Hot corrosion of four superalloys: HA-188, S-57, IN-617, and TD-NiCrAl

Four superalloys were subjected to cyclic oxidation and hot corrosion attack in a Mach 0.3 burner rig. Two of the alloys, HA-188 and S-57, were cobalt-base and the other two, IN-617 and TD-NiCrAl, were nickel-base. The alloys were exposed to maximum temperatures of 900 and 1000°C. For hot corrosion tests the burner rig flame was doped with various concentrations of sea salt and one concentration of sodium sulfate. Samples were evaluated based on maximum depth of attack. These data were subjected to a regression analysis for the development of model equations relating corrosion to temperature and for determining how significantly changes in salt concentration and composition affected the corrosion. The ranking of the alloys with respect to their corrosion resistance was found to vary with temperature, sea salt concentration, and salt composition. Some of the variation was attributed to changes in the mode of attack from straight oxidation to hot corrosion. Under those test conditions where the mode of attack was readily discernible S-57 was found to be the most hot corrosion-resistant alloy and TD-NiCrAl was the least resistant. This order was reversed when the attack was straight oxidation, TD-NiCrAl being the most resistant alloy and S-57 the least.     

Corrosion behavior of T24, T92, VM12, and AISI 304 steels exposed to KCl–NaCl–K2SO4–Na2SO4 salt mixtures

The corrosion mechanisms of T24, T92, VM12, and AISI 304 steels are studied under the influence of NaCl–KCl, NaCl–Na₂SO₄, and KCl–K₂SO₄ salt mixtures in a dry air atmosphere at 650°C for 15 days. NaCl–KCl was the most aggressive deposit and AISI 304 stainless steel exhibited the highest corrosion resistance. There was no relation between the Cr content of the ferritic steels and their corrosion resistance in NaCl–KCl. In contrast, the resistance of high-Cr steels was better when exposed to NaCl–Na₂SO₄ and KCl–K₂SO₄. The high-Cr and the low-Cr steels were more susceptible to NaCl–Na₂SO₄ and to KCl–K₂SO₄, respectively.     

高度耐腐蚀、耐温、耐磨、高韧性重防腐蚀涂料ChemLINE 784

面对复杂的腐蚀介质和苛刻的腐蚀环境，国内现有常用的树脂、涂料、橡胶、不锈钢等传统防腐蚀材料都存在一定的局限性。本文介绍一种具有高度耐腐蚀、耐温、耐磨，高韧性、环保、长效等诸多优点的重防腐蚀涂料ChemLINE 784，弥补了传统耐蚀材料的不足，为我国的防腐蚀材料领域提供了一种优异、可靠、长效的技术解决方案。     

Effect of thermal exposure on the microstructure,tensile properties and the corrosion behaviour of 6061 aluminium alloy sheet

Sheet material of the Al‐Mg‐Si alloy 6061 in the tempers T4 and T6 was thermally exposed at temperatures ranging from 85 to 120°C for 1000 h. The microstructure, tensile properties and the corrosion behaviour in the different heat treatment conditions were investigated using differential scanning calorimetry and transmission electron microscopy as well as performing tensile tests and various corrosion tests. The additional heat treatments, which should simulate aging during long‐term service usage, caused an increase in strength of 6061‐T4 sheet, associated with changes in the naturally aged microstructure. Thermal exposure at 120°C for 1000 h resulted in tensile and corrosion properties being similar to those obtained for peak‐aged sheet. Alloy 6061 in the T6 temper exhibited microstructural stability when additionally heat treated at 85 and 120°C for 1000 h. No significant alterations in the microstructure, tensile properties, and corrosion performance were observed after exposure to slightly elevated temperatures.     

Influence of commercial corrosion-inhibiting compounds on the atmospheric corrosion of the magnesium alloys EV31A,WE43B,ZE41A and pure magnesium

The influence of four commercial corrosion-inhibiting compounds on the atmospheric corrosion of EV31A, WE43B, ZE41A and pure Mg was studied at two hot, humid, tropical sites for test periods of 3–12 months. LPS 3 and AMLGuard significantly reduced the corrosion rates, with AMLGuard being most effective with inhibition efficiencies above 85%. In contrast, Ardrox 3961 and LPS 2 were ineffective with typical corrosion rates comparable with those of the bare alloys. Corrosion inhibition was tentatively attributed to protective durable barrier films formed by chemical adsorption for LPS 3 and AMLGuard.     

