Method For Constructing Transportation Pipes And Heat Generating Pipes Utilizing Skin-effect Current

Abstract

Units of transportation pipes heated by the skin-effect current flowing concentratedly only through the inner wall skin portion of a ferromagnetic pipe in which an insulated conductor line forming a primary circuit is placed to pass AC therethrough are constructed by electrically connecting the skin-effect current heat-generating pipes at all connecting parts of the transportation pipe so as to form a secondary circuit in all units of the transportation pipe by an electric connection between the said unit of the transportation pipe and the corresponding part of the skin-effect current heat-generating pipe.

Description

BACKGROUND OF THE INVENTION

This invention relates to a method for constructing liquid transport pipes heated by the skin-effect current appearing in attached heat-generating pipes made of highly ferromagnetic metal.

The principle of the heat-generating pipe which utilizes the skin-effect current applied in the method of the present invention will be explained by referring to FIGS. 1 to 3.

In FIG. 1, 1 is a heat-generating pipe having a strong magnetic property such as a steel pipe, 2 is an insulated conductor line passed through the steel pipe, one end of which is connected to one terminal of an electric source and the other end of which is farther from the electric source and connected to the end of the steel pipe which is farther from the electric source. A conductor line 4 connects the remaining other end of the electric source to the other end of the steel pipe which is nearer to the electric source to form an electric circuit.

In such a circuit, let a resistivity of the steel pipe be .phi.(.OMEGA.cm), a permeability be .mu., frequency be f (Hz), S(cm) which is called a depth of skin is expressed by a formula

If there are relations expressed by formulas

t> 2S, d>>S, 1>>d (2)

Between S(cm), thickness t(cm), length 1(cm), and inside diameter d(cm) of the steel pipe, alternating current flows concentratedly only through the neighborhood of the inside surface of the steel pipe and no potential appears on the outside surface thereof. In other words, even when two points of the outside surface of the steel pipe are shorted with a low impedance conductor, no electric current flows therethrough.

There is an invention which utilizes the above-mentioned phenomenon; for example, U.S. Pat. No. 3,293,407 entitled "Apparatus for Maintaining Liquid being Transported in a Pipeline at an Elevated Temperature."

FIG. 2 shows a case where an electric source is of single phase and two heat-generating pipes are used.

FIG. 3 is a case where an electric source is of three phases and three heat-generating pipes are used. The circuits of FIGS. 2 and 3 are the fundamental circuits utilized in the present invention. According to the transportation pipe to which a heat-generating pipe is attached, two or more single phase circuits such as that of FIG. 2, i.e., even numbers such as 4, 6 and 8 of heat-generating pipes; two or more three phase circuits such as that of FIG. 3, i.e., a multiple of 3, such as 3, 6 and 9, of heat-generating pipes are used.

In FIG. 2, 1 and 1' are heat-generating pipes having strong magnetic property e.g., steel pipe, and 2 and 2' are insulated conductor lines passed through the steel pipes. One circuit is formed by an electric source 3, a conductor line 2, a short-circuit line 7 which connects the steel pipes 1 and 1', a connecting line 5, the heat-generating pipe 1, another short-circuit line 6 and a connecting line 4. Another circuit is likewise formed by an electric source 3', a conductor line 2', a short-circuit line 7, a connecting line 5, the heat-generating pipe 1', another short-circuit line 6 and a connecting line 4. If two circuits are equivalent, it is possible to omit connecting lines 4 and 5 or 4 and make the electric sources 3 and 3' into one source. Of course in this instance the short-circuit lines 6 and 7 remain connected and form a secondary circuit relative to the electric source.

