RU2645946C2 - Method of protection from corrosion for welded part of plastic lined steel pipe and fixing tape with pressure-sensitive adhesive for corrosion preventing heat-shrink sheet - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method of corrosion protection for welded part, in which an anticorrosion treatment is applied to welded part of the plastic lined steel pipe by using a corrosion preventive shrink sheet including: step of fixing the end part of the sheet wound around the peripheral surface of at least welded part, by using a fixing tape with a pressure-sensitive adhesive for sheet, having a pressure-sensitive adhesive, in which the shear force at a temperature, at which the sheet shrink force becomes maximum, is greater than the maximum shrink force, and also the step of heat shrinking of the sheet and fixing tape with a pressure-sensitive adhesive for the corrosion-preventing shrink sheet, which has a layer of pressure-sensitive adhesive comprising a pressure-sensitive cross-linkable adhesive, crosslinkable by heating on one side of the heat-resistant base film and in which the shear force of the adhesive at a temperature, at which the shrink force of the sheet becomes maximum, is greater than the maximum shrink force.

EFFECT: method of protection against corrosion is proposed.

10 cl, 7 dwg

Description

FIELD OF THE INVENTION

{0001} The present invention relates to a method for corrosion protection of a welded portion of a plastic-coated steel pipe with a corrosion-preventive shrink sheet and a fixing tape with a pressure sensitive adhesive to prevent corrosion of the shrink sheet.

BACKGROUND

{0002} A plastic-lined steel pipe is preferably used in a pipeline to transport fluids such as gas, oil, and chemicals. The welded portion of a plastic-coated steel pipe is usually machined to protect it from corrosion. Specific examples of a method for preventing corrosion of a welded portion in a plastic-lined steel pipe include a method of using a cylindrical anti-corrosion shrink sleeve having a sufficient length to cover a welded anti-corrosion portion, a method for winding a corrosion-preventing tape from one end to the other end of the peripheral the surface of the welded part and the method of using a corrosion-preventive shrink sheet with which the entire periphery can be covered welded part surface.

{0003} Corrosion protection methods using a corrosion preventing heat shrink sleeve and a corrosion preventing heat shrink sheet require heating to cause shrinkage of the corrosion preventing heat shrink sleeve or corrosion preventing heat shrink sheet. Specific examples of the heating method applicable to these corrosion protection methods include a direct fire heating method using a gas burner and the like, as well as an automatic heating method using a heating device and the like. Specific examples of the automatic heating method include a method in which a far infrared heater is used (see Patent Document 1).

LITERATURE LITERATURE

PATENT LITERATURE

{0004} Patent Document 1: JP-A 2005-307329 (“JP-A” means Unexamined Published Japanese Patent Application)

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

{0005} When a corrosion-resistant heat-shrink sleeve is used, in many cases it is difficult to put a cylindrical anti-heat-shrink sleeve on an already welded plastic-lined steel pipe.

Accordingly, in this case, when welding steel pipes lined with plastic, it is necessary to first put a corrosion-resistant heat-shrink sleeve onto the plastic lined steel pipe. However, when the plastic-lined steel pipe is already welded, as in an existing plastic-lined steel pipe (also called an existing pipe), a corrosion-resistant heat shrink sleeve cannot be put on it and a corrosion-resistant heat-shrink sleeve cannot be used.

{0006} Specific examples of a preferred corrosion protection method in this case include a method of using a corrosion preventing heat shrink sheet, for example, by cutting a corrosion preventing heat shrink sleeve along its length. Thus, a method is used in which a corrosion preventing heat-shrink sheet is wound around the peripheral surface of the welded part in a tubular shape, and then both end parts (part of the beginning of the winding and part of the end of the winding) of this corrosion-preventing heat-shrink sheet are fixed using a pressure sensitive adhesive tape sticky substance, etc., after which the heat shrink of the entire anti-corrosion shrink sheet is performed.

However, in the method of using the corrosion-resistant heat-shrink sheet, a conventional fixing tape with a pressure sensitive adhesive did not have any ability to fix the corrosion-resistant heat-shrink sheet because the pressure-sensitive adhesive of this tape softened during the shrinkage of the corrosion-resistant heat-shrink sheet. Therefore, the automatic heating method could not be used.

{0007} In order to prevent the corrosion-preventing shrink sheet from falling off when using a fixing tape with a pressure sensitive adhesive, there is no choice but to depend on the method of heating with an open flame. This open fire heating method relates to a method in which construction is performed when the fixing state of the corrosion preventing heat shrink sheet is confirmed, and if necessary, fixing is performed manually.

However, in order for the corrosion prevention effect to be exhibited, the method of heating with an open flame requires technological skill for uniform shrinkage of the corrosion preventing heat shrink sleeve and the like. Moreover, when an open flame of a gas burner or the like is used, or when a corrosion preventing heat shrink sheet is manually attached and the like, safety issues are also of concern.

{0008} The present invention aims to solve the above problems of conventional technology and to propose a method of corrosion protection of a welded part of a plastic-coated steel pipe, in which the welded part of a plastic-coated steel pipe could be subjected to a technology-free and safe anti-corrosion treatment by using a corrosion-preventing heat shrink sheet, so that in the corrosion protection method of the welded portion and for the above-described corrosion-preventing thermo sedimentary sheet is preferably used fixing tape with pressure-sensitive adhesive for preventing the corrosion of heat-shrinkable sheet.

SOLUTION

{0009} The objectives of the present invention can be solved by the following means.

(1) A method of corrosion protection of a welded part, in which anticorrosion treatment is applied to a welded part of a plastic pipe lined with steel by using a corrosion-preventing heat-shrink sheet, which includes:

the step of fixing at least the end portion of the corrosion preventing heat-shrink sheet wound around the peripheral surface of the at least the welded portion of the plastic-lined steel pipe by using a fixing tape with a pressure sensitive adhesive to prevent the heat-shrinkable sheet which has a pressure sensitive adhesive in which the shear force at a temperature at which the shrink force of the corrosion preventing heat shrink sheet becomes the maximum is greater than the maximum shrink force; and

a heat shrink step of a corrosion preventing heat shrink sheet.

(2) A method for protecting against corrosion of a welded portion of a plastic-lined steel pipe as described in (1) above, wherein the pressure-sensitive adhesive is a pressure-sensitive adhesive that crosslinkes when heated, and its shear strength at a temperature of 90 ° C is more than 15 N / cm.

(3) A method for protecting against corrosion of a welded portion of a plastic-lined steel pipe as described in (1) or (2) above, wherein the pressure sensitive adhesive is a crosslinkable pressure sensitive adhesive from butyl rubber containing from 0.5 to 5 , 0 mass parts of quinoid vulcanizer and from 5 to 30 mass parts of plasticizer per 100 mass parts of butyl rubber.

(4) A method of protecting against corrosion of a welded portion of a plastic-lined steel pipe as described in any of the above (1) to (3), wherein the heat shrink step is performed using a decompression-type heating device.

(5) A method for protecting a welded portion from a plastic-lined steel pipe against corrosion, as described in any one of the above (1) to (4), wherein the heat shrink step is a step in which the atmosphere around the corrosion preventing heat shrink sheet is decompressed so as to achieve a vacuum degree (pressure) of the atmosphere, constituting from 0.049 to 0.080 MPa, and then the corrosion-preventive shrink sheet is heated in this decompression state, and the decompression of the atmosphere is removed simultaneously with the completion of heating or after him.

(6) A method for protecting against corrosion of a welded portion of a plastic-lined steel pipe as described in any one of the above (1) to (4), wherein the heat shrink step is a step in which the atmosphere around the corrosion preventing heat shrink sheet is decompressed so as to achieve a vacuum degree (pressure) of an atmosphere of 0.049 to 0.080 MPa, and then this atmosphere is heated in a state in which a vacuum of 0.049 MPa or more is maintained, decompression stops after the temperature of the atmosphere is reached m heating temperature prevents corrosion shrinkable sheet is heated and decompressed atmosphere is removed simultaneously with the completion of the heating, or after it.

(7) A fixing tape with a pressure sensitive adhesive to prevent the heat-shrinkable sheet and to fix the corrosion-resistant heat-shrinkable sheet wound around the plastic coated steel pipe, in which a layer of pressure-sensitive adhesive containing pressure-sensitive adhesive that is crosslinkable by heating , is located on one side of the heat-resistant base film, and the shear strength of the crosslinkable pressure sensitive adhesive at a temperature of and which the shrink force of the corrosion preventing heat shrink sheet becomes maximum, is greater than the maximum shrink force.

(8) A adhesive tape with a pressure sensitive adhesive for preventing the heat shrink sheet described in the above (7), wherein the shear strength of the layer of pressure sensitive adhesive is 15 N / cm or more when the adhesive tape is with a pressure sensitive adhesive agent is pasted on a crosslinked stretched polyethylene sheet, and the resultant product is heated at a temperature of 300 ° C for 20 minutes under a load of 1 N / cm ² and then cooled to 25 ° C and further heated at 90 ° C for 10 min.

(9) A fixing tape with a pressure sensitive adhesive to prevent corrosion of the heat shrink sheet described in (7) or (8) above, in which the heat-resistant base film is a base film formed from cross-linked polyethylene.

(10) A fixing tape with a pressure sensitive adhesive for preventing the heat shrink sheet described in any of the above (7) to (9), wherein the pressure sensitive adhesive is a crosslinkable pressure sensitive adhesive from butyl rubber containing quinoid vulcanizer.

