Corrosion rate determination of austenic steels in calcium hypochlorite solutions

Abstract

This paper presents the results of testing the corrosion resistance of austenitic chromium-nickel steel X6 CrNiTi 18-10 and X6 CrNiNb 18-10 in solutions of calcium hypochlorite. For the tests were used potentiodynamic measurement methods. By graphical method of linear polarization, corrosion currents and corrosion potential were obtained on the intersection of the Tafel real E = f(log i) on the basis of potentiodynamic curves for the examined steels. The comparative method to determine the corrosion current density is the polarization resistance method. Based on corrosion currents were calculated corrosion rate of tested steel. Anodic polarization curves for both austenitic steel in the investigated solutions were shot in the interval of stationary potential of up to + 2.5V, to determine the areas of activity. Test results show that with increasing of calcium hypochlorite solution concentration, increase the pH of the solution and the concentration of active chlorine which causes a reduction in the corrosion resistance of the tested steel. These steels are resistant to corrosion in a 1% solution, stable in 10% solutions, and less resistant in 50% suspensions of calcium hypochlorite.

U ovom radu dati su rezultati ispitivanja korozione otpornosti austenitnih hrom-nikl čelika Č 4572 i Č 4583 u rastvorima kalcijum-hipohloriita. Za ispitivanja su korišćene potenciodinamičke metode merenja. Grafičkom metodom linearne polarizacije koroziona struja i korozioni potencijal dobijani su u preseku Tafelovih pravih E = f(log i) na osnovu potenciodinamičkih krivih za ispitivane čelike. Komparativna metoda za određivanje korozione struje je metoda polarizacionog otpora. Na osnovu korozionih struja, izračunate su brzine korozije ispitivanih čelika. Anodne polarizacione krive za oba austenitna čelika u ispitivanim rastvorima snimane su u intervalu potencijala od stacionarnog do +2,5V, da bi se odredila područja aktivnosti. Rezultati ispitivanja pokazuju da sa porastom koncentracije rastvora kalcijum-hipohlorita, raste rN vrednost rastvora i koncentracija aktivnog hlora što izaziva smanjenje korozione otpornosti ispitivanih čelika. Ovi čelici su otporni na koroziju u 1% - nim rastvorima, postojani u 10% - nim rastvorima i manje otporni u 50% - nim suspenzijama kalcijum - hipohlorita.