(54cv) Use of Various High-Nickel Alloys for Supercritical Water Reactions at Severe Temperature and Pressure Conditions

Supercritical water has increased in popularity as a reaction medium for hydrocarbons due to its greatly enhanced solvent capabilities towards these substances in the supercritical fluid region. While a supercritical condition could be achieved for water as long as it is subjected to both high temperature (T>374°C) and high pressure (P>22.1MPa), the realistic process conditions that are required for some of the supercritical water reactions far exceed the water’s critical point barrier. Such reactions potentially include selective oxidation, gasification, reformation, and more. These elevated temperatures and pressures, along with corrosion considerations, require the use of special materials in the reactor hardware, pipes, and fittings utilized in these reaction systems. Some commonly used materials are various high-nickel alloys due to their great mechanical properties and corrosion resistance at elevated temperature and pressure conditions. This paper will focus on a comparison of five commonly used high-nickel alloys, viz., Hastelloy C276, Inconel 625 (Grades 1 and 2), Haynes 230, and Haynes 282, based on prior experimental reformation studies conducted in our laboratory on the reactors made of these specialty alloys and material data sheets. This study is intended to provide a comprehensive comparison of the yield and tensile strengths, creep and rupture strengths, corrosion resistance, and varying degrees of catalytic properties of the individual alloy materials. The comparisons of the different strengths will be made over temperature ranges that are commonly encountered in supercritical water reformation reactions, thereby establishing the safe operational limits and ranges for the system.