WO2024105867A1 - Method for repairing damage to anticorrosive coating layer of metallic material - Google Patents

Abstract

The present invention provides a repair method by which an anticorrosive coating layer 2 of a metallic material 1 can be repaired in a simple manner to give a repaired portion excellent in terms of stability and durability.　This repair method at least includes: an uncovered-portion formation step in which a damaged portion 21 of the anticorrosive coating layer 2 and a portion 22 which surrounds the damaged portion 21 and has lifted up are removed to thereby form an uncovered portion 23 where the metallic material 1 is exposed; and a filled-portion formation step in which filling polyolefin sheets (31A, 32A, 33A) are stacked as two or more sheet layers (31, 32, 33) in the uncovered portion 23 and bonded together to fill the uncovered portion 23, thereby forming a filled portion having approximately the same height as the anticorrosive coating layer 2 surrounding the uncovered portion 23. The sheet layers each are configured of a plurality of filling polyolefin sheets jointed together, and hence have joint lines (31B, 32B, 33B). Any adjoining two of the sheet layers are configured so that each joint line of one sheet layer does not lie in the same position as any of the joint lines of the other sheet layer.

Description

Method for repairing damage to corrosion-protective coating layer on metal material

The present invention relates to a method for repairing damage to a corrosion-resistant coating layer on a metal material coated with the coating layer, the coating layer being made of polyolefin.

Polyolefins are easy to process and have excellent resistance to moisture, soil, gas, etc., so they are widely used as anti-corrosion coatings for metal materials such as steel pipes.

Metal materials are subjected to various physical shocks during storage, transportation, installation, etc., and the corrosion-resistant coating layer of metal materials coated with polyolefin for corrosion protection may be damaged during such shocks. Damage can cause the corrosion protection properties of the polyolefin to decrease, so when damage occurs, it is necessary to repair it. Various methods for repairing the damage have been proposed.

For example, there are several known methods for filling exposed areas of the corrosion protection coating with a filler (sealant) (Patent Documents 1 to 3).

Patent Document 1 discloses a repair method in which a damaged area formed as a recess in a corrosion-resistant coating layer is filled with a sealant that is heat-fusible or adhesive and fluid at room temperature, so that its upper surface is at the same level as the surface of the corrosion-resistant coating layer, and then a repair member consisting of a cross-linked polyolefin sheet with an adhesive layer on one side is heat-pressed to the damaged area of the corrosion-resistant coating layer via the adhesive layer so as to cover the corrosion-resistant coating layer surrounding the damaged area as well, and then a reinforcing heat-fusible polyolefin sheet that has a softening point higher than that of the adhesive used in the adhesive layer of the repair member is heat-pressed to cover at least the outer periphery of the repair member and the corrosion-resistant coating layer adjacent to the outer periphery continuously.

Patent Document 2 discloses a repair method in which a filler is filled into damaged areas of the coating of polyethylene-coated corrosion-resistant steel material, a polyethylene sheet is placed over the filler, and the polyethylene sheet is ultrasonically welded to the polyethylene coating on the surface of the steel material.

Patent Document 3 discloses a repair method in which a primer containing a reactive curing resin that exhibits adhesion to polyolefins is applied to at least the surface of a polyolefin corrosion protection coating layer around the exposed surface of a steel pipe that is intended to come into contact with a sealant, a sealant containing a reactive curing resin that exhibits adhesion to a steel pipe is then applied to the surface intended to come into contact with the sealant and the exposed surface of the steel pipe, and a heat-shrinkable coating material with a primer applied to one side is then placed on at least the sealant layer so that the primer-coated surface faces the sealant layer, and the heat-shrinkable coating material is heated and heat-shrunk while being pressed onto at least the sealant layer at the latest before the completion of the curing reaction of the primer.

In addition, a method is known for repairing exposed areas of the anticorrosive coating layer using a polyolefin sheet (Patent Documents 4 and 5).

Patent Document 4 discloses a repair method in which a modified polyethylene sheet is heated and pressed onto the damaged area of the mill-coated polyethylene coating layer of steel and onto the surface of the coating layer surrounding the damaged area, and then a two-layer sheet (lower layer: modified polyethylene, upper layer: polyethylene) is heated and pressed onto the modified polyethylene coating layer to cover it.

Patent Document 5 discloses a repair method in which a primer containing an organometallic compound is applied to the damaged area of polyolefin-coated steel and the surrounding mill-coated polyolefin coating layer, the primer is applied to one side and both sides of a repair polyolefin sheet shaped to be inserted into the damaged area, and then an α-cyanoacrylate resin composition is applied to at least one of the primer-coated surfaces of the damaged area and the surrounding mill-coated polyolefin coating layer and the primer-coated surface of the repair polyolefin sheet, with the primer-coated surfaces facing each other and the repair polyolefin sheet adhered to the damaged area.

