JPS6112333A - Corrosion-resistant coated steel pipe and manufacture thereof - 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 [Technical Field of the Invention] The present invention relates to a corrosion-resistant coated steel pipe, particularly a corrosion-resistant coated steel pipe used for transporting combustible gas such as city gas, and a method for manufacturing the same.

[Technical background]

Conventionally, the steel pipes used for gas transportation piping and water supply piping, which are buried underground, are galvanized f! Four-pipe pipes were the mainstream, but methods such as wrapping anti-corrosion tape around the outer surface of galvanized steel pipes were also adopted in an attempt to maintain corrosion-proofing performance over a long period of time.

However, winding with this force-negative tape has poor workability and is not always reliable in overlapping areas, and even if the tape is carefully wound around irregularly shaped areas, complete corrosion protection is not achieved. It's difficult to say it's effective.

If the anticorrosion effect is not sufficiently exhibited, corrosion will progress from that part and eventually the hole will penetrate.

Even if a steel pipe is susceptible to pitting corrosion, it will not be a serious problem if the fluid being transported inside the pipe is tap water, but for example, if city gas or LPG is being transported. In the case of steel pipes, the leakage of flammable gas from the pipes may continue, causing explosions or fires, posing a danger not only to nearby facilities but also to people, and having a large social impact.

For this reason, coating galvanized steel pipes with synthetic resin has been considered for about 10 years and has already been carried out.

These methods include, for example, as shown in Figure 8, the raw steel pipe is cleaned, then plated, and then chemically treated to coat it with a synthetic resin, and as shown in Figure 9, the inner and outer surfaces of the steel pipe are plated. There is a method of removing unnecessary plating on the inner or outer surface, and then subjecting the plated surface to a chemical conversion treatment and coating it with a synthetic resin.

However, these conventional methods have many steps;
Not only are there operational inconveniences such as the high unit consumption and the difficulty of removing only one side (in this case, separate equipment is required), but also the hydrogen gas generated when chemical conversion treatment is performed. is occluded and released in the next synthetic resin coating step, which may affect the adhesion of the synthetic resin coating and prevent it from exhibiting a stable anticorrosion effect.

Generally, when water enters a plated surface and corrosion occurs, the corrosion progresses gradually, reducing the adhesion of the synthetic resin coating and causing peeling.

Under these circumstances, the development of new technology for stable corrosion-resistant pipes and their manufacturing methods has been awaited.

[Purpose of the invention]

The object of the present invention is to provide a corrosion-resistant coated steel pipe that does not or hardly corrode over a long period of time in underground pipes for fluid transport, especially gas pipes, which are laid underground. It is.

[Summary of the invention]

In order to achieve the above-mentioned object, various studies have been carried out to achieve the present invention, and in providing a synthetic resin layer on the surface of a steel pipe, at least an iron-zinc alloy layer, a zinc hydroxide layer, and a pretreatment layer are provided on the surface of the steel pipe. Corrosion-resistant coated steel pipes that are then coated with a synthetic resin layer; and corrosion-resistant coated steel pipes that are plated in a high-temperature galvanizing bath, pretreated by spraying steam, and then coated with synthetic resin. They had arrived at a method for manufacturing steel pipes.

The iron-zinc alloy layer that forms on the surface of the steel pipe results when the steel pipe is immersed in a molten zinc bath. The temperature of this molten zinc bath is usually up to about 455°C, but in the case of the present invention, the temperature is higher than this, about 460°C to 480°C.
Good results can be obtained by keeping the temperature at °C.

At the same time, the iron-zinc alloy layer is treated so that a zinc hydroxide layer is located on the outer layer. In addition to zinc hydroxide, the zinc hydroxide includes basic zinc chloride, basic zinc carbonate, and the like. This zinc hydroxide layer does not need to be extremely thick as long as it is covered with at least a monomolecular film, but from the viewpoint of actual work, it is sufficient to have a thickness of about 1 μm.

Examples of the pretreatment layer include a chromate treatment layer, a phosphate treatment layer, an organic adhesive layer, and the like. The thickness of the pretreatment layer is not uniform depending on the type of treatment agent. For example, the thickness of the pretreatment layer is not uniform depending on the type of treatment agent. For example, in the case of chromate treatment, the maximum thickness is approximately 10 μm, in the case of phosphate treatment, the maximum thickness is approximately 20 μm, and in the case of organic adhesive treatment, the maximum thickness is approximately 10 μm. A thickness of about 1 (11) μm may be formed.

This pretreatment layer improves the adhesive function between the metal layer and the synthetic resin coating layer, and also improves the corrosion resistance function.

