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Failure Analysis Of Hydrotested 12-Inch Type 304 SS Pipe Sections

Pre-commissioning hydrostatic testing of pipelines and the resulting corrosion (MIC) issues are often linked to test water quality, as well as post-test cleaning operations. In a 1998 study, it was reported that localized corrosion (pitting/crevice corrosion) accounted for 20% of failures in the chemical process industry with an estimated one half of those being MIC failures. Identification of MIC failures is not straightforward. Common characteristic features such as pit clustering, “tunneling” of pits, tuberculation, high microbiological counts, presence of sulfides (in the case of sulfate reducing bacteria (SRB)) and preferential weld attack have been used to anecdotally pinpoint field failures towards MIC.

Product Number: 51322-17852-SG
Author: Sudhakar Mahajanam, Chris Miller, Cody Robinson, Scott Harding, Amilcar Oberto
Publication Date: 2022
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Hydrostatic testing of pipelines is an important step prior to commissioning. In this paper, we discuss two case studies wherein leaks were detected during hydrotesting of a newly constructed 12-inch pipeline at a client site. The first failure occurred in the body of a pipe segment coated with fusion bonded epoxy. The second failure occurred at a girth weld of a different pipe segment in the same line, which had been coated with an abrasion resistant outer wrap. Visual examination and stereomicroscopy revealed the presence of pits adjacent to the leaks. Scanning electron microscopy, energy dispersive x-ray spectroscopy, bacteria culture testing and metallography confirmed that the pitting occurred as a result of internal microbiologically induced corrosion.

Hydrostatic testing of pipelines is an important step prior to commissioning. In this paper, we discuss two case studies wherein leaks were detected during hydrotesting of a newly constructed 12-inch pipeline at a client site. The first failure occurred in the body of a pipe segment coated with fusion bonded epoxy. The second failure occurred at a girth weld of a different pipe segment in the same line, which had been coated with an abrasion resistant outer wrap. Visual examination and stereomicroscopy revealed the presence of pits adjacent to the leaks. Scanning electron microscopy, energy dispersive x-ray spectroscopy, bacteria culture testing and metallography confirmed that the pitting occurred as a result of internal microbiologically induced corrosion.