ABSTRACT Fabrication of Hutton tension leg platform (TLP) required the implementation of welding and materials engineering technology in a manner that had not been generally experienced in the offshore industry. This paper addresses several issues that were necessary to ensure the successful and sound fabrication of the Hutton TLP. These issues include project planning and organization, materials and fabrication specification, the primary causes of fabrication problems, defect tolerances, and fabrication problem prevention and resolution. INTRODUCTION The tension leg platform (TLP) is an evolutionary form of semi submersible, connected to piled foundation templates on the seabed by vertical mooring lines instead of the cautionary mooring used on drilling semi submersibles. The TLP's dynamic behavior is similar to that of an inverted multifilar pendulum where the TLP's excess buoyancy provides the restoring force, instead of gravity, to keep it on station. Lateral plane movements of surge, sway, and yaw are compliantly restrained, while vertical plane movements of heave, pitch, and roll are stiffly restrained. The TLP concept provides several advantages over other structural concepts in exploiting deep water reservoirs. These prospective advantages include accessibility and maintainability of well and riser systems because of the TLP minimal vertical motions, simplification of field abandonment, and reduction of the expensive and weather sensitive offshore work by completing fabrication, outfitting, and hookup of the structure and facilities inshore. The TLP also has the advantage that the structural costs are not greatly increased for deeper water. Several of these advantages have been demonstrated by the TLP which was installed in 1984 at the UK Hutton Field in the North Sea. General descriptions of the design features of the Hutton TLP have been presented in several descriptive papers.l–3 Since the Hutton TLP (Figure 1) represented the first application of this new platform concept, several engineering tasks, including fabrication, had to be carefully addressed. Although the fabrication of the Hutton TLP was accomplished using conventional technology, it was unique because it required an implementation of that technology in a manner that had not been generally experienced in the offshore industry. In addition to its larger size, integrated deck, and relative structural complexity, the Hutton TLP is different from semi submersibles in that it will stay on station for its entire life without the possibility of dry docking. The importance of fabrication quality control cannot be overestimated in respect to this significant factor. The relative structural complexity that exists in the Hutton TLP hull is illustrated in Figure 2. This degree of complexity, in addition to its many kilometers of welds, results in poor welder and inspector access. It presents a challenge to achieving the requisite quality control standard and cannot rationally be used to condone low quality levels (i.e., quality control must match the job requirements and not be applied at the same level for every job).