Inner surface Anti-corrosion cast-iron pipe

Abstract

To provide a cast-iron pipe used for a sewage line that can be constructed more easily than powder coating and secure durability and acid resistance comparable to a powder coating film.SOLUTION: An inner surface anti-corrosion cast-iron pipe includes: a mortar lining layer 21; a primer layer 22 formed of a vinyl ester resin; and a coating film layer 23 formed of a vinyl ester resin coating on an inner surface side of a cast-iron pipe 1 in the order from a pipe inner side surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This invention relates to corrosion protection of cast iron pipes. [Background technology]

[0002] Ductile iron pipes are stronger than plastic pipes and are widely used for water supply and sewerage pipes, including main water pipes. However, because they are made of cast iron, they will corrode if left in their cast state. Therefore, both the exterior and interior surfaces, including the joints, must be thoroughly anti-corrosive treated before use.

[0003] Due to this demand, mortar linings and other materials are applied to the inside of cast iron pipes. However, most sewers use a gravity flow system, and the pipes are often not filled with water, with both liquid and gas phases existing inside. The liquid phase is an anaerobic environment, where anaerobic bacteria produce hydrogen sulfide, which diffuses into the gas phase. The gas phase is an aerobic environment, where aerobic bacteria produce sulfuric acid from hydrogen sulfide, creating an acidic environment inside the sewer pipes. However, mortar linings are not sufficiently acid-resistant, so there is a problem in that they are difficult to apply as is in a sewage environment.

[0004] In response to this, Patent Document 1 proposes an inner surface corrosion-resistant cast iron pipe in which a coating of solvent-free epoxy resin paint is formed on the surface of the cement mortar layer on the inner surface of the pipe. This prevents the mortar from coming into direct contact with the acidic environment inside the pipe, and prevents the mortar itself from dissolving in the acid and leaching out.

[0005] Furthermore, Patent Document 2 proposes applying a seal coating agent to an inner mortar-lined ductile cast iron pipe, which not only provides excellent durability when water is passed through the pipe for a long period of time, but also suppresses cracks caused by the hardening and drying shrinkage of the mortar. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-109215 A [Patent Document 2] Patent No. 4663681 Summary of the Invention [Problem to be solved by the invention]

[0007] However, solvent-free epoxy resin paints have a high viscosity and therefore must be heated and pressurized when applied, making application complicated.

[0008] In addition, in the case of the inner surface corrosion-resistant cast iron pipe in which a coating film is formed on a mortar lining described in Patent Document 1, in a sulfuric acid corrosive environment, acidic substances may penetrate the coating film made of solventless epoxy resin paint, causing the mortar lining to deteriorate. Furthermore, the epoxy resin powder coating generally used on the inner surface of cast iron pipes requires heating the entire pipe to harden the paint, which makes it difficult to apply, particularly to large-diameter pipes with a nominal diameter of 1800 or more.

[0009] Furthermore, the protective layer formed by the seal coating agent described in Patent Document 2 has a coating weight of 100 g / m 2 The actual calculated film thickness was only about 10 μm, which is effective in preventing penetration, but is not enough to provide durability in an acidic environment.

[0010] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a sewer pipe having excellent acid resistance, which is easier to apply than powder coating and can ensure the same level of durability as a powder coating film. [Means for solving the problem]

[0011] As a first solution, the present invention solves the above-mentioned problems by providing an internally corrosion-resistant cast iron pipe having, on the internal surface of the cast iron pipe, a primer layer formed from a vinyl ester resin and a coating layer formed from a vinyl ester resin paint that does not contain glass flakes, in that order from the internal surface of the pipe.

[0012] The present invention also solves the above problem by providing, as a second means for solving the problem, an inner surface corrosion-resistant cast iron pipe having, on the inner surface of the cast iron pipe, in this order from the inner surface surface, a mortar lining layer, a primer layer formed of a vinyl ester resin, and a coating layer formed of a vinyl ester resin paint that does not contain glass flakes. That is, the second means for solving the problem is a configuration in which, in addition to the configuration of the first means for solving the problem, a mortar lining layer is formed on the inner surface of the cast iron pipe.

