JP4796362B2 - Heat transfer tube for LNG vaporizer and method for manufacturing the same - Google Patents

Heat transfer tube for LNG vaporizer and method for manufacturing the same Download PDF

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JP4796362B2
JP4796362B2 JP2005265666A JP2005265666A JP4796362B2 JP 4796362 B2 JP4796362 B2 JP 4796362B2 JP 2005265666 A JP2005265666 A JP 2005265666A JP 2005265666 A JP2005265666 A JP 2005265666A JP 4796362 B2 JP4796362 B2 JP 4796362B2
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heat transfer
lng
transfer tube
alloy
film
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JP2007078237A (en
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龍哉 安永
亘 漆原
淳 加藤
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Kobe Steel Ltd
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Kobe Steel Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
    • F28F19/02—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings
    • F28F19/06—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings of metal

Description

この発明は、防食効果に優れたＬＮＧ（液化天然ガス）気化器用伝熱管およびその製造方法と、この伝熱管を用いたＬＮＧ気化器に関する。   The present invention relates to a heat transfer tube for an LNG (liquefied natural gas) vaporizer having an excellent anticorrosion effect, a method for producing the same, and an LNG vaporizer using the heat transfer tube.

液化天然ガス（以下ＬＮＧと記す）は、通常、低温高圧の液状で移送あるいは貯蔵され、使用される前に気化される。この気化には、大量のＬＮＧを気化させることができるオープンラックベーパライザ（以下ＯＲＶと記す）と称される気化器が用いられる。図１は、このＯＲＶの一例を示したもので、ＯＲＶは、海水との熱交換によってＬＮＧを加熱して気化させる熱交換器の一種である（例えば、特許文献１参照）。海水は、海水ヘッダー６から散水ノズル７を経てトラフ８に溜められ、トラフ８の側縁部から溢流、伝熱管３ａをカーテン状に配列して形成されたパネル３の外面を濡らしながら垂下する。一方、ＬＮＧは、ＬＮＧマニホールド１に導入されてパネル３の下部に連結されたＬＮＧが流通する下部ヘッダー２に送られ、海水との熱交換によって加熱されてパネル３の各伝熱管３ａ内で気化して上昇し、気化した天然ガス（ＮＧ）は、上部ヘッダー４、４からＮＧマニホールド５へ導出される。   Liquefied natural gas (hereinafter referred to as LNG) is usually transported or stored in a liquid at a low temperature and high pressure, and is vaporized before being used. For this vaporization, a vaporizer called an open rack vaporizer (hereinafter referred to as ORV) capable of vaporizing a large amount of LNG is used. FIG. 1 shows an example of this ORV. The ORV is a kind of heat exchanger that heats and vaporizes LNG by heat exchange with seawater (see, for example, Patent Document 1). Seawater is accumulated in the trough 8 from the seawater header 6 through the watering nozzle 7, overflows from the side edge of the trough 8, and hangs down while wetting the outer surface of the panel 3 formed by arranging the heat transfer tubes 3a in a curtain shape. . On the other hand, the LNG is introduced into the LNG manifold 1 and sent to the lower header 2 through which the LNG connected to the lower portion of the panel 3 circulates. The LNG is heated by heat exchange with the seawater and air is passed through each heat transfer tube 3 a of the panel 3. The natural gas (NG) that has risen and vaporized is discharged from the upper headers 4 and 4 to the NG manifold 5.

前記パネル３を形成する伝熱管３ａの材質として、熱伝導性が良好であること、およびパネル３として要求される複雑な形状に加工しやすいことなどの観点から、通常アルミニウム合金が使用されている。アルミニウム合金は、海水に浸漬された状態では腐食しやすく、一旦腐食し始めると、腐食部分が集中的に侵食され、孔があく孔食を受けやすい欠点がある。このため、海水に浸漬されるなどの用途に用いられるアルミニウム合金については、防食処理が盛んに研究され、現在、犠牲防食作用を利用した防食処理が主流となっている。前記特許文献１では、前記ＬＮＧ気化器で、パネル３の外面を濡らしながら垂下した海水が溜まった海水ポンド中に浸漬したＬＮＧが流通する下部ヘッダー２に、パネル３（伝熱管３ａ）の材質であるアルミニウム合金よりも腐食されやすい亜鉛（Ｚｎ）などの金属、すなわちイオン化傾向の大きい金属または合金バルク（図示省略）を電気的に接続して犠牲陽極とし、この犠牲陽極が電気化学的に溶解して消耗することにより、対極となる下部ヘッダー２およびパネル３の表面を防食する防食処理法が開示されている。しかし、ＬＮＧ気化器では、パネル３を構成する伝熱管３ａの表面にトラフ８の側縁部から溢流した海水が直接当たるため、前記犠牲陽極を設けていても、いわゆるエロージョン・コロージョンによる腐食の発生は避けがたい。このため、海水が直接接触しないように、また、被覆合金が局部的に剥がれた場合でも、その防食作用によって伝熱管表面の腐食が防止されるように、伝熱管３ａの表面に、その材質のアルミニウム合金よりもイオン化傾向の大きい合金（以下被覆合金と記す）を被覆することが望ましい。従来、このような犠牲防食作用を有する合金としてＡｌ−Ｚｎ合金がよく知られ、Ａｌ−２％Ｚｎ合金、またはＡｌ−１５％Ｚｎ合金などがよく使用されている。この被覆合金を溶射して伝熱管表面に皮膜を形成することにより、腐食が有効に防止される。  As a material of the heat transfer tube 3a forming the panel 3, an aluminum alloy is usually used from the viewpoints of good thermal conductivity and easy processing into a complicated shape required for the panel 3. . Aluminum alloys are easily corroded when immersed in seawater, and once corroded, the corroded portion is eroded intensively and is susceptible to pitting corrosion. For this reason, with respect to aluminum alloys used for applications such as being immersed in seawater, anticorrosion treatment has been actively studied, and at present, anticorrosion treatment using sacrificial anticorrosive action has become mainstream. In Patent Document 1, the material of the panel 3 (heat transfer tube 3a) is attached to the lower header 2 in which the LNG immersed in the seawater pond in which the drooping seawater accumulated while wetting the outer surface of the panel 3 is wet with the LNG vaporizer. A metal, such as zinc (Zn), that is more susceptible to corrosion than an aluminum alloy, that is, a metal or alloy bulk (not shown) that has a high tendency to ionize, is electrically connected to form a sacrificial anode. An anticorrosion treatment method is disclosed in which the surfaces of the lower header 2 and the panel 3 serving as counter electrodes are anticorrosive by being consumed. However, in the LNG vaporizer, since the seawater overflowing from the side edge of the trough 8 directly hits the surface of the heat transfer tube 3a constituting the panel 3, even if the sacrificial anode is provided, corrosion caused by so-called erosion / corrosion is caused. Occurrence is inevitable. For this reason, the surface of the heat transfer tube 3a is made of the material so that the seawater is not in direct contact and the corrosion of the heat transfer tube surface is prevented by the anticorrosion action even when the coating alloy is locally peeled off. It is desirable to coat an alloy having a higher ionization tendency than an aluminum alloy (hereinafter referred to as a coating alloy). Conventionally, an Al—Zn alloy is well known as an alloy having such sacrificial anticorrosive action, and an Al-2% Zn alloy, an Al-15% Zn alloy, or the like is often used. Corrosion is effectively prevented by spraying this coating alloy to form a film on the surface of the heat transfer tube.

前記伝熱管表面に形成する皮膜の防食性にさらに向上させるために、例えば、特許文献２では、アルミニウムまたはアルミニウム合金の伝熱管（押出管材）の表面に、第１層として、電気化学的に犠牲層として働くＺｎを被覆し、熱交換器製造時のろう付けによるＺｎの蒸発を防止するために、第１層の上に、ＡｌまたはＡｌ−Ｃａ、Ａｌ−Ｚｎ−Ｃａ系等のＡｌ合金を溶射して耐食性を改善したアルミニウム製熱交換器用管材が開示されている。また、特許文献３では、伝熱管表面に、Ａｌ−Ｚｎ合金層を形成し、さらにその表面にＩｎ，Ｓｎ、ＨｇおよびＣｄから選ばれる１種または２種以上の元素を含むＡｌ−Ｚｎ合金層を形成して高い耐食性を有するようにしたＡｌ合金製伝熱管が開示されている。一方、特許文献４では、Ａｌ合金母材管の表面に、Ａｌ−Ｚｎ合金材をクラッドして厚膜の犠牲陽極被膜を形成したＯＲＶ型気化器用のフィンチューブ（フィン型伝熱管）が開示されている。
特開平９−１７８３９１号公報 特開平１−１１４６９８号公報 特公平７−１１５７号公報 特開平５−１６４４９６号公報 In order to further improve the corrosion resistance of the film formed on the surface of the heat transfer tube, for example, in Patent Document 2, the surface of the heat transfer tube (extruded tube material) of aluminum or aluminum alloy is electrochemically sacrificed as a first layer. In order to coat Zn acting as a layer and prevent evaporation of Zn due to brazing at the time of manufacturing a heat exchanger, Al or Al-Ca, Al-Zn-Ca-based Al alloy or the like is formed on the first layer. An aluminum heat exchanger tube with improved corrosion resistance by thermal spraying is disclosed. In Patent Document 3, an Al—Zn alloy layer is formed on the surface of the heat transfer tube, and further, an Al—Zn alloy layer containing one or more elements selected from In, Sn, Hg, and Cd on the surface thereof. A heat transfer tube made of an Al alloy is disclosed which has a high corrosion resistance by forming the structure. On the other hand, Patent Document 4 discloses a fin tube (fin type heat transfer tube) for an ORV type vaporizer in which an Al—Zn alloy material is clad on a surface of an Al alloy base material tube to form a thick sacrificial anode coating. ing.
JP-A-9-178391 Japanese Patent Laid-Open No. 1-114698 Japanese Patent Publication No.7-1157 Japanese Patent Laid-Open No. 5-16496

