The corrosion behavior of alloys in HCl-Cl2 gases is being studied for a wide range of conditions. Corrosion in these gases is influenced by the evaporation of volatile chloride corrosion product species. The three components of the study are: compilation of corrosion data and preparation of correlations between corrosion rate and exposure conditions; preparation of thermochemical models, which can then be used in analyzing corrosion of alloys by HCl-Cl2 gases; and measurement of alloy corrosion in welldefined conditions containing HCl-Cl2 gases. This study is emphasizing commercial, heat-resistant alloys, which are widely used in high-temperature process equipment. The exposure conditions include temperatures of 473 ? 1073 K, times up to 400 hr, and gases, which contain HCl-Cl2 concentrations up to 100% volume (but do not contain O2) at one atmosphere total pressure. The traditional method of reporting gas phase corrosion by weight change/area often measures only 10-20% of the total metal penetration for many of the alloys. Most of the alloys experience metal penetration by internal corrosion product formation or void formation. The dependencies of metal penetration and penetration rate upon exposure time show that the rate of corrosion tends to slow with time.
BACKGROUND
There is a compelling opportunity to increase the accuracy used in predicting equipment lifetimes that are often limited by corrosion in high-temperature gases. Benefits in improving corrosion management will be far reaching in the chemical industry and the U.S. economy. Examples are improvement in process safety, reduction in maintenance costs of process operation, more cost-effective use of expensive alloys in equipment designs, reduction in the use of energy, moderation in the release of CO2 into the atmosphere and more confident use of alloys in extreme operating conditions in terms of allowable temperatures and gas compositions. Equipment maintenance will be better scheduled, and unplanned outages due to unexpected corrosion will be reduced, as this project technology is distributed. These benefits will be a direct result of accurate predictions of the modes and rates of corrosion of commercial metals and alloys exposed to complex, high-temperature gases. Processes are usually implemented with equipment for which the maximum allowable temperatures, or other process limitations, are limited by the extent of equipment corrosion expected. Equipment which contains corrosive gases like HCl-Cl2 is found in heaters, flares, waste incinerators, heat treatment ovens, fossil-fuel fired equipment, process instrumentation, electric heaters, pigment plants, reactive metals plants, caustic or chlorine plants, bleaching operations in paper manufacturing, and catalyst regenerations in the petroleum industry.
