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07196 Pitting Corrosion Problems of Stainless Steels in a PTA Plant

Product Number: 51300-07196-SG
ISBN: 07196 2007 CP
Author: Oluwatoyin Ashiru and Abdullah Al-Refaie
Publication Date: 2007
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Severe pitting corrosion problems occurred in a Purified Terephthalic Acid (PTA) production plant. The materials of construction of the various vessels, columns, and piping that are of concern are 316L and 2205-Duplex stainless steels. The process stream consists of acetic acid solvent, para-xylene, and catalyst (Br-, Co++, and Mn++) at high temperature. In some instances, the corrosion pits developed into perforations through piping wall in units made of 316L-stainless steel which led to shutdowns. Failure analysis was undertaken to investigate the cause of the pitting corrosion in the plant. Dye penetrant NDT method was used to locate the pitted regions of the PTA plant. Compositional analyses of the deposits that were obtained from the inner surface of the vessels and piping systems were carried out using the EDS, XRF and XRD techniques. The objective of the analysis was to identify the elemental constituent of the deposits that were removed from various vulnerable locations of the plant. Scanning electron microscopy revealed the nature and extent of pits and pinhole on samples that were cut off from severely pitted piping sections that were replaced in the plant. The study showed that the pitting corrosion was aggravated by process upsets and the presence of some aggressive contaminants. This paper discusses the failure analysis investigation. It also highlights the remedial measures that were successfully implemented to avert the reoccurrence of the problem in the plant.
Severe pitting corrosion problems occurred in a Purified Terephthalic Acid (PTA) production plant. The materials of construction of the various vessels, columns, and piping that are of concern are 316L and 2205-Duplex stainless steels. The process stream consists of acetic acid solvent, para-xylene, and catalyst (Br-, Co++, and Mn++) at high temperature. In some instances, the corrosion pits developed into perforations through piping wall in units made of 316L-stainless steel which led to shutdowns. Failure analysis was undertaken to investigate the cause of the pitting corrosion in the plant. Dye penetrant NDT method was used to locate the pitted regions of the PTA plant. Compositional analyses of the deposits that were obtained from the inner surface of the vessels and piping systems were carried out using the EDS, XRF and XRD techniques. The objective of the analysis was to identify the elemental constituent of the deposits that were removed from various vulnerable locations of the plant. Scanning electron microscopy revealed the nature and extent of pits and pinhole on samples that were cut off from severely pitted piping sections that were replaced in the plant. The study showed that the pitting corrosion was aggravated by process upsets and the presence of some aggressive contaminants. This paper discusses the failure analysis investigation. It also highlights the remedial measures that were successfully implemented to avert the reoccurrence of the problem in the plant.
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