JP2006194368A - Anti-corrosion coating structure for field welds - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anticorrosion coating structure for an on-site welded portion, which is particularly improved in anticorrosion performance, in a coating structure of a pipe welded joint portion for anticorrosion coating of a welded joint portion of various pipes such as a gas conduit and an oil feed pipe.
In a field welded portion in which a pipe end of a polyethylene-coated steel pipe is welded,
In the first layer, a heat shrink material in which the inner layer material is a butyl rubber-based adhesive material and the outer layer material is a crosslinked polyethylene is coated by heat shrinkage under reduced pressure,
In the second layer, a heat-shrinkable material having a longer longitudinal width than the first layer, the inner layer material being a hot-melt adhesive, and the outer layer material being a cross-linked polyethylene, is heat-shrinked under reduced pressure and covered with lap winding. An anti-corrosion coating structure for welds on site.
[Selection] Figure 1

Description

  The present invention relates to a pipe welded joint covering structure for anticorrosive coating of welded joints of various pipes such as gas conduits and oil feed pipes, and particularly relates to improvement of anticorrosion performance.

  Steel pipes used for underground pipes such as gas pipes are coated with an outer surface for the purpose of preventing corrosion. Usually, a method of carrying out polyethylene coating at a factory is common.

  In order to connect the steel pipes at the burial site, it is necessary to cover the welded joints that have been circumferentially welded on site. In order to prevent corrosion at the welded joints locally, the outer layer material is covered with a heat-shrinkable polyethylene material with crosslinked polyethylene and the inner layer material is a rubber-based adhesive, and heated using a heating device that uses a burner or far-infrared rays. In general, a method of forming a corrosion-resistant coating layer by shrinking a cross-linked polyethylene that is going to return to the shape of the rubber and adhering the rubber-based adhesive material to the polyethylene coating and the steel surface of the welded joint is generally applied.

  A heat-shrinkable polyethylene material that covers a normal pipe-welded joint is a one-layer winding in which an outer-layer material is a heat-shrinkable polyethylene crosslinked and an inner-layer material is a rubber-based adhesive material. However, when it is difficult to repair and prevent corrosion after laying the pipe, the pipe has a double pipe structure, or when the anticorrosion-coated pipe is further covered with mortar, the heat-shrinkable polyethylene with the outer layer material crosslinked in the first layer After coating the inner layer material so as to be in close contact with the steel surface of the steel pipe material including the polyethylene coating layer of the steel pipe to which the heat-shrinkable polyethylene material made of the rubber-based adhesive material is connected and the welded joint portion, it is longer than the first layer. A measure is taken to improve the anticorrosion safety by winding two layers of heat-shrinkable polyethylene having a large width and a cross-linked outer-layer material and an inner-layer material made of a rubber-based adhesive material. By winding the heat-shrinkable polyethylene material in two layers, the anticorrosion barrier property and the mechanical strength due to the increase in the coating thickness are increased as compared with the one-layer winding.

However, the rubber-based pressure-sensitive adhesive material that is an inner layer material of the heat-shrinkable polyethylene material exhibits viscoelasticity at room temperature, but when the temperature rises, the cohesive strength of the material decreases and plastic deformation tends to occur. Therefore, the piping has a region where the temperature is higher than normal temperature, for example, the shear strength of the adhesive material at 50 ° C. is lower than 10 N / cm ² , and the displacement or peeling occurs with a small stress. For example, when piping is covered with mortar, there has been a problem that the occurrence of damage such as slippage of the mortar due to the heat generated by curing and turning of the mortar is a concern.

  Further, the rubber-based adhesive material of polyethylene heat-shrinkable material serves to adhere to the polyethylene coating layer or the steel surface of the welded joint, but the adhesion mechanism is physical adhesion. Therefore, when long-term service is assumed, there is a problem that there is a concern that the anticorrosion property is deteriorated due to the invasion of corrosion factors such as water from the adhesion surface.

On the other hand, in the coating structure of the steel pipe joint part used in the direct propulsion method, as shown in FIG. 2A, in order to solve the problem that the anticorrosive coating layer is crushed by friction due to the resistance of earth and sand during propulsion. Two steps of stepped portions 8A and 8B are formed stepwise in advance on the front and rear ends of the coating layer 8 of the steel pipe 7, and after the joint portion 3 is welded, the first outer layer material 5-1 has a heat shrink function. First step of anticorrosion coating step except for the uppermost portion of the coating layer end on both sides of the welded joint portion 3 at the end portion of the adhesive type heat shrinkable tube 5 in which the applied material, the inner layer material 5-2 is attached with a rubber adhesive. The heat-shrinkable tube 5 intended to return to the original shape is shrunk and coated on the portion 8A, heated by a torch, and then a heat-shrinking function is imparted to the outer layer material 5′-1 of the two layers (the uppermost layer). Adhesive heat-shrinkable tube 5 'with a rubber adhesive attached to the material, inner layer material 5'-2 The end portion in the propulsion direction is overlapped with the second anti-corrosion coating step portion 8B with a gap 9 between them, heated with a torch to shrink the heat-shrinkable tube 5 ', and then covered with the gap 9 and two layers. An adhesive heat shrinkable tube in which the coating end portion of the adhesive type heat shrinkable tube 5 ′ of the eye is formed by attaching a material having a heat shrinking function to the outer layer material 6-1 and a hot melt type adhesive material on the inner layer material 6-2 ( Alternatively, a method of coating a steel pipe joint portion is proposed, in which the adhesive-type heat-shrink tape (6) is heated with a torch and thermally contracted (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 9-178080 (paragraphs “0012” to “0033”, FIG. 1)

  However, in the coating structure of the steel pipe joint portion by the coating method described in Patent Document 1, it is necessary to coat so that the boundary surface of the adhesive heat shrinkable tube coating of two or more layers of the steel pipe joint portion does not protrude from the upper surface of the steel pipe coating layer. In addition, the thickness of the steel pipe coating layer has to be increased to three times or more as shown in FIG. 2A, which is uneconomical. In addition, it is not only costly to cut the covering stepped portion in a staircase shape in advance on the front and rear end portions of the steel pipe coating layer, but there is also a problem that stress due to cutting is added at that time. Also, in order to allow the dimensional tolerance of the covering step part, it is necessary to create a gap in the covering step part in the propulsion direction, and it is necessary to wrap a heat shrink tube or heat shrink tape separately here, There was a problem of increasing. Especially in the harsh working environment, such as anticorrosion coating work for steel pipe joints laid in underground tunnels, there was a problem that the increase in coating man-hours would greatly reduce production and work efficiency. In addition, even if a gap is formed when the first heat shrinkable tube is covered, it is not done until the gap is closed. By leaving such a gap, a void is formed in the coating layer. When the adhesion strength is reduced, especially when long-term service is assumed, a leak path leading to the outside through the void is formed, and the corrosion resistance is reduced due to the invasion of corrosion factors such as water through the path in the adhesion surface. There was also a problem of concern. Furthermore, the structure of the covering step portion on the opposite side in the propulsion direction is a measure to improve the anticorrosion safety by winding two layers of the existing adhesive heat shrinkable tube. The problem remains. In addition, in the heating by the torch, it is difficult to ensure reliability by work, and depending on the worker, the entire surface is strongly heated to obtain high adhesion strength and the surface part is burnt, etc. There was also a problem that variations were likely to occur among workers.

  The present invention has been made to solve such a problem (technical problem), and after the heat-shrinkable adhesive-type heat-shrinkable material is heated and shrunk under reduced pressure in the first layer, it is longer than the first layer. The wrapping surface of the second heat-shrinkable material and the polyolefin coating of the steel pipe coating layer is obtained by heat-shrinking the adhesive-type heat-shrinkable material with a hot melt adhesive, which is large in width, under reduced pressure The remaining area of the air at can be suppressed and can be securely bonded.

A hot melt adhesive is an adhesive such as modified polyethylene, and has a high shear strength even at high temperature (100 N / cm ² or more at 50 ° C.) compared to a butyl rubber-based pressure-sensitive adhesive. Less likely to cause turning or peeling. When the hot melt adhesive is bonded to the polyolefin coating of the steel pipe coating layer, the bonding surface is heated to a temperature higher than the melting point of the hot melt and the polyolefin coating of the steel pipe coating layer, and the resin of the hot melt adhesive and the steel pipe coating layer are heated. Adhesion close to the fusion in which the polyolefin-coated resin is entangled with the resin is produced, so that it is possible to bond with excellent barrier properties that can reliably prevent the entry of corrosion factors such as water.

  The present invention has been made to solve the above problems, and the gist thereof is as follows.

