Internal corrosion-resistant cast iron pipes

Abstract

For cast iron pipes used in water and sewage systems, the internal corrosion-resistant cast iron pipes should exhibit excellent initial adhesion of the corrosion-resistant layer, adhesion after water resistance, and adhesion at the time of cutting. [Solution] The cast iron pipe 1 is provided with an internal corrosion-resistant cast iron pipe having, in order from the inner surface of the pipe, a mortar layer 21, a primer layer 25 containing urethane resin, and a coating layer 26 formed of paint containing vinyl ester resin on its inner surface.

Description

Technical Field

[0001] This invention relates to the anticorrosion of cast iron pipes.

Background Art

[0002] Ductile iron pipes have higher strength than resin pipes and are widely used in water supply and drainage pipes including main water pipes. Especially when used as sewer pipes, the inside of the pipe becomes an acidic environment due to sulfuric acid, so not only strength but also corrosion resistance and acid resistance of the inner surface of the pipe are required. Therefore, when used as a sewer pipe, epoxy resin powder coating is applied to the inner surface of the cast iron pipe, or as described in Patent Document 1, a solventless epoxy resin paint may be further applied to the surface of the mortar lining applied to the inner surface of the cast iron pipe.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to use this inner surface anticorrosion cast iron pipe as a water supply and drainage pipe, it is required that each layer of the inner surface of the pipe constituting the inner surface anticorrosion cast iron pipe has sufficient performance regarding adhesion. Conventionally, the adhesion that has been focused on is the initial adhesion and the adhesion after water resistance. The initial adhesion means that when manufacturing the inner surface anticorrosion cast iron pipe, each layer to be formed can sufficiently adhere to the layer below it, and the production yield can be sufficiently ensured. Also, the adhesion after water resistance means that after the water supply and drainage pipe is actually exposed to moisture, each layer can maintain its function without peeling off over a long period.

[0005] However, in actual installation sites, in addition to the initial adhesion and adhesion after water resistance mentioned above, another type of adhesion is required. This is because the manufacturing and installation of internally corrosion-resistant cast iron pipes are separate processes. Generally, internally corrosion-resistant cast iron pipes are manufactured in the factory to a specified length. These pipes are then transported to the installation site, where they are cut to the appropriate length as needed and then installed. However, when cutting the pipes, significant force is applied to each layer on the inner surface of the internally corrosion-resistant cast iron pipe, which can cause the layers to peel off from the cut surface, swell due to the heat generated during cutting, or crack. If the pipes are laid with such irregularities and peeling remaining, the layers will deteriorate after installation, requiring repairs to the surface of the cut surface at the construction site. In installation sites where rapid progress is required, this repair work leads to a decrease in work efficiency. Therefore, internally corrosion-resistant cast iron pipes are required to have both "peel resistance," which prevents them from peeling or bulging from the end face when the pipe is cut, and "crack resistance," which prevents them from cracking from the end face, thus providing adhesion during cutting.

[0006] However, while the internal corrosion-resistant cast iron pipe described in Patent Document 1 focuses on initial adhesion during manufacturing and adhesion after water resistance during manufacturing, it does not consider adhesion during cutting. Therefore, it is believed that there is still room for improvement in achieving a balance between these three types of adhesion.

[0007] Therefore, the objective of this invention is to provide an internally corrosion-resistant cast iron pipe with superior adhesion properties in terms of three indicators: initial adhesion, adhesion after water resistance, and adhesion at the time of cutting. [Means for solving the problem]

[0008] This invention, as a first solution, The above problems were solved by providing an internally corrosion-resistant cast iron pipe with a mortar layer derived from cement mortar, a primer layer containing urethane resin, and a coating layer containing vinyl ester resin on the inner surface of the pipe, in that order from the inner surface.

[0009] Furthermore, in the first solution, this invention A second solution can be adopted, which involves having a paste layer derived from the cement mortar following the mortar layer, and having the paste layer and the primer layer in contact.

