972 Gong, Yang, Yao and Yang Materials and Corrosion 2011.62 Ne existed in the left part, and their average depth was about 0.04 mm peculiar shape of heart was also detected, whose diameter was with largest value of 0.06 mm for some specific one, seen from the only 0. 2 mm. It should be particularly pointed out that a localized 3D profile image in Fig. 6d. As for the right part, pits with pit with diameter of only 0.06 mm and depth of just 0.02mm diameters around 0. 1 mm were also detected( Fig. 6e), while their existed in the midst of the"heart'as well(Fig. 7d). It could be average and largest depths were, respectively, 0.02 and 0.04 mm, inferred that the two concaves were actually the morphologies in seen in Fig. 6f. To sum up the morphologies of the peanut-like two different growth stages of an eventually large and deep concave, from Fig 6a-f, it can be inferred that far smaller pits with concave just like the"peanut: the heart-like concave in Fig. 7c similar diameters(about 0. 1 mm) and depths(about 0.05 mm) was in the initial stage, while the concave in Fig. 7a was in the were prone to be connected with each other to engender larger and mid-term stage deeper concaves, while connection of two neighboring concaves was the cause of formation of the"peanut. 2.4 SEM and EDS analysis Besides the most distinct defect, i. e, the peanut-like concave another two minor defects were also observed on the failure pipe In order to thoroughly study the formation causes of the peanut surface. Figure 7a and b present the morphologies of a concave like concave, SEM was employed to observe its microscopic with diameter of approximately 0.8 mm and depth of 0.04 mm. morphologies. Figure 8a displays the total morphology. After Meanwhile, as is shown in Fig. 7c, an even smaller concave with a magnification, randomly and densely distributed white spots 9) 8. SEM of the peanut-like concave bottom surface: (a)total morphology, (b)densely distributed spots, (c)magnification of spots, (d)three oring"coins"with cavities, (e)three neighboring"coins"with cracks, ()coin"with both a cavity and a crack, (g) coral structure, and (h) of cracks o 2011 WILEY-VCH Verlag Gmbh Co KGaA, Weinheim www.matcorr.comexisted in the left part, and their average depth was about 0.04 mm with largest value of 0.06 mm for some specific one, seen from the 3D profile image in Fig. 6d. As for the right part, pits with diameters around 0.1 mm were also detected (Fig. 6e), while their average and largest depths were, respectively, 0.02 and 0.04 mm, seen in Fig. 6f. To sum up the morphologies of the peanut-like concave, from Fig. 6a–f, it can be inferred that far smaller pits with similar diameters (about 0.1 mm) and depths (about 0.05 mm) were prone to be connected with each other to engender larger and deeper concaves, while connection of two neighboring concaves was the cause of formation of the ‘‘peanut.’’ Besides the most distinct defect, i.e., the peanut-like concave, another two minor defects were also observed on the failure pipe surface. Figure 7a and b present the morphologies of a concave with diameter of approximately 0.8 mm and depth of 0.04 mm. Meanwhile, as is shown in Fig. 7c, an even smaller concave with a peculiar shape of heart was also detected, whose diameter was only 0.2 mm. It should be particularly pointed out that a localized pit with diameter of only 0.06 mm and depth of just 0.02 mm existed in the midst of the ‘‘heart’’ as well (Fig. 7d). It could be inferred that the two concaves were actually the morphologies in two different growth stages of an eventually large and deep concave just like the ‘‘peanut’’: the heart-like concave in Fig. 7c was in the initial stage, while the concave in Fig. 7a was in the mid-term stage. 2.4 SEM and EDS analysis In order to thoroughly study the formation causes of the peanut￾like concave, SEM was employed to observe its microscopic morphologies. Figure 8a displays the total morphology. After magnification, randomly and densely distributed white spots 972 Gong, Yang, Yao and Yang Materials and Corrosion 2011, 62, No. 10 Figure 8. SEM of the peanut-like concave bottom surface: (a) total morphology, (b) densely distributed spots, (c) magnification of spots, (d) three neighboring ‘‘coins’’ with cavities, (e) three neighboring ‘‘coins’’ with cracks, (f) ‘‘coin’’ with both a cavity and a crack, (g) coral structure, and (h) group of cracks
2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.matcorr.com