JP5401964B2 - Metal tube manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing a metal tube in which a scale is formed on the inner surface of the tube by heat treatment. The metal pipe obtained by the present invention is, for example, a pipe body used in a carburizing gas atmosphere containing hydrocarbon gas or CO gas, more specifically, a cracking furnace pipe, modified in a petroleum refining or petrochemical plant or the like. It can be used for quality furnace tubes, heating furnace tubes, heat exchanger tubes and the like.

  Cracking furnace tubes, reforming furnace tubes, heating furnace tubes, heat exchanger tubes, and the like in oil refining and petrochemical plants are used in a carburizing gas atmosphere containing hydrocarbon gas or CO gas. In the use environment described above, the inner surface of the metal tube is exposed to a carburizing atmosphere. For this reason, it is preferable to form a Cr-based oxide scale layer to prevent carburization. The Cr-based oxide scale layer has a high density, a high shielding property against the penetration of carbon into the steel, and has a small catalytic action against coking, and therefore suppresses coking on the steel surface. As a result, the thermal conductivity to the fluid in the tube is maintained for a long time, and when used as, for example, a decomposition reaction tube, the yield of the reaction product such as olefin is stabilized. For this reason, for example, a metal tube having excellent high-temperature strength and corrosion resistance containing 20 to 55% Cr and 20 to 70% Ni in mass% is used as the metal tube used in the above environment. It is like that.

  That is, Patent Document 1 discloses that the Cr concentration in the Cr-deficient layer is 10% or more on the surface of the base material containing 20 to 55% by mass of Cr, or the Cr content is 50% or more on the outer side. Stainless steel for use in a carburizing gas atmosphere with an oxide scale layer is disclosed.

  As a heat treatment method for forming a Cr-based oxide scale layer, for example, Patent Document 2 discloses a stainless steel pipe containing 12 to 20% by mass of Cr and 40% by mass or less of Ni in a high-temperature and high-pressure water environment. In order to prevent elution of Ni from the atmosphere, a method of forming a scale layer by heat treatment in an inert gas atmosphere containing 0.01 to 0.5% by volume at a heating temperature of 800 to 1100 ° C. and a heating time of 2 to 20 minutes It is disclosed.

  Patent Document 3 discloses an invention in which austenitic stainless steel is heat-treated at 1100 ° C. or higher while the CO concentration in the barrel furnace is controlled to 150 ppm or higher to prevent scale unevenness due to abnormal oxidation of the steel surface.

JP 2005-48284 A JP-A-2-47249 Japanese Patent Laid-Open No. 3-197617

  As shown in Patent Document 1, if the metal tube has a high Cr content of 20 to 55% by mass, a sufficiently thick Cr-based oxide scale layer can be formed. However, depending on the manufacturing conditions, there may be a case where the unevenness of the scale in which the metal surface is exposed occurs on the inner surface of the metal tube, particularly in the vicinity of the center of the inner surface of the metal tube.

  On the other hand, Patent Documents 2 and 3 also describe a technique for forming an oxide scale on a metal tube by performing a heat treatment using a barrel, but the metal tube targeted in these documents contains a Cr-containing material. The amount is less than 20% by mass. For example, Patent Document 3 has a reference regarding unevenness of scale, and here, it is supposed to be “local abnormal growth of scale”. That is, although the knowledge about the scale which grew abnormally locally is disclosed, the partial exposure of the metal surface is not considered at all.

  The present invention has been made in order to solve the above-described problems of the prior art, and the Cr-based oxide scale layer is uniformly formed on the inner surface of the metal tube without causing partial exposure of the metal surface. It is an object of the present invention to provide a method of manufacturing a metal tube that can form a metal.

  When heat treatment was performed on a metal tube containing 20 to 55 mass% Cr using a barrel furnace, the following experiment was conducted in order to examine the cause of scale unevenness occurring near the center of the inner surface of the tube and its prevention. It was.

  That is, by mass%, 0.11% C, 1.51% Si, 0.18% Mn, 0.014% P, 0.0007% S, 25.02% Cr, 37. Contains 55% Ni, 1.05% Mo, 0.394% Ti, 0.0028% B, 0.022% Al and 0.0112% N, the balance being iron and impurities It has a chemical composition, an outer diameter of 69.85 mm, a wall thickness of 9.53 mm, a length of 13,800 mm, and 12 rib-shaped protrusions in the longitudinal direction of the pipe (rib height 4.57 mm) The metal tube was prepared, inserted into a barrel furnace (furnace length 7,000 mm) maintained at 1230 ° C., held at this temperature for 3 minutes, and then subjected to a solution heat treatment by water cooling.

