Localized corrosion of lean duplex stainless steels in H2S-containing wet atmosphere from urban wastewater treatment units

With lower alloying costs and higher mechanical properties, lean duplex stainless steels can be a good alternative to the more commonly used austenitic stainless steels. A study was initiated to define the limits of the use of lean duplex stainless steels for urban wastewater treatment (WWT) units. This paper gives and discusses the corrosion results in an aerated wet atmosphere containing H₂S at different levels. Exposures were performed both at laboratory scale and in the field WWT plant for 1 year. A specific probe was also designed to study the corrosion process below water condensate film contaminated with H₂S. Under such conditions, the properties of stainless steel were strongly modified with an enhanced risk of localized corrosion. The results obtained on lean duplex materials (UNS S32101, S32202, and S32304) are compared with austenitic UNS S30403 and UNS S31603 and with the more standard duplexes UNS S82441 and UNS S32205. The results show that lean duplexes can be used in aerated wet atmospheres in case of moderate contamination of H₂S (<10 ppm) and chloride (<200 ppm). For higher contaminations (e.g., H₂S around 100 ppm/chloride around 1000 ppm) the duplex S32205 should be preferred.     

不同热处理条件下双相钢的磨损腐蚀

采用失重法、极化曲线法对不同热处理条件下双相钢 在流动的35% NaCl中性盐水中的磨损腐蚀规律及机理进行了探讨.结果表明，随着流速的 增大，不同热处理的双相钢腐蚀速度均增大，并存在一个使腐蚀速度急剧上升的临界流速值 ；流速相同时，经1050℃固溶后500℃2 h时效强化的双相钢耐蚀性最好.双相钢的腐蚀主要 受阳极的自钝化控制.     

Corrosion resistance of low‐nickel duplex stainless steel rebars

The use of stainless steel bars in reinforced concrete structures may be an effective method to prevent corrosion in aggressive environments where high amounts of chlorides may penetrate in the concrete cover. For an estimation of the service life of structures where stainless steel bars are used, the chloride threshold for these rebars should be defined, and the influence of chemical composition and metallurgical factors that may affect the corrosion resistance (strengthening, welding, etc.) should be assessed. To reduce the cost of stainless steel reinforcement, duplex stainless steels with low nickel content have been recently proposed as an alternative to traditional austenitic steels, even though, few results are available regarding their corrosion performance in chloride contaminated concrete. This paper deals with the corrosion resistance of low‐nickel duplex stainless steel rebars (1.4362 and 1.4162) as a function of the chloride content. Comparison is made with traditional austenitic steels. An attempt to define a chloride threshold for the different stainless steels is made by comparing the results of several test procedures both in concrete and in solution.     

Localized corrosion of (lean) duplex stainless steels in immersion units of urban wastewater treatment plants

With lower alloying cost and higher mechanical properties, lean duplex stainless steels can be an alternative to the more commonly used austenitic stainless steels. However, these alloys are still not the preferred choice, probably due to a lack of field experience. A study was thus initiated in view of defining the limits of use of selected (lean) duplexes for urban wastewater treatment units. The present paper shows the localized corrosion performance of selected lean duplexes in chloride contaminated solutions. The results are compared with austenitic S30403 and S31603 and with the more standard duplexes S82441 and S32205. The effect of welding was also investigated. Exposures in field municipal wastewater plants were conducted for 1 year in low and high chloride content units. The results show that lean duplexes S32101 and S32202 can be used as alternatives to S30403 and S31603 in low chloride electrolytes. At 500 ppm of chloride content, duplex stainless steel S32304 showed better corrosion resistance than S30403 and S31603. For higher chloride contents (1000 ppm and above) the standard duplexes S82441 and S32205 shall be preferred.     

