Corrosion behaviour of some stainless steels in chlorinated Gulf seawater

The corrosion resistance of conventional and high alloy stainless steels (specifically 316L, 317L, 904L, duplex 2205, 3127hMO, 1925hMO, 254SMO, 654SMO and Remanit-4565) was determined electrochemically in chlorinated and unchlorinated Arabian Gulf Seawater at 25 and 50 °C. The stainless steels 316L and 317L were used as reference alloys. The electrochemical potentiodynamic cyclic polarization method was used to determine the passive film break down potential (E _b), protection potential (E _prot) and maximum current attained on scan reversal (I _max). It was found that at 25 °C in chlorinated and unchlorinated seawater and at 50 °C in unchlorinated seawater, stainless steels 316L and 317L have poor resistance to corrosion, Stainless steels 904L and duplex 2205 at 25 °C in chlorinated and unchlorinated seawater showed good resistance to corrosion but at 50 °C these steels failed to resist. The high alloy stainless steels such as 3127hMO, 1925hMO, 254SMO, 654SMO and Remanit-4565 showed better corrosion resistance under all the test conditions.     

Bio-film formation on stainless steels Part 2. The role of seasonal changes, seawater composition and surface roughness

Bio-film formation on type 254 SMO stainless steel in Arabian Gulfwater was followed by measuring the variation of the open circuit potentials of test coupons under a variety of conditions. The time-potential curves exhibited two plateaus corresponding to oxide thickening and later to bio film development. The rate of film formation was found to depend on the ambient seawater temperature, which varied with the season. The reduction of the biological activity of the water through additions of pre-boiled and cooled seawater resulted in the retardation of bio-film formation and in the shift of the final steady-state potential towards less positive values. Similar behaviour was obtained when concentrating seawater by the addition of solid salt. The simultaneous reduction of biological activity and of salt content resulted. The characteristics ofthe formed bio-film depend on the nature ofthe metal surfaces. Smooth surfaces allowed the development of thin clear films while thicker dark films formed on coarse rough surfaces. These were usually associated with the growth of worm-like structures, initiating crevice and pitting corrosion.     

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.     

敏化不锈钢在含溴醋酸溶液中的点蚀研究

用电化学法对敏化热处理的奥氏体不锈钢316L和双相不锈钢SAF2205在含溴醋酸溶液中的点蚀行为进行了研究，并用光学显微镜观察了敏化试样浸泡前后的金相组织。结果发现：随着Br^-浓度的增加，两种不锈钢原始材料和敏化材料的点蚀电位都降低，敏化热处理使两种不锈钢的耐点蚀性能下降；无论是两种不锈钢的原始材料还是敏化材料，SAF2205的耐点蚀性能均优于AISI316L。对于敏化的AISI316L不锈钢，Br^-诱发点蚀优先发生在奥氏体晶界附近；对于敏化的SAF2205不锈钢，Br^-诱发点蚀优先发生在γ晶界、某些α／γ相界及α晶界附近。     

湿法脱硫后烟气腐蚀现场实验研究

基于提升排放烟羽高度以及排烟脱白的需求,必须对燃煤锅炉烟气湿法脱硫后的湿烟气进行妥当处理。但湿法脱硫后的湿烟气腐蚀性很强,将对下游设备造成严重腐蚀。本文在91 MW层燃供热锅炉湿法脱硫系统后烟道进行了现场腐蚀实验,测试和评估了5种钢材的耐腐蚀能力。实验结果表明,钢材的表面温度对腐蚀过程具有关键影响。随着表面温度的升高,钢材的腐蚀程度首先因为表面沉积物中氯离子浓度升高而加剧,然后因电解质的匮乏而减轻。     

Initiation and propagation of pitting and crevice corrosion of hydrogen-containing passive films on X70 micro-alloyed steel

Hydrogen promoted initiation and propagation of pitting and crevice corrosion of X70 micro-alloyed steel were characterized by potential dynamic measurements, the scanning reference electrode technique (SRET) and electrochemical impedance spectra (EIS). At open circuit potential, in situ SRET results show that hydrogen accelerates the nucleation and propagation of pitting of X70 steel. The pitting potential E_p of X70 steel gradually decreases with an increase of chloride ion concentration in NaHCO₃ solution. Pre-charged hydrogen does not have a significant effect on the pitting potential E_p and open circuit potential E_corr of the steel in 0.5 M NaHCO₃ solution. However, a synergistic effect of hydrogen and Cl⁻ on the anodic dissolution and pitting potential of X70 steel is observed in 0.5 M NaHCO₃ solution containing chloride ions. When crevices are present in X70 steel, hydrogen accelerates the initiation and progress of crevice corrosion. The mechanisms by which hydrogen promotes the initiation and propagation of pitting and crevice corrosion are proposed and discussed.     