Metal materials repaired using methods that use a filler (sealant) as described in Patent Documents 1 to 3 have a structure in which different materials (filler and polyolefin) are bonded together. Therefore, in an environment in which the temperature around the metal material may rise, there is a concern that the repaired area may be damaged due to differences in thermal expansion coefficients.
Furthermore, in the case of the methods using polyolefin sheets as described in Patent Documents 4 and 5, there are drawbacks such as the need for heating or the need for special materials as adhesives or primers to ensure sufficient adhesion between the polyolefin sheet and the underlying metal material or the surrounding polyolefin corrosion-resistant coating layer.

Therefore, there is a need to develop a repair method that can easily repair damage to the corrosion protection coating layer of metal materials and that ensures excellent stability and durability of the repaired area.

Japanese Patent Application Laid-Open No. 61-170586 JP 2001-129892 A Japanese Patent Application Laid-Open No. 61-193832 Japanese Patent Application Laid-Open No. 1-95029 Japanese Patent Application Laid-Open No. 1-275032

The present invention has been made in consideration of the above-mentioned background technology, and its objective is to provide a repair method that can easily repair damage to a corrosion-resistant coating layer on a metal material (e.g., repairs can be made even by unskilled personnel) and that produces repaired parts with excellent stability and durability.

As a result of extensive research into solving the above-mentioned problems, the present inventors have found that when repairing a corrosion-protective coating layer by filling the removed coating area with a polyolefin sheet made of the same material as the corrosion-protective coating layer, uniform adhesion can be achieved by laminating and adhering the polyolefin sheets in two or more sheet layers, and each sheet layer being constructed by joining multiple polyolefin sheets.
When each sheet layer is constructed from multiple sheets in this manner, there is a risk that liquids such as water will enter through the seams between the sheets; however, by constructing the seams between adjacent sheet layers vertically so that they do not overlap, the inventors discovered that this risk can be reduced and the stability and durability of the repaired area can be ensured, which led to the completion of the present invention.

That is, the present invention provides a method for repairing damage to a corrosion-resistant coating layer of a metal material coated with the corrosion-resistant coating layer made of a polyolefin, comprising the steps of:
a coating removal portion forming step of forming a coating removal portion in which the metal material is exposed by removing the damaged portion of the corrosion-resistant coating layer and the raised portion around the damaged portion; and
The method includes at least a filling portion forming step of laminating and adhering two or more sheet layers of a filling polyolefin sheet to the coating removal portion to form a filling portion having approximately the same height as the anticorrosive coating layer surrounding the coating removal portion,
The repair method is characterized in that each of the sheet layers has a seam line formed by joining a plurality of filling polyolefin sheets, and the seam lines of adjacent sheet layers are prevented from overlapping.

The present invention also provides the above-mentioned repair method, which further includes a cover forming step of forming a cover that covers the boundary between the filling portion and the corrosion-resistant coating layer that surrounds the filling portion by adhering a covering polyolefin sheet to the boundary.

In this specification, "polyolefin sheet" may be abbreviated as "sheet," "filling polyolefin sheet" as "filling sheet," and "cover polyolefin sheet" as "cover sheet."

According to the present invention, damage to a corrosion-protective coating layer in a metal material can be repaired in a simple manner, and a repair method can be provided in which the repaired portion has excellent stability and durability.
In particular, metal materials such as steel pipes to which the present invention is applied are often used in locations with high moisture or in environments where they are exposed to chemicals, but metal materials repaired using the method of the present invention can demonstrate sufficient durability even in such locations.

The method of the present invention does not require heating when attaching the polyolefin sheet to metal materials, so repairs can be made even in places and situations where open flames must be avoided.

In the method of the present invention, the sheet filled in the area where the coating was removed and the anticorrosive coating layer remaining around the area where the coating was removed are made of the same polyolefin, so the thermal expansion coefficients of both are roughly the same, and the repaired area is less likely to be damaged even in an environment where the temperature around the metal material may rise.

In the method of the present invention, the sheet layer is made up of multiple sheets joined together, so the size of each sheet is relatively small. Therefore, the method of the present invention has various advantages compared to repairing by filling with a single polyolefin sheet.

First, with the method of the present invention, even an unskilled worker can easily apply primer or adhesive to the sheet evenly. In addition, the method of the present invention is easy to deal with damage of various shapes. In particular, when the metal material is a curved pipe or a tower or tank, if damage occurs to a curved portion such as a bent portion or branch portion, it is extremely difficult to apply primer or adhesive evenly to the sheet using a method of filling it with a single polyolefin sheet, but the method of the present invention makes it easy to repair such curved portions.

