Subsea pipeline protection design subjected to dropped anchor using concrete mattress

Abstract

Out of the many potential hazards, certain critical possible hazards need to be assessed, and actions need to be taken to improve the probabilities and consequences to an acceptable degree. One of the major hazards commonly found in subsea pipeline operations is a dropped anchor, especially for pipelines located near jetties, where many ships are expected to move across the pipeline. One of the possible protection methods is the use of a concrete mattress. The dropped anchor hazard to a pipeline is characterized by the impact of energy, which will mostly be absorbed by the internal strain energy of the pipeline. The safety criteria for a pipeline subjected to a dropped anchor are given by DNV RP-F107 for the maximum dent depth and DNV OS-F101 for the maximum stress. A finite element analysis using ANSYS software was performed to obtain the maximum equivalent stress and dent depth for a pipeline. The effects of the length and height of a concrete mattress in redistributing the impact energy were obtained.