The exploration and exploitation of deep seawater presents promising prospects for many industries. Hence the use of reliable materials resistant to corrosion is required.In natural seawater many parameters can influence the kinetics of corrosion such as: temperature oxygen content biofilm and fouling activity flow rates and hydrostatic pressure.For passive material such as Cr Ni Mo stainless steels and nickel-based alloys the specificity of the above parameters in deep sea environment might have an impact on both initiation and propagation phases of localized corrosion e.g. pitting and crevice corrosion. Currently there are still many uncertainties on the corrosion behavior of these materials in deep seawater; Actually the results obtained in laboratory cannot be extrapolated to deep seawater since the levels measured in deep sea of some of these influential parameters weren’t reproduced accurately in these experimental studies. In parallel field data on the corrosion behavior in deep seawater is rather scarce especially for recent materials such as Lean Duplex Stainless Steel. For example phenomena that are induced by biofilm formation and can increase the localized corrosion risk such as the so-called potential ennoblement i.e. an increase in the open circuit potential (OCP) by about + 0.350 V and the increase of the cathodic current are not yet well documented.In this study 13-Cr Stainless Steel Austenitic Lean Duplex Duplex Super Duplex Super Austenitic Hyper Duplex Stainless Steels and Nickel based alloys were exposed during 11 months at 1020 and 2020 m water depth in the Atlantic Ocean. For comparison non-resistant materials such as carbon steel and 13-Cr were also exposed. The susceptibility to pitting and to crevice corrosion were assessed. PVDF crevice gaskets at two different pressures namely 3 and 20 N/mm² were used to assess the crevice corrosion. Potential monitoring was performed in-situ in order to characterize the formation of the biofilm at the material surface. At each exposure depth the environment was characterized using environmental sensors e.g. temperature flow velocity dissolved oxygen salinity and biofilm sensors.The obtained results allow i) ranking the passive material in terms of corrosion resistance to pitting and crevice in deep water at 4°C ii) comparing biofilm activity and kinetics of corrosion at 1020 and 2020 m depth.
Recently several localized corrosion and cracking failures happened to API 5CT Grade C110 tubing in high-density formate completion fluid at high temperature because of the leakage of CO2 and the mechanical damage on the tubing surface. In this paper the hydrochemical simulation software is used to calculate the needed content of pH buffer. The corrosion behavior of C110 tubing is investigated by autoclave scanning electron microscopy (SEM) energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The results show that 1% Na2CO3 and 1%NaHCO3 can maintain the pH of formate completion fluid with the mix of 3 MPa CO2 up to 6.35 which means CO2 corrosion restrained effectively. The simulated experiments show that the general corrosion rate of C110 tubing decreases from 0.49 mm/a to 0.24 mm/a and the C110 tubing have little localized corrosion and cracking susceptibility in formate completion fluid when buffered with 1% Na2CO3 and 1%NaHCO3. The results of XRD and SEM-EDS indicate that the pH buffer is helpful to general compact and effective FeCO3 corrosion product film.