Corrosion and stress corrosion cracking in coal liquefaction processes

The liquefaction of coal to produce clean-burning synthetic fuels has been demonstrated at the pilot plant level. However, some significant materials problems should be solved to enable economic and reliable scale-up to commercial levels of production. Failures due to inadequate materials performance have been reported in many plant areas; in particular, stress corrosion cracking has been found in austenitic stainless steels in the reaction and separation areas, and severe corrosion has been observed in fractionation components. In order to screen candidate materials of construction, racks of U-bend specimens in welded and as-wrought conditions and unstressed surveillance coupons were exposed in pilot plant vessels and examined. Failed components were analyzed on-site and by subsequent laboratory work. Laboratory tests were also performed. These studies have identified alloys that are suitable for critical plant locations.