JPH0358903B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention is applicable to civil engineering, construction work, etc.
Alternatively, the present invention relates to a method of coating the periphery of the weld joint part of a steel pipe pile to be driven on a coastline, particularly the weld joint part of a steel pipe pile whose main body is mill-coated except for the end part to be welded. [Background of the Invention] Steel pipe piles are driven into the ground at construction sites for the purpose of protecting the ground, or on the coastline for the purpose of protecting the coastline. Conventionally, such steel pipe piles have been made of steel pipes that have not undergone any special processing other than normal anti-rust processing. However, in recent years, with the aim of ensuring long-term use of steel pipe piles and corrosion protection reliability, the application of resin coating to steel pipe piles has been studied in recent years. Initially, a method of applying resin coating to the surface of the steel pipe pile by spraying a liquid resin material such as resin paint to form a resin coating was considered.
The problem with these resin coatings is that it is difficult to obtain practically sufficient corrosion resistance. On the other hand, polyolefin resins such as polyethylene have long been known as highly corrosion-resistant resin materials, but these are difficult to dissolve in ordinary solvents, and for this reason, methods for forming resin coatings using spraying, etc. Therefore, it is not possible to form a polyolefin resin film on the surface of steel pipe piles. For this reason, a coating layer of highly anti-corrosion resin such as polyolefin resin is applied in advance during construction when manufacturing steel pipe piles, such as extrusion coating with molten resin, melting resin powder, wrapping with resin tape or resin sheet, etc. It is conceivable to use a method of forming the film (ie, mill coat). According to studies conducted by the present inventors, it has been found that when steel pipe piles are mill-coated with polyolefin resin or the like as described above, a product with high anticorrosion performance and useful in practical use can be obtained. However, as a result of further examination of the practicality of mill-coated steel pipe piles, it was found that there were also problems with the anti-corrosion coating of the weld joints of steel pipe piles. In other words, when long steel pipe piles are required, a normal steel pipe pile driving machine is not tall enough to drive the long steel pipe piles as they are, so first, at the construction site, etc. It is common to drive a steel pipe pile of normal length halfway, then weld and connect another steel pipe pile to its upper end, and then drive it. This welding work is usually
This is done by driving one steel pipe pile part way in advance, placing the lower end of another steel pipe pile on top of it, and welding the ends together. The steel pipe piles joined in this way are then buried by a continuous driving method. Mill-coated steel pipe piles designed for such welding are usually manufactured with the surface of the steel pipe portion exposed at the end in order to facilitate welding work. Therefore, since the surface of the steel pipe is exposed at the welded portion (weld joint), it is necessary to apply an anti-corrosion coating to this portion after welding. As a corrosion-proof coating method for the weld joint, it is possible to form a resin coating by spraying resin paint on the surface of the weld joint, but as with the case of coating steel pipes, these resin coatings However, there is a problem in that it is difficult to obtain practically sufficient corrosion resistance. Traditionally, tube-shaped,
Alternatively, it is known to cover with a sleeve-shaped thick heat-shrinkable crosslinked polyolefin inner cover sheet to provide corrosion resistance and resistance to the impact of earth and sand during burial work. The present inventor has focused on the anti-corrosion coating technology for the weld joints of the above-mentioned transportation pipelines, and has conducted intensive research into whether the anti-corrosion technology can be used for anti-corrosion treatment of steel pipe piles with similar shapes. I did it. As a result, the tube-shaped heat-shrinkable sheathing materials that have been commonly used in the past are difficult to heat-shrink, especially when welding and joining steel pipe piles with the steel pipe piles partially driven. It has been found that it is difficult to temporarily fix the coating material at the weld joint, which is performed prior to coating the weld joint with the heat-shrinkable coating material (covering by utilizing the heat shrinkability of the coating material). For this reason, next, a sleeve-shaped thick heat-shrinkable cover sheet is wrapped around the weld joint, and with both ends of the sheet overlapped, a fixing device is used to form a tube shape, and then the heat-shrinkable cover We also investigated applying heat from a burner to the surface of the sheet to make the cover sheet heat-shrinkable to cover the weld joint. As a result, it was confirmed that this