Calculation of the Collapse Rating of Individual Pipe Joints for OCTG Casing and Tubing

Commonly accepted procedures in the industry for calculating high collapse ratings of OCTG casing and tubing are described in Annexes G and H of API 5C3. Both approaches are limited to the analysis of historical data. Moreover, modern pipe dimensional mapping during production allows to provide properties specific to each individual pipe joint that were impossible before. In this paper, a method for calculating the collapse rating of each individual pipe produced is presented. In the developed method, the uncertainties on the quantification of each parameter are accounted for and the collapse rating of individual pipes is calculated to a pre-defined target reliability level (TRL). The statistical approach used to arrive at the collapse rating for a pipe joint is explained, and the consistency with the conventional method based on sample data is demonstrated. The developed method, therefore, enables practices long expected by the Oil & Gas industry, such as the clustering of the produced pipes based on their collapse performance. This allows the pipe manufacturer to assign high-performing pipes to the location of most severe loads in a well, while avoiding the delivery to the rig of the worst performing pipes.