Localized Corrosion -- Measurement, Mechanisms and Mitigation: High Temperature Corrosion
Sponsored by: MS&T Organization
Program Organizers: Gerald Frankel, Ohio State University

Tuesday 10:00 AM
October 18, 2011
Room: D244/245
Location: Greater Columbus Convention Center

Session Chair: Gerald Frankel, The Ohio State University

10:00 AM
A Review of Experiences with AL-6XNŽ and ZERONŽ 100 Alloys in Air Pollution Control Systems: Devin Wachowiak¹; ¹Rolled Alloys
    Coal fired power plants are faced with increasingly strict air quality control laws and EPA rules controlling a wider range of emissions especially sulfur compounds. A significant number of flue gas desulfurization (FGD) units employ wet scrubbing to reduce sulfur dioxide emissions by more than 90 percent. Due to the inherent contaminants generated by the combustion of coal, wet FGD’s require the use of corrosion resistant materials in their construction. AL-6XN and ZERON 100 are alloys that have been chosen for these systems when conditions are too severe for either 317L stainless steel or 2205 duplex stainless steel and have proven to be cost effective materials of construction that fill the gap between the lower alloyed stainless steels and the high molybdenum and nickel based alloys such as C-276. My presentation will review the use of AL-6XN and ZERON 100 alloys in various FGD applications around the world.

10:20 AM
Effect of Applied Stress, Crystal Orientation, and Phase on Hot Corrosion of CMSX-4 by Sodium Sulfate: Pongpat Lortrakul¹; Rodney Trice¹; Kevin Trumble¹; ¹Purdue University
    Gas turbine blades without thermal barrier coatings experience significant hot corrosion at the bare metal under the platform part. Of particular importance is the effect of sodium sulfate on uncoated superalloys, the effects of which can lead to pitting or uniform corrosion depending on the exposure temperature. Additionally, stress may also affect the blade lifetime by enhancing the diffusion kinetics. In the present work, CMSX-4 (a single crystal nickel-based superalloy) specimens with a blunt notch were stressed while simultaneously exposing them to a hot-corrosion environment. The stress distribution on the surface varied as a function of the position from 750 MPa to -300 MPa. The testing temperature was either 700°C or 900°C, with 0.3 mg/cm2 Na2SO4 deposited on the surface in 1000 ppm-SO2 (O2 balance) environment. Microstructure analysis as a function of position in the stress field and crystallographic orientation (as well as gamma or gamma prime phases) was examined.

10:40 AM
Localized Attack in FGD Air Pollution Control Vessels: Debajyoti Maitra¹; Lewis Shoemaker¹; Jim Crum¹; ¹Special Metals Corporation
    To control emissions of sulfur dioxide from coal-fired electric power generation plants, wet limestone flue gas desulfurization (FGD) air pollution control systems are used. In recent times duplex stainless steels have been used for construction of the absorber vessels in these systems. The aggressive acid / halide conditions in the vessels have resulted in severe localized corrosion ... both pitting and crevice attack. Laboratory and in-situ testing programs were conducted to evaluate this attack and determine resistant materials for repair and future construction.

11:00 AM
An Atomistic Study of Oxidation Initiation on Different Kinds of FCC Fe-Cr Binary Alloy Surfaces: Nishith Das¹; Tetsuo Shoji¹; ¹Tohoku University
    Oxidation is an indispensable process of alloys that could happen prior to crack initiation in the high temperature environment. The continuous mass transfer enhances localized oxidation and film degradation. Scientist and engineers have made significant advances over the last few decades but the problem still remains. The computational chemistry can be a complementary tool to understand the fundamental mechanism. In this study, quantum chemical molecular dynamics (QCMD) will be applied to study multilayer water molecules adsorption and dissociation phenomena on fcc Fe-Cr(111), Fe-Cr(110) and Fe-Cr(100) binary alloy surfaces at 288 oC and to elucidate the fundamental mechanism of initial stage oxidation process. The surface morphologies and diffusion of dissociated atoms and molecules into metal surface will be analyzed. Mulliken population method will be applied to analyze the charge transfer process between atoms. Thus, QCMD study attempts to clarify the early stage of surface oxidation process from the atomistic level.