Abstract

API Specification 5L (2018) pipe is commonly used as surface casing. Recent deepwater failures have led to a review of collapse performance of 5L pipe as part of the larger root cause investigation.

A survey of pipeline industry publications generated a database of over 80 collapse tests of cold-expanded line pipe. The data are compared to casing collapse ratings per API Technical Report 5C3 (2018) and to alternative ratings included in API Recommended Practice 1111 (2015) for offshore pipelines and in the submarine pipeline standard DNVGL-ST-F101 (2017). The comparison showed that the pipeline ratings provide a better fit to the collapse data and that API TR 5C3 overpredicts collapse performance of the subject pipe.

Further investigation revealed that, for two operators, the vast majority of offshore surface casing is line pipe that has been cold-expanded without stress relief. Several risk mitigation alternatives were considered. In the short term, the risk can be managed through learning bulletins, design guidelines and operational procedures. The preferred mitigation is to change the collapse rating for cold-expanded line pipe used as casing. This is a long-term solution involving industry standards and the subsequent adoption through commercial design software.

The work described in this paper has led to a ballot change for the next edition of API TR 5C3. This paper is presented to provide drilling industry awareness of the lower collapse performance of cold-expanded line pipe and to add context for selection of an appropriate alternative rating.

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