Thermomechanical analysis of insulated subsea flowlines

Abstract

This paper presents a novel finite element with cylindrical symmetry that can be used to analyse multilayered flowline systems subject to internal and external pressure and heating. Implicit in the method is the ability to model (a) an elastic modulus as a function of temperature and (b) thermal conductivity as a function of volume change in the coating. The method is validated against the analytical solution as determined by the Lamé equation and by comparisons with a previous analytic model applied to two different flowline systems designed for deep water. The results show that thermal effects can have a considerable impact on the stress distribution and the U-value. Although for these systems a linear solution is adequate, where a strong thermomechanical coupling exists, a modified, iterative algorithm is required. A further ‘non-jacketed’ system is examined to illustrate this. The equations used to model the variation in materials property can only be considered to be a first approximation, but do serve to demonstrate the need to consider these factors in greater detail.