S-M Hu et aL/Case Studies in Engineering Failure Analysis 3(2015)52-61 西? physical expansion Fig. 2. Appearance of heat-exchange tube samples(a) failed tubes;(b) no trace of physical expansion on the tube end 1314011们110 Fig. 3. Schematic illustration about relative positions of 2* and 10" tubes.Fig. 2. Appearance of heat-exchange tube samples (a) failed tubes; (b) no trace of physical expansion on the tube ends. Fig. 3. Schematic illustration about relative positions of 2# and 10# tubes. 54 S.-M. Hu et al. / Case Studies in Engineering Failure Analysis 3 (2015) 52–61