One of the cornerstones of BP's Mardi Gras transportation system project has been the testing and verification of the new technologies and equipment being developed.
Among the major components that received extensive testing and trials were riser welding, pipe performance, subsea connections, and pipelaying.
Riser welding
To test its proprietary design techniques for the large-diameter steel catenary risers, Mardi Gras will test to verify that the riser welds would be suitable for the life of the Mardi Gras system.
Of all the riser components, these welds are the most susceptible to the stresses caused by both vessel motion and vortex-induced vibrations that result from current fluctuations at multiple water depths.
Test joints of SCR pipe are being welded together by Heerema Group, the project's installation contractor, using the welding equipment and procedures to be used in the field. The welded lengths will then be subjected to fatigue testing by Stress Engineering Services Inc., Houston, before the designs are accepted.
Pipe performance
In 2001, BP America bought samples of the heavy-walled line pipe it intended to use from Sumitomo Metals. In a $1-million testing program, the Center for Frontier Engineering & Research (CFER), Edmonton, performed full-scale collapse tests, applying external pressure and bending forces until the pipe failed.
The experimental data underpinning existing design codes do not extend to wall thicknesses, diameters, and installation stresses of the Mardi Gras system. The testing program's goal, therefore, was to verify that the existing codes could be extrapolated to cover this new application.
The tests confirmed the pipe's suitability for the intended application and also verified that the heat treatment applied during the coating process actually enhanced the pipe's resistance to collapse at depth as predicted. The pipe performed so well in both tests that BP was able to reduce the wall thickness slightly and still maintain pipe integrity.
Pipe connections, laying
To verify that the pipe, equipped with wye-sled assemblies and pipeline end terminations, was actually layable with the newly modified Balder J-lay vessel, BP performed extensive J-lay trials in December 2002 and January 2003.
BP asked Omega Natchiq Inc., New Iberia, La., to supply one trial WSA and one PLET for installation during the pipelay trials. The trials consisted of laying 6 miles of 28 and 24 in. pipe in deep water, including the installation of the trial WSA and PLET. The trials proceeded successfully, after which all pipe and sleds were recovered and inspected.
In addition to the pipelay trials, Omega Natchiq conducted system integration tests (SITs) to verify connectivity, functionality, and proper operations of all subsea equipment for the tie-in systems.
The SITs involved simulating topsides preparation, subsea jumper installation, commissioning, and contingency operations on a dry land test site, including the simulation of ROV interfaces to verify operability. The test also included connecting the jumpers to the collet connectors with structural jacking bases fabricated by Omega Natchiq and supporting the WSAs and PLETs to simulate in-place misalignment.
After completion of SITs, the structures were loaded and sea-fastened onto a Heerema barge to be transported to the Balder for installation.