복합하중에대한 파이프 극한 강도

Abstract

Pipeline is one of the most important equipment to transport produced hydrocarbon in deepwater oil & gas production facility. Pipeline falls into three categories: flowline, riser and pipeline. Flowline is an intrafield pipeline, in the sense that it is used to connect subsea wellheads, manifolds and the platform within a particular development field. Riser is vertical pipeline which transport resource from seabed to processing facility on surface of the water. Pipeline sometimes referred to as an export pipeline, is used to bring the resource to shore. Even though the size and loading conditions are different each other, design method is same for all three types of pipelines. Most typical design specifications for pipeline design are DNV and API code. And there are several structural design codes for pipe structures. Considering pipelines are loaded axial force, bending moment and pressure simultaneously, all design codes have provisions for combined loading criteria. However, interaction effects needed to be investigated accurately, because each design code has different interaction formulas for combined loading. To investigate the ultimate strength of pipelines including interaction effect of combined loading, series of non-linear finite element analysis was performed. First, various parametric studies were performed for no-interaction analysis to verify design formulas for each single loading condition. Second, 2-type loading interactions were analyzed. Various combination analyses were preformed for axial force and bending moment combinations, axial force and pressure combinations, and pressure and bending moment combinations, respectively. Finally, 3-type loading interaction analysis for axial force, bending moment, and pressure were performed. From the series of analysis results for no-interaction conditions, existing formulas in DNV code are adequate to estimate ultimate strength for single loading condition. However, from 2-type loading analyses, interaction formulas could lead unsafe or over-conservative design according to circumstances. Therefore 8 new interaction formulas are proposed conservatively. Finally, depends on the results of 3-type loading combined analyses, simple one interaction formula was developed to express interaction effect when all loads are applied simultaneously.