[0010] Furthermore, in the first solution, this invention A third solution can be adopted in which the mortar layer and the primer layer are in contact.

[0011] Furthermore, this invention provides a fourth solution: The step of forming a cement mortar layer on the inner surface of the cast iron pipe while rotating the cast iron pipe, After the cement mortar layer has hardened, the laitance layer present on the surface side of the cement mortar layer is polished off to expose the mortar layer or paste layer. The step of applying a primer containing urethane resin to the surface of the exposed mortar layer or paste layer described above to form a primer layer, The step of applying a vinyl ester resin to the surface of the above-mentioned primer layer to form a coating layer. The above problems were also solved by a method for manufacturing internally corrosion-resistant cast iron pipes that sequentially performs the following steps.

[0012] Furthermore, in the fourth solution, this invention The amount of primer applied to form the above-mentioned primer layer is 50 g / m². 2 More than 500g / m 2 The following fifth solution can be adopted. [Effects of the Invention]

[0013] In the internally corrosion-resistant cast iron pipe according to this invention, the combined mortar layer, primer layer, and coating layer result in overall superior adhesion of the three components mentioned above. This reduces the labor involved in laying the pipe. [Brief explanation of the drawing]

[0014] [Figure 1] Cross-sectional view showing an overview of an embodiment of an inner surface corrosion-resistant cast iron pipe according to the present invention [Figure 2] Enlarged cross-sectional view of a straight pipe portion showing a first embodiment of an inner surface corrosion-resistant cast iron pipe according to the present invention [Figure 3] Enlarged cross-sectional view of a straight pipe portion showing a second embodiment of an inner surface corrosion-resistant cast iron pipe according to the present invention [Figure 4] Cross-sectional view at the stage of forming a cement mortar layer in the production of an inner surface corrosion-resistant cast iron pipe according to the present invention [Figure 5] Cross-sectional view at the stage of polishing and removing the urethane layer from the cement mortar layer [Figure 6] Cross-sectional view at the stage of applying a primer layer [Figure 7] Flow chart showing an example of the procedure of a manufacturing method of an inner surface corrosion-resistant cast iron pipe according to the present invention [Figure 8] Photograph of a test piece in Example 1b [Figure 9] Photograph of a test piece in Comparative Example 1a [Figure 10] Photograph of a test piece in Comparative Example 1b [Figure 11] Photograph of a test piece in Comparative Example 2a [Figure 12] Photograph of a test piece in Comparative Example 2b [Figure 13] Photograph of a test piece in Comparative Example 3a

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be specifically described. An inner surface corrosion-resistant cast iron pipe according to an embodiment of the present invention includes, on the inner surface side of a cast iron pipe, in order from the surface of the inner surface of the pipe, a mortar layer derived from cement mortar, a primer layer containing a urethane resin, and a coating film layer containing a vinyl ester resin. According to this configuration, the obtained inner surface corrosion-resistant cast iron pipe is excellent in terms of three indexes of adhesion: initial adhesion, adhesion after water resistance, and adhesion at the time of cutting. Further, according to this configuration, the obtained inner surface corrosion-resistant cast iron pipe can be used for water supply, sewerage, industrial water, and / or agricultural water.

[0016] This invention relates to an internally corrosion-resistant cast iron pipe, in which a corrosion-resistant layer 20 or 20a is provided on the inner surface of a straight section 13 formed between a socket 11 and a receiving end 12 in a straight-tube type cast iron pipe 1 as shown in Figure 1.

[0017] In the first embodiment of this invention, the corrosion protection layer 20 has, in order from the inner surface of the cast iron pipe 1, a mortar layer 21, a primer layer 25, and a coating layer 26, as shown in the enlarged cross-sectional view of Figure 2. In the second embodiment of this invention, the corrosion protection layer 20a has, between the mortar layer 21 and the primer layer 25, as shown in the enlarged cross-sectional view of Figure 3.