Selektive Korrosion von Duplexstahl. Teil 2: Lokale Korrosionserscheinungen an Duplexstahl X2CrNiMoN22‐5‐3 unter Einwirkung von Chloriden und mechanisches Verhalten in Abhängigkeit vom Gefügezustand

Selective corrosion of duplex stainless steel. Part 2: Localized corrosion manifestations under exposure of chlorides on duplex stainless steel X2CrNiMoN22‐5‐3 and mechanical behavior in dependence of the microstructure In completion to part 1 of this paper this part deals with interrelations between localized corrosion manifestations, mechanical properties and the microstructure of duplex stainless steel X2CrNiMoN22‐5‐3. The pit formation on duplex stainless steels is substantially determined by the distribution of the alloying elements within single phases and by defects in the oxide layer. The positive properties of molybdenum become ineffective at thicker oxide layers due to the fact, that molybdate, which is responsible for inhibition of pitting, can not be formed. Depletion areas caused by precipitations are preferential attack places for corrosion. The influence of chlorides for duplex stainless steels in rolled and welded conditions is characterized by a logarithmic dependence.     

Corrosion behavior of engineering alloys in synthetic wastewater

The corrosion behavior of 1018, 410, and 800 steels exposed to synthetic wastewater have been studied using linear polarization resistance, cyclic potentiodynamic curves (CPCs), electrochemical noise (EN), and electrochemical impedance spectroscopy (EIS) tests. The conditions were: a biochemical oxygen demand of 776 ppm; a chemical oxygen demand of 1293 ppm; a pH of 8; and a cell temperature of 25 °C. From the CPC and EN results, no localized corrosion was found for the stainless steels. However, small indications of a possible localized corrosion process were detected for the 1018 steel. The EIS results revealed that different corrosion mechanisms occurred in the carbon steel compared with the stainless steels. The results show that the corrosion mechanism strongly depends on the type of steel. Overall, the 1018 steel exhibited the highest corrosion rate, followed by the 410 alloy. The highest corrosion resistance was achieved by the 800 alloy. In addition, scanning electron microscopy analyses were carried out to explain the experimental findings.     

Susceptibility of stainless steel alloys to crevice corrosion in ClO2 bleach plants

Stainless steels, including duplex stainless steels, are extensively used for equipment in pulp bleaching plants. One serious corrosion problem in chlorine dioxide bleach plants is crevice corrosion of stainless steels, which is frequently the factor that limits their use in bleach plants. Crevice corrosion susceptibility of alloys depends on various environmental factors including temperature, chemical composition of environment and resulting oxidation potential of system. Upsets in the bleaching process can dramatically change the corrosivity of the bleaching solutions leading to temperatures and chemical concentrations higher than those normally observed in the bleach process. When the environmental limits are exceeded the process equipment made of stainless steel can be severely affected. Environmental limits for crevice corrosion susceptibility of eight stainless steel alloys with PRE numbers ranging from 27 to 55 were determined in chlorine dioxide environments. Alloys used in this study included austenitic, ferritic-austenitic (duplex), and superaustenitic stainless steels. The performance of the different stainless steel alloys mostly followed the PRE numbers for the respective alloys. The 654SMO alloy with the highest PRE number of 55 showed the highest resistance to crevice corrosion in this environment. Under the most aggressive chlorine dioxide bleach plant conditions tested, even alloys Nicr3127 and 654SMO with PRE numbers 51 and 55 respectively were susceptible to crevice corrosion attack. The two factors that seem to contribute the most to crevice corrosion and pitting in the investigated environments are temperature and potential.     

Long-term corrosion behaviour of stainless reinforcing steel in mortar exposed to chloride environment

Long-term corrosion behaviour of six stainless reinforcing steels embedded in mortar and exposed to chloride media was monitored by electrochemical impedance spectroscopy at the open circuit potential during the period of 2 years. Corrosion behaviour of studied steels was divided into two phases characterized by different interfacial behaviour: (i) passive phase and (ii) pitting propagation phase. After 2 years, duplex steel 1.4362 showed very good corrosion performance similar to austenitic steel 1.4401. Steel types with low Ni content but with high N and Mn content, 1.4597 and 1.4162, showed lower corrosion resistance compared to austenitic steel 1.4301.     