In the method of the present invention, the filling section is formed by stacking multiple sheet layers. As a result, the present invention has various advantages over forming a filling section with a single sheet layer.

For example, anti-corrosion coating layers for metal materials come in a variety of thicknesses, and the method of the present invention, which uses multiple sheet layers, can accommodate anti-corrosion coating layers of various thicknesses.

In addition, in the method of the present invention, which uses multiple sheet layers, even if a defect occurs in one of the sheet layers, it is unlikely to affect the underlying metal material.

Furthermore, in an environment where the temperature around the metal material may rise, the adhesive layer between the metal material and the polyolefin sheet is prone to deterioration due to the difference in thermal expansion coefficient between the metal material and the polyolefin sheet. However, when multiple sheet layers are laminated as in the present invention, there is no difference in the thermal expansion coefficient between the sheet layers, so deterioration is unlikely to occur in the adhesive layer between the sheet layers.

As described above, the method of the present invention uses multiple sheet layers, each of which is constructed by joining multiple sheets together, making repairs extremely easy and enabling the repaired area to have excellent stability and durability.

FIG. 2 is a schematic cross-sectional view of a metal material. 1 is a schematic cross-sectional view of a damaged portion of a corrosion-resistant coating layer of a metal material and its surrounding area. 4 is a schematic cross-sectional view of the metal material after a coating removal portion forming step is performed. FIG. 10 is a plan view of the metal material after the coating removal portion forming step is performed. FIG. 10 is a plan view of the metal material after the coating removal portion forming step is performed. FIG. 4 is a schematic cross-sectional view of the metal material after a filling portion forming process is performed. FIG. Schematic cross-sectional view showing the process of the filling portion formation step. (a) State after the first sheet layer has been formed (b) State after the second sheet layer has been formed (c) State after the third sheet layer has been formed This is a plan view showing the process of the filling portion formation step. (a) State after the first sheet layer has been formed (b) State after the second sheet layer has been formed (c) State after the third sheet layer has been formed This is a plan view showing the process of the filling portion formation step. (a) State after the first sheet layer has been formed (b) State after the second sheet layer has been formed (c) State after the third sheet layer has been formed 10 is a schematic cross-sectional view of the metal material after a cover portion forming step is performed. FIG. 13 is a plan view of the metal material after the cover portion forming process is performed. FIG. 10 is a schematic cross-sectional view of the metal material after a cover portion forming step is performed. FIG. 13 is a plan view of the metal material after the cover portion forming process is performed. FIG. Schematic cross-sectional views showing the processes of the filling portion forming step and the cover portion forming step (when a partially coated portion is formed in the filling portion forming step). (a) State after the first sheet layer has been formed (a') State after the partially coated portion has been formed after the first sheet layer has been formed (b) State after the second sheet layer has been formed This is a continuation of Figure 14. (b') State after the second sheet layer has been formed and a portion of the coating has been removed (c) State after the third sheet layer has been formed (d) State after the cover portion forming process has been carried out

The present invention will be described below, but it is not limited to the following embodiment and can be modified in any way.

The present invention relates to a method for repairing damage to a corrosion-resistant coating layer 2 of a metal material 1 coated with the corrosion-resistant coating layer 2 made of polyolefin. Figure 1 shows a schematic cross-sectional view of the metal material 1 before repair in the present invention. The metal material 1 is coated with a corrosion-resistant coating layer 2 made of polyolefin.

There are no particular limitations on the type of metal that constitutes the metal material 1, and examples include iron, aluminum, copper, zinc, steel, etc.

There are no particular limitations on the shape of the metal material 1, and examples include metal plates, metal pipes, metal rods, and metal containers such as tanks.

When the metal material 1 is a metal pipe, the metal pipe may have an anticorrosive coating layer 2 on its inner surface, may have an anticorrosive coating layer 2 on its outer surface, or may have metal layers on both its inner and outer surfaces. The repair method of the present invention is applicable to the anticorrosive coating layer 2 on either the inner or outer surface.
Furthermore, when the metal material 1 is a metal pipe, the metal pipe may be a straight pipe, a curved pipe (a metal pipe having a bent portion), a branch pipe, a reducer, or the like.

When the metal material 1 is a metal pipe, there is no particular limitation on its inner diameter. The inner diameter of the metal pipe is, for example, 20 cm or more, 40 cm or more, or 50 cm or more, and 10 m or less, 5 m or less, or 3 m or less.

When the metal material 1 is a steel pipe whose inner and/or outer surface is coated with the anticorrosive coating layer, particularly when the steel pipe is a steel pipe for transporting liquids (water, chemicals, etc.), there are many opportunities for damage to occur, and such steel pipes are widely used, so the advantage of the present invention, that a repaired portion with excellent stability and durability can be formed by a simple method, can be easily utilized.