  The furnace atmosphere was controlled at an air-fuel ratio (air mass / air fuel mass required for complete combustion of fuel): 1.05 using LNG as fuel.

  When the inner surface of the obtained metal tube was visually observed, no scale unevenness occurred at the end of the tube, but scale unevenness occurred at the center of the tube. Therefore, elemental surface analysis of the inner surface of the tube end portion and the tube center portion by EPMA was performed. In addition, in the analysis by EPMA, a part of the oxide scale of the test piece was previously shaved to expose the base material. The results are shown in FIGS.

  FIG. 1 is a diagram showing an analysis result by EPMA at a tube end portion of a conventional inner surface of a metal tube, and FIG. 2 is a diagram showing an analysis result by EPMA at a tube center portion of a conventional inner surface of the metal tube. ) Shows a Cr amount analysis diagram, and (b) shows a Ni amount analysis diagram. In any of the figures, a part of the test piece was scratched and the base material was exposed (the left end portion is the portion where the base material was exposed).

  As shown in FIG. 1, Cr derived from the scale was detected on the entire surface at the end of the tube, but Ni derived from the base material was hardly detected. That is, it can be seen that the oxide scale layer mainly composed of Cr is formed uniformly and sufficiently. However, as shown in FIG. 2, although Cr was detected on almost the entire surface in the central portion of the tube, there was a portion where Cr was partially reduced, and Ni was detected there. That is, an oxide scale layer mainly composed of Cr is formed to some extent in the central portion of the tube, but there is a portion where the base material is exposed in part.

  That is, the oxide scale layer on the inner surface of the metal tube is formed in a solution heat treatment performed to improve performance such as mechanical characteristics and corrosion resistance after the tube is processed into a predetermined size by hot working or cold working. As the heat treatment furnace used for the heat treatment, the barrel furnace described above is used, and the atmosphere in the furnace is controlled by the mixing ratio of LNG and air supplied from the burner.

  Here, as a heating furnace for continuously heat-treating a metal tube, a barrel furnace in which burner furnaces are cascaded and connected between them with a cover is frequently used from the viewpoint of simplicity of equipment and economy. However, the length of the barrel furnace may be shorter than the length of the metal tube subjected to this heat treatment.

  In this barrel furnace, the metal tube is inserted into the barrel furnace in a direction parallel to the axial direction, and at the initial stage of the heat treatment, the tip portion of the metal tube is inside the heating furnace and the rear end portion is outside the heating furnace. Due to the pressure difference, the oxidizing gas in the furnace flows from the front end to the rear end in the metal tube, and an oxide scale is formed on the inner surface of the metal tube. On the other hand, in the final stage of the heat treatment, conversely, the tip of the metal tube is outside the heating furnace and the rear end is in the heating furnace, so that the pressure difference causes the metal tube to move from the rear end toward the tip. The oxidizing gas in the furnace flows, and an oxide scale is formed on the inner surface of the metal tube. However, in the intermediate stage of the heat treatment, both ends of the metal tube are outside the heating furnace, so that the flow of the oxidizing gas in the furnace becomes insufficient and the formation of oxide scale becomes insufficient.

  As a result, at the front and rear ends of the metal tube, the inner surface has a sufficient thickness and a uniform oxide scale can be formed, but the metal tube surface is partially exposed at the center. In addition, a non-uniform oxide scale may be formed.

  Therefore, in order to prevent the unevenness of the scale at the center of the inner surface of the metal tube, it is necessary to supply an oxidizing gas sufficient for forming the scale to the center of the inner surface of the metal tube. The method of supplying the oxidizing gas from the end of the tube is not applicable because the tube becomes abnormally hot and temperature control becomes difficult.

  Therefore, the present inventor has conducted intensive research and found that by adjusting the oxygen potential of the atmospheric gas, unevenness of oxide scale mainly composed of Cr on the inner surface of the high Cr content metal tube can be prevented. Was completed.

  The gist of the present invention is a method for producing a metal tube as shown in the following [1] to [4].

