What question did this study set out to answer?

This research aims to develop a numerical model that accurately predicts the collapse pressure of flexible pipes under hydrostatic conditions.

May 22, 2026Open Access

On the development and calibration of a beam-theory based model to calculate the collapse pressure of flexible pipes

Key Points

This research aims to develop a numerical model that accurately predicts the collapse pressure of flexible pipes under hydrostatic conditions.
Developed a finite element analysis model using beam-theory elements to simulate flexibility.
Calibrated material properties accounting for manufacturing effects and structural response.
Conducted sensitivity analyses considering various configurations, lengths, and frictional influences.
The proposed model accurately predicts collapse pressure with acceptable levels of precision.
Sensitivity analyses indicate significant effects of gap, length, and friction on the collapse behavior.
FEA results reveal a critical impact of rigidity differences between armor layers on collapse modes.

Abstract

• This paper proposes a simple numerical model to predict collapse pressure of flexible pipes. • Test results in flexible pipes considering multiple configurations are presented and a numerical correlation with FEA analysis results is presented. • A calibration of the material used in the composition of the inner carcass and pressure armor is implemented. This calibration incorporates manufacturing effects to the structural response of the metallic layers resisting external pressure. • Results show the model and material calibration proposed is capable to predict collapse pressure with acceptable accuracy. Sensitivity analyses show the influence of length, friction and gap between layers. • FEA results also show the influence of the relative rigidity difference between pressure armor and inner carcass on the resulting collapse mode of the wet collapse. As the oil and gas industry operational scenarios move to ultra-deep waters, failure mechanisms in flexible pipes such as instability of the armor layers under compression and hydrostatic collapse are more likely to occur. Therefore, it is important to develop reliable numerical tools to reproduce the failure mechanisms that may occur in flexible pipes. These tools can be used in the design stage or during service-life to assess the structural integrity of pipes under specific operational conditions. This paper presents a methodology to develop simple finite element models capable of reproducing the behavior of structural layers of flexible pipes under external hydrostatic pressure up to collapse. These models use beam elements and, in multi-layer analyses, include nonlinear contact between layers. Because of the material anisotropy induced by the manufacturing process, an inverse method was carried out to estimate the average stress-strain curves of the metallic layers used in the numerical simulations. The simulations are performed for two different configurations: one where the flexible pipe is composed only of the interlocked armor, and another considering interlocked armor and pressure armor. The adequacy of the numerical models is finally evaluated in light of experimental tests on flexible pipes with nominal internal diameters of 101.6 and 152.4 mm (4 and 6 in), proving excellent correlation.

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