Critical review of subsea structures in the Gulf of Guinea : "Finite element analysis to predict the behaviour of a multi-layer non-bonded flexible pipe under hydrate plug in a static application"

Student thesis: Doctoral Thesis

Abstract

The concept of blockages in a non-bonded flexible pipe during oil and gas mining operations have over the years shown to be a persistent problem, and the need for a standardized remediation approach is paramount. This research work studies the behaviour of non-bonded flexible pipes with methane hydrate blockage under the influence of diverse loading conditions. Nonlinear tridimensional finite element models were used on two (2) scenarios, blocked and unblocked conditions. These models recreate a seven-layer flexible pipe with two tensile armour layers, an external polymeric sheath, high strength tape, orthotropic equivalent carcass, and pressure armour layers with an internal polymetric sheath. With these models, several studies were conducted to verify the influence of key parameters on the instability phenomenon when the flexible pipe is under hydrate blockage. The internal pressure and compressive loads can be considered one of these parameters, and their variation causes a significant change in the stability response of the pipe layers. This work includes a detailed description of the finite element model and a case study where the non-bonded flexible pipe is blocked by methane hydrate. The procedure of this analysis is here described, along with the results. For in-depth knowledge of hydrate formation and its consequences in flexible pipes, this thesis used ABAQUS, a standard finite element (FE), in modelling, simulating, and investigating a hydrate blocked and unblocked non-bonded flexible pipe. It is divided into two Samples, A and B, respectively, under the influence of various load conditions. FE model was adopted to investigate the effects of hydrate on the layers as were not detailed in America Petroleum Institute codes [1]. This was carried out under various conditions such as pipe with and without blockage at various pressure, forces (longitudinal and compressive) values, different hydrate lengths, coefficients of friction and stiffness constants. In addition to the FE analysis, an experimental investigation was carried out on the samples and where necessary mathematical analyses were undertaken to reverify results. The studies carried out were to determine the non-bonded flexible pipes responses under certain load conditions. This determines the deformation, stress concentration on individual layers, making sure the results are within the recommended API standards, hoop, axial and radial stresses, reactive force, and contact pressure between the layers. A simplified model was employed and a finer mesh to resolve the issue with the FE model. And progress the effect of the hydrate on the pipe layers. Importantly, this present work considered and investigated a 7-layers 6" diameter non-bonded flexible pipe as a case study. The results were obtained from the numerical and experimental investigations, analysed, and presented accordingly. Obtained results showed a significant influence of methane hydrate on Sample A, while Sample B behaves normally under various load conditions. The detailed outcome and further research works are presented in this thesis.
Date of Award18 Nov 2021
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorDavid Nash (Supervisor) & Donald MacKenzie (Supervisor)

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