Effect of Physical Properties of Molten Deposits on High Temperature Corrosion of Alloys in Waste Incineration Environment

Kawahara, Yuuzou; Kira, Masaharu

doi:10.3323/jcorr1991.46.8

Cited by 15 publications

(5 citation statements)

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“…There are more alkali sulfates on the specimen as the deposit thickness increases. Similar results were seen by Kawahara and Kira [91] with the deposition of alkali sulfate deposits on steel alloys used in waste incineration plants. The amount of corrosion is significantly greater using the powder deposit than the slurries.…”

Section: Slurry Methodssupporting

confidence: 76%

“…The powder deposit tests could be considered as having a much larger thickness of alkali sulfates available on the surface compared to the slurry tests, so the amount of degradation is much greater. Kawahara and Kira [91] found that submerging specimens in powder deposits was the best means of simulating fireside corrosion due to the corrosion intensity and the stability of the model ash.…”

Section: Slurry Methodsmentioning

confidence: 99%

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Determination of the Initiation and Propagation Mechanism of Fireside Corrosion

2015

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A variety of deposit compositions were examined in short-term laboratory tests with the aim of determining the corrosion mechanisms of fireside corrosion for a range of chromiaforming alloys in various combustion systems. The deposits formed in boilers are complex, and despite decades of study, the propagation mechanism of fireside corrosion is not well understood. Alkali iron trisulfates, which are stabilized by SO 3 in the gas atmosphere, have been believed to be the major corrosive species for many years. The propagation mechanism for fireside corrosion was investigated using T92 (a typical ferritic boiler steel) and a model austenitic Fe-Ni-Cr alloy and synthetic coal ash deposits. The metal loss, corrosion product morphologies, and compositions were carefully characterized in order to define a propagation mechanism. The corrosive species responsible for degradation was a (Na,K) 2 SO 4 -Fe 2 (SO 4 ) 3 solution and not alkali iron trisulfates, which is contrary to what has been believed for decades.The formation of the liquid deposit is similar to Type II hot corrosion of gas turbine engines.The mechanism is a synergistic dissolution process similar to that which can occur for hot corrosion as well. Simultaneous basic and acidic dissolution of protective Cr 2 O 3 and Fe 2 O 3 disrupts protective oxide formation and locally produces negative solubility gradients at the oxide/salt interface. The dissolved Fe 2 O 3 and Cr 2 O 3 reprecipitate where there is lower solubility, creating the observed corrosion products. The effect of the deposit composition, gas atmosphere iii composition, alloy composition, temperature, and deposit thickness were examined with respect to the proposed fireside corrosion mechanism. These measurements were found to be consistent with the proposed mechanism based on synergistic fluxing.iv Oxy-fuel firing is one of three ways in which CCS can be accomplished. The other two ways are post-combustion capture, where the CO 2 is removed from the flue gas after combustion, and pre-combustion capture, where the CO 2 is removed from the fuel before combustion. Oxy-1 fuel firing is carrying out the combustion in an environment consisting of recirculated flue gases containing primarily CO 2 , steam and pure oxygen instead of air in order to create a flue gas with minimal amounts of N 2 . A schematic diagram of the oxy-fuel process is shown below in Figure 1. Figure 1: Schematic diagram of oxy-fuel combustionOxy-fuel combustion produces flue gases containing approximately 60%CO 2 -30%H 2 O-4%O 2 -5%N 2 , whereas traditional air-fired combustion produces flue gases containing 74%N 2 -[2] The flue gases in oxy-fuel systems are able to be recycled through the fuel burners leading to decreased CO 2 emissions. However, with the reduced amounts of nitrogen, the products of the oxy-fuel combustion process have increased amounts of CO 2 , steam and corrosive gases, such as SO 2 that can cause significant corrosion in superheater and reheater 2 tubes when compared to air-fired combustion. Bu...

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Section: Slurry Methodssupporting

confidence: 76%

Section: Slurry Methodsmentioning

confidence: 99%

Determination of the Initiation and Propagation Mechanism of Fireside Corrosion

2015

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“…Highly efficient waste power generation is being actively promoted for the effective use of waste energy. However, in the superheater in a high-efficiency waste incineration boiler, molten salt containing chloride and sulfate forms in the ash attaches to the gas side pipe surface due to the high temperature of steam, causing high-temperature corrosion [1]. Further, when residual stress exists in a bent or welded portion of a pipe, high-temperature corrosion and local corrosion due to molten salt may be accelerated.…”

Section: Introductionmentioning

confidence: 99%

Thermal Stress Relaxation and High-Temperature Corrosion of Cr-Mo Steel Processed Using Multifunction Cavitation

et al. 2018

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This research investigated high-temperature corrosion (500 °C) of Cr-Mo steel processed using water jet peening or multifunction cavitation (MFC), and the suitability of such steel for high-temperature boilers and reaction vessels. High-temperature corrosion was induced using an embedment test and a coating test using sulfide-type K2SO4-Na2SO4 powder. To measure the relaxation of the residual stress due to the decrease in work hardening caused by an increase in specimen temperature and the difference in thermal shrinkage between the surface and interior of the specimen, a thermal cycling test was conducted. For the MFC-processed specimen, the oxide film that formed on the surface suppressed mass loss, prevented crack formation, and reduced the compressive residual stress caused by high-temperature corrosion. MFC-processed Cr-Mo steel is thus suitable for a high-temperature corrosion environment.

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“…Metal chlorides and alkali chlorides can form mixtures with low first melting temperatures. If the deposit is partly molten, the corrosion rate will increase [13,15]. However, these mechanisms are general and the corrosion behaviour of commercial alloys in waste environment is not fully understood.…”

Section: Introductionmentioning

confidence: 99%

Field test of superheater corrosion in a CFB waste boiler: Part II – Scale formation characteristics

Andersson

Norell

2005

Materials & Corrosion

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This study concerns the scales formed on the steels T22 , Alloy 310, Alloy 28 and the nickel-based Alloy 65 in a superheater test coil at 460 -540 8C in a CFB waste boiler. The methods used for the characterisation of the scales included SEM, EDX, Auger spectroscopy and XRD. The deposits on the tubes consisted mainly of alkali chlorides and calcium sulphate. The scales formed consisted of Fe 2 O 3 and Fe 3 O 4 on the T22 steel, NiFe 2 O 3 and Cr 2 O 3 on Alloy 310 and Alloy 28, and Cr 2 O 3 and NiO on Alloy 65. Rapid corrosion on the steel T22 was associated with the growth of an open columnar iron oxide below a thick porous chlorine-containing scale. Pitting corrosion on Alloy 310 occurred and it may be associated with selective corrosion, first following the grain boundaries then uniformly attacking the metal. The only protective oxide was observed on Alloy 28 that formed an inner chromium oxide separating the chlorides from the metal. Dense thin chromium oxides were observed in the scale on Alloy 28, but no major cracks were found perpendicular to the tube. Alloy 65 suffered from grain boundary attack and was locally attacked under thick porous chromium oxide with nickel chlorides in the advancing front. Molybdenum was enriched at the interface to the metal on both Alloy 28 and Alloy 65.

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Effect of Physical Properties of Molten Deposits on High Temperature Corrosion of Alloys in Waste Incineration Environment

Cited by 15 publications

References 0 publications

Determination of the Initiation and Propagation Mechanism of Fireside Corrosion

Determination of the Initiation and Propagation Mechanism of Fireside Corrosion

Thermal Stress Relaxation and High-Temperature Corrosion of Cr-Mo Steel Processed Using Multifunction Cavitation

Field test of superheater corrosion in a CFB waste boiler: Part II – Scale formation characteristics

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