Measuring the corrosion rate of steel in concrete – effect of measurement technique,polarisation time and current

Both on‐site investigations and laboratory studies have shown that different corrosion rates are obtained when different commercially available corrosion rate instruments are used. The different electrochemical techniques and the measurement parameters used, i.e. polarisation current and time, are in some studies considered the main reasons for the variations. This paper presents an experimental study on the quantitative effect of polarisation time and current on the measured polarisation resistance – and thus the corrosion current density – of passively and actively corroding steel. Two electrochemical techniques often used in instruments for on‐site corrosion rate measurements are investigated. On passively corroding reinforcement the measured polarisation resistance was for both techniques found to be highly affected by the polarisation time and current and no plateaus at either short or long polarisation times, or low or high polarisation currents were identified. On actively corroding reinforcement a large effect of the polarisation time was also found, but only a minor effect of the polarisation current. The effect of the polarisation time was, however, practically independent of the corrosion rate for actively corroding steel. For both techniques guidelines for polarisation times and currents are given for (on‐site) non‐destructive corrosion rate measurements on reinforcement steel in concrete.     

Corrosion behaviour of pure Mg,AS31 and AZ91 in buffered and unbuffered sulphate and chloride solutions

Abstract

The low corrosion resistance of magnesium limited its application in industrial affairs. The main corrosive anions for magnesium are sulphate and chloride. This paper deals with their effect at low concentrations on the corrosion behaviour of Mg and Mg based alloy (AS31 and AZ91) in presence/absence of buffer solutions (pH 8). The electrochemical measurements used are open circuit potential and potentiodynamic polarisation. The results exposed that in the absence of a protective layer, general corrosion is observed to occur at greater rate than when sulphate is present; however, the general corrosion is transformed to localised corrosion faster in presence of chloride. In the presence of a protective layer, the localised corrosion is perceived in the case of chloride more than sulphate. The presence of aluminium in the alloys has two contradictory actions. One increases the passivity of the formed layer and the other increases the localised corrosion. The percentage of aluminium in the alloy controls these actions.     

温度、CO2分压、流速、pH值对X65管线钢 CO2均匀腐蚀速率的影响规律

研究了温度、流速、CO2分压以及pH值对X65管线钢腐蚀速率和腐蚀产物膜的影响规律。结果表明,温度升高以后,腐蚀产物膜的致密度明显增大,对基体的保护作用增强,降低腐蚀速率。在中低温区形成的腐蚀产物膜容易被流体破坏,导致了高的腐蚀速率。CO2分压对腐蚀产物膜的致密度没有明显的影响,分压增加10倍,腐蚀速率增加3～4倍。溶液中NaHCO3的含量增加以后pH值增加,腐蚀速率会明显下降。     

Mechanism of improved corrosion resistance of type 304l stainless steel,nitric acid grade,in nitric acid environments

Materials for critical components in nuclear fuel reprocessing plants are required to have low corrosion rates and long designed life because access for repairs is not possible. Stainless steel type 304L, nitric acid grade (NAG), is the new material suitable for such applications. It has guaranteed low corrosion rates and is not susceptible to intergranular corrosion (IGC) in nitric acid environments. The corrosion behavior of type 304L stainless steel, NAG, and type 304L stainless steel, commercial purity (CP), in nitric acid environments is investigated in detail. Studied are: microstructural mapping in the three directions (longitudinal, long transverse, and short transverse), effect of sensitization heat treatment, resolution annealing and sensitization heat treatment for the as-received and cold-worked samples of the two varieties on the resultant microstructures. The anodic polarization characteristics along the three directions for both varieties in 1N HNO₃ are compared. The susceptibility of both varieties to end grain corrosion in 9N HNO₃ + 1 g Cr⁺⁶/liter boiling solution is assessed, and microstructural examination of the exposed sample is carried out to compare the degree of end grain corrosion. Their susceptibility to IGC due to segregation of impurity elements to grain boundaries is also compared. It is shown that controlled microstructure (fine grain size, retained cold work, and discrete precipitation at grain boundaries) along with controlled chemical composition is responsible for improved corrosion resistance of the NAG variety. The NAG variety has much less susceptibility to corrosion along the long- and short-transverse directions and, therefore, less susceptibility to end grain corrosion. The means and consequences of controlling chemical composition are also discussed.     