In FIG. 3, 1, 1' and 1" are heat-generating pipes having strong magnetic property, e.g., steel pipes, and 2, 2' and 2" are conductor lines passed through these steel pipes. A circuit is formed by an electric source 3, a conductor line 2, short-circuit line 7 which connects the steel pipes 1 and 1' wherein the conductor lines 2 and 2' are passed, a connecting line 5, another short-circuit line 6 which connects the steel pipes 1 and 1' wherein the conductor lines 2 and 2' are passed and a connecting line 4. Similarly, respective circuits are formed with regard to electric sources 3' and 3". If each phase is electrically balanced with the phases as in FIG. 2, either or both of connecting lines 4 and 5 can be omitted. Of course in this case of FIG. 3, short-circuit lines 6, 7, 6', 7', etc., remain as in FIG. 2 and form a three-phase secondary circuit relative to the electric source. According to the study of the present inventor, if the respective circuits of heat-generating pipes are electrically balanced with each other in FIGS. 2 and 3, either or both of the connecting lines 4, 5 can be omitted; therefore, the method of the present invention utilizes this fact to provide the readiness of fabrication in constructing an apparatus of long transportation pipe heated by skin-effect current. Namely when a transportation pipe is long, unit transportation pipes of a unit length having a plurarity of suitable heat-generating pipes of skin-effect current which are made convenient for its transportation and construction, are constructed on the spot. In such a case, it is often desirable to avoid use of a heat-generating steel pipe which is electrically connected so perfectly as shown in FIGS. 1 to 3, because the fitting of heat-generating pipes on the spot by way of, e.g., welding or the like is difficult or even when the fitting is possible, fabrication cost, safety and the like often prevent its use.

As above-mentioned, in the method of the present invention, such an arrangement is made that a part of the secondary circuit is formed in every unit heat-generating pipe relative to the primary current flowing through the conductor line passing through the inside of the heat-generating pipe.

The above-mentioned arrangement will be illustrated referring to FIGS. 4 to 7. FIGS. 4 and 5 show single-phase circuits which correspond to FIG. 2 of the fundamental drawing and FIG. 6 is a cross-sectional view.

In FIGS. 4 to 6, 1 and 1' are heat-generating pipes having strong magnetic property, e.g., steel pipes and are electrically connected to a unit transportation pipe 8, e.g., by way of welding. 2 and 2' are conductor lines passed through the inside of these steel pipes. In the drawing, an electric source is omitted but these conductor lines form a go- and-return circuit relative to the electric source.

In FIG. 4, a unit transportations pipe 8 has flanges 9 by which the unit transportation pipe 8 is connected to the next one on the spot to complete the arrangement. In this instance, since a heat-generating pipe 1 is attached, e.g., by welding to the transportation pipe 8 as a unit heat-generating pipe, it is fairly difficult to connect neighboring heat-generating pipes mutually.

In FIG. 4, however, when a unit transportation pipe 8 is an electric conductor such as a steel pipe, each heat-generating pipe is not necessarily to be connected with each other. Of course, the conductor lines 2 and 2' must be connected as above-mentioned. As shown in FIG. 4, when the heat-generating pipes 1 and 1' are divided by a flange part 9, a secondary current which flows from the heat-generating pipes 1 and 1' into the transportation pipe, further flows into a part 6 - 7 of the transportation pipe thereby to form a secondary circuit as in case of FIG. 2 wherein the heat-generating pipes constitute the secondary circuit relative to the primary circuit constituted by the conductor lines 2 and 2'. Since the part 6 - 7 of the transportation pipe has extremely low impedance, this current never flows to the outside of the transportation pipe. Particularly since the transportation pipe of this kind is enclosed by a heat-insulating layer 11, there is no danger of contact of the metal part with an outside material. Even provided that the contact of the metal part should happen, the leakage current between two neighboring heat-generating pipes is only a trifle extent as much as several tens milivolt and practically negligible because the distance between the two neighboring heat-generating pipes is usually less than 1 meter.

FIG. 5 shows a case where neighboring unit transportation pipes 8 are laid by welding and heat-generating pipes are connected by a connecting box 10. The method which uses this connecting box can also be used in case of the flange connection as shown in FIG. 4 where unit transportation pipes 8 are connected with a flange 9.

Even when such a connecting box 10 is used, it is often difficult to electrically connect the connecting box by e.g., welding perfectly.

