Page 228 - Corrosion Engineering Principles and Practice

202 C h a p t e r 6 R e c o g n i z i n g t h e F o r m s o f C o r r o s i o n 203

6.5.3 Fretting Corrosion
Fretting corrosion refers to corrosion damage at the asperities of
contact surfaces (Fig. 6.50). This damage is induced under load and in
the presence of repeated relative surface motion, as induced, for
example, by vibration. Pits or grooves and oxide debris characterize

(a)

(b)
FIGURE 6.49 (a) As-received appearance of boiler tube section with crack
failure. Note remnants of tack weld to strap on the back of the tube and
that the top of tube is marked for establishing orientation; (b) Close-up of
ID surface of failed tube section showing band of numerous parallel partial
through-wall cracks in line with through-wall crack (arrow). (2× original
magnification); (c) Photomicrograph showing as polished longitudinal
metallographic specimen through cracked area on failed tube section.
Cracks originate on ID surface. Note wedge- or needle-shaped, nonbranching
cracks typical of corrosion fatigue. Faint black line near bottom of photo is
an inclusion not related to the failure. (125× original magnification)
(Courtesy of Corrosion Testing Laboratories, Newark, Delaware, USA).