Fig. 14. FT-IR spectra for the various samples of corrosion product taken from piles showing no evidence of ALWC (bottom three traces) and those showing the typical red–black deposit associated with ALWC (top two traces). The top two traces show intense peaks at wavenumbers associated with the presence of SRB. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)Figure optionsDownload full-size imageDownload as PowerPoint slide
The specimens cut from the tubular piles were examined in a scanning Epoxomicin microscope using EDS to characterise the corrosion product associated with the pitting. They were then cleaned to reveal the steel surface (Fig. 15) and the depth of typical pits measured using an Olympus LEXT confocal laser scanning microscope (CLSM). EDS spectra acquired from pits in the specimens taken from piles showing evidence of ALWC typically exhibited a sulphur peak, which was absent from piles which did not show the red and black corrosion product on their surface. Pits were measured by CLSM as having maximum depths of around 0.2 mm, indicating an annual rate of perhaps 0.4 mm which is hydrostatic skeleton in the expected range for ALWC and well above the anticipated rates of corrosion for unprotected steel pilings in a marine environment (Table 1).