Papers by Keyword: Pitting Corrosion

Abstract: Lacquered copper membranes are sometimes used in operate equipment containing low aggressive corrosive water-based fluids. In some cases, the lacquer coating does not prevent the occurrence of corrosive processes leading to through damage to the product and equipment failure. In this work, a review of the most common copper corrosion mechanisms is carried out. During a visual inspection of the products, the peculiarities of the state of the membrane surfaces and corrosive damage were noted. On the basis of metallographic, X-ray structural and electrochemical studies, the assumptions put forward at the stage of visual inspection were confirmed. The conclusions contain assumptions about the reasons for the formation of pitting corrosion on copper membranes.

Abstract: Corrosion behavior of 7A52 aluminum alloy plasma arc welding (PAW) joint was investigated in simulation of marine atmosphere environment with salt water spray test. The surface morphologies were observed by scanning electron microscopy (SEM), and the effect of corrosion time on corrosion behavior was discussed. The depth of spot corrosion, the corrosion dynamic characteristics, and the distribution of element of 7A52 aluminum alloy welding joint were analyzed by 3D and XRD Microscope. Results show that pitting corrosion is main morphology in heat effect zone at initial stage, pitting corrosion appears in matrix and welding joint with time. The main component compounds existing in the film include Al and O. The depth of pitting corrosion in the heat effect region is the maximum (3.008μm). The law of power function is followed in both phases of the corrosion weight increasing curve, and the corrosion rate decreases with time.

Abstract: The paper contains the results of surface modification on the properties of the pure titanium Grade II, obtained by the SLM procedure. In the paper, the analysis of the results of physicochemical properties, such as pitting corrosion test and contact angle measurements and Surface Free Energy calculated were performed. Additionally, the microscopic observation with microchemical analysis, surface topography analysis using Atomic Force Microscopy, surface roughness measurements and wear test were performed too. The studies were carried out on three groups of samples in an initial state (1) (after mechanical treatment - mechanical grinding and polishing) and after surface modification by PVD method using CrN layer (2) and TiN layer (3). Based on the obtained results it can be concluded that the samples with TiN layer were characterized by the optimum properties.

Abstract: Super Austenitic Stainless Steels (SASS) belongs to the category of austenitic stainless steels which were known for their excellent corrosion resistance when used in structural applications like desalination plants, oil piping systems, heat exchanger equipments which demands high temperature service and harsh environments. Several works on SASS dealt about the corrosion resistance of the material in its normal base metal form. But structural uses needs SASS to be welded with similar or dissimilar materials to fit into the applications. This study aims to present a detailed view on issues related to the weldability of super austenitic stainless steels and the future scope of welding on SASS.

Abstract: It is well known that the mechanical resistance of austenitic stainless steels can be increased considerably by cold rolling process.¶ The cold rolling effect on corrosion resistance of AISI 304L stainless steel in 3% Sodium Chloride solution was investigated by potentiodynamic polarisation and by Scanning Electronic Microscopy (SEM). The pitting corrosion in this environment is related to the rate of cold deformation. The cold rolling induces important changes in the microstructure and involves phase transformation (γ→a'). The AISI 304L developes martensitic structure after 16% cold working. The potentiodynamic results show a moderate variation of the passivity zone, a remarkable decrease in the pitting potential and a free potential. The results also show an increase in the current density. However, it seems that the critical deformation rate appears to start at approximately 50% of the rolling deformation where the passivation current is minimal. After the polarisation tests, metastable pits are observed using SEM and the most probable initiation causes are discussed

Abstract: According to the observation of a metallurgical microscope, surface morphology of 2219 aluminium alloy under several corrosion circumstances, such as corrosion pits and grain boundary corrosion, is directly perceived. Furthermore, with a laser range finder, corrosion depth data can be measured, and by using some methods of data processing, the affection for this material of certain solution components and immersion time is studied quantitatively. This binary study mean not only provides both graphical and statistical analysis, but also gives the relationship between them, which makes the result more reliable.

