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 200-1000uC) or in a temperature gradient. The pitting corrosion propensities of such specimens were assessed by exposure to FeCl 3 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 600uC. The removal of thermal oxides formed at 200-800uC 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 1000uC, pitting tendencies are increased by pickling.

This paper presents the research regarding the influence of glyoxal on electrochemical and corrosion behaviour of austenitic stainless steel in water. For this purpose, model solutions containing glyoxal in water in concentrations ranging from 0.1 to 1 % were prepared. Spring water was used as control electrolyte. From the potentiostatic polarisation data (using the standard three-electrode system), the corrosion current (i corr ), corrosion potential (E corr ) and polarisation resistance (R p ) were calculated. The research included also the conductivity, total dissolved soils, salinity, resistivity and pH, absolute potential, and relative potential of model solutions. The presence of glyoxal at the highest concentration of 1 % in the water solution has accelerating effect on corrosion.Key words: stainless steel, localized corrosion, water, glyoxalIn dieser Arbeit wurde die Auswirkung des Glyoxals auf das elektrochemische und korrosieve Verhalten von austenitischem Edelstahl im Quellwasser untersucht. Für diese Erforschung wurden Wasserlösungen vorbereitet, die von 0.1 bis 1 % Glyoxal enthalten haben. Das Quellwasser wurde als blinde Probe benutzt.Für die potenziostatische Polarisation wurde das Standard DreiElektroden-System benützt, mit Hilfe von diesem wurde der Korrosionsstrom, das Korrosionspotenzial und die Widerstandsfähig-keit des Materials berechnet.In den vorbereiteten Wasserlösungen mit Glyoxal wurden die Leitfähigkeit, die gesammten gelösten Feststoffe, der Salzgehalt, die Widerstandfähigkeit, pH und das absolute und relative Potenzial bestimmt. Die Konzentrationen von Glyoxal zeigen schon ab 1 % und mehr die beschleunigte Korrosion auf der Oberfläche des austenitischen Edelstahls.

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.

Effect of thermal oxidation on the behaviour of stainless steel (SS) in an ferrichlorid solution was investigated. Sheet specimens of austenitic AISI 316L with the observed area S = 90 cm2 were immersed into the solutionin the initial state,after heating in air isothermally at 200, 400, 600, 800 and 1000°C respectively or in temperature gradient, andafter heating and subsequent cleaning of specimens in an nitric acid/hydrofluoride acid mixture.Spot potential profiles of specimens were taken up using a simple device with graphite counter-electrode i.e. by measuring local potential differences between specimen and graphite. The presence of thermal oxides enhances the non-uniformity of profile, which decreases after the removal of oxides by cleaning in the nitric acid/hydrofluoride acid mixture. However, the initial degree of uniformity is not re-established. Prolonged exposure to ferrichlorid solution provokes pitting corrosion of specimens heated isothermally at 400° C and above it or heated in temperature gradient. On such specimens pits number np, their depths hp and orifice areas Sp.

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