Finite Element Analysis of `Loadshare' for the Installation of Pipe-in-Pipe Flowline by S-Lay and J-Lay Methods

Abstract

Development of deep water oil reservoirs are presently being considered in the Gulf of Mexico (GoM) where the flowline product temperatures is approaching 177degC (350degF), and the water depths are in excess of 3,050 m (10,000 ft). The installation of Pipe-in- Pipe (PIP) flowline in deep water, by either the S-Lay method or J-Lay method, can present real challenges due to the effect of locked-in compressive loads on the inner pipe, due to gravity during installation. The effect of this compressive load is to reduce the ultimate loading capacity of the inner pipe during operation, when temperature and pressure are applied. One such way to overcome this locked- in compressive load, is to apply tension on the inner pipe during installation on the lay barge, and insert a device called 'Loadshare' to distribute the load between the inner and outer pipe. The objective of this paper is to present the results of a finite element study, to investigate the effects of inserting the Loadshare(s) during installation of a PIP system. A finite element model has been created, using ABAQUS, to simulate the laying process with the inclusion of Loadshares. The model is used to determine the shear force imposed on the Loadshare, and the lock-in axial load inside the pipeline prior to operational start-up of the pipeline. Also, the relaxation of the Loadshare tension as the pipeline is lowered, is investigated. The model, load steps and results are presented in this paper. This work is part of a larger GoM project that aims at bridging technology gaps for increasing the boundaries of what is possible with PIP designs, for extra high pressure and high temperature (XHPHT) applications in the GoM region. This finite element model could be used as a starting point for future deep water PIP developments.