WO2017159054A1

WO2017159054A1 - Member formed from aluminum alloy and lng vaporizer

Info

Publication number: WO2017159054A1
Application number: PCT/JP2017/002449
Authority: WO
Inventors: 真司阪下; 亘漆原; 祐二澄田; 龍生吉田; 康行堀家; 大造青木
Original assignee: 株式会社神戸製鋼所
Priority date: 2016-03-17
Filing date: 2017-01-25
Publication date: 2017-09-21
Also published as: JP6838864B2; JP2017166771A; TW201741468A

Abstract

Members formed from an aluminum alloy (a heat transfer pipe 13, a lower header pipe 14 and a trough 12) comprise a base that is formed from an aluminum alloy and a coating film that is formed on the surface of the base. The coating film contains from 0.8% by mass to 20.7% by mass (inclusive) of magnesium and from 0.004% by mass to 1.20% by mass (inclusive) of chromium, with the balance made up of aluminum and unavoidable impurities. An LNG vaporizer 1 is provided with a heat transfer pipe 13, a lower header pipe 14 and a trough 12, which are formed of the above-described members formed from an aluminum alloy.

Description

Aluminum alloy members and LNG vaporizer

The present invention relates to an aluminum alloy member and an LNG vaporizer. The present invention particularly relates to an aluminum alloy member having excellent corrosion resistance and an LNG vaporizer provided with the aluminum alloy member.

DESCRIPTION OF RELATED ART Conventionally, the aluminum alloy member which has favorable heat conductivity is used abundantly as heat-transfer members, such as a heat exchanger tube used for a liquefied natural gas (LNG) vaporizer and various heat exchangers, and a header pipe. Such aluminum alloy members may locally undergo corrosion (pitting corrosion) by being exposed to the air or water for a long time, and as a result, they may lead to penetration. Therefore, it is necessary to take some anticorrosion measures on the aluminum alloy member. As one of them, the cathodic protection method is often used. Specifically, an anticorrosive effect can be obtained by bringing a sacrificial anticorrosion film or fin material formed of an Al-Zn alloy or the like, which has a potential lower than that of an aluminum alloy base material, to the base material. Are known. In addition, in a closed system such as the inner surface of a heat transfer tube in a heat exchanger, adding a corrosion inhibitor (inhibitor) to circulating water is also used in combination.

In recent years, LNG has attracted attention as clean energy, and is usually stored and transported in a liquefied state at a cryogenic temperature of -162 ° C or less. Then, in the open rack type LNG vaporizer (ORV), the LNG is vaporized before use by heat exchange using seawater as a heat source. Generally, in the ORV, a heat transfer tube made of aluminum alloy is arranged in a panel shape, and LNG flows from the lower side to the upper side inside the heat transfer tube, and seawater flows from the upper side to the lower side of the outer surface of the panel It has a structure that flows down. For this reason, since the heat exchanger tube of ORV exposes the outer surface to seawater, the progress of corrosion becomes a problem. On the other hand, as disclosed in Patent Documents 1 and 2 below, a countermeasure is proposed to form a sacrificial anticorrosive coating made of an Al-Zn alloy or an Al-Mg alloy on the outer surface of a heat transfer tube by a thermal spraying method or a cladding method. It is done.

In the heat transfer tube of ORV, seawater intrudes into pores inevitably present in the sacrificial coating, and thereby corrosion progresses preferentially at the interface between the sacrificial coating and the substrate. There is a problem that swelling or peeling of the sacrificial anticorrosive coating occurs as a result of volumetric expansion caused by freezing of the corrosion products formed with this corrosion or seawater entering into the pores, and as a result, the life of the heat transfer tube becomes short. . On the other hand, in the following patent document 1, preventing the swelling and peeling of a sacrificial anticorrosive coating is proposed by adjusting the roughness in the interface of a sacrificial anticorrosive film and a base material.

As disclosed in Patent Documents 1 and 2 below, the durability of the heat transfer tube of ORV exposed to a corrosive medium such as seawater by forming a sacrificial anticorrosive coating made of Al-Zn alloy or Al-Mg alloy. The quality can be improved to some extent. However, the anticorrosion effect by these conventional measures is not sufficient, and in order to improve the safety of the LNG vaporizer and various heat exchangers from the viewpoint of stable energy supply, further reduction of corrosion and life extension are required.

In addition, copper ions contained in trace amounts in seawater precipitate on the surface of the aluminum alloy and act as a cathode, thereby significantly promoting the corrosion of the aluminum alloy. For this reason, in the sea area where the content of copper ions is large, the sacrificial anticorrosive coating is extremely deteriorated and the corrosion life becomes extremely short, so that effective measures for corrosion reduction are further required. When corrosion on the outer surface side is required as in the heat transfer tube of ORV, since the use of a corrosion inhibitor is also difficult, corrosion prevention measures from the material side are necessary.

JP, 2014-157009, A JP, 2007-78237, A

An object of the present invention is to provide a long-life aluminum alloy member having excellent corrosion resistance and an LNG vaporizer including the aluminum alloy member.

