THE COMBINED EFFECTS OF DOWNTIME CORROSION AND SULFIDATION ON THE DEGRADATION OF COMMERCIAL ALLOYS

The behaviour of Incoloy 800H and AISI 310 stainless steel has been st udied in a simulated coal gasification atmosphere (CGA) with and witho ut the presence of deposits at 550 degrees C. The samples were also ex posed to two test procedures to simulate downtime corrosion (DTC); one in which the samples were simply withdrawn to a cooler region of the furnace were condensate formation took place, and the other type of DT C was the EPRI test.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 Na Cl. The EPRI DTC test induced the most severe attack when combined wit h exposure to the CGA, but the addition of salt to the deposit appeare d to make little difference to the aggressiveness the test. In contras t to many laboratory tests, chlorine-containing compounds were found a t the scale - alloy interface of the most severely attacked samples, a nd thus represented a good simulation of corrosion encountered in oper ating 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 se vere conditions produced metal losses comparable with those found in o perating plant.