JP5067755B2 - Steel pipe repair method - Google Patents

Description

  The present invention relates to a technique that enables seismic reinforcement by repairing a steel pipe and controlling buckling of the steel pipe when repairing a steel pipe that is damaged and partially thinned.

When a gas pipe or a water pipe is buried underground, a coated steel pipe having a coating film for preventing corrosion on the outer periphery of the steel pipe may be used. For example, by coating the periphery of the steel pipe with a resin-based material such as polypropylene or polyethylene, the steel pipe is prevented from being corroded by moisture from the outside.
When such a coated steel pipe is buried underground, when a person who manages and maintains the buried coated steel pipe (buried pipe) is working, it is less likely to be a problem because the buried place is clear. The buried piping may be damaged by so-called other construction that other people construct.

This is because the buried place of the buried pipe is often located along the road, and there are many cases where a plurality of buried pipes are buried in parallel relatively close to each other.
When constructing such buried piping, it is customary to confirm the location of the buried piping in advance and pay sufficient attention not to damage the buried piping. However, care should be taken not to damage the buried piping. In practice, it will be left to the operator who operates the construction vehicle. There is a worry.

As a repair method when such buried piping is damaged, there is a repair method disclosed in Non-Patent Document 1, for example.
The piping repair method described in Non-Patent Document 1 includes a method called a build-up welding method as shown in FIG. 8 (A) and a welding sleeve method as shown in FIG. 8 (B).
That is, in the build-up welding method, as shown in FIG. 8 (A), build-up welding 70 is provided by performing build-up welding on the damaged portion 14 in which the steel pipe 11 is damaged and the thickness is partially reduced. Thus, the wall thickness is recovered by the build-up welded portion 70.

  Further, as shown in FIG. 8B, the welding sleeve construction method is such that a semicircular sleeve 80 having the same radius as the outer radius of the steel pipe 11 is placed on the damaged portion 14 of the steel pipe 11 and the sleeve 80 is covered. The end portion in the axial direction, the outer peripheral surface of the steel pipe 11 and the joint portion of the sleeve 80 are welded to provide fillet weld portions 71 and 72 to repair the damaged portion 14.

Although not described in Non-Patent Document 1, as shown in FIG. 8C, a patch 81 is applied to the damaged portion 14 (not shown) and the periphery thereof is welded to fillet welds 71 and 72. There is also a method of repairing by installing.
These repair methods are used to perform permanent repairs without replacing the buried pipes when the buried pipes are deeply thinned due to minor corrosion or damage. The coated steel pipe can also be repaired by such a method.

  In addition, clamps for use in repairing water leakage in pipe pinholes and corrosion cracked parts (for example, Straub clamps manufactured by Showbond Coupling Co., Ltd.) are commercially available. This clamp is configured such that one end of a belt that is complicatedly formed into a semicircular shape by press molding so as to match the diameter of the pipe is hinged and the other end is coupled with a screw member to cover the pipe.

Japan Gas Association Gas Works Technical Standards Investigation Committee, “High Pressure Pipeline Guide JGA Finger-204-06”, 375p-379p

However, the prior art as described above has the following problems.
That is, the conventional overlay welding method and welding sleeve method perform welding when repairing the buried piping, and therefore it is necessary to prevent the ignition of the welding spark to the gas. It is necessary to depressurize or cut off the gas supply.
In particular, in the repair of coated steel pipes used for trunk buried pipes through which high-pressure gas flows, there is a risk of causing major accidents when gas leaks occur, so repairs must be carefully performed. (In the above Non-Patent Document 1, the above-mentioned construction method is carried out while continuing the gas supply, but in practice, the gas is decompressed or shut off for safety reasons.)
In addition, when repairing buried steel pipes by welding, it is necessary to secure the heat necessary for welding, but due to the effect of high-pressure gas flowing in the gas piping, the input heat is rapidly deprived, There is also a problem that poor welding is likely to occur.

Furthermore, when piping is repaired by the overlay welding method or the welding sleeve method, the strength of the welded portion may be reduced. According to an experiment based on the high-pressure gas pipe seismic design guideline that applies a load to the pipe performed by the applicant, it has been found that buckling occurs before and after the repaired portion.
If such a buckling occurs in the steel pipe used for the high-pressure gas pipe, which is the backbone, and a gas leak occurs, there is a risk of causing a serious accident, which may interrupt the lifeline. There is a need for a method of repairing steel pipes that takes into account the properties of steel pipes.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a method of repairing a steel pipe that does not lower the earthquake resistance after repairing regardless of welding.