The aluminum alloy member according to an aspect of the present invention includes a base made of an aluminum alloy, and a film formed on the surface of the base. The film is made of an aluminum alloy containing 0.8% by mass or more and 20.7% by mass or less of magnesium and 0.004% by mass or more and 1.20% by mass or less of chromium.

An LNG vaporizer according to another aspect of the present invention includes the above-described aluminum alloy member.

It is a schematic diagram which shows the structure seen from the side of the open rack type LNG vaporizer in Embodiment 1 of this invention. It is a schematic diagram which shows the cross-section of the said open rack type LNG vaporizer. It is a schematic diagram which shows the cross-section of the heat exchanger tube which comprises the said open rack type LNG vaporizer. It is a schematic diagram which shows the cross-section of the lower header pipe which comprises the said open rack type LNG vaporizer. It is a schematic diagram which shows the cross-section of the trough which comprises the said open rack type LNG vaporizer. It is a schematic diagram which shows the structure of the intermediate medium type LNG vaporizer in Embodiment 2 of this invention. It is a schematic diagram which shows the cross-section of the heat exchanger tube which comprises the said intermediate-medium type LNG vaporizer. It is a schematic diagram which shows the test material for evaluating the swelling resistance of a film. It is a schematic diagram which shows the test material for evaluating the sacrificial corrosion resistance of a film.

First, an outline of an aluminum alloy member and an LNG vaporizer according to an embodiment of the present invention will be described.

The aluminum alloy member according to the present embodiment includes a base made of an aluminum alloy, and a film formed on the surface of the base. The film is made of an aluminum alloy containing 0.8% by mass or more and 20.7% by mass or less of magnesium and 0.004% by mass or more and 1.20% by mass or less of chromium.

The present inventors diligently studied measures for improving the corrosion resistance of aluminum alloy members exposed to a corrosive medium such as seawater. As a result, in the film made of an aluminum alloy formed on the surface of the substrate, adjusting the composition range of magnesium (hereinafter also represented by the chemical symbol “Mg”. The same applies to other elements) and Cr as appropriate. Thus, the present inventors have found that the anti-corrosion property of the substrate is improved by suppressing the film swelling which is the initial deterioration of the film, and reducing the consumption of the film after the substrate exposure.

In the aluminum alloy member, the film formed on the surface of the base contains 0.8% by mass or more and 20.7% by mass or less of Mg. Mg in the coating improves the sacrificial corrosion resistance by causing the potential of the aluminum alloy to grow. In addition, Mg relaxes the pH in the vicinity of the surface and interface in a corrosive environment such as seawater to near neutrality by interaction with Cr in the coating, thereby suppressing local corrosion and interfacial peeling. In order to acquire such an effect, it is necessary to contain 0.8 mass% or more of Mg in a film. On the other hand, when the Mg content in the film becomes excessive, the corrosion progresses as the pH approaches alkalinity, and the consumption rate of the film increases, making it difficult to obtain a desired life. For this reason, it is necessary to adjust the Mg content in the film to 20.7% by mass or less.

In the aluminum alloy member, the corrosion resistance of the film is improved by adjusting the Mg content in the film to 0.8% by mass or more and 20.7% by mass or less, whereby the life is extended. There is. Moreover, it is preferable that it is 1 mass% or more, as for Mg content in a film, it is more preferable that it is 1.2 mass% or more, and it is more preferable that it is 1.5 mass% or more. Further, the Mg content in the film is preferably 20% by mass or less, more preferably 19% by mass or less, and still more preferably 18% by mass or less.

Further, in the aluminum alloy member, the coating contains 0.004% by mass or more and 1.20% by mass or less of Cr. By interaction with Mg, Cr in the film relaxes the pH in the vicinity of the surface and interface in a corrosive environment such as seawater so that it approaches neutrality, thereby suppressing local corrosion and interfacial peeling. In addition, Cr in the coating forms a protective film by densifying the corrosion product deposited on the surface of the aluminum alloy, and the protective film suppresses the penetration of corrosive substances, thereby preventing the corrosion of the aluminum alloy. Improve. These effects are particularly effective in seawater containing Cu ions. In order to obtain this effect, it is necessary to adjust the Cr content in the film to 0.004% by mass or more. On the other hand, when the Cr content in the film is excessive, a large amount of intermetallic compound of Al and Cr is formed, and the local corrosion is promoted, whereby the corrosion resistance is lowered. In order to prevent this, it is necessary to adjust the Cr content in the film to 1.20% by mass or less.

In the aluminum alloy member, in addition to the fact that the Mg content in the coating is adjusted within the above range, the Cr content is adjusted within the range of 0.004 mass% or more and 1.20 mass% or less . Thereby, the corrosion resistance of the film is improved. The Cr content in the film is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and still more preferably 0.03% by mass or more. The Cr content in the film is preferably 1.0% by mass or less, more preferably 0.9% by mass or less, and still more preferably 0.8% by mass or less.

In the aluminum alloy member, the coating may have a thickness of 50 μm to 1000 μm.

If the thickness of the coating is too small, it will be difficult to sufficiently suppress the entry of corrosive substances such as chloride ions and oxygen into the substrate. In addition, since the coating is dissolved early, it is difficult to obtain a sufficient anticorrosion effect over a long period of time. On the other hand, if the thickness of the film is too large, peeling occurs at the interface between the film and the substrate, and cracks occur in the film, making it difficult to obtain a sufficient anticorrosion effect.

