DESIGN AND FATIGUE ANALYSIS OF MULTI-SPANNING SUBSEA PIPELINES IN SOUTH CHINA SEA

• Main Author: Fathira Kaysandini S, Alyana
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/84967
• Institution: Institut Teknologi Bandung

Excessive free spans in subsea pipelines have the potential to cause fatigue failure. Uneven seabed can lead to subsea pipelines being laid in a suspended condition, resulting in the formation of free spans. When the position of one free span is close to another, it creates a multi-span system with interacting spans. This study involves the design of a subsea pipeline and fatigue analysis due to interacting multi-spans with a steel pipe with X65 pipe grade, a diameter of 28 inches, wall thickness of 15.9 mm, and concrete coating thickness of 72.4 mm. Using the DNV-RP-F105 standard, the allowable free span length is found to be 34.44 m based on fatigue screening criteria and ultimate limit state (ULS). Fatigue analysis of the multi-span is conducted through modal analysis using ABAQUS to extract the natural frequency values of the multi-span structure. Variations in span lengths of 15, 30, and 45 meters are considered relative to the allowable span length in free span analysis to observe how the fatigue life of the multi-span structure is affected when the span length meets or exceeds the allowable span length. Based on the fatigue analysis performed, the probability of fatigue damage to the multi-span structure is 0%, with the primary mode impact of fatigue damage being influenced by the first mode with in-line oscillation direction. The natural frequency values obtained are inversely related to span length and directly related to fatigue life, where smaller frequency values affect the amplitude of vortex-induced vibrations (VIV) and result in a lower fatigue life.