Abstract: The influence of recrystallization annealing on the microstructure, mechanical properties and corrosion behaviour of an austenitic TWIP steel bearing medium Mn and V alloying was investigated. The steel undergone a heavy cold deformation of 65 % reduction. Subsequently, recrystallization annealing at 1000 °C and 1100 °C for 15 min was conducted to achieve different grain structures. The microstructural evolution was studied using optical microscopy and electron backscatter diffraction technique. Mechanical properties were determined using tensile tests at room temperature. Corrosion behaviour was measured by cyclic potentiodynamic polarization at 3.5 pct NaCl. For comparison, austenitic stainless-steel Type 201 was used in this study. It was observed that at 1000 °C, a non-uniform austenitic grain structure with vanadium carbides distributed throughout the matrix was obtained. However, a coarse grain structure without carbides was induced at 1100 °C. The fine-grained structure enhanced at 1000 °C exhibited higher strength and good ductility. Contrary to this, the corrosion results showed that a significant deterioration in the corrosion resistance could be observed in sodium chloride solution for the achieved structure at 1000 °C compared to 201 stainless steel.

Abstract: The Oxide Precipitation Hardened (OPH) steel is a new developed group of materials from Oxide Dispersion Strengthened (ODS) alloys which are well known advanced materials for high temperature properties. Besides, the corrosion resistance of these types of material is so important regarding to their practical usage. The production of OPH alloys, the same as ODS alloys, involves mechanical alloying process to create material with ductile matrix and hard oxide dispersion. Six variants of Fe-Al base OPH steel which developed and manufactured by the authors, were prepared with different chemical composition to evaluate the role of main component on the mechanical properties and corrosion resistance of new-developed OPH steels. The corrosion tests were done using potentiodynamic polarization methods. The results show that the Aluminum content has a main role both on mechanical properties and corrosion resistance.

Abstract: The failure analysis of 110S tubing during acidizing process was addressed. Results showed that serious pitting corrosion occurred on the outer wall of tubing, and there was no obvious pitting on the inner wall. The maximum pitting depth on the outer wall was 1019 μm. According to the results of simulation corrosion test, needle-shaped pitting appeared on the sample surface in the test without inhibitor, the maximum depth of pitting was 158 μm; and no pitting was found on the sample surface in the test within 1.5% TG501 inhibitor; the original pitting were deepened after spent acid test, and the sample with no pitting at the beginning also showed deep pitting corrosion after 96 hours spent acid test. It was indicated that the spent acid accelerated the development of pitting significantly. The external surface corrosion of the 110S tubing was caused by the chemical reaction between the high-concentration acidifying liquid and the outer wall of the tubing. There is a gap between the tubing and coupling threaded connection, which caused the acid solution entered into the thread position, and hence the severe corrosion of the thread and pin end of the tubing happened, the joint strength was continuously reduced with corrosion development till the tripping of the coupling, and then the lower string dropped. Some suggestions were proposed for avoiding or slowing down this kind of failure based on this study.

Abstract: Magnesium (Mg) alloys constitute an attractive structural material for transportation industries, due to their low density and high strength/weight ratio. However, high susceptibility to corrosion of Mg alloys limits their use. Therefore, there is a growing interest for development of new Mg alloys with good mechanical properties and superior corrosion resistance. Production of wrought Mg alloys results in enhancement of mechanical properties, whereas addition of alloying elements may result in improved corrosion behavior. In this study we distinguish the role of aluminum, zinc, tin and calcium additions on the corrosion performance of new wrought Mg alloys. Overall, addition of alloying elements resulted in precipitation of second phase particles with cathodic behavior (relatively to Mg matrix). This enhanced the micro-galvanic effects and the corrosion resistance in short periods of immersion was deteriorated. However, in longer periods of immersion the passive characteristics of the oxide layer played a significant role in improving the alloys' corrosion resistance. The contribution of each element to the oxide layer will be discussed in detail. In general, the quantities of alloying element should be sufficient to stabilize the corrosion products layer; yet as low as possible, in order to reduce the micro-galvanic effects.