The corrosion behavior of 70/30 copper‐zinc alloy under the biofilm of sulfate‐reducing bacteria

A laboratory study was carried out on the effect of the biofilm of sulfate‐reducing bacteria (SRB), which plays an important role in corrosion of 70/30 copper‐zinc alloy in culture media under anaerobic condition. The API medium was used to culture the SRB in Zhongyuan oilfield. Potential/time measurement showed that the presence of SRB makes the corrosion potential more active with SRB growth metabolite. Electrochemical impedance spectroscopy (EIS) was used to analyse the electrode process of 70/30 Cu‐Zn alloy with SRB biofilm. Scanning electron microscopy (SEM) examinations revealed the formation of biofilm and corrosion products during exposure to SRB‐containing culture medium. X‐ray diffraction and EDS were used to analyse the corrosion products. The results show that the variation of activity of the SRB biofilm changes with SRB growth by the linear polarization resistance (R_p) and the EIS in culture medium inoculated SRB.     

一种低碳低合金钢的纳米压痕表征

对具有两种不同组织状态的一种低碳低合金钢进行了纳米压痕表征．结果表明,在双相组织试样中,马氏体的硬度高于铁索体的70％以上．在纳米压痕实验过程中,由于马氏体相的尺寸较小并被软的铁素体基体所包围,当压痕深度超过40nm时,纳米压痕硬度呈现出明显的基底效应．由于在铁索体一奥氏体两相区加工过程中发生C元素向奥氏体的分配,双相组织试样中的马氏体中富集了数倍于钢的名义含量的C元素．结果导致双相组织试样中马氏体的平均纳米压痕硬度比同一钢的全马氏体组织试样高出30％以上．此外,还讨论了C的富集分配对马氏体Poisson比和Young’s模量的可能影响．     

Biocorrosion of carbon steel alloys by an hydrogenotrophic sulfate-reducing bacterium Desulfovibrio capillatus isolated from a Mexican oil field separator

The hydrogenotrophic sulfate-reducing bacterium (SRB) Desulfovibrio capillatus (DSM14982^T) was isolated from an oil field separator with serious corrosion problems; this is the study of its role in the corrosion of carbon steels under anaerobic conditions. Immersion tests with two steel alloys, St-35.8 (typical carbon steel employed in European naval industry), and API-5XL52 (weathering alloy steel employed in Mexican oil industries) were performed. Total exposure was 45 days and different concentrations of thiosulfate as electron acceptor for bacterial growth were employed. The samples immersed in media with SRB undergo fast activation and numerous active sites form on the surface. Microscopic observations were made by environmental scanning electron microscopy (ESEM). Weight loss and electrochemical testing included open circuit potential (E_corr), polarization resistance (R_p), electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) were measured with and without bacteria in the culture medium in order to determine corrosion rates and mechanisms. All electrochemical techniques have shown that after the end of the exponential phase the corrosion activity notably increased due to the high concentration of bacterial metabolites. Finally, the corrosion behavior of API-5XL52 was worse than St-35.8.     

低合金钢电子束焊焊接接头金相组织

焊接方法 :电子束焊母　　材 :低合金钢亲爱的焊接工作者朋友们 :从 1999年第 1期至 2 0 0 1年第 12期 ,《焊接金相》栏目共发表了 36组焊接金相组织图片 ,概括描述了不同焊接材料、焊接工艺及焊接方法对金相组织的影响 ,并展示了一些常见的焊接缺陷图片。该专栏暂告一段落 ,若焊接工作者朋友们需要了解特殊焊接材料工艺方法对组织的影响 ,可与哈尔滨焊接研究所金相室联系 ,共同商榷。联系人 :于　捷　郭力力　孙秀芳　电话 :0 45 1-6 336 43低合金钢电子束焊焊接接头金相组织$哈尔滨焊接研究所!(150080)@于捷 $哈尔滨焊接研究所!(150080…     

Comparison of sulphide corrosivity of sulphate‐ and non‐sulphate‐reducing prokaryotes isolated from oilfield injection water

