F-f. Chen et aL/ Engineering Failure Analysis 37(2014)29-41 a -3 mm- b Fig. 12. Microscopic morphology of the wear zone in tube 1B160012-14 (a) irregularly curved crack(b)deposit morphology 4. 2. Eccentric contact wear and three-body contact wear Let us analyze the appearance of the wear zone of the first failure case. Firstly, the wear zone was a band around the tube cause of gravity induced contact between the tube and the internal boring. But as the wear zone was also distributed else- where, we might think that it was caused by the abrasive wear of the corrosion products that had sagged into the internal orings because of gravity. Then the second point must be noted. The wear extent was different in the forward direction and the backward direction of the tubes. If the wear was only caused by the corrosion products, the wear extent should uniform in these two directions. Therefore, there must be processing defects on the wall of the internal borings. Only the unevenly distributed negative deviation of the diameter of the internal borings could cause this special selective concen- rated wear phenomenon and the localized offset of the tube resulting from the grindings depositing in the internal borings aggravated the wear extent. The thinning process was like this: under the undulation of steam and water during operation, irregular relative vibration of the tubes and the internal borings caused the contact wear between them and with the pro- cessing defects distributed unevenly in the internal borings, eccentric wear occurred in different positions around the tubes and to various extents. Meanwhile, the corrosion products on the vertical support plates kept sagging into the internal bor- ings because of gravity. The position change of the corrosion products and grindings led to the offset of the tube. The result ras the three body contact wear between the tube, the grindings and corrosion products, and the internal boring In con- clusion, the localized wall thinning of titanium tube 1B134027-1 was rooted in eccentric contact wear ascribed to the poor processing of the internal borings and the corrosion products and grindings. Then it comes to the second failure case. The main wear morphology of titanium tube 1B160012-14 was similar with tube 1B134027-1, i.e. wear at different positions around the tube and to various extents. However, there was an irregular S- shaped furrow crack with a circumferential length of 10 mm.4.2. Eccentric contact wear and three-body contact wear Let us analyze the appearance of the wear zone of the first failure case. Firstly, the wear zone was a band around the tube instead of just at the bottom. It could be easily understood that wear was supposed to happen at the bottom of the tube be￾cause of gravity induced contact between the tube and the internal boring. But as the wear zone was also distributed else￾where, we might think that it was caused by the abrasive wear of the corrosion products that had sagged into the internal borings because of gravity. Then the second point must be noted. The wear extent was different in the forward direction and the backward direction of the tubes. If the wear was only caused by the corrosion products, the wear extent should be uniform in these two directions. Therefore, there must be processing defects on the wall of the internal borings. Only the unevenly distributed negative deviation of the diameter of the internal borings could cause this special selective concen￾trated wear phenomenon. And the localized offset of the tube resulting from the grindings depositing in the internal borings aggravated the wear extent. The thinning process was like this: under the undulation of steam and water during operation, irregular relative vibration of the tubes and the internal borings caused the contact wear between them and with the pro￾cessing defects distributed unevenly in the internal borings, eccentric wear occurred in different positions around the tubes and to various extents. Meanwhile, the corrosion products on the vertical support plates kept sagging into the internal bor￾ings because of gravity. The position change of the corrosion products and grindings led to the offset of the tube. The result was the three body contact wear between the tube, the grindings and corrosion products, and the internal boring. In con￾clusion, the localized wall thinning of titanium tube 1B134027-1 was rooted in eccentric contact wear ascribed to the poor processing of the internal borings and the corrosion products and grindings. Then it comes to the second failure case. The main wear morphology of titanium tube 1B160012-14 was similar with tube 1B134027-1, i.e. wear at different positions around the tube and to various extents. However, there was an irregular S￾shaped furrow crack with a circumferential length of 10 mm. Fig. 12. Microscopic morphology of the wear zone in tube 1B160012-14 (a) irregularly curved crack (b) deposit morphology. 38 F.-J. Chen et al. / Engineering Failure Analysis 37 (2014) 29–41