Performance of a Swage Pile/Sleeve Connection When Subjected to Cycle Loading
Authors: Lowes J.M. , Holmes Robert , Peel J.W. 
Published: October 2008

Previous papers have described the development and application of the swage pile connection system. The system has been available for some 10 years for application to subsea structures and jackets. The papers have also detailed the extensive testing undertaken to evaluate the connection under primarily static load conditions.

More recently designed offshore structures including lightweight jackets, TLP's and compliant towers, particularly in deep water, require foundations that are designed to withstand extensive cyclic loading. Due to the interest in swage pile/sleeve connections a £300,000 project has been funded by a number of major oil companies and the UK Department of Energy to investigate the performance under this type of loading.

The paper describes the testing undertaken on 5.25" and 16.0" model piles. The tests consisted of axial and bending tests both "in air" and "in seawater" conducted under various loading conditions including unidirectional and through zero. The results are presented in the standard stress-endurance format and compared with the "F", "F" and "C" design classifications for weldment tubulars. The conclusion reached is that, within the test parameters of the project, fatigue related damage is not a problem.

Completion of the programme has satisfied the project participants as to suitability of the swage pile/sleeve connection for application to fatigue dominated structures.

1.0 INTRODUCTION

Swage pile connections have been used for almost 10 years to secure subsea structures to their tubular piled foundations (1, 2, 3). As experience has been gained in Europe and the USA, their versatility and advantages have been recognised by jacket designers who have also considered and applied the system. The additional connection design challenges raised by jacket requirements has led to considerable further development of the connection. In a previous OTC paper (4) the refinement of the weight of the swage sleeve was discussed, however, the issue of cyclic performance remained to be addressed.

A large number of offshore structures are required to endure cyclic loading. In some instances, particularly in the more gentle climates, this is of little significance during design. In the North Sea however, and in deep water as found in the more recent Gulf of Mexico developments, the performance of a pile/structure connection can be dominated by fatigue considerations.

As the possible financial and technical benefits of swage pile connections were recognised, several operators expressed an interest in funding a joint industry project to investigate the cyclic performance. A £300,000 project was established in 1986 with the financial support of five major oil companies and the UK Department of Energy (Petroleum Engineering Division, now the Health and Safety Executive, Offshore Division).

The project would investigate the cyclic performance of 5.25" and 16.0" diameter model piles under extensive dynamic load conditions in both axial and bending modes. The programme was conducted under the guidance of a steering committee consisting of representatives of each of the participants.