JPS5814957B2 - Corrosion prevention method for connecting parts of corrosion-resistant steel pipes - Google Patents

Description

[Detailed description of the invention] TECHNICAL FIELD The present invention relates to a method for preventing corrosion of a connecting portion of a corrosion-resistant steel pipe.

Recently, a method of coating steel pipes with polyethylene has been widely adopted as a corrosion-protection method for steel pipes used for gas piping and the like.

One of the factors is that corrosion-resistant steel pipes can now be manufactured efficiently by coating the steel pipes with polyethylene by extrusion.

However, since it is not possible to weld steel pipes with a corrosion-resistant layer in I size, it is necessary to separately provide a corrosion-resistant layer at the connecting portions of the steel pipes.

As a result of various studies on corrosion prevention of this connection part, it was found that the method of using a stretched sheet is very efficient, and when sealing both ends of the sheet, an uncrosslinked tape mixed with a crosslinking agent is sandwiched between both sides of the sheet. It was concluded that by heat-sealing, the reliability of the sealed portion could be made sufficiently durable for use, and the present invention was completed.

One way to prevent corrosion at the joints of steel pipes is to first apply a compound mainly made of asphalt, and then reinforce the joints with plastic tape.

However, applying tape to steel pipes in a small space is extremely inconvenient and inefficient.

Next, a method of applying a compound mainly composed of asphalt or the like and then reinforcing it with a heat shrinkable tube, or a method of using a shrinkable tube coated with the compound can be considered.

However, heat-shrinkable tubes obtained by the conventional expansion method of applying internal pressure while heating the tube have an inner diameter of about 30 cr at most, which is too small for corrosion protection of steel pipes.

If you try to make a heat-shrinkable tube with a larger inner diameter using the conventional method, you will need very complicated equipment to cross-link the tube, expand it, etc.
There are also many problems in terms of manufacturing technology, such as the difficulty of preventing so-called vertical growth.

On the other hand, if the method of the present invention involves winding a stretched sheet, a large diameter sheet can be easily obtained.

Further, either a method of attaching the adhesive layer to a sheet in advance or a method of covering the steel pipe with the adhesive layer can be adopted.

Also, both the method of sealing after wrapping the sheet and the method of sealing it in advance and making it into a tube shape are more efficient than wrapping tape around the layer as well.

Another point of the present invention is a method for improving the reliability of the seal portion.

First, it was found that the strength of adhesion differs depending on the degree of crosslinking of the polyethylene used as the sheet 3, that is, one using uncrosslinked polyethylene.

Products using cross-linked polyethylene with a gel content of 70% tended to have problems such as the sealing part coming off when heated and shrunk, but sheets with a gel content of 10~
It has been found that such troubles can be largely prevented by using 60-inch cross-linked polyethylene.

Furthermore, uncrosslinked polyethylene (or polyethylene copolymer) containing peroxide between the crosslinked polyethylenes to be heat-sealed
It was found that a reliable seal could be achieved by sandwiching the tape and applying heat and pressure at the same time as the sheet.

Known methods for gluing cross-linked polyethylene sheets include applying liquid peroxide between the sheets and applying heat and pressure; and inserting uncross-linked polyethylene tape coated with liquid peroxide and simultaneously applying heat and pressure. However, this method has the disadvantage that depending on the state of application of the liquid peroxide, voids may remain in the seal area when fused. I found that it was easier to work with, and the seal was more reliable.

Example A polyethylene sheet having a width of 1 m and a thickness of 2 mm was crosslinked by irradiation with an electron beam, and then stretched with a roll to a thickness of about 1 m while heating to about 80°C.

After applying an adhesive layer mainly composed of asphalt to this stretched sheet, it is cut into a predetermined length, spread in a direction perpendicular to the direction of stretching, and dicumyl coated with 100 parts by weight of polyethylene in advance between both ends. A polyethylene tape having a thickness of 0.2 mm and a width of 5 mm, kneaded with 3 parts by weight of peroxide, was sandwiched and heated and pressurized at the same time as the sheet to make a tube-shaped product.

Figures 1a and 1b are partial perspective views of the heat-shrinkable tube made as described above, where a is the heat-shrinkable tube made by sandwiching the polyethylene tape between the overlapping parts of both ends of the sheets, and b is the polyethylene tape. The heat-shrinkable tubes that are inserted between the palms at both ends of the sheet are shown.

In FIG. 1, 1 is a peroxide-containing tape, and 2 is a stretched polyethylene sheet.

The corrosion-resistant layer obtained in this way is placed over the joints of the steel pipes,
By shrinking the steel pipes by heating, the joints of the steel pipes and the corrosion-resistant layer were integrated, and the joints of the steel pipes were able to have the desired corrosion-resistant performance.

[Brief explanation of the drawing]

FIG. 1 is a partial perspective view of a heat shrinkable tube according to the present invention.
1 is a peroxide-containing tape, and 2 is a stretched polyethylene sheet.

Claims (1)

[Claims] 1. A sheet of cross-linked polyethylene (or polyethylene copolymer) with a gel content of 10 to 60 is uniaxially stretched and wound around the connecting part of a steel pipe in a direction perpendicular to the stretching direction.
A tape of uncrosslinked polyethylene (or polyethylene copolymer) mixed with peroxide is sandwiched between both ends of the sheet, and both ends of the sheet are heat-sealed by heating field soil, or by the method described above. A corrosion-resistant steel pipe connection characterized by sealing both ends to form a tube and covering the connection part of the steel pipe, and then heating and shrinking the whole to integrate the connection part of the steel pipe and a corrosion-resistant layer. How to prevent corrosion of parts.