Development of Composite Pipes for Riser Application in Deep Water

This work deals with the development of composite pipes for riser application in deep water. 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. As expected, due to the fact that the modulus of the CTBN is much lower than that of the epoxy phase, the tensile modulus decreased with the addition of CTBN, from 3.45 to 2.75 GPa, and the elongation at fracture increased from 2.96 to 5.24%. On the other hand, the glass transition temperature (T_g) of the CTBN-epoxy system changed from 141°C to 136°C. Later, composite tubes were prepared and mechanically characterized. The influence of matrix toughening and the number of composite layers on the mechanical behavior of the tubes were studied using hydrostatic and split-disk tests. In both tests, the results indicate that the matrix plays an important role in composite fracture processes. In the split-disk tests, the tensile strength and the elongation at fracture increased with the addition of CTBN, from 731 to 831 MPa and from 2.34 to 3.09%, respectively. In the case of the hydrostatic tests, the pipes colapse and bursting pressures increased about 14% and 19%, respectively, with the rubber addition to the polymeric matrix. At last, it was verified that the strength of the tubes increases linearly with the number of layers. These results confirm the feasibility of the developed tubes for application as risers in deep water.