When the metal material 1 is a steel pipe, more specific examples include electric resistance welded steel pipe, forged steel pipe, galvanized steel pipe, seamless steel pipe, spiral steel pipe, UOE steel pipe, etc., but are not limited to these.

The corrosion-resistant coating layer 2 is made of polyolefin and serves to protect the metal material 1 from corrosion and impact.

There is no particular limitation on the polyolefin that is the raw material of the corrosion-resistant coating layer 2, and examples thereof include low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, polybutene, and copolymers thereof.
The anticorrosive coating layer 2 may be formed using one kind of these alone, or the anticorrosive coating layer 2 may be formed using two or more kinds of these in combination.

The thickness of the corrosion-resistant coating layer 2 (hereinafter, in this specification, "thickness" means the average thickness unless otherwise specified) is preferably 0.5 mm or more, more preferably 1 mm or more, particularly preferably 1.2 mm or more, and most preferably 1.5 mm or more. Also, it is preferably 5 mm or less, more preferably 4.5 mm or less, and particularly preferably 4 mm or less.
When the thickness is equal to or greater than the lower limit, the anticorrosive property and the impact resistance are excellent, whereas when the thickness is equal to or less than the upper limit, it is advantageous in terms of cost.

In the repair method of the present invention, first, a coating removal portion forming process is performed. In the coating removal portion forming process, the damaged portion 21 of the corrosion protection coating layer 2 and the raised portion 22 around the damaged portion 21 are removed to form a coating removal portion 23 where the metal material 1 is exposed.

Figure 2 is a schematic cross-sectional view showing the vicinity of a damaged portion 21 in the corrosion-resistant coating layer 2 of the metal material 1. The damaged portion 21 occurs in the corrosion-resistant coating layer 2 due to contact with other materials during storage or transportation, or contact with tools during maintenance. It can be visually confirmed that the area around the damaged portion 21 is raised above the surrounding surface of the corrosion-resistant coating layer 2 (raising portion 22) (note that the damaged portion 21 and the raised portion 22 are exaggerated in Figure 2).

In the coating removal portion forming step, the damaged portion 21 and the raised portion 22 around the damaged portion 21 are removed.
The raised portion 22 can be removed by a known method using a cutter, scissors, a power tool, or the like.

FIG. 3 shows a schematic cross-sectional view of the metal material 1 after the coating removal portion formation process, and FIG. 4 shows a plan view. In the portion where the damaged portion 21 and the raised portion 22 have been removed, the corrosion protection coating layer 2 has been removed, and the metal material 1 is exposed (representing the coating removal portion 23).

In the coating removal portion forming process, at least the corrosion-resistant coating layer 2 is removed from the damaged portion 21 and the raised portion 22 (i.e., the portion that can be visually confirmed to be raised above the surface of the surrounding corrosion-resistant coating layer 2), but a generous amount (more than enough) of the corrosion-resistant coating layer 2 may be removed, including the corrosion-resistant coating layer 2 on the outside of the raised portion 22.

In addition, if the coating removal portion 23 has a random shape as shown in FIG. 4, it becomes necessary to cut a fixed-shaped polyolefin sheet to match the shape of the coating removal portion 23 in the filling portion formation process described below. In order to reduce the labor required for such cutting, the corrosion-resistant coating layer 2 may be removed including the corrosion-resistant coating layer 2 on the outside of the raised portion 22, thereby forming, for example, a rectangular coating removal portion 23 as shown in FIG. 5.

The area of the coating removal portion 23 is preferably ⁵⁰ cm2 or more, more preferably ⁷⁵ cm2 or more, and particularly preferably ¹⁰⁰ cm2 or more. Also, the area is preferably ⁵⁰⁰ cm2 or less, more preferably ⁴⁰⁰ cm2 or less, and particularly preferably ³⁰⁰ cm2 or less.

In the repair method of the present invention, the coating removal portion forming step is followed by the filling portion forming step. In the filling portion forming step, the coating removal portion 23 is filled by stacking and adhering two or more sheet layers (31, 32, 33) of filling polyolefin sheets (31A, 32A, 33A) to form a filling portion 3 having approximately the same height as the corrosion protection coating layer 2 surrounding the coating removal portion 23.

FIG. 6 shows a schematic cross-sectional view of the metal material 1 after the filling portion formation process has been performed. By performing the filling portion formation process, the polyolefin sheet is filled in the area that was previously the coating removal area 23 formed by removing the damaged area 21 and the raised area 22 around the damaged area 21.

