Benguela-Belize Compliant Piled Tower: Tower Fabrication

Abstract Kiewit Offshore Services, Ltd. (KOS) was subcontracted by DSME to fabricate two of the major components of the Benguela-Belize Compliant Piled Tower (CPT). KOS' work scope included the fabrication and loadout of the Tower Base Template (TBT) weighing 3,200 tons and the Tower Base Section (TBS) weighing 28,000 tons. Materials used in the fabrication of the TBT and TBS included high-end API grade plates and tubulars. KOS used German, Japanese, and domestic steel mills to supply the tower material. The TBS and TBT were divided into several major subassemblies weighing from 100 to 2,000 tons. Subassembly components such as tower legs and flex legs were fabricated by domestic subcontractors and required intense subcontract coordination efforts. Due to the offshore installation window, the fabrication schedule was critical from beginning of the project and had to be accelerated to meet the delivery date. Dimensional control was a major fabrication effort and required extensive involvement and coordination between all parties involved to achieve acceptable tolerances. Given the aggressive fabrication schedule, all the riser joints and field splice coatings were applied in the air, resulting in a critical path activity which had its own unique set of challenges. KOS loaded out the TBT using self-propelled modular transporters. Due to the heavy weight of the TBS, KOS utilized strand jacks in a skidding operation to loadout thestructure onto Heerema's H-851 launch barge. Production KOS was responsible for the procurement, fabrication, loadout and sefastening of the Tower Base Section (TBS) and Tower Base Template (TBT) structures of the CPT. KOS' traditional safety program combined with Chevron's Incident and Injury Free (IIF) program resulted in a strong safety performance on an extremely fast track project. Committed to constructing a quality product, the KOS project team implemented these new programs:ekly client quality meetingsaft Quality Tool Box meetingslity stand-downs The TBS structure was 110' × 110' square, 830' long and weighed 28,000 tons. The structure consisted primarily of tubular members ranging in size from 16' to 144' in diameter, with wall thicknesses up to 4'. In addition to four main legs, the TBS had twelve pre-installed flex legs starting from Elev. (-) 485' and extending down to Elev. (-) 1,216'. These flex legs were attached to the tower main legs at the top via shear and yoke plate assemblies. Additionally, each flex leg was freely supported by a series of eight flex leg guides, which were evenly spaced along the main legs. The TBS structure is illustrated in Figure 1. The TBT structure was 110' × 110' square, 46' tall and weighed 3,200 tons. This structure had four main and four dummy legs, which were 72' in diameter with wall thicknesses up to 3.5'. Additionally, there were twelve pile sleeves (119' in diameter with wall thicknesses up to 3.5') which were connected to the main legs via short horizontal and diagonal braces. This structure was constructed and loaded out in an upright position.