{0010} In the present invention, the “welded portion” includes a welded portion (a weld portion) in which plastic-coated steel pipes are welded, and also a part subjected to anti-corrosion treatment, namely, the exposed surface of the steel with which the plastic liner is peeled .

In addition, the “corrosion protection method of the welded part” includes a corrosion protection method of the welded part, in which anticorrosion treatment is applied to the welded part of the newly laid steel pipe with plastic lining, and also a corrosion protection method of the welded part, in which anticorrosion is applied to the welded part of the existing pipe (method of repairing corrosion protection of the welded part).

In addition, in accordance with the present invention, a joined body is made of plastic-coated steel pipes (also called a corrosion-protected joined pipe body), in which at least the welded portion is coated with a corrosion-resistant heat-shrink sheet and subjected to anti-corrosion treatment, as well as a pipe, etc. P. Accordingly, the corrosion protection method of a welded portion of a plastic-lined steel pipe in the present invention may also be referred to as a manufacturing method or method of repairing corrosion protection of a connected pipe, pipeline, or the like.

In the present invention, the “degree of vacuum" is determined by gauge pressure at which atmospheric pressure (pressure before decompression) is taken as 0 MPa and becomes correspondingly greater, the stronger the pressure decreases.

USEFUL EFFECTS OF THE INVENTION

{0011} In accordance with the present invention, a corrosion preventing heat shrink sheet can be manufactured in which peeling of the ends of the heat shrink corrosion preventing sheet wound around the welded portion of the plastic coated steel pipe is prevented with excellent corrosion prevention performance, safely and without the need for special skills . As a result, a corrosion-protected joint body, conduit or the like can be produced or restored, in which the welded portion is subjected to anti-corrosion treatment with excellent corrosion prevention efficiency.

Other and further features and advantages of the present invention will become more apparent from the following description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

{0012} {FIG. 1} FIG. 1 is a front view showing one example of a joined body of plastic-coated steel pipes, to which a corrosion protection method of a welded portion of a plastic-coated steel pipe in accordance with the present invention is applied.

{FIG. 2} FIG. 2 is a front view showing one example of a joined body of plastic-coated steel pipes to which anti-corrosion treatment is applied by applying a corrosion protection method of a welded portion of a plastic-coated steel pipe in accordance with the present invention.

{FIG. 3} FIG. 3 is a schematic cross-sectional view showing a state in which a corrosion preventing heat-shrink sheet is installed on a welded portion of a plastic-lined steel pipe by using a fixing tape with a pressure sensitive adhesive to prevent corrosion of the heat-shrink sheet in a method of protecting the welded portion of the plastic-lined steel pipe against corrosion. in accordance with the present invention.

{FIG. 4} FIG. 4 is a partially cut-away schematic explanatory diagram for explaining a heat shrink step performed by using a far-infrared decompression type heating device in a corrosion protection method of a welded portion of a plastic-lined steel pipe in accordance with the present invention.

{FIG. 5} FIG. 5 is a diagram showing decompression conditions and heating conditions in the heat shrink step in Example 1.

{FIG. 6} FIG. 6 is a diagram showing decompression conditions and heating conditions in the heat shrink step in Example 2.

{FIG. 7} FIG. 7 is a diagram showing decompression conditions and heating conditions in the heat shrink step in Example 3.

MODE FOR CARRYING OUT THE INVENTION

{0013} Preferred embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these embodiments.

{0014} The corrosion protection method of a welded part of a plastic-coated steel pipe in accordance with the present invention (hereinafter also referred to as the method of the present invention) is applied to a welded part of a joined body of a plastic-coated steel pipe produced by welding.

{0015} The joined body of the plastic-coated steel pipe to be used in the present invention is not particularly limited, and specific examples thereof include a product in which at least two parts of the plastic-coated steel pipes are joined, as well as a product in which the plastic-coated steel pipe with plastic, the steel pipe is connected to such a pipe element as an elbow, valve, gearbox and tee.

A preferred joined body of a plastic-lined steel pipe is described with reference to FIG. one.

This joined body 3 of the plastic-coated steel pipe is a product in which two parts of the plastic-coated steel pipes 11 are connected, and a weld 5a is formed in the connecting part 5. Each plastic-coated steel pipe 11 in each end part has a part 7 with an open steel surface in which the plastic lining 11a is peeled off and the surface of the steel is exposed. The welded portion 5 is formed of a weld 5a and parts 7 with an open steel surface, between which a weld 5a is located.

{0016} Plastic coated steel pipe 11 is not particularly limited if the steel pipe 11 is a steel pipe coated with plastic (resin) at least on a peripheral surface. Specific examples of such a pipe include a plastic-lined steel pipe, preferably used in a pipeline for conveying a fluid, such as gas, oil, and chemicals.

Specific examples of such a plastic-lined steel pipe 11 include a steel pipe lined with a polyolefin such as polyethylene and polypropylene, and a polyethylene-lined steel pipe is preferred.

{0017} The method of the present invention can be applied to a welded portion of a newly laid plastic coated steel pipe. This method can also be applied to the welded part of an existing plastic-coated steel pipe. Accordingly, the plastic lined steel pipe may be a newly laid plastic lined steel pipe or an existing pipe. In particular, given the lack of anticorrosion treatment using a heat-shrink anticorrosion sleeve, the method of the present invention is preferably applied to an existing pipe.

{0018} Corrosion protection of a connected pipe body, etc. produced by applying the method of the present invention to a connected body of plastic-coated steel pipe. In addition, the joined body of plastic-coated steel pipe, piping, and the like. can be restored.

One preferred example of corrosion protection of a connected pipe body by the method of the present invention is described with reference to FIG. 2. The corrosion protection of the joined body 1 of the pipe is the same as that of the joined body 3 of the plastic-lined steel pipe, except that the welded part 5 and each part of the polyethylene lining 11a adjacent to the welded part 5 are coated with a heat-shrink resistant corrosion sheet 21. Thus, the welded portion 5 is subjected to anti-corrosion treatment.

{0019} The method of the present invention uses a corrosion preventing heat shrink sheet.

Accordingly, the method of the present invention may also be referred to as a method of constructing a corrosion preventing heat shrink sheet.

In the corrosion preventing heat-shrink sheet used in the method of the present invention, the other structure is not particularly limited, provided that the sheet has at least a heat-shrink base material and a pressure sensitive adhesive layer (adhesive) formed from an adhesive substance (adhesive) pressure sensitive and located on the base material.

A preferred corrosion preventing shrink sheet is described with reference to FIG. 3. The corrosion-resistant heat-shrink sheet 21 has a base material 22 and a layer of a pressure sensitive adhesive (adhesive) 23 located on the base material 22.

{0020} The base material 22 is usually formed from resin and is preferably formed into a sheet shape. The base material 22 has a shrink characteristic.

The resin that forms the base material 22 is not particularly limited, provided that the base material 22 exhibits heat-shrink properties when the resin is formed into the base material 22, and specific examples include stretch pre-treated polyethylene and polypropylene. In addition, taking into account the efficiency of heating by infrared radiation in the far range, it is preferable to polyethylene subjected to tensile treatment.

{0021} Considering the percentage of heat shrinkage and its strength, the resin that forms the base material 22 is preferably crosslinked (crosslinked). The degree of crosslinking of the resin to be crosslinked (also called crosslinked resin) is preferably from 20 to 50%, and more preferably from 25 to 40% in terms of a gel fraction. Here, the gel fraction means indicating the remainder of the melt in the crosslinked resin, and its measurement is carried out in accordance with Japanese industrial standard JIS C 3005. However, when the crosslinked resin contains a filler, the filler content is subtracted from the measured mass of the sample to calculate the gel fraction.

The crosslinking method of the resin is not particularly limited, and specific examples thereof include a chemical crosslinking method and a physical crosslinking method. Specific examples of the chemical crosslinking method include a radical crosslinking method using a radical generator, as well as a silane crosslinking method using a silane compound. Specific examples of the physical crosslinking method include an electron beam crosslinking method in which an electron beam is irradiated. As a crosslinking method, taking into account productivity, crosslinking strength and the like, an electron beam crosslinking method is preferred.

As a crosslinked resin, taking into account the characteristics of water resistance, wear resistance, heat resistance and the like, crosslinked polyethylene is preferred. Here, crosslinked polyethylene means polyethylene having a high molecular weight, in which molecules are formed into a three-dimensional crosslinked structure using the polyethylene crosslinking reaction.

{0022} As a resin, taking into account the percentage and strength of the heat shrink, a pre-stretched resin (called a stretched resin) is preferred, and a uniaxially stretched resin is more preferable. The stretching conditions in the above case are not particularly limited. For example, taking into account the possibility of use in construction and storage stability, the stretching temperature is preferably from 60 ° C to 100 ° C, more preferably from 70 ° C to 90 ° C, and even more preferably from 80 ° C to 90 ° C .

{0023} The base material 22 is not particularly limited in the percentage of heat shrinkage, provided that the base material 22 has the property of heat shrink. Considering good workability, excellent corrosion prevention performance, and the ability to guarantee tight contact on the pipe body, the percentage of heat shrinkage is preferably 10% or more, more preferably 15% or more, and even more preferably 20% or more. On the other hand, taking into account the excellent durability and tear resistance, the percentage of heat shrinkage is preferably 50% or less, more preferably 40% or less, and even more preferably 30% or less.