From such a point of view, the thickness of the coating is preferably in the range of 50 μm to 1000 μm. With respect to the lower limit value, the thickness of the coating is more preferably 60 μm or more on average, and still more preferably 70 μm or more on average. With respect to the upper limit value, the thickness of the coating is more preferably 980 μm or less on average, and still more preferably 950 μm or less on average.

In the aluminum alloy member, the film may further contain 0.01% by mass or more and 20% by mass or less of Zn.

Since Zn in the film has a function of promoting the corrosion potential, the sacrificial corrosion resistance can be further improved. However, if the Zn content in the film becomes excessive, the disappearance rate of the film increases and it becomes difficult to obtain the desired life. For this reason, it is preferable that Zn content in a film is 0.01 mass% or more and 20 mass% or less. With regard to the lower limit value, the Zn content in the film is more preferably 0.02% by mass or more, and still more preferably 0.03% by mass or more. With regard to the upper limit value, the Zn content in the film is more preferably 19% by mass or less, and still more preferably 18% by mass or less.

In the above-mentioned aluminum alloy member, the film is made of 0.01% by mass to 1.0% by mass of Si, 0.01% by mass to 1.0% by mass of Fe, 0.01% by mass to 1.0% And at least one element selected from the group consisting of Cu by mass or less, Mn of 0.01 to 1.0 mass% and Ti of 0.01 to 1.0 mass%, and It may be

Si, Fe, Cu, Mn and Ti in the film contribute to the reduction of the film consumption rate by reducing the anodic reaction rate of Al. However, when the content of these elements in the film is excessive, the corrosion potential may be noble and the sacrificial corrosion resistance may be reduced. Therefore, the content of Si, Fe, Cu, Mn and Ti in the film is preferably 0.01% by mass or more and 1.0% by mass or less. With respect to the lower limit value, the content of these elements is more preferably 0.02% by mass or more, and still more preferably 0.03% by mass or more. With respect to the upper limit value, the content of these elements is more preferably 0.9% by mass or less, and still more preferably 0.8% by mass or less.

In the aluminum alloy member, the base material may be made of any one of 3000 series, 5000 series and 6000 series aluminum alloys. Here, "3000 series, 5000 series and 6000 series" are international aluminum alloy names.

In the above-mentioned aluminum alloy member, as the base material, one made of an aluminum alloy having good thermal conductivity and no brittle fracture even at low temperatures is used. Further, among the aluminum alloys, in view of strength, it is preferable to use ones of 2000 series, 3000 series, 5000 series, 6000 series or 7000 series. In particular, it is preferable to use ones of 3000 series, 5000 series or 6000 series. By using these aluminum alloys, good strength and corrosion resistance can be obtained. Specifically, A3003, A3203, A5052, A5154, A5083, A6061, A6063, or A6N01 can be used. Moreover, what heat-treated, such as hardening, tempering, and artificial aging, may be used as needed.

The aluminum alloy member may be used in a low temperature environment of 0 ° C. or less. The above-mentioned aluminum alloy member has a coating excellent in corrosion resistance formed on the surface of a substrate, and therefore can be used continuously with a long life even when used in a low temperature environment of 0 ° C. or less .

The aluminum alloy member may be a heat transfer pipe or a header pipe of an LNG vaporizer.

The aluminum alloy member is a member having a coating excellent in corrosion resistance formed on the surface of a substrate. For this reason, high corrosion resistance is achieved even when used under an environment where it is exposed to seawater, which is a corrosive medium, and is subjected to temperature change between low temperature and normal temperature, such as a heat transfer pipe or header pipe of an LNG vaporizer. You can get it.

The LNG vaporizer which concerns on this embodiment is equipped with the said aluminum-alloy-made members. The aluminum alloy member has the coating excellent in corrosion resistance formed on the surface of the base material, and by providing this, the life of the LNG vaporizer can be further extended.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

(Embodiment 1)
[LNG vaporizer]
First, the configuration of the LNG vaporizer 1 according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 schematically shows the configuration as viewed from the side of the LNG vaporizer 1. FIG. 2 schematically shows the cross-sectional structure of the LNG vaporizer 1 along the line segment II-II in FIG.

The LNG vaporizer 1 is an open rack type LNG vaporizer (ORV). The LNG vaporizer 1 uses seawater as a heat source (fluid), and is liquefied liquefied gas of cryogenic temperature (-162 ° C. or less) flowing inside the heat transfer tube 13 and seawater at normal temperature flowing outside the heat transfer tube 13 The LNG is gasified by heat exchange between The LNG vaporizer 1 mainly includes a plurality of heat transfer pipe panels 11 which exchange heat between LNG and seawater, and a trough 12 which supplies the heat transfer pipe panels 11 with seawater. The seawater may contain Cu ions.