しかし、ＯＲＶのパネル３の下部および下部ヘッダー２は、ＬＮＧ（液体状態の天然ガス）が流通するため、氷点下まで冷却されている。このようなＯＲＶの低温領域で溢流垂下する海水に接触する状態では、伝熱管母材のアルミニウム合金表面に酸化皮膜が形成されにくくなり、伝熱管母材の電極電位が、特許文献１〜４に記載されたＡｌ−Ｚｎ合金皮膜の電極電位よりも低くなり、Ａｌ−Ｚｎ合金皮膜の犠牲防食作用が発揮されなくなり、伝熱管母材が保護されない虞がある。例えば、海水温度が高い場合、またはパネル３のＬＮＧ流通による冷却負荷が大きい場合などの環境条件によっては、Ａｌ−Ｚｎ合金皮膜の高い電位にアルミ合金伝熱管母材が引っ張られて、伝熱管母材がガルバニック腐食される虞がある。   However, the lower and lower headers 2 of the ORV panel 3 are cooled to below freezing point because LNG (liquid natural gas) flows. In the state of contact with seawater overflowing and dripping in such a low temperature region of ORV, it becomes difficult to form an oxide film on the aluminum alloy surface of the heat transfer tube base material, and the electrode potential of the heat transfer tube base material is set to Patent Documents 1-4. The electrode potential of the Al—Zn alloy film described in 1) is lower, the sacrificial anticorrosive action of the Al—Zn alloy film is not exhibited, and the heat transfer tube base material may not be protected. For example, depending on the environmental conditions such as when the seawater temperature is high or when the cooling load due to LNG distribution on the panel 3 is large, the aluminum alloy heat transfer tube base material is pulled to the high potential of the Al-Zn alloy film, and the heat transfer tube mother There is a risk of galvanic corrosion of the material.

この発明は、このような問題点に鑑みてなされたものであり、その課題は、冷却負荷が大きいため、表面に酸化皮膜が形成されにくいパネル下部側や下部ヘッダーに配置しても、Ａｌ合金母材表面の腐食損傷を防止する効果に優れたＬＮＧ気化器用伝熱管およびその製造方法と、この伝熱管を用いたＬＮＧ気化器を提供することである。   The present invention has been made in view of such problems, and the problem is that even if it is arranged on the lower panel side or the lower header where the oxide film is difficult to be formed on the surface because the cooling load is large, the Al alloy An object of the present invention is to provide a heat transfer tube for an LNG vaporizer excellent in the effect of preventing corrosion damage on the surface of a base material, a method for manufacturing the same, and an LNG vaporizer using the heat transfer tube.

前記の課題を解決するために、この発明では以下の構成を採用したのである。   In order to solve the above problems, the present invention employs the following configuration.

即ち、請求項１に係るＬＮＧ気化器用伝熱管は、内部にＬＮＧが流通し、外表面に海水が供給され、この海水と前記ＬＮＧとが熱交換してＬＮＧを気化させる、外表面に防食皮膜が形成されたＡｌ合金からなるＬＮＧ気化器用伝熱管であって、前記防食皮膜が、Ｍｇを前記Ａｌ合金のＭｇ組成よりも多い３〜５０質量％含有したＡｌおよびＭｇよりなるＡｌ合金皮膜であると共に、溶射加工によって形成されたＡｌ合金皮膜であることを特徴とする。 That is, the heat transfer tube for an LNG vaporizer according to claim 1 has an anticorrosive coating on the outer surface, in which LNG circulates and seawater is supplied to the outer surface, and the seawater and the LNG exchange heat to vaporize LNG. A heat transfer tube for an LNG vaporizer made of an Al alloy formed with an anti-corrosion coating, wherein the anticorrosion coating is an Al alloy coating made of Al and Mg containing 3 to 50% by mass of Mg higher than the Mg composition of the Al alloy. In addition, it is an Al alloy film formed by thermal spraying.

前述のように、伝熱管のアルミニウム合金母材表面に酸化皮膜が形成されにくい環境条件下では、これらの母材合金よりもＺｎの自然電極電位が高くなるため、Ａｌ−Ｚｎ溶射皮膜の方が伝熱管または下部ヘッダーの母材合金よりも電位が高くなり、犠牲防食効果が得られなくなる。このため、伝熱管母材のアルミニウム合金表面に酸化皮膜が形成されにくい環境条件下でも、犠牲防食作用を発揮させるためには、熱力学的にＡｌよりも電位が低い金属の、例えば溶射加工による皮膜を形成する必要がある。このような金属としては、Ｍｇが最適であり、Ｍｇを含有する合金皮膜で、伝熱管や下部ヘッダーの材質として用いられるＡｌ合金母材よりも「卑」な皮膜であれば、犠牲防食皮膜として良好に適用できる。なお、熱力学的にＡｌよりも電位が低い金属としては、Ｍｇの他に、Ｈｆ（ハフニウム）、Ｔｉ（チタン）、Ｂｅ（ベリリウム）がある。この中、Ｔｉ、Ｂｅの酸化皮膜はＡｌの酸化皮膜よりも強固であり、これらの金属が熱力学的にＡｌよりも「卑」な金属であっても、ＬＮＧ気化器が運転される環境を考えると、実質的にＡｌよりも「貴」な金属となる。また、ＨｆやＴｉを含有する金属は伸線性が著しくわるく、皮膜形成手段であるフレーム溶射に用いる溶射材に加工することも困難である。したがって、Ｈｆ、Ｔｉを犠牲防食用皮膜に適用することはできない。一方、Ｂｅには毒性があるため、皮膜形成作業時の危険性やＯＲＶ運転時の海洋汚染の問題があり、また、非常に高価な材料であるため、犠牲防食用皮膜としては不適である。   As described above, since the natural electrode potential of Zn is higher than that of the base metal alloy under an environmental condition in which an oxide film is not easily formed on the surface of the aluminum alloy base material of the heat transfer tube, the Al-Zn sprayed coating is more preferable. The potential becomes higher than the base metal alloy of the heat transfer tube or the lower header, and the sacrificial anticorrosive effect cannot be obtained. For this reason, in order to exert a sacrificial anticorrosive action even under environmental conditions in which an oxide film is not easily formed on the surface of the aluminum alloy of the heat transfer tube base metal, for example, by thermal spraying of a metal having a lower potential than Al thermodynamically It is necessary to form a film. As such a metal, Mg is optimal, and an alloy film containing Mg, which is a “base” film than an Al alloy base material used as a material for heat transfer tubes and lower headers, can be used as a sacrificial anticorrosive film. Applicable well. In addition to Mg, there are Hf (hafnium), Ti (titanium), and Be (beryllium) as thermodynamically lower metals than Al. Among these, Ti and Be oxide films are stronger than Al oxide films, and even if these metals are thermodynamically “base” metals than Al, the environment in which the LNG vaporizer is operated When considered, the metal is substantially more noble than Al. Moreover, the metal containing Hf and Ti has remarkably poor drawability, and it is difficult to process it into a thermal spray material used for flame spraying as a film forming means. Therefore, Hf and Ti cannot be applied to the sacrificial anticorrosive film. On the other hand, since Be is toxic, there is a risk of film formation work and marine pollution during ORV operation, and it is a very expensive material, so it is not suitable as a sacrificial anticorrosive film.

