Offshore Shipping Online

A publication for the offshore shipping industry published by Clarkson Research

  • Offshore Intelligence Monthly
  • Menu

    INTEC undertakes largest project to date

    News // May 9, 2003
    INTEC Engineering completed detailed design this spring of some 330 miles of deepwater pipeline and associated subsea equipment for the installation of the BP-operated Mardi Gras transportation system planned for the Gulf of Mexico. John Stearns, INTEC's project manager, says the project is going well.

    "We're challenged, we're busy and everything is coming together on schedule, with pipeline installation under way," said Stearns. He adds the installation plan calls for several phases, the first of which is the largest with all the oil and gas pipelines initially commencing in southern Green Canyon. Pipeline installation began in March this year.

    Pipelines ranging from 16 inches in diameter to a record 28 inches in diameter are destined for water depths ranging between 4,300 feet to 7,250 feet. Installations using the Heerema heavy-lift semi-submersible barge "Balder"-newly converted to accommodate the J-lay method-will continue through 2004.

    INTEC-contracted to BP for the design/engineering, procurement and installation support for the Mardi Gras subsea system from deepwater host facilities to shallow-water platforms-is undertaking its largest, most complex project to date, says Stearns. Atpeak, INTEC has dedicated up to 100 people to the project. The project, he adds, is pushing the envelope for subsea pipeline design.

    "While we're using proven technologies, we're doing things that have never been done in these ultra-deep waters while creating avenues for new infrastructure and future deepwater tie-ins," said Stearns.

    The most critical part of the design, he advises, are the steel catenary risers (SCRs)-two for each of the four deepwater floating host platforms for a total of eight gas and oil SCR installations to accommodate both gas and oil production."We've put together a team of the industry's most qualified engineers to extend riser technology," said Stearns.

    The challenge, he advises, is designing the SCRs to address fatigue due to phenomenon such as vortex-induced vibration from the floating structures-two spars and two semi-submersibles. Risers measuring 16 inches to 24 inches in diameter will be suspended from the platforms using flex joints. Strakes, spiraling down each riser, are then planned to substantially reduce the SCR vibration to manage fatigue.

    Equally challenging, says Stearns, are the subsea connections between the main pipelines and laterals, which incorporate piggable wye sleds and jumpers. Twenty sleds-some weighing as much as 110 tons and measuring approximately 60 feet by 20 feet-are planned, with asymmetrical vertical wyes selected for the subsea tie-ins to allow bi-directional pigging of the main pipeline during commissioning. Multi-diameter wyes planned for the tie-ins also will accommodate the varying sizes of the pipelines.

    "We're undertaking stringent testing procedures and system integration tests (SIT) on all this equipment to ensure its reliability for the ultra-deepwater," said Stearns.

    Pigging is a vital component of the flow assurance plan, he adds, with specially designed pigging tools and "smart" pigs integrated into the complete project scope to measure metal loss and monitor any corrosion that may occur. Pigging challenges include adjustment changes in pipe and equipment diameter; wye geometries and associated subsea jumpers; back-to-back bends; and flow variations.

    "It's imperative that the pigs are sufficiently robust and durable to withstand the environmental conditions, diameter changes and lengths associated with these pipelines," said Stearns.

    INTEC is responsible for managing the development of the pigging tools and will support BP in the testing and commissioning of the equipment. The testing process will use a test loop designed with assistance from INTEC. The commissioning program will include hydrotesting, dewatering and drying and introduction of hydrocarbons.

    For the large subsea pipelines, some 120,000 tons of steel are planned for the southern Green Canyon Area and another 70,000 tons of steel are planned for the Mississippi Canyon Area. In the southern Green Canyon Area, pipelines are planned to transportgas and oil from the Mad Dog, Holstein and Atlantis Fields; in the Mississippi Canyon Area, pipelines are planned to transport gas and oil from the Thunder Horse Field. The scope of trunklines and laterals to develop these fields is complex, with pipeline diameters including 16, 20, 24 and 28 inches.

    The Caesar Oil Pipeline System in the southern Green Canyon Area includes a trunkline from the Holstein spar to a shallow-water platform at Ship Shoal Block 332 in 430 feet of water. A lateral pipeline from the Mad Dog spar ties into the Caesar pipeline; and another lateral pipeline from the Atlantis semi-submersible facility ties into the Mad Dog lateral.