[0018] In this invention, a cast iron pipe 1 produced by centrifugal casting is preferably used as the cast iron pipe 1. The type of cast iron pipe is not particularly limited, and general ductile iron pipes can be used. The inner surface of the cast iron pipe 1 is lined with mortar to prevent corrosion of the surface.

[0019] The mortar layer 21 is a layer derived from cement mortar and is part of the cement mortar layer 30 formed by lining with cement mortar. The cement mortar layer 30 is formed by supplying cement mortar to the inner surface of the cast iron pipe 1 while applying centrifugal force and allowing it to harden. Cement mortar is a common type of mortar made by mixing cement with aggregates such as sand.

[0020] Figure 4 shows a cross-sectional view of the cast iron pipe 1 at the stage when a cement mortar layer 30 has been formed on its inner surface during the manufacturing of the internally corrosion-resistant cast iron pipe according to this invention. The cement mortar layer 30 is formed by mortar lining, consisting of a mortar layer 21, a paste layer 22, and a laitance layer 23, in that order from the inner surface side of the pipe. These layers are formed when the aggregate contained in the cement mortar gathers on the outer side (lower side in Figure 4) due to the centrifugal force of the pipe rotating during manufacturing, while lighter impurities gather on the inner side (upper side in Figure 4). The mortar layer 21 is a layer containing aggregate, and the paste layer 22, which follows the mortar layer 21, is a layer that contains almost no aggregate. There is no strict boundary line between the mortar layer 21 and the paste layer 22, and the mortar layer 21 may include a part of the paste layer 22. However, it can be visually determined from the cross-section that the mortar layer 21 and the paste layer 22 are layer-separated.

[0021] The laitance layer 23 is a layer formed from lightweight impurities contained in the cement mortar. If the laitance layer 23 remains, it will reduce adhesion with the primer layer 25, so it is necessary to remove at least the laitance layer 23. Figure 5 shows a cross-sectional view of the cement mortar layer 30a formed after the laitance layer 23 has been removed from the cement mortar layer 30 after lining, exposing the paste layer 22. As a method for removing the laitance layer 23, removal by polishing from the surface is preferable, and for example, a flap wheel can be used. Furthermore, the thickness of the mortar lining layer 30a or mortar layer 21 after the laitance layer 23 has been removed is preferably 4 mm or more and 15 mm or less. If it is less than 4 mm, the surface of the mortar lining layer 30a (i.e., the surface of the paste layer 22) or the surface of the mortar layer 21 will not be smooth due to the irregularities formed on the inner surface of the straight section 13 after casting, and if it is thicker than 15 mm, the water passage cross-sectional area on the inner surface of the pipe will be reduced more than necessary.

[0022] In the example shown in Figure 5, the paste layer 22 remains, but the paste layer 22 may be completely removed along with the laitance layer 23 to expose the mortar layer 21. If the internal corrosion-resistant cast iron pipe is manufactured with the paste layer 22 completely removed, it will be the first embodiment shown in Figure 2. If the internal corrosion-resistant cast iron pipe is manufactured with the paste layer 22 remaining, it will be the second embodiment shown in Figure 3. However, as described above, the boundary line between the paste layer 22 and the mortar layer 21 is not clear, so even if polishing is performed with the intention of exposing the mortar layer 21, some of the paste layer 22 without aggregate may remain. In the present invention, the mortar layer 21 may be accompanied by the paste layer 22, or the paste layer 22 may be completely removed. However, from the viewpoint of adhesion at the time of cutting, it tends to exhibit better properties when the paste layer 22 is completely removed. That is, from the viewpoint of adhesion at the time of cutting, it is preferable that the amount of paste layer 22 remaining on the surface of the mortar layer 21 is small, and it is more preferable that the paste layer 22 is completely removed and the mortar layer 21 is exposed.

