21 - Pipeline Ends and In-Line Structures

Abstract

As oil/gas field developments move further away from existing subsea structures, it becomes advantageous to consider subsea tie-ins of their export systems with existing deepwater pipeline systems that offer spare transport capacity. This necessitates incorporating pipeline end manifolds (PLEMs) at both pipeline ends to tie in the system. A PLEM is a subsea structure set at the end of pipeline that is used to connect a rigid pipeline with other subsea structures, such as manifolds or trees, through a jumper. It is also called a pipeline end termination (PLET), especially when serving as a support for one pipeline valve and one vertical connector. The purpose of the PLEM is to provide an installation structure to attach these piping components and then lower them to the seafloor in the desired orientation. The structure must not only withstand the installation loads while being lowered to the seafloor but also retrieval to the surface should a failure occur. The PLEM foundation provides support for the structural frame of the piping system. In addition to their normal functions, PLEMs are designed to accommodate reasonable thermal expansion of the pipeline during operation.