The microbiologically influenced corrosion (MIC) of water injection systems by sulphate‐reducing prokaryotes (SRP) has caused many problems in the oil industry. These prokaryotes produce H₂S, which reacts aggressively with steel and is thus widely considered to be the main cause of bacterial corrosion of industrial oil equipment. However, current microbiological treatments and controls have not taken into account other groups of sulphidogenic prokaryotes, which also produce H₂S or its derivatives and with the same adverse effects of MIC. In the present work, sulphidogenic prokaryotes were isolated from water injection systems and identified by DNA sequencing. The identified species included sulphate‐reducing Desulfovibrio termitidis and non‐sulphate‐reducing Escherichia coli. Biocorrosion tests were carried out on API 5L grade X65 carbon steel. Electrochemical impedance spectroscopy, polarisation resistance, open circuit potential and weight loss were carried out. Steel corrosion resulting from the production of the metabolite H₂S by SRP and non‐SRP was observed, with sulphide generation by SRP much greater than that by non‐SRP. These results confirm the need to investigate and consider the role of not only SRP but also non‐SRP in order to improve the control over bacterial corrosion of oil‐industry equipment.     

钢材品种升级——从低合金高强度到低成本高性能

低合金高强度钢材曾经在我国的钢材发展历史上起到过非常重要的作用,在资源、能源、环境问题日益突出,炼钢、轧钢的技术水平和控制能力均得到大幅度提高的新形势下,钢材品种的升级成为当务之急。需要转变观念,改变依靠添加合金元素来获得理想性能的传统做法,转而通过轧制工艺和冷却工艺的优化来提高钢材性能,细晶粒钢和细晶+复相强化钢的成功开发证明这是一条可行之路。实现从低合金高强度(HSLA)到低成本高性能(HPLC)的转变将成为钢铁材料的一个发展方向。     

Determination of lower bound fracture toughness of a high strength low alloy steel welded joint

Abstract

The use of high strength low alloy steels for high performance structures (e.g. pressure vessels and pipelines) requires high strength consumables to produce an overmatched welded joint. This globally overmatched multipass welded joint contains two significantly different microstructures, as-welded and reheated. In this paper, the influence of weld metal microstructure on fracture behaviour is estimated in comparison with the fracture behaviour of composite microstructures (as-welded and reheated). The lower bound of fracture toughness for different microstructures was evaluated by using the modified Weibull distribution. The results, obtained using specimens with crack front through the thickness, indicated low fracture toughness, caused by strength mismatching interaction along the crack front. In the case of through thickness specimens, at least one local brittle microstructure is incorporated in the process zone at the vicinity of the crack tip. Hence, unstable fracture occurred with small, or without, stable crack propagation. Despite the fact that the differences between the impact toughness of a weld metal and the that of base metal are insignificant, the fracture toughness of a weld metal can be significantly lower.     

Corrosion‐erosion damage of heat exchanger tubes by desalted crude oil flowing at shell side

Heat exchanger tubes were locally heavily damaged by desalted crude forming a shell side stream under the pressure of 2.6 MPa and at the temperature of 385–395 K. Boiler steel tube temperature was 97 K higher compared to that of the crude oil at its inlet to the exchanger. Two types of segmental baffles effected cross vortex type flow that was lowered nearly to a standstill at locations where the highest damage occurred. Close to the baffles where the damage was the highest the flow was completely different from that of the window flow. These were found from analyses of the flow and of locations of perforations. Most of the tube surface was with no damage and was covered with protective organic‐inorganic deposit. Electrochemical investigation proved a cathodic character of the deposited film against bare steel. Metallography examination of the steel showed typical structures that could not affect much the damage. The crude with low water content was not found aggressive when a corrosion test was performed at elevated temperature. The tests excluded the possibility for high rate of electrochemical corrosion at the surfaces with removed protective layers. The only reason of the damage may be cavitation corrosion at the ways of crude slow vortex flow at which temperature was high enough to allow explosions of low volatile components [1].     

Influence of the sulphate reducing bacteria on API‐X70 steel corrosion

The corrosion behaviour of API X70 immersed in a specific medium with a strain of thermophilic sulphate reducing bacteria (SRB) was analysed. Anaerobic corrosion test was carry out for 32 days at 50 °C. During the exposure time, pH, sulphate (SO) and hydrogen sulphide (H₂S) concentration were measured. Corrosion potential, linear polarization resistance and potentiodynamic polarization curve were used in order to get the influence of the SRB in the corrosion phenomenon. Scanning electron microscopy was used to determine corrosion morphology. Results show that the SRB activity influenced the overall corrosion process. The anodic branches in the polarization curves show a passivity feature, whereas, the cathodic branches were not affected. A localized corrosion attack was found.     