In order to solve the above problem, the steel pipe repair method according to claim 1 repairs a damaged portion of the steel pipe in which the reduced thickness portion is formed when the reduced thickness portion is formed by damaging the steel pipe. In the method of repairing a steel pipe, the heat-shrinkable tube is in close contact with the damaged portion by filling the thinned portion with an elastic filler and heating the damaged portion with a heat-shrinkable tube. And covering the outer periphery of the heat-shrinkable tube with a clamp having a metal casing and an elastic sleeve provided on the inner periphery of the casing, and fixing the clamp to the damaged portion, The damaged portion of the steel pipe is repaired , the deformation generated in the thinned portion is absorbed by the elastic filler, the heat-shrinkable tube, and the elastic sleeve to suppress the deformation of the casing, and the earthquake resistance of the steel pipe is improved. Spoiled Never, and it said.

Therefore, the outer periphery of the thinned portion is covered with a triple elastic body of an elastic filler, a heat shrinkable tube and an elastic sleeve, and the outer periphery is covered while being reinforced with a metal casing of the clamp, so no welding is used. It is safe to repair, and there is no need to depressurize or shut off the gas.
In addition, even when an external force acts on the steel pipe due to an earthquake or the like and the thinned portion is deformed, the elastic body absorbs the deformation, and the buckling of the steel pipe can be controlled by suppressing the deformation of the casing as much as possible. Can be repaired, and does not reduce earthquake resistance after repair.

The steel pipe repair method according to claim 2 is the steel pipe repair method according to claim 1, wherein the casing of the clamp is formed in a cylindrical shape from a flat plate. Each of the two ends has a flange portion, and is tightened with a plurality of screw members arranged in the axial direction so as to reinforce and cover the outer periphery of the damaged portion.
Therefore, it is not necessary to press-mold the casing in a complicated manner, it can be manufactured at a low cost, and can be easily applied to repair of a large-diameter buried pipe.

The steel pipe repair method according to claim 3 is the steel pipe repair method according to claim 1, wherein the casing has a thickness of 10 mm and the elastic sleeve has a thickness of 5 mm. .
Therefore, if the thickness of the casing is less than 10 mm, the casing is pressed by the deformation of the thinned portion, causing the casing to bulge outward. As a result, the thinned portion buckles outward. Further, if the thickness of the casing is thicker than 10 mm, the rigidity of the casing is too high, and the deformation of the thinned portion buckles inward and greatly deforms. When the thickness of the casing is 10 mm, it is possible to control the buckling of the steel pipe so that the thinned portion undulates moderately, repair the casing without deforming it, and perform seismic reinforcement.

The effect of the steel pipe repair method provided with the said structure is demonstrated.
(1) Since the steel pipe repair method of the present invention does not use welding at all, repair is possible while supplying gas at normal pressure, and repair and seismic reinforcement are possible without causing inconvenience to local residents. .
(2) Since the casing corresponding to the size of the thinned portion can be easily procured, the repair period can be shortened, and the construction period can be shortened and repaired at low cost.
(3) Since the deformation of the thinned portion is moderately suppressed by the triple elastic body, repair and seismic reinforcement can be performed while controlling the buckling of the thinned portion.

Next, an embodiment of a steel pipe repair method according to the present invention will be described with reference to the drawings. The steel pipe repair method of the present embodiment is applied to a main pipe having a diameter of 600 mm in a gas pipe.
Here, FIG. 1 is a side view showing a repaired portion of the main conduit. FIG. 2 is a sectional view taken along the line II-II, and FIG. 3 is a sectional view taken along the line III-III.

The structure of the repair portion of the steel pipe repair method will be described. The coated steel pipe 10 of this Embodiment is provided with the steel pipe 11 and the coating film 12 coated by the outer surface, as shown in FIG. 1, FIG. The steel pipe 11 is used for a main conduit having a diameter of 600 mm and a pipe thickness of 10.3 mm. The coating film 12 is a film formed by applying a synthetic resin such as polypropylene or polyethylene to a steel pipe. Thus, the steel pipe 11 buried underground is processed so as not to corrode.
Then, as an example of the thinned portion 13 and the repaired portion 1 of the damaged portion 14, as shown in FIG. 4, the description will be made using what is used in an experiment for confirming the steel pipe repairing method of the present invention.

  The damaged portion 14 assumes that the heavy machinery by other construction collided and the coating film 12 was partially broken, the steel pipe 11 was removed, the pipe thickness was reduced, and the reduced thickness portion 13 was generated. The size of the thinned portion 13 is set such that the circumferential length × the axial length is 300 mm × 300 mm and the depth is about 4 mm (thickness reduction rate 40%). The thinned portion 13 is filled with a silicon-based elastic filler 20, and the outer peripheral surface thereof is substantially flush with the outer peripheral surface of the steel pipe 11.

