Understanding API ICP653 Reading 7-Worksheet-04 Part1

C. Tank Roofs/Support Structure
Should corrosion be found in the upper shell, the potential for a like loss
should be suspected on the internal roof plates, the rafter/structural members
and the roof support columns. These specific areas are exposed to the same
environment as the upper, non-wetted shell surface. If only the two (2) lower
shell rings show accelerated corrosion, closely check the roof support
columns. Problems to the same degree and elevation may be present.
4.3.5 Distortions
4.3.5.1 Includes out-of-roundness, buckled areas, flat spots, peaking and
banding at welded joints.
4.3.5.2 Potential causes:
a. Foundation settlement
b. Over or under-pressuring
c. High winds
d. Poor shell fabrication/erection
e. Repair Techniques
Charlie Chong/ Fion Zhang