coating method could easily cover the weld joints of steel pipe piles in an erected state. However, according to the study of the present inventor, when a bonded steel pipe pile whose weld joint part is covered with an anti-corrosion coating sheet as described above is further driven, and both ends of the cover sheet are fixed by mechanical engagement, It was found that the engaging part was easily damaged. It has also been found that the cover sheet closely covering the weld joint part deteriorates and the mechanical properties tend to deteriorate. If this cover sheet for corrosion protection coating deteriorates, it becomes difficult to protect the driven steel pipe pile from corrosion over a long period of time, which poses a major problem in the practical use of steel pipe piles. The present inventor conducted research to determine the cause of the deterioration of the cover sheet that tightly covers the weld joint, and found that the deterioration is mainly caused by the following:
It was discovered that this is due to thermal deterioration of the cover sheet that occurs during the process of shrinking and adhering the cover sheet using a heating burner, and residual air in the adhesive layer inside the cover sheet. In other words, when performing heat shrinkage and adhesion work using a heat-shrinkable cover sheet on the weld joint of a pipeline for transporting crude oil, natural gas, etc., the area around the center (bead) of the weld joint is first heated with a burner. and then sequentially heat both sides,
A commonly used method is to cause the cover sheet to shrink due to heat, thereby causing the cover sheet to adhere tightly to the periphery of the joint. This is said to be because the bead portion tends to protrude slightly outward, and when heat shrinkage starts from both ends, air is likely to be trapped around the bead. Furthermore, according to the study of the present inventor, when a bonded steel pipe pile whose weld joint part is covered with an anti-corrosion coating sheet as described above is further driven and buried, the lower end of the coated part It was found that the anti-corrosion coating sheet peeled off, and as a result, corrosion was more likely to occur at the joining joint. The inventor of the present invention conducted further research to investigate the cause of the peeling of the anti-corrosion coating sheet, and as a result found that the overlapping portion of the coating sheet became extremely thick, and at that point, a step was removed from the surface of the steel pipe pile. Because of the formed and protruding shape, the lower end (step part) of the overlapping part cannot resist the impact that mainly acts in the length direction of the pile, which occurs when driving the steel pipe pile into the ground. It has been found that the appearance of peeling of the anti-corrosion coating sheet at the lower end is the main cause of the peeling of the anti-corrosion coating sheet. It has also been found that this peeling cannot be effectively solved by simply increasing the bonding strength of the overlapped portion of the covering sheets. In other words, conventional methods for joining the overlapping parts of the coating sheets include using mechanical joining means, or using heat-sealing tape to connect the joined parts (the outer edge of the anti-corrosion sheet and the other edge wound inside). Some methods have been used, such as attaching the adhesive to the side surface of the sheet), but no matter which method improves the bonding strength, it does not effectively solve the above-mentioned problem of peeling. For example, in Japanese Patent Application Laid-open No. 56-75825, after covering the joints of steel pipes or electric wire cables with a heat-shrinkable cover sheet, By adhering the rolled-up part (the part that contacts the sheet surface on the other end side) with heat-sealing tape in such a way that both ends of the tape enter into the inside of the stacked part of the cover sheet in a leap shape. ,
A method for easily and firmly establishing the edge of a cover sheet is disclosed. However, even if this method is used to bond the sheathing parts of steel pipe piles, the problem of the difference in level will become larger, and the above-mentioned problem (when driving welded steel pipe piles, the lower end of the overlapping part of the anti-corrosion sheathing sheet) It is not an effective solution to the problem of peeling of anti-corrosion coating sheets. [Structure of the Invention] The present inventor has discovered that when a weld joint is coated with the above-mentioned heat-shrinkable anti-corrosion coating sheet, the anti-corrosion performance is reduced due to thermal deterioration that occurs in the anti-corrosion coating sheet, and the welded steel pipe pile covered with the anti-corrosion coating is As a result of further research aimed at solving the problem of peeling (turning up) of the anticorrosive coating sheet that occurs at the lower end of the overlapped part of the anticorrosive coating sheet when pouring, we found that The shrink adhesion operation is changed, and the heat seal tape is applied so as to cover substantially the entire area of the overlapping part.
