Abstract

WONG-MORENO, A; LOPEZ-LOPEZ, D  and  MARTINEZ, L. UNDERSTANDING THE CORROSION BEHAVIOR OF 35Ni19Cr ALLOY USING X-RAY MICROANALYSIS . Rev. LatinAm. Met. Mat. [online]. 2001, vol.21, n.2, pp.27-35. ISSN 0255-6952.

X-ray microanalysis of corroded specimens of 35Ni19Cr austenitic steel was performed in order to understand its oil-ash corrosion behavior. Corrosion testing involved the exposure of the alloy at temperatures in the range of 600°C - 900°C, to a sulfate-rich oil ash, which is also constituted by low melting point sodium vanadates. The curve describing the corrosion behavior as a function of temperature exhibits two relative maximums at 715°C and around 800°C, suggesting that there is an evolution of corrosion mechanisms as temperature is increased. X-ray microanalysis of the corrosion product scale and of the metal subjacent to the interface metal/scale let characterize three corrosion mechanisms prevailing along the temperature range: metallic dissolution caused by molten vanadium compounds, accelerated oxidation and sulfidation. Microanalysis also provided evidence of internal degradation at temperatures above 675°C consisting in internal oxidation, sulfidation or both. It was concluded that the resultant corrosion behavior depends on both: the oxidation, oil-ash corrosion and sulfidation resistance of the alloy, and the stability of the oil ash, which determines the chemical compounds responsible for the corrosion process observed.

Keywords : X-ray microanalysis; oil ash corrosion; 35Ni19Cr austenitic steel; sulfidation; high temperature oxidation.