According to the method of the present invention, even when heat-generating pipes are not electrically connected mutually by a special way, the heat-generating pipe constitutes a secondary circuit and generates heat as in case of FIG. 4.

Namely in FIG. 5, insulated conductor lines 2 and 2' form a go- and-return primary circuit relative to an electric source after passed through the insides of heat-generating pipes 1 and 1' though the electric source and parts of terminal connection are omitted in the drawing. 9 is a connecting part of unit transportation pipes. In this case, the welding of transportation pipe provides a connection which is almost electrically perfect; hence a part of the secondary circuit formed in the transportation pipe 8 appears also at such a part as 6 and 7 of FIG. 5.

On account of the existence of a connecting box 10 in one part 12 of the heat-generating pipe in which the neighboring parts of the heat-generating pipes 1 and 1' and the connecting box 10 are not welded as shown in FIG. 5, the secondary current which flows through the inside surface skin of the heat-generating pipes 1 and 1' passes the outside skin of the heat-generating pipe and appears in one part of the transportation pipe, i.e., 6 and 7. Accordingly, it should be noted that in the part 12 of the heat-generating pipe, current flows through both the inside and the outside surface skins and the amount of heat generation is increased there compared with that in other parts of the heat-generating pipe.

In FIG. 4, a case is shown when neighboring flanges 9 are mutually electrically insulated, and in FIG. 5, a case is shown where a connecting box 10 is made of an insulating material. However, in actual case, flanges and connecting boxes are, mostly, made of a material such as steel which allows electric current to flow, hence one part of the secondary current flows through this part as a separate stream.

In actual transportation pipe facility, distribution of currents in FIGS. 4 and 5 are slightly different but they have nothing to do with the true nature of the method of the present invention.

FIGS. 6 and 7 are cross-sectional views of the part which are close to the connecting part of a transportation pipe 8 in which the method of the present invention is applied.

FIG. 6 shows a case of single phase where two heat-generating pipes 1 and 1' are used and FIG. 7 shows a case of three phases where three heat-generating pipes are used. In both the cases, 2 is a conductor line passed through the inside of a heat-generating pipe and 6 or 7 is a path of current.

The foregoing explanation is directed to cases where transportation pipes are constructed with a material having electric conductivity such as steel, but when unit transportation pipes are constructed with a material having electric insulating property such as plastic, it is possible to connect heat-generating pipes mutually in such a way that the impedance of the connecting part is as low as possible by use of a material having a good electric conductivity instead of the paths of the current on the surface of the above-mentioned transportation pipe 6, 7, 6', 7', etc.

Claims

What is claimed is:

1. Apparatus for heating a transportation pipe including a plurality of discontinuous heat-generating pipe sections, a source of electrical energy, an insulated conductor connected to said source forming a primary current path, said discontinuous heat-generating pipe sections forming series-connected portions of a secondary current path, other series-connected portions of said secondary current path being formed of portions of said transportation pipe.

2. The apparatus of claim 1 wherein said transportation pipe is made of a metallic material.

3. The apparatus of claim 2 wherein said discontinuous heat-generating pipe sections are welded to said transportation pipe.

4. The apparatus of claim 1 wherein said transportation pipe is made of non-metallic material, said plurality of discontinuous heat-generating pipe sections are attached to said transportation pipe and said discontinuous heat-generating pipe sections are mutually connected electrically.

5. A method for constructing units of transportation pipe heated by skin-effect current flowing through the inner wall skin portion of a ferromagnetic pipe including the steps of,

providing said ferromagnetic pipe of a length shorter than said units of transportation pipe,

providing a source of electrical current,

providing a primary circuit path for said current comprising an insulated conductor passing through said ferromagnetic pipe and connected to said source,

providing a portion of a secondary path for said current through a wall of said ferromagnetic pipe,

and providing a further secondary path for said current comprising a portion of said units of transportation pipe to form the respective secondary circuits in said units of transportation pipe.