(1) In the field weld where the pipe end of the polyolefin coated steel pipe is welded,
A first heat-shrinkable material comprising at least the first layer having an inner layer material as a mastic-based adhesive material and an outer layer material having a heat-shrink function, is heat-shrinked by far-infrared rays under reduced pressure, preferably under reduced pressure. A first covering layer forming portion,
The inner layer material is a hot melt adhesive and the outer layer material is thermally shrunk on at least both ends of the first coating layer forming portion where the first heat shrink material is coated in one layer or multiple layers and the steel pipe coating layer portion on the outer side in the longitudinal direction. The second heat-shrinkable material, which is a material having a function, has a second coating layer forming portion that is heat-shrinked by far infrared rays under reduced pressure, preferably under reduced pressure, and is covered with multiple layers. Anti-corrosion coating structure for welds on site.

(2) In the first layer, the first coating layer forming portion is formed using the first heat shrink material,
In the second layer, the second coating layer forming part is formed by lap winding using a second heat shrinkable material having a longer longitudinal width than the first layer. Anti-corrosion coating structure.

  (3) The anticorrosion coating structure according to (1) or (2) above, wherein the heat shrinkable material is heat-shrinked in a reduced pressure atmosphere, preferably in a reduced pressure atmosphere of 0.05 MPa or less.

  (4) The anticorrosion coating according to any one of (1) to (3) above, wherein the coating layer end of the steel pipe has a taper angle, preferably a taper angle of 25 ° or less. Construction.

(5) In the field weld where the pipe end of the polyolefin coated steel pipe is welded,
At least the first layer is coated with a first heat-shrinkable material having a mastic-based adhesive material as an inner layer material and a heat-shrinkable material as an outer layer material under reduced pressure, preferably under reduced pressure, by far-infrared rays. A first coating step to perform,
The inner layer material is hot-melted on at least both end portions of the coating layer forming portion in which the first heat-shrinkable material is coated in one layer or multiple layers by the first coating step and the steel pipe coating layer portion (on the outer peripheral portion) outside the longitudinal direction. A second coating step in which the second heat-shrinkable material using the adhesive material and the outer layer material as a material imparted with a heat-shrinking function is subjected to heat-shrinkage by far-infrared rays under reduced pressure, preferably under reduced pressure, and wrap-wrapping. The manufacturing method of the anticorrosion coating | coated structure of a local weld part characterized by these.

(6) A first coating step of coating the first layer by heat-shrinking the first heat-shrinkable material;
The second coating step of heat-shrinking a second heat-shrinkable material having a longer longitudinal width than that of the first layer and covering the second layer with the second layer is characterized in that it is described in (5) above. Production method.

  (7) The manufacturing method according to (5) or (6) above, wherein the heat shrinkable material is heated and shrunk in a reduced pressure atmosphere, preferably in a reduced pressure atmosphere of 0.05 MPa or less.

  (8) In the step before the first coating step, the end portion of the coating layer of the steel pipe is chamfered so as to have a taper angle, and preferably a taper angle of 25 ° or less. The manufacturing method as described in any one of 5)-(7).

According to the anticorrosion coating structure of the field welded portion of the present invention, in the coating structure of the pipe welded joint portion for anticorrosion coating of the welded joint portion of various pipes such as gas conduits and oil feed pipes, the first layer is adhesive type heat shrinkage After heat-shrinking the material with far-infrared rays under reduced pressure, preferably under reduced pressure, an adhesive heat-shrink material with a hot melt adhesive having a longer longitudinal width than the first layer is preferably reduced under reduced pressure. Below, by heat shrinking with far-infrared rays and lap winding, a decrease in cohesive strength and plastic deformation of the material due to temperature rise can be greatly suppressed. Therefore, the piping has a higher temperature than normal temperature, for example, the shear strength of the adhesive at 50 ° C. is as high as 100 N / cm ² or more, and even if a temperature rise or stress is applied during the pipe embedding work, Misalignment and peeling can be prevented. In particular, when piping is covered with mortar, it should be maintained for a long time without damaging the coating structure with high anti-corrosion performance, such as the occurrence of damage such as slippage and turning of the coating due to mortar heat generation. Can do. Furthermore, in the above-described coating structure of the present invention, the steel pipe coating layer has excellent adhesion to the polyolefin coating and the steel surface of the welded joint. Therefore, even when long-term use is assumed, intrusion of corrosion factors such as water from the adhesion surface Can be stably prevented for a long period of time, and the corrosion resistance of the welded joint can be remarkably improved. Therefore, the present invention can be suitably applied to a pipe laying application where it is difficult to repair and prevent corrosion after laying the pipe, the pipe has a double pipe structure, or the anticorrosion-coated pipe needs to be further covered with mortar.

  In addition, it is not necessary to finely process the steel pipe coating layer in a stepped manner at the factory as in the past. In addition, in order to finely process the steel pipe covering layer in a stepped manner, it is necessary to form a very thick steel pipe covering layer, which is required to be precisely processed since it requires more than three times the thickness of the heat shrinkable material (Fig. 2A), because it is extremely expensive, application to other than the direct propulsion method is practically limited. However, in the present invention, as shown in FIG. There is no limitation on the applicable polyolefin-coated steel pipe, and it is advantageous. In addition, it is easy to receive scratches and stresses (distortions, etc.) due to external loads when precision processing is performed in a staircase at the factory, and such scratches and distortions are caused by thermal stresses during on-site welding and heat shrinkage of heat shrinkable materials. Since it may be promoted, a treatment for removing such scratches and stress is necessary and the cost is higher. However, the polyolefin-coated steel pipe used in the present invention is advantageous in that such processing is not necessary.

  Moreover, in the said anti-corrosion coating structure of this invention, the 1st coating layer formation part is formed in the 1st layer using the 1st heat shrink material, and it is longer than the 1st layer in the 2nd layer. By forming the second coating layer forming portion by wrapping using the second heat shrinkable material having a large width, the number of parts can be suppressed and a low-cost anticorrosion coating structure can be realized. It is advantageous. In particular, when performing anti-corrosion coating in a narrow laying site such as in a tunnel, carefully align the steel pipe covering step and take measures such as locking to prevent it from shifting, or to the steel pipe covering step. This is extremely advantageous in that it does not require extra labor for further heat-shrinking a heat-shrinkable tube or tape around the generated gap.

  Further, in the anticorrosion coating structure of the present invention, the heat shrinkable material is a coating structure that is heat-shrinked by far infrared rays under reduced pressure, preferably under reduced pressure, thereby reducing the remaining air area (air entrainment). It is extremely excellent in that air voids are hardly generated at the interface between the coated surface and the steel pipe (attachment surface) (see the column of the remaining air area ratio of the inventive product in Table 3 of Examples described later). . In particular, when anticorrosive coating is applied to a welded steel pipe laid in an underground tunnel, the inside of the tunnel often has a higher humidity environment than the ground. In such a case, moisture (condensation) tends to adhere to the surface of the heat-shrinkable material, the steel pipe, the steel pipe coating layer, etc., and the condensed moisture tends to be taken into the anticorrosion coating surface (adhesion surface). For this reason, when heated simply using a torch or far-infrared rays, the adhesiveness and adhesiveness are lowered by such moisture, and there is a possibility that the adhesion is not reliably performed. However, in the present invention, since heating is performed in a reduced pressure atmosphere, a dry environment in which the water vapor concentration is extremely reduced is obtained, which is advantageous in that adhesion is ensured.

  In addition, heating with far infrared rays under reduced pressure, which is a preferred mode, is less likely to cause a local temperature difference during heating shrinkage compared to far infrared heating performed under atmospheric pressure, thereby greatly reducing the burning of the coating. Can be suppressed. For this reason, there is no local variation in the adhesive strength, and a coated portion bonded extremely evenly can be formed, which is excellent in both performance and quality. In particular, when cross-linked polyethylene obtained by electron beam cross-linking of polyethylene material is used as a material with heat shrink function, it has a large heat absorption band in the far-infrared region, so that it can uniformly and quickly shrink efficiently. Has the advantage that

  Further, in the anticorrosion coating structure of the present invention, the heat shrinkable material is coated with a heat shrinkable material by making the heat shrinkable material heat shrunk in a reduced pressure atmosphere, preferably in a reduced pressure atmosphere of 0.05 MPa or less. Air entrainment on the (attachment surface) can be significantly reduced. As a result, the adhesion area or the adhesion area at the covering portion can be increased, and the anticorrosion and waterproof performance can be improved. Therefore, particularly in the case of assuming a long-term service, it is excellent in that the deterioration of the corrosion resistance due to the invasion of corrosion factors such as water from the adhesion surface can be significantly suppressed.

  In the anticorrosion coating structure of the present invention, the coating layer end portion of the steel pipe has a taper angle, and preferably has a taper angle of 25 ° or less, thereby effectively eliminating a gap at the step corner portion of the end portion. Can be prevented.

The anticorrosion coating structure of the field welded portion of the present invention has a mastic adhesive material as the inner layer material and a heat shrink function as the outer layer material in at least the first layer in the field welded portion where the pipe end of the polyolefin coated steel pipe is welded. The first heat-shrinkable material as the material is coated under heat-shrinkage by far infrared rays under reduced pressure, preferably under reduced pressure,
The inner layer material is a hot melt adhesive and the outer layer material is thermally shrunk on at least both ends of the first coating layer forming portion where the first heat shrink material is coated in one layer or multiple layers and the steel pipe coating layer portion on the outer side in the longitudinal direction. The second heat-shrinkable material, which is a material having a function, has a second coating layer forming portion that is heat-shrinked by far infrared rays under reduced pressure, preferably under reduced pressure, and is covered with multiple layers. Is.