[1] Metal tube containing 20% to 55% Cr and 20% to 70% Ni by mass and forming an oxide scale on the surface of the metal tube by a barrel furnace shorter than the length of the metal tube The metal tube is in an environment in which the oxygen potential is adjusted to 0.01 to 0.2 atm by controlling the mixing ratio of LNG and air supplied from the burner , and at a temperature of 1150 to 1250 ° C. A method of manufacturing a metal tube, characterized in that the heat treatment is carried out by transferring in a direction parallel to the tube axis into the furnace controlled to a range.

  [2] The metal tube is% by mass, C: 0.01 to 0.6%, Si: 0.1 to 5%, Mn: 0.1 to 10%, P: 0.08% or less, S : 0.05% or less, Cr: 20 to 55%, Ni: 20 to 70% and N: 0.001 to 0.25%, the balance having the chemical composition consisting of Fe and impurities [1] Metal tube manufacturing method.

[3] The method for producing a metal tube according to the above [2], wherein the metal tube has a chemical composition containing at least one element selected from the following (a) to (g) in mass%.
(A) Cu: 5% or less,
(B) Co: 5% or less,
(C) one or more selected from Mo: 3% or less, W: 6% or less, and Ta: 6% or less,
(D) one or more selected from Ti: 1% or less and Nb: 2% or less,
(E) one or more selected from B: 0.1% or less, Zr: 0.1% or less, and Hf: 0.5% or less,
(F) one or more selected from Mg: 0.1% or less, Ca: 0.1% or less, and Al: 1% or less,
(G) One or more selected from Y: 0.15% or less and Ln group: 0.15% or less

  [4] The method for producing a metal tube according to any one of the above [1] to [3], wherein the metal tube has a rib-like protrusion on the inner surface of the tube.

  According to the present invention, a metal tube with less unevenness of scale formed on the inner surface of the tube can be manufactured, so that the appearance is good. Furthermore, since the scale layer can be formed on the entire surface of the pipe, a metal pipe having excellent carburization resistance and coking resistance, high strength at high temperatures, and excellent corrosion resistance can be obtained. This metal pipe is, for example, a pipe body used in a carburizing gas atmosphere containing hydrocarbon gas or CO gas, more specifically, a cracking furnace pipe, a reforming furnace pipe in an oil refining or petrochemical plant, Suitable for use in heating furnace tubes, heat exchanger tubes, etc.

  In the method for manufacturing a metal tube according to the present invention, 20% to 55% Cr and 20% to 70% by mass% (hereinafter, “%” for the content of each element means “% by mass”). It is intended for metal tubes containing% Ni. This is because of the stable formation of a Cr-based oxide scale, tube manufacturability, structural stability at high temperatures, and the like. Details will be described later.

In the metal tube manufacturing method according to the present invention, the metal tube is transferred in a direction parallel to the tube axis, and an oxide scale is formed on the surface of the metal tube by a barrel furnace shorter than the length of the metal tube. To do. This is because, as described above, in such a barrel furnace , scale unevenness is likely to occur at the central portion of the inner surface of the tube, and the main point of the present invention is to solve this problem.

The barrel furnace needs to be controlled in an oxygen potential environment of 0.01 to 0.2 atm and in a temperature range of 1150 to 1250 ° C.

Here, the oxygen potential means a value obtained by converting the oxidizing gas supplied into the furnace into oxygen, and can be calculated using, for example, commercially available thermodynamic calculation software MLT2. When the oxygen potential is less than 0.01 atm, scale unevenness is likely to occur in the central portion of the metal tube. On the other hand, when the oxygen potential exceeds 0.2 atm, local abnormal oxidation is caused. Therefore, the atmosphere of the barrel furnace was an oxygen potential environment of 0.01 to 0.2 atm. The upper limit of the oxygen potential is preferably 0.1 atm. Note that the oxygen potential can be controlled, for example, by changing the air-fuel ratio.

On the other hand, when the heating temperature is less than 1150 ° C., the scale is not sufficiently uniformly formed. If it exceeds 1250 ° C., it will be heated near the melting point, and the performance of the material will be greatly impaired. Therefore, the heating temperature of the barrel furnace is controlled to a temperature range of 1150 to 1250 ° C.

  Next, the chemical composition of the metal tube that is the subject of the present invention will be described.