[0023] The primer layer 25 is a layer formed by applying a primer containing urethane resin to the inner surface (inner circumference side of the pipe) of the mortar layer 21 or paste layer 22. By interposing a primer containing urethane resin between the mortar layer 21 or paste layer 22 and the coating layer 26, the adhesion between the mortar layer 21 or paste layer 22 and the coating layer 26 is greatly improved, resulting in excellent adhesion, especially during cutting, and enabling the production of an internally corrosion-resistant cast iron pipe with a balanced adhesion index.

[0024] The urethane resin content of the above primer is preferably 5% to 50% by weight, more preferably 7% to 40% by weight, even more preferably 9% to 30% by weight, and particularly preferably 10% to 20% by weight. With this configuration, the adhesion between the mortar layer 21 or paste layer 22 and the coating layer 26 is greatly improved, and in particular, the adhesion at the time of cutting is excellent, and an internal corrosion-resistant cast iron pipe with a balanced ratio of the three indicators of adhesion can be obtained.

[0025] The mortar layer 21 is followed by a paste layer 22 derived from cement mortar, and the paste layer 22 and the primer layer 25 may be in contact. In other words, the laitance layer 23 is removed to the extent that a portion of the paste layer 22 derived from cement mortar remains on the inner circumference surface of the mortar layer 21, and the paste layer 22 and the primer layer 25 may be in contact. This configuration has the advantage that the resulting internally corrosion-resistant cast iron pipe has excellent adhesion when cut.

[0026] It is preferable that the mortar layer 21 and the primer layer 25 are in contact. In other words, it is preferable that the primer layer 25 comes into contact with the surface of the exposed mortar layer 21 by polishing the inner surface of the pipe until aggregate can be seen, and both the laitance layer 23 and the paste layer 22 are removed. With this configuration, the resulting internally corrosion-resistant cast iron pipe has the advantage of having particularly superior adhesion at the time of cutting compared to one in which the paste layer 22 remains.

[0027] The coating layer 26 is formed by applying a paint containing vinyl ester resin onto the primer layer 25. Because vinyl ester resin exhibits high acid resistance, the internal corrosion-resistant cast iron pipe according to this invention can prevent acidic substances from penetrating to the mortar layer 21 even in acidic sewage environments, thereby exhibiting high durability by suppressing deterioration of the mortar lining. The film thickness of the coating layer 26 is preferably 100 μm or more and 800 μm or less. If the film thickness of the coating layer 26 is less than 100 μm, the protective effect on the mortar layer 21 and / or the cast iron pipe 1 tends to be insufficient, even when using a paint containing vinyl ester resin. On the other hand, if the film thickness of the coating layer 26 is thicker than 800 μm, the reduction in the water-permeable cross-sectional area on the inner surface of the pipe becomes significant. It is preferable that the paint containing vinyl ester resin does not contain additives such as glass. This configuration has the advantage of improving the adhesion between the paint containing vinyl ester resin and the primer.

[0028] As the vinyl ester resin mentioned above, for example, an epibis-based vinyl ester consisting of a combination of epichlorohydrin and bisphenol A can be used.

[0029] The vinyl ester resin content of the paint containing vinyl ester resin is preferably 30% to 80% by weight, more preferably 40% to 70% by weight, even more preferably 45% to 65% by weight, and particularly preferably 50% to 60% by weight. With this configuration, the adhesion between the mortar layer 21 or paste layer 22 and the coating layer 26 is greatly improved, and in particular, the adhesion at the time of cutting is excellent, making it possible to obtain an internally corrosion-resistant cast iron pipe with a balanced ratio of the three indicators of adhesion.

[0030] The primer layer 25 and the coating layer 26 described above can be formed by methods such as roller coating, brush coating, or spray coating.

