Abstract
During a series of test campaigns for CO2 capture using monoethanolamine (MEA) at the Technology Centre Mongstad (TCM), a failure occurred in the reboiler of the amine plant caused by severe damage to the plate heat exchanger made of AISI 316L Stainless Steel. Considerable material loss (ca. 200-250 µm reduction in thickness) including two perforations led to leakage between the solvent and heating fluid sides. Preliminary investigations by TCM revealed that during a test period when oxygen scavenger was injected, a rise in the concentration of metal cations occurred; it was considered very likely that the failure was related to this “scavenger period”. A collaboration was subsequently started with the Institute for Energy Technology (IFE) to assess the failure mode of the reboiler plates. As reported earlier elsewhere, three plausible hypotheses were identified: the “erosion” hypothesis considers that erosion alone is sufficient to cause the failure by damaging the passive film from the stainless-steel surface and allowing corrosion attacks to develop even under normal operation conditions (or abrading the steel itself); the “erosion and enhanced corrosivity” hypothesis considers that erosion could remove passivity, but the specific chemistry in the scavenger period is also required to prevent rapid re-passivation and to sustain severe corrosion; the “enhanced corrosivity” hypothesis implies that the specific chemistry in the scavenger period can cause depassivation and sustain a considerably high corrosion rate, even in the absence of erosion. This paper presents the results of laboratory testing to validate the erosion and enhanced corrosivity hypothesis. An experimental setup based on the radial impeller concept was developed around a commercial glass autoclave. Experiments were conducted with used solvent from the TCM plant, simulating i.a. different plant conditions: anoxic rich MEA with an excess of oxygen scavenger and oxygenated rich MEA with scavenger and an excess of oxygen. Significant damage of the stainless-steel specimens occurred with erosive action in a used rich solvent with excess oxygen scavenger (i.e. anoxic conditions). The observations agree with damage of passive film, allowing activation of the corrosion process. The surface likely fails to re-passivate in an anoxic environment. The same mechanism is not sustained in an oxygenated environment where the surface can re-passivate. The results obtained suggest that the erosion and enhanced corrosivity hypothesis is valid and plausible. This mechanism may be the actual failure mode in the TCM reboiler.