As shown in FIG. 2, the heat transfer tube panels 11 are arranged to be spaced apart from each other in the lateral direction in the posture that the heat transfer tube panels 11 are vertically erected. As shown in FIG. 1, the heat transfer pipe panel 11 includes a plurality of heat transfer pipes 13 spaced apart from one another, lower header pipes 14 connected to the lower ends of the heat transfer pipes 13, and heat transfer pipes 13. And an upper header pipe 15 connected to the upper end. The lower header pipe 14 is connected to an inlet manifold 16 communicating therewith. An outlet manifold 17 communicating with the upper header pipe 15 is connected to the upper header pipe 15.

The heat transfer pipe 13 and the lower header pipe 14 are heat transfer members, and are used in a low temperature environment of 0 ° C. or less because cryogenic LNG flows. The heat transfer pipe 13 and the lower header pipe 14 are members made of an aluminum alloy according to the present embodiment, and the details will be described later.

The trough 12 is a member made of an aluminum alloy according to the present embodiment, and is formed of a container which is open at the upper side and in which seawater is accumulated. As shown in FIG. 2, the troughs 12 are disposed on the upper side (lower side than the upper header pipe 15) of the heat transfer pipe panel 11 between the adjacent heat transfer pipe panels 11. The trough 12 stores the seawater supplied from the seawater header pipe (not shown). Then, as shown by the arrows in FIG. 2, the seawater overflowing from the trough 12 flows down along the outer surface of the heat transfer tube 13 in each heat transfer tube panel 11. The details of the trough 12 will also be described later.

A gasification process of LNG by the LNG vaporizer 1 will be described. First, LNG flows in the order of the inlet manifold 16 and the lower header pipe 14. Thereafter, the LNG is diverted to each heat transfer tube 13. Then, as shown in FIG. 2, the LNG flows from the lower side to the upper side in the flow paths 7 formed inside the heat transfer tubes 13. Meanwhile, the seawater supplied from the trough 12 to the heat transfer tube panel 11 flows down along the outer surface of the heat transfer tube 13. In this process, LNG is vaporized by heat exchange with seawater (heat absorption from seawater) through the heat transfer tube 13 and becomes NG. Then, the NG gathers in the upper header pipe 15, passes through the outlet manifold 17, and is discharged as a gas at a normal temperature.

In the above-mentioned LNG vaporizer 1, a member through which seawater flows such as the heat transfer tube 13, the lower header tube 14 and the trough 12 which are aluminum alloy members, or a member for collecting seawater is corrosive in the LNG gasification process as described above. It is exposed to the medium seawater. Specifically, the outer surfaces of the heat transfer tube 13 and the lower header tube 14 and the inner surface of the trough 12 are exposed to seawater. For this reason, corrosion of aluminum progresses by being exposed to seawater over a long period of time during operation of the LNG vaporizer 1, which may cause problems such as pitting. In particular, when seawater contains Cu ions, the progress of corrosion is remarkable. In addition, since the heat transfer tube 13 and the lower header tube 14 are subjected to temperature changes at a low temperature and a normal temperature, corrosion is more likely to progress. On the other hand, in the heat transfer tube 13, the lower header tube 14 and the trough 12, which are aluminum alloy members according to the present embodiment, a sacrificial anticorrosive coating having excellent corrosion resistance is formed on the surface of each base material (base material). It has become This can effectively prevent the progress of corrosion. The heat transfer pipe 13, the lower header pipe 14, and the trough 12 will be described in detail below.

[Heat transfer tube]
FIG. 3 shows the cross-sectional structure of the heat transfer tube 13 along the radial direction. The heat transfer tube 13 is one in which a flow path 7 through which LNG flows is formed inside. The heat transfer tube 13 has a base 21 made of an aluminum alloy and a coating 22 formed on the surface of the base 21.

The base 21 has a cylindrical tube body 23 and a plurality of fins 24 projecting radially outward from the outer surface of the tube body 23. The fins 24 are provided to widen the heat transfer area of the heat transfer tube 13 and are formed at equal intervals along the outer surface of the tube main body 23 as shown in FIG.

The substrate 21 is made of an aluminum alloy of any of 3000 series, 5000 series and 6000 series. Specifically, the base 21 is made of an aluminum alloy such as A3003, A3203, A5052, A5154, A5083, A6061, A6063 or A6N01, which is excellent in strength and corrosion resistance.

The coating 22 is a sacrificial anticorrosion coating for preventing the corrosion of the base 21, and is formed on the outer surface of the base 21 so as to conform to the shapes of the tube main body 23 and the fins 24. The coating 22 is made of an aluminum alloy containing appropriate amounts of Mg and Cr, thereby having excellent corrosion resistance. That is, the film 22 contains 0.8% by mass or more and 20.7% by mass or less of Mg and 0.004% by mass or more and 1.20% by mass or less of Cr, and consists of the balance aluminum and unavoidable impurities. Functions as an excellent sacrificial anticorrosive coating. In addition, "an unavoidable impurity" is contained by the quantity which is a grade which does not impair the anti-corrosion performance of the film 22, for example, H, O, C, B etc. can be mentioned.

Mg contained in the film 22 improves the sacrificial corrosion resistance by causing the potential of the aluminum alloy to grow. Further, Mg interacts with Cr contained in the film 22 to relax the pH in the vicinity of the surface and interface in a corrosive environment due to seawater so as to approach neutrality, thereby suppressing local corrosion and interfacial peeling. The coating 22 has such an anticorrosion effect by containing 0.8% by mass or more of Mg. However, when the Mg content of the coating 22 is excessive, the consumption rate of the coating 22 is increased, and as a result, the life of the heat transfer tube 13 is reduced. In order to prevent this, the Mg content in the film 22 is adjusted to 20.7 mass% or less.

