Composite Flowlines, Risers, and Pipework in Offshore Applications
Authors: Carpenter Chris 
Published: January 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 24049, ’Strategy Concerning Composite Flowlines, Risers, and Pipework in Offshore Applications,’ by Luiz C.M. Meniconi, Walter Carrara Loureiro Jr., Fernando Costa dos Santos Jr., and Carlos Cunha Dias Henriques, Petrobras, prepared for the 2013 Offshore Technology Conference, Houston, 6–9 May. The paper has not been peer reviewed. Reproduced by permission.

Composite materials can offer technologically viable and cost-effective solutions for the production of highly corrosive fluids in very deep water, although there is a need to access the key issues of durability and integrity assurance of these components. Research in this area seeks to address their safe use during the operating life of production systems. This paper gives an overview of ongoing research activities on the subject of offshore use of composite flowlines, risers, and topside piping.

Introduction

The operator developed a plan to deploy an instrumented composite drilling-riser joint in different positions along a drilling riser operating at a given platform. The idea was to submit the composite joint to different load levels— dependent on the position of the joint alongside the riser—and by doing so address its structural behavior in a real operational environment. In the meantime, the operator also followed the development of composite wires for tensile armors of flexible unbonded risers, research newly spurred by the presalt scenario with its deeper waters and very corrosive fluids. At the same time, the idea of using thermoplastic-composite bonded pipes became a reality through the studies and efforts of companies new to the offshore pipe market.

Drilling and Workover Risers

The additional advantages of composite materials for these applications are the reduced buoyancy needed because of their low submerged weight and the inherently good insulation properties. For a given tensioner capacity, the rig maximum operating depth is increased. New rigs designed to use composite drilling risers will require smaller tensioners. Besides, a drilling riser is retrieved every time a well is completed, allowing for frequent inspections of the structural integrity of the riser. Production risers are even more demanding because they are supposed to be installed and left in place for 20 years or more.

In 2001, a 21-in.-diameter riser joint was intended to be deployed in 700-m waters offshore Brazil by a drilling platform. The 25-ft-long joint was to be monitored with strain gauges in order to measure the loading imposed on it at different positions along the riser, with at least one gauge located near the center and another close to the top. The bending moments and top-tension histories were to be compared with the design-limit values. Laminate strengths were stress levels above which 90% of a test population fails within a 95% confidence level. These strengths were further reduced by 25% from autoclave-cured properties to account for the filament-winding process. The resulting values were finally reduced by 50% to consider hot/wet scenarios. There was a total strength reduction of 68% in relation to the properties measured soon after cure. The failure criteria were maximum fiber tensile and compressive stresses, considering a safety factor of 2.0. The design basis of the joint was 1.5 million lbf of axial force and 3,000-psi internal pressure. (For a discussion of other efforts involving composite risers, please see the complete paper.)