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الأحد، 23 مارس، 2014

Case Study for Offshore Pipeline Design

Title             :   Case Study for Offshore Pipeline Design
Author        :  Mohamed Ibrahim Mohamed Harfosh
Collection   :  M.Eng. Marine

Abstract:  
Marine pipeline design is a sophisticated, iterative and critical process. This design process is broken down into various analysis modules mashed together where inputs and results are dependent on each other, this is why it is iterative process.
This report represents a simple approach for marine pipeline design in the prospect of stress and on bottom stability analysis. Two main topics are considered the main core of this report, the first topic is dedicated to address the main stresses acting on a marine pipeline through its lifetime starting from installation and passing by hydrotest until pipeline operation. The equations and checks of pipe wall thickness verification is illustrated in details based on DNV-OS-FJOI methodology. The second topic of this report is dedicated to highlight the hydrodynamic forces acting on marine pipeline due to waves and current forces and its relation to on-bottom stability analysis. The three different methods ofDNV-RP-FI09 and Morison method for marine pipeline on bottom stability analysis are highlighted. The equations and checks for the absolute and general methods are discussed in details as per the DNV -RP-Fl 09 for the on-bottom stability analysis. Also it is included in this topic how the stabilization mattresses spacing is calculated when an additional weights is needed to be added to the pipeline when pipe concrete thickness has reached its maximum without achieving pipeline stability.
The report also includes a complete stress and on-bottom stability analysis to select the pipe wall thickness and the pipe concrete coating for 24inch marine pipeline based on DNV -OS- FJ 01 and DNV -RP-Fl 09. This 24inch pipeline connecting an onshore facility to an offshore platform is designed by ENPPI and constructed by PMS at the end of2007. Two excel spread sheets are developed to achieve the required calculations for stress and on-bottom stability analysis. The results of this analysis is compared to ENPPI results for the same pipeline which revealed that the calculated report results is nearly identical with ENPPI stress analysis results but the results of the on-bottom stability analysis revealed that the generalized method used by this report required more stability weights compared to ENPPI analysis that uses a commercial software based on DNV-RP-FJ09 dynamic stability method that implements the finite element in the analysis.

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