垃圾渗滤液处置设备材质选择的研究

垃圾渗滤液的处理是目前较为复杂的废水处理之一,高盐高COD使得可生化性差。由于Cl离子高达20~30g/L,在渗滤液储存处理过程中,设备材质的耐腐要求很高。借鉴海水淡化的研究工作基础,通过电化学工作站研究了以渗滤液为工作介质的钛材、双相钢2205、双相钢2507三种材质的极化曲线关系,从而得到三种材质的腐蚀速率。实验认为,钛材具有明显的耐腐性能和抗极化性能,双相钢2507的耐腐性能良好,但抗极化性能较差,双相钢2205对耐氯介质无抗腐蚀能力。根据材质的腐蚀速率以及实际工况,对三种材质进行经济评价,认为中短期项目选择双相钢2507较好,长期项目还是应以钛材为宜。     

超滤膜预处理在胶州湾海水淡化的应用

采用3种中空纤维超滤组件处理胶州湾海水,从超滤膜材质、运行参数和出水水质等方面对这3种组件在海水淡化反渗透预处理中的应用进行了评价。结果表明：超滤组件运行和出水水质都很稳定,完全符合SWRO进水要求。     

Mikrobiologisch beeinflusste Korrosion nichtrostender Stähle und ihre Vermeidung

Microbiologically Influenced Corrosion (MIC) is not a new type of corrosion, but refers instead to the influence of microbiological activity on known forms of corrosion. Typically MIC promotes pitting corrosion and — to a lesser degree — crevice corrosion. The extent of this promoting effect can vary widely. Raw water with a high content of organic and inorganic matter requires special attention. Typically MIC starts on stainless steels at sites where the corrosion resistance has been lowered by manufacturing methods, e.g. at or around welded joints. The remedial measures are the same as those taken to avoid pitting and crevice corrosion. However, they have to be applied much more rigorously to prevent bacterial action. The most effective remedial action is clearly biocidal water treatment wherever permissible and possible.     

Pre-treatment strategies for seawater desalination by reverse osmosis system

A good quality pre-treatment process is instrumental to the successful operation of a seawater reverse osmosis (SWRO) plant. The compounds that are susceptible to foul the reverse osmosis (RO) membranes are inorganic suspended solids, sand, oil, clays, bacteria, and dissolved organic matters. In order to prevent the fouling, a pre-treatment of the raw water needs to be conducted. The pre-treatment technologies to prevent membrane fouling and to extend the lifetime of the RO membrane are commonly grouped into two categories, conventional and non-conventional. Both of these treatments are currently applied in SWRO plants in the world. The pre-treatment system applied is highly site specific and depending on the type of the feed water. This paper reviews the recent representative researches that are related to SWRO antifouling strategies and answers the most crucial questions about design and operating parameters of SWRO and its pre-treatment process. Also the economic evaluation of the SWRO system in regards to antifouling strategies' experience is discussed.     

PITTING CORROSION OF SAF2205 DUPLEX STAINLESS STEEL IN ACETIC ACID CONTAINING BROMIDE AND CHLORIDE

Development of duplex stainless steels has been linked strongly with the increasing requirements of the industry for resistance of materials to highly aggressive environments. In the present work, the effects of bromide and chloride ion concentrations and temperature on the pitting corrosion of commercial grade SAF2205 duplex stainless steel were studied. Cyclic polarization and scanning electron microscopy (SEM) techniques were used to study the pitting corrosion behavior of this steel in 80%v/v acetic acid solution containing 0.01, 0.1, 0.2, and 0.5 M sodium bromide and sodium chloride, respectively. Pitting potential was found to decrease with the increase of the temperature and bromide ion concentration. In the presence of chloride ions, pitting corrosion was not observed at room temperature. Critical pitting temperature in chloride-containing solutions was estimated to be above 35°C. In the case of pitting, SEM observation revealed that pit initiation is in the austenite phase regions.     