また、前記Ａｌ合金皮膜のＭｇ含有量が１％を下回ると、犠牲防食効果が不十分となる。このため、犠牲防食効果をより発現させるためには、Ｍｇ含有量は３質量％以上とする必要があり、犠牲防食効果がより有効となる。一方、Ｍｇ含有量の増加に伴い、Ａｌ−Ｍｇ合金皮膜の犠牲防食作用は高まるが、温度などの環境条件によっては皮膜の消耗速度が大きくなり過ぎる。このため、Ｍｇ含有量は５０質量％以下とする必要があり、２０質量％以下が好ましい。すなわち、Ｍｇ組成が３〜５０質量％の場合、皮膜の密着性、犠牲防食効果と皮膜耐久性とがいずれも好適に満足される。On the other hand, when the Mg content of the Al alloy film is less than 1%, the sacrificial anticorrosive effect is insufficient. For this reason, in order to express a sacrificial anticorrosive effect more, Mg content needs to be 3 mass% or more, and a sacrificial anticorrosive effect becomes more effective. On the other hand, as the Mg content increases, the sacrificial anticorrosive action of the Al—Mg alloy film increases, but the consumption rate of the film becomes too high depending on environmental conditions such as temperature. For this reason, Mg content needs to be 50 mass% or less, and 20 mass% or less is preferable. That is, when the Mg composition is 3 to 50% by mass, the adhesion of the film, the sacrificial anticorrosive effect, and the film durability are all preferably satisfied.

請求項２に係るＬＮＧ気化器用伝熱管は、前記Ａｌ合金皮膜の膜厚が１００〜１０００μｍの範囲にあることを特徴とする。The heat transfer tube for an LNG vaporizer according to claim 2 is characterized in that the film thickness of the Al alloy film is in the range of 100 to 1000 μm.

上記Ａｌ合金皮膜を、前述のように、ＯＲＶに適用する場合には、耐膨れ剥離性を向上させるために、膜厚を適切に制御することが重要である。膜厚が１００μｍを下回ると、溶射皮膜自体の腐食代が不足するため、伝熱管または下部ヘッダーのアルミ合金母材が容易に海水に露出するようになる。最小膜厚として１００μｍ以上、好ましくは１５０μｍ以上、２００μｍ以上がさらに好ましい。また、早期の腐食を防止するためには、溶射皮膜は厚い方がよいが、膜厚が１０００ｍｍを超えると、溶射による成膜時の残留応力により剥離が助長されるため、膜厚は１０００μｍ以下、好ましくは８００μｍ以下、さらに好ましくは６００μｍ以下にすることが好ましい。As described above, when the Al alloy film is applied to ORV, it is important to appropriately control the film thickness in order to improve the blistering resistance. When the film thickness is less than 100 μm, the corrosion allowance of the spray coating itself is insufficient, so that the aluminum alloy base material of the heat transfer tube or the lower header is easily exposed to seawater. The minimum film thickness is 100 μm or more, preferably 150 μm or more, more preferably 200 μm or more. In order to prevent premature corrosion, it is better that the thermal spray coating is thicker, but if the film thickness exceeds 1000 mm, peeling is promoted by the residual stress during film formation by thermal spraying, so the film thickness is 1000 μm or less. The thickness is preferably 800 μm or less, more preferably 600 μm or less.

請求項３に係るＬＮＧ気化器用伝熱管は、前記Ａｌ合金皮膜と前記伝熱管との界面の中心線平均粗さ（Ｒａ７５）が１０〜１００μｍの範囲にあることを特徴とする。 The heat transfer tube for an LNG vaporizer according to claim 3 is characterized in that the center line average roughness (Ra75) of the interface between the Al alloy film and the heat transfer tube is in the range of 10 to 100 μm.

前記溶射皮膜と前記伝熱管または前記下部ヘッダー、すなわちＡｌ合金母材との界面の凹凸を大きくすることにより、溶射皮膜の内部欠陥と溶射皮膜表面との間に形成される酸素濃淡電池による界面の優先溶解が前記欠陥周囲に拡大する速度が抑制され、溶射皮膜の耐膨れ剥離性が向上する。この方法は、Ａｌ−Ｚｎ合金などの他の溶射皮膜に比べて密着性が確保しにくいＡｌ−Ｍｇ合金溶射皮膜の密着性改善に有効な方法である。この密着性改善について詳細に検討した結果、低温域で流動海水が接触する環境下でのＡｌ合金母材への溶射皮膜の耐剥離性は、溶射皮膜とＡｌ合金母材の界面の中心線平均粗さＲａが１０μｍ以上の場合に向上し、優れた密着特性が得られることが判明した。密着性改善の観点から、前記界面の中心線平均粗さＲａ７５は、１２μｍがより好ましく、１４μｍがさらに好ましい。一方、溶射皮膜とＡｌ合金母材の界面の凹凸が大きすぎると、界面で溶射皮膜が充填されない空隙が形成されやすくなり、この空隙に海水が侵入し、界面の優先腐食が助長される。このため、界面の凹凸は、中心線平均粗さＲａ７５が１００μｍ以下が好ましく、８０μｍ以下がより好ましく、６０μｍ以下がさらに好ましい。   By increasing the unevenness of the interface between the sprayed coating and the heat transfer tube or the lower header, that is, the Al alloy base material, the interface of the oxygen concentration cell formed between the internal defect of the sprayed coating and the surface of the sprayed coating is increased. The speed at which the preferential dissolution spreads around the defect is suppressed, and the blistering resistance of the sprayed coating is improved. This method is an effective method for improving the adhesion of an Al—Mg alloy sprayed coating, which is difficult to secure the adhesion compared to other sprayed coatings such as an Al—Zn alloy. As a result of a detailed examination of this adhesion improvement, the peel resistance of the thermal spray coating to the Al alloy base material in an environment where fluid seawater contacts in a low temperature range is the average of the center line at the interface between the thermal spray coating and the Al alloy base material. It was found that when the roughness Ra was 10 μm or more, the roughness Ra was improved and excellent adhesion characteristics were obtained. From the viewpoint of improving adhesiveness, the centerline average roughness Ra75 of the interface is more preferably 12 μm and even more preferably 14 μm. On the other hand, if the unevenness at the interface between the thermal spray coating and the Al alloy base material is too large, voids that are not filled with the thermal spray coating are likely to be formed at the interface, and seawater enters the voids, thereby promoting preferential corrosion at the interface. For this reason, as for the unevenness | corrugation of an interface, centerline average roughness Ra75 has preferable 100 micrometers or less, 80 micrometers or less are more preferable, and 60 micrometers or less are further more preferable.

請求項４に係るＬＮＧ気化器用伝熱管は、前記界面の粗さが、＃１６以上のブラスト粒子を含有するブラスト剤を前記溶射皮膜が形成される前記伝熱管の外表面に吹き付けて形成されたことを特徴とする。 The heat transfer tube for an LNG vaporizer according to claim 4 is formed by spraying a blasting agent containing blast particles having a roughness of # 16 or more on the outer surface of the heat transfer tube on which the sprayed coating is formed. It is characterized by that.

このように、＃１６以上の細粒のブラスト粒子を含有するブラスト剤を用いてブラスト粗面処理を行なうことにより、前記界面の粗さ（凹凸）を、１０〜１００μｍの範囲に調整することが可能である。   Thus, by performing a blast roughening process using a blasting agent containing fine blast particles of # 16 or more, the roughness (unevenness) of the interface can be adjusted in the range of 10 to 100 μm. Is possible.

請求項５に係るＬＮＧ気化器用伝熱管は、前記Ａｌ合金皮膜の、前記伝熱管の中心を通る断面での最表面から深さ１００μｍまでの領域に存在する気孔の面積率が１５％以下であることを特徴とする。 In the heat transfer tube for an LNG vaporizer according to claim 5 , the area ratio of pores existing in a region from the outermost surface to a depth of 100 μm in a cross section passing through the center of the heat transfer tube of the Al alloy film is 15% or less. It is characterized by that.

このように、Ａｌ合金皮膜の表層部の気孔面積率を１５％以下に、望ましくは１０％以下に抑制すれば、膨れ剥離面積率が顕著に低下するため、良好な犠牲防食効果が得られる。   Thus, if the pore area ratio of the surface layer part of the Al alloy film is suppressed to 15% or less, preferably 10% or less, the blistering and peeling area ratio is remarkably lowered, and thus a good sacrificial anticorrosive effect can be obtained.

請求項６に係るＬＮＧ気化器は、前記溶射皮膜が形成された伝熱管を複数カーテン状に配列したパネルと、このパネルの上部および下部にそれぞれ連結された気化ガス排出用の上部ヘッダーおよびＬＮＧ供給用の、下部ヘッダーとからなるパネルユニットを備え、前記パネルユニットの上部からパネルの表面に沿って流下させた海水と前記伝熱管内を下部ヘッダー側から上部ヘッダー側へ流通するＬＮＧとの熱交換により、ＬＮＧを気化させるようにしたＬＮＧ気化器である。 An LNG vaporizer according to claim 6 is a panel in which a plurality of heat transfer tubes on which the thermal spray coating is formed are arranged in a curtain shape, an upper header for discharging vaporized gas connected to an upper portion and a lower portion of the panel, and an LNG supply. Heat exchange between seawater flown down from the upper part of the panel unit along the surface of the panel and LNG flowing in the heat transfer pipe from the lower header side to the upper header side Thus, the LNG vaporizer is configured to vaporize LNG.

