Collapse happens when differential between external and internal pressure exceeds a collapse rating pressure of material. This situation can happen due to several cases, such as pressure testing in annulus, trapped pressure in the annulus or well fully evacuated with gas, etc.
Figure 1 – Collapse Pressure Diagram
Collapse pressure equations come from experiments from test specimens and the full details can be found in API Bulleting 5C3, Formulas and Calculations for Casing, Tubing, Drillpipe, and Line Pipe Properties. From the experimental results, there are 4 collapse regimes based on Diameter of pipe/Wall thickness (D/t) and yield strength of material which are yield strength collapse, plastic collapse, transitional collapse and elastic collapse. Continue reading