[0013] That is, the coating layer made of vinyl ester resin paint exhibits high chemical resistance even against acidic liquids, and strongly prevents the penetration of acidic liquids into the layer below. If there is a mortar lining layer below, it prevents the acidic liquid from reaching the mortar lining, suppressing the deterioration of the mortar lining, which is vulnerable to acid. Even if there is no mortar lining layer, it can strongly prevent the acidic liquid from penetrating into the cast iron pipe, which is even more vulnerable than the mortar lining. The chemical resistance of such a configuration can be achieved only with the vinyl ester resin itself, without containing scaly glass that improves the durability of the coating layer, or other pigments that form a structure in the coating layer that is an obstacle to the penetration of the solution, similar to scaly glass. As a result, the resin paint that forms the coating layer does not need to contain scaly glass or other pigments, so that the coating device is not clogged or damaged by scaly glass, and the cost of finishing to a corrosion-resistant state can be reduced.

[0014] Furthermore, in addition to the first or second solution, the internally corrosion-resistant cast iron pipe according to the present invention can employ a third solution in which the thickness of the coating layer is 100 μm or more and 800 μm or less. Since it is not necessary to contain glass flakes, the surface of the coating layer can be made smoother easily, and even if the coating layer is made thinner than a coating layer containing glass flakes, it is possible to achieve both smoothness and durability. Effect of the Invention

[0015] In the case of the internal corrosion-resistant cast iron pipe of the present invention, it is not necessary to heat the entire pipe to a high temperature to melt the powder as in the case of conventional powder coating, and a highly acid-resistant and durable protective layer can be formed by using a vinyl ester resin paint that can be applied at room temperature to form a coating layer, and even in a harsh environment such as acidic sewage, it is possible to prevent the mortar lining layer from being deteriorated by the penetration of acidic substances into the mortar lining layer or cast iron pipe. In the case of conventional powder coating, the entire pipe must be heated, which limits the environments and sizes of pipes that can be manufactured, and even if it can be manufactured, the heating burden is large. In the case of the internal corrosion-resistant cast iron pipe of the present invention, there is no restriction due to the size of the heating furnace or waste of heating during manufacturing, and corrosion prevention can be achieved stably regardless of the size of the pipe. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1A is a cross-sectional view showing an outline of an embodiment of an internally corrosion-resistant cast iron pipe according to the present invention; FIG. 1B is an enlarged cross-sectional view of a straight pipe portion showing a first embodiment of an internally corrosion-resistant cast iron pipe according to the present invention; and FIG. 1C is an enlarged cross-sectional view of a straight pipe portion showing a second embodiment of an internally corrosion-resistant cast iron pipe according to the present invention. [Diagram 2] (a) A cross-sectional view of a stage in which a mortar lining layer is formed in the manufacture of an internally corrosion-resistant cast iron pipe according to the present invention; (b) A cross-sectional view of a stage in which the mortar lining layer has hardened and separated; (c) A cross-sectional view of a stage in which the laitance layer has been removed; (d) A cross-sectional view of a stage in which a primer layer has been formed on the paste layer; and (e) A cross-sectional view of a stage in which a coating layer has been formed on the primer layer. [Diagram 3] (a) Data showing the results of the sulfur permeability test of Example 1; (b) Data showing the results of the sulfur permeability test of Comparative Example 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the embodiment of the present invention will be described in detail. This invention relates to an internally corrosion-protected cast iron pipe in which a corrosion-protective layer 20 is provided on the inner surface of a straight portion 13 formed between a spigot 11 and a socket 12 in a straight cast iron pipe 1 as shown in Fig. 1(a). The corrosion-protective layer 20 in a first embodiment of this invention has a mortar lining layer 21, a primer layer 22, and a coating layer 23, in this order from the inner surface of the cast iron pipe 1, as shown in the enlarged cross-sectional view of Fig. 1(b). In a second embodiment of this invention, a corrosion-protective layer 20a is provided directly on the inner surface of the cast iron pipe 1 without providing a mortar lining layer 21, and a primer layer 22 and a coating layer 23, as shown in the enlarged cross-sectional view of Fig. 1(c). The following description will be made mainly of the first embodiment as an example.

