Abstract
Severe corrosion has been observed in fractionating columns at the Fort Lewis, Washington, and Wilsonville, Alabama, Solvent Refined Coal pilot plants. This corrosion is most severe for materials exposed in the 230 to 250°C (446–482°F) range and results in corrosion rates of as much as 6.4 mm/y (250 mils/y) for type 18-8 stainless steels. ORNL studies of this corrosion problem include exposure of coupons in the columns, analysis of failed components from the pilot plants, chemical analyses of liquids from the pilot plants, and operation of laboratory experiments. From coupon exposures we have established that titanium and certain nickel-base alloys have adequate corrosion resistance for the environment. Chemical analyses of the liquids have shown that the presence of appreciable levels of water-soluble chloride is a necessary but not sufficient condition for these oils to be corrosive. By analysis of oils from the solvent recovery areas at Fort Lewis and Wilsonville, we have ascertained the path of chlorine (and other elements) through the plant and assessed the effects of process changes. Laboratory tests have shown that water washing effectively removes much of the chlorides from the oils. Experiments have also shown that certain fractions of the oils are much more corrosive than others and that corrosivity is affected by the addition or removal of key constituents of the oils. We think the corrosion mechanism is related to the oxidation of iron by HCl dissolved in acidic organic compounds followed by the formation of a soluble iron complex.
