Analytical study on the upheaval thermal buckling of sandwich pipes

Abstract

Sandwich pipe is one of the most promising subsea pipelines for oil and gas transportation in deep waters due to its high-strength performance and thermal insulation. The gradient of the temperature distribution through the cross-section of sandwich pipes may be significant due to good thermal insulation of the core layer, so it is necessary to consider the temperature distribution in the upheaval thermal buckling analysis. In this study, analytical solutions are derived for the temperature distribution through the cross-section of a sandwich pipe by using the heat conduction equation, and they agree well with the results in the literature. Taking the temperature distribution into account, a mathematical model is proposed to simulate the upheaval buckling of sandwich pipes based on the von-Kármán type of geometrical nonlinearity and the Euler-Bernoulli beam theory. The coupled transverse and axial deflections of sandwich pipes are considered. The buckled section and the slip section are connected by the continuous boundary conditions. The force and moment resultants in the inner pipe, the core layer and the outer pipe are solved separately. Different material properties of different layers can be considered in this mathematical model. Semi-analytical solutions are derived and verified. The typical buckling process is analysed, and the forces, moments and stresses in different layers of sandwich pipes are discussed. Finally, several simplified models for the temperature distributions are proposed. The results show that the temperature distributions in the inner and outer pipes can be assumed to be constant and equal to the temperatures of the internal and external fluids, respectively.