GB2161565A - Improved pipe for building thermally insulated conduits, and process using same - Google Patents

Abstract

Pipe for building a thermally insulating conduit, obtained by butt welding at 131 prefabricated pipe sections or bars 11 to each other, each formed by two concentrical pipes 21, 31 connected at their ends by special cylindrical joints 41 substantially having the shape of a horizontal Y fork, the annular gap 101 being filled with thermally insulating material. Additionally the area (14, Fig. 1) external to the cylindrical joints at the butt weld can be filled with insulating material after the pipe sections are connected. The connection can readily be checked for faults and prevents any undesirable cavities being formed as might happen with conventional concentric pipe joints. <IMAGE>

Description

SPECIFICATION Improved pipe for building thermally insulated conduits, and process using same The present invention relates to an improved pipe, which allows submarine conduits to be obtained free from discontinuities, and with a higher degree of thermal insulation, without varying the costs and building times relatively to a conventional conduit.

More specifically, the present invention relates to an improvement of the pipe which is the object of the preceding U.S. Patent Application No 485.437 filed on April 15, 1983.

The invention relates also to the specific process for building submarine conduits by using the said pipe.

As it is well known, when delivering several products, such as e.g. crude oil with high solidification temperature, which must be kept, while being delivered, at a temperature higher than room temperature, or liquefied gas, which requires delivery temperatures lower than the temperatures of surrounding environment, the thermal insulation is necessary of the delivery pipeline by covering it with heat insulating material, to the purpose of maintaining a temperature difference between the delivered fluid, and the surrounding environment, so as to control the fluid temperature decrease or increase within predetermined values, and for a prefixed time period.

On the other hand, for the conduit covering insulating material to maintain its efficaciousness unaltered in time, it is necessary that it be protected against any possibilities of damages, from which it could suffer during the laying of the conduit, due to its handling, as well as during its operation, by the action of environmental agents or due to accidental causes, or because of the possible penetration of water.

To this purpose, according to the teachings of the above mentioned patent application the thermally insulated conduit is built by butt welding to each other some prefabricated pipe sections, denominated "bars", each one of which is formed by two concentrical pipe, one having the diameter of the conduit to be built, and the other being of greater diameter, connected to each other at their ends by means of special cylindrical joints having their longitudinal section of double T shape, which are butt welded to the two pipes, so as to define together with them a tightly sealed annular gap, which is filled with thermally insulating material, both by applying the insulating material onto the pipe with lower diameter, coating it before of its introduction inside the pipe of greater diameter, and of the welding of the special joints to the two concentrical pipes; and, at the end of the weldings, by injecting special resins capable of forming thermally insulating foams inside said gap through suitable holes, which are then sealed.

Such a known structure fulfills evidently two typical requirements of offshore market, which consist of ensuring the preservation of heat insulating properties during the time, by protecting the insulating layer with an external tightly sealed metal covering, and of limiting the welding times on the field within the ranges of conventional conduits.

The adoption of the special joint allows indeed to join already in the factory the outside pipe and the inside pipe, with the related insertion of thermally insulating material, and therefore to have available at the moment of the installing "jacketed" bars, i.e, double-pipe bars, apparently completely equal to conventional single pipes and thus needing the same calking and welding process as the latter on the field, and therefore the same costs.

On the other hand, in said known structure, due to the particular shape of the double T joints, which are butt welded only along their outside wing, cavities are formed between welded joints which, being subsequently filled by the delivered fluid passing through the slots, render the same pipe substantially discontinuous.

The presence of said cavities, in addition to determining undesirable discontinuities in the inside delivery pipe, deprecated by the users because they create serious problems with regard to the obtainment of the necessary authorizations for the use of conduit by responsible Authorities, causes also the drawbacks of a loss ot thermal insulation by the conduit, as well as a leakage of fluid inside the said cavities. On the other side, the presence of stagnant fluid inside the cavities increases the possibility of arising of noxious corrosions and finally, as further drawbacks, problems exist as regards the check of the conditions of bar joining weldings and the monitoring of the arising of corrosions, as, said joining weldings are placed on the outside pipe, the checking systems cannot act efficaciously in a direct fashion.

Purpose of the present invention is precisely to obviate the drawbacks mentioned, and to provide a pipe which allows conduits to be obtained free from internal discontinuities, and provided with a perfect thermal insulation.

This is substantially achieved by means of the fact that the said two concentrical pipes of each bar are connected to each other at their ends by special joints of cylindrical shape, with longitudinal generatrix section substantially shaped as a horizontal Y fork, in which an external ring, welded at one of its ends to the higher diameter pipe of the bar, is connected at its other end, by means of an intermediate ring of cone frustum shape, to a lower internal cylindrical ring to be welded at its corresponding end to the pipe of the bar, which has the same diameter as of the pipe line to be assembled.

In this way indeed, when the said joints of horizontal Y shape are butt welded at their free ends, internal cavities are not generated, with the already mentioned negative results, but a conduit is formed with its inside delivery pipe being free from discontinuities, the further advantage being provided by so doing, of an improved and more efficacious checking of the state of the welds, and of the corrosion by the checking systems, as such checking can be done now by means of this structure, in a direct fashion.

