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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.
EIS is one of the techniques which is frequently used for studying electrochemical reactions on a metal surface in an aqueous environment. However, one of the main challenges in using EIS is the interpretation of results. Various interpretation methods and their associated uncertainties lead to ambiguous outcomes and often end up with a biased analysis One of the methods frequently used is the so-called “equivalent electrical circuit” method which models the response of and electrochemical system by matching it to that of a combination of “analogous” electrical circuit components, such as resistors, inductors, capacitors, etc.
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Hydrofluoric acid (HF) is used as a catalyst in the alkylation process to react isobutane with olefin feeds to manufacture a high octane alkylate product used in gasoline blending. The HF catalyst is added in its anhydrous liquid form (< 400 ppmw H2O) but as it circulates in the reaction system, residual water in the Paper No. 17520 liquid hydrocarbon feed is absorbed by the acid such that the circulating reaction acid builds up a small percentage (0.5 to 2.0 mass%) of water. This water/HF mixture is also referred to as rich HF (RHF). In addition, the alkylation reactions also will generate fluorocarbons and acid soluble oils (ASOs).
Copper alloys such as copper nickel (CuNi) and Admiralty Brass (CuZn) are often successful material selections for seawater coolers. The copper alloys successes in these highly corrosive environments can be attributes to the ability of copper to form a protective scale, thus stopping corrosion of the material. On copper alloys in seawater, the protective scale formed comprises a mix of cuprous oxide (Cu2O), copper oxide (CuO) and copper hydroxy chlorides.