JP4430783B2 - Protective cover for buried steel pipe welds - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a covering for protecting a welded portion of a buried steel pipe that is electrically protected for fluid transportation such as gas, petroleum, chemicals, and water.
[0002]
[Prior art and problems to be solved by the invention]
The buried steel pipe is coated with a plastic material or the like and is subjected to anticorrosion processing, but it cannot be completely anticorrosion only by covering processing, and is used in combination with electrocorrosion protection. Although there exist an external power supply system, a galvanic anode system, etc. in an anticorrosion, any may be sufficient as this invention.
[0003]
As described above, the buried steel pipe is pre-corrosion-treated with a plastic material or the like, but the welded portion of the steel pipe cannot be pre-corrosion-prevented, and after welding, the welded-part protective cover is attached and then buried in the ground. Is. This protective covering uses heat-shrinkable tubes, covers the welded part and the left and right ends of the anticorrosion coating part near the welded part, heat-shrinks them, adheres to the periphery of the welded part, and then covers them with a corrosion-resistant synthetic resin. It was normal to tighten.
[0004]
However, the work of heat-shrinking the heat-shrinkable tube and bringing it into close contact with the surface of the welded steel pipe is more difficult as the pipe diameter of the buried steel pipe increases, and an anticorrosive adhesive layer is applied to the inner surface of the heat-shrinkable tube. The work is more difficult. If something with poor construction is buried in the ground, water will accumulate between the heat shrinkable tube and the surface of the welded steel pipe, and rust will occur on the surface of the welded steel pipe. Cannot be protected.
[0005]
On the other hand, the basics of cathodic protection are to prevent electricity from flowing from the ground to the steel pipe, but current does not easily flow from the ground to the steel pipe welded portion covered with the corrosion-resistant synthetic resin.
[0006]
In such a state, it cannot be said that the anticorrosion is carried out and is not preferable.
[0007]
Therefore, even if water accumulates between the heat-shrinkable tube and the surface of the steel pipe welded portion, current is prevented from flowing from the surface of the steel pipe welded portion to the ground, and electric power is supplied from the external power source to the surface of the steel pipe welded portion through the ground. It is conceivable to wind a conductive tape of a certain width on a heat shrinkable tube covering the surface of the welded steel pipe so that it is easy to flow, but it is expensive and impractical.
[0008]
As described above, the prior art has insufficient protection of the welded portion of the buried steel pipe, but the present invention intends to provide a cover that efficiently protects the welded portion of the buried steel pipe with an inexpensive material. That is, it is easy for current to enter the protective cover from the ground.
[0009]
[Means and Actions for Solving the Problems]
The present invention solves the above-described problem, and is a cover for protecting a welded portion of an embedded steel pipe that is electrically protected by an external power supply system, and includes a welded portion and left and right end portions of the steel tube anticorrosive coating portion near the welded portion. Welding of buried steel pipes, characterized in that the heat-shrinkable tube is heated and brought into close contact with the steel pipe, the biodegradable resin foam sheet and the plastic net are wound on the tube, and the entire cover is tightened with a plurality of holding tapes. This is a protective covering for the part.
[0010]
Although a commercially available heat-shrinkable tube can be used as it is, a heat-shrinkable tube for corrosion prevention in which an adhesive layer having a high anticorrosion property is applied to the inner surface is preferable. The heat-shrinkable tube may be inserted into the steel pipe before welding, and after welding, the tube may be moved and contracted by heat so that the central portion of the tube comes to the welded portion.
[0011]
The heat shrinkage may be applied to both end portions of the steel pipe anticorrosion coating portion sequentially starting from the central welded portion. The heat shrinkable tube may be made of any material such as polyethylene, polypropylene, or crosslinked polyethylene, and a commercially available product can be used as it is.
[0012]
The plastic net is wound to make it easier for current to enter from the ground into the steel pipe weld cover. The biodegradable resin foam sheet is a biodegradable resin foam sheet that is completely decomposed into water and carbon dioxide by microorganisms in nature. If there are two layers of plastic nets, they should be interposed between them. .
[0013]
By doing so, it is possible to more reliably prevent the surface of the steel pipe anticorrosion coating and the heat-shrinkable tube from being damaged by sand and soil during backfilling and until the soil is stabilized thereafter.
[0014]
【Example】
Example 1
FIG. 1 is a schematic cross-sectional illustration in the center of the tube axis direction showing a state in which an external power source and its electrodes are omitted and a welded portion protective cover for a buried steel pipe according to the present invention is attached.
[0015]
In FIG. 1, 1 is a buried steel pipe having a diameter of 1000 mm, 2 is an anticorrosion coating previously applied to the surface of the steel pipe, 3 is a welded portion, 4 is a heat-shrinked thickness of about 2.0 mm (cross-linked polyethylene layer of outer layer agent) And a butyl rubber adhesive layer as an inner layer agent), a heat-shrinkable tube having a width of 550 mm (Rapco tube E50 manufactured by Furukawa Electric), 5 is a flexible plastic net made of medium- and low-pressure polyethylene having a thickness of about 1 mm and a width of 100 cm (Takirontori) Carnet N-11, scale 0.4 to 0.8), which is cut slightly longer than the circumference of the pipe and wound so as to partially overlap the pipe side face.
[0016]
