Development of an Unmanned Deepwater Pipeline Repair System

Abstract

ABSTRACT A pipeline repair system has been designed for performing all tasks required to locate, assess, and repair damage to pipelines in water depths beyond diver capability. Trade-off studies indicate that the system is also applicable for water depths within diver capability. A cooperative industry development program sponsored both the detailed preliminary design for the entire system and detailed fabrication level design of critical components. Critical components have or will undergo model and prototype testing. The system is designed to be able to perform such activities as soil excavation, pipe-coating removal, pipe cutting, end preparation, and transport and positioning of replacement sections. The technology to implement these activities constitutes a significant advance in offshore pipeline repair technology when combined into a single system. INTRODUCTION The capability to repair marine pipelines damaged by corrosion, storms, earth movement, third parties, etc. in water depths beyond the practical reach of divers is a near-term requirement for offshore oil and gas producing operations. To meet this requirement, a cooperative industry program to develop an unmanned pipeline repair system was initiated in late 1973. The result of this program was a detailed preliminary design of equipment and procedures as well as prototype testing of selected critical components. SYSTEM DESCRIPTION The basic system consists of two separate vehicles for deployment of tools and pipe-repair components to the seafloor work site. The Work Vehicle (WV}, Fig. 1, is an unmanned, umbilically tethered, tool platform used for observation, excavation, pipe preparation, and light manipulative tasks. The Vertical Transport Vehicle (VTV), Fig. 2, is a buoyant, umbilically tethered, heavy load lowering platform for transporting the large, heavy pipe connection and replacement equipment. In areas where relatively calm seas persist, two large workboats could be used to deploy these vehicles. Other equipment includes a power and control cable to each of the two vehicles, plus the pipeline repair and replacement components. A key feature of the repair system is that it can adapt to a wide variety of damage situations including damage to a buried pipeline. The design is based on a maximum diameter of 36-in for a concrete coated pipe. Equipment is designed for a depth of 4000 ft, but the system is relatively insensitive to water depth.(Equation available in full paper) Structure. Principal elements comprising the vehicle are two mirror image trussed hull structures joined at their top by six composite beams upon which are attached six buoyancy units. The hulls are completely floodable simple trusses having a light-weight sole plate and a sheet fairing on the outboard sides. All structural elements are of special alloy aluminium. The hulls carry the principal items of machinery including electric motors, hydraulic systems, switch gear, etc.