請求項７に係るＬＮＧ気化器は、前記伝熱管の溶射皮膜が、少なくともパネル下部および下部ヘッダーの外表面に形成されたＬＮＧ気化器である。 The LNG vaporizer which concerns on Claim 7 is an LNG vaporizer by which the sprayed coating of the said heat exchanger tube was formed in the outer surface of the panel lower part and the lower header at least.

前述のように、この種のＬＮＧ気化器では、下部ヘッダーおよびパネル下部ではＬＮＧが液体状態であるため、氷点下まで冷却されており、このような低温領域で溢流垂下する海水に接触する状態では、伝熱管母材のアルミニウム合金表面に酸化皮膜が形成されにくくなる。このため、少なくともこの低温域のパネル下部および下部ヘッダーに前述の溶射皮膜を被覆しておくと、良好な防食効果が得られる。   As described above, in this type of LNG vaporizer, since LNG is in a liquid state in the lower header and the lower part of the panel, it is cooled to below freezing point, and in a state where it contacts seawater that overflows in such a low temperature region. Further, an oxide film is hardly formed on the surface of the aluminum alloy of the heat transfer tube base material. For this reason, if the above-mentioned sprayed coating is coated on at least the lower part of the panel and the lower header in this low temperature region, a good anticorrosive effect can be obtained.

請求項８に係るＬＮＧ気化器用伝熱管の製造方法は、内部にＬＮＧが流通し、外表面に海水が供給され、この海水と前記ＬＮＧとが熱交換してＬＮＧを気化させる、外表面に防食皮膜が形成されたＡｌ合金からなるＬＮＧ気化器用伝熱管の製造方法であって、前記防食皮膜を、Ｍｇを前記Ａｌ合金のＭｇ組成よりも多い３〜５０質量％含有するＡｌおよびＭｇよりなるＡｌ合金の溶射加工により皮膜を形成した後に、この溶射皮膜の表面に溶射皮膜の気孔面積率を下げるための機械加工処理を施すことを特徴とする。 The method of manufacturing a heat transfer tube for an LNG vaporizer according to claim 8 is the anticorrosion on the outer surface, wherein LNG is circulated inside, seawater is supplied to the outer surface, and the seawater and the LNG exchange heat to vaporize LNG. A method for producing a heat transfer tube for an LNG vaporizer made of an Al alloy having a film formed thereon, wherein the anticorrosion film is made of Al containing 3 to 50% by mass of Mg larger than the Mg composition of the Al alloy and Al made of Mg After the coating is formed by thermal spraying of the alloy, the surface of the thermal spray coating is subjected to a machining process for reducing the pore area ratio of the thermal spray coating .

このように、溶射皮膜の表面に、グラインダー研削やショットピーニングなどの機械加工を施せば、溶射皮膜に存在する気孔欠陥が減少するため、使用中の膨れや剥離などの損傷が抑制され、良好な犠牲防食効果が発揮される。   In this way, if the surface of the thermal spray coating is subjected to machining such as grinder grinding or shot peening, pore defects present in the thermal spray coating are reduced, so that damage such as blistering and peeling during use is suppressed, which is favorable. Sacrificial anti-corrosion effect is demonstrated.

請求項９に係るＬＮＧ気化器用伝熱管の製造方法は、前記機械加工の前処理または／および後処理として、前記溶射皮膜に封孔剤含浸処理を行なうことを特徴とする。 The method for manufacturing a heat transfer tube for an LNG vaporizer according to claim 9 is characterized in that the sprayed coating is impregnated with a sealant as a pretreatment or / and a posttreatment of the machining.

このように、機械加工に加えて封孔剤含浸処理を行なえば、溶射皮膜に存在する気孔がさらに減少するため、膨れや剥離などの損傷が一層抑制される。 As described above, when the sealing agent impregnation treatment is performed in addition to the machining, the pores existing in the sprayed coating are further reduced, and thus damage such as blistering and peeling is further suppressed.

この発明では、ＬＮＧ気化器の、低温領域で海水に接触する、Ａｌ合金からなる合金伝熱管の少なくともパネル下部側の外表面および下部ヘッダーの外表面に、熱力学的にＡｌよりも電位が低い金属であるＭｇを、前記Ａｌ合金よりも多い３〜５０質量％含有するＡｌおよびＭｇよりなるＡｌ合金皮膜を形成したので、伝熱管や下部ヘッダーのアルミニウム合金表面に酸化皮膜が形成されにくい環境条件下でも、前記Ｍｇを含有する合金皮膜は伝熱管や下部ヘッダーのＡｌ合金母材よりも電極電位が低いため、良好な犠牲防食効果が得られる。また、適正な粒子径のブラスト剤を用いてブラスト処理を行うことにより、界面の凹凸を所要の中心線平均粗さ（Ｒａ７５）の範囲に収めたので、溢流垂下する海水と接触する環境下での前記Ａｌ合金皮膜の耐剥離性が、実用上支障のないレベルにまで向上した。さらに、前記合金皮膜を形成した後に、機械加工や封孔剤含浸処理を施すことが耐剥離性の向上に顕著な効果が得られ、これらにより、伝熱管の腐食損傷が回避されてＬＮＧ気化器の操業効率および耐用年数が向上する。 In the present invention, at least the outer surface of the lower part of the panel and the outer surface of the lower header of the alloy heat transfer tube made of an Al alloy that contacts seawater in the low temperature region of the LNG vaporizer has a thermodynamically lower potential than Al. Since the Al alloy film made of Al and Mg containing 3 to 50% by mass of Mg, which is a metal, is larger than the Al alloy, it is difficult to form an oxide film on the aluminum alloy surface of the heat transfer tube and the lower header. Even under the above, since the alloy film containing Mg has a lower electrode potential than the Al alloy base material of the heat transfer tube and the lower header, a good sacrificial anticorrosive effect can be obtained. In addition, by performing blasting using a blasting agent having an appropriate particle size, the unevenness of the interface is within the required centerline average roughness (Ra75), so that the environment is in contact with the overflowing seawater. The peel resistance of the Al alloy film at 1 is improved to a level where there is no practical problem. Furthermore, after forming the alloy film, performing machining or impregnating treatment with a sealant has a significant effect on improving the peel resistance, thereby avoiding corrosion damage to the heat transfer tube and reducing the LNG vaporizer. Operating efficiency and service life of

以下に、この発明の実施形態を添付の図１に基づいて説明する。   Embodiments of the present invention will be described below with reference to FIG.

図１は、実施形態の伝熱管が組み込まれたＬＮＧ気化器を示したもので、複数の伝熱管３ａをカーテン状に配列したパネル３と、このパネル３の上部および下部にそれぞれ連結されたＬＮＧ供給用の下部ヘッダー２および気化ガス（ＮＧ）排出用の上部ヘッダー４とからなるＡｌ合金（例えば、Ａ３２０３などのＡｌ−Ｍｎ系合金、Ａ５０８３などのＡｌ−Ｍｇ系合金、Ａ６０６３などのＡｌ−Ｍｇ−Ｓｉ系合金）製の複数のパネルユニットＵが並列に配置されている。前記下部ヘッダー２および上部ヘッダー４は、それぞれ下部のＬＮＧマニホールド１および上部のＮＧマニホールド５に接続されている。各パネルユニットＵのパネル３間の上方には、ＬＮＧを気化させる熱源としての海水を流下させるトラフ８がそれぞれ配置されている。ＬＮＧは、下部のＬＮＧマニホールド１から下部ヘッダー２に送られ、パネル３の各伝熱管３ａ内を上昇する過程で前記海水と熱交換して気化し、上部ヘッダー４から上部のＮＧマニホールド５を経て、ガスライン（図示省略）に供給される。   FIG. 1 shows an LNG vaporizer in which the heat transfer tube of the embodiment is incorporated. A panel 3 in which a plurality of heat transfer tubes 3a are arranged in a curtain shape, and an LNG connected to the upper and lower portions of the panel 3, respectively. An Al alloy (for example, an Al-Mn alloy such as A3203, an Al-Mg alloy such as A5083, or an Al-Mg such as A6063) composed of a lower header 2 for supply and an upper header 4 for discharging vaporized gas (NG). A plurality of panel units U made of (Si-based alloy) are arranged in parallel. The lower header 2 and the upper header 4 are connected to a lower LNG manifold 1 and an upper NG manifold 5, respectively. Above each panel unit U of the panel units U, troughs 8 are provided for flowing down seawater as a heat source for vaporizing LNG. The LNG is sent from the lower LNG manifold 1 to the lower header 2 and is vaporized by exchanging heat with the seawater in the process of rising in the heat transfer tubes 3a of the panel 3, and from the upper header 4 through the upper NG manifold 5. , Supplied to a gas line (not shown).