  As described above, the metal tube may have a chemical composition containing 20 to 55% Cr and 20 to 70% Ni, but in particular, C: 0.01 to 0.6%, Si: 0.00. 1-5%, Mn: 0.1-10%, P: 0.08% or less, S: 0.05% or less, Cr: 20-55%, Ni: 20-70% and N: 0.001 It preferably has a chemical composition containing 0.25%, the balance being Fe and impurities.

  In addition, an impurity means the component mixed from raw material ores, scraps, etc., and permitted within a range that does not adversely affect the present invention.

  Hereinafter, the range of the content of each element and the reason for limitation will be described.

C: 0.01 to 0.6%
C is an element effective for ensuring high temperature strength, and may be contained. However, the effect becomes remarkable when the content is 0.01% or more, but when the content exceeds 0.6%, the toughness of the stainless steel may be remarkably lowered. Therefore, C is preferably contained in an amount of 0.01 to 0.6%. A more preferred lower limit is 0.02%. A more preferred upper limit is 0.45%, and a more preferred upper limit is 0.3%.

Si: 0.1 to 5%
Since Si has a strong affinity for oxygen, it is an element effective for promoting uniform formation of a Cr-based oxide scale layer, and may be contained. These effects become significant when the content is 0.1% or more. However, when the content exceeds 5%, the weldability is deteriorated and the structure may be unstable. Therefore, it is preferable to contain Si 0.1 to 5%. A more preferred lower limit is 0.3%. A more preferred upper limit is 3%, and a more preferred upper limit is 2%.

Mn: 0.1 to 10%
Since Mn is an element effective for deoxidation and workability improvement, it may be contained. This effect becomes remarkable when the content is 0.1% or more. Since Mn is an austenite generating element, it is possible to substitute a part of Ni with Mn. However, if the content exceeds 10%, formation of a Cr-based oxide scale layer may be hindered. Therefore, it is preferable to contain 0.1 to 10% of Mn. A more preferable upper limit is 5%, and a further preferable upper limit is 2%.

P: 0.08% or less,
S: 0.05% or less P and S are segregated at the grain boundaries and deteriorate the hot workability. Therefore, although it is preferable to reduce as much as possible, excessive reduction causes high cost. Accordingly, P is acceptable up to 0.08% and S up to 0.05%. More preferable upper limit is 0.05% or less for P and 0.03% or less for S. Further preferable upper limits are P for 0.04% or less and S for 0.015% or less.

Cr: 20 to 55%
Cr is an important element in the present invention. In order to stably form a Cr-based oxide scale, it is necessary to contain 20% or more. However, excessive content lowers the tube manufacturability and the structure stability at high temperatures during use, so the upper limit is made 55%. Therefore, Cr is contained in an amount of 20 to 55%. In order to prevent deterioration of structure stability as well as workability, the upper limit is preferably made 35%. A more preferred upper limit is 33%. A preferred lower limit is 22%.

Ni: 20 to 70%
Ni is an element necessary for obtaining a stable austenite structure depending on the Cr content, and needs to be contained in an amount of 20% or more. Moreover, when C penetrate | invades in steel, since there exists a function which reduces the penetration | invasion speed | rate, it is preferable to contain. However, excessive content causes high cost and manufacturing difficulty. Therefore, Ni is contained in an amount of 20 to 70%. A preferred lower limit is 23%, and a more preferred lower limit is 25%. Moreover, a preferable upper limit is 60% and a more preferable upper limit is 50%.

N: 0.001 to 0.25%
N is an element effective for improving high-temperature strength, and therefore may be contained. In order to obtain this effect, it is preferable to contain 0.001% or more. However, an excessive content greatly impairs workability, so the upper limit is preferably 0.25%. Therefore, N is preferably contained in an amount of 0.001 to 0.25%. A more preferred upper limit is 0.2%.

  In addition to the above components, the metal tube preferably further contains one or more elements selected from the following (a) to (g).

(A) Cu: 5% or less Cu stabilizes the austenite phase and is effective in improving the high-temperature strength, so it may be contained. In order to acquire said effect, it is preferable to make it contain 0.01% or more. On the other hand, if the content exceeds 5%, the hot workability may be significantly reduced. Therefore, when Cu is contained, the content is preferably 5%. A more preferred upper limit is 3%.

(B) Co: 5% or less Co can be contained because it can stabilize the austenite phase and replace a part of Ni. In order to acquire said effect, it is preferable to make it contain 0.01% or more. On the other hand, when the content exceeds 5%, the hot workability is remarkably lowered. Therefore, when Co is contained, it is preferable to contain 5% or less. A preferable range is 0.01 to 3%.

