2. Design Factors
The axial load on the casing can be either tensile or compressive, depending on the operating conditions.

3. Design Factors
The force Ften tending to pull apart the pipe is resisted by the stregth of the pipe walls, which exert a counterforce F2.
Where syield is the minimum yield strength and As is the cross- sectional area of steel. Thus, the pipe-body strength:
Equation 2 is used to calculate the minimum force that would be expected to cause permanent deformation of the pipe.
For the body only

4. Design Factors Burst
The casing will experience a net burst loading if the internal radial load exceeds
the external radial load

5. Design Factors Burst
If casing is subjected to internal pressure higher than external, it is said that casing is exposed to burst pressure. Burst pressure conditions occur during well control operation or squeeze cementing.
Equation (4) is used to calculate the internal pressure at which the tangential stress at the inner wall of the pipe reaches the yield strength of the material. The factor represents the allowable manufactruing tolerance of % on wall thickness.
Because a burst pressure failure will not occur until after the stress exceeds the ultimate tensile strength, using a yield strength criterion as a measure of burst strength is an inherently conservative assumption.

6. Design Factor Burst
Let q be small enough

7. Design Factors Burst 3
where ss is the nominal steel strength. Equation (3) is used only for thin-wall casing. In drilling application, it is suggested that one should use Barlow’s equation to calculate Pbr for thick-wall casing. 4
API recommends use of this equation with wall thickness rounded to the nearest 0.001’’ and the results rounded to the nearest 10 psi.

8. Design Factors Burst Example
Compute the burst-pressure rating for 20’’, K-55 casing with a nominal wall thickness of 0.635’’ and a nominal weight per foot of 133 lbf/ft
Solution:
Rounded to the nearest 10 psi:

9. Design Factor Collapse
The casing will experience a net collapse loading if the external radial load exceeds the internal radial load. The greatest collapse load on the casing will occur if the casing is evacuated (empty) for any reason.