Issue 20

A. Borruto et alii, Frattura ed Integrità Strutturale, 20 (2012) 22-31; DOI: 10.3221/IGF-ESIS.20.03 28 Figure 16 : SEM analysis. External pipe section scale – 350 X. Figure 17 : SEM analysis. Magnification of a detail from Fig. 16. – 1300 X. A map has been executed on a section of the scale (fig. 18). The map shows sulphur presence (sulphur compounds) at the interface between compressed and porous scale with a build-up immediately behind the compacted scale. A major Cr concentration appears in the penetrated area, while the oxygen is diffused. Figure 18 : SEM analysis. Map of corrosion crust – 800 X. The pipe surface scale was examined (Fig. 7 – sample 2 section): micrographic analyses have been performed on particles removed from the surface scale. The following figures show two different crust types. The first one (Fig. 19) appears to be non homogeneous and porous. Channels rich in chlorine and sulphur formed by pressured gas are visible (Fig. 20), EDS analysis (Tab. 3). The second crust type (Fig. 21) seems to be compacted, with sulphuric and chloride compounds present, as the EDS analysis detected (Tab. 4).