JPS6360280B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to coated piping used for transporting high temperature water, steam, and the like.

[Conventional technology]

Conventional covered piping of this type is shown in Figure 1.
The outer circumferential surface of the pipe 1 is covered with a heat insulating layer 3 made of laminated heat insulating material such as asbestos fiber cloth, silica fiber cloth, etc., and the outer circumferential surface of this heat insulating layer 3 is covered with a waterproof material such as aluminum, stainless steel, carbon steel, etc. It is covered with a waterproof layer 4 made of a thin metal plate or a synthetic resin sheet such as nylon, vinyl, or polyethylene.

[Problem that the invention seeks to solve]

As shown above, connect piping 1 to heat insulation layer 3 and waterproof layer 4.
Even if the pipe 1 is coated with double layers, the outer peripheral surface of the pipe 1 is not completely shielded from the outside environment. It flows and reaches the outer circumferential surface of the pipe 1. Therefore, moisture (temperature) contained in the atmosphere condenses on the surface of the pipe 1 during the cooling and heating cycle and adheres to the surface, making it easy for electrochemical corrosion reactions to occur. Furthermore, corrosive chlorine ions and the like are eluted from asbestos fiber cloth, silica fiber cloth, etc. forming the heat insulating layer 3, and there is a fear that the passive film on the outer circumferential surface of the pipe 1 may be destroyed and a corrosion phenomenon may occur.

The above-mentioned corrosion phenomenon tends to result in general corrosion in carbon steel coated pipes, and pitting corrosion in stainless steel coated pipes. In particular, in coated stainless steel piping that transports high-temperature water and steam, there is a risk that stress corrosion cracking may occur from the outer surface of the piping due to the synergistic effect of a corrosive environment and thermal stress. In addition, if the outermost coating layer of the covered pipe, that is, the waterproof layer 4, is formed of a metal body, the inner surface of the metal body, that is, the surface that is bonded to the heat insulating layer 3, may be corroded and damaged in the same manner as described above. There is.

In view of the above, an object of the present invention is to prevent corrosion of the outer circumferential surface of a pipe provided with a heat insulating layer and the inner surface of the metal body of the outermost waterproof layer, and to provide a long-life coated pipe.

[Means for solving problems]

In order to achieve the above object, the present invention provides a coated pipe in which a heat insulation layer made of a heat insulating material is provided on the outer peripheral surface of the pipe, and a waterproof layer made of a waterproof material is provided on the outer peripheral surface of this heat insulation layer. Parts by weight, 5 to 350 parts by weight of zinc fine powder, 10 parts by weight of electrostatically charged carbon fine powder
~20 parts by weight and 20~ fine magnesium oxide powder
This is achieved by providing an anti-corrosion layer of 100 parts by weight of a rubber coating material on the outer peripheral surface of the pipe.

[Effect]

Zinc in the anti-corrosion layer is polarized to the anode side, preventing a dissolution reaction on the metal surface of the pipe and preventing corrosion of the pipe. Fine carbon powder and fine magnesium oxide powder help consume zinc effectively. In addition, the outermost waterproof layer serves to maintain the anti-corrosion function of the anti-corrosion layer and the insulation effect of the heat-retaining layer for a long period of time.

〔Example〕

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

In Fig. 2, 1 is a pipe for transporting high-temperature water, steam, etc., and the outer peripheral surface of this pipe 1 is coated with a corrosion protection layer 2.
covered with. This anti-corrosion layer 2 is made of a rubber material consisting of 100 parts by weight of a rubber base material, 5 to 350 parts by weight of zinc fine powder, 10 to 200 parts by weight of electrostatically charged carbon fine powder, and 20 to 100 parts by weight of magnesium oxide fine powder. It is formed from a covering material. The rubber base material resists the high temperature of the fluid flowing through the pipe 1.
It is selected considering its heat resistance. 3 is a heat insulating layer that covers the outer peripheral surface of the anticorrosive layer 2; 4 is a waterproof layer that covers the outer peripheral surface of the heat insulating layer 3; this waterproof layer 4 and the heat insulating layer 3 are similar to the conventional example shown in FIG. , so its explanation will be omitted.

Next, the functions of each of the above-mentioned coating layers will be explained.

First, the anticorrosion layer 2 can impart electrical conductivity to the rubber fabric by dispersing fine carbon powder having chargeability in the rubber base material. By adding fine zinc powder to the rubber base material, when the rubber material comes into contact with a metal surface, the zinc powder makes the rubber fabric an electrical conductor and facilitates anodic polarization.

