Pipes and tubular conduits – Reinforced
Reexamination Certificate
1999-10-04
2001-05-08
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
Reinforced
C138S115000, C138S148000
Reexamination Certificate
active
06227252
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a reinforced pipe and method for making same and in one aspect relates to a reinforced pipe comprised of two concentrically positioned pipes having a honeycombed, reinforcement material therebetween wherein said reinforced pipe is capable of withstanding the high external pressures nominally encountered where the reinforced pipe is used to construct a submerged pipeline for transporting gas in deep water environs.
2. Background
As is well known, large volumes of natural gas (i.e. primarily methane) are produced from submerged wells which lie in varying depths of water throughout the world. This gas has significant commercial value if it can be economically transported to market. Where the situation permits, submerged pipelines are laid along the marine bottom from the producing well(s) to the shore or to a collection riser which, in turn, brings the produced fluids to the surface for further handling. In relatively shallow depths, e.g. 2000 feet or less, a heavy, single-wall, large-diameter pipe is routinely used to construct such submerged, gas pipelines. However, as exploration and development efforts move into deeper and deeper waters, the use of such single-wall pipe for submerged pipelines becomes more and more limited.
For example, hydrocarbon deposits are now known to exist in subsea reservoirs which lie under extreme water depths; i.e. 6000 feet or more. However, the hydrostatic head at these depths (e.g. 3000 psi at 6600 feet) will collapse most single-wall pipes now commonly used in submerged pipeline construction unless a substantially equal internal pressure (e.g. 3000 psi) is maintained within the pipeline. Unfortunately, this is not always possible since these deep-water pipelines must be vented down to ambient pressure (e.g. about 15 psi) at various times during operation whereupon most, if not all, single-walled, submerged pipelines of the type now commonly used would collapse due the large differential between the internal and external pressures being applied on the pipe.
Also, for any deep water pipeline to be practical, it must be capable of being installed from existing lay barges using the “J-lay” or similar method. While theoretically it may be possible to build a single-walled, large diameter pipe having a wall thickness great enough to resist collapse under the high differential pressures encountered during installation and operation in deep water, the size and weight of such a pipe would be so great as to make its use impractical. That is, for any pipe to withstand the external pressures at these extreme water depths, the thickness of the pipe wall will have to be in excess of about 3.75 inches. This, in turn, requires that every joint of such pipe to be post-weld, heat-treated. Such a process would take in excess of 24 hours per weld thereby making use of such pipe impractical and commercially unacceptable, especially where the submerged line is to be several miles long.
Accordingly, for a pipe to find practical use in deep water environments, the wall thickness of the pipe must be less than 1.25 inches to avoid the need for post-weld heat treatment. Also, the pipe has to be light enough in weight to be installed from existing lay barges after the barges have had only minor modifications.
SUMMARY OF THE INVENTION
The present invention provides a reinforced pipe capable of withstanding large differentials in external and internal pressure which is especially useful in constructing pipelines which, in turn, are to be submerged in great water depths and a method for constructing said reinforced pipe and for joining two lengths thereof together.
More specifically, a length of the reinforced pipe in accordance with the present invention is comprised of a length of an outer pipe concentrically positioned over a length of inner pipe to form an annulus there between. A honeycomb, reinforcing material which is comprised of rows of cells is positioned in the annulus with the longitudinal axis of each cell being aligned with a radius of said inner pipe. The reinforced pipe may be constructed in number using different techniques.
For example, the outer pipe may be heated to expand its inner diameter before it is positioned over the honeycomb material, the outer pipe is then allowed to cool to shrink into contact the honeycomb material to tightly contain the honeycomb material within the annulus. Another technique involves splitting the outer pipe along one side to open a seam therein. The outer pipe is then spread to effectively increase its inner diameter before it is fitted over the honeycomb material. The outer pipe is then allowed to return to its original configuration and the seam is closed by welding or the like to tightly contain the honeycomb material within the annulus between the inner and outer pipes.
Preferably, the honeycomb material is positioned along only a portion of the length of the inner pipe and the length of the outer pipe is shorter than the length of the inner pipe so that each end of the inner pipe of each length of joint of reinforced pipe is bare and exposed. In joining two adjacent lengths of the reinforced pipe together, the respective exposed ends of the two lengths are abutted and joined together by welding or the like. Additional honeycomb material is positioned around the joined, exposed ends and extends between the ends of the honeycomb material on the respective lengths of reinforced pipes.
A short length of additional outer pipe is next secured around the honeycomb material between the respective ends of the outer pipe of the respective lengths of reinforced pipe to complete the connection between the adjacent lengths of reinforced pipe. When constructing a submerged pipeline, these connections are made at the surface on a lay barge or similar vessel and the pipeline is continuously lowered to the marine bottom as the respective lengths are joined together.
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Brinson Patrick
Mobil Oil Corporation
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