JPH01177384A - Method for preventing corrosion at connection of resin-coated steel pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for preventing corrosion of a resin corrugated RR steel pipe joint, and more specifically, to a method for preventing corrosion of a joint portion of a resin corrugated steel pipe. The present invention relates to a method for preventing corrosion of a resin-coated steel pipe joint, which involves removing a resin layer near the end of the steel pipe and preventing corrosion of a joint consisting of an exposed part of the steel pipe when the two ends are connected by welding or the like.

[Conventional technology]

When the coating resin layer near the ends of two resin-coated steel pipes coated with polyolefin resin is removed and the ends of the two are connected by welding, etc., to prevent corrosion of the connection consisting of the exposed parts of the steel pipes. Generally, the connecting portion is covered with a shrinkable sleeve made of polyolefin resin having a width that overlaps the coating resin layer of each of the two resin-coated steel pipes via an adhesive layer.

In the above corrosion prevention method, the connection portion of the shrink sleeve is coated via an adhesive layer, but since the exposed portion of the steel pipe is directly coated, a sufficiently high temperature cannot be ensured. Therefore, the adhesive constituting the adhesive layer has a softening point (RING AND
Since only adhesives with a low softening point (value measured by the BALL method) of about 120° C. can be used, adhesives with a low softening point that contain a rubber component or an adhesive agent are generally used.

[Problem that the invention seeks to solve]

However, since the above-mentioned adhesive with a low softening point has high water permeability, corrosive substances such as water and salt water can penetrate through the adhesive layer into the connection area after it has been covered with a shrink sleeve, resulting in damage to the connection area. There was a problem in that it caused corrosion.

It is also possible to heat the steel pipe itself to a high temperature using an induction heating device and use an adhesive with a high softening point and low water permeability. At construction sites, there is a problem that it lacks practicality because it requires large equipment.

Therefore, it is an object of the present invention to provide a resin-wrapped r! An object of the present invention is to provide a method for preventing corrosion of steel pipe joints.

[Means for Solving the Problems] As a result of various studies, the present inventors have found that it is possible to cover both ends of the shrink sleeve coated on the connection portion with a specific resin by heat-sealing the resin-coated steel pipe. It has been found that this method is effective in preventing corrosion of connections, and that the above objectives can be achieved.

The present invention has been made based on the above findings, and consists of two resin sheets coated with a polyolefin resin.
In a corrosion prevention method in which a connecting portion of a pipe is covered with a shrinkable sleeve made of a polyolefin resin by polymerizing the coating resin layer of each of the two resin-coated steel pipes via an adhesive layer, both ends of the shrinkable sleeve are The present invention provides a method for preventing corrosion of resin-coated steel pipe joints, which is characterized by covering each joint with a modified polyolefin sheet by heat-fusion.

EMBODIMENT OF THE INVENTION Hereinafter, one preferable embodiment of the corrosion prevention method of the resin-coated steel pipe connection part of this invention is demonstrated based on drawing.

FIG. 1 is a partial cross-sectional view schematically showing an embodiment of the present invention, and FIG. 2 is an enlarged partial cross-sectional view showing an enlarged main part thereof.

In FIGS. 1 and 2, 1 and 1a are two resin-coated steel pipes coated with coating resin layers 2 and 2a respectively made of polyethylene (polyolefin resin),
Both resin-coated steel pipes 1 and 1a are welded and connected at approximately the middle position in FIG. 1. Both of the above resin-coated steel pipes 1 and 1a
Since the coating resin layer of the connecting portion having a predetermined width sandwiching the welding point is peeled off when the two are welded, the coating resins M2 and 2a are not present in the connecting portion. Therefore, after welding, the surface of the steel pipe is exposed in the connection section.

Corrosion prevention of the above-mentioned joint where the surface of the steel pipe is exposed is achieved by placing the shrinkable sleeve 3 made of stretched polyethylene (polyolefin resin) coated with adhesive on the inside in a predetermined position. At the same time, the adhesive layer 4 (the first
This is done by tightly covering the connecting portion with the shrinkable sleeve 3 via a sleeve (not shown in the figure). At this time, the shrinkable sleeve 3 is of a width that overlaps the resin layers 2 and 2a of the two resin-coated steel pipes 1 and 1a, respectively, and when the covering with the shrinkable sleeve 3 is completed, The vicinity of both ends of the shrink sleeve 3 are made to overlap each of the coating resin layers 2 and 2a.

It should be noted that the shrinkable sleeve 3 is not particularly limited and can be manufactured by a conventional method. Specifically, for example, after polyethylene is formed into a sheet by extrusion molding or the like, it is irradiated with radiation such as electron beams, It can be manufactured by performing a so-called stretching process in which the crosslinked sheet is formed, then heated to a predetermined temperature, stretched, and cooled in that state.

In the method of the present invention, both ends 3a of the shrinkable sleeve are further provided.
is characterized by being covered with a modified polyolefin sheet such as an acid-modified polyolefin sheet, for example, a modified polyethylene sheet 5, by heat-fusion.

Preferred specific examples of the modified polyethylene resin constituting the modified polyethylene sheet 5 include maleic anhydride-modified polyethylene, which can be prepared by, for example, adding a reaction initiator and maleic anhydride to polyethylene and melt-kneading it, or It is prepared by dropping a reaction initiator and maleic anhydride into a solution of polyethylene. This modified polyethylene resin has excellent water permeability and has a softening temperature of approximately 15% by the RING AND BALL method.
The temperature is 0°C or higher.