Now, when the rubber coating material is formed into a strip and this strip is wound around the outer circumferential surface of the pipe 1 to form the anticorrosion layer 2, condensed water will enter the interior from between the strips and the outer circumferential surface of the pipe 1. and the corrosion protection layer 2. Therefore, the electrode potential of the metal surface (mainly the iron surface) of the pipe 1 with respect to the aqueous solution is located in the more noble potential series than the electrode potential of zinc branched in the rubber fabric, so zinc is used as an anode with the rubber fabric as an electrical conductor. The dissolution reaction shown in equation (1) below is performed.

Zn→Zn ²⁺ +2e ...(1) Also, on the metal surface of the pipe 1, the cathode reaction of the following formula (2) takes place, which is equivalent to the electrons released by the Ard reaction of the formula (1) above. No dissolution reaction occurs on the metal surface itself, and corrosion is prevented.

H ₂ O + 1/2O ₂ + 2e → 2OH ... (2) On the other hand, in the process of dissolving zinc, the liquid quality is made weakly alkaline, so the passivity of the metal surface of the pipe is maintained, so the metal surface is almost completely It can be maintained in a corrosion-proof state.

Furthermore, heat dissipation due to heat transfer from the outer circumferential surface of the pipe 1 is suppressed by the rubber material, but since this rubber fabric results in solid heat transfer, the heat insulating layer 3 is necessary. In order to utilize air with poor thermal conductivity, the heat insulating layer 3 is constructed in a laminated form mainly of silica glass fiber, foamed urethane, polystyrene resin, etc., each having a large space volume. Even if cations such as chlorine ions, which cause corrosion, are eluted from these resin layers due to the aforementioned dew condensation phenomenon, these cations are captured by zinc in the rubbery outermost layer of the anti-corrosion layer 1 and accumulate as zinc chloride. There is no possibility that the outer peripheral surface of No. 1 will be reached.

The outermost waterproof layer 4 is a coating layer necessary to maintain the anticorrosive function of the anticorrosive layer 2 and the heat insulating effect of the heat insulating layer 3 for a long period of time. When the waterproof layer 4 is a metal body, it is stable in terms of mechanical strength, but it is possible that it will be damaged by corrosion, so it is necessary to apply anti-corrosion treatment to the inner surface. That is, when the waterproof layer 4 is made of aluminum or stainless steel, 100 parts by weight of a polymer mainly composed of polybdenum, 30 to 50 parts by weight of fine zinc powder, and 20 to 200 parts by weight of ester oil charged with static charge. A layer of a mixture of
Provided on the outer peripheral surface of the pipe to suppress the occurrence of crevice corrosion.

On the other hand, when the waterproof layer 4 is made of synthetic resin,
Although it is resistant to corrosion, it has low mechanical strength and is susceptible to deterioration due to ultraviolet rays, so it is necessary to replace it with a new one at an appropriate time.

Next, the reasons for limiting the component compositions forming the anticorrosion layer 2 and the waterproof layer 4 will be explained.

In the anti-corrosion layer 2, if the amount of fine zinc powder relative to the rubber fabric is less than 5 parts by weight per 100 parts by weight of the rubber base material, the anti-corrosion effect cannot be maintained;
If it exceeds 350 parts by weight, the rubber will become brittle, so 5 to 350 parts by weight.
Limited to parts by weight.

In addition, fine carbon powder with static charges has the effect of adsorbing each other and is connected in a chain and dispersed in the rubber formation, imparting conductivity, but it has no effect when it is less than 10 parts by weight, and when it is less than 200 parts by weight. The amount of fine carbon powder added was limited to 10 to 200 parts by weight since the rubber fabric would become brittle if the amount exceeded 100 parts by weight.

Furthermore, magnesium oxide is effective in performing the appropriate moisture absorption action necessary to promote the electrochemical action of the anti-corrosion layer 2, and the amount of magnesium oxide added is
It has no effect if it is less than 20 parts by weight per 100 parts by weight.
If it exceeds 100 parts by weight, the rubber fabric becomes brittle, so 20
~Limited to 10 copies.

When the waterproof layer 4 is made of a metal body as described above, the layer provided on the inner peripheral surface of the metal body or the outer peripheral surface of the heat insulating layer 3 contains 30 parts by weight of fine zinc powder added to 100 parts by weight of polybdenum polymer. If it is less than 350 parts by weight, it will not be effective, and if it exceeds 350 parts by weight, workability will deteriorate.
The amount added was limited to 30 to 350 parts by weight. The amount of ester oil added to effectively consume the added zinc is 100 parts by weight of the rubber base material.
If it is more than 20 parts by weight, the effect will be small, and if it is more than 200 parts by weight, it will be corrosive, so it was limited to 20 to 200 parts by weight.

