The combined effects of downtime corrosion and sulphidation on the degradation of commercial alloys

Abstract

The behaviour of Incoloy 800H and AISI 310 stainless steel has been studied in a simulated coal gasification atmosphere (CGA) with and without the presence of deposits at 550°C. The samples were also exposed to two test procedures to simulate downtime corrosion (DTC); one in which the samples were simply withdrawn to a cooler region of the furnace were condensate formation took place, and the other type of DTC was the EPRI test. Two types of deposit were used; one was a typical coal char and the other consisted of the char with added FeCl2 and NaCl. The EPRI DTC test induced the most severe attack when combined with exposure to the CGA, but the addition of salt to the deposit appeared to make little difference to the aggressiveness the test. In contrast to many laboratory tests, chlorine-containing compounds were found at the scale—alloy interface of the most severely attacked samples, and thus represented a good simulation of corrosion encountered in operating plant. After 530 h exposure a maximum metal loss of 0.24 mm was found on Incoloy 800H exposed to the most aggressive test, but less severe conditions produced metal losses comparable with those found in operating plant.