Stress analysis of the Lower Riser Package (LRP) funnel when landing on the Composite Valve Block (CVB) hub of the Enhanced Vertical Deepwater Tree (EVDT)

• Main Author: Goh, Samuel Yuheng.
• Other Authors: Ang Hock Eng
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Mechanics and dynamics
• Online Access: http://hdl.handle.net/10356/53638
• Institution: Nanyang Technological University

The Emergency Disconnect Package (EDP) / Lower Riser Package (LRP) stack lands on the Enhanced Vertical Deepwater Tree (EVDT) through the top drive of the rig. This process is facilitated by the use of a guide funnel to ensure that the Composite Valve Block (CVB) hub of the EVDT interfaces correctly with the LRP. However, due to wave currents which might affect both the rig and the risers, the EDP/LRP stack will not land vertically downwards. The top drive serves to ensure that the maximum tilt angle of the EDP/LRP stack is 3° from the vertical and the maximum downwards speed is 0.5 m/s. This project aims to investigate the structural integrity of the LRP funnel to withstand the impact load. Using theoretical knowledge of stress and strain in elasto-plastic materials as well as impact loading, an approximate analytical solution was derived. However, due to the complexity of dynamic problems and the lack of accurate and reliable formulas, the finite element method was employed. By comparing results derived from finite element analysis (FEA) and the theoretical solutions, it was found that they are in close agreement. Upon verification of the validity of FEA, critical outputs such as deformation, von Mises stress and plastic strain were obtained. The results showed that the LRP funnel experienced high stresses and consequent yielding, but it did not undergo local failure as the plastic strain was less than the fracture strain. Parametric variations are an integral part of design optimization, and the effect of additional stiffeners and greater LRP funnel thickness were investigated. It was concluded that the addition of stiffeners had a greater reducing effect on the plastic strain than the increase in thickness of the funnel. This is probably due to the increased mass of the funnel which offsets the effect of its increased thickness. Hence, the increase in thickness must be studied carefully to determine whether it will result in any adverse effects.