MJ Lay, A Modular Deepwater Pipelay System
Authors: Coutarel Alain 
Published: October 2008

The discovery of oil-fields in deepwater (up to 5000ft) requires pipelay techniques to be developed in support of these facilities. Many of the associated flowlines are small diameter (&lt;16"), perhaps insulated, and relatively short (e.g. 10 miles), connecting the deepwater field to host export facilities in shallow water. End connections may be by subsea tie-in or steel catenary riser (SCR). This paper describes the design and construction of a Modular J-Lay System for installing rigid steel flowlines from a medium-sized vessel of opportunity. This equipment incorporates a 200ton tensioning device suitable for soft insulation as well as hard anti-corrosion pipe-coatings. Pipe production is by automated gas metal arc welding. The system is adaptable to incorporating sections of flexible pipe in the flowline. It offers operational flexibility and low cost installation of flowlines and SCR's in water depths ranging from 200ft to 5000ft. Anal)1ical methods and issues relating specifically to deepwater pipelay are presented, and their influence on the J-Lay system evolution is discussed. Production methods and operational speeds are addressed. Ancillary techniques for deploying PLEM's and handover of SCR's are presented. The dynamics of a monohull vessel are considered with particular reference to areas such as Gulf of Mexico, offshore Brazil and West Africa. A Case Study is presented with installation of the Modular J-Lay System, currently under construction, on a 6000 ton dwt DSV.

Introduction

During the summer 1997, Coflexip Stena Offshore (CSO) decided to invest in a new pipelay system in order to respond to the increasing demand for deepwater field developments. The purpose of this paper is to present this system which has been named MJ Lay for 'Modular J-Lay'. The system has been designed by the Offshore Engineering Division of the Coflexip Stena Offshore group(CSO) and it includes a number of novel features which are the object of patent applications.

MJ Lay specification

MJ-Lay will be transferable between different vessels, it will initially be installed on board the CSO Constructor in May 1998 and shall be capable of attaching pipeline end manifolds PLEMS to the pipeline and deploying them through the moonpool. Plem up to 5m long × 3m x3m to the end of the pipeline for deployment through the moonpool. Welding coating equipment will be supplied by specialist subcontractors.

Pipelay parameters.

Pipeline sizes will be in the range 6" to U" nominal bore. Pipe will be coated externally with one of a variety of coating systems from fusion-bonded epoxy (FBE) less than 1 mm thick to insulation coatings 50mm thick. The pipe may (or may not) be equipped with buckle arrestors consisting of local increased wall thickness (up to 20mm on external diameter) over up to 1m length. The pipe tensioning system shall be capable of holding the pipe on the above range of pipe coatings without reliance on intermittent buckle arrestors as holding points. It shall also be capable of passing such buckle arrestors without interruption to the lay process and shall be capable of passing flanges up to 26" diameter with provision for attachment of anodes and VIV suppression strakes.