Erosion-corrosion of a stainless steel distillation column in food industry

Unusual extended corrosion phenomena were detected in a distillation column made in AISI type 316 stainless steel (UNS S31600) of a plant for natural pectins extraction from citrus. The column was the first of a series of two distillation columns representing the unit core. Corrosion problems were observed only in that column and mainly along the surface of the trays located in the lower section of the column. The phenomenon was observed subsequently to a modification of the original plant layout that caused an increase of the operating temperatures and turbulence of the process stream inside the column.     

Determination of the best behavior among AISI D3 steel, 304 stainless steel and CrN/AlN coatings under erosive-corrosive effect

The erosive-corrosive effect of aqueous NaCl slurries on metals and metals coated with a multilayer system was analyzed. The erosion-corrosion experiments were performed in a test machine in which the impingement velocity, impact angle, concentration of solids and pH of the solution were controlled. Polarization curves were simultaneously obtained to correlate the electrochemical effects to the erosive wear mechanisms. The slurry used consists of silica particles suspended in a mixture of acid solution and 3.5% NaCl, with a pH value of 5.6. Electrochemical results showed the best corrosion resistance for steel coated with CrN/AlN system deposited with 50 bilayer. Additionally, the surface analysis by SEM micrograph revealed formation of cracks in CrN/AlN multilayers coating and plastic deformation in both steel substrates (AISI D3 steel and 304 stainless steel), especially when the mean impact angle is a critical value of 90°. Measurements of critical and passive current densities showed that the behavior of coated materials differed depending on the substrate that is used. Nonetheless, in a general way, by increasing the impact angle and by changing its incidence from normal to grazing, it led to an improved resistance to erosion-corrosion processes.     

Erosion-corrosion of candidate HVOF aluminium-based marine coatings

This paper describes gravimetric results of HVOF sprayed commercially pure Al and Al/12% Si eutectic alloy coatings obtained under erosion-corrosion conditions. The performance of these coatings are compared to a hot-dipped zinc coating. These coatings have been applied to AISI 1020 carbon steel substrates and tested in a free jet impingement rig with a variety of fluids and slurries to enable the erosion and corrosion contributions to the total erosion-corrosion removal of the surface to be determined. Tests have been conducted at 30° and 90° jet impingement angles at jet velocities of 3.5 m/s.Erosion damage mechanisms are identified and the erosion-corrosion mass loss results discussed in terms of the contributions made by erosion and corrosion. Zinc was found to suffer severely from flow corrosion, while the other targets did not. All target materials under sand erosion lose mass in a way directly proportional to kinetic energy, and inversely related to hardness. Corrosion losses are relatively small while the generation of solid products sometimes results in net weight gains. There are greater mass losses at nominally normal incidence than at nominally oblique incidence, due to particle interference effects. Synergy is found to be both positive and negative and appears to be angle dependent, but is difficult to determine precisely.     

Some perspectives on modelling the effect of temperature on the erosion-corrosion of Fe in aqueous conditions

In this paper, a model is generated of the effect of temperature on the erosion-corrosion of Fe in aqueous conditions, for room temperature to 373 K. The results indicate how the transition from active to passivation dominated regimes for Fe is favoured as the temperature is increased. 2D and 3D maps are constructed showing the transitions between erosion-corrosion regimes.     

机坪输油管道冲刷腐蚀研究

研究了冲刷腐蚀过程的发生机理,分析了流体的流速、管道的结构、流体中的第二相、流体的流动状态等因素对冲刷腐蚀过程的影响。就机坪输油管道系统中常见的易腐蚀管件90°弯管和T形管的冲刷腐蚀问题展开讨论,采用ANSYS 3.0软件中Fluent模块进行数值模拟,计算在不同工况下管道冲蚀减薄规律和特点,从而解释腐蚀的破坏程度。最后考虑到管材冲刷腐蚀的减薄程度和机坪输油系统的设计使用年限,得出冲刷腐蚀对于机坪输油管道使用寿命的影响。     

CrN/NbN coatings deposited by HIPIMS: A preliminary study of erosion-corrosion performance

Nanoscale CrN/NbN multilayer PVD coatings have exhibited resistance to erosion-corrosion. However growth defects (under dense structures and droplets) in the coating produced by some deposition technologies reduce the ability to offer combined erosion-corrosion resistance. In this work a novel High Power Impulse Magnetron Sputtering (HIPIMS) technique has been utilised to pretreat substrates and deposit dense nanoscale CrN/NbN PVD coatings (HIPIMS-HIPIMS technique). This new technique, rich with metal ion plasma, deposits very dense structures and offers virtually defect free coatings (free of droplets as observed in cathodic arc technique and under-dense structures observed in standard dc sputtering). Plasma diagnostic studies revealed a high metal ion-to-gas ion ratio (Cr:Ar) of 3:1 for HIPIMS pretreatment conditions with the detection of 14% Cr²⁺ and 1% Cr³⁺ ions and J_s of 155 mAcm^− 2. For deposition conditions the metal ion-to-gas ratio was approximately 1:4 which is significantly higher compared to DC at 1:30. Characterisation results revealed a high adhesion of L_C 80 N, high hardness of 34 GPa and Young's modulus of 381 GPa. Low friction coefficient (0.46) and dry sliding wear coefficient, K_C (1.22 × 10^− 15 m³Nm^− 1) were recorded. The effect of deposition technique (droplet defect and intergranular void free coatings) on erosion-corrosion resistance of CrN/NbN coatings has been evaluated by subjecting the coatings to a slurry impingement (Na₂CO₃ + NaHCO₃ buffer solution with Al₂O₃ particles of size 500-700 µm) at 90° impact angle with a velocity of 4 ms^− 1. Experiments have been carried at − 1000 mV, + 300 mV and + 700 mV representing 3 different corrosion conditions.     