Further, Cr contained in the film 22 relaxes the pH in the vicinity of the surface and interface in a corrosive environment to be close to neutrality by interaction with Mg in the film 22 and suppresses local corrosion and interfacial peeling. Further, Cr contained in the film 22 densifies the corrosion product deposited on the surface of the aluminum alloy, and the dense layer prevents the corrosive substances (such as chloride ions and oxygen) from entering the substrate 21 side. Improve corrosion resistance. The coating 22 has such an anticorrosion effect by containing 0.004% by mass or more of Cr. However, when the Cr content of the film 22 is excessive, a large amount of an intermetallic compound of Al and Cr is formed, and the local corrosion is promoted, whereby the corrosion resistance is lowered. In order to prevent this, the Cr content in the film 22 is adjusted to 1.20% by mass or less.

The coating 22 is formed on the outer surface of the substrate 21 by, for example, a thermal spraying method. As the thermal spraying method, a usual method such as flame spraying, high speed flame spraying, detonation spraying, arc spraying, plasma spraying or laser spraying can be used. As a fuel for flame spraying, a mixed gas of propane and oxygen, a mixed gas of acetylene and oxygen, or the like can be used. Moreover, as a thermal spray material, the wire and powder of an aluminum alloy which have the same composition as the film 22 can be used.

Moreover, the adhesion between the base 21 and the coating 22 can be improved by performing an appropriate pretreatment on the outer surface (the surface on which the coating 22 is formed) of the base 21 before the application of the thermal spraying. Specifically, adjusting the surface roughness of the outer surface of the substrate 21 by shot blasting, grid blasting, or the like can be mentioned. The surface roughness of the substrate 21 can be, for example, 1 μm or more and 30 μm or less in average roughness Ra, and can be 10 μm or more and 100 μm or less in maximum roughness Rmax. In addition, when the cleaning material used for the blast treatment remains on the outer surface of the substrate 21, the adhesion between the film 22 formed by thermal spraying and the substrate 21 is reduced. For this reason, after blasting, it is preferable to remove the cleaning material by brushing or the like.

The thickness T1 of the coating 22 can be adjusted depending on the conditions at the time of thermal spraying, but is 50 μm or more and 1000 μm or less. If the thickness T1 of the film 22 is too small, it will be difficult to sufficiently suppress the entry of corrosive substances such as chloride ions and oxygen into the substrate 21. Furthermore, since the coating 22 is dissolved early, it becomes difficult to obtain a sufficient anticorrosion effect over a long period of time. On the other hand, if the thickness T1 of the coating 22 is too large, peeling of the coating 22 occurs due to temperature change of low temperature and normal temperature, and a crack occurs in the coating 22 to make it difficult to obtain sufficient anticorrosion effect become. For this reason, the thickness T1 of the film 22 is adjusted in the range of 50 μm to 1000 μm.

[Lower header pipe, trough]
FIG. 4 shows a cross-sectional structure along the radial direction of the lower header pipe 14. FIG. 5 shows the cross-sectional structure of the trough 12. As shown in FIG. 4, the lower header pipe 14 has a cylindrical base 31 in which a flow path 33 through which LNG flows is formed, and a coating 32 formed on the entire outer surface of the base 31 by thermal spraying or the like. . Further, as shown in FIG. 5, the trough 12 has a base 41 which is a container in which the opening 43 is formed, and a coating 42 formed on the entire surface of the base 41 by thermal spraying or the like. The

substrates

31 and 41 are made of an aluminum alloy having excellent thermal conductivity, as with the substrate 21 constituting the heat transfer tube 13. The

coatings

32 and 42 are the same as the coating 22 constituting the heat transfer tube 13. That is, the

coatings

32, 42 contain 0.8% by mass or more and 20.7% by mass or less of Mg and 0.004% by mass or more and 1.20% by mass or less of Cr, with the balance being aluminum and unavoidable impurities. It will be Thus, the

coatings

32, 42 function as excellent sacrificial coatings.

[Summary of Embodiment 1, Modified Example]
As described above, the aluminum alloy members (heat transfer pipes 13, lower header pipes 14 and troughs 12) according to the present embodiment are made of an aluminum alloy containing appropriate amounts of Mg and Cr on the surfaces of the

base members

21, 31 and 41. The

coating

22, 32, 42 has been formed. Therefore, excellent corrosion resistance can be exhibited even when used in an environment exposed to a corrosive medium such as seawater, which is subject to temperature changes of low temperature and normal temperature. As described above, since it is difficult for the corrosion and deterioration to progress, the life of each member can be extended, and the number of regular repairs can be reduced. Therefore, the safety of the LNG vaporizer 1 can be improved and the maintenance cost can be reduced.

The coating 22 may be made of an aluminum alloy further containing 0.01% by mass or more and 20% by mass or less of Zn in addition to Mg and Cr. That is, the coating film 22 contains 0.8 mass% or more and 20.7 mass% or less of Mg, 0.004 mass% or more and 1.20 mass% or less of Cr, and 0.01 mass% or more and 20 mass% or less of Zn And may be composed of the balance aluminum and unavoidable impurities.

