Local structural analysis of flexible pipes subjected to traction, torsion and pressure loads

•It shows a clear derivation of linear operators for flexible pipes including the effect of internal and external pressures.•The effects of both internal and external pressures have not been discussed in the technical literature so far.•It presents both the extended and the reduced forms for the linear operators and the relation between them.•Application for a 2.5″ flexible pipe is provided, where all the coefficients of the presented linear operators are given.•Comparisons between the proposed method and experimental results have been recently published showing good results.

Helically armored cables or pipes find a wide range of applications as structural members in engineering. An example of this is the increasing use of flexible pipes in the oil offshore production. Although keeping a geometrical similarity with other helically armored structures such as wire ropes and ACSR conductors, and borrowing from them a useful methodology for the structural analysis, some care must be taken in order not to indiscriminately use an approach which was not thought for a flexible pipe: internal and external pressures, for instance, are a great concern in the analysis of flexible pipes, but obviously not for wire ropes. This work aims at giving some additional contribution to the structural response of flexible pipes when subjected to axisymmetric loads, including the effect of both internal and external pressure in pipe displacements. Derivation of linear operators, relating the stress-resultants to their related displacements or deformations in each of the layers of the pipe, as well as the process of deriving an analogous linear operator to represent the behavior of the pipe as a whole, are clearly presented, highlighting interesting mathematical aspects and their associated physical meaning. A numerical case study of a 2.5″ flexible pipe subjected to traction and internal pressure is also presented and discussed.