Failure analysis in high pressure thermoplastic hose fittings submitted to cold forming by swaging process

摘要

Umbilical cables are important components in underwater oil extraction, providing electro-hydraulic connection between platform and manifold in oil well, through elements such as electrical cables and thermoplastic hoses. The connections of thermoplastic hoses are made with fittings installed by a cold forming process, called swaging, to ensure a perfect seal. These fittings are made of SAE AISI 316L stainless steel, but in order to reduce manufacturing costs, SAE AISI 1045 carbon steel fittings are used in hose factory acceptance tests. However, longitudinal cracks were produced during swaging of carbon steel of a specific supplier. In this work, samples from two different suppliers were characterized before and after installation to understand the failure cause. The characterization was made by visual inspection, dimensional control, hardness tests, chemical composition, microstructural and fracture surface analyses. In addition, swaging process simulations by finite element method (FEM) using a commercial software were performed. The results indicated large variations in material elements percentage from the supplier with failed connections history. This fact resulted in elevated amounts of non-metallic inclusions which promoted the cracks. Finally, corrective actions were recommended to mitigate the failure occurrence. (C) 2017 Elsevier Ltd. All rights reserved.