Date of Award

August 2017

Degree Type

Thesis

Degree Name

Master of Science

Department

Engineering

First Advisor

Benjamin Church

Committee Members

Nidal Abu-Zahra, David Yu

Keywords

AFA, Austenitic Stainless Steel, Carburization, Characterization, Metal Dusting, Pre-Oxidation

Abstract

Metal dusting is a catastrophic form of corrosion and carburization, and is a disintegration of alloys into a dust of metal particles, oxides and graphite deposition products. Metal dusting and related coking phenomenon happen in industrial fields where carburizing syngas appears in the process. Metal dusting would cause damage in the form of pits and notches in pipes and other metallic equipment often causing a loss of production time or reduced component lifetimes. It is of great importance to prevent this corrosion from happening to the metal materials used by the industry.

To counter the corrosion, a new generation of iron-based austenitic stainless steel alloys have been developed that are alumina formers. A series of alloys were selected to test the oxidation and metal dusting performance of these new alumina-forming-austenitic (AFA) materials and were compared to currently-available alloys often employed in these conditions. The nickel-iron-chromium austenitic stainless steels of 310 and 800H were purchased as wrought sheet samples and while the chromia-forming HP alloy and alumina-forming G3607A and G3610A were centrifugally cast. Experimental high temperature oxidation and metal dusting atmospheres were set up using a tube furnace in order to observe the high temperature oxidation and metal dusting corrosion in these five different kinds of alloys. Oxidation test was conducted for 30 hours in a 950°C pure steam tube furnace environment. Industrial processes such as steam reforming, synthesis gas reaction, steam cracking used to generate clean fuels often use a similar kind of environment to form continuous oxide layers prior to exposing the materials to the high-carbon processes conditions. Metal dusting test was carried out under a H2-CO-CO2 environment at 650°C with carbon activity (ac) of 10 for 500 hours. Mass changes from the oxidation and dusting tests were tracked.

Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Diffraction (XRD) were applied to characterize the oxide layers formed and the corrosion that occurred to the alloys. The alumina formers were able to form continuous protective oxide layer and also displayed less pits from metal dusting attack than the chromia formers. We can therefore conclude that when exposed to these metal dusting environment, the alumina-forming alloys could provide better corrosion resistance and is worth to be applied for economic and environmental advantages.

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