In addition, the method for producing a corrosion-resistant coating structure for an on-site welded portion according to the present invention is such that, in the on-site welded portion where the pipe end of a polyolefin-coated steel pipe is welded, the inner layer material is a mastic adhesive and the outer layer material is heated at least in the first layer. A first coating step of coating the first heat-shrinkable material, which is a material imparted with a shrinking function, under reduced pressure, preferably under reduced pressure, by heat-shrinking with far infrared rays,
The inner layer material is hot-melted on at least both end portions of the coating layer forming portion in which the first heat-shrinkable material is coated in one layer or multiple layers by the first coating step and the steel pipe coating layer portion (on the outer peripheral portion) outside the longitudinal direction. A second coating step in which the second heat-shrinkable material using the adhesive material and the outer layer material as a material imparted with a heat-shrinking function is subjected to heat-shrinkage by far-infrared rays under reduced pressure, preferably under reduced pressure, and wrap-wrapping. It is characterized by.

  Hereinafter, these embodiments will be described with reference to the drawings with regard to the anticorrosion coating structure of the field welded portion and the manufacturing method thereof according to the present invention. FIG. 1 is a cross-sectional configuration diagram schematically showing a typical embodiment of an anti-corrosion coating structure for an on-site welded portion (pipe welded joint portion) according to the present invention. In the first layer, the first heat-shrinkable material is shown. The first coating layer forming portion is formed using the second heat-shrinkable material having a longer longitudinal width than the first layer, and the second coating layer forming portion is overwrapped using the second layer. Is formed. Such an anticorrosion coating structure includes a first coating step in which the first heat-shrinkable material is coated on the first layer by heat-shrinking with far-infrared rays under reduced pressure, preferably under reduced pressure, and the first layer in the second layer. And a second coating step in which the second heat-shrinkable material having a longer longitudinal width is heat-shrinked with far-infrared rays under reduced pressure, preferably under reduced pressure, and is wound over.

  As shown in FIG. 1, in order to produce the anticorrosion coating structure of the field welded part (pipe welded joint part) of the present invention, the pipe end part of the polyolefin-coated steel pipe 1 is welded and, after welding, the steel surface exposed part 2 ′. Remove the welding spatter and dirt with a power tool. As the first covering step, a first heat is used in which the inner layer material 5-2 is a mastic-based adhesive material and the outer layer material 5-1 is a material having a heat shrink function so as to completely cover the steel surface exposed portion 2 ′. The shrinkable material 5 is covered and coated by heating and shrinking with far infrared rays under reduced pressure, preferably under reduced pressure.

  Next, as the second coating step, after the first layer of the heat shrink material 5 is coated, the inner layer material 6-2 is a hot melt adhesive, and the outer layer material 6-1 is a material having a heat shrink function. The heat-shrinkable material 6 of FIG. 1 is heat-shrinked with far infrared rays under reduced pressure, preferably under reduced pressure, and is lap-wrapped to obtain the anticorrosion coating structure for the on-site welded portion (tube weld joint portion) in FIG.

  The second heat-shrinkable material 6 of the second layer needs to cover at least both ends of the first coating layer forming portion and the steel pipe coating layer portion on the outer side in the longitudinal direction. Preferably, as shown in FIG. 1, the longitudinal width of the second heat-shrinkable material 6 of the second layer is larger than that of the first coating layer forming portion of the first layer, and the first coating layer forming portion of the first layer. By covering all of the above and further covering the outer steel pipe coating layer, the steel pipe coating layer and the second heat-shrinkable material coating surface are in close contact with each other so as not to entrain air and are firmly bonded. desirable.

  Here, as the outer layer material 5-1 of the first heat shrink material 5 of the first layer and the outer layer material 6-1 of the second heat shrink material 6 of the second layer, materials having a heat shrink function, for example, , Polyethylene, polypropylene, ethylene vinyl acetate copolymer, thermoplastic resin such as fluororesin, or silicon rubber. Considering the functions and roles required for the first layer and the second layer, the outer layer materials 5-1 and 6-1 may be the same or different from each other. A thing may be used.

  Among the materials imparted with the heat shrink function used as the outer layer materials 5-1 and 6-1 above, the balance of various properties such as waterproofness, weather resistance, chemical resistance, crack resistance, electrical insulation, etc. is achieved. A crosslinked polyethylene obtained by electron beam crosslinking of an inexpensive polyethylene material is preferable. Cross-linked polyethylene is an ultra-high molecular weight resin having a three-dimensional network structure by cross-linking polyethylene. Cross-linked polyethylene is chemically cross-linked by a cross-linking method such as a radical cross-linking method in which a radical generator is kneaded with polyethylene and cross-linking by heat or a water cross-linking method in which a silane graph in which a silane monomer is added to polyethylene is cross-linked by water. They are broadly divided into physical crosslinks that are directly crosslinked by electron beams, radiation, and infrared rays. Cross-linked polyethylene that is widely used is chemical cross-linking, but the productivity is low including the time until the end of cross-linking, and the strength of cross-linking is weak. Is inexpensive (addition of an extra radical generator and silane monomer is unnecessary), has good productivity and moldability, and has a stronger crosslinking strength than chemical crosslinking. Therefore, the outer layer material of the heat shrinkable material of the present invention Is particularly suitable.

  The thickness of the outer layer material 5-1 and the outer layer material 6-1 is a thickness that can effectively maintain the various properties such as waterproofness, weather resistance, chemical resistance, crack resistance, and electrical insulation for a long period of time. May be determined appropriately in consideration of the outer diameter of the steel pipe, the presence or absence of the mortar coating, the environmental conditions (humidity, temperature, etc.) at the time of embedment or after embedment, and further the required service life, Usually 1 mm or more.

  In addition, the application of the mastic adhesive to the inner layer material 5-2 of the first heat shrink material 5 of the first layer is adhesive even at room temperature, and has adhesion to both the steel surface and the outer layer material. This is because it is high and has excellent corrosion resistance and waterproof performance. Here, the mastic-based adhesive material is one of existing adhesive materials, and refers to an adhesive material in which an appropriate amount of a tackifier and an anti-degradation agent is blended in asphalt or synthetic rubber. There are no particular limitations on the tackifier and the deterioration inhibitor blended in the mastic-based pressure-sensitive adhesive, and conventionally known ones can be used as appropriate.

  Of the mastic-based pressure-sensitive adhesive materials used as the inner layer material 5-2, a butyl rubber-based pressure-sensitive adhesive material that is excellent in adhesion and corrosion resistance is preferable. Further, the base adjustment in the field work of the steel surface exposed portion 2 ′ is limited by work environment, work time, etc., using an electric tool. It is desirable to apply a butyl rubber-based pressure-sensitive adhesive material to the inner layer material from the viewpoint of ensuring close contact with the substrate adjustment surface 2 ′ performed using such an electric tool. This is because the butyl rubber-based adhesive material exhibits extremely high adhesion to both the substrate adjustment surface 2 ′ formed by the electric tool and the outer layer material. In the present invention, an embodiment using an adhesive such as a hot-melt adhesive for the first inner layer material 5-2 is not included, but it is formed by using an electric tool in the field work as described above. This is because there is a possibility that high adhesive strength (adhesiveness) cannot be given to the substrate-adjusting surface 2 ′.

  The thickness of the inner layer material 5-2 is high enough to adhere to both the steel surface and the outer layer material, and can maintain various properties such as anticorrosion and waterproof performance effectively for a long period of time. Well, taking into account the outer diameter of the steel pipe, the material and thickness of the outer layer material 5-1, the presence or absence of mortar coating, the environmental conditions (humidity, temperature, etc.) during and after embedding, and the required service life What is necessary is just to determine suitably, but it is about 1 mm normally.

  The hot-melt adhesive material that is the second-layer inner layer material 6-2 includes the hot-melt adhesive material of the inner-layer material 6-2, the polyolefin coating layer 4 of the steel pipe 1, and the thermal contraction of the first-layer outer layer material 5-1. By heating the bonding surface of the material having a function (preferably, electron beam cross-linking type cross-linked polyethylene) to the melting point or higher, the hot-melt adhesive material of the inner layer material 6-2 and the polyolefin coating layer of the steel pipe 1 What produces the fusion | melting which entangles 4 resin is suitable. Further, between the hot-melt adhesive material of the second inner layer material 6-2 and the resin (preferably electron beam cross-linked polyethylene) having a heat shrink function of the first outer layer material 5-1. However, it is more preferable to cause fusion in which resins are similarly entangled with each other.

