Papers by Keyword: Pitting Corrosion

Abstract: The condition of a dynamic machine (equipment) can be estimated at the current level, by measuring the vibration levels. Each component of a machine produces a vibration with one or more specific frequencies. Knowing the components of the spectrum of frequencies of the global vibration, it is possible to determine which of the components of the moving assembly the problem occurred. Thus, by measuring the vibration, a multitude of defects can be detected, for a wide variety of dynamic machines. Unlike other diagnostic devices, spectrum analyzers have the widest use in the evaluation of vibrations and specific stresses on fixed structures or on rotor blades. Other experiments evaluate the natural frequencies of the rotors, the influence of the cavity of the rotor-stator interaction. Model or prototype studies establish the influence of pressure pulsations at partial load for radial axial turbines [5]. In the work, the vibrational behavior of a Kaplan hydraulic turbine with 6 rotor blades of high power (P=200MW, Dn=9.5m), was analyzed when mechanical failures (wear) appeared after several years of operation, the graphs being taken from the diagnostic system of the studied hydrogen generator.

Abstract: During the study of laser cladding processes for manufacturing of structural elements from high-alloy corrosion-resistant steel on a thin-walled base, the issue of reduction of the powder material corrosion durability, applied by such technologies, during their use in corrosive environments, was considered. The aim of this study is to determine the effect of laser radiation intensity, used to form a deposited layer on a thin-walled base made from AISI 316L high-alloy corrosion-resistant steel, on its corrosion resistance. Samples, utilizing a laser cladding method, developed for creation of structural elements on pre-made thin-walled parts, were tested for pitting and intergranular corrosion (IGC) resistance using standard methods. IGC resistance was assessed by optical metallography. According to the results of corrosion tests, it was determined that samples of the layers of high-alloy corrosion-resistant steel AISI 316L, applied utilizing laser cladding technology on a thin-walled base, made from high-alloy corrosion-resistant steel, can be considered resistant to pitting and intergranular corrosion, while maintaining the range of values of power density at 30...50.0 kW/cm². These results align with the results of various studies by other authors who have been testing similar cases in other industries. The results of this study were used for further development of laser surfacing technologies for thin-walled parts used in various extreme conditions and further deepening of knowledge about modern laser cladding processes and expansion of the scope of this technology.

Abstract: This study investigates the corrosion resistance of Stainless Steel 201 through varying surface treatments and testing in a 3.5 wt% NaCl solution, mimicking seawater conditions. Given its prevalent use in industries like oil, Stainless Steel 201's resistance to pitting corrosion is crucial, primarily when used in pipes. The research employs electrochemical techniques, specifically Cyclic Voltammetry and Immersion, to treat the material's surface. The surface treatment using citrict acid (C₆H₈O₇) varying the concentration of 1, 1.5, and 2 M. Corrosion tests utilize open circuit potential, anodic polarization patterns, and characterization via optical microscopy and SEM-EDS. Results indicate that the material subjected to a Cyclic Voltammetry treatment with 2M citric acid exhibited the lowest corrosion rate at 0.001243 mmpy, with 21 instances of pitting corrosion. Conversely, untreated Stainless Steel 201 showed a higher corrosion rate of 0.006177 mmpy and 87 instances of pitting corrosion. This underscores the significant improvement in corrosion resistance achieved through the specified surface treatment, highlighting its potential value for enhancing Stainless Steel 201's longevity and performance in corrosive environments. Keywords: Stainless Steel 201, Cyclic Voltammetry, Immersion, Open Circuit Potential (OCP), Anodic polarization Patterns, Corrosion Rate, Pitting Corrosion.

Abstract: It is commonly believed that stainless steel cannot rust. However, this erroneous assumption is very often disproved in practice. Either the stainless steel is chosen for the manufacture of a piece of equipment working in the conditions where its corrosion resistance is no longer satisfactory, or, more often, the prescribed procedures for its protection are not followed during operation. The article gives examples where an incorrectly chosen disinfecting procedure for a food processing plant with a chlorine-based product caused pitting corrosion of ceiling panels and low-quality weld joints caused crevice corrosion of cold drinking water pipes in food processing plants.

Abstract: This study investigates the failure mechanism of a steel pipeline used for transporting methane gas. The investigation revealed extensive pitting corrosion on the pipe's external surface, leading to localized perforation. Analysis of the corrosion products identified iron oxide-hydroxides, primarily goethite and akaganeite, suggesting an oxidizing environment with the presence of chloride ions. Elemental distribution analysis further supported the formation of iron oxides, showing a lower Fe content and a higher oxygen concentration in the corrosion deposit compared to the base metal. The findings highlight the critical role of the three-phase boundary (steel-water-oxygen) in initiating pitting corrosion, emphasizing the importance of effective corrosion prevention and mitigation strategies for ensuring pipeline integrity and safety.