Zn in the coating 22 has a function of warming the corrosion potential, whereby the sacrificial corrosion resistance of the coating 22 can be further improved. However, if the Zn content in the film 22 is excessive, the disappearance rate of the film 22 is increased, and as a result, the life of the heat transfer tube 13 is reduced. For this reason, the Zn content in the film 22 is adjusted to 0.01% by mass or more and 20% by mass or less.

In addition to Mg and Cr, the coating 22 contains 0.01% by mass or more and 1.0% by mass or less of Si, 0.01% by mass or more and 1.0% by mass or less of Fe, and 0.01% by mass or more. It further contains at least one element selected from the group consisting of 0 mass% or less Cu, 0.01 mass% or more and 1.0 mass% or less Mn, and 0.01 mass% or more and 1.0 mass% or less Ti. May be made of an aluminum alloy. That is, the coating film 22 contains Mg of 0.8% by mass or more and 20.7% by mass or less, Cr of 0.004% by mass or more and 1.20% by mass or less, and 0.01% by mass or more and 1.0% by mass or less Element M (at least one element of Si, Fe, Cu, Mn and Ti), and the balance may be made of aluminum and unavoidable impurities.

Si, Fe, Cu, Mn and Ti in the coating 22 reduce the rate of consumption of the coating 22 by reducing the anodic reaction rate of Al. However, if the content of these elements in the coating 22 is excessive, the corrosion potential may become noble and as a result, the sacrificial corrosion resistance of the coating 22 may be reduced. Therefore, the contents of Si, Fe, Cu, Mn and Ti in the film 22 are adjusted to 0.01% by mass or more and 1.0% by mass or less. The film 22 may also be made of an aluminum alloy to which both Zn and element M are further added in addition to Mg and Cr.

In the first embodiment, the case where the aluminum alloy member of the present invention is applied to all of the heat transfer pipe 13, the lower header pipe 14 and the trough 12 has been described, but the present invention is not limited thereto. The aluminum alloy member of the present invention may be applied. That is, any of the members of the heat transfer tube 13, the lower header tube 14 and the trough 12 may be a coating formed of an aluminum alloy containing appropriate amounts of Mg and Cr on the surface of the base material.

In the first embodiment, the thickness of the

coatings

22, 32 and 42 may be less than 50 μm or more than 1000 μm.

In the first embodiment, the case where the

base materials

21, 31 and 41 are made of 3000 series, 5000 series or 6000 series aluminum alloy has been described, but other types of aluminum alloys such as 2000 series and 7000 series are used. May be

In the first embodiment, the

coatings

22 and 32 are formed on the

base members

21, 31 and 41 by thermal spraying to produce the heat transfer tube 13 and the lower header tube 14, but a cladding tube is formed by extrusion or the like. May be used. Thus, when manufacturing by a clad, the adhesiveness of the

base materials

21 and 31 and the

films

22 and 33 can be improved.

When the heat transfer pipe 13 and the lower header pipe 14 are respectively manufactured by cladding and these are combined to manufacture the heat transfer pipe panel 11, it is necessary to weld the lower end of the heat transfer pipe 13 and the lower header pipe 14 by welding. is there. In this case, it is necessary to scrape and remove the fins 24 at the lower end of the heat transfer tube 13, and the coating 22 is also removed at this time. For this reason, after the lower end of the heat transfer tube 13 is joined to the lower header tube 14 by welding, it is necessary to further form the coating 22 on the welded portion by the thermal spraying method.

Second Embodiment
Next, the LNG vaporizer 2 according to Embodiment 2 of the present invention will be described with reference to FIG. The LNG vaporizer 2 is an intermediate medium vaporizer (IFV) that performs heat exchange via an intermediate medium 61 having a boiling point and a condensation point between the temperature of seawater as a heating source and the temperature of the LNG. The LNG vaporizer 2 has an intermediate medium evaporation unit 51, a vaporization unit 52, and an NG heating unit 53.

The intermediate-medium evaporating unit 51 is a portion on the bottom side in the shell 70, and has a plurality of (three in the present embodiment) heat transfer pipes 71 disposed in the shell space on the bottom side. The intermediate medium evaporation unit 51 exchanges heat between the seawater 72 flowing inside the heat transfer tube 71 and the liquid intermediate medium 61 accumulated at the bottom of the shell 70. By this heat exchange, the liquid intermediate medium 61 evaporates, and an intermediate medium gas 61A is generated. That is, the heat transfer tube 71 is a heat transfer member for performing heat exchange between the seawater 72 and the intermediate medium 61.

The vaporizing unit 52 is an upper portion in the shell 70, and has an LNG pipe 73 through which LNG flows as indicated by arrows in FIG. The vaporization unit 52 performs heat exchange between the LNG flowing inside the LNG pipe 73 and the intermediate medium gas 61A. As a result, the LNG is vaporized to generate an NG. The NG is sent to the NG heating unit 53 through the NG pipe 74. On the other hand, the intermediate medium gas 61A is condensed by heat exchange with the LNG, and is accumulated at the bottom of the shell 70 as a liquid intermediate medium 61.