Further, the viscosity of the hot-melt adhesive of the inner layer material 6-2 of the second layer rises sharply near the melting point, the shear strength is high at a temperature lower than that, and the cohesive strength at 50 ° C. is 100 N / cm ^2. Is preferred. Compared with the mastic adhesive (preferably a butyl rubber adhesive) of the inner layer material 5-2 of the first layer, the use of an adhesive having a high shear strength prevents the occurrence of turning and peeling against external stress. It is possible to prevent. Examples of the hot melt adhesive satisfying such conditions include, but are not limited to, modified polyethylene materials and polyamide materials.

  Furthermore, the inner layer material 6-2 of the heat-shrinkable material 6 used for lap winding is preferably sharp at the softening temperature, exhibits several times higher adhesive strength than the adhesive material at room temperature, and is sufficient only at a high temperature exceeding about 100 ° C. It is a hot-melt adhesive based on polyolefin that provides good fluidity and adhesion. Among these, a modified polyethylene hot melt adhesive having excellent adhesiveness and anticorrosion properties is preferable. In addition, when cross-linked polyethylene is used for the steel pipe coating layer, it is preferable in that a high adhesion effect is obtained because the same kind of resin is entangled at the interlayer adhesion surface (interface) of these overlapping portions. is there.

  The thickness of the inner layer material 6-2 has a high adhesive strength, prevents the occurrence of turning and peeling against external stress, and can maintain various properties such as anticorrosion and waterproof performance effectively for a long period of time. The outer diameter of the steel pipe, the material and thickness of the outer layer material 6-1, the presence or absence of mortar coating, the environmental conditions (humidity, temperature, etc.) at the time of embedding and after embedding, and the required service life, etc. It may be determined appropriately in consideration of the above, but it is usually only about 0.5 mm or more.

  Further, when the second heat shrinkable material 6 having a longer width than the first heat shrinkable material 5 of the first layer is used for the second layer, It is desirable to increase the longitudinal width of the second heat shrinkable material 6 by 100 to 400 mm, preferably about 200 to 300 mm. If the longitudinal width of the second heat-shrinkable material 6 is larger than the first heat-shrinkable material 5 by only less than 100 mm, it is difficult to superimpose or the second inner-layer The overlapping width (adhesion surface) of the hot melt adhesive of the material 6-2 and the polyolefin coating layer 4 of the steel pipe 1 is small, and there is a possibility that it is difficult to obtain sufficient adhesive strength therebetween. On the other hand, when it is larger than 400 mm, it is difficult to produce the heat shrink material, and the overlap width of the hot melt adhesive of the second inner layer material 6-2 and the polyolefin coating layer 4 of the steel pipe 1 ( Adhesive surface) is large, and sufficient adhesive strength is obtained in the meantime. Further, increasing the longitudinal width is uneconomical in terms of heat shrink material cost and enlargement of the decompression device.

  In addition, also about the 1st heat shrinkable material 5 of the 1st layer, the overlap width with the polyolefin coating layer 4 of the steel pipe 1 has the 2nd heat shrinkable material 6 of the 2nd layer, the polyolefin coating layer 4 of the steel pipe 1, and It is desirable to determine the width of the heat-shrinkable material 5 so as to be as large as the overlapping width of the above, that is, about 50 to 100 mm on the left and right sides.

  In addition, the form of the heat shrinkable material that can be used in the present invention is not particularly limited, and a sheet-like form can be wound around and used in addition to a tubular form. In the tubular form, since there are no joints or overlapping portions in the circumferential direction of the steel pipe, a uniform appearance can be obtained and a high quality product can be provided. On the other hand, in the tubular form, the length of one steel pipe is several tens of meters to hundreds of tens of meters, and is moved from the end of the non-welded part of the steel pipe to the welded part through the tubular heat-shrinkable material. Although it is necessary, a sheet-like heat-shrinkable material is excellent in terms of work efficiency because it may be wound directly around the welded portion. Furthermore, depending on the application, other conventionally known forms such as a tape form may be used.

  In addition, the polyolefin coating layer 4 of the steel pipe 1 is not particularly limited, and can be applied by coating a polyolefin material such as polyethylene or polypropylene. However, it is inexpensive, has high electrical insulation, and hardly allows moisture and oxygen to pass therethrough. Since it is a material, a material coated with a polyethylene material is suitable.

  The thickness of the coating layer 4 may be any thickness that can effectively maintain various properties such as waterproofness, weather resistance, chemical resistance, crack resistance, and electrical insulation for a long period of time. The diameter may be appropriately determined in consideration of the environmental conditions (humidity, temperature, etc.) at the time of embedding or after embedding, and the required service life, but it is usually about 2 to 6 mm.

  The steel pipe 1 applicable to the present invention is not particularly limited, and can be widely applied to steel pipes used for underground pipes such as gas conduits that require anticorrosion measures. In this invention, it is especially suitable for what carries out anticorrosion coating | coating of the welded joint part on-site. For example, as shown in FIG. 6, particularly in a gas pipe laid in an underground tunnel or a gas pipe buried in a deep underground where it is difficult (impossible) to apply the direct propulsion method of moving the pipe after anticorrosion coating. Is suitable.

  In the present invention, (1) air (air) entrainment, prevention of scorching of the coated skin, (2) prevention of deterioration of adhesion performance (reactivity) due to OH group (water vapor) in dry environment, (3) skilled worker Not required (4) From any viewpoint capable of working in a small space, it is characterized by being heat-shrinked by far-infrared rays under reduced pressure, preferably under reduced pressure. When heating under such reduced pressure, preferably when the far-infrared heating under reduced pressure is over 0.05 MPa, air entrainment tends to increase even if the pressure is reduced. The following is desirable. In particular, as described above, in the present invention, the direct propulsion method of moving the pipe after the anticorrosion coating is difficult (impossible) to use in a pipe laid in an underground tunnel or a gas pipe buried in a deep underground. In some cases, unlike the ground, the environment may be very humid. Therefore, when performing heat shrinkage under atmospheric pressure, in addition to air entrainment and scorching of the coating, condensation is likely to occur on the steel pipe and coating surface, and such moisture adheres to the adhesive surface or adhesive surface, and adhesive performance or There is a problem of lowering the adhesion performance. For this reason, in the present invention, it is extremely advantageous to perform the coating operation under a reduced pressure atmosphere of 0.05 MPa or less that can be in a dry environment, in order to ensure adhesion or adhesion. In addition, by carrying out under a reduced pressure atmosphere of 0.05 MPa or less, air (air) entrainment on the adhesive surface or adhesive surface of the heat-shrinkable material can be significantly reduced when the heat-shrinkable material is coated. For this reason, the adhesive strength or the adhesive strength, and thus the waterproof / corrosion-proof performance can be secured for a long time, and the long-term reliability can be expressed. Moreover, as a method for heating the heat shrinkable material, it can be heated using a torch (gas burner), hot air heating, heating wire heating, high frequency induction heating, etc. can be used, but it has a high heating capacity and a small space. From the standpoint of uniform heating work, it is particularly advantageous to use the far infrared rays described above.

  The heating conditions for heat-shrinking the first heat-shrinkable material depend on the type of material used for the first heat-shrinkable material and the coating layer of the steel pipe that is the underlayer, the thickness of the heat-shrinkable material, and the like. Thus, it may be determined as appropriate so as to obtain the optimum adhesion or adhesion strength. Further, as will be described later, since the heating temperature may be adjusted to be different depending on the longitudinal direction or the circumferential direction of the steel pipe, it is difficult to define it uniquely. When far-infrared heating is performed in a range of 05 MPa or less, particularly preferably 0.03 MPa or less, the outer layer material 5-1 of the first heat-shrinkable material 5 contracts without scorching, and the inner layer material 5-2. So that the temperature of the far-infrared heater can be 250 to 400 ° C., preferably 350 to 380 ° C., and the heating time is 10 to 40 minutes, preferably 10 to 15 minutes. Heating can be performed. When the far-infrared heater set temperature is less than 250 ° C., the coating shrinkage is likely to occur due to insufficient heating, and when it exceeds 450 ° C., scorching due to excessive heating tends to occur. In addition, when the heating time is less than 10 minutes, the coating shrinkage due to insufficient heating tends to occur, and when it exceeds 40 minutes, scorching due to excessive heating tends to occur.

  As the heating conditions when the second heat shrinkable material is heated and shrunk, the type of material used for the second heat shrinkable material, the coating layer of the steel pipe to be the underlayer, or the outer layer material of the first heat shrinkable material, What is necessary is just to determine suitably according to the thickness etc. of this heat shrink material so that optimal adhesion | attachment thru | or adhesion strength may be obtained. Further, as will be described later, since the heating temperature may be adjusted to be different depending on the longitudinal direction or the circumferential direction of the steel pipe, it is difficult to define it uniquely. When far-infrared heating is performed at 05 MPa or less, particularly preferably 0.03 MPa or less, the outer layer material 6-1 of the second heat shrinkable material 6 shrinks without burning, and the inner layer material 6-2 softens. The far infrared heater set temperature is 300 to 450 ° C., preferably 370 to 420 ° C., and the heating time is 15 to 30 minutes, preferably 15 to 20 minutes so that the temperature can be reached. When the temperature is lower than 300 ° C., poor adhesion due to insufficient heating tends to occur, and when it exceeds 450 ° C., scorching due to excessive heating tends to occur. Moreover, when the heating time is less than 15 minutes, adhesion failure due to insufficient heating tends to occur, and when it exceeds 30 minutes, scorching due to excessive heating tends to occur.