[0018] As the cast iron pipe 1 used in this invention, a centrifugally cast cast iron pipe can be suitably used. The type of cast iron pipe is not particularly limited, and a general ductile iron pipe or the like can be used. It may be a pipe that protects the surface of a mortar-lined pipe from corrosion as in the first embodiment, or a pipe that protects the surface of a cast iron pipe directly from corrosion without mortar lining as in the second embodiment.

[0019] The mortar lining layer 21 is formed by supplying cement mortar to the inner surface of the cast iron pipe 1 while applying centrifugal force and hardening the layer. The cement mortar is a common mixture of aggregate such as sand and cement. The mortar lining layer 21 formed by hardening the cement mortar contains a laitance layer on the surface of the mortar lining layer 21, which is a collection of impurities contained in the cement mortar. Therefore, it is preferable to remove the laitance layer before applying the primer layer 22. For example, a flap wheel can be used to remove the laitance layer. In addition, the thickness of the mortar lining layer 21 after removing the laitance layer is preferably 4 to 15 mm. If the thickness is less than 4 mm, the surface of the mortar lining layer 21 will not be smooth due to the unevenness formed on the inner surface of the straight portion 13 after casting, and if the thickness is more than 15 mm, the cross-sectional area of ​​water flow on the inner surface of the pipe will be reduced more than necessary.

[0020] The primer layer 22 is a resin layer formed by applying a vinyl ester resin primer to the surface of the mortar lining layer 21 or the inner surface of the cast iron pipe 1. By using a vinyl ester resin as a primer, adhesion can be achieved without using the primer in a high-heat environment as in powder coating. The coating does not have to be a single coat, and the primer layer may be formed by applying multiple coats. The thickness of the primer layer 22 is preferably 50 μm or more and 100 μm or less. If the thickness is less than 50 μm, the adhesion stabilizing effect with the coating layer 23 becomes insufficient, and if the thickness is greater than 100 μm, the adhesion stabilizing effect does not increase. Although not shown, the primer layer 22 can be applied directly to the inner surface of the cast iron pipe 1 without forming the mortar lining layer 21. However, in this case, since the smoothness of the mortar lining layer 21 cannot be ensured, processing such as grinding or blasting is required.

[0021] The coating layer 23 is formed by applying a vinyl ester resin paint onto the primer layer 22. Since the vinyl ester resin exhibits high acid resistance, the inner surface corrosion-resistant cast iron pipe according to the present invention can prevent the penetration of acidic substances into the mortar lining layer even in an acidic sewage environment, and can exhibit high durability by suppressing the deterioration of the mortar lining. The thickness of the coating layer 23 is preferably 100 μm or more and 800 μm or less. If it is less than 100 μm, the protective effect on the mortar lining layer 21 and the cast iron pipe 1 is likely to be insufficient even if it is a vinyl ester resin paint. However, since the vinyl ester resin paint forming the coating layer 23 in the present invention does not contain scaly glass or other pigments that similarly form a structure that is an obstacle to the penetration of the solution in the resin, even if it is thinner than a coating containing scaly glass, which is likely to be affected by the unevenness caused by scaly glass, there is almost no effect on the flow rate of the liquid flowing through the pipe. For this reason, it can be made thinner than a coating layer containing scaly glass. Specifically, the coating layer 23 can be suitably thinned to a thickness of 300 μm or less, which is likely to cause problems when it contains glass flakes, etc. Even if it does not contain glass flakes, the coating layer 23 of this invention can achieve practical acid resistance as long as it has a thickness within the above range. On the other hand, if it is thicker than 800 μm, the reduction in the cross-sectional area of ​​water flow on the inner surface of the pipe cannot be ignored.

[0022] As the vinyl ester resin, for example, an epibis-vinyl ester made of a combination of epichlorohydrin and bisphenol A can be used.

[0023] The primer layer 22 and the coating layer 23 can be formed by, for example, roller coating, brush coating, or spray coating.

[0024] Since the inner surface of the socket 12 and the outer surface of the insertion hole 11, which are not provided with the mortar lining layer 21, are exposed to an acidic environment, these areas can be protected by providing these areas with the primer layer 22 and the coating layer 23. Also, the surface of the coating layer 23 superimposed on the area without the mortar lining layer 21 can be provided with a topcoat layer in this embodiment.