Here, the percentage of heat shrinkage of the base material 22 corresponds to complete shrinkage. In particular, the square base material 22 in the form of a square with a side of 100 mm is heated in a talc bath at a temperature of 200 ° C for 2 hours, after which it is naturally cooled to normal temperature (25 ° C). Then, the size of the base material 22 is measured in order to calculate the percentage of shrinkage.

The percentage of heat shrink can be set in a predetermined range depending, for example, on the conditions of stretching, etc.

{0024} The thickness of the base material 22 is not particularly limited, but is preferably, for example, from 0.5 to 2.0 mm.

{0025} Considering the excellent corrosion prevention and adhesion efficiencies, the pressure sensitive adhesive that forms the pressure sensitive adhesive layer 23 preferably comprises a resin such as polyamide resin, (meth) acrylic resin, elastomer and resin modified with maleic acid.

{0026} Specific examples of a maleic acid modified resin include a resin such as a maleic acid modified olefin polymer. This olefin polymer is not particularly limited, provided that the polymer is an olefin homopolymer or a copolymer containing an olefin as at least one constituent. Specific examples of this include polyethylene, a copolymer of ethylene and vinyl acetate (EVA) or a copolymer of ethylene and ethyl acrylate (EEA).

Considering the effectiveness of high temperature adhesion, a maleic acid modified polyethylene resin is most preferred.

Here, the maleic acid modified resin is a resin modified by adding a functional group to the resin, preferably the polyolefin resin, by using maleic acid (including maleic anhydride), and also includes the maleic acid grafting modified polyolefin resin. The degree of modification with maleic acid is not particularly limited, but is, for example, from 0.1 wt.% To 7 wt.% In one molecule of the resin.

{0027} The pressure sensitive adhesive may, in addition to the resin, contain a filler, a plasticizer, a tackifier, and the like.

The filler is not particularly limited, and specific examples thereof include calcium carbonate and aluminum hydroxide.

The plasticizer is not particularly limited, and specific examples thereof include mineral oil and polybutene.

The tackifying reagent is not particularly limited, and specific examples thereof include a coumaronindene resin prepared by performing a polymerization reaction of a portion of a crude oil cracking by-product from the petrochemical industry, and in particular include a coumaronindene resin based on fractions C5, C6 etc.

{0028} Specific examples of the pressure-sensitive adhesive used in the present invention include an agent containing the above-described resin, as well as a pressure sensitive adhesive based on synthetic rubber, such as butyl rubber, and an additional pressure-sensitive adhesive containing asphalt.

{0029} Considering workability, corrosion prevention efficiency and adhesion efficiency, the pressure sensitive adhesive preferably softens or melts during heat shrinkage of the corrosion preventing heat shrink sheet. The softening point or melting point (melting point) of the pressure sensitive adhesive is not particularly limited, but taking into account workability and adhesion efficiency, this temperature is preferably, for example, from 60 ° C to 120 ° C, and more preferably from 70 ° C up to 115 ° C. In the present invention, the softening point and melting point are temperatures measured by differential scanning calorimetry (DSC). As a method for measuring them, the measurement is performed using a differential scanning calorimeter at a heating rate of 10 ° C / min, without purging with nitrogen, in an atmosphere in which air exists.

{0030} In order to soften or melt the pressure sensitive adhesive during heat shrinkage, a non-crosslinkable adhesive is preferably used. A “non-crosslinkable” substance includes a substance which is not crosslinkable by heating, as well as a substance which is partially crosslinkable to such an extent that it remains softening or melting.

{0031} The pressure sensitive adhesive layer 23 is a layer formed by arranging the pressure sensitive adhesive on the base material 22. The thickness of the pressure sensitive adhesive layer 23 is not particularly limited, but is preferably, for example, from 0.5 to 1 5 mm.

{0032} The anti-corrosion shrink sheet 21 has a shrink force (also called shrink stress) produced by the heat shrink of the base material 22.

This shrink force usually gradually increases as the heat shrink of the base material 22 increases, and after the shrink force becomes maximum, the shrink force gradually decreases. When the corrosion preventing heat shrink sheet 21 includes a base material 22 formed from a stretched resin, a maximum shrink force occurs near the stretch temperature of the base material 22.

The maximum shrink force is not particularly limited, but in the case where the maximum shrink force is too small, the corrosion prevention efficiency is insufficient, and the corrosion preventing heat shrink sheet 21 in some cases does not come into contact with the pipe body. On the other hand, in the case where the maximum shrink force is too large, the corrosion preventing heat shrink sheet 21 in some cases cannot be attached to the welded portion. In the present invention, “shrink force” means the converted force per unit width (1 cm) (also called unit shrink force), and is preferably 5 to 15 N / cm, and more preferably 10 to 15 N / cm.

{0033} The force of shrinkage can be set in a predetermined range depending, for example, on the conditions of stretching.

The maximum shrink force can be obtained by measuring the temperature dependence of the shrink force.

Here, the temperature dependence of the shrink force can be determined on a sample having a strip shape of a width of 20 mm by using a tensile testing machine such as a dynamometer with a constant temperature bath, as described below. In particular, for example, the end parts of the above-described sample are fixed (clamped) in one set of vertically arranged clamping chucks, the measured values are continuously read out, while the temperature increases from normal temperature at a rate of 10 ° C / min, and the ratio between the converted values by the unit of width and temperature is drawn in the form of a graph in order to obtain a curve of the dependence of shrinkage force on temperature.

The shrink force of the corrosion preventing heat shrink sheet 21 is the same as the heat shrink force of the base material 22 when the pressure sensitive adhesive is not heat shrink.

{0034} The anti-corrosion shrink sheet 21 has an adhesive force. The adhesion force must be such that the corrosion preventing heat-shrink sheet 21 adheres to the welded portion 5, and is accordingly set depending on the application, etc. For example, when a corrosion preventing heat shrink sheet 21 is used for anticorrosion treatment of a pipeline, taking into account the adhesion efficiency, corrosion prevention efficiency and durability, the adhesion force at 80 ° C when a primer suitable for pressure sensitive adhesive is used is preferably 10 N / cm or more and more preferably from 20 to 50 N / cm.

Specific examples of the primer used in the above case include an epoxy primer, as will be described later.

The adhesion strength can be set in a predetermined range depending on the type, content, etc. pressure sensitive adhesive, and further depending on the degree of modification with maleic acid and the like, when a resin modified with maleic acid is used for this.

The adhesion strength can be measured as described below. The corrosion preventing heat shrink sheet 21 is adhered to a steel pipe having a diameter of approximately 100 mm in an adhered state by using the primer described above. The force can then be measured as the value at which the end parts of the glued corrosion-preventive heat-shrink sheet 21 are torn off at an angle of 90 ° under conditions of a temperature of 80 ° C and a tearing speed of 50 mm / min by using a tensile testing machine such as a load cell.

{0035} A corrosion-resistant heat-shrink sheet 21, in particular a corrosion-resistant heat-shrink sheet 21 having a pressure sensitive adhesive layer 23 formed from a maleic acid modified resin can be produced by forming a pressure sensitive adhesive in the form of a film (in the form of a layer ) on the main material 22.

As a corrosion preventing shrink sheet 21, a commercial product may also be used. Specific examples of such a product include WRAP CO SHEET SE (trademark, manufactured by Furukawa Electric Co., Ltd.) and WRAP CO SHEET SH-80 (trademark, manufactured by Furukawa Electric Co., Ltd.).

{0036} The method of the present invention uses a fixing tape 31 with a pressure sensitive adhesive to prevent corrosion of the shrink sheet (simply called a fixing tape with a pressure sensitive adhesive in some cases).

The pressure sensitive adhesive adhesive tape used in the present invention is not particularly limited, but at least it has a pressure sensitive adhesive material layer formed from a pressure sensitive adhesive in which shear strength at a temperature at which shrink force corrosion-resistant shrink sheet becomes maximum, greater than the maximum shrink force. Thus, a fixing tape with a pressure sensitive adhesive can fix the corrosion preventing heat-shrink sheet around the welded part until the heat-shrink of the sheet causes tight contact or adhesion to the welded part of the plastic-coated steel pipe, and an automatic heating method can be used for this, requiring no technological skill and being safe.

{0037} A fixing tape with a pressure sensitive adhesive for this should only have a layer of pressure sensitive adhesive and preferably a base film (also simply called a base material) that supports a layer of pressure sensitive adhesive. The pressure sensitive adhesive layer comprises a pressure sensitive adhesive and is preferably located on one surface (one side) of the base material.

A preferred pressure sensitive adhesive adhesive tape is described with reference to FIG. 3. A pressure sensitive adhesive adhesive tape 31 has a base material 32 and a pressure sensitive adhesive layer 33 located on the surface of the base material 32.

This base material 32 is formed from resin. This resin is not particularly limited, and specific examples thereof include polyethylene, EVA, EEA, and polypropylene. Most preferred is polyethylene.

{0038} The base material 32 preferably has a heat resistance such that neither softening nor melting occurs during heat shrinkage of the corrosion preventing heat shrink sheet (heat resistant base material). As the heat resistance of the base material 32, for example, no melting preferably occurs even if heating is performed at a temperature of 300 ° C. for 30 minutes. The heat resistance can be confirmed in such a way that the corrosion-resistant heat-shrink sheet is suspended in the oven at a temperature of 300 ° C, and even after 30 minutes no melting of the base material 32 takes place.