As the synthetic resin coating layer, polyvinyl chloride resin, polyamide resin represented by nylon, polyester resin represented by polyethylene terephthalate, ABS resin, polyolefin resin, etc. can be used, but polyolefin resin is most commonly used. Possible use of resin.

Polyolefin resins include polyethylene resins, polypropylene resins, polybutene resins, and the like, and they can be selectively used depending on the purpose of use or the performance required in the situation.

When a polyolefin resin is used, a two-layer structure is used in which a modified polyolefin resin layer is placed in contact with the above-mentioned pretreatment layer, and a polyolefin resin layer is placed in the outermost layer.

The modified polyolefin resin used here is used to improve adhesive function, and the polyolefin resin layer is used to withstand various stresses from the external environment and exhibit a stable rust prevention effect over a long period of time. It is.

Behind the synthetic resin layer coated for this purpose, the modified polyethylene layer has approximately o, 1 to 1. Owm, and the polyethylene layer is arbitrary from about 0.3 to 2.5 layers? Select this,
Good results can be obtained if the maximum thickness of the synthetic resin layer is approximately 3.0 WM.

Figure 1 shows the anti-corrosion coated steel pipe with each layer formed in this way, where 1 is the steel pipe, 2 is the iron-zinc alloy layer, 3 is the zinc hydroxide layer, and 4 is the pretreatment agent. Layer 5 is a synthetic resin coating layer.

When manufacturing a corrosion-resistant coated steel pipe according to the present invention, it is first necessary to perform preliminary adjustments on the steel pipe, such as degreasing and pickling, as in conventional methods. This process is shown in Figure 2, which includes degreasing (a), water washing (b), and pickling (Cl.

Water washing (d) and flux treatment (e) are sequentially shown. After the steel pipe has been conditioned in this manner, the steel pipe 1 is continuously or intermittently immersed in a galvanizing bath 6 to form a zinc coating on its surface, as shown in FIG. 3, for example. Note that 6 in FIG. 3 is a zinc bath containing molten zinc.

When coating the steel pipe 1 with zinc, for example, as shown in FIG. 3, the rotating steel pipe holder 7 may be rotated so that the steel pipe 1 is removed every time the holder 7 rotates once.

The steel pipe 1 taken out from the molten zinc bath passes through a blow nozzle 8 as shown in FIG. Take over by. In addition, when applying corrosion-resistant treatment to the inner surface of steel pipes,
This blow 5.゛Of course, for example, the fifth
Use one facing the inner surface of the tube as shown in the figure.

The steam used at this time is approximately 1 to 10kp/
It is preferable to use water vapor of about 1-J.

On the surface of a steel pipe that has passed through a molten zinc bath and been sprayed with steam, a layer of iron-free zinc hydroxide is formed, with or without a zinc layer, in addition to an iron-zinc alloy layer. We have confirmed that there are.

The zinc-coated steel pipe 10 thus obtained is then led to a pretreatment tank 11 to treat the surface of the zinc-coated steel pipe, and then a synthetic resin is extruded and coated onto the surface of the steel pipe using a crosshead type extruder. The synthetic resin is first coated with a modified polyolefin resin 11, and then the surface thereof is coated with a polyolefin resin 12 by extrusion. When performing this synthetic resin coating, the adhesion can be further improved by preheating the zinc coated steel pipe 10 in advance.

If two types of synthetic resins are extruded using a coextruder, handling after extrusion coating can be simplified.

After being coated with synthetic resin by the extruder, it passes through a cooling zone 14 and a pinhole inspection zone 15 to become a product.

[Embodiments of the invention]

The present invention will be further explained below using Examples.

20AS cleaned by the operation shown in Figure 2
After immersing the GF steel pipe in a zinc bath at the temperature shown in the table below for 60 seconds, one side was lifted from the zinc bath by a take-out device and taken out by a magnet roller I while being passed through a blow nozzle. From the blow nozzle, 4kf/+! The excess zinc on the surface of the steel pipe was blown off with steam. After applying a coating other than epoxy resin adhesive to the zinc steel pipe prepared as described above to form a film of approximately 10 pm, a modified polyethylene resin layer is placed on the inside using a co-extruder that can extrude two types of materials at the same time. The coating was performed by extrusion molding to form an anti-corrosion polyethylene resin layer on the outside.

The effects on the properties of the final product, the corrosion-resistant coated steel pipe, were investigated by varying the zinc bath temperature and by using air to blow off the excess zinc, and the following results were obtained.

