Comparison Between Predicted and Measured Umbilical Bending Stresses During Manufacturing

Abstract

The present paper addresses comparison between predicted and measured bending stresses in one umbilical cross section during manufacturing. A factor with significant uncertainties has been which stresses that will occur during the manufacturing procedure when the umbilical is reeled on and off storage drums. The umbilical components may not only be exposed to pure elastic bending stresses due to the curvature radius but also second order axial stresses due to the combination of curvature gradients and finite length to the end fittings. In cooperation with Aker Kværner Subsea a.s., Marintek has developed a tool for stress analysis of Aker Kværner umbilical cross-section designs. The main motivation behind the development has been to reduce technical risk and costs associated with umbilical manufacturing, installation and operation. This is obtained by increasing the basic understanding of the umbilical cross-sections mechanical behaviour and the ability to quantify the stress response when exposed to various loads. In order to calibrate the mathematical model with regard to manufacturing stresses a 70 m long umbilical prototype was instrumented by strain gauges and reeled on an off a storage reel with radius 4.4 m. The paper presents the model applied to simulate this operation as well as the results from comparing predicted and measured stresses.

An Overview of Structural Design, Analysis and Common Monitoring Technologies for Floating Platform and Flexible Cable and Riser

“…Kraincanic and Kebadze (2001) proposed an analytical equation to predict the bending moment-curvature relationship of unbonded flexible pipes based on the Coulomb friction model and the principle of virtual work and found that the bending stiffness of the pipe was a function of the bending curvature, the friction coefficient between the layers, and the contact pressure between the layers. Saevik et al (2006) simulated the actual bending of a 70 m long umbilical cable stowed on a storage reel with a 4.4 m bending radius and found agreement between the simulated stresses and the experimental measurements. Zhou et al (Zhou et al, 2020;Zhou and Vaz, 2017) developed an analytical model of an unbonded flexible pipe with two layers of metal armor, considering the friction effect between the layers, and studied the pipe bending and fatigue behavior by this model.…”

Friction, Contact Pressure, and Nonlinear Behavior of Steel Tubes in Subsea Umbilicals

“…In each of these verifications, one must note that due to larger pitch length of an umbilical structural element (e.g., 15-20m) either the test sample length should be long enough to reduce the end fitting effects on bending of the sample or the modeling methods need to include such effects. Among these efforts are the studies done by Saevik et al [13] to compare bending stress calculations and measurements during umbilical manufactur ing as well as Le Corre and Probyn [14] to validate a 3D finite ele ment analysis model for steel tube umbilical and the work by Pesce et al [15,16] to compare a mathematical model with experimental results on a steel tube umbilical sample.…”