The heat resistance of the base material 32 can be set in a predetermined range depending on the degree of crosslinking (gel fraction) in the formed resin or the amount of added antioxidant, etc.

{0039} Considering the ability to exhibit the above heat resistance, the base material 32 is preferably formed from a crosslinked resin. The degree of crosslinking of the crosslinked resin is preferably from 20 to 40%, and more preferably from 25 to 40% from the point of view of the gel fraction. Here, the crosslinking method, the gel fraction and the method for measuring it are described above.

As a crosslinked resin, taking into account the waterproofing efficiency, electrical insulation efficiency, heat resistance and the like, crosslinked polyethylene is preferred in the above resins.

{0040} Considering the absence of heat shrinkage, the base material 32 is preferably formed from unstretched resin. The unstretched resin covers, in addition to the resin not subjected to any positive tensile treatment, the resin subjected to a tensile treatment to such an extent that does not adversely affect the fixation of the corrosion preventing heat-shrink sheet 21.

{0041} The base material 32 has a single layer structure, but may have a multilayer structure. The thickness of the base material 32 is not particularly limited, but is preferably, for example, from 0.5 to 1.0 mm.

{0042} The pressure-sensitive adhesive is not particularly limited, provided that the pressure-sensitive adhesive has a shear force (N / cm) greater than the maximum shrink force (N / cm) of the corrosion shrink sheet at a temperature at which the shrink force of the anti-corrosion shrink sheet is maximized. In particular, the pressure sensitive adhesive has a shear force (N / cm) greater than the maximum shrink force (N / cm) of the corrosion preventing heat shrink sheet at a temperature at which the shrink force of the corrosion preventing heat shrink sheet becomes maximum. In other words, the pressure sensitive adhesive at a temperature at which the shrink force of the corrosion preventing heat shrink sheet becomes maximum has a total shear force (H) that is greater than the maximum total shrink force (H) developed between this sheet 21 and pressure with an adhesive substance, over the entire width of adhesion, and develops a force opposing this full force of shrinkage.

Here, the temperature is at which the shrink force of the corrosion preventing heat shrink sheet becomes maximum, and this maximum shrink force itself is described above, and both depend on the material used as the base material 22 and the like. However, as an indication of the shear force that is greater than this maximum shrink force of the corrosion preventing heat shrink sheet 21 at a temperature at which the shrink force of the corrosion preventing heat shrink sheet becomes maximum, for example, a shear force at a temperature of 90 ° C, which is preferably more than 15 N / cm. This shear force is more preferably 20 N / cm or more. The upper limit of the shear force is not particularly limited, but is, for example, 50 N / cm.

{0043} Shear force refers to the shear strength of adhesion per unit width (N / cm) of a fixing tape with a pressure sensitive adhesive after gluing the fixing tape with a pressure sensitive adhesive to prevent the heat-shrink sheet from corrosion on the surface of the base material and prevent the heat-shrink sheet 21 by pressure sensitive adhesive. In other words, in the present invention, shear force means the converted force per unit width (1 cm) (also called unit shear force).

This adhesion shear force is measured by gluing the fixing tape 31 with a pressure sensitive adhesive (adhesive length: 100 mm) onto the surface of the base material 22 of a sufficiently seated corrosion preventing heat-shrink sheet 21, and heating the resulting material at a temperature of 90 ° C for 2 hour or more, e.g., for 2 hour in a state where a load is applied to it the value 1 N / cm ^2, and at the same time as the resulting material is stretched in a direction pairs llelnom to the bonding surface, under the conditions of stretching of 50 mm / min using a device speed "testing machine load cell type heating device with a gap" (trade name: Autograph, production company Shimadzu Corporation).

{0044} In addition, in addition to the shear force described above at a temperature of 90 ° C, as an indication of shear forces greater than the maximum shrink force of corrosion-preventive shrink sheet 21, shear forces at a temperature of 90 ° C after heating at 300 ° C in for 20 minutes while applying a load of 1 N / cm ² , then cooling to 25 ° C, and then additional heating at 90 ° C for 10 minutes, preferably 15 N / cm or more. This shear force is more preferably 20 N / cm or more. The upper limit of this shear is not particularly limited, but is, for example, 50 N / cm. The method for cooling a pressure sensitive adhesive layer to a temperature of 25 ° C is not particularly limited, and may be natural cooling or may be cooling using known cooling means.

{0045} This shear force refers to shear force with the surface of the crosslinked stretched polyethylene sheet (the base material 22 of the corrosion preventing heat-shrink sheet 21) and pressure sensitive adhesive tape 31. This shear force can be measured as described below. Pressure-sensitive adhesive tape 31, in which a layer 33 of pressure-sensitive adhesive (width: 20 mm × length: 100 mm × thickness: 0.5 mm) is applied to the base material 32 (crosslinked unstretched sheet of polyethylene, width: 20 mm × length: 250 mm), glued onto a crosslinked stretched sheet of polyethylene (degree of crosslinking: 35% in terms of the gel fraction, tensile temperature: 90 ° C, tensile: 1.3 times, percent heat shrink: 25%). A load of 1 N / cm ^{2 is} applied to it in the direction of lamination, and the resulting material is heated at a temperature of 300 ° C for 20 minutes and cooled to a temperature of 25 ° C. Then, the resulting material is additionally heated at a temperature of 90 ° C for 10 min without applying a load, and in the state in which the material is heated at a temperature of 90 ° C, the shear force between the base material 32 and pressure-sensitive adhesive tape 31 is measured while pulling this material in a direction parallel to the adhesion surface, with a tensile speed of 50 mm / min, using the device: "tensile testing machine type dynamometric sensor with a heating device" (trade I am a brand: Autograph, manufactured by Shimadzu Corporation). The shear force can be obtained by converting this measured value into force per unit width.

{0046} Considering the ability to prevent the corrosion preventing shrink sheet 21 from falling off, the shear force of the pressure sensitive adhesive is more preferably greater than the shrink force generated in the corrosion preventing shrink sheet 21 during the heat shrink of the corrosion preventing shrink sheet 21.

With regard to the relationship between shear and shrink force, in the present invention, the shear force is preferably greater than the shrink force, regardless of temperature.

{0047} The shear force of the pressure sensitive adhesive tape 31 having the pressure sensitive adhesive layer 33 and the above-described base material 32 is equal to the shear strength of the pressure sensitive adhesive layer 33. The shear force of the pressure sensitive adhesive tape 31 having the pressure sensitive adhesive layer 33 can be set in a predetermined range depending on the adhesion efficiency of the pressure sensitive adhesive, characteristics, types, composition, and the like. pressure sensitive adhesive, as will be mentioned later.

{0048} Composition of pressure-sensitive adhesive, and the like. not particularly limited, provided that the pressure sensitive adhesive has the shear strength described above. For example, a rubber pressure-sensitive adhesive (admixture) containing rubber such as butyl rubber, acrylic rubber, nitrile rubber and chloroprene rubber is preferred, and taking into account the adhesion and corrosion prevention effectiveness, pressure-sensitive rubber adhesive containing butyl rubber is more preferred.

{0049} Butyl rubber can be used without particular restrictions, provided that butyl rubber is a synthetic rubber obtained by cationic copolymerization between isobutylene and isoprene. The content of the isoprene component in the butyl rubber is preferably, for example, from 0.6 mol.% To 3 mol.%.

{0050} The pressure-sensitive adhesive is not particularly limited provided that it exhibits the above-described shear strength, but taking into account the ability to prevent softening and increase the adhesion force, the pressure-sensitive crosslinkable adhesive that can be crosslinked by heating is preferred. Such a crosslinkable pressure-sensitive crosslinkable adhesive is not particularly limited provided that it has a thermal crosslinking property in which crosslinking is caused by heat, and specific examples thereof include a means containing a crosslinking agent (also called a vulcanizing agent).

{0051} The pressure sensitive adhesive may contain an additive or the like. In particular, the crosslinkable pressure sensitive crosslinkable adhesive substance preferably comprises a vulcanizing agent. A vulcanizer is only required to cause crosslinking of the above rubber when heated, but taking into account the adhesion and crosslinking efficiency, a vulcanizer that causes crosslinking of the rubber at low temperatures (e.g. 60 ° C) is preferred.

Specific examples of such a vulcanizer include a quinoid vulcanizer as well as a peroxide vulcanizer.

Specific examples of a quinoid vulcanizer include p-quinondioxime, as well as oʹ, oʹ-dibenzoyl-p-quinondioxime.

{0052} Considering the excellent adhesion efficiency and strength, the cure in the pressure sensitive adhesive is preferably from 0.5 to 5.0 parts by weight, and more preferably from 0.5 to 3.0 parts by weight per 100 parts by weight rubber.

{0053} Examples of additives, with the exception of the vulcanizer, include a plasticizer, a filler, a tackifier, an antioxidant, a vulcanization accelerator, and the like.

The plasticizer is not particularly limited, and specific examples thereof include mineral oil and polybutene. The content of the plasticizer in the pressure-sensitive adhesive is not particularly limited, but preferably ranges from 5 to 30 parts by weight per 100 parts by weight of rubber. In the case where the plasticizer content is within the above range, the pressure sensitive adhesion improves and the workability of bonding before heating, especially at low temperatures, improves. In addition, the pressure-sensitive adhesive is practically incapable of heat shrinkage, and the deviation of the pressure-sensitive adhesive, and ultimately the deviation of the fixing tape with the pressure-sensitive adhesive, can be suppressed.

