Vesna Alar

Influence of thermal oxides on pitting corrosion of stainless steel in chloride solutions

Abstract X-ray diffraction analysis, Auger electron spectroscopy, X-ray photoelectron spectrometry, optical micrography, and spot potential measurements have been used to characterise AISI 316L stainless steel specimens with oxide films formed by heating in air, either isothermally (at 200–1000°C) or in a temperature gradient. The pitting corrosion propensities of such specimens were assessed by exposure to FeCl3 solution and the evaluation of nine topographical criteria. Testing was also performed on previously heated specimens after removal of the thermal oxides by pickling. It is demonstrated that thermal oxides facilitate the nucleation of corrosion pits but do not influence their propagation. The effect on nucleation is caused by stresses and lattice defects in oxide film and metal substrate. The maximum susceptibility to pitting liability occurs after heating at 600°C. The removal of thermal oxides formed at 200–800°C by pickling improves the pitting resistance but the initial stability is never restored because of residual stresses and lattice defects on the cleaned metal surface. Indeed, after heating at 1000°C, pitting tendencies are increased by pickling.

Development of Models for Prediction of Corrosion and Pitting Potential on AISI 304 Stainless Steel in Different Environmental Conditions

Stainless steels are found in various aerated aqueous electrolytes in a passive state which protects them from corrosion. In many aggressive solutions, stainless steels are easily depassivated, which can lead to different types of corrosion. This paper tested the impact of chloride ions at different concentration, temperatures and pH values on the corrosion and pitting potential of AISI 304 stainless steel. In order to predict the behaviour of AISI 304 stainless steel design of experiment and artificial neural network methods were applied. Results of the developed models showed good agreement with the experimental results and no significant differences between models.

Dependence of steel workpiece corrosion rate on the emulsion concentration for machining

Abstract In todays manufacturing, the emulsions for cooling and lubricating are an extremely important and necessary factor for the performance of machining processes. Depending on their composition, properties and production, emulsions in metal cutting operations have various technology functions such as lubricating the surfaces of the tools, facilitating the process of deformation of the cut layer, improving the quality of machined surface as well as cooling the tool and workpiece by removing the part of the heat created by deformation and friction. Corrosion protection of workpieces and tools during and after treatment is also one of the important functions of technological emulsions for cooling and lubricating. In this paper the effects of different concentrations of three emulsions on the corrosion rate of steel workpieces is reported. The results indicate that a higher concentration of emulsion does not provide better protection against corrosion.Abstract In todays manufacturing, the emulsions for cooling and lubricating are an extremely important and necessary factor for the performance of machining processes. Depending on their composition, properties and production, emulsions in metal cutting operations have various technology functions such as lubricating the surfaces of the tools, facilitating the process of deformation of the cut layer, improving the quality of machined surface as well as cooling the tool and workpiece by removing the part of the heat created by deformation and friction. Corrosion protection of workpieces and tools during and after treatment is also one of the important functions of technological emulsions for cooling and lubricating. In this paper the effects of different concentrations of three emulsions on the corrosion rate of steel workpieces is reported. The results indicate that a higher concentration of emulsion does not provide better protection against corrosion.

Effects of Thermal Oxidation and Subsequent Pickling on Pitting Geometry of Austenitic Stainless Steels in Chloride Solutions

Abstract Harmful effects of thermal oxides formed on austenitic stainless steels (SS) like AISI 304 and 316L by heating in air or other oxidizing gases on their pitting liability in chloride solutions have been studied by pursuing geometric characteristics of corrosion process (pits density, their depths, and mouth areas, ie. penetrating and superficial detrimental consequences etc.). The possibility of preventing the decay of thermally oxidized austenitic SS by chemical removal (pickling) of oxides before exposure to chloride solutions was successfully applied on simple specimens but serious difficulties arose on welded parts and on parts exposed to other temperature gradients during manufacture or in exploitation.

Waste Water Treatment after Removal of Thermic Oxides from Stainless Steel Welding Joints

This work describes chemical methods of removal of thermic oxides from stainless steel welding joints, as well as waste water treatment. Thermal oxides were removed from the stainless steel surface using chemical and electrochemical procedures. A pickling paste that contains HNO3 and HF in different ratios was used for chemical cleansing of thermal oxides (A, B, and C). Electrochemical removal was done using an apparatus Magic Cleaner, and as electrolyte a solution H2SO4

Characteristics of modified martensitic stainless steel surfaces under tribocorrosion conditions

Abstract Stainless steel samples were tested in the laboratory and under real conditions of tribocorrosion wear. Electrochemical tests were also carried out to verify the corrosion resistance of modified steel surfaces. Metallographic analysis and hardness testing were conducted on stainless steel samples X20Cr13 and X17CrNi16 2. The possibilities of applications of modified surfaces of the selected steels were investigated by testing the samples under real wear conditions. The results have shown that the induction hardened and subsequently nitrided martensitic steels achieved an average wear resistance of up to three orders of magnitude higher as compared to the delivered condition.

Examples of measurement uncertainty evaluations in accordance with the revised GUM

The paper presents examples of the evaluation of uncertainty components in accordance with the current and revised Guide to the expression of uncertainty in measurement (GUM). In accordance with the proposed revision of the GUM a Bayesian approach was conducted for both type A and type B evaluations.The law of propagation of uncertainty (LPU) and the law of propagation of distribution applied through the Monte Carlo method, (MCM) were used to evaluate associated standard uncertainties, expanded uncertainties and coverage intervals. Furthermore, the influence of the non-Gaussian dominant input quantity and asymmetric distribution of the output quantity y on the evaluation of measurement uncertainty was analyzed. In the case when the probabilistically coverage interval is not symmetric, the coverage interval for the probability P is estimated from the experimental probability density function using the Monte Carlo method. Key highlights of the proposed revision of the GUM were analyzed through a set of examples.

Crevice corrosion resistance of high alloyed materials in 3.5 % NaCl solution

Abstract The effects of applied torque on the corrosion behaviour of W.-Nr. 1.4404 and 1.4462 stainless steels and W.-Nr. 2.4605 and 2.4858 nickel alloys with crevices were investigated using the cyclic potentiodynamic polarization method. Crevice corrosion (material-to-polytetrafluoroethylene) was tested in 3.5 % NaCl solution at 22 °C. The corroded surface was examined using scanning electron microscopy. The results indicate similar trends in susceptibility to crevice corrosion with increasing torque. Among the four specimens, the W.-Nr. 1.4404 is the most susceptible to crevice corrosion.

Properties of aluminium coatings produced using manual and robotized flame spraying processes

Abstract Aluminium coatings applied using arc or flame spraying processes are frequently employed for protection of steel structures in maritime applications. Results of comparative testing of aluminium coatings produced by manual and robotized flame spraying on steel substrate are reported in the contribution. Particular attention during the investigation of coating properties has been given to the uniformity of coating thickness, adhesion and corrosion resistance. Analysis of the results yielded conclusions on the quality, adhesion and corrosion resistance of the aluminium coating when the coating is applied to the flat steel plate.

Experimental study of imidazoline as an inhibitor of carbon steel in acid media

Abstract The electrochemical behaviour of a carbon steel in deaerated acid media with concentrations of 20 ppm, 50 ppm, 100 ppm and 200 ppm imidazoline at different temperatures and with different stirring rates has been evaluated by using anodic and cathodic polarization curves (Tafel) and electrochemical impedance spectroscopy (EIS) to compare the corrosion inhibition efficiency. The experimental results suggest that imidazoline is a good corrosion inhibitor at 50 ppm concentration.