Corrosion Kinetics of Low- and High-Alloy Steels in Chlorine-Containing Gas Atmospheres

Abstract

combustion and coal gasification, waste incinerators, fossil-fuel-fired boilers, and gas turbines is hightemperature corrosion. Most materials, when exposed at high temperatures to aggressive gaseous compounds, such as hydrogen sulfide, oxygen and hydrogen chloride or chlorine, are rapidly attacked. 1-3 Less information exists considering the performance of materials in coal gasification atmospheres containing small amounts of hydrogen chloride gas or chlorine.Additional corrosion problems have been associated with high concentrations of chlorine. For example, the chlorine content of British coal lies between 0.02 and 0.75%, 4 which corresponds to 150 to 1,000 ppm hydrogen chloride gas, which is unusually high compared with coals from most of the world. The chlorine was present mostly as inorganic chloride compounds, such as sodium, potassium, or calcium. It has been reported that the chlorine is partly bonded as sodium chloride, as well as a part present as chloride ions weakly bound to the coal matter. The chlorine in coal is rapidly released as hydrogen chloride gas during the initial stage of gasification or combustion processes.The mechanisms of attack by oxygen and/or sulfur are reasonably well understood, but the corrosion rate and mechanism may be altered by the high chlorine content. Presently, the effect of chlorine on the corrosion mechanism is still unclear. There is a well-accepted relationship between the corrosion rate ABSTRACT The effect of chlorine on the high-temperature corrosion of high-alloy steels Monit † , Al29-4C, Sanicro † 28 (UNS N08028), Sanicro † 31, Incoloy † 800H (UNS N08810) and AISI 310 (UNS 531000), and of low-alloy steels 10CrMo9.10, Mod.9Cr1Mo, X20CrMoV12.1, and 15Mo3 in atmospheres with low oxygen and high sulfur partial pressures were investigated. The addition of 500 ppm HCl (pCl 2 = 2.5 x 10 -20 atm) to the oxidizing/sulfidizing atmosphere at 450°C increases the corrosion rate and the void fraction in the sulfide scale and decreases the adherence causing spallation of the scale. Depending on the experimental procedure, locally condensed chloride compounds could be formed. For AISI 310, additional experiments on the effect of temperature and pCl 2 on the corrosion rate were performed. With increasing temperature or pCl 2 , the corrosion rate increased. Only the high-alloy steels showed promising results. Some models are discussed to explain the enhanced corrosion rate due to the presence of chlorine.KEY WORDS: corrosive atmospheres, high-temperature corrosion, hydrogen chloride, sulfidation, thermogravimetry FIGURE 9. Electron micrograph (SEI) of the surface of a 10CrMo9.10 alloy for 70 h at 450°C in an oxidizing/sulfidizing environment.

The mechanical properties of thin alumina films deposited by metal-organic chemical vapour deposition

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“…It was found before [29] that the films contain alumina and boehmite (AlO( OH)). X-Ray photoelectron spectroscopy measurements revealed that the amount of boehmite decreased with increasing temperature.…”

Tailoring a High Temperature Corrosion Resistant FeNiCrAl for Oxy-Combustion Application by Thermal Spray Coating and HIP

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