  As a method of heating and shrinking with far-infrared rays under such reduced pressure, preferably under reduced pressure, for example, the apparatus shown in FIGS. 4 to 6 used in Examples described later can be used. First, as shown in FIG. 6, the tube-shaped first heat-shrinkable material 5 is passed through the polyolefin-coated steel pipe 1 and moved to the weld zone 3 where the pipe end of the polyolefin-coated steel pipe 1 is welded. Let Next, a cylindrical decompression chamber 15 containing a far infrared heater 13 (a heating wire or a high frequency induction coil may be used instead of the far infrared heater 13) is covered. For example, as shown in FIG. 6, along the polyolefin-coated steel pipe 1, the upper and lower separation type decompression chambers 15-1 and 15-2 are moved to the field welding part 3 where the pipe end of the polyolefin-coated steel pipe 1 is welded. First, the lower pressure reducing chamber 15-1 is moved on the upper part of the polyolefin-coated steel pipe 1, is moved by 180 degrees at the field welded portion 3, and then installed on the upper pressure reducing chamber 15-. 2 is moved and mounted, and upper and lower separation type decompression chambers 15-1 and 15-2 are connected to each other and covered with the polyolefin-coated steel pipe 1 for sealing. Thereafter, the decompression pump 16 connected to the decompression chamber 15 (the connection hose, the exhaust hose, the decompression control panel, the power cord, etc. are omitted) is operated to decompress the interior of the decompression chamber 15 to a desired degree of decompression ( And after reaching a predetermined degree of decompression, energization is performed through the far-red heating control panel 17 connected to the far-infrared heater 13 under the reduced pressure (connection lead wires, power cords, etc. are omitted). The heat-shrinkable material 5 is heated and shrunk by heating with far infrared rays for a predetermined time. Thereafter, the power is turned off and the pressure is returned to normal pressure in a non-heated state. After the decompression chamber 15 is removed, the second heat-shrinkable material 6 in the tube shape (unshrinked) is passed through the polyolefin-coated steel pipe 1. Then, the heat-shrinkable material 5 is moved to the spot welded portion 3 where the pipe end portion of the polyolefin-coated steel pipe 1 is welded to a portion where the heat-shrinkable material 5 is coated by heat shrinkage. Thereafter, in the same manner as the heat shrinkage of the first layer of heat shrinkable material 5, the second layer of heat shrinkable material 6 is subjected to reduced pressure using a cylindrical decompression chamber 15 containing a far infrared heater 13. Preferably, the film is heat-shrinked with far-infrared rays under reduced pressure to coat the layers.

  Here, as shown in FIGS. 4 and 5, the seal structure of the decompression chamber 15 is such that both end portions 15 a (made of a sealing material) of the vertically-separated decompression chamber 15 are made of the polyolefin coating layer 4 of the steel pipe 1. Although the thing reduced to the diameter so that it may contact | adhere to an outer peripheral surface (pressing contact) etc. is mentioned, It is not restrict | limited to these.

  Further, as shown in FIGS. 4 and 5, the far-infrared heater (panel) 13 is attached to the steel pipe by a far-infrared heater attachment jig 14 so as to be positioned on the entire inner peripheral surface of the decompression chamber 15. A plurality of them are installed at substantially equal intervals in each of the longitudinal direction and the circumferential direction. Instead of the far-infrared heater 13, a heating wire or a high-frequency induction coil may be used to appropriately arrange the same effect.

  In addition, when the individual far-infrared heaters 13 are equally energized and heated, the temperature contraction (up / down or left / right) is applied to the heat-shrinkable materials 5 and 6 that are heated and shrunk in the decompression chamber 15 by heat conduction or movement of heated air. Temperature difference) may occur. Therefore, as shown in FIGS. 4 and 5, a plurality of far infrared heaters 13 are installed in each of the longitudinal direction and the circumferential direction of the steel pipe, and the far red heating control panel 17 connected to these far infrared heaters 13. It is desirable that the heat-shrinkable materials 5 and 6 to be heated and shrunk can be individually and independently controlled by far-red heating so that the entire surface is heat-shrinked. In the case of the heat-shrinkable material 6 to be heated and shrunk, in the longitudinal direction of the steel pipe, as shown in FIG. 5, the temperature of the far-infrared heaters 13a and 13d outside the center far-infrared heaters 13b and 13c is set higher. Good. Similarly, in the circumferential direction, as shown in FIG. 4, it is preferable to set the temperature of the far-infrared heater 13-2 on the lower side higher than that of the far-infrared heater 13-1 on the upper side. Even when a heating wire or a high-frequency induction coil is used in place of the infrared heater 13, temperature control using a heating wire or a high-frequency induction coil can be performed individually and independently so that the entire surface is equally heated and shrunk. good.

  Moreover, in this invention, it is desirable for the polyolefin coating layer 4 edge part of the steel pipe 1 to have a taper angle, Preferably it has a taper angle of 25 degrees or less. The heat-shrinkable material 5 of the first layer needs to be coated including the field welded portion 3 and the polyolefin coating layer 4 portion of the steel pipe 1 on the outer side in the longitudinal direction of the welded portion. Therefore, when the heat shrinkable material 5 of the first layer is coated by reducing the step between the steel surface 2 ′ of the field welded portion 3 and the end of the steel tube coating layer 4 and gradually angling the steel pipe coating layer 5. Air entrainment at the end of the layer 4 can be suppressed. Since this air entrainment (air remaining) can be a starting point of peeling and turning, it is desirable that it is not generated as much as possible. Usually, the end portion of the coating layer 4 of the steel pipe is generally provided with a taper angle of about 45 ° by non-working or general chamfering. However, if it is about 90 ° (unprocessed) to about 45 °, air entrainment may still occur in part of the end portion of the coating layer 4 of the steel pipe. In particular, when the taper angle of the end portion of the coating layer 4 of the steel pipe is 25 ° or less, it is excellent in that air entrainment at the end portion of the coating layer 4 of the steel pipe can be effectively prevented. Further, when coating is performed by heating under reduced pressure, preferably by far-infrared heating under reduced pressure, it is particularly effective in suppressing air entrainment at the end of the coating layer of the steel pipe.

  In the representative embodiment of the present invention described with reference to FIG. 1 and FIGS. 4 to 6 described above, the first coating layer forming portion is formed in the first layer using the first heat shrinkable material. An anticorrosion coating structure and a method of manufacturing the same, wherein the second coating layer forming portion is formed by lap winding using a second heat shrinkable material having a longer longitudinal width than the first layer. However, the present invention is not limited to these.

  As another embodiment of the present invention, for example, (1) the first coating layer forming part is formed in the first layer using the first heat shrink material, and the second layer The anticorrosion coating structure characterized in that the second coating layer forming portion is formed by wrapping around the two ends of the first coating layer forming portion using a shrink material, (2) the first layer, The first layer of the first coating layer forming portion is formed using the heat shrinkable material of 1, and the second layer has the same longitudinal width as the first layer or a longer longitudinal width than the first layer. A first coating layer forming portion (two-layer overlap structure) is formed using the first heat shrink material, and a second heat shrink material having a longer longitudinal width than the second layer is formed on the third layer. The anticorrosion coating structure in which the second coating layer forming portion is formed by lap winding, or (3) the first or second heat shrinkable material is The inner layer material of the part is a mastic-based adhesive material, the outer layer material is a material with a heat shrink function, the inner layer material of the end part is a hot melt adhesive based on polyolefin, and the outer layer material is a material with a heat shrink function Embodiments such as an anticorrosion coating structure characterized by a certain point can be exemplified, but are not limited thereto.

  These anticorrosion coating structures are also coated by heat shrinkage under reduced pressure, preferably 0.05 MPa or less as described above, and more preferably by heat shrinkage by far-infrared rays under the above reduced pressure. Needless to say, it is desirable that the end portion of the coating layer has a taper angle, preferably 25 ° or less.

  Next, also about the manufacturing method of the anti-corrosion coating structure of the field welding part of this invention, (1) The 1st coating process which heat-shrinks and coat | covers the 1st heat-shrink material in the 1st layer, and the 2nd layer And a second coating step in which the second heat-shrinkable material is heated and shrunk to overlap and coat the two ends of the first-layer coating layer forming portion, and (2) the first layer The first heat-shrinkable material is coated by heat-shrinking, and the second layer is coated with the first heat-shrinkable material having the same longitudinal width as that of the first layer or a longer longitudinal width than the first layer. A first coating step for heat-shrinking and lap-coating and a second coating step for heat-shrinking a second heat-shrinkable material having a longer longitudinal width than the second layer to lap-coating the third layer. (3) As the first or second heat shrinkable material, the inner layer material at the center is a mastic adhesive material, and the outer layer material. Embodiments such as a method characterized by using a material having a heat shrink function, using a hot melt adhesive based on polyolefin as an inner layer material at an end, and a material having a heat shrink function as an outer layer material, etc. Although it can illustrate, it is not restrict | limited to these.

