We experienced selective weld metal corrosion in a rich amine section of a H2S removal plant using Ucarsol solvent (MDEA-based amine solvent). The selective corrosion was found in quite a few of welds in the carbon steel piping between a lean/rich exchanger and an amine regenerator. 316L stainless steel piping downstream the pressure let down valve and the regenerator showed no corrosion. HSAS level in the lean solution was below 0.2 %. Little or no increase in HSAS and organic acid level was found in the lean solution during recent operation. Constant H2S loading within the supplier’s recommendation was maintained. Thus, we have believed that raising the amine concentration from 35 wt% (7.5 mol%) to 50 wt% (13.1 mol%) in recent years resulted in the preferential corrosion at weld metals, even though it was within the recommended concentration. From the microstructural observation and chemical analysis, no apparent feature leading to the preferential corrosion at weld metal was found. Has anyone had similar experiences? I would like to know the cause of such preferential corrosion at the weld metal in the amine unit. Thank you Teppei SUZUKI

David, Thank you for helpful comment on our inquiry. Regarding your comment, all the concerned welds were PWHTed. We replaced the concerned piping with 304 SS. Extensive inspection program of carbon steel welds in other MDEA units is planed. Many thanks, Teppei SUZUKI