ABSTRACT
This paper presents the findings of an investigation that was carried out to determine the root cause of the premature failure of Ni-coated carbon steel fittings on the water injection composite piping system installed at an oil production facility in Western Canada. The facility had been in operation since 2011 without major corrosion issues. Many of the Ni-coated fittings, which are expected to have a service life of 20 years, started to fail (developed leaks) unexpectedly after about 4 years. The core structure of composite pipe is a high-density polyethylene (HDPE) inner pipe, a middle layer of high-strength dry fiberglass, and a protective thermoplastic outer jacket. The interconnecting fittings are made of carbon steel coated with a thin, ~40 micron (1.5 mil) layer of Nickel.
The failure investigation results (bacteria, water, and corrosion product analyses as well as photographic documentation of the corrosion damage morphology) provided quite convincing evidence that the premature failures observed in the fittings occurred as a result of MIC (Microbiologically Influenced Corrosion) due to the presence of high counts of SRB (sulfate reducing bacteria) and APB (acid producing bacteria) in the system. Of course, under-deposit corrosion, crevice type corrosion and galvanic corrosion may also have occurred in conjunction with MIC. It is also to be noted that if the integrity of the thin Ni coating is compromised in any way, such as pitting damage due to MIC, or manufacturing flaws, accelerated galvanic corrosion attack of the carbon steel substrate would be expected at that location, since Ni is cathodic to carbon steel.
