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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.
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.
H2S corrosion, also known as sour corrosion, is one of the most researched types of metal degradation in oil and gas transmission pipelines requiring a wide range of environmental conditions and detailed surface analysis techniques. This is because localized or pitting corrosion is known to be the main type of corrosion failure in sour environments which caused 12% of all oilfield corrosion incidents according to a report from 1996. Therefore, control and reduction of this type of corrosion could prevent such failures in oil and gas industries, and significantly enhance asset integrity while reducing maintenance costs as well as eliminating environmental damage.
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Caustic stress corrosion cracking (SCC) is known to occur in carbon steels under tensile stress and exposure to caustic solutions from 115°F to boiling temperatures. Alternating wet and dry conditions tend to increase SCC susceptibility. Localized overheating of the metal, such as solar radiation, heat tracing, steam outs and excursions should also be considered. Caustic SCC was first reported in 1980 when the top of a continuous kraft digester vessel blew off in Pine Hill, Alabama. It was found that the tensile residual stresses present in non-stress relieved carbon steel weld seams and the corrosive environment (caustic) were responsible for the cracking
The success of corrosion protective coating systems relies, to a great extent, on the coatings’ inherent barrier properties. This barrier property signifies the coating’s ability to withstand the permeation of sea water and oxygen, thus minimizing corrosion of the underlying metal. While various additives or pigments can promote the barrier property of coatings, one of the most common pigments is aluminum flakes [1-4].The idea behind their use is simple, and essentially relies on having the aluminum flakes in the coating oriented parallel to the underlying substrate. With them in place, the pathways for sea water and oxygen effectively increase, thus preventing the progression of corrosion. However, while having been employed in numerous coating formulations for many years, the evidence for the success of aluminum flakes as barrier pigments is still lacking.