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Title: High temperature corrosion of Cr-W alloys in simulated syngas

Abstract

Search for new high temperature materials for energy applications continues. This presentation will focus on degradation of Cr alloys containing 0-30%W by weight in a flowing gas mixture containing 30%CO, 8%CO2, 20%H2, 2%CH4, 0.8%H2S, 0.02%HCl, and 40%N2 by volume at temperatures up to 1000ºC. A pseudo-cyclic test involving heating the specimens, holding them at temperature for varying periods, and cooling them to room temperature was employed. Mass change of the specimens was determined after each cycle. Corrosion scale on the specimens was characterized using SEM, WDX, and XRD. Various sulfides, oxides, carbides, and nitrides were determined in different layers of the scale.

Authors:
; ;
Publication Date:
Research Org.:
National Energy Technology Laboratory (NETL), Pittsburgh, PA, and Morgantown, WV
Sponsoring Org.:
USDOE - Office of Fossil Energy (FE)
OSTI Identifier:
912977
Report Number(s):
DOE/NETL-IR-2007-077
TRN: US200802%%503
DOE Contract Number:
None cited
Resource Type:
Conference
Resource Relation:
Conference: 2007 TMS Annual Meeting: Symposium on Materials in Clean Energy Systems II, Orlando, FL, Feb. 25-Mar. 1, 2007
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALLOYS; CARBIDES; CORROSION; ENERGY SYSTEMS; HEATING; MIXTURES; NITRIDES; OXIDES; SULFIDES; X-RAY DIFFRACTION

Citation Formats

Dogan, O.N., Bullard, S.J., and Covino, B.S., Jr. High temperature corrosion of Cr-W alloys in simulated syngas. United States: N. p., 2007. Web.
Dogan, O.N., Bullard, S.J., & Covino, B.S., Jr. High temperature corrosion of Cr-W alloys in simulated syngas. United States.
Dogan, O.N., Bullard, S.J., and Covino, B.S., Jr. Thu . "High temperature corrosion of Cr-W alloys in simulated syngas". United States. doi:. https://www.osti.gov/servlets/purl/912977.
@article{osti_912977,
title = {High temperature corrosion of Cr-W alloys in simulated syngas},
author = {Dogan, O.N. and Bullard, S.J. and Covino, B.S., Jr.},
abstractNote = {Search for new high temperature materials for energy applications continues. This presentation will focus on degradation of Cr alloys containing 0-30%W by weight in a flowing gas mixture containing 30%CO, 8%CO2, 20%H2, 2%CH4, 0.8%H2S, 0.02%HCl, and 40%N2 by volume at temperatures up to 1000ºC. A pseudo-cyclic test involving heating the specimens, holding them at temperature for varying periods, and cooling them to room temperature was employed. Mass change of the specimens was determined after each cycle. Corrosion scale on the specimens was characterized using SEM, WDX, and XRD. Various sulfides, oxides, carbides, and nitrides were determined in different layers of the scale.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}

