Understanding API ICP653 Reading 7-Worksheet-04 Part1

B.2 Types of Settlement
B.2.1 Elevation measurements around the circumference and across the tank
diameter are the best method for evaluating shell and bottom settlement
problems. Local depressions may require other techniques.
B.2.2 Shell Settlement Evaluation
Tank settlement results from either one or a combination of the following
three (3) settlement components:
B.2.2.1 Uniform settlement. May vary in magnitude, depending on soil
characteristics. It is the least severe or threatening settlement problem. It
does not introduce stress in tank structure, but does present a potential
problem for piping, nozzles and attachments.
B.2.2.2 Planar Tilt (rigid body tilting). Rotates the tank in a tilted plane. This tilt
will cause an increase in the liquid level and an increase in the shell hoop*
stress. Can also cause binding of peripheral seals in a floating roof and inhibit
roof travel. This may be visible in the form of elongation of top shell ring in
floating roof tanks. Can affect tank nozzles that have piping attached to them.
Charlie Chong/ Fion Zhang