According to the present invention, by heat-sealing the modified polyethylene sheet 5 as described above, the adhesive layer 4 for fixing the shrinkable sleeve 3 has the property of being easily permeable to corrosive substances such as water and salt water. Even if the resin-coated steel pipe connection portion is made of a rubber-based adhesive, it is possible to reliably prevent the corrosive substances from penetrating the resin-coated steel pipe connection portion. Furthermore, since the heat-sealing of the modified polyethylene sheet 5 is performed on the coating resin layer 2.2a and the shrink sleeve 3, the modified polyethylene sheet 5 is heated to a higher temperature than when it is melt-sealed to the exposed surface of the steel pipe. Can be heated. Therefore, even if the modified polyethylene sheet 5 has a high softening point, the sheet 5
can be reliably fused.

Next, the method for preventing corrosion of resin-coated steel pipe joints according to the present invention will be described in more detail.

The diameter of the resin-coated steel pipe to which the method of the present invention can be applied is not particularly limited, but a preferred range is a pipe diameter of 200 fi to 2000 fi. In addition, the polyolefin resin constituting the coating resins W12 and 2a in the resin-coated steel pipe is not limited to the polyethylene shown in the above embodiment, but also olefin polymers such as polypropylene, which are usually used for the purpose of corrosion prevention, Alternatively, olefin copolymers containing ethylene, propylene, etc. as one monomer can be mentioned.

The polyolefin resin constituting the shrinkable sleeve 3 that can be used in the method of the present invention is not limited to the above-mentioned stretched polyethylene, and examples include polypropylene, ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, and polyvinyl chloride. Preferred examples include thermoplastic resins produced by stretching according to conventional methods.

Although there is no particular restriction on the adhesive to be applied to the shrinkable sleeve 3, the method of the present invention uses a highly water permeable adhesive such as a rubber adhesive or an adhesive containing an adhesive agent. It is particularly effective when used.

Furthermore, the shrinkable sleeve 3 is not limited to being formed into a sleeve shape; for example, by forming it into a tape shape and wrapping the tape-like shrink sheet around the connecting portion, the sleeve shape can be changed as a result. It may be formed. In addition, when using the shrinkable sleeve 3 which is previously formed into a sleeve shape, the resin corrugation rj and the steel pipe 1 or 1a are usually inserted into the shrinkable sleeve 3 before welding the steel pipe.

The modified polyolefin constituting the modified polyolefin sheet that can be used in the method of the present invention is not limited to the modified polyethylene shown in the embodiment above,
In addition to maleated polyethylene and polypropylene,
Examples include ethylene vinyl acetate copolymer, ethylene lower alkyl acrylate or methacrylic acid copolymer, and ethylene acrylic acid or methacrylic acid copolymer, and these may be used alone or as a mixture of two or more types.

Further, as a method of heat-sealing the modified polyethylene sheet 5 to the predetermined position, the modified polyethylene sheet 5 having a single layer structure is attached to both ends 3a of the shrinkable sleeve 3.
After placing it around the entire tube in a position that covers each of the
There is a method in which the sheet is heated to a softening temperature or higher before being fused to be fused. At this time, heating may be performed by applying hot air to the modified polyethylene sheet 5, or by placing a glass cloth sheet over the sheet and heating with a propane torch or the like from above.

Note that the modified polyolefin sheet may have a laminated structure, for example, laminated on a shrinkable polyolefin sheet. In this case, the shrinkable polyolefin sheet may be in the shape of a sleeve or a tape.

In the case of a sleeve shape, a layer of modified polyolefin sheet is formed on the inner surface as in the case of the shrink sleeve. That is, it has a structure in which a shrink sheet is laminated on the outside of a modified polyolefin sheet.

The heat-sealing of the modified polyolefin sheet having the laminated sleeve shape can be carried out through substantially the same process as that for covering the former shrink sleeve.

In the case of a tape shape, a layer of modified polyolefin sheet is wound around the steel pipe, and then heat treatment is performed in the same manner.

〔Effect of the invention〕

According to the corrosion prevention method of the present invention, corrosion protection of a resin-coated steel pipe joint covered with a shrink sleeve can be reliably and easily performed.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view schematically showing an embodiment of the present invention;
FIG. 2 is an enlarged partial sectional view showing the main part thereof. 1.1a...Resin coated steel pipe 2.2a...Coating resin layer 3...Shrinkable sleeve 3a...End portion 4...Adhesive layer 5...Modified polyethylene sheet Patent applicant Nippon Steel Corporation Ube Industries Co., Ltd. Figure 1-54.

Claims (2)

[Claims] (1) The connecting portion of two resin-coated steel pipes coated with polyolefin resin is polymerized into the coating resin layer of each of the two resin-coated steel pipes through an adhesive layer using a shrink sleeve made of polyolefin resin. A method for preventing corrosion of a resin-coated steel pipe joint, characterized in that both ends of the shrink sleeve are covered by heat-sealing modified polyolefin sheets. (2) The method for preventing corrosion of a resin-coated steel pipe joint according to claim (1), wherein the modified polyolefin sheet is a single layer, or a shrinkable polyolefin sheet is laminated on the outside thereof.