The NG heating unit 53 has a plurality of (three in the present embodiment) heat transfer tubes 81 through which seawater, which is a heating source, flows. An NG is sent to the NG heating unit 53 from the vaporization unit 52 via the NG pipe 74, and the NG exchanges heat with the seawater 72 flowing inside the heat transfer tube 81. Thereafter, the NG heated by the seawater is discharged as a gas at normal temperature. That is, the heat transfer tube 81 is a heat transfer member for exchanging heat between the seawater 72 and the NG.

In the above-mentioned LNG vaporizer 2, since the

heat transfer tubes

71 and 81 are exposed to seawater 72 which is the corrosive medium at the inner surface, the corrosion progresses to cause problems such as pitting. Here, the heat transfer tubes 71 81 are aluminum alloy members according to the present embodiment, and contain appropriate amounts of Mg and Cr, as in the first embodiment (heat transfer tube 13, lower header tube 14, trough 12). A film made of an aluminum alloy is formed on the surface of the substrate. For this reason, the

heat transfer pipes

71 and 81 have improved corrosion resistance. Specifically, as shown in the cross-sectional view of FIG. 7, the

heat transfer tubes

71 and 81 extend along the inner surface of a cylindrical base 91 having a flow path 91A through which seawater flows, and a base 91. It has the formed film 92. The film 92 contains 0.8% by mass or more and 20.7% by mass or less of Mg and 0.004% by mass or more and 1.20% by mass or less of Cr, with the balance being aluminum and unavoidable impurities. ing. For this reason, even if corrosive seawater flows in the flow path 91A, the film 92 can prevent the corrosion of the base 91, and the life of the

heat transfer tubes

71, 81 can be further lengthened. In addition to

heat transfer tubes

71 and 81, sacrificial corrosion protection made of an aluminum alloy containing appropriate amounts of Mg and Cr is also applied to members that may be corroded by being exposed to seawater 72, similarly to heat

transfer tubes

71 and 81. You may form a film.

(Other embodiments)
In the first and second embodiments, the case where the aluminum alloy member of the present invention is used as the

heat transfer pipes

13, 71, 81, the lower header pipe 14 and the trough 12 in the LNG vaporizers 1 and 2 has been described. I will not. For example, the aluminum alloy member of the present invention can also be used as a heat transfer member in a liquefied petroleum gas (LPG) vaporizer. Moreover, it can use also as plate-shaped heat-transfer members, such as a heat-transfer panel in a plate heat exchanger, and a plate fin in a fin and tube type heat exchanger.

Moreover, such a plate-shaped aluminum alloy member can be produced by clad rolling. Specifically, first, an aluminum alloy base material and a coating material are respectively melted and cast, and if necessary, subjected to homogenization heat treatment to obtain respective ingots. Next, the ingot is rolled (hot rolling, cold rolling) or cut to obtain a plate of a desired size. Thereafter, these plate materials are stacked and pressure-bonded by hot rolling to obtain an integrated plate material. Then, cold rolling is performed until a predetermined final thickness is achieved, whereby a plate-like aluminum alloy member having a film formed on the surface of the base material can be produced. At this time, the thickness of the film can be controlled by adjusting the thickness of the plate material corresponding to the film and the rolling reduction in the hot rolling.

[Preparation of test material]
The swelling resistance and the sacrificial corrosion resistance of the aluminum alloy member were evaluated to confirm the effects of the present invention. First, two types of

test materials

100 and 101 shown in FIGS. 8 and 9 were manufactured. FIG. 8 is a test material for evaluation of the blister resistance, which assumes a sound portion of an aluminum alloy member, and was used to evaluate initial deterioration in practical use. FIG. 9: is a test material for sacrificial corrosion resistance evaluation, Comprising: Deterioration of the aluminum alloy member progresses to a certain extent, and the state which the base material exposed is assumed.

First, as a base material, what consists of various aluminum alloys of 50 mm (L1) x 50 mm (L2) x 20 mm (thickness) in size was prepared. And, in preparation of any of the

test materials

100 and 101, 50 mm (L 1) of shot blasting using alumina as a cleaning material so that the average roughness Ra is 10 ± 2 μm as pretreatment for film formation. ) Was performed on one side of x 50 mm (L2). Then, the abrasive was removed by brushing. Thereafter, a coating was formed on the surface of the base material subjected to the shot blasting treatment by flame spraying using a mixed gas of propane and oxygen, and

test materials

100 and 101 were produced. The component composition (mass%) of each element in the film, the thickness (μm) of the film, and the type of aluminum alloy used for the substrate are as shown in Table 1 below. The composition of the coating was adjusted by the composition of the thermal spray material.

In preparation of the test material 101 for sacrificial-corrosion evaluation, the base-material exposed part 100A of the magnitude | size of 20 mm diameter was formed by cutting. Also, in all the

test materials

100 and 101, the surfaces other than the 50 mm (L1) × 50 mm (L2) size on which the film is formed are sealed with a Teflon (registered trademark) tape, and then the next heat cycle corrosion is performed. Tested.