In the filling section formation process, filling polyolefin sheets (31A, 32A, 33A) are laminated as two or more sheet layers (31, 32, 33) in the coating removal section 23, and each sheet layer (31, 32, 33) has a seam line because it is formed by joining multiple filling polyolefin sheets (31A, 32A, 33A), and the seam lines (31B, 32B, 33B) of adjacent sheet layers are prevented from overlapping.

Figures 7, 8, and 9 show a specific example of the filling section formation process, using an example in which three sheet layers are laminated in the coating removal section 23.

First, a filler polyolefin sheet 31A is adhered onto the metal material 1 exposed in the coating removal portion 23 to form a first sheet layer 31 (FIGS. 7(a), 8(a), and 9(a)).
As shown in Figures 8(a) and 9(a), the first sheet layer 31 is constructed by joining together a plurality of filling polyolefin sheets 31A, and seam lines 31B are formed between the sheets 31A.

Sheet 31A is made by cutting a commercially available standard (e.g. rectangular) polyolefin sheet to fit the shape of coating removal section 23. If coating removal section 23 is formed in a rectangular shape, for example, as shown in FIG. 5, in the coating removal section formation process, first sheet layer 31 will also be rectangular, as shown in FIG. 9(a), reducing the effort required for cutting the sheet in the filling section formation process.

After the first sheet layer 31 is formed, a filler polyolefin sheet 32A is adhered thereon to form a second sheet layer 32 (FIGS. 7(b), 8(b), and 9(b)).
As shown in Figures 8(b) and 9(b), the second sheet layer 32 is also constructed by joining a plurality of filling polyolefin sheets 32A, and a seam line 32B is formed between the sheets 32A.

Here, the seam line 32B in the second sheet layer 32 is formed so as not to overlap with the seam line 31B in the first sheet layer 31 (the adjacent sheet layer) (note that in Figures 8(b) and 9(b) the seam line 31B in the first sheet layer 31 is shown by a dotted line).
By preventing the seams of adjacent sheet layers from overlapping, when the filling section 3 comes into contact with a liquid such as water, the liquid is less likely to penetrate into the lower sheet layer and ultimately into the metal material 1, improving the stability and durability of the collection section.

To make it easier to prevent the intrusion of liquids such as water, it is better to position the seam lines ( seam lines 32B and 31B) of adjacent sheet layers as far apart as possible. For example, as shown in Figures 8(b) and 9(b), it is desirable to form seam line 32B in a position approximately halfway between two seam lines 31B.

After the second sheet layer 32 is formed, a filler polyolefin sheet 33A is adhered thereon to form a third sheet layer 33 (FIGS. 7(c), 8(c), and 9(c)).
As shown in Figures 8(c) and 9(c), the third sheet layer 33 is also constructed by joining together a plurality of filling polyolefin sheets 33A, and a seam line 33B is formed between the sheets 33A.

Similar to the case of the second sheet layer 32, the seam line 33B of the third sheet layer 33 is formed so as not to overlap with the seam line 32B of the second sheet layer 32 (the adjacent sheet layer) (note that the seam line 32B of the second sheet layer 32 is shown by a dashed line in Figures 8(c) and 9(c)).

To make it easier to prevent the intrusion of liquids such as water, it is better to position seam line 33B and seam line 32B as far apart as possible. For example, as shown in Figures 8(c) and 9(c), it is desirable to form seam line 33B at a position approximately halfway between two seam lines 32B. In other words, the position of seam line 33B of the third sheet layer 33 may be approximately the same as the position of seam line 31B of the first sheet layer 31.

When there are three sheet layers, forming the third sheet layer 33 results in a filled portion 3 being formed in the area that was previously the damaged portion 21 and its surroundings in the corrosion-resistant coating layer 2 of the metal material 1 (Figure 6).

The corrosion-resistant coating layer 2 is made of polyolefin, and the filling portion 3 is formed by adhering a filling polyolefin sheet. As a result, the thermal expansion coefficients of the filling portion 3 and the surrounding corrosion-resistant coating layer 2 are approximately the same, and even in an environment where the temperature around the metal material 1 may rise, the repaired portion of the metal material repaired by the method of the present invention is less likely to break.

Specific examples of the polyolefin resin that is the raw material of the corrosion-resistant coating layer 2 are as described above. The polyolefin that constitutes the corrosion-resistant coating layer 2 and the polyolefin that constitutes the filling polyolefin sheets (31A, 32A, 33A) are desirably chemically identical. That is, it is desirably to select a polyolefin sheet that is chemically identical to the polyolefin that constitutes the corrosion-resistant coating layer 2 of the metal material 1 to which the method of the present invention is applied, and use it as the filling polyolefin sheet (31A, 32A, 33A).
By doing so, it becomes easier to prevent damage to the repaired portion in an environment where the temperature around the metal material 1 may rise.