(C) one or more selected from Mo: 3% or less, W: 6% or less, and Ta: 6% or less,
Mo, W, and Ta are all effective as a solid solution strengthening element for improving the high temperature strength, and may be contained. In order to exhibit the effect, it is preferable to contain 0.01% or more. However, excessive content may impair processability deterioration and tissue stability. Therefore, when one or more of these elements are contained, it is preferable to contain 3% or less of Mo, 6% or less of W, and 6% or less of Ta. In any element, the upper limit of the content is more preferably 2.5%, and further more preferably 2%. Moreover, when it contains one or more of these elements, it is preferable that the total content shall be 10% or less.

(D) One or more selected from Ti: 1% or less and Nb: 2% or less Ti and Nb may be contained because they have a great effect in improving high-temperature strength, ductility, and toughness even if contained in a very small amount. . In order to acquire said effect, it is preferable to make it contain 0.01% or more. If Ti exceeds 1% and Nb exceeds 2%, workability and weldability may be deteriorated. Therefore, when one or more of these elements are contained, Ti is preferably contained at 1% or less and Nb is contained at 2% or less. When Ti and Nb are contained in combination, the total content is preferably 2% or less.

(E) One or more selected from B: 0.1% or less, Zr: 0.1% or less, and Hf: 0.5% or less B, Zr, and Hf all strengthen grain boundaries and are hot worked It may be contained because it is an effective element for improving the properties and strength properties at high temperatures. In order to acquire the effect, it is preferable to contain 0.001% or more of any element. However, excessive content may deteriorate weldability. Therefore, when one or more of these elements are contained, it is preferable to contain B in an amount of 0.1% or less, Zr in an amount of 0.1% or less, and Hf in an amount of 0.5% or less.

(F) One or more selected from Mg: 0.1% or less, Ca: 0.1% or less, and Al: 1% or less Mg, Ca, and Al are all effective in improving hot workability. Since it is an element, it may be contained. In order to obtain the above effect, it is preferable to contain 0.0005% or more for Mg and Ca and 0.01% or more for Al. However, if any element is excessively contained, the weldability may be deteriorated. Therefore, when one or more of these elements are contained, it is preferable to contain Mg in an amount of 0.1% or less, Ca in an amount of 0.1% or less, and Al in an amount of 1% or less. The minimum with more preferable content of Mg and Ca is 0.0008%, and a preferable upper limit is 0.05%. Moreover, the upper limit with preferable content of Al is 0.6%.

(G) One or more selected from Y: 0.15% or less and Ln group: 0.15% or less Y and Ln groups may be contained because they are effective elements for improving oxidation resistance. In order to obtain the above effect, 0.0005% or more is preferably contained in any element. On the other hand, even if contained excessively, workability may be reduced. Therefore, when one or more of these elements are contained, it is preferable that Y is contained in an amount of 0.15% or less and the Ln group is contained in an amount of 0.15% or less. Among Ln groups, it is particularly preferable to use one or more selected from La, Ce, and Nd. The Ln group refers to elements from La with element number 57 to Lu with element 71.

  There is no particular limitation on the shape of the metal tube to be subjected to the above heat treatment, but it is preferable to have a rib-like protrusion on the inner surface of the tube. This is because cracking furnace tubes or reforming furnace tubes, heating furnace tubes, or heat exchanger tubes piped in reaction furnaces in oil refining, petrochemical plants, etc., supply hydrocarbons together with steam into the tubes. Then, by applying heat from the outer surface of the pipe, hydrocarbons are pyrolyzed inside the pipe to obtain olefinic hydrocarbons (ethylene, propylene, etc.). In the above pyrolysis reaction, In order to prevent hydrogen from being unreacted and discharged outside the reactor, it is necessary to efficiently transfer heat applied from the outer surface of the tube to the inner surface of the tube. That is, the tube needs excellent “heat exchange characteristics”. Therefore, in order to increase the inner surface area of the tube as a means for improving the heat exchange characteristics, it is preferable to use a ribbed tube (or finned tube) in which rib-like protrusions are formed on the inner peripheral surface of the tube.