22Cr双相不锈钢与304L、316L钢在氯化物溶液中耐应力腐蚀性能的比较

采用恒载荷法、恒应变法研究了22Cr双相不锈钢在不同Cl-浓度、不同温度的氯化物渗液中耐应力腐蚀的性能,并与316L和304L普通奥氏体不锈钢进行了对比.结果表明,22Cr双相不锈钢在氯化物环境中具有更好的应力腐蚀破裂(SCC)抗力.     

衣康酸介质中Cl^—和NO3^—对不锈钢点蚀电位的影响

利用动电位法测定３１６Ｌ奥氏体不锈钢和Ｒ１双相不锈钢在Ｃ５Ｈ６Ｏ４－Ｃｌ＾－－ＮＯ３＾－水溶液体系中的阳极极化曲线和点蚀电位,探讨了衣康酸（Ｃ５Ｈ６Ｏ４）介质中Ｃｌ＾－和ＮＯ３＾－对点蚀的影响。结果表明：（１）Ｃｌ＾－浓度［Ｃｌ＾－］的提高导致不锈钢点蚀电位Ｅｂ降低,其关系为Ｅｂ＝ａ－ｂｌｇ［Ｃｌ＾－］。同样条件下,Ｒ１不锈钢的点蚀电位比３１６Ｌ不锈钢高３００￣４００ｍＶ;（２）在含Ｃｌ＾－的衣康     

热带海洋大气环境下不锈钢的腐蚀寿命评估

目的 给出一种模拟万宁海洋大气环境的室内加速环境谱并对典型不锈钢材料进行寿命预测。方法 采用失重法对4种不锈钢的耐蚀性进行宏观分析。采用X射线光电子能谱分析仪（XPS）对4种不锈钢的腐蚀产物类型进行分析。采用扫描电子显微镜（SEM）对4种不锈钢的腐蚀产物进行微观分析。采用腐蚀电化学法对4种不锈钢进行宏观电化学分析。采用灰色关联度分析法研究室内加速环境谱与万宁海洋大气环境下户外暴露试验的相关性。结果 4种不锈钢的腐蚀失重速率都随着试验时间的增加而降低,其中430不锈钢腐蚀速率的减小程度最明显。4种不锈钢均在室内加速腐蚀试验中表现出较好的耐蚀性,耐蚀性由好到差依次为2205、316L、304、430不锈钢。XPS结果显示,304不锈钢与316L不锈钢的腐蚀产物主要为Fe₂O₃和Fe₃O₄;2205不锈钢的腐蚀产物主要包括Fe₂O₃以及Fe OOH或FeCr₂O₄;430不锈钢的腐蚀产物属于典型不锈钢的腐蚀产物,主要由...     

Corrosive-wear resistance of stainless steels for the impeller of slurry pump used in zinc hydrometallurgy process

1. IntroductionA number of pumps have been widely used in thefollowing fields: water power, electric power, smelting,coal mine, oil field, chemical plant, papermaking and soon. The wet parts of pump (mainly consists of impellerand pump shell etc.) can easily be damaged due to theerosion and corrosion of the slurry, namely the combinedcorrosion wear (C-W) or erosion-corrosion (E-C) [1-3]. Ithas been reported that C-W is responsible for more than5 % of the total wear encountered in industrial …     

Microbially influenced corrosion on stainless steels in waste water treatment plants: Part 1

Abstract

Field tests on stainless steels have been carried out at five waste water treatment plants for one year. Three grades of stainless steel, i.e. AISI 304 (UNS S30400), AISI 316 (UNS S31600), and duplex 2205 (UNS S31803) were tested in the final settling tank in the plants. The time dependence of the open circuit potential (OCP) was measured for all coupons. Ennoblement of the OCP, similar to that reported from investigations in sea water, was found in one of the plants. Waters from three of the exposure sites, containing dispersed deposits from exposed coupons, were chemically analysed. Pitting corrosion was observed after the field test on steel grade AISI 304 in three of the five plants, and on AISI 316 in one plant. No corrosion was found on 2205 in any of the plants. Laboratory measurements of the OCP were carried out for the AISI 304, AISI 316, and duplex 2205 steels in water collected from one of the plants. Cathodic polarisation curves were recorded in waste water from the same plant. T he cathodic reaction rate increased at the highest OCP. Simulation of the ennoblement was carried out by potentiostatic polarisation in a 600 ppm chloride solution. The current response indicated corrosion of welded AISI 304 material and of AISI 304 and AISI 316 steels in crevice assemblies after a long induction time. Part 2 of this study presents the results of further testing and a risk assessment design.     