Research on intercrystalline corrosion,exfoliation corrosion,and stress corrosion cracking of Al–Zn–Mg–Sc–Zr alloy

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al–Zn–Mg–Sc–Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al–Zn–Mg–Sc–Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al–Zn–Mg–Sc–Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively.     

Microbial consortium influence upon steel corrosion rate,using the electrochemical impedance spectroscopy technique

The Electrochemical Impedance Technique was used to evaluate the influence of a microbial consortium, isolated from a gas pipeline, upon API XL52 steel corrosion rate. The bacteria growth exhibited two different kinetics behavior, one for the plancktonic and the other for the sessile phase. The sessile bacteria were found to be the main responsible for the corrosion rate increment observed during the experiments and no relationship between the plancktonic microorganisms and the corrosion rate increment was found. The diagrams obtained from the electrochemical impedance measurements, indicated a biofilm formation and that the system changed from activation to diffusion control. Although the system was under diffusion control, an increment on the corrosion rate was detected, and a localized corrosion process was induced. The results were complemented with some surface analysis using Scanning Electron Microscopy.     

温度对三种Cr钢腐蚀行为的影响

利用高温高压釜模拟油田高CO_2分压和高矿化度的生产环境进行腐蚀试验,测定在不同温度条件下1Cr、3Cr和13Cr钢的腐蚀速率,利用扫描电镜(SEM)、X射线衍射仪(XRD)等手段分析了腐蚀产物形貌和成分。结果表明:1Cr、3Cr钢的腐蚀速率随温度升高先增大后减小,二者的腐蚀速率均在80℃达到最大值,分别为7.515mm/a和4.339mm/a;13Cr钢的腐蚀速率在温度低于110℃时随温度的升高缓慢增大,在温度高于110℃时腐蚀速率迅速增大;1Cr、3Cr油管钢在试验温度范围内均出现局部腐蚀,13Cr油管钢在整个试验的温度区间表现出优秀的耐蚀性。     

Zn,Al 合金涂层在膨润土中的加速腐蚀实验研究

采用高速电弧喷涂技术在16MnR钢基体上制备Zn,Al合金涂层,针对其实际应用环境,设计并通过模拟洞室膨润土填埋环境的加速腐蚀实验对涂层的耐腐蚀性能进行研究。结果表明:随着加速腐蚀时间的延长,Zn,Al系合金涂层的腐蚀速率降低;Zn,Al系合金涂层对16MnR钢的防护作用明显,起到了牺牲阳极的阴极保护作用;与Zn涂层和Zn-Al合金涂层相比,Al涂层表现出较优的耐腐蚀性能。     

高温高压CO_2腐蚀环境中含Cr低合金钢耐蚀机理的研究进展

阐述了含Cr低合金钢耐CO_2腐蚀的机理,并介绍了如何通过极化曲线来确定含Cr低合金钢是否耐蚀的方法,同时也列举了含Cr低合金钢腐蚀产物膜沉积机制的最新进展,并提出了含Cr低合金钢耐蚀机理研究中亟待解决的问题。     

CO2驱油田注采井油套管腐蚀速率控制值

腐蚀控制是CO2驱的关键技术,国内外CO2驱油田普遍采用普通碳钢(J-55、N-80等)油套管通过添加缓蚀剂的措施来控制腐蚀.国内普遍采用0.076mm/a作为腐蚀速率控制值,而国外则没有统一的标准.0.076mm/a来自于标准《碎屑岩油藏注水水质推荐指标及分析方法》,从测试环境、腐蚀源和腐蚀环境来看,直接把它作为CO2驱油田腐蚀环境条件下的选材与腐蚀控制衡量指标是不合理的.通过最危险工况条件下油套管的强度计算所获得的寿命周期内允许的平均腐蚀速率可以作为发生均匀腐蚀材料的选材依据.没有必要设定一个平均腐蚀速率标准值来作为CO2驱油田腐蚀环境条件下优选和评价缓蚀剂的衡量指标.     