The experiment research of corrosion behaviour about Ni-based alloys in simulant solution containing H2S/CO2

Aimed at the problem of tubing corrosion in environment that containing hydrogen sulfide (H₂S), carbon dioxide (CO₂), and chlorides (Cl⁻), the corrosion behaviour of two nickel based alloys (UNS 06985 and UNS 08825) in 15 wt%NaCl solution containing H₂S/CO₂ in high temperature and high pressure environment was investigated. The pitting corrosion behaviour of Ni-based alloys was studied in FeCl₃·6H₂O solution by means of polarisation curve and immersion tests. The scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) was applied to analyse the microstructure and corrosion performance of the samples. The results showed that the pitting-resistant of nickel alloy UNS 06985 was superior to UNS 08825. With the rising of experimental temperature, the corrosion increased and some slight pitting attacks appeared on the surface of UNS 08825. The test temperature was the crucial factor that influenced not only the compactness and the growing rate of corrosion product scale, but also the corrosion rate of the alloys. Elemental sulfur is a strong oxidant, the presence of S0 leads to a serious localized corrosion. XRD showed that the corrosion films formed on nickel base alloys consisted of NiS, CrO₃, and the oxides of Ni and Fe. The polarisation curves showed a different corrosion behaviour of two alloys, anodic curve of UNS 06985 has a wider passivation area, and there has higher transpassive potential.     

Studies of the localised-corrosion behaviour of some stainless steels,incology 825 and titanium in seawater

The localised-corrosion behaviour of several high-grade materials has been investigated in a range of conditions of relevance to desalination plant. Under the conditions studied, no evidence has been found of pitting, crevice corrosion or stress-corrosion cracking in titanium. The remaining materials, all chromium -containing, have exhibited similar immunity as titanium in the least aggressive environments but, to an extent depending upon the material and conditions, they have been found to be susceptible to pitting and crevice corrosion in the more severe conditions featured in this work. The relevance of the observations to distillation-plant operation is discussed.     

Specification of surface parameters effects on corrosion behavior of the AISI 316Ti in dependence on experimental methods

Stainless steels usually suffer localized corrosion, such as pitting and crevice corrosion, in chloride containing oxidizing environments. Their corrosion resistance depends on materials chemical composition, microstructure, heat treatment, surface finishing, and also on environment character (composition of electrolyte, temperature, pH, flow, etc.). The subject of the work is investigation of mechanical (grinding) and combined (grinding + pickling) surface treatment effect on corrosion behavior of stainless steel AISI 316Ti. The selected properties of surfaces are determined including surface roughness, surface-free energy, topography (by atomic force microscopy) and chemical composition using scanning electron microscopy. Corrosion susceptibility of the specimens with ground or ground and pickled surfaces to local corrosion has been studied by the three types of corrosion tests (exposure test, potentiodynamic polarization, and electrochemical impedance spectroscopy). The experiments enable not only to compare corrosion resistance after different surface treatment, but to follow response of the surface state on corrosion mechanism of the different experimental methods.     

High-temperature corrosion during the thermal treatment of footwear leather wastes

The footwear leather waste (FLW) has shown some distinct features of a conventional biomass, among which high concentrations of sulfur and chromium. The paper presents the obtained experimental results from gasification and combustion of FLW performed in a semi-pilot plant (350 kW_th). The corrosion tests were carried out with one low carbon steel and three stainless steels at temperature around 500 °C. The obtained corrosion rates for all the tested alloys were significantly lower than those observed on other types of biomass. The presence of chromium oxide and sulfur dioxide in the flue gas was associated with reduction in the corrosion rate.     

2Cr13不锈钢在含饱和CO_2盐溶液中的缝隙腐蚀行为研究

通过电化学动电位极化方法研究了2Cr13不锈钢在含饱和CO2盐溶液中的缝隙腐蚀行为。考察了温度、NaCl浓度以及HAc浓度对缝隙腐蚀的影响规律,结果表明:2Cr13钢缝隙腐蚀击破电位低于点蚀击破电位,同条件下更易引发缝隙腐蚀,且随温度、NaCl浓度、HAc浓度升高,缝隙腐蚀击破电位逐渐下降,缝隙腐蚀诱发阻力减小,缝隙腐蚀倾向增大,2Cr13钢耐缝隙腐蚀性能降低。在该介质中,腐蚀发生时,缝隙部位作为阳极加速腐蚀,缝隙外部作为阴极而得到保护。     

Corrosion and passivation behaviors of some stainless steel alloys in molten alkali carbonates