{0054} A filler is not particularly limited, and specific examples thereof include calcium carbonate, aluminum hydroxide, magnesium hydroxide, clay and talc.

The vulcanization accelerator is not particularly limited, and specific examples thereof include various vulcanization accelerators such as a thiazole-based vulcanization accelerator, sulfenamide-based vulcanization accelerator, tetramethylthiuram disulfide-based vulcanization accelerator and hydrochloric acid dithiocarbamine vulcanization accelerator. The content of the vulcanization accelerator in the pressure sensitive adhesive is preferably from 0.5 to 10 mass parts per 100 mass parts of rubber.

{0055} The pressure sensitive adhesive is preferably a pressure sensitive crosslinkable butyl rubber adhesive containing a vulcanizer, preferably 0.5 to 5.0 mass parts quinoid vulcanizer per 100 mass parts of butyl rubber, and more preferably is a pressure sensitive crosslinkable adhesive substance from butyl rubber containing from 5 to 30 mass parts of plasticizer. In these crosslinkable butyl rubber pressure sensitive adhesives, butyl rubber crosslinkes at low temperatures (e.g. 60 ° C), and these materials may exhibit a shear force that becomes greater than the maximum shrink force at a temperature at which the shrink force prevents corrosion of the heat shrink sheet becomes maximum.

Butyl rubber usually has a pressure-sensitive adhesion efficiency at room temperature (25 ° C), but is easily deformed with increasing temperature, and also causes a decrease in pressure-sensitive adhesion. However, the inventors of the present invention have found that the above-described pressure-sensitive butyl rubber adhesive advances the effectiveness of pressure-sensitive adhesion at room temperature even without vulcanization, and also develops a shear force that becomes greater than the shrink force, and preferably a shear force satisfying the above indication in the process of heat shrinkage preventing corrosion shrink sheet. The development of this shear force is believed to be achieved by rapid vulcanization of butyl rubber at a temperature lower than the temperature at which the corrosion-preventive heat-shrink sheet 21 starts heat-shrink due to the vulcanizer, without adversely affecting the shape of the pressure sensitive adhesive layer (without sagging layer pressure sensitive adhesive), as well as the higher effect of vulcanization on improving the strength of pressure sensitive adhesion compared to a decrease in strength a pressure-butyl adhesion by increasing the temperature.

{0056} The pressure sensitive adhesive layer 33 is a layer formed by positioning the pressure sensitive adhesive on the base material 32. The thickness of the pressure sensitive adhesive layer 33 is not particularly limited, but is preferably, for example, from 0.5 to 1 , 0 mm.

{0057} According to the method of the present invention, anticorrosion treatment can be applied by using a corrosion-preventing heat-shrink sheet and wrapping this sheet around the peripheral surface of the pipe, even on a welded portion to which no anti-corrosion treatment can be applied using a corrosion-preventing heat-shrink sleeve .

{0058} The method of the present invention includes at least a fixing step and a heat shrink step, as described below:

a step of fixing at least an end portion of a corrosion preventing heat-shrink sheet wound around a peripheral surface of at least a welded portion of a plastic-lined steel pipe, a fixing tape with a pressure sensitive adhesive, and

a heat shrink step of a corrosion preventing heat shrink sheet fixed in the above fixation step.

{0059} In the method of the present invention, including each step described above, peeling off of the ends of the corrosion preventing heat shrink sheet can be prevented in the heat shrink step, and anti-corrosion treatment can be applied to the welded part in a safe manner and without requiring special skills, preferably using the automatic heating method.

{0060} A preferred method of the present invention will be described in detail with reference to the drawings.

In a preferred method of the present invention, when anti-corrosion treatment is applied to a welded portion of a plastic-lined newly laid steel pipe, a plastic-lined steel pipe and the like. welded into a joined body 3 of a plastic-coated steel pipe, shown, for example, in FIG. one.

Each plastic lining 11a at the end portion of the plastic-lined steel pipe 11 is smoothed to expose the surface of the steel. Then the end parts are joined together and welded using a known welding method. This connected body 3 of the plastic-coated steel pipe has a welded portion 5 formed from the exposed portion 7 of the steel surface in which the steel surface is exposed, and the weld 5a. Dirt, welding slag, etc. on the welded portion 5 is removed when necessary.

{0061} On the other hand, in the preferred method of the present invention, when the anti-corrosion treatment is applied to an existing pipe, the welded portion subjected to the anti-corrosion treatment is exposed, and dirt on the welded portion and the like. deleted. Thus, the connected body 3 is formed by the plastic-lined steel pipe, as shown in FIG. one.

{0062} In a preferred method of the present invention, primer treatment can be applied to the welded portion in the case of a new installation, as well as in the case of an existing pipe, when necessary.

{0063} In a preferred method of the present invention, a fixing step is then performed.

As shown in FIG. 3, the corrosion preventing heat-shrink sheet 21 is wound tubularly around the peripheral surface of at least the welded portion 5, preferably around the welded portion 5 and both end parts of the plastic cladding 11a adjacent to the welded part 5. In the aforementioned case, the end portion 21A of the winding and the end portion 21B of the end of the corrosion preventing shrink sheet winding 21 overlap. The amount of overlap of both end parts is set appropriately depending on the shrink force, shear force and the like, and is not particularly limited. For example, in the case of a plastic-coated steel pipe 600A, the length of the overlap in the circular direction can be from 100 to 150 mm.

{0064} In this state, the end parts 21A and 21B at both ends of the corrosion preventing heat-shrink sheet 21, namely the overlapped part, are fixed with the pressure-sensitive adhesive tape 31 described above. With respect to the gluing of the pressure-sensitive fixing tape 31, in order to fix the state, wherein the corrosion preventing heat-shrink sheet 21 is wound around the pipe as shown in FIG. 3, the pressure-sensitive adhesive tape 31 is adhered to the corrosion-preventing shrink sheet 21 in the direction of the center line of the plastic-lined steel pipe 11 across the end portion 21B of the end of the winding.

In the aforementioned case, the length of the pressure sensitive fixing tape 31 adhered to the end portion 21B of the winding end is suitably set depending on the shear force and the shrink force so that the shear force becomes greater than the shrink force.

{0065} As the pressure-sensitive fixing tape 31 used at this stage, a tape having a pressure-sensitive adhesive substance with a shear force at a temperature at which a shrink force of the corrosion preventing heat-shrink sheet 21 wound around the peripheral surface of the welded portion is selected 5, becomes maximum, becomes greater than the maximum shrink force. Thus, peeling of both end parts can be prevented by resistance to the shrink force produced by the heat shrink of the corrosion preventing heat shrink sheet 21 in the heat shrink stage, and the corrosion preventing heat shrink sheet 21 can be fixed during the heat shrink stage.

{0066} The combination between the corrosion-preventive shrink sheet 21 and the pressure-sensitive adhesive tape 31 is not particularly limited, provided that the above relationship is satisfied, and accordingly selected from the above-described corrosion-resistant heat-shrink sheet 21 and the above-described pressure-sensitive adhesive tape 31.

As a corrosion preventing heat shrink sheet 21 and pressure sensitive adhesive tape 31, a combination between a corrosion preventing heat shrink sheet 21 having a base material 22 formed from a crosslinked stretched polyethylene resin and a pressure sensitive adhesive layer 23 formed from modified maleic acid is preferred resin, as well as pressure-sensitive adhesive tape 31 having a layer 33 of pressure-sensitive adhesive formed from the above crosslinkable pressure sensitive adhesive from butyl rubber. Thus, the corrosion preventing heat-shrink sheet 21 can be fixed at the fixing stage, as well as at the heat-shrink stage, as mentioned above, the pressure sensitive adhesive layer 33 develops a large shear force from the low temperature region, and the corrosion preventing heat-shrink sheet 21 can be in sufficiently fixed. In addition, an automatic heating method using a decompression type heating device, as will be mentioned later, and the like, can be used.

{0067} Thus, as shown in FIG. 3, the corrosion preventing heat shrink sheet 21 is fixed by using pressure sensitive adhesive tape 31.

{0068} In a preferred method of the present invention, a heat shrink step is further performed by heating the corrosion preventing heat shrink sheet 21. Thus, the corrosion preventing heat shrink sheet 21 can tightly contact or adhere to the welded portion 5 of the plastic-coated steel pipe.

The means of heating the corrosion-preventing heat-shrink sheet 21 is not a method of heating with an open flame, and it only needs to be a means by which the corrosion-preventing heat-shrink sheet 21 can be heated to the temperature at which the heat-shrink occurs. Specific examples of this include long-range infrared heating, hot air heating, high-frequency induction heating, and high-resistance wire heating. Thus, the heat shrink stage can be performed safely and without requiring special skills.

{0069} In a preferred method of the present invention, the heat shrink step can also be performed at atmospheric pressure without any decompression.

When the corrosion preventing heat shrink sheet 21 is wound around the pipe, a space 9 (see FIG. 3) with a thickness of the corrosion preventing heat shrink sheet 21 is formed in the overlapped part of both end parts. When the corrosion preventing shrink sheet 21 is heated, the pressure sensitive adhesive layer of the corrosion preventing shrink sheet 21 is softened to fill the space 9, but when the air outlet from the space 9 is blocked, the air remains as an air pocket (hollow) between the lined plastic steel pipe 11 and heat-shrink corrosion-preventing sheets 21.