[0031] In a method for manufacturing an internally corrosion-resistant cast iron pipe according to one embodiment of the present invention (hereinafter sometimes referred to as "this manufacturing method"), the following steps are performed in order: forming a cement mortar layer on the inner surface of the cast iron pipe while rotating the cast iron pipe (hereinafter sometimes referred to as "cement mortar layer formation step"), grinding off the laitance layer present on the surface side of the cement mortar layer after the cement mortar layer has hardened to expose the mortar layer or paste layer (hereinafter sometimes referred to as "mortar layer remaining step"), applying a primer containing urethane resin to the surface of the exposed mortar layer or paste layer to form a primer layer (hereinafter sometimes referred to as "primer layer formation step"), and applying vinyl ester resin to the surface of the primer layer to form a coating layer (hereinafter sometimes referred to as "coating layer formation step"). With this configuration, the internally corrosion-resistant cast iron pipe obtained by this manufacturing method can have a corrosion-resistant layer with high adhesion in three indicators.

[0032] The general outline of this manufacturing method will be explained using Figure 7.

[0033] [Cement mortar layer formation process] In the cement mortar layer formation process, a cement mortar layer 30 is formed on the inner surface of the cast iron pipe 1 while the pipe is rotated. Due to the centrifugal force applied during and after coating, the distribution of aggregate (sand) in the cement mortar layer 30 becomes uneven, with the aggregate content increasing towards the cast iron pipe 1 side (outer circumference side of the pipe). As shown in Figure 4, a mortar layer 21 is formed in the area on the outer circumference side of the pipe (lower part of Figure 4) where there is a lot of aggregate, and a paste layer 22 is formed in the area on the inner circumference side of the pipe (upper part of Figure 4) where there is less aggregate. Furthermore, lightweight impurities contained in the cement mortar accumulate on top of the paste layer 22 (on the inner surface of the pipe), forming a laitance layer 23. This cement mortar layer formation process creates a layered cement mortar layer 30 as shown in Figure 4.

[0034] [Mortar layer remaining process] In the mortar layer retention process, after the cement mortar layer 30 has hardened, the laitance layer 23 present on the surface side of the cement mortar layer 30 is polished off to expose the mortar layer 21 or paste layer 22. In the mortar layer retention process, as shown in Figure 5, the mortar layer 21 and paste layer 22 may be left intact and the paste layer 22 exposed by polishing off only the laitance layer 23 of the cement mortar layer 30. Alternatively, in the mortar layer retention process, the mortar layer 21 may be left intact and the mortar layer 21 exposed by polishing off both the laitance layer 23 and the paste layer 22 of the cement mortar layer 30. In this case, there is no strict boundary between the mortar layer 21 and the paste layer 22. Therefore, the mortar layer 21 may be accompanied by a part of the paste layer 22, or the paste layer 22 may be completely removed. From the viewpoint of adhesion when cutting the internally corrosion-resistant cast iron pipe, it is preferable to remove the laitance layer 23 and paste layer 22 of the cement mortar layer 30 by grinding them off, thereby leaving only the mortar layer 21 and exposing the mortar layer 21.

[0035] [Primer layer formation process] In the primer layer formation process, a primer containing urethane resin is applied to the surface of the exposed mortar layer 21 or paste layer 22 to form a primer layer 25 (Figure 6).

[0036] The primer does not need to be applied only once; the primer layer 25 may be formed by applying multiple coats. The amount of primer applied when forming the primer layer 25 is 50 g / m². 2 More than 500g / m 2 Preferably, it is 100 g / m² or less. 2 More than 300g / m 2 It is more preferable that the following conditions are met: 50 g / m 2 If the amount is less than 500 g / m², the adhesion stability effect with the coating layer 26 will be insufficient. 2 Too much may actually reduce adhesion.

[0037] [Coating film layer formation process] In the coating layer formation process, a vinyl ester resin is applied to the surface of the primer layer 25 to form a coating layer 26 (Figures 2 and 3).

