Materials Science Forum Vol. 818

Abstract: This contribution solves the character of corrosive damage of the tubes, steam generating tubes of dry-bottom boiler combustion chamber in power plant engineering, and deals with the aspects related to the corrosion criteria of the carbon steel. The laboratory test results of samples applied on tubes that were subject to non-destructive and destructive tests are analyzed in one part of the work. The samples of greater incidence of corrosion products, which caused the failure of the integrity of the steam generating tubes, were tested. The work deals in details with the results of laboratory and chemical analysis of boiler water from the previous periods. The thesis evaluates the amount and frequency of P₂O₅ dosing cycles. The work also deals with the proposal of corrective measures that shall lead to the chemical balance of the boiler water. It proposes a continuous correlation methodology for chemical stabilization.

Abstract: The study investigated the possibilities of determination of corrosion resistance of metal and non-metal (organic) coatings deposited to steel surface in the corrosion environment. To determine the corrosion rate of metal PVD coating based on Ti, we used the method involving measurement of polarization conductivity. Corrosion resistance of galvanic Ni or Ni-Co coatings was determined by measuring free corrosion potential E_SCE (against that of saturated calomel electrode SCE), or by means of potentiodynamic polarization relationships according to Tafel. These methods provided the basic corrosion characteristics: corrosion potential E_corr, instantaneous corrosion rate j_corr and polarization resistance R_p. Corrosion resistance of organic coating Woerodur, which was applied by pressure spray to the substrate pre-treated in various ways, was tested in a salt-fog environment. After the exposure to the respective environment we evaluated the appearance of coating. The aim of the study was to point out to the availability of methods suitable for evaluation of corrosion resistance of coatings, and to the possibilities of their application under real practical conditions.

Abstract: Nowadays, cans are used widely to store and keep safely juices, drinks and liquid products with different taste. Especially in food industry one has to consider the effects of the content of inner side of the can due to the fact that some of the liquids can be very aggressive to the metals and surface treatment. The subject of this paper was to investigate the run-off-effect of metals from can into the solutions and analyze the data retrieved by Electrochemical Impedance Spectroscopy (EIS) and Linear Voltammetry (LV) techniques. We have observed phenomenon that release of metals is not only time but also temperature dependent. We have built equivalent circuits models for various conditions for both aluminum and tin cans. The aim of the project was to calculate “run-off” effect of Al and Sn from cans into drink during short-term storage and compare it with WHO norm.

Abstract: The steel sheets used for the car body production are protected against corrosion by zinc coating. Resistance spot welding is used mainly for joining these sheets, because of its high speed and adaptability for automation in high-rate production. However, resistance spot welding has a negative influence on the corrosion resistance of joints. The paper focuses on the analysis of quality of welds on galvanized steel sheets and their corrosive properties. Tensile test and accelerated corrosion test in corrosive environment were used for evaluation of the welds’ quality. Protective efficiency of zinc coatings for automobile sheets was evaluated as well, based on the determination of their electrochemical characteristics in passivated and non-passivated state, as well as their corrosion resistance in simulated corrosion environments. Two types of DX54D+Z material were used for experiments: non-passivated and passivated with Cr3+.

Abstract: The paper presents the results of research aimed at determining the corrosive properties of steel surfaces after mechanical treatment by grinding and blasting. The aim of the study was to determine the changes in the electrochemical characteristics of the material during exposure in the 1 M NaCl solution in distilled water, and establish the optimal time of application the coatings on pre-treated surface without reducing the adhesion. With help of potentiodynamic tests and electrochemical impedance spectroscopy there were determined polarization resistance (R_p), the anodic and cathodic Tafel plots, corrosion current (I_corr)​​, corrosion rate (r_corr) and corrosion potential (E_corr). The results pointed to the fact that after the mechanical treatment by grinding and blasting with aluminum oxide and steel shot the highest surface activity was found within 1 hour since the pretreatment. After this time, the activity decreases and corrosion products appear causing a reduction in adhesion of subsequently applied coatings. After blasting with cut wire the reduction of the adhesion appear not before 8 hours after blasting because of the different shape of the resulting surface. Potentiodynamic test proved that the highest corrosion rate showed a ground surface. Lower corrosion rate reached blasted surfaces depending on the type of abrasive used, which is closely related to the kinetic energy of the impacting grains and the actual surface area.

Abstract: Titanium and its alloys are still popular in different kind of industry. Ti-6Al-4V alloy is usually used due to its two-phased composition, which cause good mechanical properties. Corrosion resistance of this material can be improved by anodic oxidation. This electrochemical method is used to increase the thickness of titanium dioxide. The aim of the research was color anodizing of the Ti-6Al-4V alloy in the 7% H₂SO₄ acid solution at 20 ± 0.5°C and for 30 seconds at different voltages (15-90V). The electrochemical characteristics were determined by potentiodynamic tests in the 0.1M NaCl solution. The obtained results were analyzed by the Tafel-extrapolation method. Finally, the corrosion current densities and corrosion rates were evaluated. In fact, the corrosion rates of anodized alloys were 6 to 85 times lower against to ground surface.

Abstract: The dismantled tubes of the steam-boiler operated by the “Kalush Heat and Power Plant” were investigated. Defects of various nature, pitting of the indefinite shape were found during the examination. Since pitting is a deepening in the material and contains dark products of the corrosion process. It looks like a darkened area that stands out against the light background of the non-damaged surface in the optical images. The efficiency of such processing for identification of the corrosion defects is analyzed. The suitability of the proposed methods for the calculation of Shannon entropy of the surface analyzed was tested, as well as for determining the area and number of pitting defects.

Abstract: The cathodic protection is used in combination with organic coatings to protect steel constructions in soil and water environment, when their long lifetime and safety are expected. The parameters of the cathodic protection must be respected very strictly because the exceeded protective potential can evoke degradation of polymeric coatings and delamination. Our paper comprises the results of experiments those determine the impact of various applied protective potential on degradation of the selected polymeric coatings. The specimens were prepared of sheet steel 425310.11. Prior to the application of organic coatings, one set of specimens was treated by blasting (classic method) the second set by laser. The behavior of the physically (based on polyisobutene PIB) and chemically cured (based on polyurethane PU) coatings were studied after one year lasting exposure in the soil. The experiment was carried out by exposure of specimens in soil without and with cathodic protection of different intensity.

Abstract: Steel constructions are an integral part of our lives, surrounding us almost everywhere. They are used for erection of various halls, bridge structures, railings etc. Each steelwork is more or less impaired by corrosion, respectively a certain level of corrosion aggressiveness of the environment. Corrosion is the cause of material degradation - referred to rusting. In order to avoid this unwanted phenomenon to the maximum extent possible, we use various methods and technologies protecting the relevant material and preventing from corrosion occurrence and development. This article deals with one of the methods aimed at corrosion protection of structural steelwork - duplex coating system that is assured by means of hot dip galvanizing followed by paint system application.

Abstract: Water-based coating systems are becoming increasingly popular among consumers due to their simple application and a wide range of colours. A common mistake made by users of these coating systems is neglecting of diagnostics of the corrosive environment and failing to eliminate the factors that cause corrosion aggressiveness. On the boundary of two different environments there can be corrosion products developed and dust particles deposited, which may cause, under certain circumstances, development of deeply hidden corrosion, and thus reduce the level of protection of the substrate. In order to provide long-term protection of the substrate the coating system must be able to eliminate the corrosion agents effectively. In addition to the requirements for aesthetic value set by the consumers, also environmental aspects must be taken into account in the long-term protection of the substrate.