Variables affecting mixed oxidant corrosion of stainless steels in gasifiers

This paper is the final installment of EPRI's project on corrosion in synga s coolers of integrated coal gasification combined cycle plant. In previous papers we explored the effect of chloride species on mixed oxidant corrosi on of stainless steels (CORROSION 97, Paper 134) and iron aluminides (CORRO SION 98, Paper 185). It was found that the amount of chloride species in th e gas and in deposits largely determined the rate of corrosion. Armed with this understanding the effect of a few common process variables is explored in this paper. It was found that corrosion rates decline at higher tempera tures, when chloride-enhanced mixed oxidant corrosion occurs at lower tempe ratures, but corrosion rates increase with temperature for pure sulfidation /oxidation, as may he expected. System pressure was generally of secondary importance, but again higher corrosion rates were generally experienced at elevated pressure, when chloride-enhanced corrosion was predominant, especi ally at lower temperatures. A simulated temperature excursion below the syn gas dewpoint had similar effects, and also caused chloride-enhanced corrosi on in 310 stainless steel, which usually does not show this type of corrosi on, except when exposed to aqueous corrosion during downtime. A pleasant su rprise was the almost complete lack of corrosion when H2S and HCl levels we re reduced to those expected downstream from gasifiers using in-bed desulfu rization. It would appear that 12Cr steels may be adequate here. This is be ing explored further.