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首页> 外文期刊>Corrosion: The Journal of Science and Engineering >Thermodynamics of the Corrosion of Alloy 625 Supercritical Water Oxidation Reactor Tubing in Ammoniacal Sulfate Solution
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Thermodynamics of the Corrosion of Alloy 625 Supercritical Water Oxidation Reactor Tubing in Ammoniacal Sulfate Solution

机译：Thermodynamics of the Corrosion of Alloy 625 Supercritical Water Oxidation Reactor Tubing in Ammoniacal Sulfate Solution

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摘要

During the process of supercritical water oxidation (SCWO), organic chemical streams are oxidized at temperatures and pressures in excess of 647 K and 221 bar. Due to high operating temperatures and pressures, severely corrosive environments often ensue and eventually lead to SCWO reactor tube failures. This case study looked at one such failure of Alloy 625 (61Ni-21.5Cr-9Mo UNS N06625) tubing, which occurred at the UBC SCWO pilot plant while treating a feed of waste-water containing approx 0.1 m.2,4 dinitrophenolate (C_6H_4N_2O_5), approx 0.25 m ammonium sulfate (NH_4_2SO_4, and approx 1.3 m free ammonia (NH_3). The feed pH was approximately 10 and therefore not expected to be corrosive; in fact, the tube failed when exposed to this feed (with oxygen) for a period of about 1 hat two sections subjected to temperatures in the 650 KAPPA to 655 KAPPA range. Through a detailed thermodynamic examination of the Ni-H_2O-NH_3 system at 373, 473, 573, and 653 KAPPA, as well as scanning electron microscopy (SEM) and energy-dispersive x-ray (EDX) analysis of the ruptured portions of tubing, it was found that the addition of ammonia and sulfate lead to solution acidification and NiO instability, which resulted in little protection for the alloy when subjected to the oxidative high-temperature medium. The alloy ultimately failed by transpas-sive dissolution.

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