  In the present invention, a multilayer anticorrosion coating structure having three or more layers can be provided, and a method for producing such a multilayer anticorrosion coating structure can also be provided. As described above, under reduced pressure, preferably under reduced pressure, In order to heat-shrink with far-infrared rays, it is necessary to detach the device for each layer. Although the anti-corrosion safety can be further improved by increasing the number of layers to 4 or more, the manufacturing cost and the number of parts increase accordingly, so the optimal number of anti-corrosion coating layers is considered in consideration of economy, productivity and performance. It can be said that it may be determined.

  Examples of the present invention will be further described below.

Example 1
As shown in FIG. 3, the polyethylene coating at the center of the polyethylene coated steel pipe 1 having a pipe thickness of 14 mm, a factory polyethylene coating thickness of 5 mm, a diameter of 620 mm, and a length of 2000 mm is removed in a circumferential direction with a length of 300 mm, and the polyethylene coating is removed. A test body 12 of a simulated on-site welded portion in which a weld bead 11 was formed at the central portion of the exposed portion 10 of the steel pipe substrate was produced.

  In this test body 12, the inner layer material 5-2 of the first layer of the present invention is replaced with a butyl rubber adhesive so as to completely cover the exposed portion 10 of the steel pipe substrate in place of the steel surface exposed portion 2 ′ shown in FIG. 1. The first heat-shrinkable material 5 (trade name: RAPCO TUBE E50 manufactured by FPCO Corporation) is a cross-linked polyethylene (thickness 1.5 mm) obtained by electron beam cross-linking a polyethylene material as the outer layer material 5-1 (thickness 1.5 mm). , A longitudinal width of 600 mm) was covered with a chamber containing a far-infrared heater shown in FIGS. 4 and 5, and heat-shrinked in a reduced pressure atmosphere of 0.03 MPa.

  Thereafter, the inner layer material 6-2 having a longer width than the first layer was modified polyethylene-based hot-melt adhesive (thickness 0.6 mm), and the outer layer material 6-1 was electron beam crosslinked with a polyethylene material. A second heat-shrinkable material 6 (trade name: RAPCO TUBE EH manufactured by EFCO Co., Ltd., longitudinal length: 900 mm) to be crosslinked polyethylene (thickness: 1.5 mm) is placed on the chamber containing the far-infrared heater, and 0.03 MPa. The anti-corrosion coating structure (corrosion protection coating structure shown in FIG. 1) of the simulated on-site welded portion that was heat-shrinked under reduced pressure and covered with lap winding was formed.

  When the first layer of heat shrinkable material 5 is coated, the outer layer material 5-1 of the first heat shrinkable material 5 shrinks without burning, and the inner layer material 5-2 has a softening temperature of about 70 ° C. In order to reach the temperature, the installation temperature of the far infrared heater 13 was set to 380 ° C. and heated for 14 minutes. When coating the second layer of heat-shrinkable material 6, the outer layer material 6-1 of the second heat-shrinkable material 6 shrinks without burning, and the inner layer material 6-2 has a softening temperature of about 130 ° C. In order to reach the temperature, the installation temperature of the far infrared heater 13 was set to 400 ° C. and heated for 18 minutes.

  At 50 ° C, a cut is made in the longitudinal direction of the two-layer wound coating of the anti-corrosion coating structure of the obtained simulated on-site welded portion with a 10 mm wide cutter to reach the steel pipe surface, and a tensile tester is provided at the coating end to provide a 180 ° direction. A peel test was carried out to measure the strength required for peeling. The test was conducted at a test temperature of 50 ° C. in order to investigate the influence of the adhesive force on the temperature at which heat is generated when the anticorrosion-coated pipe is further coated with mortar.

(Comparative Example 1)
As a comparative material, in the test layer 12 shown in FIG. 3 which is the same as that in Example 1, the first layer was formed so as to completely cover the exposed portion 10 of the steel pipe substrate in place of the steel surface exposed portion 2 ′ shown in FIG. 2C. The inner layer material 5-2 that is the same as 1 is a butyl rubber-based adhesive material (thickness 1.5 mm), and the outer layer material 5-1 is a crosslinked polyethylene (thickness 1.5 mm) obtained by electron beam crosslinking of a polyethylene material. A heat-shrinkable material 5 (trade name: RAPCO TUBE E50 manufactured by EFCO Co., Ltd., longitudinal width: 600 mm) was put on and heat-shrinked with a propane torch.

  Thereafter, the inner layer material 5′-2, which is the same material as the first layer except that the longitudinal width is larger than that of the first layer, is replaced with a butyl rubber adhesive (thickness 1.5 mm), and the outer layer material 5′-1. Is covered with a first heat-shrinkable material 5 ′ (trade name: FPCO lapco tube E50, longitudinal width: 800 mm) made of a polyethylene material cross-linked polyethylene (thickness 1.5 mm) obtained by electron beam cross-linking with a propane torch. An anti-corrosion coating structure (conventional anti-corrosion coating structure in which two layers are wound as shown in FIG. 2C) of a simulated on-site welded portion that is heat-shrinked and overwrapped is formed. This comparative example 1 is an improvement of Patent Document 1 (the steel pipe coating layer is cut into a step shape, and the adhesive heat-shrink material is wound as a third layer in the gap between the second-layer adhesive heat-shrink material and the stepped portion. It can be said that it is a form of the previous conventional anticorrosion coating structure. When coating the first and second heat shrinkable materials 5, 5 ', the heating power of the torch was adjusted so that the temperature of the adhesive was about 70 ° C. This conventional anticorrosion coating structure was also tested in the same manner as in Example 1.

  As a result, as shown in Table 1, the anti-corrosion coating structure of the simulated on-site welded portion according to Example 1 of the present invention showed higher peel strength than the conventional anti-corrosion coating structure of the comparative material according to Comparative Example 1, and the deviation was stopped. It became clear that it was excellent in prevention of bruise.

(Example 2)
As shown in FIG. 3, the polyethylene coating at the center of the factory polyethylene-coated steel pipe 1 having a pipe thickness of 14 mm, a polyethylene coating thickness of 5 mm, a diameter of 620 mm, and a length of 2000 mm is removed in a circumferential direction with a length of 300 mm, and the polyethylene coating is removed. A test body 12 of a simulated on-site welded portion in which a weld bead 11 was formed at the central portion of the exposed portion 10 of the steel pipe substrate was produced.

  In this test body 12, the inner layer material 5-2 of the first layer of the present invention is replaced with a butyl rubber adhesive so as to completely cover the exposed portion 10 of the steel pipe substrate in place of the steel surface exposed portion 2 ′ shown in FIG. 1. The first heat-shrinkable material 5 (trade name: RAPCO TUBE E50 manufactured by FPCO Corporation) is a cross-linked polyethylene (thickness 1.5 mm) obtained by electron beam cross-linking a polyethylene material as the outer layer material 5-1 (thickness 1.5 mm). , A longitudinal width of 600 mm) was covered with a chamber containing a far-infrared heater shown in FIGS. 4 and 5, and heat-shrinked in a reduced pressure atmosphere of 0.03 MPa.

  Thereafter, the inner layer material 6-2 having a longer width than the first layer was modified polyethylene-based hot-melt adhesive (thickness 0.6 mm), and the outer layer material 6-1 was electron beam crosslinked with a polyethylene material. A second heat-shrinkable material 6 (trade name: RAPCO TUBE EH manufactured by EFCO Co., Ltd., longitudinal length: 900 mm) to be crosslinked polyethylene (thickness: 1.5 mm) is placed on the chamber containing the far-infrared heater, and 0.03 MPa. The anti-corrosion coating structure (corrosion protection coating structure shown in FIG. 1) of the simulated on-site welded portion that was heat-shrinked under reduced pressure and covered with lap winding was formed.

  When the first layer of heat shrinkable material 5 is coated, the outer layer material 5-1 of the first heat shrinkable material 5 shrinks without burning, and the inner layer material 5-2 has a softening temperature of about 70 ° C. In order to reach the temperature, the installation temperature of the far infrared heater 13 was set to 380 ° C. and heated for 14 minutes. When coating the second layer of heat-shrinkable material 6, the outer layer material 6-1 of the second heat-shrinkable material 6 shrinks without burning, and the inner layer material 6-2 has a softening temperature of about 130 ° C. In order to reach the temperature, the installation temperature of the far infrared heater 13 was set to 400 ° C. and heated for 18 minutes.

