JPH0140110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a corrosion-resistant cladding tube used in general water/sewage and gas transportation, chemical plants, solar thermal systems, and the like.

[Background of the invention]

Conventional piping of this type has been coated with paint,
It is well known that carbon steel pipes with anti-corrosion coatings such as galvanized and resin lined and uncoated stainless steel are commonly used.

However, when the piping is buried underground, the surface treatment layer of the piping may be damaged by vibrations from machinery, earthquakes, etc. through the underground sandstone particles. On the other hand, when the pipe is installed in the atmosphere, the surface treatment film deteriorates, so there is a risk that condensed water and rain may penetrate inside and corrode the pipe surface.

Corrosion prevention measures such as surface coating and resin lining are highly effective, but water can enter the interior through the interface between reinforcing additives and color vehicles and the resin, as well as through air bubbles, and this water can damage the pipe surface. Many of them corrode and have no anti-corrosion effect. In addition, the anticorrosion means of zinc plating has an anticorrosion effect immediately below the plating layer, but the anticorrosion effect is insufficient in the damaged portion of the plating layer. If the piping is left in such an environment, stress corrosion cracking may occur due to the residual stress added during the manufacturing and construction of the piping.

On the other hand, stainless steel used in an uncoated state may cause localized crevice corrosion due to adhesion of chlorides, sulfates, dust, etc. contained in wind and rain. There is a drawback that gas and water leakage from underground pipes may occur due to insufficient anti-corrosion construction to prevent such corrosion.

[Purpose of the invention]

In view of the above, it is an object of the present invention to prevent corrosion of pipes and extend their service life by simple means.

[Summary of the invention]

In order to achieve the above object, the present invention includes a rubber base material with a weight ratio of zinc fine powder of 5 to 350%, magnesium oxide of 20 to 100%, and a surface area of 900 to 1100 m ² /
This product is characterized in that one or both of the inner and outer surfaces of the piping is coated with an anticorrosion agent containing 20 to 200% gr graphite fine powder.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

In Fig. 1, 1 is a pipe made of stainless steel (SUS304), 2 is a corrosion-proofing material that coats the outer surface of the pipe 1, and this corrosion-proofing material 2 is a rubber base material containing fine zinc powder of 5 to 350% by weight. Magnesium oxide:
It consists of a composition material to which 20-200% of fine graphite powder with a surface area of 900-1100 m ² /gr is added. The corrosion protection 2 prevents liquid and dust from coming into direct contact with the surface of the pipe 1, and the corrosion protection 2 itself can sufficiently adapt to the expansion and contraction of the pipe 1.

Since fine zinc powder is added to the rubber base material as described above, when condensation water infiltrates the interface between the surface of the pipe 1 and the corrosion protection material 2, the zinc dissolves preferentially, and the corrosion protection material 2 becomes the anode. Along with the polarization, the pipe 1 is cathodically polarized to provide corrosion protection. The dissolved zinc ions become amorphous zinc hydroxide through hydrolysis, making the liquid alkaline and helping to stabilize the passive film on the surface of the pipe 1. Further, the amount of zinc fine powder added was limited to 5 to 350% by weight because if it was less than 5% by weight, there would be no anticorrosion effect, and if it was more than 350%, it would inhibit the elasticity of the rubber base material.

Furthermore, the purpose of adding magnesium oxide is to impart hygroscopicity to the rubber base material, which is necessary for effectively consuming the fine zinc particles uniformly dispersed in the inner layer of the rubber base material. The amount added is limited to 20 to 100% by weight because if it is less than 20%, the effect will be small, and if it is more than 100%, the elasticity of the rubber base material will be impaired.

In order to anodically polarize the coating material 2 and cathodically polarize the piping 1 by dissolving the zinc fine particles uniformly dispersed in the base material as described above, it is necessary to impart electrical conductivity to the rubber base material. Fine graphite powder was added to reduce the electrical resistance to about 3KΩ・cm or less. The amount added is preferably the minimum from the viewpoint of corrosion protection, and it is desirable that the particle size of the graphite fine powder is made very small. Therefore, the surface area
If fine graphite powder of 900 to 1100 m ² /gr is dispersed,
It is possible to provide the necessary electrical conductivity for corrosion prevention, and if the amount added is less than 20% by weight, there will be no electrical conductivity, and if it is more than 200%, corrosive effects will appear on the rubber base material, so the addition amount should be 20 to 200%. Limited. Furthermore, if the surface area of the graphite fine powder is less than 900 m ² /gr, the required addition amount becomes large, which is undesirable, and if it is more than 1100 m ² /gr, it becomes expensive and uneconomical, so it is 900 to 1100 m ² /g.
limited to r.