Abstract: Stainless steels are the material that has chromium as a main component. The chromium content reacts with oxygen in air, subsequently, forms thin chromium oxide film on the surface of stainless steels. Thus, when these steels are exposed to high temperature for a long period of time in many applications, chromium carbide could precipitate along the grain boundary and reduce the corrosion resistance. This project is conducted to study annealing time effect on stainless steels when exposed to high temperature at various exposure time periods. Three different kind of stainless steels, namely, AISI 304, AISI 304D and AISI 2205 were used in this study. Stainless steels were heated at 600°C for 0, 6, 24, 48 and 96 hours, then cool down in air. Consequently, the investigations were performed by using double-loop Electrochemical Potentiokinetic Reactivation (DL-EPR) and Cyclic Potentiodynamic Polarization (CPP) to study degree of sensitization and film properties. In addition, chromic acid and oxalic acid were used as reagent of acid etching to observe microstructures. Finally, Vickers hardness test were also conducted. Percentage degree of sensitization increased from 2.93% to 62.20% in AISI 304, increased from 5.26% to 55.54% in AISI 304D and from 12.19% to 69.35% in AISI 2205. The pitting potential decreased from 0.47 mV to 0.23 mV for AISI 304 but remained relatively constant for AISI 304D and AISI 2205. The results indicated that after the specimens were exposed to high temperature for a long period of time, all specimens had more chromium depleted areas, more carbide along the grain boundaries, worse film quality and small changes in hardness value.

Abstract: Runner blades of Kaplan turbines are elements subject to multiple mechanical and chemical stresses. For these reasons they suffer from pitting corrosion. Taking them out of production for repair involves relatively high costs, such actions can take up to 6 months. The identification of a technological or constructive solution for increasing pitting corrosion resistance is thus desirable. The paper proposes a combined technological and constructive solution for increasing corrosion resistance by pitting leading edges, the areas most affected by this type of corrosion. The experimental program highlighted the fact that the use of a similar material in terms of chemical composition and characteristics or a duplex stainless steel, deposited with linear energies lower than 1 kJ/mm, can lead to the generation of a layer that has good behaviour at pitting corrosion. The generated layer must have a thickness limited to 3 mm to avoid the appearance of additional vibrations at the blade level.

Abstract: Superduplex stainless steels have great mechanical and corrosion properties. However, its chemical composition makes it prone to intermetallic phase precipitation during thermal processing. Sigma (σ), chi (χ), and chromium nitrides (Cr₂N) remove Cr and Mo from the matrix, reducing the corrosion and mechanical resistance. Understanding the effects of thermal processing on the secondary phase’s precipitation and depletion of the material’s performance is crucial to its applications. Thus, this work aims to analyze the behavior of the corrosion performance of the UNS S32750 after thermal treatment at 800°C, for 60, 180, 300, and 420 minutes, in comparison to the as-received material. Optical emission spectrometry, X-ray diffraction, and SEM with backscattered electrons (BSE) were used to evaluate the material. The corrosion performance was evaluated with the cyclic potentiodynamic polarization technique. The main results and conclusions obtained in the study were a decomposition of the ferrite phase into the χ and σ phases, with the formation of the χ phase being predominant in shorter times, while for longer aging times σ formed in greater quantities. It was also possible to verify a more aggressive corrosion trend for aged samples in the regions adjacent to the formation of the χ and σ phases. It was also possible to observe that the losses generated in corrosion resistance were greater for aging times longer than 60 minutes. The aging treatment significantly reduced the material’s corrosion resistance in conjunction with the formation of precipitates.

Abstract: The addition of hydrogen in shielding gas has been found to contribute to increasing the productivity of gas tungsten arc (GTA) welding compared to the processes using argon-nitrogen shielding gas. In this report, the GTA welding joints of AISI 304 stainless steel with Ar-N₂ and Ar-N₂-H₂ addition were fabricated. The microstructure and pitting corrosion resistance were studied in this work. The corrosion characterisation of welds metal was investigated by a potentiodynamic method in NaCl solution. It was found that H₂ addition also had effects on delta-ferrite microstructures and corrosion behaviour. Increasing hydrogen in argon-nitrogen shielding gas increased the delta-ferrite content and improved pitting corrosion resistance.

Abstract: Full functioning of wells in oil and gas fields is impossible without the use of tubing. Main function of tubing is transportation of gases and liquids produced in productive zone to well surface. In addition, tubing acts as a kind of insulator that protects the gas and liquid transported through them from the walls of the well, and also prevents the occurrence and development of corrosion, deposits of paraffin and asphaltene on casing pipes. The tubing pipe placed in the well is also necessary in order to ensure the carrying out of downhill and repair work, which is regularly necessary. Standard tubin g (tubing) as a result of technological difficulties does not undergo a strengthening operation. When manufacturing tubing and locks to them from alloyed steels, the main attention is paid to improving mechanical properties, which is achieved by thermal and chemical-thermal treatment. However, the practice of operating tubing shows that the introduction of these measures does not solve the issue of reliability, since threaded connections for the coupling and nipple remain vulnerable sections of tubing. Tubing (tubing) during its operation experiences significant loads and is in constant contact with aggressive media, which leads to serious requirements for their quality. The possibility of replacing its production from alloyed steels with aluminum alloys, for example, AlCuMg₂ will facilitate the design by 2.5 times, prevent the tendency to stress corrosion cracking (SCC) in a hydrogen sulfide-containing medium and eliminate inhibitory protection. The main disadvantage of aluminum alloys is the tendency to pitting corrosion. It is possible to improve the protective properties of the passive film on aluminum alloys by anodizing.