  The obtained anti-corrosion coating structure of the simulated field weld was immersed in warm water at 40 ° C. for 120 days. A peel that measures the strength required to pull and peel in the 180 ° direction by providing a notch reaching the steel pipe surface with a 10 mm wide cutter in the longitudinal direction of the anticorrosion coating wound in two layers after the test. The test was conducted. At the same time, the evaluation of visual observation of the intrusion width of water from the coating end was also performed.

(Comparative Example 2)
As a comparative material, in the test layer 12 shown in FIG. 3 which is the same as that in Example 2, the exposed portion 10 of the steel pipe substrate is completely covered in place of the steel surface exposed portion 2 ′ shown in FIG. 2C. The inner layer material 5-2 that is the same as 1 is a butyl rubber-based adhesive material (thickness 1.5 mm), and the outer layer material 5-1 is a crosslinked polyethylene (thickness 1.5 mm) obtained by electron beam crosslinking of a polyethylene material. A heat-shrinkable material 5 (trade name: RAPCO TUBE E50 manufactured by EFCO Co., Ltd., longitudinal width: 600 mm) was put on and heat-shrinked with a propane torch.

  Thereafter, the inner layer material 5′-2, which is the same material as the first layer except that the longitudinal width is larger than that of the first layer, is replaced with a butyl rubber adhesive (thickness 1.5 mm), and the outer layer material 5′-1. Is covered with a first heat-shrinkable material 5 ′ (trade name: FPCO lapco tube E50, longitudinal width: 800 mm) made of a polyethylene material cross-linked polyethylene (thickness 1.5 mm) obtained by electron beam cross-linking with a propane torch. An anti-corrosion coating structure (conventional anti-corrosion coating structure in which two layers are wound as shown in FIG. 2C) of a simulated on-site welded portion that is heat-shrinked and overwrapped is formed. This comparative example 2 is an improvement of Patent Document 1 (the steel pipe coating layer is cut into a step shape, and the adhesive heat-shrink material is wound as a third layer in the gap between the second-layer adhesive heat-shrink material and the stepped portion. It can be said that it is a form of the previous conventional anticorrosion coating structure. When coating the first and second heat shrinkable materials 5, 5 ', the heating power of the torch was adjusted so that the temperature of the adhesive was about 70 ° C. This conventional anticorrosion coating structure was also tested in the same manner as in Example 2.

  As a result, as shown in Table 2, the anticorrosion coating structure of the simulated on-site welded portion according to Example 2 of the present invention showed no reduction in peel strength even after being immersed in warm water at 40 ° C. for 120 days. No water intrusion was observed. On the other hand, the conventional anticorrosion coating structure of the comparative material according to Comparative Example 2 did not have a decrease in peel strength, but water intrusion was observed about 2 to 3 mm from the coating edge. Therefore, the anticorrosion coating structure of the simulated on-site welded portion according to Example 2 of the present invention is applied to the adhesive surface in a dry environment by heating far infrared rays under reduced pressure when the hot melt adhesive and the polyethylene coating layer 4 are bonded. Water and air entrainment (remaining air area) are remarkably reduced, and the adhesive surface is heated to a temperature higher than the melting point of hot melt and polyethylene, so that the resin of the hot melt adhesive and the resin of the polyethylene coating layer 4 As a result, adhesion close to the melting point where the two are intertwined occurs, and it has become clear that adhesion with excellent barrier properties that can reliably prevent the entry of corrosion factors such as water is possible.

(Example 3)
As shown in FIG. 3, the polyethylene coating at the center of the polyethylene coated steel pipe 1 having a pipe thickness of 14 mm, a factory polyethylene coating thickness of 5 mm, a diameter of 620 mm, and a length of 2000 mm is removed in a circumferential direction with a length of 300 mm, and the polyethylene coating is removed. A test body 12 of a simulated on-site welded portion in which a weld bead 11 was formed at the central portion of the exposed portion 10 of the steel pipe substrate was produced.

  In this test body 12, the inner layer material 5-2 is attached to the first layer of the present invention so as to completely cover the exposed portion 10 of the steel pipe substrate in place of the steel surface exposed portion 2 ′ shown in FIG. 1. First heat-shrinkable material 5 (trade name: FPCO manufactured by FPCO Co., Ltd.) made of a material (thickness: 1.5 mm) and an outer layer material 5-1 that is a crosslinked polyethylene (thickness: 1.5 mm) obtained by electron beam crosslinking of a polyethylene material. (E50, longitudinal width: 600 mm) was covered with a chamber containing a far-infrared heater shown in FIGS. 4 and 5, and heat-shrinked in a reduced pressure atmosphere of 0.03 MPa.

  Further, after that, the inner layer material 6-2 has a longer width than the first layer, the modified polyethylene-based hot-melt adhesive (thickness: 0.6 mm), and the outer layer material 6-1 is cross-linked with a polyethylene material by electron beam. A second heat-shrinkable material 6 (trade name: RAPCO TUBE EH, manufactured by EFCO Co., Ltd., longitudinal length: 900 mm) to be crosslinked polyethylene (thickness: 1.5 mm) is put on the chamber containing the far-infrared heater, and 0 An anti-corrosion coating structure (corrosion protection coating structure shown in FIG. 1) of a simulated on-site welded portion that was heat-shrinked under a reduced pressure of 0.03 MPa and was covered by lap winding was formed.

  When the first layer of heat shrinkable material 5 is coated, the outer layer material 5-1 of the first heat shrinkable material 5 shrinks without burning, and the inner layer material 5-2 has a softening temperature of about 70 ° C. In order to reach the temperature, the installation temperature of the far infrared heater 13 was set to 380 ° C. and heated for 14 minutes. When coating the second layer of heat-shrinkable material 6, the outer layer material 6-1 of the second heat-shrinkable material 6 shrinks without burning, and the inner layer material 6-2 has a softening temperature of about 130 ° C. In order to reach the temperature, the installation temperature of the far infrared heater 13 was set to 400 ° C. and heated for 18 minutes.

  At 50 ° C, a cut was made in the longitudinal direction of the two-layered coating of the anti-corrosion coating structure of the obtained simulated on-site weld with a 10 mm wide cutter, and a tensile tester was provided at the coating end and a 180 ° direction A peel test was carried out to measure the strength required for peeling. The test was conducted at a test temperature of 50 ° C. in order to investigate the influence of the adhesive force on the temperature at which heat is generated when the anticorrosion-coated pipe is further coated with mortar. Further, the entire surface of the coating layer was peeled off, and a visual inspection was performed on the remaining air area (air entrainment area) when the heat-shrinkable material contracted. It is desirable that the remaining air does not occur as much as possible because it can be a starting point for peeling and turning.

  As a result, as shown in Table 3, the appearance of the anticorrosion structure according to the present invention was good. The peel end also showed high peel strength and was found to be excellent in preventing slippage and turning. Moreover, as a result of peeling and observing the entire surface of the coating layer, it was revealed that the remaining air was very small because of the reduced pressure atmosphere.

(Comparative Example 3)
As Comparative Example 3, the end of the polyethylene coating of the test body 12 shown in FIG. 3 was cut into a step shape as shown in FIG. 2B, and the same inner layer material 5-2 as in Example 3 was added to the first layer as butyl rubber. First heat-shrinkable material 5 (trade name: FCO Co., Ltd.), which is a cross-linked polyethylene (thickness 1.5 mm) obtained by cross-linking polyethylene (electron beam-crosslinked polyethylene material) as an adhesive material (thickness 1.5 mm) A company-made Rapco tube E50 (longitudinal width 600 mm) was placed on the plate and heat-shrinked with a propane torch.

  Further, after that, the inner layer material 6-2 has a longer width than the first layer, the modified polyethylene-based hot-melt adhesive (thickness: 0.6 mm), and the outer layer material 6-1 is cross-linked with a polyethylene material by electron beam. A second heat-shrinkable material 6 (trade name: RAPCO TUBE EH manufactured by EFCO Co., Ltd., longitudinal width: 900 mm), which is made to be a cross-linked polyethylene (thickness 1.5 mm), is covered and heat-shrinked with a propane torch, as shown in FIG. The conventional anticorrosion coating structure of Patent Document 1 was formed. Note that when the first layer of the heat shrinkable material 5 was coated, the heating power of the torch was adjusted so that the temperature of the adhesive was about 70 ° C. When the second layer of heat shrinkable material 6 was coated, the heating temperature of the torch was adjusted and heated so that the temperature of the adhesive exceeded about 100 ° C. and the coating did not burn. However, in order to cut in a stepped manner, it is necessary to increase the thickness of the polyethylene coating layer of the test body 12 by three times or more. However, since the same test body 12 as in Example 3 was used, it is necessary for the cutting process. Since the thickness of the polyethylene coating layer was insufficient, the place where the three layers were formed was omitted in two steps. In accordance with this, the first-layer adhesive-type heat-shrinkable material was wound in a range narrower than the width of the stepped portion, and the second-layer adhesive-type heat-shrinkable material was omitted. Furthermore, the adhesive heat shrink material of the third layer that was originally wound only in the gap of the step portion was changed to be wound so as to overlap the step portion as the second layer heat shrink material (FIGS. 2B and 2C). Refer to the contrast.)