前記伝熱管３ａと下部ヘッダー２のそれぞれの外表面には、Ｍｇ組成が１〜８０質量％、好ましくは３〜３０質量％ のＡｌ合金皮膜、すなわちＡｌ−Ｍｇ合金皮膜が、溶射加工により、１００〜１０００μｍ 、好ましくは２００〜６００μｍの範囲の膜厚に形成されている。この溶射加工によるＡｌ−Ｍｇ合金皮膜の伝熱管３ａおよび下部ヘッダー２、すなわちＡｌ合金母材への密着性を向上させるために、溶射加工による皮膜形成の前処理として、粒径＃１６以上の細粒のブラスト剤を用いて、前記Ａｌ合金母材の外表面に、中心線平均粗さＲａ７５が１０〜１００μｍ、好ましくは１４〜６０μｍの範囲に、ブラスト粗面処理が施され、溶射皮膜とＡｌ合金母材の界面の凹凸が調整される。そして、溶射膜形成後、Ａｌ−Ｍｇ合金皮膜への浸透性に優れた、例えば、高分子エポキシ樹脂を溶射膜表面に少なくとも１回塗布する封孔剤含浸処理を施すことが望ましい。なお、伝熱管３ａへのＡｌ−Ｍｇ合金皮膜の被覆は、必ずしも、伝熱管３ａの全表面に施す必要はなく、少なくともパネル３の下部１ｍ程度までの被覆でよい。 On the outer surface of each of the heat transfer tube 3a and the lower header 2, an Al alloy film having an Mg composition of 1 to 80% by mass, preferably 3 to 30% by mass, that is, an Al—Mg alloy film is formed by thermal spraying. The film thickness is in the range of ˜1000 μm, preferably 200 to 600 μm. In order to improve the adhesion of the Al—Mg alloy film to the heat transfer tube 3 a and the lower header 2, that is, the Al alloy base material by the thermal spraying process, as a pretreatment for the film formation by the thermal spraying process, a fine particle having a particle size of # 16 or more is used. Using a grain blasting agent, the outer surface of the Al alloy base material is subjected to a blast roughening treatment in a range of centerline average roughness Ra75 of 10 to 100 μm, preferably 14 to 60 μm, and a sprayed coating and Al The unevenness of the interface of the alloy base material is adjusted. Then, after forming the sprayed film, it is desirable to perform a sealing agent impregnation treatment that is excellent in permeability to the Al—Mg alloy film, for example, applying a polymer epoxy resin to the surface of the sprayed film at least once. Note that the Al—Mg alloy coating on the heat transfer tube 3a does not necessarily have to be applied to the entire surface of the heat transfer tube 3a, and may be at least about 1 m below the panel 3.

前記伝熱管および下部ヘッダーのＡｌ合金母材と溶射皮膜との界面の凹凸、即ちＲａ７５が、少なくとも１０〜１００μｍの範囲にあることは、局所的に実現しても意味がなく、溶射膜被覆面全体で実現する必要がある。このため、本実施形態では、予め、溶射皮膜を被覆するＡｌ合金母材の対象表面域から、無作為に１０箇所以上測定点選んで、JIS B 0031・JIS B 0061の付属書で定義されている測定方法により、中心線平均粗さＲａ７５を測定する。そして、全測定値の相加平均が前記Ｒａ７５の範囲にあることを確認してから、溶射皮膜の成膜を行なう。このＡｌ合金母材と溶射皮膜との界面の凹凸は、溶射皮膜を成膜した後に測定することも可能である。この場合には、同一ブラスト処理、同一溶射皮膜形成処理のロットから任意に抽出した前記Ａｌ合金母材の、溶射皮膜の被覆面から無作為に１０点以上の測定箇所を選んで、溶射膜被覆面の断面をＳＥＭ観察し、画像処理を行なうことにより、Ｒａ７５を算出することができる。この場合も、全測定値の相加平均が前記Ｒａ７５の範囲にあることが必要である。なお、前記界面の凹凸は、ブラスト処理の代わりに機械加工により付与することも可能である。   The unevenness of the interface between the Al alloy base material of the heat transfer tube and the lower header and the sprayed coating, that is, Ra75 is in the range of at least 10 to 100 μm, even if locally realized, it is meaningless, the sprayed coating surface It needs to be realized as a whole. For this reason, in this embodiment, 10 or more measurement points are selected at random from the target surface area of the Al alloy base material that covers the thermal spray coating, and defined in the appendix of JIS B 0031 and JIS B 0061. The center line average roughness Ra75 is measured by a measuring method. Then, after confirming that the arithmetic average of all the measured values is within the range of Ra75, the thermal spray coating is formed. The unevenness at the interface between the Al alloy base material and the thermal spray coating can also be measured after the thermal spray coating is formed. In this case, 10 or more measurement points are selected at random from the coating surface of the sprayed coating of the Al alloy base material arbitrarily extracted from the same blasting process and the same sprayed coating forming lot, and the sprayed coating is applied. Ra75 can be calculated by observing the cross section of the surface with SEM and performing image processing. Also in this case, it is necessary that the arithmetic average of all the measured values is in the range of Ra75. In addition, the unevenness | corrugation of the said interface can also be provided by machining instead of blasting.

ＬＮＧ気化器（ＯＲＶ）のパネル３と下部ヘッダー２（図１参照）付近の環境を模擬するため、まず、直径１６ｍｍ、厚さ４ｍｍの純アルミニウムの円板を準備し、この円板の中心を通る直線を境界として、一方の領域表面に、表１に示す各種組成の溶射皮膜を３００μｍの厚さで成膜し、溶射後は特に何の処理も施さずに、供試材とした。そして、この供試材の、溶射加工を施していない他方の領域裏面に、ペルチェ素子を密着させることにより、前記供試材の円板裏面を氷点下２０℃まで冷却した、溶射皮膜が成膜された一方の領域表面を前記氷点下２０℃の温度状態で、３０℃の市販の人工海水（富田製薬製「マリンアートハイ」）に２０時間曝した後、腐食により形成された前記円板素地のくぼみ量、および溶射皮膜のくぼみ量を表面粗さ計で測定した。測定結果を表１に示す。表１から、従来のＡｌ−Ｚｎ系溶射皮膜（NO.15、NO.16）の場合は、溶射皮膜のくぼみ量は１〜２μｍと少なく、一方円板素地のくぼみ量は１２μｍ程度と多く、前記海水暴露環境では溶射皮膜の犠牲防食効果があまり発揮されていないことがわかる。これに対し、Ａｌ−Ｍｇ系溶射皮膜の場合は、Ａｌ−Ｚｎ系溶射皮膜の場合に比べて溶射皮膜のくぼみ量は多く、円板素地のくぼみ量は少なくなっており、Ｍｇ含有量が１％以上では、溶射皮膜のくぼみ量が５μｍ以上と多くなって、溶射皮膜の犠牲防食効果が発現されており、それに伴って、円板素地のくぼみ量が８μｍ以下と少なくなっている。とくに、前記純アルミ円板素地のくぼみ量を少なくする観点からは、Ｍｇ組成は、１質量％以上、より好ましくは３質量％以上、さらに好ましくは５質量％以上とするのが有効である。なお、Ｍｇ組成が５質量％以上では、前記円板素地のくぼみ量はあまり変化しないが、Ａｌ−Ｍｇ溶射皮膜のくぼみ量が大きくなり、Ｍｇ組成が８０質量％を超えて９０質量％になると、溶射皮膜の消耗が著しくなるため、Ｍｇ組成は、８０質量％以下とするのが好ましい。溶射皮膜の過度の消耗を防止するという観点からは、Ｍｇ組成は、より好ましくは５０質量％以下、さらに好ましくは３０質量％以下とするのが有効である。なお、表１で、Ｇ１、Ｇ２、Ｇ３は、犠牲防食効果の評価レベルを表しており、Ｇ１＜Ｇ２＜Ｇ３の順に犠牲防食効果が大きくなる。 In order to simulate the environment near the panel 3 of the LNG vaporizer (ORV) and the lower header 2 (see FIG. 1), first, a pure aluminum disk having a diameter of 16 mm and a thickness of 4 mm is prepared. With a straight line passing as a boundary, a sprayed coating having various compositions shown in Table 1 was formed on the surface of one region with a thickness of 300 μm, and after the thermal spraying, no treatment was performed to obtain a test material. And the thermal spray coating which cooled the disk back surface of the said test material to 20 degreeC below freezing by making a Peltier device closely_contact | adhere to the other area | region back surface which has not performed thermal spraying processing of this test material is formed into a film. The surface of the other area is exposed to 30 ° C. commercial artificial seawater (“Marine Art High” manufactured by Tomita Pharmaceutical Co., Ltd.) for 20 hours at a temperature of 20 ° C. below the freezing point. The amount and the amount of indentation of the sprayed coating were measured with a surface roughness meter. The measurement results are shown in Table 1. From Table 1, the conventional Al-Zn-based thermal spray coating (NO.15, NO. 16) in the case of the amount of depression of the thermal spray coating is as small as 1 to 2 [mu] m, whereas the amount recesses of the disc matrix Many about 12 [mu] m, It can be seen that the sacrificial anticorrosive effect of the thermal spray coating is not sufficiently exhibited in the seawater exposure environment. On the other hand, in the case of the Al—Mg-based sprayed coating, the amount of indentation in the sprayed coating is larger than that in the case of the Al—Zn-based sprayed coating, the amount of indentation in the disk substrate is small, and the Mg content is 1. If it is% or more, the indentation amount of the thermal spray coating is increased to 5 μm or more, and the sacrificial anticorrosive effect of the thermal spray coating is exhibited, and accordingly, the indentation amount of the disk substrate is reduced to 8 μm or less. In particular, from the viewpoint of reducing the amount of indentation in the pure aluminum disc substrate, it is effective that the Mg composition is 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more. In addition, when the Mg composition is 5% by mass or more, the indentation amount of the disk substrate does not change so much, but the indentation amount of the Al—Mg sprayed coating increases, and when the Mg composition exceeds 80% by mass and becomes 90% by mass. And, since the consumption of the sprayed coating becomes remarkable, the Mg composition is preferably 80% by mass or less. From the viewpoint of preventing excessive wear of the sprayed coating, it is effective that the Mg composition is more preferably 50% by mass or less, and further preferably 30% by mass or less. In Table 1, G1, G2, and G3 represent evaluation levels of the sacrificial anticorrosive effect, and the sacrificial anticorrosive effect increases in the order of G1 <G2 <G3.

