Comprehensive analysis of corrosion failure of sour water stripper in a coal chemical plant.

• The corrosion failure cause of sour water stripper was thoroughly investigated. • Identify Fe 4 [Fe(CN) 6 ] 3 and FeS as the predominant corrosion products. • The interaction of electrochemical corrosion and fluid erosion was the primary culprit for stripper failure. • Corrosion prevention and control countermeasures were developed based on a comprehensive analysis of the failure. In this paper, a study was performed on the corrosion failure of a sour water stripper in a coal chemical plant. Two field samples of 316L stainless steel taken from the most corroded areas were used for failure analysis. Instruments including ultrasonic thickness gauge, super-depth-of-field microscope (SDFM), scanning electron microscopy with energy dispersive spectrometer (SEM-EDS) and X-ray diffraction (XRD) were applied to test the samples. All test experiments were carried out under normal temperature and pressure working conditions, except for the vacuum environment of SEM-EDS. Besides, the chemical compositions of various process mediums were statistically analyzed. The results showed that the process medium composition fluctuated dramatically, and NH 3 -N content in the feed reached a maximum of 3750 mg/L, which was as much as 12.5 times the design value. The stripper wall was severely thinned, with the overall thickness reduced by more than 50 %. It was depicted that the typical morphology of corroded surfaces mainly consists of three regions of corrosion pit region, pore region and rough region. The corrosion products contained over 20 % nitrogen and a small amount of sulphur, identifying the phase composition as Fe 4 [Fe(CN) 6 ] 3 and FeS. The interaction of electrochemical corrosion and fluid erosion was the major reason for stripper failure. In addition, the extreme conditions resulting from the unstable operation further accelerated the corrosion process. To avoid future failures, optimizing the operational parameters of upstream units, reducing the operational load of the stripper, reselecting the inner wall material and adopting the advanced corrosion monitoring system were recommended. [ABSTRACT FROM AUTHOR]