Definition Of Drill Pipe Collapse Pressure
The Drill Pipe may at certain times be subjected to external pressure which is higher than the internal pressure. This condition usually occurs during drill stem testing and may collapse the drill pipe.
The differential pressure (external pressure minus internal pressure) required to produce collapse is calculated for various sizes and grades of new and used drill pipe and is presented in API RP7G Tables (3), (5) and (7).
Collapse pressure ratings for new drill pipe are presented in Hand Books Tables. The tabulated collapse pressure ratings must be divided by a safety factor in order to establish the allowable collapse pressure.
- Pc = theoretical collapse pressure rating from tables, psi
- Pac = allowable collapse pressure, psi
- S.F. = safety factor = 1.1 to 1.2
If the drill pipe is subjected to an axial tensile load, the collapse pressure ratings from the tables must be derated. The effective collapse corrected for tension load can be calculated from the equation,