Titanium alloy Ti-6AI-4V ELI is selected for a high-pressure drilling riser application due to its high specific strength, corrosion resistance, and favorable elastic properties. The qualification of this titanium alloy requires assessing its resistance to hydrogen embrittlement and stress corrosion cracking due to seawater with/without cathodic protection, evaluating its wear resistance against a rotating steel drill string, and studying the influence of service-induced defects on fatigue and crack growth behavior when subjected to the operating environment. The paper presents an overview of the design requirements for a titanium drilling riser, and the material properties of the Ti-6AI-4V ELI alloy proposed for this application. The paper also highlights recent efforts to merge titanium and composite technologies to develop cost-effective drilling risers. [S0892-7219(00)01001-3]

High pressure drilling risers represent the most challenging application for composite materials in the offshore industry. Therefore, their successful field qualification should serve to eliminate the emotional barriers and pave the way for the broad usage of composites in similar but less demanding applications such as production risers, catenary risers, tubings, etc. The primary goal of the project discussed in this paper is to demonstrate the technical feasibility and cost effectiveness of advanced composite materials for high-pressure drilling risers. This is achieved by the design, manufacture, qualification, certification and field testing of a 558 mm ID (22 in.) composite drilling riser joint on Heidrun Tension Leg Platform (TLP) A composite drilling riser (CDR) joint is designed to be interchangeable with the Standard Titanium Drilling Riser Joints (STDRJ's) currently in use on the Heidrun platform. The CDR joint has identical flange configurations as the titanium joints and is designed to satisfy all dimensional constraints to make it suitable for installation on Heidrun. The tube body weight of the CDR joint is 87 lb/ft versus 130 lb/ft for an equivalent Ti joint. The fatigue life of the CDR joint exceeds 150 years (10 times the 15 year service life), and its internal pressure rating exceeds 12,600 psi, which is about 2-¾ times the maximum operating pressure of 4500 psi. In addition, the CDR joint, without the need for any special impact protector, maintains its pressure and structural integrity after being subjected to a dropped object impact of 50kJ.The structural capability of the CDR tube body is provided by a carbon fiber/epoxy composite overwrap, with load transfer between the composite overwrap and Ti flange extensions accomplished through a carefully designed traplock Metal-to-Composite Interface (MCI). Detailed analysis of the CDR joint confirmed that it is capable of safely supporting all of the expected loadings, including internal and external pressures, axial tension, bending moments, and impact loads. The bore of the CDR joint is provided with a 0.125-inch (3.2 mm) Ti liner welded to the flanges for fluid-tightness and damage resistance, and an elastomeric wear liner identical to the one currently in use on Heidrun. The design, analysis and qualification of the CDR joints have benefited from the design and the extensive qualification activities on the 10-¾ inch high pressure composite production riser joints as part of the NIST ATP project.The paper summarizes the performance requirements called for by Heidrun TLP Drilling Riser System, and presents the design and analysis procedures and results to ensure that the composite riser joint satisfies all requirements. The paper reviews the basis for the analysis and the validation of its accuracy, and presents the rationale for the qualification program.

No abstract