Figure 0004796362
Figure 0004796362

厚さ５ｍｍの２００ｍｍ四方のアルミ合金（A5083）板の片面に機械加工によって種々の粗さの表面凹凸を付与して、アルミ母材とした。この機械加工直後に、表面粗さ計を用いて各アルミ母材の中心線平均粗さＲａ７５を測定した。試験条件ごとに、機械加工時の目標表面粗さが同じである各アルミ母材を１０枚（Ｎ数＝１０）準備し、この１０枚のＲａ７５の平均値を各アルミ母材と溶射皮膜の界面の凹凸（Ｒａ７５）として、表２に記載した。アルミ母材との良好な接着性を確保するため、機械加工後直ちに、Ａｌ−５質量％Ｍｇ線材を用いたフレーム溶射により、厚さ３００μｍまでのＡｌ−５質量％Ｍｇの皮膜を、アルミ母材の機械加工を施した表面に成膜した。また、一部のアルミ母材の機械加工を施した表面には、Ａｌ−９０％質量Ｍｇ線材を用いたフレーム溶射により、厚さ３００μｍのＡｌ−９０％Ｍｇ皮膜を成膜した。溶射後はとくに何の処理も施さずに供試材とした。試験条件ごとの、溶射皮膜組成と膜厚を表２に記載した。   Surface irregularities with various roughnesses were imparted to one surface of a 200 mm square aluminum alloy (A5083) plate having a thickness of 5 mm to obtain an aluminum base material. Immediately after this machining, the center line average roughness Ra75 of each aluminum base material was measured using a surface roughness meter. For each test condition, 10 aluminum base materials having the same target surface roughness during machining (N number = 10) were prepared, and the average value of the 10 Ra75s was determined for each aluminum base material and the thermal spray coating. It was shown in Table 2 as the unevenness | corrugation (Ra75) of an interface. In order to ensure good adhesion to the aluminum base material, an Al-5 mass% Mg film having a thickness of up to 300 μm is formed by flame spraying using an Al-5 mass% Mg wire immediately after machining. A film was formed on the machined surface of the material. Further, an Al-90% Mg coating having a thickness of 300 μm was formed on the surface of the machined part of the aluminum base material by flame spraying using an Al-90% mass Mg wire. After thermal spraying, it was used as a test material without any particular treatment. Table 2 shows the thermal spray coating composition and film thickness for each test condition.

Figure 0004796362
Figure 0004796362

表２に記載したＮＯ．１〜２１の溶射皮膜を成膜した各アルミ母材１０枚をそれぞれ試験片として、膨れ剥離試験を実施した。まず、前記試験片をそれぞれ、２０℃、ｐＨ8.2、流速３ｍ／ｓの人工海水に３ヶ月間浸漬し、浸漬後の溶射皮膜の表面に発生した膨れ剥離の面積率を測定し、１０枚の試験片の平均値を、ＮＯ．１〜２１の溶射皮膜を成膜した各アルミの膨れ剥離の面積率として表２に記載した。表２で、溶射皮膜とアルミ母材の界面の凹凸（Ｒａ７５）と膨れ剥離面積率との関係に着目すると、界面の凹凸（Ｒａ７５）が約１０μｍ以上（ＮＯ．２、ＮＯ．３試験片）になると、膨れ剥離面積率は２０％程度に急激に低下し、流動海水環境中での耐剥離性が向上することがわかる。また、この膨れ剥離面積率は、界面の凹凸（Ｒａ７５）が約１２μｍ以上（ＮＯ．４、ＮＯ．５試験片）になると半減し、さらに約１４μｍ以上（ＮＯ．６試験片）になると、２〜３％程度と著しく減少する。従って、前記界面の凹凸（Ｒａ７５）は、１０μｍ以上、好ましくは１２μｍ以上、さらに好ましくは１４μｍ以上とするのが有効である。   The NO. A blister peel test was conducted using 10 aluminum base materials each having a thermal spray coating of 1 to 21 as test pieces. First, each of the test pieces was immersed in artificial seawater at 20 ° C., pH 8.2, and flow rate of 3 m / s for 3 months, and the area ratio of blistering and peeling generated on the surface of the sprayed coating after immersion was measured. The average value of the test pieces of NO. It was described in Table 2 as the area ratio of blistering and peeling of each aluminum film having a thermal spray coating of 1 to 21. In Table 2, paying attention to the relationship between the unevenness (Ra75) at the interface between the thermal spray coating and the aluminum base material and the bulging and peeling area ratio, the unevenness (Ra75) at the interface is about 10 μm or more (NO.2 and NO.3 test pieces). Then, the swollen peel area ratio rapidly decreases to about 20%, and it can be seen that the peel resistance in a flowing seawater environment is improved. In addition, the swelling peeling area ratio is halved when the unevenness (Ra75) at the interface becomes about 12 μm or more (NO.4, NO.5 test piece), and further becomes about 14 μm or more (NO.6 test piece). Remarkably reduced to about 3%. Therefore, it is effective that the unevenness (Ra75) of the interface is 10 μm or more, preferably 12 μm or more, more preferably 14 μm or more.

表２に記載したＮＯ．１〜２１の溶射皮膜を成膜した各アルミ母材１０枚をそれぞれ試験片として、膨れ剥離試験を実施した。まず、前記試験片をそれぞれ、２０℃、ｐＨ8.2、流速３ｍ／ｓの人工海水（富田製薬製「マリンアートハイ」）に３ヶ月間浸漬し、浸漬後の溶射皮膜の表面に発生した膨れ剥離の面積率を画像解析により測定・算出し、１０枚の試験片の平均値を、ＮＯ．１〜２１の溶射皮膜を成膜した各アルミの膨れ剥離の面積率として表２に記載した。表２で、溶射皮膜とアルミ母材の界面の凹凸（Ｒａ７５）と膨れ剥離面積率との関係に着目すると、界面の凹凸（Ｒａ７５）が約１０μｍ以上（ＮＯ．２、ＮＯ．３試験片）になると、膨れ剥離面積率は２０％程度に急激に低下し、流動海水環境中での耐剥離性が向上することがわかる。また、この膨れ剥離面積率は、界面の凹凸（Ｒａ７５）が約１２μｍ以上（ＮＯ．４、ＮＯ．５試験片）になると半減し、さらに約１４μｍ以上（ＮＯ．６試験片）になると、２〜３％程度と著しく減少する。従って、流動海水環境中で前記溶射皮膜の耐剥離性が向上させるためには、前記界面の凹凸（Ｒａ７５）は、１０μｍ以上、好ましくは１２μｍ以上、さらに好ましくは１４μｍ以上とするのが有効である。   The NO. A blister peel test was conducted using 10 aluminum base materials each having a thermal spray coating of 1 to 21 as test pieces. First, each test piece was immersed in artificial seawater (Tomita Pharmaceutical's “Marine Art High”) at 20 ° C., pH 8.2, and flow rate of 3 m / s for 3 months, and blisters formed on the surface of the sprayed coating after immersion. The area ratio of peeling was measured and calculated by image analysis, and the average value of 10 test pieces was determined as NO. It was described in Table 2 as the area ratio of blistering and peeling of each aluminum film having a thermal spray coating of 1 to 21. In Table 2, paying attention to the relationship between the unevenness (Ra75) at the interface between the thermal spray coating and the aluminum base material and the bulging and peeling area ratio, the unevenness (Ra75) at the interface is about 10 μm or more (NO.2 and NO.3 test pieces). Then, the swollen peel area ratio rapidly decreases to about 20%, and it can be seen that the peel resistance in a flowing seawater environment is improved. In addition, the swelling peeling area ratio is halved when the unevenness (Ra75) at the interface becomes about 12 μm or more (NO.4, NO.5 test piece), and further becomes about 14 μm or more (NO.6 test piece). Remarkably reduced to about 3%. Therefore, in order to improve the peel resistance of the thermal spray coating in a flowing seawater environment, it is effective that the unevenness (Ra75) of the interface is 10 μm or more, preferably 12 μm or more, more preferably 14 μm or more. .

