INFLUENCE OF TEMPERATURE AND EXPOSURE TIME ON THE MORPHOLOGICAL AND ELECTROCHEMICAL PROPERTIES OF CORROSION PRODUCTS FORMED IN AISI 316 STEEL EXPOSED TO OPPORTUNITY CRUDE

摘要

In this research was determined the influence of temperature and exposure time on the morphological and electrochemical properties of corrosion products formed on the surface of AISI 316 Grade Stainless Steel, exposed to conditions of a transfer line into the unit of atmospheric distillation in the processing opportunity crude, using gravimetric and electrochemical measurements. Exposure times used in gravimetric trials were 36, 48 and 60 hours at temperatures of 250, 285 and 330°C each, with a single percentage by weight of sulfur (2.55%) and one stirring speed. To perform the electrochemical study, a glass cell with three electrodes was adapted: Ag/AgCl reference electrode, auxiliary graphite and working electrode AISI 316 Grade Stainless Steel, connected to a Gamry 3000 potentiostat/galvanostat. To determine the electrochemical properties of the corrosion products formed on the surface of the material, it was applied electrochemical impedance spectroscopy in a frequency range between 100,000 to 0.01 Hz with amplitude of 10 mV. Morphology was characterized on the surface of AISI 316 Grade Stainless Steel through atomic force microscopy (AFM), X-ray diffraction (XRD) and through X-ray fluorescence by energy dispersive (Energy-dispersive X-ray spectroscopy - EDS) in combination with Scanning Electron Microscopy (Scanning Electron Microscopy - SEM). From the above it was determined the influence of the operating conditions in the possible formation of iron sulfide layers (FeS) on the material surface, where they may have protective properties against corrosion of other contaminating species.