The cover sheet is arranged so as to slightly protrude from the edge of the cover sheet, and the protruding portion is heat-bonded to the surface of the mill coating portion of the steel pipe pile at least before burying the covered weld joint portion. We have discovered that by reducing (smoothing) the large step difference at the lower end of the overlapping portion, it is possible to effectively prevent the anticorrosive coating sheet from turning over at the weld joint of a steel pipe pile, and have arrived at the present invention. The present invention provides heating around the weld joint of a steel pipe pile in which another mill-coated steel pipe pile is connected by welding to the upper end of a mill-coated steel pipe pile that is driven vertically into the ground. A heat-shrinkable cross-linked polyolefin cover sheet with a fusible adhesive layer is wrapped around it, both ends of the cover sheet are overlapped with each other, and a heat seal tape is applied on the overlapping part, and the bottom end of the cover sheet is wrapped with a heat-shrinkable cross-linked polyolefin cover sheet. The overlapping portions of the heat-shrinkable cover sheets and the heat-seal tape are heat-sealed together so that they protrude from the edges in the driving direction of the steel pipe pile, and the heat-shrinkable cover sheets A tubular body is formed, and then the flame of a gas burner is applied sequentially upward from the bottom of the tubular body to heat and shrink the tubular body, so that the tubular body is brought into close contact with the circumferential surface of the steel pipe pile. The present invention provides a method for coating a weld joint of a mill-coated steel pipe pile in an erected state, characterized in that the weld joint portion of a mill-coated steel pipe pile in an erected state is bonded with the adhesive layer to form an anticorrosive coating. That is, according to the study of the present inventor, when covering an upright steel pipe pile with a heat-shrinkable cover sheet, in a known method, the upper surface of the tubular body of the heat-shrinkable cover sheet is exposed to high heat due to flame for a long time. A corrosion-resistant coating layer with poor durability is formed due to thermal deterioration due to exposure to rising air currents of steel pipe piles. It has been found that the inclusion of air bubbles causes disadvantages. Therefore, the inventors of the present invention have found that the above-mentioned drawbacks can be solved at the same time by a simple method of changing the heating direction, and have arrived at the present invention. Further, according to the covering method of the present invention, when a thick heat-shrinkable cover sheet is wrapped around a steel pipe pile and the tips thereof are overlapped to form a tubular body,
A long and wide heat-seal tape is made to protrude from the edge of the heat-shrinkable cover sheet in the driving direction of the steel pipe pile so as to substantially cover the overlapped portion. The overlapped portions of the heat-shrinkable cover sheet and the heat-sealing tape are bonded together to form a tubular body of the heat-shrinkable cover sheet, and the anticorrosion coating layer is applied by heating the tubular body. At the same time, the protruding portion of the heat-sealing tape covers the large step difference in the overlapping portion of the anticorrosion coating layer, smoothing out the step, and protecting the step portion by the coating. , it is possible to form an excellent anti-corrosion coating layer that can sufficiently withstand the impact during driving of steel pipe piles. Hereinafter, the coating method of the present invention will be explained in more detail with reference to the drawings. FIGS. 1a to 1d are perspective views sequentially showing one example of the steps of the coating method of the present invention. First, as shown in Fig. 1a, the joint part (welded joint part) of a steel pipe pile 1 having a mill coating layer (plastic resin layer) 2 driven underground, As shown in figure b, wrap a heat-shrinkable cross-linked polyolefin cover sheet 4 around the entire exposed part) 3, and overlap the ends of the cover sheets 4 in the longitudinal direction (heat-shrinkable direction) with each other. , Next, on the overlapping portion 5 of the cover sheet 4, a material is placed on the overlapping portion 5 which is longer than the length in the width direction of the cover sheet 4 (the length in the direction perpendicular to the heat shrinking direction) and wider than the overlapping portion 5. A heat-resistant heat-sealing tape 6 having a width is applied so as to cover almost the entire area of the overlapped portion, and from the edge of the cover sheet 4 in the driving direction of the steel pipe pile 1 (the direction of the arrow in figure a). Place it so that it slightly protrudes. Next, the overlapping portion 5 of the heat-shrinkable cover sheet 4 and the heat seal tape 6 are heated and fused together to form a tubular body of the heat-shrinkable cover sheet 4. The next heat-shrinking operation of the heat-shrinkable cover sheet 4 is performed by directing the flame of the gas burner so as to move sequentially upward from the bottom of the tubular body.
This heating operation can also be performed mechanically using a device in which a heating member (such as a ring burner) equipped with a plurality of gas burners can be moved up and down. In the covering method of the present invention, it is particularly important to heat and heat-shrink the tubular body of the heat-shrinkable cover sheet placed around the steel pipe pile from the bottom upwards. If the tubular body is heated from the upper part downward with the flame of a gas burner, even if the upper part of the tubular body has completed its thermal contraction, the lower part of the tubular body will be heated, so the heating process will be delayed. Over time, the upper part of the tubular body is exposed to the high-temperature rising air generated by the flame of the gas burner, and the surface of the tubular body partially burns and deteriorates, but the coating method of the present invention Now, as shown in Fig. 1c, the high-temperature rising air current of the flame of the gas burner 7 does not reach the part 8 of the tubular body that has been completely heat-shrinked. If care is taken to prevent such deterioration, the tubular body will not suffer from the above-mentioned firing deterioration due to the high-temperature rising air current after the surface of the tubular body is heated and shrunk. Furthermore, when the tubular body is heated from the top to the bottom with the flame of a gas burner, the gas existing between the steel pipe pile and the tubular body is heated by the heating operation and exhausted upward. However, the escape route is blocked by the heat shrinkage in the upper part of the tubular body, and the stagnant gas that cannot escape is absorbed into the surface of the steel pipe pile and the coating layer 4.