[0038] The primer layer 25 and the coating layer 26 described above can be formed by methods such as roller coating, brush coating, or spray coating. [Examples]

[0039] The invention will be specifically illustrated below with examples of actual manufacturing of internally corrosion-resistant cast iron pipes according to this invention. First, the materials used will be described. [Primer containing vinyl ester resin] • Tough Barrier #200 Primer: Manufactured by Nippon Special Paint Co., Ltd. (Vinyl ester resin content: 35% to 45% by weight) • Tough Barrier #200 Metal Primer M: Manufactured by Nippon Special Paint Co., Ltd. (Vinyl ester resin content: 55% to 65% by weight) [Primer containing acrylic resin] • Seal Coat KS-1 Maru Shinpo: Manufactured by DIC Corporation (Acrylic resin content 15% by weight) [Primer containing urethane resin] • RS#123LLR-2 Primer: Manufactured by Sotec Co., Ltd. (15% by weight of urethane resin) • RegiGuard UR Primer: Manufactured by Dainippon Paint Co., Ltd. (Urethane resin content: 15% by weight) [Paint containing vinyl ester resin] • Tough Barrier #200 Topcoat Gray: Manufactured by Nippon Special Paint Co., Ltd. (Vinyl ester resin content: 50% to 60% by weight)

[0040] <Method for manufacturing test specimens: Cement mortar layer formation process> As a cast iron pipe, a ductile iron pipe with a nominal diameter of 150 mm, manufactured by Kurimoto Iron Works Co., Ltd., was rotated while a mortar lining of cement mortar was applied to the inner surface of the pipe to form a cement mortar layer, creating a mortar-lined pipe. A portion of this pipe was cut to 150 mm x 90 mm to be used as a test specimen.

[0041] <Polishing method and mortar layer retention process> • As a "normal polishing" procedure, the surface of the cement mortar layer 30 of the test specimen was polished with a flap wheel #40 (manufactured by Noritake Co., Ltd.) to remove the laitance layer 23 to the extent that the paste layer 22 remained partially intact, thereby exposing the paste layer 22. • For "aggregate polishing," the surface of the cement mortar layer 30 of the test specimen was polished with a flap wheel #40 (manufactured by Noritake Co., Ltd.) until aggregate could be seen on the surface of the test specimen, removing the laitance layer 23 and paste layer 22 to expose the mortar layer 21.

[0042] <Method and process for forming a primer layer> The exposed paste layer 22 or mortar layer 21 was coated with the primers listed in Table 1 in the amounts listed in Table 1. In comparative examples 4a and 4b, where a secondary coating was performed, a primary coating was applied, and the secondary coating was performed after the primary coating had hardened.

[0043] <Method and process for forming a coating layer> The paint Tough Barrier #200 topcoat gray, containing the vinyl ester resin listed in Table 1, was applied to a film thickness of 300 μm.

[0044] [Table 1]

[0045] Each test specimen produced using the above procedure was evaluated as follows. The results are shown in Table 1. In Comparative Examples 3 and 4, when a paint containing vinyl ester resin was applied to the surface of a primer containing acrylic resin, the paint containing vinyl ester resin reacted with the primer, resulting in a dissolved paint film (in this specification, this state may be referred to as "redissolution").

[0046] <Method for evaluating adhesion during cutting> Seven days after the coating layer had formed, test pieces were cut with a band saw (manufactured by Rex Industries Co., Ltd.: Mantis 180WA, model XB180WA, cutting blade: grid saw (product number 4752201)), and the presence or absence of peeling of the coating layer from the cut end was checked. × (unacceptable) indicates that irreparable cracking, peeling, or blistering occurred; ○ (acceptable) indicates that cracking, peeling, or blistering occurred to a repairable extent; and ◎ (good) indicates that no cracking, peeling, or blistering occurred. In this specification, when an internally corrosion-resistant cast iron pipe is said to have "excellent adhesion at the time of cutting," it means that the above evaluation of adhesion at the time of cutting is ○ (acceptable) or ◎ (good).

