Failure analysis of metallic structures and components: Part II - A case study

This is the second of two papers dealing with failure analysis, where methodology and tools were illustrated in the first paper. In this paper, an application of the failure analysis of an oil drilling pipe is presented. A logical approach for failure analysis steps is proposed based on the available information originating from the site data, failed parts, loading records, and service conditions. The plan compromised of three basic phases; mechanical testing, chemical analysis, and stress calculations and crack propagation simulations. Mechanical testing revealed a high tensile strength steel with very low ductility, while chemical analysis proved the contamination of the inner and outer surface of the pipe with sulphur. Plane of failure for both preliminary stress calculation and crack propagation simulation under recorded failure loads, gave the same angle of inclination as observed for the failed part. Recommendations have been drawn regarding liability for the case that overloading and hydrogen embrittled pipes, concurrently accelerated failure. Also, guidelines for current pipes in use, and a proposal for prospective pipes have been suggested. This study introduces a very useful application for failure analysis procedure in such situations.