Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,... – Submerging – raising – or manipulating line of pipe or cable...
Patent
1997-03-07
1999-04-13
Graysay, Tamara L.
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
Submerging, raising, or manipulating line of pipe or cable...
4051681, F16L 123
Patent
active
058936823
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the laying of pipelines under water, and especially to a method and an apparatus for controlling the stress and strain experienced by a pipe while it is being laid.
One method of installing submarine pipelines for use, for example, in the oil industry, is to form the pipeline on the deck of a vessel known as a laybarge, by welding together lengths of previously prepared pipe. The laybarge moves forward continuously, and as it does so the pipeline is fed into the sea from the rear of the laybarge. As the pipeline is fed into the sea, further lengths of pipe are welded onto the end of the pipeline that remains on the laybarge. The pipeline may be up to about 1.8 meters in diameter, and typically consists of steel pipe clad in concrete. At the "field joints" where two lengths of pipe are welded together on board the laybarge, there is of course a gap between the concrete claddings, which is usually filled with pitch or the like flush with the surface of the concrete.
The pipeline is supported on the laybarge by a number of pipe support rollers, which allow the pipeline to run freely as it is fed into the sea. The pipeline descends from the laybarge down to the seabed in a curve that is determined by the stiffness of the pipe, the tension on the pipe (which is controlled by tensioners acting as brakes near the front end of the series of rollers), the depth of the sea, and the angle at which the pipe leaves the laybarge.
The steeper the angle at which the pipeline leaves the laybarge, the more directly it descends to the seabed, and the smaller the tension necessary to maintain a satisfactory path without, in particular, an abrupt downward curve where the pipeline leaves the laybarge.
There are practical limits on the steepness of the path of the pipeline as it extends along the laybarge, and it is therefore known, in order to increase the angle at which the pipeline leaves the barge, for its path along the series of rollers to be appreciably curved.
This curvature results in stress on the pipeline; the greater the curvature of the pipeline, the greater the stress. As any stress causes strain in the material that reduces the quality and lifetime of a pipeline, pipelayers have recently been required to ensure that the stress on the pipeline does not rise above a specified maximum level. It has been proposed to calculate the optimum curvature for a particular pipe-laying operation so as to minimise the stress and strain on the pipe, and to adjust the exact vertical positions of the pipe-support rollers, before pipe-laying begins, in order to give the calculated path.
The calculated stress and strain analysis assumes that the pipeline has a smooth surface and a uniform cross-section and stiffness. In practice, however, the pipeline is not uniform. For example, irregularities as high as several cm on a 1 meter diameter pipe may occur in the surface of the concrete cladding of the pipeline, field joints may not be perfectly flush, integral cylinder buckle arresters or anodes may project from the surface of the pipe, or the pipe may be out of roundness.
When such a local imperfection passes over a pipe support roller, it results in a sudden alteration in the load distribution on the pipe support rollers, and consequently may result in a sudden increase in the stress and strain on the pipe at the point of the imperfection. For example, when a section of pipeline having a greater diameter than that used when calculating the optimum heights of the pipe support rollers passes over a pipe support roller, it will result in a sharp increase in the stress on the pipe at the point where it passes over that roller, and a sharp decrease in the stress at the rollers adjacent to that roller.
Even if the pipe is in fact uniform, the movement of the laybarge under the action of wind and waves may cause changes in the load distribution on the pipe-support rollers and, in the worst case, the pipeline may actually lift off the last roller or the last few rollers and slam down again with a sudden stress and st
REFERENCES:
patent: 3658222 (1972-04-01), Dressel et al.
patent: 3669329 (1972-06-01), Blanchet et al.
patent: 3872680 (1975-03-01), Nicholson et al.
patent: 4015435 (1977-04-01), Shaw
patent: 4030311 (1977-06-01), Rafferty
patent: 4230420 (1980-10-01), Chow
patent: 4260287 (1981-04-01), Uyeda et al.
patent: 4802794 (1989-02-01), Lynch
patent: 5044825 (1991-09-01), Kaldenbach
patent: 5106070 (1992-04-01), Reist
patent: 5413434 (1995-05-01), Stenfert et al.
European Marine Contracters Limited
Graysay Tamara L.
Lagman Frederick L.
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