Flow-Induced Vibrations of High Gas Rate Well Jumpers: Tees vs. Bends

Abstract

Subsea well jumpers are steel pipe sections that connect the flow path between the tree and the manifold. They are designed with bends to accommodate limited expansion due to variations in temperature and pressure. The unsteady change of flow direction in these bends induces fluctuating forces with broadband frequency content. If the fluctuating forces are of significant amplitude and/or induced in the right frequency range, they may lead to flow-induced vibrations (FIV) of the well jumper. FIV poses structural integrity concerns for subsea piping in terms of cyclic stressing and, over time, a threat of fatigue failure. A comprehensive FIV screening approach, based on computational fluid dynamics (CFD) and structural finite element analysis (FEA), and associated fluid-structure interaction (FSI) is used to estimate well jumper fatigue life due to FIV — for high gas rate production conditions. Although the FIV screening approach itself is novel, the main contribution of this work is in comparing FIV response and fatigue life of a well jumper outfitted with the traditional impact tees Vs. one outfitted with short radius bends. We find that the resulting flow-induced stress cycling is similar in magnitude in both geometries, but with different frequency spectra — giving the well jumper with short radius bends a 2x increase in fatigue life, relative to the well jumper with impact tees. We also perform a sand erosion analysis comparison between the two well jumpers, and find that the well jumper with short radius bends has a 3x diminished erosion rate, relative to the well jumper with impact tees.