However, in the coating method of the present invention, the upper part of the tubular body is opened until the heating operation is completed, as shown in FIG.
As mentioned above, there is almost no possibility that gas that cannot escape is trapped between the surface of the steel pipe pile 1 and the anticorrosive coating layer 4. As described above, the entire cover sheet 4 of the tubular body is heated and thermally contracted, as shown in Figure d.
It is closely bonded to the circumferential surface of the steel pipe pile 1 to form the anticorrosive coating layer 4, and the protruding portion 7 of the heat seal tape 6 is heat bonded to the surface (mill coat portion) of the steel pipe pile 1. Note that the heat-bonding of the protruding portion of the heat-sealing tape to the surface of the mill coat portion can be performed at any time. For example, the period is selected immediately after the formation of the tubular body of the heat-shrinkable cover sheet, or after the heat-shrinkable cover sheet is tightly joined to the weld joint. The heat-shrinkable cover sheet used in the coating method of the present invention may be any type of known heat-shrinkable crosslinked polyolefin cover sheet as long as it is composed of a heat-shrinkable sheet layer and a heat-adhesive adhesive layer. It may be. This heat-shrinkable sheet layer has a heat-shrinkage temperature of, for example, about 80 to 200°C, particularly preferably 90 to 200°C.
At about 180℃, the shrinkage rate is about 20-80%,
It is particularly preferably formed from a cross-linked polyolefin sheet, particularly a cross-linked polyethylene sheet having a content of about 30 to 70%. The heat-shrinkable sheet has a degree of crosslinking of approximately 20 to 90%, particularly 30 to 80%, as indicated by the gel fraction described below.
From the viewpoint of heat resistance, it is preferable that the crosslinked polyolefin be made of a crosslinked polyolefin having a certain degree of heat resistance. The above gel fraction can be determined by placing the sample (cross-linked plastic film or sheet) in xylene,
It is the value obtained by dividing the weight (Ag) by the weight (Bg) of all the samples used while refluxing at a temperature of about 130° C. for about 10 hours, multiplied by 100, and is expressed by the following formula. Gel fraction = (A/B) x 100 (%) In addition, the adhesive layer of the heat-shrinkable cover sheet has an adhesive strength of about 2 at room temperature to the metal surface of the steel pipe pile.
-20Kg/cm, particularly preferably about 5-15Kg/cm, and about 0.05-5Kg/cm at about 60-80℃.
cm, particularly preferably about 0.1 to 3 kg/cm, is preferably made of a heat-fusible adhesive. For example, an adhesive composition containing an olefin polymer or a modified polymer thereof as a main component and appropriately blending additives such as other thermoplastic polymers, tackifiers, antioxidants, and inorganic fillers. An adhesive layer having a thickness of about 0.1 to 3 mm, particularly about 0.2 to 2 mm, is suitable from the viewpoint of adhesive strength and ease of application. The heat-sealing tape may be, for example, a flexible, strong, thin, heat-resistant tape comprising a cross-linked plastic layer and a heat-adhesive adhesive layer. In addition, the heat seal tape mentioned above is
A structure may also be employed in which a heat-resistant reinforcing layer (for example, a glass cloth layer, an aluminum foil layer, a silicone resin layer) is further provided on the outer surface of the crosslinked plastic layer. The cross-linked plastic layer can be cross-linked to an appropriate degree of cross-linking (for example, approximately 20 to 90% as expressed by the gel fraction described below) using active energy rays such as electron beams, α rays, γ rays, and β rays. Particularly preferably 25-80%
polyolefins (polyethylene, ethylene-vinyl acetate copolymers,
(ethylene-propylene copolymer, ethylene-acrylonitrile copolymer, polypropylene, etc.),