两种涂层和两种钢在液/固两相流中冲刷与腐蚀的交互作用

用失重法和电化学法系统地研究了20钢基体、两种Ni基涂层(Ni60JH和Delelo50)以及对比材料lCrl8Ni9Ti不锈钢在液／固两相流(5％H2SO4 15％石英砂)中冲刷与腐蚀的交互作用．实验表明：(1)在冲刷速率为5—10m／s时，Ni60JH涂层的耐冲刷腐蚀性能比基体高8—15倍多，并优于1Crl8Ni9Ti不锈钢；DelelO50涂层的耐冲刷腐蚀性能比基体高3—5倍多．(2)随着冲刷速率的提高，4种材料的冲刷腐蚀交互作用失重率在冲刷腐蚀总失重率中所占比例显著增大，由低速时的45％增加到高速时的80％，从而使冲刷腐蚀交互作用失重率在冲刷腐蚀总失重率中占主导地位．(3)在纯腐蚀中，Ni60JH涂层和1Crl8Ni9Ti不锈钢以均匀腐蚀为主要特征，而DelelO50涂层和20钢以选择性腐蚀为主要特征．     

Influence of sigma-phase formation on the localized corrosion behavior of a duplex stainless steel

Because of their austenitic-ferritic microstructures, duplex stainless steels offer a good combination of mechanical and corrosion resistance properties. However, heat treatments can lower the mechanical strength of these stainless steels as well as render them susceptible to intergranular corrosion (IGC) and pitting corrosion. In this study, a low-carbon (0.02%) duplex stainless steel is subjected to various heat treatments at 450 to 950 °C for 30 min to 10 h. The heat-treated samples then undergo ASTM IGC and pitting corrosion tests, and the results are correlated with the microstructures obtained after each heat treatment. In the absence of Cr₂₃C₆ precipitation, σ-phase precipitates render this duplex stainless steel susceptible to IGC and pitting corrosion. Even submicroscopic σ-phase precipitates are deleterious for IGC resistance. Longer-duration heat treatments (at 750 to 850 °C) induce chromium diffusion to replenish the chromium-depleted regions around the σ-phase precipitates and improve IGC resistance; pitting resistance, however, is not fully restored. Various mechanisms of σ-phase formation are discussed to show that regions adjacent to σ-phase are depleted of chromium and molybdenum. The effect of chemical composition (pitting resistance equivalent) on the pitting resistance of various stainless steels is also noted.     

Technical note Weight loss investigation of alternating voltage corrosion of 301, 304, and 316 stainless steels in boiling NaCI solution

Abstract

Alternating voltage corrosion of types 301, 304, and 316 stainless steels in an aqueous boiling NaCl solution under continuous reflux was investigated through weight loss measurements as a function of time. Specimens of each type of stainless steel were used as electrodes to heat the solution by the Joule effect using pure outlet alternating voltage modulation (127 V, 60 Hz). Pitting corrosion was observed in all cases, but it was severe for 304 and less marked for 301. This led to average percentage weight losses, after 1500 h of experiment, of up to 30%, 21%, and 16% for the 304, 316, and 301 steels respectively. The enhanced pitting corrosion of the 304 steel agrees with results previously reported in the literature by other authors.     