    The Cleopatra Gas Gathering System, also in the southern Green Canyon Area, is similar in configuration to the Caesar Oil line, consisting of a trunkline from the Holstein spar to the Ship Shoal facility, with laterals from Mad Dog and Atlantis tying in.

    In the Mississippi Canyon Area, the Proteus Oil Pipeline System begins with a SCR at Thunder Horse and transitions to a larger diameter trunkline to a new-build shallow-water platform at South Pass Block 89E in 400 feet of water.

    Also in Mississippi Canyon, the Okeanos Gas Gathering System consists of a lateral from Thunder Horse plus the main trunkline, which starts at NaKika and terminates at the Destin shallow-water platform on Main Pass Block 260.

    The pipelines are designed with constant outside diameters-except for the jumpers and wye sleds-to reduce the cost of pipe manufacture; for ease of installation; and to standardize subsea repair equipment. Where possible, the project team has adopted special design measures to streamline the internal bores of bends, jumpers, subsea connectors and valves.

    These measures are intended to reduce the operational risks of using pigs on a project of this complexity. The major challenges for the pig operation include multi-diameter asymmetric wyes and long-distance export pipelines.

    But before design could get under way for the mammoth project, INTEC assisted BP in confirming the viability of installing and operating large-diameter pipelines in the Gulf of Mexico's extreme water depths, verifying the design theory and structural reliability for all line pipe material and fabrication tolerances.

    "To prove the viability of the design, INTEC assisted BP in conducting a theoretical analysis and a full-scale collapse test program to verify the pipe's resistance to collapse. A full-scale fatigue test program also is under way to validate the fatiguelife of the SCRs," said Stearns.

    Results of the collapse test program included definition of:

    * Collapse envelope of the pipeline design using numerical methods

    * Strength reduction characteristics (in the circumferential direction) of line pipe material caused by the UOE pipe manufacturing process

    * Comprehensive hoop strength recovery due to thermal aging during line pipe coating

    * Structural reliability of the pipeline system and appropriate design methods for future deepwater development

    Stearns adds that one of the major concerns during the study was the impact of external hydrostatic pressure on the pipelines-ranging up to 3,245 psi in 7,300 feet of water.

    "In the final analysis, we combined the client's multiple requirements with that of the certification authority, the installation contractor and the pipe mills to produce a design that meets international standards," said Stearns.

    Bredero in Alabama is presently coating the line pipe, which is fusion-bonded epoxy-coated (FBE) for corrosion prevention. Heerema, which began sea trials in November 2002 with the J-lay vessel "Balder," is installing the pipe using standard 40-foot joints that are welded into hex-joints for J-lay.

    Subsequent to this spring's pipeline installation, in 2004 Heerema will begin installation of the SCRs, following installation of the first hulls.

    Allseas' pipelay vessel "Solitaire" began pipelay in intermediate water depths in November 2002 using the S-lay method. This work will terminate at each of the shallow-water fixed platforms.

    "INTEC will review both Heerema and Allseas installation procedures and support both contractors and BP throughout the installation process," said Stearns.

    INTEC also is helping BP facilitate permitting, which Stearns advises is "proceeding smoothly." In addition, INTEC is monitoring the assembly of the sleds and pipeline end terminals (PLETs), which is under way with Omega in Louisiana. Equipment on thesleds, including line pipe, valves, collet connectors and piggable wyes, delivered in 2002 and early 2003.

    INTEC began its participation on the Mardi Gras project in May 2000, beginning with conceptual engineering during the "Select" stage; continued through preliminary engineering during the "Define" stage; and is proceeding through detailed engineering andconstruction support for the "Execute" stage.

    Throughout each project phase, BP has placed health, safety and environmental (HSE) issues as a top priority, advises Stearns, who serves as a member of the project's HSE steering committee.

    "We've given stringent attention to safety. The entire team is safety-trained, both for occupational safety and design safety. The actual pipeline system design has undergone a complete hazard assessment to minimize risk of failure," said Stearns.

    Stearns concludes that the entire Mardi Gras project has exhibited a "can do attitude."

    "We've managed the interfaces, conducted the right research, defined the work scopes and have committed the right people to one of the industry's most dynamic projects today," said Stearns.

    More articles from this category

    More news