Design Analysis And Full Scale Prototype Testing Of Auger Tlp'S 9-5/8" Tlp Production Riser Weld-On Connector
Authors: Fox S.A. , Smith J.D. , Asbill W.T. 
Published: October 2008

The design, analysis, and full-scale prototype testing of a special threaded connector for use on the Auger TLP 9-5/8" × 0.435" wall production risers is summarized in this paper. A flush-bore production riser connector with internal and external metal-to-metal seals, a resilient seal between the external metal-to-metal seal and the external torque shoulder, radial thread interference, and high resistance to fatigue was developed, Finite element analyses and fullscale static, sealability, and fatigue tests verified that the connector satisfied all design requirements. The full-scale fatigue tests verified that the design fatigue curve and fatigue life prediction procedure used yield conservative results and that the fatigue life of the connector greatly exceeds the gkth weld.. Consideration of manufacturing methods and tolerances along with gauging, in the early stages of thedesign, resulted in a cost effective connector.

The threaded connector was designed for the Auger Tension Leg Platform production risers. However, it is envisioned that the connector will be easily scalable to other riser diameters and wall thicknesses for other TLP's and has applicability to catenary and top-tensioned risers and subsea flowlines.

In addition to resulting in an efficient long life production riser connector design, the design process illustrated the importance of interaction, between the designers, quality control personnel, machinist, gauge manufacturer, and end user, during the design. All made significant contributions to the success of the design.

INTRODUCTION

The roughly 3000 ft. Auger production riser string is made up of three different riser joint configurations; 9 5/8" 43.50 lb. 75 ft. subsea joint, 9 7/8" 55.76 lb. 75 ft splash zone joint and 9 7/8" 55.76 lb. 33 to 43 ft. atmospheric/pup joint. The internal diameters of the 9 5/8" 43.5 lb. pipe and the 9 7/8" 55.76# pipe are the same, only their outer diameters differ. Thus, the same basic connector is used for both pipe sizes. The connector outer diameter and length, as well as the threaded portion of the connector, is the same for both pipe sizes. Only the transitions from the pipe to the connector outer diameter are different.

Sacrificial bracelet anodes are used for corrosion protection on the subsea and splash zone joints. The anodes, fitted around the pipe over the polyethylene pipe coating, have an O.D. of 12.575", which is the same as the connector O.D. The anode is attached to the pin end of each joint via a flatbar strap that is welded via a fillet weld in a low stress region of the pin connector.

To date nine production risers have been run with no reported problems. The average running time has been around 7 minutes per riser joint, which highlights one of the major advantages of a threaded connector design over a flanged connector design. The mean makeup torque for allnine risers was 47,918 ft-lb with a standard deviation of 426 ft-lb and the mean shoulder torque was 16,137 ft-lb with a standard deviation of 1748 ft-lb.

DEVELOPMENT PROGRAM

The development of the connector was accomplished in three phases.