一方、前記界面の凹凸（Ｒａ７５）が約６０μｍ付近（ＮＯ．１１試験片）から膨れ剥離面積率は再び上昇し始め、１００μｍを超えたＮＯ．１６の試験片では、膨れ剥離面積率は、ＮＯ．１試験片の１０μｍを下回る場合と同程度にまで急激に上昇する。このように、界面の凹凸（Ｒａ７５）が大きくなり過ぎると、溶射皮膜とアルミ母材の間に皮膜が充填されない空隙が形成されやすくなり、この空隙に海水が浸入して界面の優先腐食を助長するため、剥離面積率が上昇し、溶射皮膜の耐剥離性が低下する。従って、界面の凹凸（Ｒａ７５）は、１００μｍ以下、好ましくは８０μｍ以下、さらに好ましくは６０μｍ以下とするのが有効である。   On the other hand, the unevenness of the interface (Ra75) swelled from around 60 μm (NO.11 test piece), and the peeled area ratio started to increase again, and the NO. For the 16 test pieces, the swollen peel area ratio was NO. It rapidly rises to the same extent as when it is below 10 μm of one test piece. Thus, when the unevenness (Ra75) at the interface becomes too large, a void that is not filled with the coating is easily formed between the sprayed coating and the aluminum base material, and seawater enters the void to promote preferential corrosion at the interface. Therefore, the peel area ratio is increased, and the peel resistance of the thermal spray coating is lowered. Therefore, it is effective that the unevenness (Ra75) at the interface is 100 μm or less, preferably 80 μm or less, more preferably 60 μm or less.

なお、Ｍｇ組成が本発明を外れて９０質量％と多い場合（試験片ＮＯ．２０、２１）には、界面の凹凸（Ｒａ７５）が本発明の範囲（１０〜１００μｍ）に入っていても、膨れ剥離面積率が著しく大きくなる。また、Ｍｇ組成および界面の凹凸（Ｒａ７５）が本発明の範囲内でも、溶射皮膜の膜厚が本発明の範囲外の５０μｍと薄い場合にも、膨れ剥離面積率が大きくなる。これは、Ｍｇ組成が９０質量％と多くなると、溶射皮膜の消耗が激しくなり、より早期にアルミ母材と合金皮膜界面に海水が浸透する状態になるため、この母材ー皮膜界面にアルミの錆が多く発生する。このため、合金皮膜の膨れや剥離が生じやすくなり、膨れ剥離面積が著しく大きくなる。溶射皮膜が５０μｍと薄い場合にも、より早期にアルミ母材と合金皮膜界面に海水が浸透する状態になるため、同様に合金皮膜の膨れや剥離が生じやすくなり、膨れ剥離面積が大きくなる。   In the case where the Mg composition deviates from the present invention and is as large as 90% by mass (test pieces NO. 20, 21), even if the unevenness of the interface (Ra75) is within the range of the present invention (10 to 100 μm), The swollen peel area ratio is significantly increased. Even when the Mg composition and the unevenness of the interface (Ra75) are within the range of the present invention, the swelled peeling area ratio is increased even when the film thickness of the sprayed coating is as thin as 50 μm outside the range of the present invention. This is because when the Mg composition increases to 90% by mass, the sprayed coating is consumed more rapidly, and seawater penetrates into the aluminum base material and alloy film interface earlier. A lot of rust occurs. For this reason, it becomes easy to produce the swelling and peeling of an alloy film, and a swelling peeling area becomes large remarkably. Even when the thermal spray coating is as thin as 50 μm, seawater penetrates into the aluminum base material and the alloy coating interface earlier, so that the alloy coating tends to swell and peel in the same manner, and the swell and peel area increases.

厚さ５ｍｍの２００ｍｍ四方のアルミ合金（A5083）板をアルミ母材として、その片面にＡｌ−５質量％Ｍｇ合金を溶射してＡｌ−５質量％Ｍｇ合金皮膜を被覆し、表３に示すように、溶射皮膜を被覆した後の処理が異なるＮｏ．１からＮｏ．７の供試材を、それぞれ１１枚ずつ作製した。   As shown in Table 3, a 200 mm square aluminum alloy (A5083) plate having a thickness of 5 mm was used as an aluminum base material, and an Al-5 mass% Mg alloy was sprayed on one side to coat an Al-5 mass% Mg alloy film. No. 2 in which the treatment after coating the sprayed coating is different. 1 to No. Eleven specimens were prepared for each of the seven specimens.

Figure 0004796362
Figure 0004796362

表３に示した溶射後の処理終了後の膜厚が３００μｍとなるように、No.1〜No.7の各供試材の溶射皮膜を成膜した。すなわち、目標溶射皮膜厚は、溶射後の機械加工を行わないNo.1、No.2の供試材で３００μｍ、溶射後にグラインダー研削（１０秒間研削）検索を行なうNo.3の供試材で４７０μｍ、ショットピーニング処理（処理時間６０秒）を行なうNo.4〜No.7の供試材で４００μｍとした。溶射後の機械加工および処理を行わないNo.1、No.2の供試材の皮膜厚、および溶射後の機械加工および各処理を施したNo.3〜No.7の供試材の皮膜厚は、１１枚（Ｎ＝１１）の同一処理材間でもバラツキがあったが、No.1〜No.7の全供試材の皮膜厚は、２５０〜３５０μｍの範囲に収まった。   The thermal spray coating of each of the test materials No. 1 to No. 7 was formed so that the film thickness after the thermal spraying treatment shown in Table 3 was 300 μm. That is, the target sprayed coating thickness is 300 μm for the No. 1 and No. 2 specimens that are not machined after thermal spraying, and the No. 3 specimen that is used for grinder grinding (grinding for 10 seconds) after spraying. 470 μm, No. 4 to No. 7 specimens for shot peening treatment (treatment time 60 seconds), and 400 μm. Film thickness of No. 1 and No. 2 specimens not subjected to machining and treatment after thermal spraying, and No. 3 to No. 7 specimens subjected to machining and various treatments after thermal spraying Although the thickness was varied among 11 (N = 11) identical processing materials, the film thicknesses of all the test materials No. 1 to No. 7 were in the range of 250 to 350 μm.

それぞれ１１枚ずつ用意したNo.1〜No.7の供試材から各１枚を、溶射皮膜の最表面から深さ１００μｍまでの領域での気孔面積率の計測用試験片として供した。各計測用試験片２００ｍｍ×２００ｍｍの全領域から、まんべんなく１０部位を選定し、この部位から計測用サンプルを切り出し、実施例１および実施例２の場合と同様に、溶射皮膜の断面をＳＥＭ観察し、溶射皮膜の最表面から深さ１００μｍまでの領域に観察される気孔面積率を画像解析により求めた。このようにして求めたNo.1〜No.7の各供試材の１０部位の気孔面積率の平均値を、溶射皮膜の最表面から深さ１００μｍまでの領域での気孔面積率として表３に記載した。   One sample from No. 1 to No. 7 specimens prepared 11 each was used as a test piece for measuring the pore area ratio in the region from the outermost surface of the thermal spray coating to a depth of 100 μm. From the entire area of each test specimen 200 mm × 200 mm, select 10 parts evenly, cut out the measurement sample from this part, and observe the cross section of the sprayed coating in the same manner as in Example 1 and Example 2. The pore area ratio observed in the region from the outermost surface of the sprayed coating to a depth of 100 μm was determined by image analysis. Table 3 shows the average values of the pore area ratios at the 10 sites of the No. 1 to No. 7 specimens thus obtained as the pore area ratios in the region from the outermost surface of the thermal spray coating to a depth of 100 μm. It was described in.

No.1〜No.7の供試材の残りの各１０枚を、それぞれ試験片として膨れ剥離試験を実施した。まず、前記試験片をそれぞれ、２０℃、ｐＨ8.2、流速３ｍ／ｓの人工海水に３ヶ月間浸漬した。この浸漬暴露試験後の各試験片を、溶射皮膜側が内側になるように曲げ加工をして溶射皮膜に圧縮応力を付与したときに発生する溶射皮膜の膨れ剥離発生状況をＳＥＭ観察し、溶射皮膜の表面に発生した膨れ剥離の面積率を画像解析により測定・算出し、No.1〜No.7の各供試材の１０枚の膨れ剥離面積率の平均値を、膨れ剥離面積率として表３に記載した。   A swelling peel test was carried out using the remaining 10 specimens of No. 1 to No. 7 as test pieces. First, each of the test pieces was immersed in artificial seawater at 20 ° C., pH 8.2, and flow rate of 3 m / s for 3 months. Each specimen after this immersion exposure test is bent so that the thermal spray coating side is inward, and the state of blistering and peeling of the thermal spray coating that occurs when compressive stress is applied to the thermal spray coating is observed by SEM, and the thermal spray coating is observed. The area ratio of blistering and peeling that occurred on the surface of the sample was measured and calculated by image analysis, and the average value of the ten blistering and peeling area ratios of each of the test materials No. 1 to No. 7 was expressed as the blistering and peeling area ratio. 3.