[0047] For reference, photographs showing the presence or absence of peeling are shown for some of the examples and comparative examples. Figure 8 is a series of photographs of the test piece of Example 1b taken from different angles. No peeling was observed at the cut end, and it was judged as "good". Figure 9 is a photograph of the cut test piece of Comparative Example 1a. A large area of ​​peeling extended from the end, and it was judged as "unacceptable". Figure 10 is a photograph of the cut test piece of Comparative Example 1b. Although the peeled area was slightly smaller than in Figure 9, it peeled from the entire end, and it was judged as "unacceptable". Figure 11 is a photograph of the cut test piece of Comparative Example 2a. Similar to Figure 9, a large area of ​​peeling extended from the end, and it was judged as "unacceptable". Figure 12 is a photograph of the cut test piece of Comparative Example 2b. Although the peeled area was slightly smaller than in Figure 11, peeling was confirmed on the right side of the figure, and it was judged as "unacceptable". Figure 13 is a photograph of the cut test piece of Comparative Example 3a. Not only did peeling occur at the edges, but significant dissolution of the coating layer was observed near the right edge in the diagram, resulting in a "failure" rating.

[0048] <Method for evaluating initial adhesion> Test specimens that had been allowed to form a coating layer for 7 days were subjected to the cross-cut method specified in JIS K5600-5-6 (ISO 2409). The classification was evaluated as ○ (acceptable) if it fell under either classification 0 (the edges of the cuts are perfectly smooth and there is no peeling at any of the grid lines) or classification 1 (small peeling of the coating at the intersection of the cuts; the impact at the cross-cut portion does not clearly exceed 5%), and as × (unacceptable) if it fell under classification 2 to 5 peeling. In this specification, when an internally corrosion-resistant cast iron pipe is said to have "excellent initial adhesion," it means that the initial adhesion evaluation described above is ○ (acceptable).

[0049] <Method for evaluating water-resistant adhesion> Test specimens, 7 days after the formation of the coating layer, were immersed in tap water for 4 weeks and then dried at 23°C for 2 hours. Subsequently, the cross-cut method specified in JIS K5600-5-6 (ISO 2409) was performed, and the specimens were evaluated using the same classification as the initial adhesion described above. In this specification, when an internally corrosion-resistant cast iron pipe is described as having "excellent adhesion after water resistance," it means that the evaluation of the adhesion after water resistance described above is ○ (acceptable). [Explanation of Symbols]

[0050] 1 Cast iron pipe 11 Socket 12 socket 13 Straight section 20, 20a Corrosion-resistant layer 21 Mortar layer 22 Paste layer 23 Laitance layer 25 Primer layer 26 Coating layer 30,30a Cement mortar layer

Claims

1. An internally corrosion-resistant cast iron pipe comprising, on the inner surface of the pipe, a mortar layer derived from cement mortar, a primer layer containing urethane resin, and a coating layer containing vinyl ester resin, in that order from the inner surface of the pipe.

2. The internal corrosion-resistant cast iron pipe according to claim 1, further comprising a paste layer derived from the cement mortar following the mortar layer, wherein the paste layer and the primer layer are in contact.

3. The internal corrosion-resistant cast iron pipe according to claim 1, wherein the mortar layer and the primer layer are in contact.

4. The step of forming a cement mortar layer on the inner surface of the cast iron pipe while rotating the cast iron pipe, After the cement mortar layer has hardened, the laitance layer present on the surface side of the cement mortar layer is polished off to expose the mortar layer or paste layer. The step of applying a primer containing urethane resin to the surface of the exposed mortar layer or paste layer described above to form a primer layer, The step of applying a vinyl ester resin to the surface of the above-mentioned primer layer to form a coating layer. A method for manufacturing internally corrosion-resistant cast iron pipes, which involves sequentially performing the following steps.

5. The amount of primer applied to form the above-mentioned primer layer is 50 g / m². ２ More than 500g / m ２ The method for manufacturing an internally corrosion-resistant cast iron pipe according to claim 4.

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