Corrosion failure of marine steel in sea‐mud containing sulfate reducing bacteria

The corrosion failure behavior of marine steel is affected by stress, which exists in offshore structures at sea‐mud region. The sulfate reducing bacteria (SRB) in the sea‐mud made the steel more sensitive to stress corrosion cracking (SCC) and weaken the corrosion fatigue endurance. In this paper, a kind of natural sea‐mud containing SRB was collected. Both SCC tests by slow strain rate technique and corrosion fatigue tests were performed on a kind of selected steel in sea‐mud with and without SRB at corrosion and cathodic potentials. After this, the electrochemical response of static and cyclic stress of the specimen with and without cracks in sea‐mud was analyzed in order to explain the failure mechanism. Hydrogen permeation tests were also performed in the sea‐mud at corrosion and cathodic potentials. It is concluded that the effect of SRB on environment sensitive fracture maybe explained as the consequences of the acceleration of SRB on corrosion rate and hydrogen entry into the metal.     

Naphthenic acid corrosion characteristic and corrosion product film resistance of carbon steel and Cr5Mo low alloy steel in secondary vacuum gas oil

Although naphthenic acid corrosion (NAC) has been studied for many years, the mechanism of NAC is not fully understood. The objective of this paper is to study high-temperature NAC in secondary vacuum gas oil of an industrial crude oil vacuum distillation tower. A high-temperature autoclave was applied to conduct high-temperature corrosion test to investigate NAC behaviour of carbon steel and Cr5Mo low alloy steel at different sulphur contents and total acid numbers (TAN). The result shows that the corrosion rate of carbon steel and low alloy steel is high at low TAN and high TAN while it keeps at a low value at medium TAN. Corrosion product film on Cr5Mo low alloy steel surface is denser and more compact than that of carbon steel at high TAN. The chromium present in Cr5Mo low alloy steel plays an important role in NAC resistance by the formation of Cr₇S₈ film in the inner layer of the scale. Corrosion rates of the two steels in secondary vacuum gas oil are high at low TAN and high TAN, but low at medium TAN which are strange and different from previous experimental results conducted in non-industrial oil solution. A tentative explanation for this new phenomenon is also put forward.     

Influence of inclusion and grain boundary on corrosion behaviour of low alloy steel in cargo oil tank bottom plate environment

Corrosion behaviours of low alloy steels with various alloying element contents were studied in simulated corrosion environment (pH?=?0·85, 10% NaCl solution) of cargo oil tank (COT) bottom plate corrosion environment. Corrosion rate was measured, and the surface morphology of test steels was characterised using scanning electron microscope (SEM). The electrochemical results were investigated using polarisation curves and electrochemical impedance spectroscopy (EIS). The corrosion behaviour of inclusion was investigated using in situ SEM images and energy disperse spectroscopy (EDS) analysis. The effect of misorientation distribution on corrosion resistance of steel was evaluated using electron backscattered diffraction microscopy. The results showed that MnS dissolved into the simulated COT corrosion solution before steel matrix, whereas TiO₂ would not be dissolved. A 10–20 μm area was formed as a circular cathode around inclusion centre. The corrosion was inclined to occur in the place where curvature radius of inclusion is small. An increase in the proportion of low energy grain boundaries was conducive to the improvement of corrosion resistance especially in the early stages of corrosion.     

3D打印一体化低合金钢/中碳钢枪钻界面表征

文中提出了3D打印快速一体化制造枪钻的方法,进行了中碳钢钻柄、低合金钢钻杆和钨钴硬质合金钻头组成的复合材料枪钻毛坯3D打印工艺试验研究. 采用SEM观测分析了3D打印复合材料枪钻毛坯低合金钢/中碳钢界面微观形貌和组织结构,采用EDS, XRD对枪钻毛坯低合金钢/中碳钢元素分布、界面相成分进行了测试与分析;测试分析了枪钻毛坯低合金钢/中碳钢界面缺陷、显微硬度、抗拉强度等;通过测试与分析复合材料枪钻毛坯界面的微观组织和性能,对其界面进行了表征. 结果表明,3D打印复合材料枪钻毛坯界面性能优于焊接枪钻界面,3D打印快速一体化制造枪钻的方法可行.     