In the preferred method of the present invention, taking into account the possibility of the formation of such a void and therefore the difficulty of further improving the corrosion prevention efficiency, the heat shrink step is more preferably performed under reduced pressure, i.e. in a state of decompression. As heating in a decompression state, taking into account the heating efficiency and its uniformity, heating by infrared radiation in the far region is more preferable.

{0070} In order to heat the sheet in a decompression state, a decompression type heating device is preferably used, taking into account the convenience of operation and the like. The decompression type heating device is not particularly limited, provided that it can heat the sheet in a decompression state, and a commercially available decompression type heating device can be used.

One preferred example of a decompression type heating device is described with reference to FIG. 4. Specific examples of the decompression type heating device 41 include a decompression type heating device 41 equipped with a heating chamber 42, hermetically surrounding the welded portion 5 and having an infrared heater 43 in the far region located on the inner surface of the circle, a vacuum pump 44 connected to the heating camera 42, and a control panel (not shown) connected to the infrared heater 43 in the far region. This heating chamber 42 is formed as a chamber of a vertically divided type or as a chamber of a horizontally divided type, and has a sealing structure (not shown) in both end parts in order to close the welded part 5 in an airtight condition with the peripheral surface of the plastic-lined steel pipe 11.

{0071} A method for heating a sheet by using a decompression type heating device, such as a far-infrared infrared heating decompression device 41, is not particularly limited, provided that the heating can be performed under reduced pressure.

{0072} A preferred method using a decompression far infrared heating device 41 is described with reference to FIG. four.

First, the welded portion 5 is surrounded by a heating chamber 42 in an airtight state. In particular, the divided heating chambers 42 overlap and are connected in a vertical direction or in a horizontal direction relative to the welded portion 5.

Then, the pressure in the inner part of the heating chamber 42 decreases, and then the temperature rises in order to heat the corrosion-resistant shrink sheet 21. Here, the degree of vacuum in the heating chamber 42 is not particularly limited at the beginning of the temperature increase or heating and can be 0 MPa, but taking attention to the ability to remove voids, this degree is preferably 0.030 MPa or higher, more preferably 0.049 MPa or higher, and even more preferably from 0.049 MPa to 0.08 MPa.

{0073} The temperature in the heating chamber 42 rises in a state in which the heating chamber 42 is maintained in a decompression state, and the degree of vacuum is adjusted so that it is equal to the above-described degree of vacuum, preferably in the range from 0.049 MPa to 0.08 MPa. After the degree of vacuum in the heating chamber 42 reaches the above degree of vacuum, preferably from 0.049 MPa to 0.08 MPa, the temperature in the heating chamber 42 rises in a state of ongoing decompression. Thus, the corrosion preventing shrink sheet 21 is heated. In the present invention, the atmosphere inside the heating chamber 42 corresponds to the atmosphere around the corrosion preventing heat shrink sheet.

{0074} Decompression in the heating chamber 42 is performed by starting the vacuum pump 44.

The heating chamber 42 may be decompressed to a degree of vacuum equal to or higher than the degree of vacuum at which the above temperature rise or heating begins. For example, taking into account the ability to remove voids, the heating chamber 42 is decompressed to a degree of vacuum, preferably equal to 0.049 MPa or higher, more preferably 0.060 MPa or higher, and even more preferably 0.080 MPa or higher.

Considering the need for complete removal of voids, decompression is preferably performed continuously during the heat shrink stage.

{0075} The heating by the infrared heater 43 in the far region is preferably performed in a state of continued decompression (the degree of vacuum becomes higher than the degree of vacuum at which the above temperature rise or heating begins), in the state of maintaining the degree of vacuum at which the above temperature rise begins or heating, or in a state of decompression stop.

From the heating temperature, it is only required that it should be the temperature at which the heat shrink of the base material 22 occurs, and at the same time the pressure-sensitive adhesive in the layer 23 of the pressure-sensitive adhesive is softened or melts, and the heating temperature is preferably from 250 ° C to 300 ° C, and more preferably from 280 ° C to 300 ° C in terms of, for example, the temperature in the heating chamber 42. In the present invention, the temperature inside the heating chamber 42 corresponds to the temperature of the atmosphere Thera around preventing corrosion shrink sheet.

In addition, the heating time is not particularly limited, provided that it is equal to or greater than the time during which the heat shrink of the base material 22 occurs and tight contact is established with the welded part 5, and this time is set appropriately in accordance with the diameter, etc. . the base material 22 or a plastic pipe coated with steel 11. For example, this time is preferably from 20 to 30 minutes.

{0076} The pressure sensitive adhesive layer 23 of the corrosion preventing shrink sheet 21 softens or melts when heated. In addition, heat shrinkage of the base material causes close contact with the welded portion 5. In this case, the shrink force of the corrosion preventing heat shrink sheet 21 gradually increases with increasing temperature, becomes maximum, and then gradually decreases.

On the other hand, no heat shrinkage occurs in the base material 32 in the pressure sensitive adhesive tape 31, but vulcanization proceeds in the pressure sensitive adhesive layer 33 and the shape is maintained. In addition, the adhesive shear force (shear force) of the pressure sensitive adhesive layer 33 gradually increases with the progress of vulcanization.

At this stage of heat shrinkage, heat shrinkage of the corrosion preventing heat shrink sheet 21 and curing of the pressure sensitive adhesive in the pressure sensitive adhesive tape 31 occur. However, as described above, the shear strength of the pressure sensitive adhesive layer 33 becomes greater than the maximum shrink force of the preventing adhesive corrosion of the heat shrink sheet 21 at a temperature at which the shrink force becomes maximum, and preferably becomes greater than the shrink force in the heat shrink step ki. In particular, in the case where the above-described crosslinkable pressure-sensitive adhesive material from butyl rubber is used, a large shear force can be manifested efficiently, starting from room temperature and to the heating temperature in the heat shrink stage.

Accordingly, no peeling of the end portion 21B of the winding end from the end portion 21A of the start of the corrosion preventing shrink sheet 21 occurs, and the sheet 21 is fixed on the peripheral surface of the welded portion 5 until the heat shrink stage is completed.

At the stage of heat shrinkage, the amount of heat shrinkage of the corrosion preventing heat shrink sheet 21 is not particularly limited, provided that it provides tight contact of the corrosion preventing heat shrink sheet 21 with the welded portion 5.

{0077} In the heat shrink phase, when the vacuum is high or the decompression time is too long, in addition to the above air in space 9, in some cases the air and volatile component contained in the pressure sensitive adhesive layer 23 substances in the corrosion preventing heat shrink sheet 21. Thus, concavities and bulges are formed on the surface of the corrosion preventing heat shrink sheet 21. Accordingly, taking into account the ability to edotvrascheniyu forming concavities and convexities for applying anticorrosive treatment and obtain a good state of the surface, it is preferable to prevent air and volatilization of the volatile component as described above. Their volatilization can be suppressed when the degree of vacuum is at a level equal to or lower than the degree of vacuum at which the above-described heating begins. In addition, their volatilization can be prevented by holding in a decompressed state with the above degree of vacuum. In the present invention, taking into account the ability to prevent volatilization of air and the volatile component due to excessive decompression in the heating chamber 42, the decompression is preferably stopped to heat the corrosion preventing heat-shrink sheet 21 at a stage (simultaneously) or later when the temperature inside the heating chamber 42 reaches the above-described temperature heating up.

When the decompression is stopped, for example, the exhaust pipe 44a connecting the vacuum pump 44 and the heating chamber 42 is blocked, and when necessary, the vacuum pump 44 is stopped.

{0078} Thus, in the heat-shrink step, the heating chamber 42 is maintained in a decompression state with the above-described degree of vacuum for at least a temperature rise time during which the temperature in the heating chamber 42 reaches the above-described heating temperature. Here, the above-described temperature rise time is preferably equal to or greater than the time during which air can be removed from the space 9, although this time cannot be unambiguously determined depending on the size of the corrosion preventing heat-shrink sheet 21, heating methods, heating efficiency, etc. . Thus, the suction of space 9, the heat shrinkage of the corrosion-resistant shrink sheet 21 and the melting of the pressure sensitive adhesive 23, as well as the stitching of the pressure sensitive adhesive 33 in the pressure sensitive adhesive tape 31 can be developed with good balance in order to ensure tight contact Corrosion-preventing shrink sheet 21 with the welded portion 5 without falling off the sheet 21.

The above-described temperature rise time is preferably, for example, from 3 to 10 minutes from the start of the temperature rise.

{0079} When decompression is stopped in the manner described above, the degree of vacuum in the heating chamber 42 gradually decreases over time. The heating chamber 42 may be opened after the decompression is stopped, but even after the decompression is stopped, the inside of the heating chamber 42 is preferably in a decompression state. In the aforementioned case, the decrease in the degree of vacuum in the heating chamber 42 may or may not be controlled. When the decrease in the degree of vacuum is controlled, this degree can gradually decrease at a constant speed, or it can be reduced stepwise, and in addition it can decrease in an irregular manner.

Preferably, the heating chamber 42 is in a decompression state even after the decompression is stopped. For example, the degree of vacuum after heating is preferably 0.02 MPa or more, and more preferably from 0.049 MPa to 0.080 MPa.

