S-M. Hu et al/Case Studies in Engineering Failure Analysis 3(2015)52-61 C Fig. 7. Composition analysis of the micro-areas on the 2 tube(a)sites a and B at outer wall; (b)site C at inner wall. vulnerable sites and endure localized whirlpool erosion. while within a severe corroded area at the inner wall( Fig. 6(b)). micro cracking just initiated from the pit, then propagated along corrosion layers which would definitely lead to serious failure in a long term. Energy disperse spectroscope(eds)analyzed chemical compositions of micro sites at both tube walls(Fig. 7). To our urprise, existences of impurity elements s and cl in the outer and inner wall were found respectively along with corrosion products(Table 3). The significant excess contents of them were detected with approximately 2.0%(wt%)in certain sites, far more than the specified contents of material (less than 0.01%) 2.3.2. 10" heat-exchange tube %o As Fig8 depicts, the ellipse pit located at the inner wall of 10* heat-exchange tube is found with maximum depth of 4 um measured by 3-D synthesis technology, up to 25% thickness of the tube wall (original value is 2 mm). Obviously, the localized degradation is rather threatening Table EDS results of micro-areas at 2 tube(wt %) Site a 8858 182 2.37vulnerable sites and endure localized whirlpool erosion. While within a severe corroded area at the inner wall (Fig. 6(b)), micro cracking just initiated from the pit, then propagated along corrosion layers which would definitely lead to serious failure in a long term. Energy disperse spectroscope (EDS) analyzed chemical compositions of micro sites at both tube walls (Fig. 7). To our surprise, existences of impurity elements S and Cl in the outer and inner wall were found respectively along with corrosion products (Table 3). The significant excess contents of them were detected with approximately 2.0% (wt.%) in certain sites, far more than the specified contents of material (less than 0.01%). 2.3.2. 10# heat-exchange tube As Fig. 8 depicts, the ellipse pit located at the inner wall of 10# heat-exchange tube is found with maximum depth of 494 mm measured by 3-D synthesis technology, up to 25% thickness of the tube wall (original value is 2 mm). Obviously, the localized degradation is rather threatening. Fig. 7. Composition analysis of the micro-areas on the 2# tube (a) sites A and B at outer wall; (b) site C at inner wall. Table 3 EDS results of micro-areas at 2# tube (wt.%). Element C O Cl S Fe Site A 1.08 5.66 0.49 1.97 88.58 Site B 1.82 13.66 0.65 2.05 78.89 Site C 2.37 7.54 1.77 1.01 83.43 S.-M. Hu et al. / Case Studies in Engineering Failure Analysis 3 (2015) 52–61 57