The corrosion and passivation behaviors of two types of stainless steel alloys (ferritic and austenitic steels) in ternary molten Li₂CO₃-Na₂CO₃-K₂CO₃ mixture at different temperatures (475-550 °C) were studied using galvanostatic polarization and cyclic voltammetry. The galvanostatic polarization curves of the investigated alloys illustrate the passivation and passivity breakdown of the alloys. The passivation potential range for the three investigated steel alloys is about 1.15-1.3 V. During this potential range different oxide and spinels are formed, the nature of which depends on the type of alloy and the anodization potential. At high anodic potentials the decomposition of carbonate takes place, leading to passivity breakdown and oxygen evolution. The values of corrosion parameters (R_p, i_o and i_corr) were calculated. The calculated values indicate that the corrosion resistance of the austenitic stainless steel is higher than that of the ferritic steel. The activation energy of the corrosion process was found to be equal to about 70 kJ mol⁻¹. The results of the cyclic voltammetric investigations indicate that the behavior of the austenitic steels is about the same and differs from that of ferritic steel. The corrosion tests in 0.2 M HCl solutions have shown that the oxide scales formed on the surface of the austenitic stainless steels are multilayered, whereas those formed on the ferritic alloy are uniform.     

The influence of nickel-aluminium bronze microstructure and crevice solution on the initiation of crevice corrosion

A new mechanistic model has been established for the chemical and electrochemical mechanisms controlling nickel-aluminium bronze crevice corrosion. The crevice corrosion was initially confined to eutectoid regions with slight attack of the copper rich α-phase within the α+κ_III eutectoid. In the presence of high chloride concentrations, copper and aluminium complexes form and the hydrolysis of these complexes leads to the acidification of the crevice solution chemistry. As the crevice solution becomes increasingly acidic the initial protection of the κ-phases due to their higher aluminium contents is lost and become anodic to the α-phase. The continuous nature of the κ_III-phase makes it vulnerable with an ∼80 μm depth of attack after only the first month which is accompanied by internal copper redeposited at cathodic sites. Crevice corrosion of copper-based alloys is often reported to be controlled by a copper-ion concentration cell, however, for nickel-aluminium bronze it appears that primarily the crevice corrosion propagation results from a combined action of localised acidification and differential aeration between the bold and occluded zones. This mechanistic understanding provides further insights in to the development of crevice corrosion experienced by nickel-aluminium bronze after long-term exposures to natural seawater for up to 3 years.     

Corrosion of similar and dissimilar metal crevices in the engineered barrier system of a potential nuclear waste repository

Crevice corrosion is considered possible if the corrosion potential (E_corr) exceeds the repassivation potential for crevice corrosion (E_rcrev). In this study, potentiodynamic polarization and potentiostatic hold were used to determine the E_rcrev of similar and dissimilar metal crevices in the engineered barrier system of the potential Yucca Mountain repository in 0.5 M NaCl, 4 M NaCl, and 4 M MgCl₂ solutions at 95 °C. The results were compared with data previously obtained using crevices formed between Alloy 22 and polytetrafluoroethylene. It was observed that, except for Type 316L stainless steel, all other metal-to-metal crevices were less susceptible to crevice corrosion than the corresponding metal-to-polytetrafluoroethylene crevices. Measurements of galvanic coupling were used to evaluate the crevice corrosion propagation behavior in 5 M NaCl solution at 95 °C. The crevice specimens were coupled to either an Alloy 22 or a Titanium Grade 7 plate using metal or polytetrafluoroethylene crevice washers. Crevice corrosion of Type 316L stainless steel propagated without repassivation. For all the tests using a polytetrafluoroethylene crevice washer, crevice corrosion of Alloy 22 was initiated at open circuit potential by the addition of CuCl₂ as an oxidant, whereas no crevice corrosion of Alloy 22 was initiated for all the tests using Alloy 22 or Titanium Grade 7 metals as crevice washer. However, crevice corrosion propagation was found to be very limited under such test conditions.     

Effects of Cr2N on the pitting corrosion of high nitrogen stainless steels

Effects of nitrogen (N) content on the precipitation behavior of Cr₂N with its relevant influences on the resistance to localized corrosion of high nitrogen stainless steels (HNSs) were examined using an electrochemical microcell. HNS of Fe-18Cr-20Mn-3Mo-1.07N was highly resistant to pitting corrosion. With aging the alloy at 900 °C, Cr₂N precipitated initially along grain boundaries, then within grain, and eventually formed a lamellar structure, accompanied with a drastic decrease in the resistance to pitting corrosion. It was found from the electrochemical microcell tests that the lamellar Cr₂N was the most susceptible site for pitting corrosion when compared with any other heterogeneity such as a (Mn, Cr)-oxide or a Cr₂N precipitated along the grain boundaries.