Abstract
Industry has been challenged to provide riser systems which are more cost effective and which can fill the technology gaps with respect to water depth, riser diameter and high temperatures left open by flexibles, steel catenary risers (SCRs) and hybrid risers. Composite materials present advantages over conventional steel risers because composite materials are lighter, more fatigue and corrosion resistant, better thermal insulators and can be designed for improving the structural and mechanical response. This paper contains a study of the toughening mechanism of an epoxy resin under rubber addition by means of fractographic analysis and its relation with the fracture process and increase of strength of a composite riser employing this polymeric matrix. Initially, an epoxy resin system was toughened by rubber CTBN addition (10 wt. (%)) as a way of improving the flexibility of future risers. Mechanical and thermal analyses were carried out for characterizing the polymeric systems. Later, composite tubes were prepared and mechanically characterized. The influence of matrix toughening on the mechanical behavior of the tubes was also studied. Split-disk tests were used to determine the hoop tensile strength of these specimens. The results indicate that the matrix plays an important role in composite fracture processes. The adding rubber to the polymeric matrix promoted a simultaneous increase of stress and elongation at fracture of the tubes manufactured herein, which is not often reported. These results, probably, is function of better adhesion between fibers and polymeric matrix observed in the CTBN-modified composite rings, which was evidenced in the fractografic analysis by SEM after the split-disk tests.
Highlights
As exploration and production of oil and gas move into deeper water, weight, cost and reliability of water-depth sensitive systems, such as risers become increasingly more important
Fractured surfaces obtained from mechanical tests were examined at different magnification by using JEOL JSM-6460LV scanning electron microscope (SEM) in order to observe the fracture behavior of the specimens, the rubber domains dispersed in the matrix, and the interaction of these domains with the epoxy matrix
Similar to polymeric samples, fractured surfaces obtained from mechanical split-disk test were examined at different magnification by using JEOL JSM-6460LV scanning electron microscope (SEM) in order to observe the fracture behavior of the specimens
Summary
As exploration and production of oil and gas move into deeper water, weight, cost and reliability of water-depth sensitive systems, such as risers become increasingly more important. Epoxy resins are considered as one of the most important class of thermosetting polymers and find extensive use in various fields These materials are rather brittle and, for this reason, their toughening has been extensively studied in the last decades[8]. The main objective of modifying the resin system with toughening agent is to increase elongation at fracture, for polymeric matrices used to manufacture composite tubes for riser application. Pipes can be subjected to very large plastic deformation up to 3%[10] in many situations, such as pipe laying operation (reeling) This manuscript contains a study of the toughening mechanism of an epoxy resin under rubber addition by means of a fractographic analysis, and its relation with the fracture process composite tubes. These tests present lower cost than hydrostatical tests, and are very efficient to determine the performance of tubular structures which are usually used under internal pressure developing high hoop
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