表３から、溶射皮膜の気孔面積率は、溶射後の機械加工およびその後の処理を施さないNo.1供試材、溶射後の機械加工は施さず、封孔剤含浸処理のみのNo.2供試材では、１７〜１８％程度と大きく、それに対応して膨れ剥離面積も大きい。溶射後、グラインダー研削またはショットピーニングの機械加工のみを施したNo.3、No.4供試材では６〜１０％程度に低下し、膨れ剥離面積率も２〜４％と大きく低下する。溶射後、封孔剤含浸処理とショットピーニングの機械加工を組み合わせた処理を施したNo.5〜No.7供試材では、気孔面積率は１．６％程度と著しく低下し、それに対応して膨れ剥離面積率も１％以下と著しく低減する。このように、溶射後に封孔含浸処理と機械加工を組み合わせた複合処理を施すことが、気孔面積率および膨れ剥離面積率の低減に極めて有効であることを把握した。   From Table 3, the pore area ratio of the thermal spray coating is No. 1 sample material that is not subjected to mechanical processing after thermal spraying and subsequent processing, and No. 2 that is not subjected to mechanical processing after thermal spraying and is only impregnated with a sealant. In the test material, it is as large as about 17 to 18%, and the swelling and peeling area is correspondingly large. After thermal spraying, the No. 3 and No. 4 specimens subjected to only grinder grinding or shot peening machining are reduced to about 6 to 10%, and the swollen peel area ratio is greatly reduced to 2 to 4%. In No.5 to No.7 specimens that were subjected to a combination of sealant impregnation treatment and shot peening machining after thermal spraying, the pore area ratio was significantly reduced to about 1.6%. As a result, the swollen peel area ratio is significantly reduced to 1% or less. As described above, it has been understood that it is extremely effective to reduce the pore area ratio and the swollen peeling area ratio by performing the combined treatment combining the sealing impregnation treatment and the machining after the thermal spraying.

ＬＮＧ気化器の斜視図である。It is a perspective view of an LNG vaporizer.

符号の説明Explanation of symbols

１・・・ＬＮＧマニホールド
２・・・下部ヘッダー
３・・・パネル
３ａ・・・伝熱管
４・・・上部ヘッダー
５・・・ＮＧマニホールド
６・・・海水ヘッダー
７・・・散水ノズル
８・・・トラフ
Ｕ・・・パネルユニット

DESCRIPTION OF SYMBOLS 1 ... LNG manifold 2 ... Lower header 3 ... Panel 3a ... Heat transfer pipe 4 ... Upper header 5 ... NG manifold 6 ... Seawater header 7 ... Sprinkling nozzle 8 ...・ Trough U ・ ・ ・ Panel unit

Claims (9)

内部にＬＮＧが流通し、外表面に海水が供給され、この海水と前記ＬＮＧとが熱交換してＬＮＧを気化させる、外表面に防食皮膜が形成されたＡｌ合金からなるＬＮＧ気化器用伝熱管であって、前記防食皮膜が、Ｍｇを前記Ａｌ合金のＭｇ組成よりも多い３〜５０質量％含有したＡｌおよびＭｇよりなるＡｌ合金皮膜であると共に、溶射加工によって形成されたＡｌ合金皮膜であることを特徴とするＬＮＧ気化器用伝熱管。   An LNG vaporizer heat transfer tube made of an Al alloy with an anti-corrosion coating formed on the outer surface, in which LNG circulates inside, seawater is supplied to the outer surface, and the seawater and the LNG exchange heat to vaporize LNG. The anticorrosion film is an Al alloy film composed of Al and Mg containing 3 to 50% by mass of Mg more than the Mg composition of the Al alloy, and is an Al alloy film formed by thermal spraying. A heat transfer tube for an LNG vaporizer characterized by the following. 前記Ａｌ合金皮膜の膜厚が１００〜１０００μｍの範囲にあることを特徴とする請求項１に記載のＬＮＧ気化器用伝熱管。   The heat transfer tube for an LNG vaporizer according to claim 1, wherein the thickness of the Al alloy film is in a range of 100 to 1000 µm. 前記Ａｌ合金皮膜と前記伝熱管との界面の中心線平均粗さ（Ｒａ７５）が１０〜１００μｍの範囲にあることを特徴とする請求項１または２に記載のＬＮＧ気化器用伝熱管。   The heat transfer tube for an LNG vaporizer according to claim 1 or 2, wherein the center line average roughness (Ra75) of the interface between the Al alloy film and the heat transfer tube is in the range of 10 to 100 µm. 前記界面の粗さが、＃１６以上のブラスト粒子を含有するブラスト剤を前記溶射皮膜が形成される前記伝熱管の外表面に吹き付けて形成されたことを特徴とする請求項３に記載のＬＮＧ気化器用伝熱管。   4. The LNG according to claim 3, wherein the roughness of the interface is formed by spraying a blasting agent containing blast particles of # 16 or more onto an outer surface of the heat transfer tube on which the sprayed coating is formed. Heat transfer tube for vaporizer. 前記Ａｌ合金皮膜の、前記伝熱管の中心を通る断面での最表面から深さ１００μｍまでの領域に存在する気孔の面積率が１５％以下であることを特徴とする請求項３または４に記載のＬＮＧ気化器用伝熱管。   5. The area ratio of pores existing in a region from the outermost surface in a cross section passing through the center of the heat transfer tube to a depth of 100 μm of the Al alloy film is 15% or less. LNG vaporizer heat transfer tube. 請求項１から５のいずれかに記載の溶射皮膜が形成された伝熱管を複数カーテン状に配列したパネルと、このパネルの上部および下部にそれぞれ連結された気化ガス排出用の上部ヘッダーおよびＬＮＧ供給用の下部ヘッダーとからなるパネルユニットを備え、前記パネルユニットの上部からパネルの表面に沿って流下させた海水と前記伝熱管内を下部ヘッダー側から上部ヘッダー側へ流通するＬＮＧとの熱交換により、ＬＮＧを気化させるようにしたＬＮＧ気化器。   A panel in which a plurality of heat transfer tubes on which the thermal spray coating according to any one of claims 1 to 5 is formed are arranged in a curtain shape, an upper header for discharging vaporized gas connected to an upper portion and a lower portion of the panel, and an LNG supply By a heat exchange between the seawater flown down from the upper part of the panel unit along the surface of the panel and the LNG circulating in the heat transfer pipe from the lower header side to the upper header side. An LNG vaporizer adapted to vaporize LNG. 前記伝熱管の溶射皮膜が、少なくともパネル下部および下部ヘッダーの外表面に形成された請求項６に記載のＬＮＧ気化器。   The LNG vaporizer according to claim 6, wherein the thermal spray coating of the heat transfer tube is formed at least on the outer surface of the lower part of the panel and the lower header. 内部にＬＮＧが流通し、外表面に海水が供給され、この海水と前記ＬＮＧとが熱交換してＬＮＧを気化させる、外表面に防食皮膜が形成されたＡｌ合金からなるＬＮＧ気化器用伝熱管の製造方法であって、前記防食皮膜を、Ｍｇを前記Ａｌ合金のＭｇ組成よりも多い３〜５０質量％含有するＡｌおよびＭｇよりなるＡｌ合金の溶射加工により皮膜を形成した後に、この溶射皮膜の表面に溶射皮膜の気孔面積率を下げるための機械加工処理を施すことを特徴とするＬＮＧ気化器用伝熱管の製造方法。 LNG is circulated therein, seawater is supplied to the outer surface, the sea water and the with LNG exchange heat to vaporize the LNG, the LNG vaporization dexterity heat transfer tube made of Al alloy anticorrosive film on the outer surface of which is formed In the production method, the anticorrosion film is formed by thermal spraying of an Al alloy composed of Al and Mg containing 3 to 50% by mass of Mg, which is higher than the Mg composition of the Al alloy. A method for producing a heat transfer tube for an LNG vaporizer, characterized in that a machining process is performed on the surface to reduce the pore area ratio of a thermal spray coating . 前記機械加工の前処理または／および後処理として、前記溶射皮膜に封孔剤含浸処理を行なうことを特徴とする請求項８に記載のＬＮＧ気化器用伝熱管の製造方法。 9. The method for manufacturing a heat transfer tube for an LNG vaporizer according to claim 8, wherein the thermal spray coating is subjected to a sealing agent impregnation treatment as a pre-treatment and / or post-treatment of the machining.
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