Next, examples will be described.

Fig. 2 shows an experimental apparatus in which a test liquid 5 whose temperature is adjusted to 25°C is circulated in a test tank 4, and a sample specimen A is placed in the test liquid 5. The corrosion test was continued for 8000 hours.

The above test solution 5 contains 1% NaCl and 1% Mg ₂ Cl,
It is a mixture _{of CaCl2.2H2O} and 1% _NaHCO3 . In addition, test piece A is a commercially available stainless steel pipe 1
(C: 0.07%, Si: 0.85%, Mn: 1.25%, Cr:
Ni: 17.52%, Ni: 7.90% SUS304) was subjected to solution treatment (1050°C x 1 hr → water toughness). Test piece B is a corrosion-resistant coated pipe (see FIG. 1) of this example, which is the same as test piece A, and the outer surface of the pipe 1 is coated with corrosion-proofing material 2. Test piece C is the same pipe 1 as test piece A, with the outer surface covered with vinyl chloride tape 3.

The results of the above corrosion test are shown in Figure 3.
Curves a and c represent the corrosion state of specimens A and C, and straight line b
indicate the corrosion state of test piece B, respectively. As is clear from this, a large number of pitting corrosion points (rust occurrence points of about ¹ mm2) were observed in test specimens A and C, but none in test specimen B, that is, the corrosion-resistant cladding of the present invention. It was confirmed that no corrosion occurred.

In another embodiment shown in FIG. 4, the inner circumferential surface of a pipe 6 made of low-grade stainless steel (13% Cr stainless steel) is lined with a corrosion-proofing material made of rubber having anti-corrosion properties, and the inner circumference of this corrosion-proofing material 7 is This is an anti-corrosion cladding tube with a reinforcing material or heat insulating material 8 made of chloroprene rubber having good weather resistance adhered to the surface. The anticorrosive material 7 is made of ethylene propylene rubber to which fine carbon powder with an average surface area of about 1000 m ² /gr is added to impart electrical conductivity.
300% (wt) fine zinc powder with an average particle size of approximately 10μm
It is made from a composition material with the addition of 30% (wt) magnesium oxide powder.

According to this embodiment configured in this way, it is possible to completely prevent crevice corrosion from occurring at the coating interface, and to further improve the anticorrosion effect. In this embodiment, a corrosion-resistant corrosion-resistant material 7 and a weather-resistant reinforcing or heat-insulating material 8 are bonded to the inside of the pipe 6. Alternatively, the same effect can be obtained by adhering it to both the inner and outer peripheral surfaces of the pipe 6.

〔Effect of the invention〕

As explained above, according to the present invention, by simply coating one or both of the inner and outer surfaces of the pipe with a special anticorrosion coating, it is possible to prevent corrosion of the pipe and extend its life. .

[Brief explanation of drawings]

1 and 4 are cross-sectional views showing embodiments of the anticorrosive cladding tube of the present invention, FIG. 2 is a cross-sectional view of a corrosion test apparatus, and FIG. 3 is a diagram showing the results of a corrosion test. 1, 6... Piping, 2, 7... Corrosion protection, 8... Reinforcement or heat insulation material.

Claims (1)

[Claims] 1. Zinc fine powder: 5 to 350% by weight to the rubber base material;
Magnesium oxide: 20-100% and surface area 900
A corrosion-proof coated pipe characterized in that one or both of the inner and outer surfaces of the pipe are coated with a corrosion-proofing material containing 20 to 200% graphite fine powder of ~1100 m ² /gr. 2. A corrosion-resistant cladding tube according to claim 1, characterized in that the corrosion-resistant cladding tube is covered with a reinforcing material or a heat insulating material.