JP2012149336A - Tube with thermally sprayed outer surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance further the corrosion resistance of a tube with a thermally sprayed outer surface made of cast iron or steel with the anticorrosion layer of the pseudo Zn-Al alloy on outside.SOLUTION: Since the anticorrosion layer formed on the outer surface of the tube by metal thermal spraying is made by a pseudo alloy layer which is a mixture of a zinc alloy layer containing a zinc layer or aluminum and an aluminum alloy layer containing silicon, a corrosion product arises which is firm and hard to exfoliate on the surface of anticorrosion layer under corrosive environment to more improve corrosion resistance of the tube compared to the one having an anticorrosion layer of the conventional pseudo Zn-Al alloy, thereby extending the anticorrosion life.

Description

  The present invention relates to an outer surface spray tube made of cast iron or steel having an anticorrosion layer formed on the outer surface by metal spraying.

  Cast iron or steel outer spray tubes having an anticorrosion layer formed on the outer surface by metal spraying are widely used, and are often used particularly for embedding applications where corrosion resistance is required. Many of these outer surface sprayed pipes have a zinc sprayed layer as the anticorrosive layer, but those having a higher corrosion resistance include an alloy of zinc and aluminum or a pseudoalloy anticorrosive layer. The reason why the anticorrosion performance of the anticorrosion layer containing aluminum is higher than that of the anticorrosion layer containing zinc alone is that aluminum suppresses elution due to ionization of zinc.

  The zinc-aluminum pseudo-alloy anti-corrosion layer is a mixture of zinc and aluminum that is sprayed simultaneously with zinc and aluminum at the same time, and has a higher anti-corrosion performance than that formed by spraying an alloy of zinc and aluminum. Is advantageous in terms of cost (see Patent Document 1). In addition, in order to improve the anticorrosion performance, there is also one in which magnesium is added to aluminum forming a pseudo alloy.

  Such an outer surface sprayed tube having an anticorrosion layer of a zinc-aluminum pseudo-alloy or a zinc-magnesium-containing aluminum alloy pseudo-alloy (hereinafter collectively referred to as a Zn-Al pseudo-alloy) can be used even in an embedded environment. Excellent corrosion resistance. However, in recent years, there has been a demand for longer life by further improving corrosion resistance.

JP-A-10-264301

  An object of the present invention is to further improve the corrosion resistance of an outer surface spray tube made of cast iron or steel having an anti-corrosion layer of Zn-Al based pseudoalloy on the outer surface.

  In order to solve the above-mentioned problems, the present inventors have conducted research on a corrosion prevention layer of a Zn-Al-based pseudoalloy, and as a result, in the conventional corrosion prevention layer, a corrosion product generated in a corrosive environment is resistant to corrosion. Although it works as a protective layer, it has been found that when silicon (Si) is added in an appropriate amount to aluminum forming a pseudo-alloy, the corrosion product becomes dense and becomes a strong protective layer to further enhance the corrosion resistance.

  Therefore, the present invention provides a pseudo-alloy in which an outer surface spray tube made of cast iron or steel having a corrosion prevention layer formed by metal spraying on the outer surface is formed by mixing the anticorrosion layer with a zinc layer and an aluminum alloy layer containing silicon. It was a layer.

  According to the above configuration, the corrosion product generated on the surface of the anticorrosion layer in a corrosive environment works as a protective layer against corrosion without peeling for a long period of time, and thus has a conventional anticorrosion layer of Zn-Al-based pseudoalloy. Corrosion resistance superior to that can be obtained.

  Moreover, the zinc layer forming the pseudo alloy layer can be replaced with a zinc alloy layer containing aluminum. In this way, excellent corrosion resistance equivalent to the case where a pseudo alloy layer is formed by the zinc layer and the aluminum alloy layer can be obtained.

  As described above, the present invention corrodes the anticorrosion layer on the outer surface of the outer surface spray tube by using a zinc layer or a pseudo alloy layer in which a zinc alloy layer containing aluminum and an aluminum alloy layer containing silicon are mixed. Since a stable corrosion product is generated on the surface of the anticorrosion layer in a corrosive environment, the corrosion resistance of the tube can be improved and the corrosion resistance life can be extended as compared with the conventional anticorrosion layer of Zn-Al system pseudoalloy. it can.

  The outer surface sprayed tube of the first embodiment of the present invention has a pseudo alloy layer (corrosion protection layer) in which a zinc layer and an aluminum alloy layer containing 12 mass% of silicon are mixed by metal spraying on the outer surface of a cast iron tube or a steel tube. Formed.

Hereinafter, a first corrosion resistance test performed for confirming the corrosion resistance of the outer surface spray tube of the first embodiment will be described. The test piece was arc sprayed at a volume ratio of 1: 1 to a 150 mm × 70 mm × 1.6 mm mild steel plate subjected to sandblasting and a zinc wire having a diameter of 1.6 mm and an aluminum alloy wire containing 12 mass% of silicon. Example 1 in which a pseudo alloy layer of 130 g / m ² was formed was used (Example 1).

