The lifting truss is composed of several truss single sections, and each truss section is connected by a holding card device, which can adjust the connection between the truss sections and switch between a fixed and hinged connection. This equipment has a pair of slide rails arranged on both sides of the moon pool on the platform deck, and two truss frames arranged on the slide rails, which guide two lifting trusses, thus allowing convenient locating at a designated position to lower the lifting trusses to the sea floor to lift the pipe. Recently, new submarine pipeline maintenance equipment has been proposed. Additionally, dredging before maintenance and trenching the pipeline after maintenance currently requires using a hydraulic jet trencher, and the substitution of these pieces of equipment or ships during construction also reduces the efficiency of pipeline maintenance. However, bundling buoys or float bags typically requires a long time, particularly when a long pipe section must be lifted from a relatively deep seabed with many buoys or float bags. When laying submarine pipelines and while they are in service, a pipeline lying on a seabed may be lifted to a barge deck for welding to repair mechanical damage or even replace local segments, which usually includes four steps: (1) underwater dredging, cutting and removing the damaged pipe section, connecting the ship's sling at the pipe cut positions, and having divers arrange buoys or float bags along the pipe segment to be raised (2) lifting the cut pipelines to the deck and lowering the pipelines back to the seabed after welding the flanges (3) connecting the cuts of both sides of the pipeline with a new pipe segment using a ball flange to replace the damaged pipeline section and (4) trenching with a hydraulic trenching machine to sink the repaired pipeline back into the trench.ĭuring these repair procedures, divers arrange buoys or float bags along the pipeline to reduce stress on the submarine pipeline during lifting to avoid damaging the pipeline. Submarine pipelines have been widely used to transport oil and gas, from offshore oil and gas fields to storage facilities and processing terminals onshore. Numerical results can then be used to design a lifting strategy to protect the pipeline. When the lifted heights at truss positions are shown, the lifting deformation, lifting forces, bending moment distribution, and axial force distribution can be analyzed using a dedicated analysis program. Also, the triple-point lifting mode of truncated maintenance and the two-point lifting mode of online maintenance are discussed.
#Orcaflex seabed friction coefficients software
The BVP4C module in MATLAB software is used to solve this multiple-point boundary value problem issued from first-order differential equations. The typical two-point sequence secant iterative technique is used to obtain the unknown lifted length and determine pipeline lifting configurations. A pipeline can be divided into the lifted portion and the touch-down portion that lies on the seabed, and each of these portions can be analyzed separately by converting the continuity conditions at the touch-down points to boundary conditions. For new submarine pipeline maintenance lifting equipment, a specialized analysis model is constructed in this study.