As shown in the cross-sectional view of FIG. 2, the repaired portion 1 that repairs the damaged portion 14 includes a heat shrinkable tube 30 that covers the damaged portion 14 by partially peeling the coating film 12, and the heat shrinkable tube 30. And a clamp 50 covering the outer periphery.
The heat-shrinkable tube 30 has a length in the axial direction that overlaps with the coating film 12 on both sides in the axial direction of the damaged portion 14. The heat-shrinkable tube 30 is covered with the damaged portion 14 and heated from the outside. It hardens while shrinking by cooling, and adheres to the damaged portion 14 to cover the outer periphery of the steel pipe 11.
Accordingly, the portion where the coating film 12 is peeled becomes a concave portion, and the portion overlapping with the coating film 12 protrudes outward by the thickness of the coating film 12.

The clamp 50 includes a metal casing 51 and an elastic sleeve 40 provided on the inner periphery of the casing 51.
The casing 51 is made of a stainless steel plate (SUS304) having an axial length shorter than that of the heat shrinkable tube 30 and superposed on the coating film 12. As shown in FIG. A flat plate having a thickness of 10 mm is wound around the damaged portion 14. The flange portions 52, 52 provided at both ends in the circumferential direction are opposed to each other and are fastened with screw members 53 such as bolts and nuts, thereby being fixed to the damaged portion 14. Is.
The elastic sleeve 40 has substantially the same axial length as that of the casing 51 and the outer periphery thereof is restrained by the casing 51. Therefore, the elastic sleeve 40 enters the recessed portion where the coating film 12 is peeled off and becomes thick. It is made of a soft (hardness 90) rubber (NBR) that is thinned at the portion where it is superposed on the film 12, and has a thickness of 5 mm when free.

  The operation of the repair portion 1 of the first embodiment configured as described above will be described using the above test results. As shown in FIG. 4, based on the high-pressure gas pipe seismic design guideline, the coated steel pipe 10 in which the damaged portion 14 is repaired by the repaired portion 1 is erected on a test apparatus capable of applying a compressive load from above, A water pressure of 2 MPa is applied, and a load of ± 0.50% strain × 5 cycles is applied from above.

As a result, with respect to the cross section of the repaired portion 1 before loading shown in FIG. 5 (A), the thinned portion 13 is appropriately deformed outward as shown in FIG. 5 (B). Only the central part of the casing is deformed inward, and as a result, it is deformed into a waveform without buckling outward or inward, and the deformation is absorbed by the three-layered elastic body, and the casing 51 having a thickness of 10 mm is not deformed. It can be seen that it has been repaired. Therefore, no buckling has occurred in the coated steel pipe 10. In other words, this repair becomes seismic reinforcement.
The maximum compression load at this time was 8753 kN in the first cycle and 8020 kN in the fifth cycle, and the reduction rate was 8.4%.

  As a comparative test, as a second embodiment, the thickness of the casing 51 is 5 mm, and the others are tested under the same conditions. As a result, the cross section of the repaired part 1 before loading shown in FIG. As shown in FIG. 6 (B), the thinned portion 13 bulges outward by being pressed by the internal pressure, and the casing 51 bulges outward and deforms and buckles without being able to hold it down. The maximum compression load at this time was 7666 kN in the first cycle and 6868 kN in the fifth cycle, and the reduction rate was 10.4%, which was higher than that in Example 1. Since the casing 51 was thin and could not withstand the internal pressure, the casing 51 was deformed, so that the seismic reinforcement was insufficient as compared with the first embodiment.

  Next, as a third embodiment, a simulation of the casing 51 having a plate thickness of 20 mm is performed. As shown in FIG. 7 (A), the cross section of the repaired portion 1 before loading shown in FIG. As shown in B), since the thickness of the casing 51 is thick, the rigidity is too high, and the steel pipe 11 cannot be deformed to the outside, so that the thinned portion 13 is expected to bend and buckle inside the pipe. Therefore, it is assumed that the rate of decline will increase in this case as well, and is not suitable for seismic reinforcement.

  As described above, according to the steel pipe repair method of the present invention, when a steel pipe is damaged and a thinned portion is formed, the repaired method of the steel pipe repairs a damaged portion of the steel pipe in which the thinned portion is formed. In this case, the thinned part is filled with an elastic filler, and the damaged part is covered with a heat shrinkable tube and heated, so that the damaged part is covered with the heat shrinkable tube to cover the outer periphery of the steel pipe. The steel pipe is covered with a clamp provided with a metal casing and an elastic sleeve provided on the inner periphery of the casing, and the clamp is fixed to the damaged part, thereby repairing the damaged part of the steel pipe. The outer periphery of the thinned part is covered with a triple elastic body of elastic filler, heat-shrinkable tube and elastic sleeve, and the outer periphery is covered while being reinforced with a metal casing of the clamp, so no welding is used Safe to repair Ri, it is not necessary to vacuum or blocking of the gas. In addition, even when an external force acts on the steel pipe due to an earthquake or the like and the thinned portion is deformed, the elastic body absorbs the deformation, and the buckling of the steel pipe can be controlled by suppressing the deformation of the casing as much as possible. Can be repaired.

