Page 362 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

340 CONSEQUENCES OF CORROSION

Figure 5.14 Exfoliation corrosion on the inner surface of panel and door around a catch
location. (Reproduced by permission of the Society of Petroleum Engineers (20).)

Figure 5.15 Cross section through panel showing exfoliation corrosion (Reproduced by per-
mission of the Society of Petroleum Engineers (20).)

Fatigue crack propagation because of cyclic and uneven loading was also a contribut-
ing factor. The use of steels of higher toughness with intrinsic weathering resistance
has been advanced as a remedial measure.
The bridge is 150 m in length with three sections. The middle section is 70 m in
length sandwiched between four columns that support tie rods. The other two sections
are 40 m in length. There are 32 tie bars, which are 90 mm in diameter. The bars are
attached to several columns, four overhead columns that rise above and eight columns
that drop below to the base of the bridge. Figure 5.18 shows a general view of the
bridge. Figure 5.19 shows a close-up view of the exposed tie rods and corrosion of
the threaded portions. Figure 5.20 is a close-up view of an upright column with a
missing tie rod.
Figure 5.21 is a close-up view of tie rods showing corroded threads, nuts, and
washer.
Metallographic examination showed the cracks initiated at the first thread immedi-
ately adjacent to the nut. Beach marks were present indicating the presence of fatigue.