When there is a large pressure differential across the CT wall, especially when combined with a large axial force, there is a risk of a CT failure (burst, collapse or break). Typically the greatest risk of burst or collapse in a CT job occurs at the wellhead, either above or below the stripper. Mathematical models are used to determine the pressure and force limits prior to performing a job to make sure that the operation stays within safe working limits.

A widely accepted model used for establishing these types of limits is the von Mises incipient yield criterion. It combines the various stresses to determine the force and pressure limits. Helical buckling, maximum expected pressures, diameter growth, and torque can all be included in this criteria.

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