Corrosão de aço superaustenítico, aços duplex e liga de níquel hastelloy em glicerina acidificada da indústria de biodiesel

Abstract

This work was a partnership between the Montes Claros Biodiesel Unit, a subsidiary of Petrobras Biofuels (PBIO), and the UFMG Chemical Engineering Department, in order to evaluate some alternative metal alloys to be used in the production unit pipes. At a certain pointof the biodiesel production process, the addition of hydrochloric acid becomes necessary in order to neutralize the excess of the used basic catalyst. The consequences of this neutralization step are the change of the glycerin pH, one of the products of the transesterification reaction,and the increase of the chloride ions concentration of in the dilute solution. Chloride ions (Cl-) increase the localized corrosion probability, especially pitting formation. The aim of this study is to evaluate the corrosion behavior of four different alloys. These alloys are AISI 904Lsuperaustenitic stainless steel, hot-rolled and cold-rolled SAF 2205 (UNS S31803) duplex steel, and the Hastelloy B3 nickel alloy. All samples were subjected to potentiodynamic polarization test, in an acidified process glycerine solution, extracted from the Montes Claros unit. After theelectrochemical tests, the surface samples were evaluated by scanning electron microscopy analysis (SEM) and energy dispersive spectroscopy (EDS) analysis. After all the tests were carried out and analyzed, it was concluded that the AISI 904L stainless steel presented the bestperformance with respect to corrosion resistance in acidic glycerin. The hot-rolled and coldrolled SAF 2205 duplex steel had slightly lower performances, and the Hastelloy B3 alloy had the worst performance among all studied samples.