Corrosion Zinc bath temperature °C Blow gas Adhesion Corrosion resistance 1 4
55 Air × ×2 455
Water vapor △ △3 460 Air
× ×4 470 #
X X5 460 Water vapor OO 6475tt Q ○Adhesion is 180
It was conducted according to the °P/1411 separation test method, and evaluated on the basis of ○: stable and strong on the entire surface, 68: partially strong, and ×: unstable.

Corrosion resistance is determined by the distance of corrosion from the cut surface of the corrosion-resistant steel pipe after 15 days of salt spray (3 times salt water, 35"C): ○: up to 10 m+, △: 11 to 50 m, ×: 5
It was evaluated as 1■ or more, and this behavior is illustrated in FIG.

Similar results were obtained when the pretreatment material was replaced with a material other than the epoxy resin adhesive, such as chromate treatment or phosphate treatment, when the required film thickness was provided.

In the figure, -〇- indicates the one according to the present invention, -Δ Ichibanban Hayabusa steam was used but the zinc bath temperature was 455'0 l/), and -x- indicates that air was used. ).

〔Effect of the invention〕

After being immersed in a high-temperature zinc bath, an iron-zinc alloy layer is formed on the surface of the steel pipe by spraying with water vapor, and iron is added to the outside of the alloy layer with or without a zinc layer. (1) Confirm that a zinc hydroxide layer is formed.1. 3. By configuring such a layer, a corrosion-resistant coated steel pipe with excellent adhesion and corrosion resistance can be obtained.

[Brief explanation of drawings]

Fig. 1 is a partial sectional view of a corrosion-resistant steel pipe constructed according to the present invention, Fig. 2 is a perspective view illustrating the process of conditioning the raw steel pipe, Fig. 3 is a perspective view showing a zinc bath, and Fig. 4 is a blow A perspective view showing the relationship between the nozzle (outer surface) and the steel pipe, Figure 5 is a perspective view showing the relationship between the blow nozzle (inner surface) and the steel pipe, and Figure 6 is a side view illustrating the process from pretreatment force to synthetic resin coating. FIG. 7 is a graph, and FIGS. 8 and 9 are process diagrams showing the conventional manufacturing process of corrosion-resistant steel pipes. DESCRIPTION OF SYMBOLS 1...Steel pipe, 2...Iron-zinc alloy layer, 3...Zinc hydroxide layer, 4...Pretreatment layer, 5...Synthetic resin coating layer Agent Patent attorney San Kimura Figure 6 Trial lock (B) Figure 8 Figure 9

Claims (11)

[Claims] (1) In providing the synthetic resin layer on the surface of the steel pipe, the synthetic resin layer is formed after providing at least an iron-zinc alloy layer, a zinc hydroxide layer, and a pretreatment layer on the surface of the steel pipe. Corrosion-resistant coated steel pipe. (2) The corrosion-resistant coated steel pipe according to claim 1, wherein a zinc layer is formed between the iron-zinc alloy layer and the zinc hydroxide layer. (3) Corrosion resistance according to claim 1, wherein the synthetic resin layer is two layers, the outermost layer is a corrosion-preventing layer, and the inner layer is a synthetic resin layer that has a property of being compatible with or adhering to the pretreatment layer. coated steel pipe. (4) The corrosion-resistant coated steel pipe according to claim 1, wherein the zinc hydroxide layer has a thickness of at least a monomolecular film and a maximum thickness of about 1 μm. (5) The corrosion-resistant coated steel pipe according to claim 1, wherein the synthetic resin layer has a thickness of approximately 3 mm. (6) Anti-corrosion layer as a synthetic resin layer of approximately 0.3 to 2.5
2. The corrosion-resistant coated steel pipe according to claim 1, wherein the synthetic resin layer having a property of being compatible with or adhering to the pretreatment layer is approximately 0.1 to 1.0 mm. (7) A method for manufacturing a corrosion-resistant coated steel pipe, which comprises plating a cleaned steel pipe in a high-temperature galvanizing bath, pre-treating it by spraying water vapor, and then applying a synthetic resin coating. (8) The method for manufacturing a corrosion-resistant coated steel pipe according to claim 7, in which galvanization is carried out in a hot-dip plating bath maintained at approximately 460 to 480°C. (9) The method for producing a corrosion-resistant coated steel pipe according to claim 7, wherein water vapor of about 1 to 10 kg/cm^2 is used as the water vapor. (10) The method for manufacturing a corrosion-resistant coated steel pipe according to claim 7, wherein one or two selected from among chromate treatment, phosphate treatment, and organic adhesive coating treatment is performed as a pretreatment. (11) A method for producing a corrosion-resistant coated steel pipe according to claim 7, which comprises extrusion coating two types of synthetic resins with different qualities.