Development and Testing of Non-Bonded Flexible Pipe for High Temperature/High Pressure/Deep Water/Dynamic Sour Service Applications
Authors: Kalman Mark , Belcher John , Chen Bin , Fraser Dana , Ethridge Andrew , Loper Cobie 
Published: October 2008

Non-bonded flexible risers are a critical element of floating systems for offshore oil and gas production. Current applications are in increasingly severe environments, with design Temperatures up to 145°C, design pressures horn 345 to 690 barg, sour production fluids, water depths exceeding 1000m, and severe wave and current conditions, challenging flexible pipe design and construction. This paper reviews product innovations and prototype testing of risers developed to cope with severe environments.

Full scale dynamic test results with combined tension, bending, internal pressure and heating, and with these structural loads combined with sour production fluids introduced into the bore of the pipe are presented. The loading conditions for the tests were based on floating production systems in North Sea environments.

End fittings are critical components of the flexible pipe. They must assure a leak tight transition to subsea and surface facilities when subjected to the pipe applied loads, thermal cycling during startup and shutdowns, and changing of the fluid barrier material properties over the service life. The ability to withstand the structural loads is well documented. The results of analyses and tests conducted to verify the integrity of the end fitting with thermal cycling and fluid barrier changes due to the high temperature production fluids is presented herein.

Conventional flexible pipe employs carbon steel for axial and hoop structural reinforcement. In deeper water, the tension loads induced by pipe weight increase stress levels in the pipe structure and deck and installation loads. As pipe stresses increase, larger cross sectional areas of the steel members are required, further increasing the weight. To reduce the unit weight, while retaining the required strength levels, composite materials have been developed to replace the steel tensile rmor. The composite consists of carbon fibers in a thermoplastic matrix. Tests to verify the suitability of the material in the flexible pipe annulus environment and to evaluate the performance of the composite pipe structure are presented.

Introduction

Floating production facilities have proven to be an economical solution for producing offshore oil and gas. Because of the motions of the production vessels, flexible risers are a key component in making floating production facilities viable, As fields are developed in both deep and shallow water with large vessel motions, the requirements for flexible risers become more challenging. To date, flexible risers have provided the primary solutions for floating production developments with large vessel motions. Therefore they are being considered for higher temperatures, higher pressures and extremely sour production fluids. Due to the limited space available in current turret designs, larger diameters are being requested to reduce the number of risers.

Table 1 summarizes design conditions for fields planned for development by 1998. These design parameters drive the pipe designs and test programs to qualify dynamic risers for these challenging applications.