Pipe joints or couplings – Having plural independent paths – For concentric tubes or pipes
Reexamination Certificate
2000-03-24
2001-05-15
Nicholson, Eric K. (Department: 3627)
Pipe joints or couplings
Having plural independent paths
For concentric tubes or pipes
C285S047000, C285S123100, C285S288100, C285S915000
Reexamination Certificate
active
06231086
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to methods and apparatus for joining sections of double-wall steel pipe. Double-wall steel pipes are typically used in specialty pipeline systems to provide an additional measure of protection for containment of the material being transported. For instance, double-wall steel pipelines are typically installed in subsea operations and are often used for the transportation of corrosive or hazardous material. The annulus between the two “walls” may be filled with an insulation material to provide thermal protection for temperature-sensitive materials, such as crude oil or heavy fuel oil, where external pipe insulation methods are not suitable. In some applications, the combination of both leak containment and thermal protection are desirable.
A double-wall steel pipe typically comprises a steel outer casing and a steel inner carrier pipe. The outer casing provides bending, and tensile strength to the pipe, in addition to providing containment of the material being transported. The inner carrier pipe provides bending and tensile strength, as well as radial strength.
Historically, sections of double-wall steel pipes have been joined by welding both the inner carrier pipe and the outer casing. The inner carrier pipe must extend beyond the outer casing on both ends of adjacent double-wall sections in order to provide access for full circumference welding and weld inspection. Welding is done either by a machine affixed to the inner carrier pipe or by hand. After the sections of inner carrier pipe are welded, a two-piece steel joint is used to join the steel outer casing. This two-piece casing joint is comprised of two half-rings of sufficient length to join adjacent sections of outer casing. The half-rings are fabricated from a section of steel pipe with the same outside diameter, wall thickness and steel grade as the steel outer casing. The steel pipe section is cut to fit the open area remaining between adjacent outer casing sections. The two half-rings are formed by cutting the steel pipe section axially 180° apart. One half-ring forms the bottom portion of the casing joint, the second half-ring the top portion. Two axial welds join the half-rings to form the outer casing joint. Two full circumference welds join adjacent sections of steel outer casing to the steel casing joint. This method of joining two sections of double-wall steel pipe is both time-consuming and labor-intensive.
The present invention eliminates the step of welding in order to join the inner steel pipe. In addition, the present invention succeeds in joining the steel outer casing of adjacent double-wall pipe sections with one weld instead of four. Reducing the number of welds required saves time and increases production.
The disadvantages of the prior art are overcome with the present invention, and novel methods and apparatus are hereinafter described for efficiently and reliably joining together sections of double-wall steel pipelines.
SUMMARY OF THE INVENTION
In an exemplary embodiment of the present invention, convenient lengths of double-wall steel pipe may be formed in a manufacturing plant, comprising a steel outer pipe or casing, a steel inner pipe or carrier, and an optional annular foam or other insulating material. If foam or another insulating material is used, both the casing and the carrier will extend a short distance beyond the annular insulating material, leaving an annular void at both ends of each pipe section. The double-wall steel pipe joint is formed in the general shape of a ring fabricated according to the diameter of the double-wall steel pipe. The joint ring is a steel band having a serrated inner circumference, or bore, which is slightly tapered at both ends. The outer circumference of the ends of the steel inner pipe is also serrated. Serration geometry provides resistance to axial tension and pullout during installation and during subsequent heating and cooling cycles. A groove may be cut in the end of each section of inner pipe to hold a hydraulic O-ring.
In the field, the double-wall steel pipe may be joined by installing the pipe joint of the present invention according to the following procedures. Prior to joining, the joint ring may be heated, causing it to expand. Epoxy is applied to the ends of the steel inner pipe, which have circumferential serrations on their outer circumferences. Epoxy is also applied to the serrated bore of the joint ring. The joint ring is then slipped into the annular space as the two pipe sections it connects are pulled together. As the joint ring cools, it contracts, locking onto the ends of the sections of inner pipe it joins. To ensure performance, taper in the bore of the steel joint ring must not be great enough to cause the steel inner pipe to yield. Inner pipe deformation should be in the elastic range. The elevated temperature of the joint ring increases the cure rate of the epoxy, reducing the time required for the epoxy to achieve its requisite strength. The sliding engagement and the contraction of the joint ring onto the serrated inner pipe ends, along with the epoxy film therebetween, seal the joint's bore to the inner pipe, without welding.
Low operating pressure systems and/or small pipe diameter systems may be joined without preheating the joint ring. These systems will typically require less insertion force for full depth insertion of the inner pipe into the joint ring. Additionally, less than optimum epoxy strength may be sufficient for form a fully-sealed joint for low operating pressure system requirements. For example, an epoxy may develop a lap shear of 2,500 psi at low temperatures and 3,000 psi or more when cured above 150° F. If the force required for insertion is not excessive and if the epoxy lap shear strength required is obtainable at lower temperatures, preheating will not be required.
After the ends of the inner pipe are joined, adjacent ends of the sections of steel outer casing are welded together, completing the joining operation. As the outer casing is welded, the joint ring acts as a heat sink. The heat absorbed by the joint ring keeps the epoxy, which is located where the joint ring contacts the surface of the inner pipe, in the desired temperature range for both minimum cure time and maximum strength development.
The joint ring is fabricated to have higher radial and tangential strength than the steel inner pipe, allowing the joint ring to form a tight seal when inner pipe is under high pressure. Sealing surfaces are axially aligned. Therefore, high pressure forces the inner pipe wall to press against the joint, sealing the joint tightly.
Double-wall steel pipe assemblies are suitable for many pipeline applications in which the use of single-wall pipe is not acceptable due to environmental, safety, thermal, negative buoyancy, and other considerations. In addition to its reliability with respect to sealing the fluids carried by the steel inner pipe, the pipe joint described herein offers cost effectiveness due to the efficiency of its installation. Therefore, its use in the installation of double-wall steel pipelines is preferable to the use of pipe joints which require welding to join both the inner pipe and the outer casing of sections of double-wall steel pipe.
The present invention may also be applied as a bell and spigot. Welding one side of a joint ring onto an end of a steel inner pipe forms the bell. The other end of the steel inner pipe, fabricated with full circumferential serrations, is the spigot. The procedure used to join the sections is similar to that described above. However, in the field, the joint ring requires no handling, and epoxy application is reduced by half.
The present invention may also be applied joining single-wall steel pipe when welding is not possible due to an explosive atmosphere or the presence of a pipe coating and/or lining that cannot withstand the heat of welding.
Accordingly, it is an object of the present invention to provide a novel joint for joining sections of double-wall steel pipe.
Another object of the p
Gaskin Mary J.
Nicholson Eric K.
Unisert Multiwall Systems, Inc.
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