Numerical analysis and material selection of functionally graded pipes based on metals and ceramics for deep offshore oil and gas operations in Gulf of Guinea

Student thesis: Doctoral Thesis

Abstract

The environmentally challenged conditions of deep offshore oil and gas operations has necessitated the demand for unique materials that could withstand both the loading conditions of the operations and the corrosion resistance. The work presented herein has explored the use of Functionally Graded Material (FGM) to validate its ability to proffer solutions to deep offshore oil and gas operations and their components, particularly in the Gulf of Guinea.FGM was specifically used in the present work due to its unique property exhibition that changes continuously throughout its thickness with no discontinuities within the material. This unique feature was utilized in this research to derive a combination of FGM’s that could meet the required strength, fracture toughness, specific stiffness and corrosion rate for oil and gas operations in Gulf of Guinea.An assessment of currently available material combinations was investigated to determine feasible FGM combinations (metal and ceramics) that could meet the unique operating requirements. In tandem, the Analytic Hierarchy Process (AHP) technique was further used to rank the materials identified and a sensitivity analysis was carried out on weight, price and density variations in the final ranking the material. The four (4) most highly ranked Metal/Ceramic combinations were used for all the finite element thermal and structural analyses undertaken in this work.Four (4) distinct FGM pipe were modelled by finite element analysis (FEA) using the Abaqus Finite Element system based on the key Metal/Ceramics materials selected, to reasonably mimic the physical behaviour of a series of offshore piping systems configurations. In practice, three piping configurations were considered; Straight, Elbow and T- Piece pipe components, all these were modelled for a range of pressure and temperature conditions.. From the reviewed literature, only a few benchmarks were available to validate the computational models, this is as a result of the evolving nature of the usage of FGM for piping in oil and gas industry.Using work by Ghannad et al. on '2D thermo-elastic model of an axisymmetric FGM hollow cylinder', the FGM parameters used for the validation were axial stress, circumferential stress and von-mises stress. The comparison of results obtained from Ghannad's Paper showed excellent agreement with deviations of most of the variables used for the within 5% with both the numerical and analytical results from the literature.As an FGM cannot have a single yield point by definition, an equation for the determination of effective yield strength for FGM’s was developed which depends on the yield strength of the FGM constituents and the non-homogeneity factor of the FGM. This equation was validated using the conventional averaging approach of the FGM yield strengths and it showed excellent agreement with less than 1% for FGM's with higher numbers of layers.Further to the determination of an ideal approach to calculate the effective yield strength of the FGM's, the Finite Element Analysis (FEA) of the four FGM combinations were modelled using the approach in the validated model with the main intent of predicting the design limits for each of the FGM material combinations. This was repeated for the three piping components considered (Straight, Elbow and T-Piece Pipe configurations).The normalized stress approach was used for the determination of the design limit, this approach compared the effective yield strength of the FGM to the effective Von-mises stress for each of the configurations to determine the FGM failure tendencies due to yielding. The FGM design limit was determined when any of the layer in the FGM normalized stress was closest to one (1), above this limit the material begins to yield (Fail). The design limit was determined using the normalized stress between the ranges of 0.99<normalized stres
Date of Award31 Jul 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorDavid Nash (Supervisor) & Donald MacKenzie (Supervisor)

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