Summarizing, the pipe for building a thermally insulated conduit, said pipe consisting of pipe sections prefabricated and butt welded to each other, each one consisting of two concentrical pipes, one of the desired diameter of the conduit to be built, and the other of greater diameter, which are connected to each other at their ends by special cylindrical joints butt welded to the said two pipes, so as to define in cooperation with these an annular tightly sealed gap, which is filled with thermally insulating material, is characterized according to the present invention in that the said special cylinder joints for joining said concentrical pipes have a longitudinal generatrix section having substantially the shape of a horizontal Y fork, in which an outer ring, welded at one of its ends, to said pipe of higher diameter, is connected, at its other end, by means of an intermediate ring of cone frustum shape, to a lower internal cylindrical ring to be welded to said pipe of desired diameter, at its corresponding end.

On the other side, as between the two Y shaped joints of two contiguous bars which are butt welded to each other a cavity is created, but facing towards the outside of the pipe, and being therefore easily accessible, it becomes now possible also a perfect and continuous heat insulation of the whole conduit, by filling said gap with thermally insulating material after the welding of the bars to each other.

More specifically, according to another feature of the present invention, the process for the building of a thermally insulated conduit comprises the steps of prefabricating pipe sections or bars by connecting to each other at their ends two concentrical pipes by means of special cylindrical joints having a longitudinal generatrix section of horizontal Y fork shape, butt welded to said pipes, and by filling with thermally insulating material the annular tightly sealed gap defined by said pipes and said joints as claimed in claim 1, of carrying said pipe sections or bars to the working area, and of joining them in succession, by butt welding said Y joints two by two, and finally of filling with thermally insulating material the external cavities between said Y joints welded two by two.

The invention is now better clarified with reference to the attached drawings, which illustrate a preferred embodiment of the invention, given for exemplifying purposes only and not for limitating purposes, in that technical or structural changes can be carried out always within the limits of the present invention.

In said drawings: Figure 1 shows a partial view in longitudinal section of a pipe having the structure according to the invention; Figure 2 is a cutaway perspective partial view on enlarged scale of the pipe, taken along the line A-A of Fig. 1.

With reference to the drawings, with li the prefabricated pipe sections or bars are respectively indicated, which must be butt welded to each other, to the purpose of building a thermally insulated conduit, and of which in Fig. 1. only two adjacent sections are shown, respectively 1, and 12.

Each section or bar li is formed by two concentrical pipes 2, and 3,, of which the internal one 2, has the desired diameter of the conduit to be built. Said concentrical pipes 2, and 3, are then joined to each other at their ends by two identical special cylindrical joints 4,, which are then butt connected to said pipes by means of the welds 5, and 6,.

Said special joints 4, have their longitudinal generatrix of substantially horizontal Y shape (see especially Fig. 2), in which an outer ring 7,, which is butt connected by the weld 6, to the pipe of greater diameter 3" is connected at its other end, by means of an intermediate cone frustum shaped ring 8j, to a lower cylindrical ring 9,, which is in its turn butt joined by means of the weld 5j to the inner pipe 2,.

In such a way, between the joints 4, and the pipes 2, and 3, a tightly sealed annular gap 10i is defined, which is filled with thermally insulating material. Said filling can be carried out both by applying the insulating material onto the inner pipe 2, before inserting it inside the outer pipe 3, and welding the special joints 4,, and by injecting special resins inside the same gap 1 0, through suitable holes, which are later on sealed.

To the purpose of forming the pipeline, the pipe sections or bars 1, so manufactured are then successively butt connected to each other, joining by means of an annular weld 12 (see Fig. 1) the end edges 13, (see Fig. 2) of cylindrical ring 9, of said special joints 4,.

Finally, according to the process of the invention, the outer cavities 14 which are formed between the adjacent joints 4, welded to each other, are they too filled with thermally insulating material.

Claims (5)

1. Pipe for building a thermally insulated conduit, formed by prefabricated pipe sections butt welded to each other, each section consisting of two concentrical pipes, one pipe having the desired diameter of the conduit to be built, and the other pipe being of greater diameter, which are connected to each other at their ends by means of special cylindrical joints butt welded to said two pipes, so as to define together with these a tightly sealed annular gap which is filled with thermally insulating material, characterized in that the said special cylindrical joints for connecting said concentrical pipes have a longitudinal generatrix section substantially shaped as a horizontal Y fork, in which an outer ring, welded at one of its ends to the said tube of greater diameter is connected at its other end, by means of an intermediate cone frustum shaped ring, to a lower inner cylindrical ring to be welded to said pipe of desired diameter at its corresponding end.

2. Process for building a thermally insulated conduit, characterized in that it comprises the steps of prefabricating pipe section or bars by joining to each other at their ends two concentrical pipes by special cylindrical joints whose longitudinal generatrix section has the shape of a horizontal Y fork, butt welded to said pipes and filling with thermally insulating material the tightly sealed annular gap defined by said pipes and said joints as claimed in claim 1, of transporting to the working area said pipe section or bars and of joining them in succession by butt welding said Y shaped joints two by two, and finally of filling with thermally insulating material the outer cavities between said Y shaped joints welded two by two.

3. Improved pipe for building thermally insulated conduits substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

4. Process for building a thermally insulated conduit, substantially as hereinbefore described with reference to the accompanying drawing.

5. A thermally insulated conduit, when produced by the process claimed in claim 2 or claim 4.