Failure analysis in high pressure thermoplastic hose fittings submitted to cold forming by swaging process. (April 2017)

• Record Type: Journal Article
• Authors: Moebus, F.; Pardal, J.M.; dos Santos, C.A.; Tavares, S.S.M.; Louzada, P.A.; Barbosa, C.; dos Santos, D.S.
• Is Part Of: Engineering failure analysis. Volume 74(2017)
• Page Start: 150
• Page End: 158
• Publication Date: 2017-04
• Subjects: Thermoplastic hose -- Fitting -- High sulfur steel -- Swaging; System failures (Engineering) -- Periodicals; Fracture mechanics -- Periodicals; Reliability (Engineering) -- Periodicals; Pannes -- Périodiques; Rupture, Mécanique de la -- Périodiques; Fiabilité -- Périodiques; Fracture mechanics; Reliability (Engineering); System failures (Engineering); Periodicals; Electronic journals; 620.112
• DOI: 10.1016/j.engfailanal.2017.01.008
• Languages: English
• ISSNs: 1350-6307

Abstract

Abstract: 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. Highlights: Low carbon steel fitting failed during swaging process. Microstructure with large inclusions caused failure. Chemical analysis of the failed fitting was out of specification, with high S and low C contents. FEM analysis was used to simulate the swaging process and preview the effect of inclusions.