Thermally sprayed aluminium (TSA) is an effective coating that has been used increasingly for the protection of carbon steel offshore structures, topside equipment and flowlines/pipelines exposed to both marine atmospheres and immersion conditions. |
In this paper the effectiveness of TSA coatings on 25%Cr duplex stainless steel (SDSS) in preventing localised corrosion, such as pitting and crevice corrosion has been investigated, for subsea applications. Welded 25%Cr SDSS (coated and uncoated) with and without defects, and surfaces coated with epoxy paint were also examined. Pitting and crevice corrosion tests, on welded 25Cr SDSS specimens with and without TSA/epoxy coatings, were conducted in recirculated, aerated, artificial seawater at 90°C for 90 days. The tests were carried out at both the free corrosion potentials and an applied cathodic potential (CP) of -1100mVSCE using a potentiostat. The acidity (pH) of the test solution was monitored daily and adjusted to between 7.5 and 8.1, using dilute HCl solution or dilute NaOH, depending on the pH of the solution measured during the test.
The test results demonstrated that TSA provided sufficient protection to welded 25%Cr SDSS to prevent pitting and crevice corrosion in artificial seawater at 90°C, even when 10mm diameter coating defect exposing the underlying steel was present.