MIC Failure of Hydrotested Type 304 SS Pipelines

Hydrostatic testing of pipelines is an important step prior to commissioning. This article discusses two leaks on a newly constructed 305 mm (12 in) pipeline during hydrotesting. The first failure occurred in a pipe body 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 from internal microbiologically induced corrosion (MIC).