Development of Gastight, Pressure-Rated, Third Generation Rotary Shouldered Connections for 20,000-psi Internal and 10,000-psi External Pressure Service
Authors: Brock James N. , Jellison Michael J. , Muradov Andrei , Vinson Barry J. 
Published: March 2008

This paper presents the results of a two-year comprehensive effort to design, test, and qualify third-generation rotary-shouldered connections (RSC) for 20,000 psi internal and 10,000 psi external pressure service. ISO13679 testing methodologies for casing and tubing were modified to evaluate the RSC pressure capability. Results from comprehensive finite element modeling and extensive laboratory testing designed to reproduce the harsh, aggressive loading modes and high pressures encountered in field use are presented.

The result of this program is a RSC that incorporates a double-start thread form to reduce the number of revolutions to assemble the connection by 50 percent reducing trip time. The thread form also provides a unique dual-radius thread root that offers a step change improvement in fatigue resistance. A metal-to-metal seal provides pressure integrity.

In addition to providing a 20,000 psi internal and 10,000 psi external pressure rating, the new connections provide increased mechanical and hydraulic performance compared to second generation high torque connections while also providing fatigue performance greater than standard API connections.

Introduction

New developments in drilling tubulars are rapidly evolving and represent enabling technologies for the industry's continued advancement of drilling deeper, further and more cost-effective wells. Much focus has been made toward the advancement of RSC technology to permit high torque drilling of extended reach, directional and horizontal wells. In response to this need, the development of third generation, ultra-high torque connections was recently announced providing reduced tripping times and the mechanical and hydraulic load requirements for drilling today's deepwater, extended reach and ultra-deep wells. The next step in the evolution of RSCs has now occurred with the development of a third-generation, gas-tight, pressure rated connection providing enabling technology for high-pressure completion and workover, drill-stem testing, UBD and intervention riser applications.

Although drill pipe, drill pipe connections and drill stem materials represent mature technologies, innovations are being developed in these areas. This third generation gas-tight, double-shoulder connection presented here represents several advancements that address some of the challenges ahead.

Double-Shoulder Connection Design Development

First generation double-shoulder connections (1st Gen. DSC), see Figure 1, were introduced in the early 1980's.4 1st Gen. DSC's were basically API rotary-shoulder connections (primarily NC or FH) with a second torque shoulder added inside the box member at the pin nose interface.1,3 These 1st Gen. DSC's incorporated the same basic design features in terms of thread form, taper, lead, pitch diameters, etc. as the API connection on which they were based. These connections yielded a simple, straight forward solution that increased the connection torsional strength by approximately 40 percent over the corresponding API connection.