In the filling portion forming step, the filling polyolefin sheet is laminated as two or more sheet layers.
The number of sheet layers is preferably 2, 3 or 4. If the sheet layers are 4 or more, the work time will increase and the number of bonding points will increase, which may reduce the stability and durability of the repaired area.

In the filling section formation process, commercially available standard shaped (e.g. rectangular) polyolefin sheets are used, cut as necessary.

The thickness of the regular polyolefin sheet is preferably 0.1 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.5 mm or more, and is preferably 5 mm or less, more preferably 4 mm or less, and particularly preferably 3 mm or less.
When the thickness is within the above range, the number of sheet layers can be easily set within the above desired range.

The area of each of the regular polyolefin sheets is preferably ⁵⁰ cm2 or more, more preferably ⁷⁵ cm2 or more, and particularly preferably ¹⁰⁰ cm2 or more. Also, the area is preferably ⁵⁰⁰ cm2 or less, more preferably ⁴⁰⁰ cm2 or less, and particularly preferably ³⁰⁰ cm2 or less.
When the area is equal to or greater than the lower limit, the workability (work time) is likely to be improved, whereas when the area is equal to or less than the upper limit, the adhesive and primer can be evenly applied to the sheet, and peeling of the sheet is unlikely to occur.

The polyolefin sheet of a fixed shape is cut to fit the shape of the coating removal area 23 before use. In particular, when the coating removal area 23 has a random shape as shown in FIG. 4, the area of the sheet after cutting may fall below the lower limit, but this does not pose any particular problem.

The bonding in the filling section formation process is preferably performed by applying a primer to the filling polyolefin sheet, drying the primer, and then applying an adhesive to the filling polyolefin sheet.

The first sheet layer 31 is formed by adhering sheet 31A onto the metal material 1 exposed in the coating removal section 23. Applying a primer or adhesive to sheet 31A allows for more uniform application and improves adhesion, rather than applying the primer or adhesive to the metal material 1.

The second and subsequent sheet layers are formed by bonding polyolefin sheets together. In this case, a primer or adhesive may be applied to the polyolefin sheet constituting the existing sheet layer, to the polyolefin sheet to be newly installed, or to both polyolefin sheets.
In order to improve adhesion, it is desirable to coat both polyolefin sheets with a primer or adhesive.

By applying a primer to the adhesion surface of a polyolefin sheet or the like prior to applying an adhesive, the adhesion between the adhesive and the adhesion surface can be improved.
Specific examples of the primer used in the filling portion forming step include an amine-based primer, a synthetic rubber-based primer, an acrylic-based primer, a urethane-based primer, and an epoxy-based primer.
These primers may be used alone or in combination of two or more kinds. From the viewpoint of work efficiency, it is preferable to use one kind alone.

The coating amount of the primer used in the filling portion forming step is preferably 0.1 g/ ^m2 or more, more preferably 0.5 g/ ^m2 or more, and particularly preferably 1.0 g/ ^m2 or more. Also, it is preferably 6.0 g/ ^m2 or less, more preferably 3.0 g/ ^m2 or less, and particularly preferably ^2.0 g/m2 or less.
When the coating amount is equal to or more than the lower limit, the workability (work time) is likely to be improved, and it is also advantageous in terms of cost. When the area is equal to or less than the upper limit, the adhesiveness is likely to be improved.

After applying the primer, the adhesive is applied on top of the primer. The timing of applying the adhesive is such that the time interval between completing application of the primer and starting application of the adhesive is preferably 0.5 minutes or more, more preferably 1 minute or more, and particularly preferably 2 minutes or more. It is also preferably 10 minutes or less, more preferably 7 minutes or less, and particularly preferably 5 minutes or less.

Specific examples of adhesives used in the filling portion formation process include polyvinyl acetate adhesives, cyanoacrylate adhesives, cellulose adhesives, polyester adhesives, polyether adhesives, polyamide adhesives, polyimide adhesives, epoxy adhesives, urethane adhesives, rubber adhesives, silicone adhesives, etc.
These adhesives may be used alone or in combination of two or more kinds. From the viewpoint of work efficiency, it is preferable to use one kind alone.

The amount of adhesive applied in the filling portion forming step is preferably 20 g/ ^m2 or more, more preferably 30 g/ ^m2 or more, and particularly preferably 40 g/ ^m2 or more. Also, it is preferably 70 g/ ^m2 or less, more preferably 60 g/ ^m2 or less, and particularly preferably 50 g/ ^m2 or less.
When the coating amount is equal to or more than the lower limit, the workability (work time) is likely to be improved, and it is also advantageous in terms of cost. When the area is equal to or less than the upper limit, the adhesiveness is likely to be improved.