Erosion-corrosion behaviour of Ni-based superalloy Superni-75 in the real service environment of the boiler

The super-heater and re-heater tubes of the boilers used in thermal power plants are subjected to unacceptable levels of surface degradation by the combined effect of erosion-corrosion mechanism, resulting in the tube wall thinning and premature failure. The nickel-based superalloys can be used as boiler tube materials to increase the service life of the boilers, especially for the new generation ultra-supercritical boilers. The aim of the present investigation is to evaluate the erosion-corrosion behaviour of Ni-based superalloy Superni-75 in the real service environment of the coal-fired boiler of a thermal power plant. The cyclic experimental study was performed for 1000 h in the platen superheater zone of the coal-fired boiler where the temperature was around 900°C. The corrosion products have been characterized with respect to surface morphology, phase composition and element concentration using the combined techniques of X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive analysis (SEM/EDAX) and electron probe micro analyser (EPMA). The Superni-75 performed well in the coal-fired boiler environment, which has been attributed mainly to the formation of a thick band of chromium in scale due to selective oxidation of the chromium.     

Cr3C2-NiCr and WC-Ni thermal spray coatings as alternatives to hard chromium for erosion-corrosion resistance

Cr₃C₂-NiCr and WC-Ni coatings are widely used for wear applications at high and room temperature, respectively. Due to the high corrosion resistance of NiCr binder, Cr₃C₂-NiCr coatings are also used in corrosive environments. The application of WC-Ni coatings in corrosive media is not recommended due to the poor corrosion resistance of the (pure Ni) metallic matrix. It is well known that the addition of Cr to the metallic binder improves the corrosion properties. Erosion-corrosion performance of thermal spray coatings is widely influenced by ceramic phase composition, the size of ceramic particles and also the composition of the metallic binder. In the present work, two types of HVOF thermal spray coatings (Cr₃C₂-NiCr and WC-Ni) obtained with different spray conditions were studied and compared with conventional micro-cracked hard chromium coatings. Both as-sprayed and polished samples were tested under two erosion-corrosion conditions with different erosivity. Tungsten carbide coatings showed better performance under the most erosive condition, while chromium carbide coatings were superior under less erosive conditions. Some of the tungsten carbide coatings and hard chromium showed similar erosion-corrosion behaviour under more and less erosive conditions. The erosion-corrosion and electrochemical results showed that surface polishing improved the erosion-corrosion properties of the thermally sprayed coatings. The corrosion behaviour of the different coatings has been compared using Electrochemical Impedance Spectroscopy (EIS) and polarization curves. Total material loss due to erosion-corrosion was determined by weight loss measurements. An estimation of the corrosion contribution to the total weight loss was also given.     

On the mitigation of erosion-corrosion of copper by a drag-reducing cationic surfactant in turbulent flow conditions using a rotating cage

Erosion-corrosion is a complex materials degradation mechanism involving the combined effects of mechanical erosion and electrochemical corrosion. It is known to be induced by high shear stresses in strong flows.One way to mitigate this phenomenon is to use additives reducing the turbulent Reynolds stresses. Oleyltrimethyl ammonium cationic surfactant and sodium salicylate as counter-ion known to form thread-like micelles behaving as drag reducers were tested in this work and successfully imaged by using AFM technique.A shear stress mapping in the rotating cage using an electrochemical method was implemented in the absence and in the presence of surfactant, showing drag reduction amounts up to 65%. In a second step, erosion corrosion of Cu in Na₂SO₄ 0.1 M in the presence of small amounts of NaCl (1 mM) was investigated on Cu microelectrodes located at different positions on plastic coupons in the cage. The surfactant effect was found to be beneficial by preventing the removal of the pre-existing oxide films, otherwise observed in the absence of surfactant. Tests performed with benzotriazole known as a good corrosion inhibitor for Cu, could not prevent either the breaking of the oxide film in strong flow conditions.     

磨损机制图的研究现状及发展趋势

磨损机制图作为一种研究方法,能更加系统和直观地表征磨损磨损机制。从磨损机制图可以得到磨损机制的分类、磨损机制间的转变关系及转变条件、磨损的控制因素及类型、磨损率、一定工况下材料的耐磨性等多种信息,从而估算磨损率、分析给定条件下的磨损机理、预测磨损机制随条件变化的趋势。为了促进磨损机制图研究方法的完善及其应用的发展,本文对国内外磨损机制图的研究现状了综述,重点讨论了磨损机制图研究的最新成果及发展动向