It may be made of a flexible, high-strength plastic film or sheet made of polyvinyl chloride, polyester, polyamide, or the like. In addition, the heat-adhesive adhesive layer described above is about 50 to
It can be heated and bonded at a temperature of 180℃, especially about 60 to 160℃, and the adhesive strength (at 25℃) to the surface of the mill coating layer of steel pipe piles is about 2 to 30Kg/cm, especially about 3 to 20Kg/cm. It is particularly suitable for the protection of the overlapping portion 5 of the covering layer 4 that it is made of a hot melt type adhesive with peel strength (180 degree peel strength). Examples of adhesives include polyethylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-(meth)acrylonitrile copolymer, ethylene-acrylonitrile-methaglycidyl acrylate copolymer, and ethylene-vinyl acetate copolymer. Ethylene polymers such as metaglycidyl acrylate copolymers, polypropylene, polyvinyl chloride, polyesters, polyamides, or modified products of these polymers (e.g., maleated polyethylene, maleated ethylene copolymers, maleated polypropylene) Suitable are hot melt type adhesives containing as a main component, a suitable tackifier (eg, coumaron resin, coumaron-indene resin, petroleum resin, aromatic hydrocarbon resin), and other additives. The adhesive is treated with active energy rays as described above so as to have an appropriate degree of crosslinking (for example, about 5 to 50%, particularly about 10 to 40%, expressed as a gel fraction). It is optimal in terms of adhesive strength (shearing force) at high temperatures that can withstand the heat shrinkage stress applied when the tubular body of the heat shrinkable cover sheet is heated. In the present invention, the thermal bonding of the tip of the heat-shrinkable cover sheet and the heat-sealing tape and the heating may be performed using various heating wires, electric heaters, gas burner flames, and the like. The coating method of the present invention is suitably applied to anti-corrosion coating of steel pipe piles used in general civil engineering and construction, particularly port dredging, seawalls, etc. Steel pipe piles coated by the coating method of the present invention can be used for an extremely long time (approximately 20 to 40
An anti-corrosion coating layer with anti-corrosion performance of 1 year) is formed. Next, Examples and Comparative Examples of the present invention will be shown. Example 1 A polyethylene-coated steel pipe pile with a diameter of 1016 mm and a length of 12 m coated with low-density polyethylene containing carbon black with a thickness of 3 mm is driven into the soil leaving the top 1 m, and another pile of the same size is driven on top of it. After welding and connecting the polyethylene-coated steel pipe piles, we removed rust and dirt from the area 150mm above and below the weld bead that was not coated with polyethylene.
The area was covered with a heat-shrinkable cross-linked polyethylene cover sheet. In other words, first heat the surface of the steel pipe to 120℃.
After preheating to above, the thickness is 1.0 mm, and the gel fraction is 50%.
It consists of a heat-shrinkable crosslinked polyethylene sheet with a shrinkage rate of 30% at 150°C, an ethylene-vinyl acetate copolymer, a styrene-butadiene copolymer, a tackifier, an antioxidant, and carbon black.
Softening temperature as measured by ASTM-E28
Width laminated with 1.5mm thick adhesive layer with 133℃
Wrap a 600mm heat-shrinkable cover sheet loosely in the circumferential direction so that both ends overlap by 75mm, then
A polyethylene heat seal tape of 150 mm, thickness 1.5 mm, and length 670 mm is arranged so that the center of the heat seal tape in the width direction matches the tip of the upper layer of the overlapping portion of both tips of the heat-shrinkable cover sheet. A heat-shrinkable cover sheet was bonded from the surface while being heated using a propane gas burner to form a tubular body of a heat-shrinkable cover sheet. At this time, the top and bottom of the tubular body are placed on the polyethylene (milcoat layer) of the steel pipe pile coating layer.