三种不锈钢在含硫酸的水砂介质中的耐腐蚀磨损性能

利用自行设计的腐蚀磨损试验装置研究了三种不锈钢在不同固液比、硫酸浓度和线速度的条件下的耐腐蚀磨损性能；结果表明，在低硫酸浓度、高固液比和高线速度的条件下，沉淀硬化马氏体不锈钢具有良好的耐腐蚀磨损性能：而在腐蚀性较强、线速度较大的条件下，双相不锈钢的耐腐蚀磨损性能优于沉淀硬化马氏体不锈钢和奥氏体不锈钢；第二相强化奥氏体不锈钢在腐蚀性较强、耐磨性较弱的环境中耐腐蚀磨损性能较好。     

Chloride-induced stress corrosion cracking of Duplex stainless steels. Models,test methods and experience

Stress corrosion cracking (SCC) induced by chlorides frequently causes problems in applications where standard austenitic stainless steels are being used. Often this problem can be solved by the use of duplex stainless steels. In this report the mechanisms for SCC have been surveyed, and the cause for the high SCC resistance of duplex stainless steels has been discussed and evaluation of test methods for SCC and how duplex stainless steels respond to them, as well as practical experience of duplex stainless steels. The study shows that no single mechanism can be attributed to the good resistance to SCC of duplex stainless steels. Probably a synergistic effect of electrochemical and/or mechanical effects is responsible for the good performance. Test methods for SCC often give relatively good correspondence with real applications, but ranking is often doubtful, and comparisons of different material types should be made with caution. Numerous cases with SCC on standard austenitic stainless steels have been solved by the use of duplex stainless steels.     

Effects of chloride and crevice on corrosion resistance of stainless steels buried in soil within Seoul Metropolitan

Field and laboratory tests were conducted to find the factors affecting corrosion of stainless steels in soil. During one-year exposure, corrosion occurred within a joint and on the surface of type 304 pipe with the joint, which was buried at the site with a high chloride concentration of about 3680 ppm; however, corrosion was not observed at any of the other sites independent of the stainless steel grade and the presence of joints. At some sites, a seasonal fluctuation of corrosion potential was observed in the soil though corrosion did not occur. This observation may be due to the activity of sulfate reducing bacteria because a decrease of corrosion potential with the inoculated bacteria did not cause corrosion of stainless steels. These results indicate that both the level of chloride and the presence of crevices are the main factors affecting corrosion of stainless steels in soil but that the activity of bacteria is not. From measurements of pitting potential, a guideline for stainless steel use in soil is drawn as follows: Corrosion of stainless steels in soil occurs when the pitting potential of stainless steel under crevices in synthetic ground water that contains the same chloride concentration as the soil is less than the saddle potential. Finally, the guideline for stainless steels applications was provided in this paper according to this criterion.     

Microstructure and pitting corrosion of similar and dissimilar stainless steel welds

Abstract

Pitting Corrosion behaviour of similar and dissimilar metal welds of three classes of stainless steels, namely, austenitic stainless steel (AISI 304), ferritic stainless steel (AISI 430) and duplex stainless steel (AISI 2205), has been studied. Three regions of the weldment, i.e. fusion zone, heat affected zone and unaffected parent metal, were subjected to corrosion studies. Electron beam and friction welds have been compared. Optical, scanning electron microscopy and electron probe analysis were carried out to determine the mechanism of corrosion behaviour. Dissimilar metal electron beam welds of austenitic–ferritic (A–F), ferritic–duplex (F–D) and austenitic–duplex stainless steel (A–D) welds contained coarse grains which are predominantly equiaxed on austenitic and duplex stainless steel side while they were columnar on the ferritic stainless steel side. Microstructural features in the central region of dissimilar stainless steel friction welds exhibit fine equiaxed grains due to dynamic recrystallisation as a result of thermomechanical working during welding and is confined to ferritic stainless steel side in the case of A–F, D–F welds and duplex stainless steel side in the case of D–A welds. Beside this region bent and elongated grains were observed on ferritic stainless steel side in the case of A–F, D–F welds and duplex stainless steel side in the case of D–A welds. Interdiffusion of elements was significant in electron beam welding and insignificant in friction welds. Pitting corrosion has been observed to be predominantly confined to heat affected zone (HAZ) close to fusion boundary of ferritic stainless steel interface of A–F electron beam and D–F electron beam and friction weldments. The pitting resistance of stainless steel electron beam weldments was found to be lower than that of parent metal as a result of segregation and partitioning of alloying elements. In general, friction weldments exhibited better pitting corrosion resistance due to lower incidence of carbides in the microstructure.