  In the same manner as in Example 3, at 50 ° C., a notch that reaches the steel pipe surface is provided in the longitudinal direction of the two-layered coating with a 10 mm wide cutter, and a tensile tester is provided at the coating end to pull and peel in the 180 ° direction. A peel test was conducted to measure the strength required for the test. Further, the entire surface of the coating layer was peeled off, and the remaining air area when the heat shrinkable material was shrunk was investigated.

(Comparative Example 4)
As Comparative Example 4, the end of the polyethylene coating of the test body 12 shown in FIG. 3 was cut into a step shape as shown in FIG. 2B, and the same inner layer material 5-2 as in Example 3 was added to the first layer as butyl rubber. First heat-shrinkable material 5 (trade name: FCO Co., Ltd.), which is a cross-linked polyethylene (thickness 1.5 mm) obtained by cross-linking polyethylene (electron beam-crosslinked polyethylene material) as an adhesive material (thickness 1.5 mm) A company-made Lapco tube E50 (longitudinal width 600 mm) was covered with the far-infrared chamber shown in FIGS. 4 and 5 and heated and shrunk under atmospheric pressure.

  Further, after that, the inner layer material 6-2 has a longer width than the first layer, the modified polyethylene-based hot-melt adhesive (thickness: 0.6 mm), and the outer layer material 6-1 is cross-linked with a polyethylene material by electron beam. A chamber containing a far-infrared ray as shown in FIG. 4 and FIG. 5 for the second heat-shrinkable material 6 (trade name: RAPCO TUBE EH manufactured by EFCO Co., Ltd., longitudinal length: 900 mm) as a crosslinked polyethylene (thickness: 1.5 mm). And was heated and shrunk under atmospheric pressure to form the same anticorrosion coating structure as in Patent Document 1 shown in FIG. 2B. When the first layer of heat shrinkable material 5 is coated, the outer layer material 5-1 of the first heat shrinkable material 5 shrinks without burning, and the inner layer material 5-2 has a softening temperature of about 70 ° C. In order to reach the temperature, the installation temperature of the far infrared heater 13 was set to 380 ° C. and heated for 14 minutes. When coating the second layer of heat-shrinkable material 6, the outer layer material 6-1 of the second heat-shrinkable material 6 shrinks without burning, and the inner layer material 6-2 has a softening temperature of about 130 ° C. The far-infrared heater 13 was set at a temperature of 400 ° C. and heated for 18 minutes so that it could be reached. However, in order to cut in a stepped manner, it is necessary to increase the thickness of the polyethylene coating layer of the test body 12 by three times or more. However, since the same test body 12 as in Example 3 was used, it is necessary for the cutting process. Since the thickness of the polyethylene coating layer is insufficient, the place where the three layers are formed is omitted in two steps. In accordance with this, the first-layer adhesive-type heat-shrinkable material was wound in a range narrower than the width of the stepped portion, and the second-layer adhesive-type heat-shrinkable material was omitted. Furthermore, the adhesive heat shrink material of the third layer that was originally wound only in the gap of the step portion was changed to be wound so as to overlap the step portion as the second layer heat shrink material. (Refer to FIG. 2B and FIG. 2C for comparison.) Furthermore, it changes so that it may heat using the far-infrared heating heater which is not disclosed by patent document 1, and it can be said to be a reference example.

  In the same manner as in Example 3, at 50 ° C., a slit having a width of 10 mm is provided in the longitudinal direction of the two-layered coating with a cutter having a width of 10 mm, and a tensile tester is provided at the end of the coating to pull it in the 180 ° direction. A peel test was conducted to measure the strength required for the test. Further, the entire surface of the coating layer was peeled off, and the remaining air area when the heat shrinkable material was shrunk was investigated.

  As a result, as shown in Table 3 below, in the case of Comparative Example 3 in which heating with a propane torch was performed, a large amount of air remaining was observed. In the case of Comparative Example 4 using a far-infrared heater, the temperature of the upper portion of the chamber became higher due to the movement of air heat to the upper surface, and scorching was recognized in the heat shrinkable material. In addition, a large amount of air remaining was observed after contraction.

It is sectional drawing of the anticorrosion coating | coated structure of the pipe welded joint part by this invention. It is sectional drawing of the typical anti-corrosion coating | coated structure of the conventional pipe welded joint part. It is sectional drawing of the other anti-corrosion coating structure of the conventional pipe welded joint part used in Comparative Examples 3 and 4. It is sectional drawing of the other anti-corrosion coating structure of the conventional pipe welded joint part used in Comparative Examples 1 and 2. It is a schematic diagram of the test body used for the Example. It is a longitudinal cross-sectional view of the chamber incorporating the far-infrared heater. It is a cross-sectional view of a chamber incorporating a far-infrared heater. In the production of the anticorrosion coating structure for a pipe welded joint according to the present invention, the state of a stage (before the first coating process) in which a vertically-separated chamber with a built-in far-infrared heater and a tubular heat-shrinkable material are prepared is schematically shown. It is the schematic represented to.

Explanation of symbols

1 anticorrosion coated steel pipe,
2 Steel pipe (main body),
2 'exposed steel surface,
3 On-site weld bead of steel pipe,
4 Polyolefin or polyethylene coating layer,
5 First layer (first) heat shrink material,
5-1 Outer layer material (crosslinked polyethylene) of the first layer of heat-shrinkable polyethylene material,
5-2 Inner layer material (butyl rubber adhesive) of the first layer of heat-shrinkable polyethylene material,
5 'second layer heat shrink material,
5′-1 Heat-shrinkable polyethylene outer layer material (crosslinked polyethylene) of the second layer,
5′-2 Heat-shrinkable polyethylene inner layer material (butyl rubber-based adhesive material) of the second layer,
6 third layer heat shrink material,
6-1 The outer layer material (crosslinked polyethylene) of the third layer heat-shrinkable polyethylene material,
6-2 3rd layer heat shrink polyethylene material inner layer material (hot melt adhesive),
7 Polyethylene-coated steel pipe (the end is cut into a step),
8 Polyethylene coating (cuts the edges into steps),
9 Clearance,
10 Steel pipe exposed part from which polyethylene coating has been removed,
11 Weld beads
12 specimens,
13 Far-infrared heater (panel),
13a, 13d Far infrared heaters (group) outside,
13b, 13c Far-infrared heater (group) in the center,
13-1 Far-infrared heater (group) on the upper side,
13-2 Far-infrared heater (group) on the lower side,
14 Far infrared heater mounting jig,
15 decompression chamber,
15-1 Lower pressure chamber,
15-2 Upper decompression chamber.

Claims (6)

In the field weld where the pipe end of the polyolefin coated steel pipe is welded,
Forming a first coating layer in which at least a first heat-shrinkable material having an inner layer material as a mastic-based adhesive material and an outer layer material having a heat-shrinking function as heat-shrinked under reduced pressure is coated in at least the first layer And
The inner layer material is a hot melt adhesive and the outer layer material is thermally shrunk on at least both ends of the first coating layer forming portion where the first heat shrink material is coated in one layer or multiple layers and the steel pipe coating layer portion on the outer side in the longitudinal direction. The second heat-shrinkable material, which is a material to which a function is imparted, has a second coating layer forming portion that is heat-shrinked under reduced pressure and is covered with an overwrapping coating. . In the first layer, the first coating layer forming portion is formed using the first heat shrink material,
The second coating layer forming portion is formed by wrapping the second layer using a second heat-shrinkable material having a longer longitudinal width than the first layer. Anti-corrosion coating structure.   The anticorrosion coating structure according to claim 1 or 2, wherein an end portion of the coating layer of the steel pipe has a taper angle. In the field weld where the pipe end of the polyolefin coated steel pipe is welded,
A first coating step of coating at least a first heat-shrinkable material with a mastic-based adhesive material as an inner layer material and a material having a heat-shrinkable function as an outer layer material under heat-shrinkage under reduced pressure;
The inner layer material is hot-melted on at least both end portions of the coating layer forming portion in which the first heat-shrinkable material is coated in one layer or multiple layers by the first coating step and the steel pipe coating layer portion (on the outer peripheral portion) outside the longitudinal direction. A second welding step in which a second heat-shrinkable material having a heat-shrinkable function as an adhesive material and an outer layer material is subjected to heat-shrinkage under reduced pressure, and is covered with a second coating step. The manufacturing method of the anticorrosion coating structure. A first coating step for coating the first layer by heat shrinking the first heat shrinkable material;
5. The production according to claim 4, further comprising a second coating step in which the second heat-shrinkable material having a longer longitudinal width than that of the first layer is heat-shrinked and overwrapped. Method.   The manufacturing method according to claim 4 or 5, wherein, in the step before the first covering step, the end portion of the covering layer of the steel pipe is chamfered so as to have a taper angle.

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