As described above, in this embodiment, the pipe 1 is coated with the anti-corrosion layer 2, the heat-retaining layer 3, and the waterproof layer 4 in this order, but the present invention is not limited to this, and the pipe 1 is coated with the anti-corrosion layer 2 and the waterproof layer 4. Of course, the waterproof layer 4 may be sequentially coated.

Next, the embodiment shown in FIG. 3 will be described.

The conventional coated piping A and the coated piping B according to the present invention shown in FIGS. After injecting, as shown in FIG. 3, the bolts 5, nuts 6, and seal rings 7 are used to connect the two test materials A and B.
is connected to a pump and a water reservoir (not shown) to form a closed-loop test apparatus.

Approximately 80 mm inside the SUS304 pipe 1 of the above sample materials A and B.
C warm water and cooling are alternately circulated to alternately heat and cool the outer peripheral surface of the pipe 1. and 725,
The pipes 1 were disassembled every 1,450 and 1,920 hours, and the condition of each outer peripheral surface of both pipes 1 was investigated. As a result, pitting-like crevice corrosion occurred on the outer circumferential surface of the pipe 1 of sample material A, which does not have the anticorrosive layer 2, but on the contrary, on the outer circumferential surface of the pipe 1 of sample material B, which has the anticorrosion layer 2. No corrosion damage was observed, confirming that corrosion protection was achieved.

FIG. 4 shows a measuring device for measuring the pH of the liquid in the gap in the anti-corrosion layer 2 of the covered pipe B in FIG. 3 and the state of the electrode potential on the surface inside the gap. FIG. Test piece b made of the same material as , or test piece b' made of commercially available rubber (nitrile butadiene).These test pieces b and b' were prepared in 3% saline solution (50℃).
It was soaked in water for 60 days. 4A and 4C show the holding member for the test piece b, and FIG. 4D shows the assembled state, respectively. Reference numerals 9 to 11 in FIG. 4D indicate a Teflon pipe, a cotton thread, and an electrode made of SUS304, respectively, and the electrode 11 is connected to a potentiostat for measurement. The PH of the liquid in the gap was determined by disassembling the assembled state shown in FIG. 4D, and then measuring the residual liquid using PH paper.

As a result, the PH in the gap when using the test piece b according to the present invention and the conventional test piece b' is as shown by lines C and D in FIG. 5, respectively. In other words, the PH in the gap gradually becomes weakly alkaline at line C for test piece b according to the present invention, but gradually becomes acidic and corrosive at line D for test piece b' of the conventional example. is easily understood.

Further, the potentials within the gap when using the test piece b according to the present invention and the conventional test piece b' are as shown by lines E and F in FIG. 6, respectively. That is, in the case of test piece b according to the present invention, the potential of the E line is:
In the case of the conventional test piece b', it is polarized to a much more base potential than the F line potential. Therefore, it is easily understood that the former is cathodically polarized by zinc and is therefore protected against corrosion.

〔Effect of the invention〕

As explained above, according to the present invention, the life of the piping can be significantly extended by preventing corrosion of the outer peripheral surface of the piping provided with the coating layer and the inner peripheral surface of the outermost waterproof metal body. .

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a conventional covered pipe, Fig. 2 is a cross-sectional view showing an example of the covered pipe of the present invention, Fig. 3 is a cross-sectional view showing an experimental example of a conventional product and a product of the present invention, and Fig. 4. A to C and D are the pH values of the liquid in the gaps in the anticorrosion layer.
Figures 5 and 6 are cross-sectional views showing parts for measuring the electrode potential on the inner surface of the gap and their assembled state.
The figure is an explanatory diagram showing the characteristics of the conventional product and the product of the present invention. 1... Piping, 2... Corrosion protection layer, 3... Heat retention layer, 4
...Waterproof layer.

Claims (1)

[Scope of Claims] 1. In a covered pipe in which a heat insulation layer made of a heat insulating material is provided on the outer peripheral surface of the pipe, and a waterproof layer made of a waterproof material is provided on the outer peripheral surface of this heat insulation layer, 100 parts by weight of a rubber base material, zinc An anticorrosive layer of a rubber coating material consisting of 5 to 350 parts by weight of fine powder, 10 to 200 parts by weight of electrostatically charged carbon fine powder, and 20 to 100 parts by weight of magnesium oxide fine powder is provided on the outer peripheral surface of the pipe. Covered piping characterized by: 2. When the waterproof layer is made of any one of aluminum, stainless steel, and carbon steel, 100 parts by weight of polybdenum polymer, 30 to 350 parts by weight of fine zinc powder, and 20 to 20 parts of electrostatically charged ester oil. A layer of a mixture consisting of 200 parts by weight,
The coated pipe according to claim 1, characterized in that it is provided on the inner surface of the waterproof layer or on the outer circumferential surface of the heat insulating layer.