低碳钢表面激光熔覆Ni60合金的工艺及性能

采用激光熔覆法,在20钢表面制备出Ni60合金熔覆层。通过金相显微镜分析了熔覆层的组织形貌,用显微硬度计测试了熔覆层的显微硬度,摩擦磨损实验仪进行了耐磨性试验,研究了激光功率、扫描速度等工艺参数对熔覆层组织性能的影响,确定了最优工艺参数。结果表明,在激光功率1800 W、扫描速度150 mm·min^-1的条件下,所得熔覆层表面光滑致密,组织细小均匀,与基体实现了良好的冶金结合;在此工艺参数下,熔覆层不仅具有较高的耐磨性能和较低的摩擦系数,且硬度提高到渗碳钢的约1.7倍。     

淬火-碳分配-回火钢的低温组织和性能

Fe-0.25C-1.5Mn-1.2Si-1.5Ni-0.05Nb(质量分数,%)钢通过淬火-碳分配-回火(Q-P-T)工艺抗拉强度可达1250 MPa以上兼具良好塑性(大于17%),显微组织为位错型板条马氏体、微合金碳化物和薄片状残留奥氏体。通过低温拉伸试验分析了Q-P-T钢在-85～25℃下的力学性能并采用透射电镜观察了试样在25℃和-85℃时拉伸前后的显微组织。结果表明,Q-P-T钢在-70～25℃时显示了良好的低温力学性能,仅当拉伸温度低于-70℃时试样塑性开始出现大幅下降;残留奥氏体在未变形前具有良好的低温稳定性,但在变形过程中会发生马氏体相变,产生相变诱发塑性(TRIP)效应,这是Q-P-T钢具有高强度和良好塑性的主要原因。     

Corrosion behavior of low‐alloy steel in the presence of Desulfovibrio caledoniensis

Sulfate‐reducing bacteria (SRB) are shown to be common inhabitants of oil reservoirs. Desulfovibrio caledoniensis isolated from a production well was used in this study. After an incubation period of 1 month with the SRB culture, two layers of corrosion products with different compositions were detected on the test coupons. The Tafel plots showed that the corrosion potential exhibited a cathodic shift and the corrosion rates increased with the incubation time. The analysis of the Nyquist diagrams revealed that the diffusion process begins to dominate with time in bacteria containing medium. These results are in good accordance with the Tafel data.     

Microbial corrosion of galvanized steel by a freshwater strain of sulphate reducing bacteria (Desulfovibrio sp.)

Microbially influenced corrosion of galvanized steel was investigated exposing coupons (2.0 × 2.0 cm) to culture of sulphate reducing bacteria strain Desulfovibrio sp. The coupons were exposed to the SRB culture for 4, 8, 24, 72, 96, 168, 360 and 744 h along with a control set in uninoculated medium. The results from the present study suggest that SRB were responsible for the corrosion of the galvanized steel. The corrosion rate of galvanized steel was not be correlated with the number of sessile SRB cells. Also Desulfovibrio sp. had an ability to produce EPS (Extracellular Polimeric Substances) and biodegrade the carbohydrate, that is the predominant component of the EPS produced by them. When Desulfovibrio sp. cells were in logarithmic phase, the concentration of dissolved zinc in the bulk solution was very toxic for Desulfovibrio desulfuricans.     

低合金高强钢激光-电弧复合热源焊接冷裂纹敏感性分析

通过扩散氢含量测定,并利用经验公式计算JFE980S低合金高强钢冷裂纹敏感性和焊前预热温度,同时采用斜Y形坡口试验、金相试验以及残余应力测定等方法,研究低合金高强钢抗冷裂性能,对比分析了激光-电弧复合焊和MAG焊工艺对接头抗冷裂性能的影响.结果表明,激光复合焊抗冷裂性优于MAG焊方法.因复合焊加入了激光,使得焊缝熔深增加,拘束减小,并且激光在前,对焊接试板有一定的预热作用,使冷裂纹形成倾向进一步降低,特别是在无法预热的情况下,激光复合焊更能够体现出优势.