  0.11% C, 1.51% Si, 0.18% Mn, 0.014% P, 0.0007% S, 25.02% Cr, 37.55% Ni, 1 .05% Mo, 0.394% Ti, 0.0028% B, 0.022% Al and 0.0112% N with the balance being a chemical composition consisting of iron and impurities; A metal tube having an outer diameter of 69.85 mm, a wall thickness of 9.53 mm, a length of 13,800 mm, and 12 rib-shaped protrusions (rib height 4.57 mm) in the longitudinal direction of the tube is prepared. The metal tube was inserted into a barrel furnace (furnace length 7,000 mm) maintained at 1230 ° C., held at this temperature for 3 minutes, and then subjected to a solution heat treatment that was cooled with water. After the heat treatment, the tube end portion and the center portion were cut out, and the presence or absence of unevenness in the scale of the inner surface was visually confirmed. Table 1 shows the conditions of the furnace atmosphere.

なお、炉内の雰囲気は、ガスクロマトグラフィーによる炉内ガスの分析を行った。また、ガスクロマトグラフィーではＨ₂Ｏの分析ができないため、完全燃焼と仮定したＨ₂Ｏ濃度で補正した。

The atmosphere in the furnace was analyzed by gas chromatography. Further, since H ₂ O cannot be analyzed by gas chromatography, it was corrected with the H ₂ O concentration assumed to be complete combustion.

As shown in Table 1, in Comparative Examples 1 and 2 in which the oxygen potential P _O2 was less than 10 ⁻² atm (that is, 0.01 atm), scale unevenness occurred at the center of the tube, but the oxygen potential was 10 ^{−. In} Example 1 of the present invention, which was ² atm (ie, 0.01 atm) or more, a uniform oxide scale layer could be formed at both the tube end and the tube center.

  According to the present invention, a metal tube with less unevenness of scale formed on the inner surface of the tube can be manufactured, so that the appearance is good. Furthermore, since the scale layer can be formed on the entire surface of the pipe, a metal pipe having excellent carburization resistance and coking resistance, high strength at high temperatures, and excellent corrosion resistance can be obtained. This metal pipe is, for example, a pipe body used in a carburizing gas atmosphere containing hydrocarbon gas or CO gas, more specifically, a cracking furnace pipe, a reforming furnace pipe in an oil refining or petrochemical plant, Suitable for use in heating furnace tubes, heat exchanger tubes, etc.

The figure which shows the analysis result by EPMA in the pipe edge part of the conventional metal pipe inner surface (a) Cr amount analysis figure (b) Ni amount analysis figure The figure which shows the analysis result by EPMA in the pipe center part of the conventional metal pipe inner surface (a) Cr amount analysis figure (b) Ni amount analysis figure

Claims (4)

A method for producing a metal tube, wherein a metal tube containing 20% to 55% Cr and 20% to 70% Ni by mass is formed on the surface of the metal tube by a barrel furnace shorter than the length of the metal tube. The metal pipe is controlled in a temperature range of 1150 to 1250 ° C. in an environment in which the oxygen potential is adjusted to 0.01 to 0.2 atm by controlling the mixing ratio of LNG and air supplied from the burner. A method of manufacturing a metal tube, wherein the heat treatment is performed by transferring the furnace in a direction parallel to the tube axis.   The said metal tube is the mass%, C: 0.01-0.6%, Si: 0.1-5%, Mn: 0.1-10%, P: 0.08% or less, S: 0.0. 5. A composition comprising 0.5% or less, Cr: 20 to 55%, Ni: 20 to 70% and N: 0.001 to 0.25%, and the balance having a chemical composition comprising Fe and impurities. 2. A method for producing a metal tube according to 1. 3. The metal tube according to claim 2, wherein the metal tube has a chemical composition containing at least one element selected from the following (a) to (g) in mass%. Production method.
(A) Cu: 5% or less,
(B) Co: 5% or less,
(C) one or more selected from Mo: 3% or less, W: 6% or less, and Ta: 6% or less,
(D) one or more selected from Ti: 1% or less and Nb: 2% or less,
(E) one or more selected from B: 0.1% or less, Zr: 0.1% or less, and Hf: 0.5% or less,
(F) one or more selected from Mg: 0.1% or less, Ca: 0.1% or less, and Al: 1% or less,
(G) One or more selected from Y: 0.15% or less and Ln group: 0.15% or less The method of manufacturing a metal tube according to any one of claims 1 to 3, wherein the metal tube has a rib-like protrusion on the inner surface of the tube.

Images