[0025] The manufacturing procedure of the inner surface corrosion-resistant cast iron pipe according to the present invention will be described with reference to Figs. 2(a)-(e). First, the inner surface of the cast iron pipe 1 is coated with a mortar lining layer 21 lined with cement mortar (Fig. 2(a)). Due to centrifugal force applied during and after coating, the distribution of aggregate (sand) contained in the mortar lining layer 21 is biased, and the aggregate content increases toward the cast iron pipe 1 side (outer periphery). The outer periphery side (lower side in the figure) where there is a lot of aggregate is called the mortar layer 21a, and the inner periphery side (upper side in the figure) where there is little aggregate is called the paste layer 21b. Furthermore, light impurities contained in the cement mortar gather on the paste layer 21b, forming a laitance layer 21c. The state in which the mortar lining layer 21 is separated is shown in Fig. 2(b). Of the mortar lining layer 21 thus separated, the laitance layer 21c on the surface side is scraped off to expose the paste layer 21b (FIG. 2(c)). A vinyl ester resin primer is applied to the surface of the mortar lining layer 21 from which the paste layer 21b is exposed to form a primer layer 22 (FIG. 2(d)). A vinyl ester resin paint that does not contain glass flakes is applied to the surface of the primer layer 22 to form a coating layer 23 (FIG. 2(e)), thereby obtaining an internally corrosion-resistant cast iron pipe with a corrosion-resistant layer 20 formed thereon.

[0026] Furthermore, when forming a corrosion protection layer 20a on a cast iron pipe 1 without a mortar lining layer 21, the above-mentioned steps of Figures 2(a) to (c) are omitted, and a step of applying a primer layer 22 to the inner surface of the cast iron pipe 1 is performed, followed by a step of applying a coating layer 23. EXAMPLES

[0027] The present invention will be specifically described below with reference to examples in which an internally corrosion-resistant cast iron pipe according to the present invention was actually manufactured.

[0028] Example 1 As a cast iron pipe, a ductile iron pipe with a nominal diameter of 150 manufactured by Kurimoto Iron Works, Ltd. was rotated while applying a mortar lining to the inner surface to form a mortar lining layer 21. After hardening, the portion of the surface that would become the laitance layer was polished off.

[0029] On the inner surface of the mortar lining layer 21 from which the laitance layer had been removed, a vinyl ester resin primer, Tough Barrier #200 Primer RC (manufactured by Nippon Tokushu Toryo Co., Ltd.), was applied with a roller to a film thickness of 80 μm to form a primer layer.

[0030] After the vinyl ester resin primer that would become the primer layer had hardened, Tough Barrier #200 (manufactured by Nippon Tokushu Toryo Co., Ltd.), an Epivis vinyl ester resin, was applied with a roller to a thickness of 300 μm to form a coating layer. This resulted in an inner surface corrosion-resistant cast iron pipe protected by three layers: a mortar lining layer, a primer layer, and a coating layer.

[0031] (Example 2: No mortar lining layer) The same cast iron pipe as used in Example 1 was used, and the inner surface of the cast iron pipe was subjected to a base treatment to produce a clean surface. The inner surface of this polished cast iron pipe, which had been ground for powder coating, was then coated with Tough Barrier #200 Primer M (manufactured by Nippon Tokushu Toryo Co., Ltd.), a vinyl ester resin primer, with a roller to a film thickness of 80 μm to form a primer layer.

[0032] After the vinyl ester resin primer that would become the primer layer had hardened, Tough Barrier #200 (manufactured by Nippon Tokushu Toryo Co., Ltd.), an Epivis vinyl ester resin, was applied with a roller to a thickness of 300 μm to form a coating layer. This resulted in an inner surface corrosion-resistant cast iron pipe protected by two layers: a primer layer and a coating layer.

[0033] (Reference example: conventional powder coating) A cast iron pipe polished in the same manner as in Example 2 was heated to 270°C, and then coated with an epoxy resin powder paint, V-PET#1600 Kurimoto Gray FH (manufactured by Dai Nippon Toryo Co., Ltd.), to a film thickness of 300 μm. The pipe was then allowed to cool and harden, yielding an internally corrosion-resistant cast iron pipe protected by a powder coating layer of epoxy resin powder paint.