Thermal cycle corrosion test
The following heat cycle corrosion test was conducted as a test to evaluate the corrosion resistance of aluminum alloy members against temperature change due to low temperature and normal temperature and corrosion action of seawater. The artificial seawater adjusted to a liquid temperature of 35 ° C is sprayed on the surface of the

test material

100, 101 on which the thermal spray coating is formed, and only the base portion of the

test material

100, 101 is immersed in liquid nitrogen. The cooling process was carried out once a day for a total of 3 months. As artificial sea water, what added copper chloride (II) so that a Cu ^<2+ > ion concentration might be 1 ppm to aquamarine for metal corrosion tests by Yashima Co., Ltd. was used. After completion of the corrosion test, a photograph of the appearance of the test material 100 for evaluation of blister resistance was taken, and the area of the swollen portion of the film was measured by image analysis.

About the test material 101 for sacrificial corrosion resistance evaluation, the corrosion product was removed by making 30% nitric acid of room temperature immerse. Thereafter, the substrate exposed portion 100A was observed with a laser microscope, and the depth of local corrosion was measured by the focal depth method to determine the deepest depth of local corrosion. Moreover, the amount of corrosion consumption of the test material 101 for sacrificial corrosion resistance evaluation was measured by the weight change before and behind a corrosion test. The weight after the corrosion test was the weight after removal of the corrosion product. The evaluation criteria of each measurement item are as follows.

[Evaluation criteria for blister area]
◎: No. The ratio of the swelling area to 1 is less than 50 ○: No. The ratio of the swelling area to 1 is 50 or more and less than 75 Δ: No. The ratio of the swelling area to 1 is 75 or more and less than 100. x: No. The ratio of blister area to 1 is 100 or more [Evaluation criteria of corrosion depth in substrate exposed portion]
:: no localized corrosion at exposed substrate part ○: maximum localized corrosion at exposed substrate less than 10 μm Δ: maximum localized corrosion at exposed substrate less than 10 μm and less than 20 μm x: localized exposed substrate Maximum value of corrosion is 20 μm or more [Evaluation criteria for corrosion loss]
◎: No. The ratio of corrosion consumption to 1 is less than 50 ○: No. The ratio of corrosion consumption amount to 1 is 50 or more and less than 75 Δ: No. The ratio of corrosion consumption to 1 is 75 or more and less than 100. x: No. Ratio of corrosion consumption to 1 is 100 or more

[Test results]
The results of the thermal cycle corrosion test are as shown in Table 1. As shown in Table 1, even when a temperature cycle is provided in a seawater environment (1 ppm) containing a relatively large amount of copper ions, Mg of 0.8% by mass or more and 20.7% by mass or less and 0.004% by mass In the case where a film made of an aluminum alloy containing 1% to 1.20% by mass of Cr (Nos. 2 to 29) is formed, a film made of an aluminum alloy containing only Zn (No. 1) In comparison with the above, the swelling area is smaller, the corrosion depth in the substrate exposed portion 100A is smaller, and the corrosion consumption amount is also reduced. From the above results, according to the aluminum alloy member of the present invention, it is possible to prevent the progress of corrosion and deterioration, thereby prolonging the life of the LNG vaporizer and the heat exchanger and reducing the maintenance load. It turned out that there is.

Claims

A substrate made of an aluminum alloy,
And a film formed on the surface of the substrate,
The coating is made of an aluminum alloy containing 0.8% by mass or more and 20.7% by mass or less of magnesium and 0.004% by mass or more and 1.20% by mass or less of chromium. Alloy members.
The aluminum alloy member according to claim 1, wherein the coating has a thickness of 50 μm or more and 1000 μm or less.
The aluminum alloy member according to claim 1, wherein the coating further contains 0.01% by mass or more and 20% by mass or less of zinc.
The film is 0.01% by mass or more and 1.0% by mass or less of silicon, 0.01% by mass or more and 1.0% by mass or less of iron, 0.01% by mass or more and 1.0% by mass or less of copper, 0 . At least one element selected from the group consisting of 0.01 mass% or more and 1.0 mass% or less of manganese and 0.01 mass% or more and 1.0 mass% or less of titanium, An aluminum alloy member according to item 1 or 2.
The film is 0.01% by mass or more and 1.0% by mass or less of silicon, 0.01% by mass or more and 1.0% by mass or less of iron, 0.01% by mass or more and 1.0% by mass or less of copper, 0 . At least one element selected from the group consisting of 0.01 mass% or more and 1.0 mass% or less of manganese and 0.01 mass% or more and 1.0 mass% or less of titanium, The aluminum alloy member according to Item 3.
The aluminum alloy member according to claim 1 or 2, wherein the base material is made of any one of 3000 series, 5000 series and 6000 series aluminum alloys.
The aluminum alloy member according to claim 3, wherein the base material is made of any one of 3000 series, 5000 series and 6000 series aluminum alloys.
The aluminum alloy member according to claim 1, 2, 5 or 7, which is used in a low temperature environment of 0 ° C or less.
The aluminum alloy member according to claim 1, 2, 5, or 7, which is a heat transfer pipe or a header pipe of an LNG vaporizer.
A LNG vaporizer comprising the aluminum alloy member according to claim 1, 2, 5, or 7.