S-M. Hu et al/Case Studies in Engineering Failure Analysis 3(2015)52-61 Table 2 Chemical composition of 2" and 10 failed tubes (wt%). Element Si 0016 0.028 GB9948-200610·15l007-0.130.17-0.3 35-0.65 <0.020 <0.20 t Fig 4 Metallographic structures of tubes in circumferential direction 500x pit Fig. 5. Appearance of 2" tube imaged by stereo microscope(a)outer wall; (b) inner wall.Table 2 Chemical composition of 2# and 10# failed tubes (wt.%). Element C Si Mn S P Cr Ni Cu 2# 0.11 0.27 0.44 0.004 0.019 0.027 0.008 0.015 10# 0.12 0.26 0.47 0.008 0.016 0.028 0.008 0.019 GB 9948-2006 10* [15] 0.07–0.13 0.17–0.37 0.35–0.65 0.020 0.030 0.15 0.25 0.20 Fig. 4. Metallographic structures of tubes in circumferential direction 500. Fig. 5. Appearance of 2# tube imaged by stereo microscope (a) outer wall; (b) inner wall. S.-M. Hu et al. / Case Studies in Engineering Failure Analysis 3 (2015) 52–61 55