A strain energy-based equivalent layer method for the prediction of critical collapse pressure of flexible risers

Abstract

Flexible risers are being required to be installed in a water depth of over 3000 meters for fewer remaining easy-to-access oil fields nowadays. Their innermost carcass layers are designed for external pressure resistance since the hydrostatic pressure at such a water depth may cause the collapse failure of flexible risers. Determining a critical collapse pressure for the carcass is of great importance to the whole structural safety of flexible risers. However, the complexity of the carcass profile always makes FE analysis computational intensive. To overcome that problem, the treatment of the interlocked carcass as an equivalent layer is adopted by researchers to accelerate the anticollapse analyses. This paper presents an equivalent layer method to enable that treatment, which obtains the equivalent properties for the layer through strain energy and membrane stiffness equivalences. The strain energy of the carcass was obtained through FE models and then used in a derived equation set to calculate the geometric and material properties for the equivalent layer. After all the equivalent properties have been determined, the FE model of the equivalent layer was developed to predict the critical pressure of the carcass. The result of prediction was compared with that of the full 3D carcass model as well as the equivalent models that built based on other existing equivalent methods, which showed that the proposed equivalent layer method performs better on predicting the critical pressure of the carcass.

Predicting the wet collapse pressure for flexible risers with initial ovalization and gap: An analytical solution

“…Bending moments at the separation point. proposed in our previous research [30], based on two equivalences between structures, i.e. strain energy, and membrane stiffness.…”

An Analytical Approach for Predicting the Collapse Pressure of the Flexible Risers With Initial Ovalization and Gap

“…According to their work, the ovalization is defined as maximum radial deviation of the carcass inner surface from circular, divided by carcass undeformed inner radius [5]. The strain energy-based equivalent layer method was employed to provide equivalent properties for the analytical models [24]. The equivalent thickness, Young's Modulus and Yield stress of the carcass is 4.5 mm, 158 GPa and 473 MPa, individually 1 .…”