Further, the casing of the clamp is formed in a cylindrical shape from a flat plate, and has clamp portions at both ends in the circumferential direction thereof, and is tightened by a plurality of screw members arranged in the axial direction. Thus, the outer periphery of the damaged portion is covered while being reinforced, so that it is not necessary to press-mold the casing in a complicated manner, it can be manufactured at low cost, and can be easily applied to repair of a large-diameter buried pipe.
Furthermore, because the thickness of the casing is 10 mm and the thickness of the elastic sleeve is 5 mm, the buckling of the steel pipe is controlled so that the thinned portion undulates appropriately, and the casing is also repaired without deformation. Can be seismically reinforced.
That is, as apparent from the above test, the maximum compressive load in the first cycle when the casing thickness is 5 mm is 7666 kN, whereas the maximum compressive load in the first cycle when the casing thickness is 10 mm is It is 8753 kN, the strength increases by about 14%, increases by 16.8% even at the fifth cycle, and can be sufficiently seismic strengthened.

In addition, this invention is not limited to the thing of the said embodiment, A various change is possible in the range which does not deviate from the meaning.
For example, in the said embodiment, although the coated steel pipe 10 which gave the coating film 12 to the steel pipe 11 was demonstrated, it is not restricted to this, It is also possible to apply to a mere steel pipe.

It is the side view which showed the repair part of the trunk conduit | pipe which concerns on 1st embodiment of this invention. It is sectional drawing which follows the II-II line of FIG. It is sectional drawing which follows the III-III line of FIG. It is a side view which shows the test condition of the trunk conduit | pipe which concerns on 1st embodiment of this invention. It is sectional drawing which shows the test condition of the trunk conduit | pipe which concerns on 1st embodiment of this invention, (A) shows the condition before a test, (B) shows the condition after a test. It is sectional drawing which shows the test condition of the trunk conduit | pipe which concerns on 2nd embodiment of this invention, (A) shows the condition before a test, (B) shows the condition after a test. It is sectional drawing which shows the test condition of the trunk conduit | pipe which concerns on 3rd embodiment of this invention, (A) shows the condition before a test, (B) shows after a test. It is the schematic which shows the conventional repair method, (A) shows the build-up welding method published in the high voltage | pressure conduit | pipe guide of a nonpatent literature 1, (B) shows a welding sleeve construction method, (C) is unpublished. The patch application welding method is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Repair part 10 Coated steel pipe 11 Steel pipe 12 Coated film 13 Thinning part 14 Damaged part 20 Elastic filler 30 Heat shrinkable tube 40 Elastic body sleeve 50 Clamp 51 Casing 52 Flange part 53 Screw member 70 Overlay welding part 71, 72 Fillet weld 80 sleeve

Claims (3)

In a steel pipe repairing method for repairing a damaged portion of the steel pipe in which the reduced thickness portion is formed when the reduced thickness portion is formed due to damage to the steel pipe,
Filling the thinned portion with an elastic filler,
By covering the damaged part with a heat-shrinkable tube and heating, the heat-shrinkable tube is in close contact with the damaged part and covers the outer periphery of the steel pipe,
The outer periphery of the heat shrinkable tube is covered with a clamp having a metal casing and an elastic sleeve provided on the inner periphery of the casing,
By fixing the clamp to the damaged part,
The damaged portion of the steel pipe is repaired , the deformation generated in the thinned portion is absorbed by the elastic filler, the heat-shrinkable tube, and the elastic sleeve to suppress the deformation of the casing, and the earthquake resistance of the steel pipe is improved. A method of repairing a steel pipe, characterized by not being damaged . In the repair method of the steel pipe described in Claim 1,
The casing of the clamp is formed in a cylindrical shape from a flat plate, and has clamp portions at both ends in the circumferential direction, and is tightened by a plurality of screw members arranged in the axial direction. The steel pipe repair method characterized by covering the outer periphery of the damaged part while reinforcing. In the repair method of the steel pipe described in Claim 1,
The method of repairing a steel pipe, wherein the casing has a thickness of 10 mm and the elastic sleeve has a thickness of 5 mm.

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