The heat seal tapes were arranged so that they overlapped by 150 mm, and the lower end of the heat seal tape protruded 70 mm below the tubular body formed by the heat shrinkable cover sheet. Next, with the steel pipe pile in between, two workers used a propane gas burner to heat-shrink the tubular heat-shrinkable cover sheet sequentially from the lower tip in the circumferential direction, thereby applying heat and shrinkage to the polyethylene layer on the steel pipe pile. Welded on top. Once the bottom circumferential direction is completed, heat shrink the upper part little by little along the circumferential direction, and repeat this process until the top circumferential direction shrinks and is tightly attached to cover the weld joint. completed. Shrink coating time was approximately 5 minutes. After shrinking, the surface of the polyethylene layer of the heat-shrinkable cover sheet was observed after being cooled to ambient temperature (approximately 30°C), and no damage due to burning was observed, indicating that it could fully demonstrate its performance. Next, peel off the top half of the polyethylene layer and use a portion of it (the center of the top half) to create an ASTM
Tensile test using D-638 (tensile strength and tensile elongation)
The oxidative deterioration induction period was measured using the DSC method, and as shown in Table 1, almost no deterioration occurred. Furthermore, after the polyethylene layer was peeled off, the flow state of the adhesive layer on the surface of the steel pipe was observed, and it was found that the adhesive layer adhered well to the surface of the steel pipe and no air bubbles were observed. Comparative Example 1 After forming a tubular body of a heat-shrinkable cover sheet at the weld joint of a steel pipe pile in the same manner as in Example 1, the cover sheet was heat-shrinked by the following method. First, the top of the weld bead located at the center of the sheet is heat-shrinked along the circumferential direction, then the upper half is heat-shrinked from bottom to top, and then the lower part is shrunk from top to bottom. I let it happen. Shrink coating time was 11 minutes. After shrinking, the surface of the polyethylene layer of the heat-shrinkable cover sheet was observed after cooling to the ambient temperature (approximately 30°C), and damage to the surface due to overheating was observed, especially at the bead and the area immediately below it. . Next, the upper half of the polyethylene layer was peeled off, and a part of it (the center of the upper half) was subjected to a tensile test and the measurement of the oxidative deterioration induction period in the same manner as in Example 1. As shown in Figure 2, it was found that the physical properties deteriorated significantly. Furthermore, when the flow state of the adhesive layer on the surface of the steel pipe was observed after the polyethylene layer was peeled off, it was found that a large number of air bubbles were present, particularly under the bead and in the area below it. Comparative Example 2 After forming a tubular body of a heat-shrinkable cover sheet at the weld joint of a steel pipe pile in the same manner as in Example 1, the cover sheet was heat-shrinked by the following method. First, with a steel pipe pile in between, two workers used a propane gas burner to heat-shrink the tubular heat-shrinkable cover sheet sequentially in the circumferential direction starting from the upper tip and placing it on the polyethylene layer on the steel pipe pile. Closely attached. Once the top circumferential direction is completed, heat shrink the lower part little by little along the circumferential direction, repeat this process until the bottom circumferential direction shrinks and is tightly attached, and cover the weld joint. completed. Shrink coating time was approximately 18 minutes. After shrinking, the surface of the polyethylene layer of the heat-shrinkable cover sheet was observed after cooling to ambient temperature (approximately 30°C), and damage to the surface due to overheating was observed throughout. Next, the upper half of the polyethylene layer was peeled off, and a part of it (the center of the upper half) was subjected to a tensile test and the measurement of the oxidative deterioration induction period in the same manner as in Example 1. As shown in Figure 2, it was found that the physical properties deteriorated significantly. Furthermore, when the fluid state of the adhesive layer on the surface of the steel pipe was observed after the polyethylene layer was peeled off, the presence of many air bubbles was observed throughout. 【table】

[Brief explanation of drawings]

1A to 1D are perspective views schematically showing an example of a method of covering a weld joint portion of a mill-coated steel pipe pile according to the present invention. 1: steel pipe pile, 2: mill coating layer, 3: weld joint part, 4: heat-shrinkable cover sheet,
5: Overlapping part, 6: Heat seal tape,
7: Gas burner.

Claims (1)

[Claims] 1 Heat-fusion bonding is applied around the weld joint of a steel pipe pile, which is formed by welding a mill-coated steel pipe pile to the upper end of a mill-coated steel pipe pile that is driven vertically into the ground. A heat-shrinkable cross-linked polyolefin cover sheet having an adhesive layer is wrapped around the cover sheet, and both ends of the cover sheet are overlapped with each other, and a heat seal tape is applied over the overlapping part, and the lower end is attached to the edge of the cover sheet. The tubular body of the heat-shrinkable cover sheet is formed by placing the heat-shrinkable cover sheet in a stacked manner so as to protrude in the driving direction of the steel pipe pile, and heat-sealing the overlapping portion of the heat-shrinkable cover sheet and the heat-sealing tape together to form a tubular body of the heat-shrinkable cover sheet. Then, the flame of the gas burner is applied sequentially upward from the bottom of the tubular body to heat and shrink the tubular body, so that the tubular body is brought into close contact with the circumferential surface of the steel pipe pile. A method for coating a weld joint part of an erected mill-coated steel pipe pile, characterized in that the weld joint part of an erected mill-coated steel pipe pile is bonded with the adhesive layer to form an anti-corrosion coating.