  As comparative examples, the anticorrosion layer is a zinc layer (Comparative Example 1), a zinc-aluminum pseudo-alloy layer (Comparative Example 2), and a pseudo-alloy layer (Comparative Example 3) with an aluminum alloy containing 5 mass% of zinc and magnesium. A test piece was prepared. The production method was such that the same amount of anticorrosion layer was formed by the same thermal spraying method except that the material of the metal wire for thermal spraying (thermal spraying wire) was different from that in the example.

  Then, after putting a crosscut having a side of 50 mm in the center of each test piece so as to reach the ground, a cycle corrosion test (cycle A: salt water) defined in JIS K5600-7-9 is performed on each test piece. The cycle of spraying 2 hr → drying 4 hr → wetting 2 hr was repeated, and the number of days until red rust occurred was measured. The measurement results are shown in Table 1.

  From Table 1, in Example 1, the number of days until the occurrence of red rust is much longer than in each Comparative Example, and the corrosion resistance is twice or more that of Comparative Examples 2 and 3 in which a conventional anticorrosive layer of Zn-Al based pseudoalloy is formed. It can be seen that Moreover, when the surface of each test piece after a test was observed, in Comparative Examples 2 and 3, the peeling of the corrosion product was often observed, whereas the corrosion product of Example 1 was stably on the surface of the test piece. Existed.

  Next, the second and third embodiments will be described. In the outer surface sprayed tube of the second embodiment, the silicon content of the aluminum alloy layer forming the pseudo alloy layer of the first embodiment is set to 5 mass%. On the other hand, the outer surface spray tube of the third embodiment is obtained by replacing the zinc layer forming the pseudo alloy layer of the second embodiment with a zinc alloy layer containing 15 mass% of aluminum.

  Regarding the second and third embodiments, the second corrosion resistance test was performed in substantially the same manner as the first corrosion resistance test described above. However, in this second corrosion resistance test, the test piece was immersed in salt water once a week in the middle of the cyclic corrosion test, and the potential measurement was performed. Therefore, a test piece corresponding to the first embodiment was also prepared, In the embodiment, the corrosion resistance can be compared. Table 2 shows the configuration of the test piece.

Of the test pieces shown in Table 2, Examples 2 to 4 correspond to the first embodiment, Examples 5 to 7 correspond to the second embodiment, and Example 8 corresponds to the third embodiment. In Example 2, the sprayed amount of the pseudo alloy layer was increased by using the same sprayed wire as in Example 1 of the first corrosion resistance test. Similarly, the comparative example 4 uses the same thermal spray wire material as the comparative example 2 of a 1st corrosion resistance test, and increased the amount of thermal spraying. In Examples 2 to 4 and Examples 5 to 7, the composition of the pseudo alloy layer is changed by changing the diameter of the sprayed wire. Then, the case where the case where the spray amount was 260 g / m ² and 325 g / m ² of the pseudo alloy layer of each test piece, subjected to the same cycle corrosion test and the first corrosion test was measured the number of days until red rust . The measurement results are shown in Tables 3 and 4 together with the sprayed coating thickness obtained from the spraying amount and composition of the pseudoalloy layer.

  From Tables 3 and 4, it can be seen that the number of days until the occurrence of red rust in each Example of the second corrosion resistance test is much longer than that in Comparative Example 4. In Example 8, the test was stopped when the number of days in which red rust did not occur reached 52 days and it was confirmed that the sample had corrosion resistance equivalent to that of the other examples. In addition, within the range of the conditions of the second corrosion resistance test, when the thermal spray amount is the same in each example, there is a correlation between the thermal spray coating thickness, the silicon content of the aluminum alloy layer, and the days until the occurrence of red rust (corrosion resistance). It can also be seen that when the spraying amount is changed in the same example (same spraying wire conditions are the same), the corrosion resistance is higher when the spraying amount is larger (the thickness of the sprayed coating is thicker).

  In Table 1 and Tables 3 and 4, when the conditions of the sprayed wire are the same, that is, when Example 1 and Example 2 or Comparative Example 2 and Comparative Example 4 are compared, Example 2 is more than Example 1. In Comparative Example 4, the number of days until occurrence of red rust is longer than that in Comparative Example 2. This is considered to be due to the fact that the amount of thermal spraying was larger in the second corrosion resistance test than in the first corrosion resistance test and that the salt water immersion was performed once a week as described above.

  From the results of the first and second corrosion resistance tests, the outer surface sprayed tube of each embodiment has much better corrosion resistance than that having a conventional anticorrosion layer of Zn-Al pseudo-alloy, and is extremely corrosion resistant. It has been confirmed that it has a long life.

Claims (1)

  In an outer surface sprayed tube made of cast iron or steel having an anticorrosion layer formed by metal spraying on the outer surface, the anticorrosion layer is a mixture of a zinc layer or a zinc alloy layer containing aluminum and an aluminum alloy layer containing silicon. An outer surface sprayed tube characterized by being a pseudo-alloy layer.