Effective axial force in multi-layered cylinders with applications to insulated offshore pipelines

To ensure high content temperature, some offshore pipelines have insulation coating made from polypropylene or polyethylene. Typical coating systems have significantly lower stiffness than ordinary carbon manganese steel, but also significantly higher temperature expansion coefficients. Due to the differences in material properties, insulation coating systems have a non-trivial influence on the critical design parameter called the effective axial force in offshore pipelines. Current offshore design codes do not contain guidance on how to include the effects of coating systems on the effective axial force. In this paper, an exact analytical formula for the effective axial force in pipelines with arbitrarily many layers is deduced, accounting also for temperature variation along the radial coordinate. A simplified approximate formula, which is more suitable for use in engineering contexts, is developed and its validity verified by comparisons to results of the exact one.