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strengthen casing resistance to burst pressures.

In the steel mill, each piece of casing is drifted, an internal measurement that

indicates the guaranteed minimum inside diameter of the joint. Drift diameter is

less than the calculated inside diameter and is an important consideration when

using downhole tools. Line pipe usually is not drifted unless this operation is

required and negotiated with the pipe manufacturer.

The maximum internal pressure for a particular casing string is given as the

minimum internal yield pressure in pounds per square inch (psi). If this pressure is

exceeded, the pipe will not retain its original form and rated strength. The well

pressure should never exceed the minimum internal yield of the innermost casing

string. Collapse resistance and internal yield pressure are critical factors when high

pressures migrate into the annulus between two casing strings. If this occurs, either

the inner casing string may collapse or the outer string may burst if the
corresponding pressure ratings are exceeded. The two most common occurrences

causing this type of problem are when high-pressure fluids or gases channel a poor
cement job or when high pressure bypasses the casing hanger packoff seal. When

casing is used to support a load in tension, the indicated minimum body yield
strength represents the maximum allowable load.

Line pipe normally is used for 30-in. and 20-in. casing strings and marine

riser rather than high-strength casing. Usually each casing string will be supported

at the mud line. One exception is the practice of hanging the 7-in. casing on a liner

hanger inside the 9%-in. casing. This reduces the amount of 7-in. casing required.

As an alternative to drilling the 36-in. diameter conductor casing, casing

may be jetted into place. This procedure establishes the 30-in. casing, permanent

guide structure, and the guidelines in one operation and does not necessarily

require the use of the temporary guide base. Soft-bottom conditions are

prerequisites to using the jetting method.

The 30-in. housing and 30-in. open-ended conductor is made up, run,

landed, and locked in the PGS, which sits on support beams as discussed
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