Failure analysis of a non-integral pipeline collet connector

This paper describes the failure analysis carried out on a 12″-non-integral pipeline collet connector, joining a 12″-pipeline with an offshore platform riser. This kind of joint allows to seal the two extremity of the pipe, by using a locking ring that slides pushed by a hydraulic jack; this movement causes the sliding of 12 fingers that allows the pipes to contact. During service, the failure of 10 fingers occurred. In order to figure out the reasons of this failure, 3-D finite element stress analysis and experimental investigation have been carried out. This latter regarded the chemical composition and the microstructure of the finger material, the analysis of the fracture surfaces and the measurement of material fracture toughness, while the FE stress analysis was executed in order to find the most stressed zones of the fingers under the service condition. All these studies allow to conclude that the stress value in the critical section together with the experimentally determined toughness can justify the finger failure.