{0080} The heating chamber 42 is disconnected from the pipe at the same time or after the heating time has elapsed and the heating has been completed. In the aforementioned case, when the heating chamber 42 is in a decompression state after heating is completed, the decompression is removed.

{0081} Thus, anticorrosion treatment can be achieved on the welded portion 5 of the plastic-coated steel pipe 11, and a connected body 1 of the plastic-coated steel pipe (see FIG. 2) is subjected to an anti-corrosion treatment.

{0082} According to the present invention, anticorrosion treatment can be applied to a welded portion of a plastic-lined steel pipe by using a corrosion-resistant heat-shrink sheet. In addition, anticorrosion treatment can also be applied to the welded part of a plastic-lined steel pipe safely and without requiring special technological skills by applying an automatic heating method using a decompression heating device, etc. instead of a method of heating with an open fire using a gas burner, etc., which requires special skills.

EXAMPLES

{0083} The present invention will be described in more detail based on the examples below, but the present invention is not limited to these examples.

{0084} Corrosion-preventive shrink sheet 21 and pressure-sensitive adhesive tape 31 used in each Example were produced as described below.

(Anti-Corrosion Shrink Sheet 21)

Modified with maleic acid resin was extruded onto the surface of the sheet base material 22 (thickness: 1.2 mm, percentage of heat shrinkage: 25%) formed from a crosslinked stretched polyethylene resin described below in order to form a film of a layer 23 sensitive thereto pressure of the adhesive, and a product with a two-layer structure was produced in which the base material 22 is glued with a layer 23 of pressure-sensitive adhesive (thickness: 1.2 mm). The resulting product was cut into pieces of the following size: width 450 mm × length 2100 mm to produce a corrosion preventing heat-shrink sheet 21.

The shrinkage force of the corrosion-preventing heat-shrink sheet 21 became maximum at a temperature of 90 ° C, and was equal to 13 N / cm.

As a crosslinked stretched polyethylene resin, a resin prepared by stretching the resin at a temperature of 90 ° C. and irradiating it with an electron beam was used to cause crosslinking (gel fraction: 35%).

The maleic acid modified resin was prepared by modifying the polyethylene resin with maleic acid, in which the softening point or melting point was 110 ° C (without heat shrink characteristics). In this corrosion preventing shrink sheet 21 having a pressure sensitive adhesive layer 23 formed from a maleic acid modified resin, the structure was made by the method in accordance with Example 1, and as a result, the adhesion force (peeling at an angle of 90 °) at room temperature ( 25 ° C) was 213 N / cm, and the adhesion force (peeling at an angle of 90 °) at a temperature of 80 ° C, determined using the above measurement method, was 43 N / cm.

{0085} (Pressure sensitive adhesive tape 31)

On the surface of the sheet (film) base material 22 (thickness: 1.0 mm) formed from a crosslinked unstretched polyethylene resin described below, a molded sheet body (thickness: 0.5 mm) of a crosslinkable pressure sensitive butyl rubber adhesive, described below, was glued as a pressure sensitive adhesive layer 33, and the resulting product was cut into pieces of the following size: width 450 mm × length 150 mm in order to produce a pressure sensitive adhesive tape 31.

When the relationship between the shrink force of the corrosion-preventing heat-shrink sheet 21 and the shear force of the pressure-sensitive adhesive tape 31 was confirmed by using a tensile testing machine such as a load cell with a heating device, the shear force after resolving the pressure-sensitive adhesion for size: unit width × length 100 mm was greater than the shrink force over the entire temperature range from 25 ° C to 250 ° C. The shear force of the pressure sensitive adhesive tape 31, determined using the measurement method described above, was 38 N / cm at a temperature of 90 ° C. In addition, the shear force determined using the above measurement method after heating at 300 ° C for 20 min by applying a load of 1 N / cm ² , followed by cooling to 25 ° C and additional heating at 90 ° C for 10 min, amounted to 42 N / cm.

A crosslinked unstretched polyethylene resin was prepared without stretching the polyethylene by performing electron beam irradiation in order to cause crosslinking (gel fraction: 35%).

The crosslinkable pressure-sensitive butyl rubber adhesive contains 2.5 parts by weight of quinoid vulcanizer (p-quinondioxime) and 28 parts by weight of plasticizer (polybutene) per 100 parts by weight of butyl rubber (isoprene component content: 3 mol%).

{0086} (Example 1)

The 600A-coated steel pipe 11 of type 600A was subjected to anticorrosion treatment with a corrosion-preventive shrink sheet 21 by using the long range infrared heating decompression device 41 shown in FIG. four.

{0087} On the welded part 5 (centerline length: 300 mm) of the joined body 3 of a polyethylene-coated steel pipe, in which two pieces of polyethylene-coated steel pipes 11 were welded, an epoxy primer was applied (trademark: WRAP CO COAT EPX , manufactured by Furukawa Electric Co., Ltd.) as a backing material in order to allow curing of the primer upon heating.

Then, as shown in FIG. 3 and FIG. 4, the corrosion preventing heat shrink sheet 21 is wound around the peripheral surface of the welded portion 5 in a tubular shape so that the center lines of the joined body 3 of the polyethylene-lined steel pipe and the corrosion preventing heat shrink sheet 21 overlap. The end portion 21B of the winding end of the corrosion preventing heat shrink sheet 21 was overlapped by its end portion 21A of the start of the winding with an overlap length of approximately 100 mm. In this state, as shown in FIG. 3, the pressure-sensitive adhesive tape 31 was glued to it completely in the direction of the axis line of the plastic-lined steel pipe 11 through the end portion 21B of the winding end in order to fix the corrosion-resistant heat-shrink sheet 21. In the aforementioned case, the length of the pressure sensitive adhesive layer 33 glued to the end portion 21B of the end of the winding in a circular direction was 100 mm. Thus, a fixation step was performed.

{0088} Then, the heat shrink step was performed under the conditions shown in FIG. 5. In FIG. 5, the dashed line shows the degree of vacuum, and the solid line shows the temperature (the same is true for Fig. 6 and Fig. 7).

In particular, the heating chamber 42 was installed in an airtight state on the welded portion 5 of the joined body 3 of the polyethylene-lined steel pipe so that the central axes of the corrosion-preventive heat-shrink sheet 21 fixed in the tubular shape and the heating chamber 42 overlap.

The vacuum pump 44 was started in order to decompress the heating chamber 42, the degree of vacuum of 0.049 MPa was confirmed, and the temperature in the heating chamber 42 was raised, while the decompression (operation of the vacuum pump 44) continued until heating started. The heating temperature was set to 300 ° C, which is a sufficient temperature at which it is heated to a temperature at which heat shrinkage of the base material 22 occurs, and the pressure-sensitive adhesive in the pressure-sensitive adhesive layer 23 softens or melts. In the aforementioned case, the corrosion preventing heat shrink sheet 21 is heated to a temperature of about 250 ° C.

{0089} It was confirmed that the temperature in the heating chamber 42 is 300 ° C (the degree of vacuum in the above case was 0.08 MPa), and then the exhaust pipe 44a was closed and the vacuum pump 44 was stopped. Thus, decompression in the heating chamber 42 was stopped. Heating continued for 30 minutes in a state in which the temperature in the heating chamber 42 was kept constant. The degree of vacuum in the heating chamber 42 decreased over the course of the heating time, but this state was left as it is. The degree of vacuum in the heating chamber 42 after heating for 30 minutes was 0.02 MPa.

The decompression in the heating chamber 42 was removed simultaneously with the completion of heating (completion of construction) to complete the heat shrink stage.

{0090} In the above-described shrink step, no falling away of the corrosion preventing shrink sheet 21 from the welded portion 5 was found.

{0091} Thus, the corrosion-protected joint body 1 of the pipe shown in FIG. 2.

In the produced corrosion-protected joined body 1 of the pipe, the space 9 (see FIG. 3) was filled with a pressure sensitive adhesive (adhesive) 23 flowing inward and the corrosion preventing heat-shrink sheet 21 was in close contact with the steel surface of the welded part 5. Therefore, Corrosion protected pipe joint body 1 shows excellent corrosion prevention performance.

In addition, the absence of concavities and bulges on the surface of the corrosion preventing heat-shrink sheet 21 was confirmed, and a smooth corrosion-protected joined body 1 of the pipe with excellent surface condition was obtained.

{0092} (Example 2)

In Example 2, a corrosion protected joint body 1 of the pipe was produced by changing the decompression conditions in the heating chamber 42.

In other words, the above fixation step was carried out in the same manner as in Example 1.

{0093} Then, the heat shrink step was performed under the conditions shown in FIG. 6.

In particular, the heating chamber 42 was installed in an airtight state on the welded portion 5 in such a way that the central axes of the corrosion preventing heat-shrink sheet 21 fixed in a tubular shape and the heating chamber 42 overlap.

The vacuum pump 44 was started in order to decompress the heating chamber 42, the degree of vacuum of 0.049 MPa was confirmed, and the temperature in the heating chamber 42 was raised, while the decompression continued until heating started. The degree of vacuum inside the heating chamber 42 increased to 0.08 MPa with increasing temperature, and after that this degree of vacuum was kept constant. The heating temperature was set to 300 ° C.