In the filling portion forming step, it is preferable to roughen the surface of the metal material 1 exposed in the coating removal portion 23 with sandpaper or the like in order to improve adhesion prior to placing the polyolefin sheet. In addition, it is preferable to clean the surface of the metal material 1 after the surface roughening with a solvent such as acetone and a rag or the like to remove rust and foreign matter.
It is also preferable to roughen and clean the surface of the polyolefin sheet to be placed in the coating removal section 23 in the filling section formation step in the same manner. It is particularly preferable to roughen and clean the surface of both sides of the polyolefin sheet before placing it in terms of work efficiency and adhesiveness.

In the repair method of the present invention, the filling portion forming step may be followed by the cover portion forming step.
In the cover portion forming process, a cover polyolefin sheet 41 is adhered to the boundary portion 34 between the filling portion 3 and the corrosion-resistant coating layer 2 surrounding the filling portion 3 to form a cover portion 4 that covers the boundary portion 34 from above (Figures 10 and 12).

In the filling portion 3 of the metal material 1 (Figure 6) after the filling portion formation process, by preventing the seam lines of adjacent sheet layers from overlapping each other, it is possible to make it difficult for liquids such as water to penetrate into the lower sheet layers and ultimately into the metal material 1. However, liquids such as water may penetrate into the metal material 1 through the boundary portion 34 between the filling portion 3 and the corrosion-resistant coating layer 2 surrounding the filling portion 3.
By carrying out the cover portion forming step, the boundary portion 34 is covered from above, making it easier to prevent the intrusion of liquids such as water.

In the cover forming step, a cover polyolefin sheet 41 is attached by adhering it onto the boundary 34 between the filling portion 3 and the corrosion-resistant coating layer 2 .
In the cover portion forming process, as shown in Figures 10 and 11, the cover portion 4 may be formed by using a single cover polyolefin sheet 41 to cover the filling portion 3 (the uppermost sheet layer) and the boundary portion 34, or as shown in Figures 12 and 13, multiple cover polyolefin sheets may be used to cover only the portion necessary to cover the boundary portion 34, and not to cover a portion of the filling portion 3 (the uppermost sheet layer).
Also, as long as it is capable of covering the border 34, the shape of the cover polyolefin sheet 41 does not have to be rectangular as shown in Figs. 11 and 13, and may be of a random shape or the like.

The thickness of the cover polyolefin sheet 41 is preferably 0.1 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.5 mm or more. It is also preferably 5 mm or less, more preferably 4 mm or less, and particularly preferably 3 mm or less.

10 and 11, when one cover polyolefin sheet 41 is used, the area of the cover polyolefin sheet 41 is preferably ¹⁰⁰ cm2 or more, more preferably 150 cm2 or more, and particularly preferably ²⁰⁰ cm2 or more. Also, it is preferably ¹⁰⁰⁰ cm2 or less, more preferably ^{800 cm2} or less, and particularly preferably ⁶⁰⁰ cm2 or less.

12 and 13, when a plurality of cover polyolefin sheets 41 are used, the area of each cover polyolefin sheet 41 is preferably ⁵⁰ cm2 or more, more preferably ⁷⁵ cm2 or more, and particularly preferably ¹⁰⁰ cm2 or more. Also, it is preferably ⁵⁰⁰ cm2 or less, more preferably ⁴⁰⁰ cm2 or less, and particularly preferably ³⁰⁰ cm2 or less.

The adhesion during the cover formation process is also preferably performed by applying a primer to the cover polyolefin sheet 41, drying the primer, and then applying an adhesive to the cover polyolefin sheet 41.

In the bonding in the cover portion formation process, a primer or adhesive may be applied to the filling polyolefin sheet (33A in the examples shown in Figures 7, 8, and 9(a)) which is the outermost layer of the filling portion 3, or to the cover polyolefin sheet 41, or to both polyolefin sheets.
In order to improve adhesion, it is desirable to coat both polyolefin sheets with a primer or adhesive.

Specific examples of primers and adhesives used for bonding in the cover portion formation process, their preferred application amounts, and the time interval between completing application of the primer and starting application of the adhesive are the same as those described above for the filling portion formation process.

The polyolefin cover sheet 41 used in the cover formation process is preferably roughened on only one side, with the roughened side being the adhesive surface for the filling section 3 and the anticorrosive coating layer 2 (there is no point in roughening the non-adhesive surface of the polyolefin cover sheet 41).

In the filling portion forming process of the present invention, before forming the second or subsequent sheet layers, a partially coated-removed portion 24 may be formed by removing the corrosion-resistant coating layer 2 around the underlying sheet layer so that the portion has approximately the same height as the "underlying sheet layer."
An example of such a process is shown in FIGS.