碳捕集、利用与封存中CO2腐蚀与防护研究

国际上将碳捕集、利用与封存(CCUS)作为实现长期减碳减排的重要措施,CCUS技术对于降低全球二氧化碳排放量至关重要。CCUS也是实现我国长期绿色低碳发展的必然选择和重要举措,然而CCUS技术高速发展必然会带来装备的腐蚀与防护难题。针对油气开采以及CCUS过程涉及到的碳捕集设备、运输管道和油井管等设备受到的CO2腐蚀问题展开研究,分析其腐蚀机理,包括CO2腐蚀过程,以及不同因素(包括水含量、离子耦合、温度、压力、流速以及混合相中的油相)对CO2腐蚀速率的影响,并进行了总结归纳,特别是高温高压超临界CO2腐蚀机理。针对目前的3种CO2防护手段进行了介绍,考虑到合金防护成本较高,缓蚀剂防护存在二次污染,防护涂层具备更好的发展前景。最后对CO2防护涂层未来研发重点与前景进行了分析和展望。     

Effect of 6-thioguanine,as an electrolyte additive,on the electrochemical behavior of an Al–air battery

In this study, the electrochemical behavior of an Al–air battery is improved by mixing 6-thioguanine into 4.0 M NaOH electrolyte. The electrochemical performance of the Al electrodes is analyzed using potentiodynamic polarization, potentiostatic oxidation, and electrochemical impedance spectroscopy. The surface morphology of the Al electrodes after discharging for 1,000 s is characterized using scanning electron microscopy coupled with X-ray elemental mapping for Al, O, C, N, and S. Furthermore, the utilization efficiencies of these samples are also determined. The results show that the corrosion resistance of the Al electrodes initially increases and then decreases with an increase in 6-thioguanine concentration. The presence of 6-thioguanine enhances the corrosion resistance to the maximum, with a corrosion current density (I_corr) of 6.170 mA/cm², and corrosion inhibition efficiency (η) of 36.56%, at 0.5 mM of 6-thioguanine.     

碳钢和不锈钢在海洋SRB、IRB和IOB下的点蚀研究现状

微生物腐蚀(Microbiological Induced Corrosion,MIC)带来的危害占海洋腐蚀危害的20%。微生物腐蚀是指由于微生物的生命活动及其代谢产物与金属材料相互作用,影响腐蚀反应的阴极和阳极过程所引发的腐蚀现象,已成为海运业面临的重大技术难题,研究海洋微生物腐蚀对推进我国海洋事业的发展有重要意义。金属材料微生物腐蚀包括全面腐蚀和局部腐蚀,局部腐蚀的危害更大,而点蚀被认为是危害最大的局部腐蚀形式。海洋微生物种类繁多,本文聚焦于硫元素的参与者硫酸盐还原菌(Sulfate-reducing Bacteria,SRB)、铁元素的参与者铁还原细菌(Iron-reducing Bacteria,IRB)和铁氧化细菌(Iron-oxidizing Bacteria,IOB)所引发的微生物点蚀问题,包括由细菌不均匀的生物膜与腐蚀产物膜以及细菌本身的特性引起的点蚀。以广泛应用于海洋平台和船舶的碳钢和不锈钢为对象,分析其在海洋SRB、IRB和IOB下的点蚀状况,从腐蚀形貌和腐蚀产物两方面对比了碳钢、不锈钢在不同细菌体系中的腐蚀差异,腐蚀形貌分析包括腐蚀产物形貌和去除腐蚀产物后金属表面形貌的分析,腐蚀产物分析主要聚焦于金属材料表面不同成分与含量的变化。从代谢产物理论、氧浓差电池作用理论阐释了碳钢和不锈钢的点蚀机理,指出微生物点蚀研究需要综合考虑多种因素,包括多菌种的相互作用和多种环境因素对金属材料的点蚀影响,以及微生物对耐蚀金属材料的点蚀影响等。