It was confirmed that the temperature inside the heating chamber 42 was 300 ° C, and heating was continued for 30 minutes in a state in which the temperature inside the heating chamber 42 was kept constant. During the aforementioned time, the vacuum pump 44 continued to operate in order to maintain decompression inside the heating chamber 42. After a heating time of 30 minutes elapsed, the decompression in the heating chamber 42 was removed at the same time as the heating was completed.

Thus, a heat shrink step was performed.

{0094} In the above-described shrink step, no falling away of the corrosion preventing shrink sheet 21 from the welded portion 5 was found.

{0095} Thus, a corrosion protected joint body 1 of the pipe was produced.

In the produced corrosion protected joint body 1 of the pipe, the space 9 (see FIG. 3) was filled with a pressure sensitive adhesive flowing in and the corrosion preventing heat shrink sheet 21 was in close contact with the steel surface of the welded portion 5. Therefore, the corrosion protected joint pipe body 1 exhibits excellent corrosion prevention performance.

Scattered concavities and bulges were found on the surface of the corrosion preventing heat shrink sheet 21.

{0096} (Example 3)

In Example 3, the corrosion-protected joined body 1 of the pipe was produced in the same manner as in Example 1, except that the degree of vacuum in the heating chamber 42 after the start of heating was changed from 0.049 MPa to 0.03 MPa, and this the degree of vacuum was maintained until the temperature reached 300 ° C.

In Example 3, a heat shrink step was performed under the conditions shown in FIG. 7. The degree of vacuum inside the heating chamber 42 upon completion of construction was 0.010 MPa.

{0097} In the shrink step, no falling away of the corrosion preventing shrink sheet 21 from the welded portion 5 was found.

The void was partially recognized in space 9 (see FIG. 3) in the produced corrosion-protected joined body 1 of the pipe, but the corrosion-prevented heat-shrink sheet 21 was in close contact with the steel surface of the welded part 5. Therefore, the produced corrosion-protected joined body 1 of the pipe showed good corrosion prevention performance.

In addition, the absence of concavities and bulges on the surface of the corrosion preventing heat-shrink sheet 21 was confirmed, and a smooth corrosion-protected joined body 1 of the pipe with excellent surface condition was obtained.

{0098} (Comparative Example 1)

Comparative example 1 is an example in which anticorrosion treatment was carried out using a pressure sensitive adhesive tape for comparison having a pressure sensitive adhesive, in which the shear force at a temperature at which the shrink force of the corrosion preventing heat shrink sheet 21 becomes maximum less than maximum shrink force.

{0099} (Pressure sensitive adhesive tape for comparison)

On the surface of the sheet base material 22 (thickness: 1.0 mm) formed from a crosslinked unstretched polyethylene resin described below, an injection molded sheet body (thickness: 0.5 mm) from a non-crosslinkable pressure sensitive butyl rubber adhesive described below was pasted as a layer of pressure-sensitive adhesive, and the resulting product was cut into pieces of the following size: width 450 mm × length 150 mm in order to produce a pressure-sensitive adhesive tape for comparison and I.

When the relationship between the shrink force of the corrosion-preventing heat-shrink sheet 21 and the shear force after gluing a pressure sensitive adhesive tape for comparison with a size: unit width × length of 100 mm was confirmed using a tensile testing machine such as a load cell with a heating device, the shear force was less than shrink force over the entire temperature range from 25 ° C to 200 ° C. The shear force of the pressure sensitive adhesive tape for comparison, determined using the above measurement method, was 1 N / cm at a temperature of 90 ° C.

A crosslinked unstretched polyethylene sheet was prepared without stretching the polyethylene by electron beam irradiation in order to cause crosslinking (gel fraction: 35%).

The non-crosslinkable butyl rubber pressure sensitive adhesive contains 28 parts by weight of a plasticizer (polybutene) and 10 parts by weight of a tackifying agent (coumaronindene resin based on fraction C6) per 100 parts by weight of butyl rubber.

{0100} The heat shrink step was performed after the fixation step using this pressure sensitive adhesive tape for comparison in the same manner as in Example 1.

As a result, at the heat shrink stage, the end portion of the end of the winding was essentially unable to fix on the end portion of the beginning of the winding with a pressure sensitive adhesive tape for comparison, the corrosion preventing heat shrink sheet 21 fell off from the welded portion 5, and anti-corrosion treatment could not be performed.

{0101} In describing our invention in the presented embodiments, it was not our intention to limit the present invention to any of the details of the description unless otherwise expressly indicated, but instead this description should be construed broadly in accordance with the spirit and scope of the present invention, as set forth in the attached claims.

{0102} This application claims the priority of patent application No. 2013-253446, registered in Japan on December 6, 2013, which is incorporated herein by reference in its entirety.

LIST OF REFERENCE NUMBERS

{0103} 1 - corrosion-protected connected pipe body;

3 - a connected body lined with plastic steel pipe;

5 - welded part;

5a - weld;

7 - part of the exposed surface of the steel;

9 - space;

11 - lined with plastic steel pipe;

11a - plastic lining;

21 - anti-corrosion shrink sheet;

21A - end part of the beginning of the winding;

21B is the end portion of the end of the winding;

22, 32 - the main material;

23, 33 - a layer of pressure-sensitive adhesive substance;

31 - fixing tape with pressure-sensitive adhesive to prevent heat shrink sheet (pressure-sensitive adhesive tape);

41 - infrared heating device in the far range of the decompression type;

42 - heating chamber;

43 - far-range infrared heater;

44 - a vacuum pump;

44a - exhaust pipe.

Claims (12)

1. A method of protecting against corrosion of a welded part, in which anticorrosion treatment is applied to a welded part of a plastic pipe coated with steel by using a corrosion-resistant heat-shrink sheet, comprising: the step of securing at least the end portion of the corrosion preventing heat-shrink sheet wound around the peripheral surface of the at least the welded portion of the plastic-lined steel pipe by using a fixing tape with a pressure sensitive adhesive to prevent the heat-shrink sheet that has a pressure sensitive adhesive in where the shear force at a temperature at which the shrink force of the corrosion-resistant shrink sheet becomes maximum, is is Busy greater than the maximum shrink force; and a heat shrink step of a corrosion preventing heat shrink sheet. 2. A method of protecting against corrosion of a welded portion of a plastic-lined steel pipe according to claim 1, wherein the pressure-sensitive adhesive is a pressure-sensitive adhesive, crosslinked by heating, and its shear strength at a temperature of 90 ° C is more than 15 N / cm. 3. A method of protecting against corrosion of a welded portion of a plastic-lined steel pipe according to claim 1, wherein the pressure sensitive adhesive is a crosslinkable pressure sensitive butyl rubber adhesive containing from 0.5 to 5.0 mass parts of quinoid vulcanizer and from 5 to 30 mass parts of plasticizer per 100 mass parts of butyl rubber. 4. A method of protecting against corrosion of a welded part of a steel-lined plastic pipe according to claim 1, wherein the step of heat shrinkage is performed by using a decompression-type heating device. 5. A method of protecting against corrosion of a welded part of a steel pipe lined with plastic according to any one of paragraphs. 1-4, in which the heat shrink stage is a stage in which the atmosphere around the corrosion preventing heat shrink sheet is decompressed so as to reach an atmospheric vacuum of between 0.049 and 0.080 MPa, and then the corrosion preventing heat shrink sheet is heated in a state in which the decompression lasts, and decompression of the atmosphere is removed simultaneously with the completion of heating or after it. 6. A method of protecting against corrosion of a welded part of a steel pipe lined with plastic according to any one of paragraphs. 1-4, in which the heat shrink step is a step in which the atmosphere around the corrosion preventing heat shrink sheet is decompressed so as to reach an atmospheric vacuum of between 0.049 and 0.080 MPa, and then the atmosphere is heated in a state in which the vacuum is maintained at 0.049 MPa or more, decompression stops after the temperature of the atmosphere reaches the heating temperature, the corrosion preventing heat shrink sheet is heated, and the decompression of the atmosphere is removed at the same time as m heating or after it. 7. A fixing tape with a pressure sensitive adhesive for preventing corrosion shrink sheet and for fixing a corrosion preventing heat shrink sheet wound around a steel pipe lined with plastic, the pressure sensitive adhesive layer containing pressure sensitive adhesive stitched when heated is located on one side heat-resistant base film, and shear strength of a crosslinkable pressure sensitive adhesive at a temperature at which the shrink force prevents roziyu shrink sheet becomes maximum is higher than the maximum force of shrinkage. 8. A fixing tape with a pressure sensitive adhesive for preventing a heat shrink sheet according to claim 7, wherein the shear strength of the layer of pressure sensitive adhesive is 15 N / cm or more when the fixing tape with a pressure sensitive adhesive is glued to a crosslinked stretched polyethylene sheet , and the resulting product is heated at a temperature of 300 ° C for 20 min at a load of 1 N / cm ² and then cooled to a temperature of 25 ° C and additionally heated at a temperature of 90 ° C for 10 min. 9. A fixing tape with a pressure sensitive adhesive for a corrosion preventing heat-shrink sheet according to claim 7, wherein the heat-resistant base film is a base film formed from cross-linked polyethylene. 10. Fixing tape with pressure-sensitive adhesive to prevent corrosion shrink sheet according to any one of paragraphs. 7-9, in which the pressure-sensitive adhesive is a crosslinkable pressure-sensitive butyl rubber adhesive containing a quinoid vulcanizer.

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