6 is a biodegradable resin foam sheet (uses Furukawa Electric Bioace, an aliphatic polyester resin) with a thickness of 0.5 mm and a width of 100 cm. It is converted to water and carbon dioxide within one year by microorganisms in the natural soil. Although it is to be decomposed, it is a flexible sheet having an appropriate tensile strength before being decomposed. This foam sheet 6 is an uncrosslinked foam sheet that is cut so as to be longer than the pipe circumference and is wound so as to partially overlap in the same manner as the plastic net 5. Although it depends on the type of soil, the temperature, the thickness of the sheet, etc., it will be completely decomposed in about 1 year. When refilling the welded protective cover of a welded steel pipe into the ground, there is a risk that sand, earth, etc. will pass through the net of the net due to earth pressure and hit the heat-shrinkable tube or anticorrosion coating part of the steel pipe directly by the net alone. In addition, after refilling, the soil does not stabilize for a while and sand and soil often move.
[0017]
Therefore, a biodegradable resin foam sheet is wound around the inside of the net to prevent the surface of the heat-shrinkable tube or steel pipe from being damaged by sand, earth, or the like. If this biodegradable resin foam sheet has been in the ground for nearly one year, it will be decomposed into water and carbon dioxide as described above and disappear.
[0018]
However, after almost a year, the soil is stable, the sand and soil will not move, and the sand and soil will hardly pass through the mesh of the net and hardly damage the surface of the anticorrosion coating part of the steel pipe or the heat shrinkable tube. It is well protected only by the net. The material of the net may be any of polyethylene, polypropylene, EVA, and the like, and commercially available plastic nets, for example, Takiron Co., Ltd. Tricarnet.
[0019]
For the pressing tape No. 7, a plastic resin having an adhesive layer having a width of 70 mm and a thickness of 0.5 mm was used. Reference numeral 8 denotes an inner plastic net provided as necessary.
[0020]
Examples of the biodegradable resin foam sheet include those obtained by foaming aliphatic polyester as a base resin with carbon dioxide, such as Bioace manufactured by Furukawa Electric. The holding tape may be made of a commercially available synthetic resin for packing, and may be tightened at a plurality of locations so that the plastic net does not come off.
[0021]
Example 2
On the other hand, as shown in claim 2 as another aspect, it is a cover for protecting a welded portion of an embedded steel pipe that is electrically protected by an external power supply system, and is provided on the left and right sides of the welded portion and the steel tube anticorrosive covering portion near the welded portion. A heat-shrinkable tube that covers the end of the tube is heated so that the tube is in close contact with the steel pipe, and a two-layer plastic net is wound on the tube, and a biodegradable resin foam sheet is interposed between the two-layer plastic net There is a protective covering for the welded portion of the buried steel pipe, characterized in that the entire covering is tightened with a plurality of pressing tapes. That is, two layers of plastic nets are wound, and a biodegradable resin foam sheet is inserted between the two layers, and the plastic nets are wound around four places. 8 is a flexible plastic net made of medium- and low-pressure polyethylene with an inner thickness of 1 mm and a width of 100 cm (Takiron Tricarnet N-24 mesh 10-25), which is provided as necessary, and has the same length as the pipe circumference. It is cut so that both ends meet at the top of the tube.
[0022]
【The invention's effect】
The welded protective cover of the buried steel pipe of the present invention may damage the surface of the anticorrosive coating of the pipe and the heat shrinkable tube due to the movement of sand and soil due to earth pressure when filling back into the ground after welding and the instability of the earth. Can be prevented by a biodegradable resin foam sheet having an appropriate strength.
[0023]
This biodegradable resin foam sheet disappears after nearly one year, but the earthen soil in which the steel pipe is embedded is stable, and the surface of the anticorrosion coating and the heat shrinkable tube of the steel pipe is damaged without the movement of sand and soil. Almost nothing. On the other hand, if the biodegradable resin foam sheet disappears and the welded portion protective cover is made only of the heat-shrinkable tube and the plastic net, an electric current can easily enter, and corrosion can be prevented by electric corrosion protection.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic illustration of a central cross section in the direction of a pipe axis showing a state where a protective cover for a welded portion of an embedded steel pipe according to the present invention, in which an anticorrosion equipment is omitted, is attached.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Embedded steel pipe 2 Corrosion-proof coating 3 Welding part 4 Heat shrinkable tube 5 Plastic net 6 Biodegradable resin foam sheet 7 Pressing tape 8 Inner plastic net provided as needed

Claims (2)

It is a cover that protects the welded part of the buried steel pipe that is electrically protected by the external power supply system, and heats the heat-shrinkable tube that covers the welded part and the left and right ends of the steel pipe anticorrosion coating part near the welded part to form a steel pipe. A protective cover for a welded portion of an embedded steel pipe, wherein the cover is tightly wound, a biodegradable resin foam sheet and a plastic net are wound thereon, and the entire cover is fastened with a plurality of pressing tapes. A cover for protecting a welded portion of an embedded steel pipe that is electrically anticorrosive by an external power supply system, and heating the heat-shrinkable tube covering the welded portion and the left and right ends of the steel pipe anticorrosion covering portion near the welded portion The plastic pipe is wrapped in two layers and a biodegradable resin foam sheet is interposed between the two layers of plastic net, and the entire cover is fastened with a plurality of pressing tapes. Protective cover for welded part of buried steel pipe.

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