣康酸介质中,Ｒ１双相不锈钢的耐全面腐蚀和耐点蚀性显著优于３１６Ｌ奥氏体不锈钢。     

The electrochemical studies of the corrosion resistance behaviour of hydroxyapatite coatings on stainless steel fabricated by electrophoretic deposition

HA was coated on stainless steel (SS) 316L by using electrophoretic deposition to impart corrosion resistance upon SS 316L. Consequently, corrosion behaviour of HA coated SS 316L deposited from applied voltages 10 V to 60 V (denoted as HA/SS316L-10V until -60V) was evaluated in comparison with pristine SS 316L by various electrochemical studies. As results, linear potentiodynamic polarisation result suggested that HA/SS316L-40V exhibits highest open circuit potential indicating that successful protection of HA coating. Additionally, cyclic polarisation studies revealed that HA coated SS 316L improves pitting corrosion resistance. Finally, EIS results demonstrated that higher polarisation resistance and lower capacitance values for HA/SS316L-40V.