Conference:
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  • High-entropy alloys are formed by synthesizing five or more principal elements in equimolar or near equimolar concentrations. Microstructure of the CoCrCuFeNiAl{sub 0.5}B{sub x} (x = 0, 0.2, 0.6, 1) high-entropy alloys under investigation is composed of a mixture of disordered bcc and fcc phases and borides. These alloys were tested gravimetrically for their corrosion resistance in simulated syngas containing 0, 0.01, 0.1, and 1 % H{sub 2}S at 500 °C. The exposed coupons were characterized using XRD and SEM. No significant corrosion was detected at 500 °C in syngas containing 0 and 0.01 % H{sub 2}S while significant corrosion wasmore » observed in syngas containing 0.1 and 1 % H{sub 2}S. Cu{sub 1.96}S was the primary sulfide in the external corrosion scale on the low-boron high-entropy alloys, whereas FeCo{sub 4}Ni{sub 4}S{sub 8} on the high-boron high-entropy alloys. Multi-phase Cu-rich regions in the low-B high-entropy alloys were vulnerable to corrosive attack.« less
  • Cr alloys containing 0-30%W by weight were investigated for use in elevated temperature applications. The alloys were melted in a water-cooled, copper-hearth arc furnace. Microstructure of the alloys was characterized using x-ray diffraction, scanning electron microscopy, and light microscopy. A pseudocyclic oxidation test was employed to study scale formation at 1000ºC in dry air. The scale was predominantly chromia and spalled upon cooling. Alloying with aluminum up to 8 weight percent reduced the spalling drastically. Furthermore, aluminizing the surface of the Cr-W alloys completely stopped the spalling.
  • An experimental apparatus has been constructed to simulate rapid thermal-cycling conditions in coal-gasification environments, as experienced by metal components of a ceramic gas-filtration system. A comparative study of the corrosion resistances of several commercial iron-nickel-chromium-base alloys in a equilibrated argon-14.1%H{sub 2}-11.1%H{sub 2}O-O.1%H{sub 2}S-O.08%HCl gas at 600 C has been undertaken. Tests were carried out under isothermal, conventional thermal-cycling and very rapid thermal-cycling conditions (1 min cooling, giving temperature decreases of 160 to 280 C, repeated every 6 min). Degradation of the alloys involved the development of oxide scales in the early stages, followed by breakdown and growth of sulfide-rich scales.more » Thermal cycling involving conventional cool-to-room-temperature cycles generally resulted in increases in the rates of degradation of the alloys, probably by facilitating failure of the transient scales and enhancing the rates of transport across the steady-state scales. However, rapid thermal cycling often resulted in reduced metal loss and thinner scales than isothermal exposure, possibly due to debonding in the scale or at the scale/alloy interface, thereby reducing the rate of cation transport across the scale.« less
  • High efficiency ultrasupercritical power systems cofired with coal and biomass offer one way of significantly extending coal reserves and reducing levels of carbon dioxide produced during electricity generation. A variety of alloys have potential for construction of the boiler superheaters, but little information is available on the resistance of the alloys to corrosion by the unique combination of ash and gas present in such systems. Therefore, seven alloys with varying amounts of iron, chromium, and nickel have been subjected to laboratory parametric tests to determine rates of wastage and mechanisms of corrosion under conditions simulating those experienced by ash-covered superheatersmore » in coal- and biomass-fired ultrasupercritical boilers. The alloys were coated with K{sub 2}SO{sub 4} and powdered coal slag to simulate an ash fouling deposit of the type formed when cofiring coal and biomass. They were then subjected to 1000-hour corrosion tests at 630 C in the presence of simulated combustion gas, with and without water and hydrochloric acid vapors. Alloys that formed iron oxide scales suffered the most corrosive attack. Measurements indicate a correlation between the amount of chromium in the alloy and the degree of corrosion resistance. The ratio of chromium to nickel in the alloy appears to be an important factor. Scanning electron microscope (SEM) analysis has also shown that the addition of small amounts of other metals to increase strength and creep resistance can provide avenues for corrosion. To date, tests with and without water vapor have been performed. Water vapor significantly increases corrosion rates. Alloys which are iron-rich and, therefore, more susceptible to sulfur attack are displaying corrosion rates over 2.5 mm/yr (100 mil/yr). Chrome- and nickel-rich alloys are displaying corrosion rates below 0.25 mm/yr (10 mil/yr). SEM analyses indicate that even with the coating of ash, sulfidation is the primary corrosion mechanism. Sulfidation destroys protective oxide scales, promotes intergranular attack, and accelerates corrosion rates. The analyses also show that the coal slag does not appear to participate directly in the formation of primary reaction products, but may affect the activity of the corrodents. Results from tests running currently that include hydrochloric acid vapor will also be described in the paper.« less
  • The 650 C corrosion of some commercial purity and high purity nickel-chromium alloys has been investigated in flowing environments of anhydrous hydrogen fluoride (AHF) and hydrogen fluoride plus steam (HF + H{sub 2} O; P{sub HF} = 0.46 a{sup +}, P{sub H2}O = 0.54 atm). The reaction kinetics have been observed over extended periods and related to the morphologies and compositions of the corrosion products, to the activities of the oxidant species in the gaseous atmospheres and to appropriate thermodynamic and phase equilibria data. The alloys studied include Inconel alloys 600, 601, X750 and 625 and a range of binarymore » alloys, Ni-5Cr to Ni-40Cr. In AHF, chromium fluorides developed beneath thin external corrosion product scales and with the nickel-chromium binary alloys an increase in the chromium content increased the rate of reaction. In the HF + H{sub 2}O atmosphere, the alloys formed either an external Cr{sub 2}O{sub 3}-rich scale with internal fluoride formation in the underlying alloy or internal Cr{sub 2}O{sub 3}-rich areas within a corrosion product network also containing chromium fluorides. The extent and rate of reaction of the nickel-chromium alloys in hydrogen fluoride-containing atmospheres, as in other high temperature systems, is dependent upon the physiochemical properties of the corrosion products formed. Pertinent data is presented for the lower oxidation state chromium fluorides which support the experimental observations and illustrate that a chromium fluoride scale does not constitute and effective barrier to further corrosion.« less