[0034] (Comparative Example 1: Liquid epoxy resin) The inner surface of a cast iron pipe polished in the same manner as in Example 2 was coated with a liquid epoxy resin paint, Eponix WP-ST Gray Summer Type (manufactured by Nippon Paint Co., Ltd.), to a film thickness of 300 μm, and after curing, was coated again in the same manner to obtain an inner corrosion-resistant cast iron pipe protected by two coating layers.

[0035] <Common procedures for each test> The coated internally corrosion-resistant cast iron pipes of Examples 1 and 2, Reference Example, and Comparative Example 1 were cut into pieces measuring 150 mm x 90 mm, and the cut surfaces were coated for protection. The following tests were carried out on these test pieces. Each test method was in accordance with the method described in the "Manual for Corrosion Inhibition and Anticorrosion Technology for Sewerage Concrete Structures" (compiled by the Japan Sewage Works Agency, a local joint corporation; hereafter abbreviated as "Manual").

[0036] <Sulfuric acid immersion test> The test pieces thus prepared were immersed in a 10% by weight aqueous solution of sulfuric acid for 60 days, after which the appearance of the coating was observed. Evaluation was carried out as follows. In the manual, the corrosion protection coating method is a coating-type lining method, the corrosive environment is Class I (an environment in which the annual average hydrogen sulfide gas concentration is 50 ppm or more, and concrete corrosion is extremely common), and the required performance corresponds to Class D. ◯: After 60 days, no cracking, softening, or dissolution was observed in the coating film. ×: After 60 days, the coating film exhibits any of the following abnormalities: cracking, softening, or elution.

[0037] <Sulfur penetration test> The prepared test pieces were immersed in a 10% by weight aqueous solution of sulfuric acid for 120 days, after which elemental analysis of sulfur was performed on the cross section of the coating using an EPMA (EPMA1720, manufactured by Shimadzu Corporation) to investigate the depth of penetration of sulfur from the coating surface. The evaluation was carried out as follows. Similarly, in the manual, the corrosion protection coating method is a paint-type lining method, the corrosive environment is Class I (annual average hydrogen sulfide gas concentration of 50 ppm or more, an environment in which extreme concrete corrosion is observed), and the required performance corresponds to Class D. Good: After 120 days, the depth of sulfur penetration from the surface was 5% or less of the film thickness and 100 μm or less. ×: After 120 days, the sulfur penetration depth from the surface is more than 5% of the film thickness or more than 100 μm.

[0038] <Organic acid immersion resistance test> The prepared test pieces were immersed in a 5% by mass aqueous solution of acetic acid for 60 days, and then the appearance of the coating film was observed. Evaluation was performed as follows. ◯: After 60 days, no cracking, softening, or dissolution was observed in the coating film. ×: After 60 days, the coating film exhibits any of the following abnormalities: cracking, softening, or elution.

[0039] These test results are shown in Table 1. All of the Examples showed good test results equivalent to those of the Reference Example using powder coating, which requires conventional high-temperature heating. On the other hand, in Comparative Example 1 (liquid epoxy resin paint), protection was insufficient in all tests, despite two coats. The results of the sulfur penetration test for Example 1 and Comparative Example 1 are shown in Figures 3(a) and (b). While there was almost no indication of sulfur in Example 1, there was a large amount of visible sulfur in Comparative Example 1, and it was confirmed that Example 1 provides sufficient corrosion protection even in environments where Comparative Example 1 cannot provide corrosion protection.

[0040] [Table 1] [Explanation of symbols]

[0041] 1 Cast iron pipe 11 Insertion port 12 socket 13 Straight section 20, 20a Anticorrosive layer 21 Mortar lining layer 22 Primer layer 23 Coating layer

Claims

1. The cast iron pipe has an inner surface that is corrosion-resistant and is provided with, on the inner surface thereof, a primer layer formed of a vinyl ester resin and a coating layer formed of a vinyl ester resin paint that does not contain glass flakes, in this order from the inner surface of the pipe.

2. The cast iron pipe has an inner surface that is corrosion-resistant and is provided with a mortar lining layer, a primer layer formed of a vinyl ester resin, and a coating layer formed of a vinyl ester resin paint that does not contain glass flakes, on the inner surface of the cast iron pipe in this order from the inner surface of the pipe.

3. 3. The cast iron pipe according to claim 1, wherein the coating layer has a thickness of 100 μm or more and 800 μm or less.

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