F-f. Chen et aL/ Engineering Failure Analysis 37(2014)42-52 ax312431p Heit288528 Im width1:219205mwdh2:215869m Lax 420.8/lum soMt3747/mdh1:219242mdh:215.96 Fig 8. Structure of the pits on tubes 052003-17, 18 and depth measurement(a)appearance of pit a(b)appearance of pit B(c)3-D contour map of pit A(d) 3-D contour map of pit B(e)depth of pit A(f) depth of pit B. shown in Fig 8. The depth of pit A is 0.288 mm, so the thinning rate of the tube wall is 41.14%. And the depth of pit e s To evaluate the extent of erosion and cavitation corrosion, we measured the depth of two pits by stereo microsco 0.377 mm which means that thickness of the tube wall has declined by 53.85% From these figures we can conclude that cav- itation corrosion is rather threatening. The depth of a lot of pits exceeds 40% of the thickness of the tube wall and the depth of some even reaches 60%. It is highly possible that perforation will occur if the tubes continue to be used, which will endan- ger the safety of both machines and personnel, so the tubes have to be replaced as soon as possibleTo evaluate the extent of erosion and cavitation corrosion, we measured the depth of two pits by stereo microscope, shown in Fig. 8. The depth of pit A is 0.288 mm, so the thinning rate of the tube wall is 41.14%. And the depth of pit B is 0.377 mm which means that thickness of the tube wall has declined by 53.85%. From these figures we can conclude that cav￾itation corrosion is rather threatening. The depth of a lot of pits exceeds 40% of the thickness of the tube wall and the depth of some even reaches 60%. It is highly possible that perforation will occur if the tubes continue to be used, which will endan￾ger the safety of both machines and personnel, so the tubes have to be replaced as soon as possible. Fig. 8. Structure of the pits on tubes 052003-17, 18 and depth measurement (a) appearance of pit A (b) appearance of pit B (c) 3-D contour map of pit A (d) 3-D contour map of pit B (e) depth of pit A (f) depth of pit B. 48 F.-J. Chen et al. / Engineering Failure Analysis 37 (2014) 42–52