GB1330091A - Method of and apparatus for burying subsea pipelines cables and the like - Google Patents

Abstract

1330091 Subaqueous pipe laying NETHERLANDS OFFSHORE CO (NEDERLANDSE MAATSCHAPPIJ VOOR WERKEN BUITENGAATS) NV 12 Feb 1973 [11 Feb 1972] 6552/72 Heading F2P A sledge for burying subaqueous pipelines or cables comprises a long rigid structure arranged to straddle the pipeline and supported on the pipeline by a series of sets of rollers disposed along the length of the sledge in such manner that a line drawn through successive sets of rollers has a shallow S-like shape, the sledge also being provided with means for fluidizing the sea bed beneath the pipeline. As shown in Figs. 4, 5 and 6, four, parallel tubes 15-18 are arranged in a saddle-like configuration and are interconnected by cross braces 24, 28 and side braces 23, 25. The rear ends of tubes 15 and 17 are interconnected for fluid flow as are the rear ends of tubes 16 and 18. The front end of each tube is flanged for connection to a source of fluid. A series of sets of rollers are secured at points along the structure, each set comprising five rollers, 27, 27a, 27b. The heights of the sets with respect to the structure are arranged to form a shallow S-bend along the sledge, the shape of the S being calculated so that it does not bend with a radius less than the minimum bend radius of the pipeline. The sledge is provided with a plurality of holes 30 along the inward facing parts of tubes 17 and 18 so that fluid introduced at flanges 19-22 may fluidize the bed between the tubes. In use, the sledge may be supported from a vessel from constant tension davits and is towed by a cable 9 (Fig. 2, not shown) from a device ahead of the sledge. The pipeline is buried in one pass of the sledge, with the weight of the sledge serving to bend the pipe into a shallow S-shape as it sinks into the fluidized sea bed. Ballast 31 and buoyancy devices 34 are used to adjust the effective weight of the sledge. Fluid is supplied to the tubes 15-18 either by four hoses from a vessel on the surface or by a pumping device on the sledge, electric cables from the vessel being used to supply saidu nit. The depth of embedment of the pipe is adjusted by adjustment of the buoyancy of the rear end of the sledge or by the use of outriggers attached thereto or by adjustment of the speed of the sledge. Rotary cutters or other means may be used to assist in loosening the soil. Adjustment of the position of the sets of rollers may be provided (e.g. by hydraulic means) so that the shape of the shallow S may be modified to compensate for variations in the level of the sea bed. The fore and aft extremities of the sledge may be vertically adjustable (e.g. by hinging) so that the curvature of the seabed may be accommodated.