The formation of the first sheet layer 31 is the same as that shown in Figure 7(a) (Figure 14(a)).

After forming the first sheet layer 31, the anticorrosive coating layer 2 around the sheet layer 31 is removed to form a partially-removed portion 24 (FIG. 14(a')). At this time, the anticorrosive coating layer 2 is removed so that the height of the anticorrosive coating layer 2 below the partially-removed portion 24 is approximately the same as the height of the first sheet layer 31.

After forming the partially-covered portion 24, the second sheet layer 32 is formed on the first sheet layer 31 (FIG. 14(b)). When forming the second sheet layer 32, a filling polyolefin sheet 32A is filled in so as to include the partially-covered portion 24.
As in the case shown in FIG. 7B, the seam line 32B of the second sheet layer 32 and the seam line 31B of the first sheet layer 31 are arranged not to overlap each other.

After forming the second sheet layer 32, the anticorrosive coating layer 2 around the periphery of the sheet layer 32 is similarly removed to form a partially-removed portion 24 (Fig. 15(b')), and then the third sheet layer 33 is formed by filling the partially-removed portion 24 with a filling polyolefin sheet 33A (Fig. 15(c)).

After forming the third sheet layer 33 (i.e., after the filling portion forming process is completed), the cover portion forming process may be performed (Figure 15 (d)).

In the filling portion forming process, by forming the partial coating removal portion 24 before forming the second and subsequent sheet layers, the filling portion 3 has a cone-like shape as shown in Figures 15(c) and 15(d).
By doing this, the boundary 34 between the filling portion 3 and the corrosion-resistant coating layer 2 surrounding the filling portion 3 is no longer in a straight line, so that the intrusion of liquid from the boundary 34 can be more effectively prevented.

The repair method of the present invention can easily repair damage to the corrosion-resistant coating layer of metal materials, and can provide a repair method that provides excellent stability and durability in the repaired portion. Therefore, metal materials repaired by the repair method of the present invention can be widely used to repair steel pipes that make up water pipes for transporting water supply and sewerage, agricultural water, industrial water, etc.; piping for chemicals and cooling water in factories and plants; pipelines for transporting gas, electricity, oil, etc.

REFERENCE SIGNS LIST 1 Metal material 2 Anticorrosive coating layer 3 Filling portion 4 Cover portion 21 Damaged portion 22 Lifted portion 23 Coating-removed portion 24 Partially-removed portion 31 Sheet layer (first layer)
31A Filling polyolefin sheet (first layer)
31B Seam line (first layer)
32 Sheet layer (second layer)
32A Filling polyolefin sheet (second layer)
32B Seam line (second layer)
33 Sheet layer (third layer)
33A Filling polyolefin sheet (third layer)
33B Seam line (third layer)
34 Boundary portion 41 Polyolefin sheet for cover

Claims (7)

1. A method for repairing damage to a corrosion-resistant coating layer of a metal material coated with the corrosion-resistant coating layer made of a polyolefin, comprising:
   a coating removal portion forming step of forming a coating removal portion in which the metal material is exposed by removing the damaged portion of the corrosion-resistant coating layer and the raised portion around the damaged portion; and
   The method includes at least a filling portion forming step of laminating and adhering two or more sheet layers of a filling polyolefin sheet to the coating removal portion to form a filling portion having approximately the same height as the anticorrosive coating layer surrounding the coating removal portion,
   The repair method is characterized in that each of the sheet layers has a seam line formed by joining a plurality of filling polyolefin sheets, and the seam lines of adjacent sheet layers are prevented from overlapping.
2. The repair method according to claim 1 further includes a cover forming step of forming a cover that covers the boundary between the filling portion and the corrosion-resistant coating layer that surrounds the filling portion by attaching a polyolefin sheet for covering the boundary from above.
3. The repair method according to claim 1 or claim 2, in which the bonding in the filling part formation process is performed by applying a primer to the filling polyolefin sheet, drying the primer, and then applying an adhesive to the filling polyolefin sheet.
4. The repair method according to claim 1 or 2, wherein the polyolefin constituting the corrosion-resistant coating layer and the polyolefin constituting the filling polyolefin sheet are chemically identical.
5. The repair method according to claim 1 or claim 2, wherein the thickness of the corrosion-resistant coating layer is 0.5 mm or more and 5 mm or less.
6. The repair method according to claim 1 or claim 2, wherein the metal material is a steel pipe whose inner and/or outer surface is coated with the corrosion-resistant coating layer.
7. 8. The repair method according to claim 7, wherein the steel pipe is a steel pipe for transporting liquids.
   
   

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