JP2005298934A - Film formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film formation method where, while gas produced from a degreasing residual material at the inside face of a metallic tube is exhausted from the inside of the tube, an oxide film for suppressing the elution of metal ions from the surface of the tube is formed. <P>SOLUTION: In the film formation method where an oxide film is formed on a metal tube subjected to cold working, after degreasing, using a continuous heat treatment furnace in which pressure changes into two or more stages in the furnace, an non-oxidizing gas is introduced into the continuous heat treatment furnace whose dew point is controlled to the range from -50°C to +50°C so as to form an oxide film. Desirably, the metallic tube is subjected to oil lubrication treatment, is then cold-rolled, is subjected to degreasing by alkali immersion and degreasing with warm water, and is thereafter heat-treated so as to form the oxide film. As the non-oxidizing gas, the one composed of hydrogen, or essentially composed of hydrogen, and comprising one or more kinds selected from nitrogen, helium and argon can be used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention prevents the generation of gas from the surface of metal pipes due to heating in metal pipes such as stainless steel pipes widely used in the fields of semiconductor manufacturing, chemical industry, food industry, thermal power or nuclear power generation equipment, etc. In addition, the present invention relates to a film forming method for forming an oxide film for suppressing elution of metal ions from the tube surface.

  For pipes that transport clean pure materials, pipes that do not allow “substance contamination” of substances passing through the pipes caused by the inclusion of foreign substances, etc., pipes that release dust and moisture from the pipe surface, elute metal ions, and heat If there is gas generation from the surface (exactly, deposits present on the surface of the pipe), the purity of the substance passing through the pipe will be reduced, and the performance of the equipment handling the substance will be reduced, and the life of the equipment will be reduced. The problem of coming will arise.

  Metal pipes (metal pipes) are generally manufactured after being subjected to heat treatment after cold working, but when cold-worked metal pipes, such as steel pipes, are cold-applied during cold rolling or drawing. Wash (degrease) the rolling oil and lubricant to remove deposits on the inner and outer surfaces of the steel pipe. When heat treatment is performed with the deposit remaining on the surface of the steel pipe without being completely removed, hydrocarbon components and chlorine (Cl) compounds contained in the rolling oil and lubricant are decomposed and evaporated to generate gas. These gases remain in the steel pipe that is particularly liable to stay. The remaining gas condenses and adheres to the inner surface of the pipe when the temperature is lowered, and when the pipe is used as a pipe, the gas is generated again, causing contamination of substances passing through the pipe.

In particular, stainless steel pipes containing chromium (Cr) (hereinafter referred to as “stainless steel pipes”) are used as heat transfer pipes for feed water heaters installed in nuclear power generation facilities. If a heat transfer tube in which an oxide film is not formed on the surface of the tube that has been pickled in the process is used, a large amount of chromium is eluted from the surface of the heat transfer tube during operation of the nuclear reactor. When the amount of elution of chromium is increased, irradiated with neutrons in the process of the reactor water is circulated reactor, with cobalt 60 ⁽⁶⁰ Co) ions increases a radionuclide in the reactor water, the equipment in the reactor Problems such as deterioration of driving performance due to adhesion of chromium occur.

  In order to prevent contamination due to elution of metal ions from the surface of the tube, such as elution of chromium from the surface of the heat transfer tube, formation of an oxide film is effective.

  For example, Patent Document 1 discloses that a continuous heat treatment furnace is used in an Ni-based alloy tube while supplying an atmosphere gas composed of hydrogen or a mixed gas of hydrogen and argon having a dew point in the range of −60 ° C. to + 20 ° C. A heat treatment method is described in which a heat treatment method is performed in which an oxide film that is charged in the tube and held at a temperature of 650 to 1200 ° C. for a predetermined time to suppress elution of Ni in a high-temperature water environment is generated. In this case, two gas supply devices provided on the outlet side (or inlet side and outlet side) of the heat treatment furnace so that the pipe to be processed can move in the traveling direction and the heat treatment furnace so as to penetrate therethrough. The atmosphere gas is supplied into the pipe using the gas introduction pipe arranged.

Further, in Patent Document 2, a steel material made of a duplex stainless steel having a predetermined chemical composition is heated and maintained at 1050 ° C. or higher in a gas atmosphere having an H ₂ concentration of substantially 100% and a dew point of −30 ° C. or lower. A method for producing a high-purity gas duplex stainless steel material in which the surface layer extending from the surface to at least 50 μm is a ferrite single phase is proposed. By heating and maintaining this duplex stainless steel material at 500 to 1000 ° C. in an inert gas atmosphere containing 10 to 1000 ppm of water vapor, a Cr oxide having a uniform Cr concentration can be generated on the surface.

  However, in the heat treatment method described in Patent Document 1, the supply of the atmospheric gas into the pipe uses a gas supply apparatus and a gas introduction pipe, and from one gas supply apparatus to the other gas in accordance with the progress of the pipe to be processed. Must be done while switching to the feeder. Further, in the method for producing a duplex stainless steel material described in Patent Document 2, it is necessary to perform an oxide film forming treatment separately from the heat treatment, and an increase in the number of steps is inevitable.

  On the other hand, in order to prevent contamination of substances passing through the pipe due to gas generation from residual deposits on the inner surface of the pipe, it is effective to completely replace the gas in the pipe with an atmospheric gas during the heat treatment. Therefore, various countermeasures have been proposed.

  For example, in Patent Document 3, a pair of open / close doors provided with elastic pads at opposing portions are provided so as to move up and down above the inlet portion of the purge chamber, respectively, and the straight pipe to be carried in is temporarily stopped at the inlet portion. An in-pipe gas purging apparatus has been proposed in which the atmosphere gas in the purge chamber is increased from above and below by an open / close door to increase the pressure of the atmosphere gas in the purge chamber.

  In addition, in the heat treatment apparatus disclosed in Patent Document 4, the side of a heat treatment furnace for heat-treating the straight tube in an atmospheric gas is charged to feed the straight tube toward the inlet of the straight tube. A negative pressure means is provided for placing a negative pressure at a position where the rear end of the straight pipe is located in a state where the front end of the straight pipe is in the heat treatment furnace. Is provided. As a result, the purging operation in the straight pipe can be performed very easily.

  However, in the apparatus proposed in Patent Document 3, since it is necessary to stop charging the straight pipe each time at the inlet of the purge chamber, the heat treatment efficiency is significantly reduced, and at the same time, the quality of the elastic pad is deteriorated in the heating atmosphere. However, there is a problem that required performance cannot be obtained or that frequent replacement is required. Moreover, since the apparatus disclosed in Patent Document 4 requires a large-capacity negative pressure means, there is a problem that a large-scale capital investment is required and the steel pipe manufacturing cost increases.

JP 2003-239060 A

Japanese Patent Laid-Open No. 10-88288 JP-A-5-320745 JP-A-6-128645

  The present invention has been made in view of such a situation, and prevents the degreasing residue that generates gas by heating from adhering to the inner surface of the metal tube, and elution of metal ions from the tube surface, in particular, nuclear power generation. It aims at providing the film formation method which forms the oxide film for suppressing the elution of Cr ion from the surface of the chromium containing stainless steel pipe used for a heat exchanger tube in feed water heaters, such as equipment.

  In order to solve the above-mentioned problem, the present inventor cleaned (degreasing) a cold-worked steel pipe, and then removed the deposits remaining on the surface, thereby suppressing the elution of metal ions from the pipe surface. Various studies were conducted on the method of forming a film for forming a film.

  As a result, in the heat treatment furnace in which the pressure in the furnace changes stepwise, the gas generated by the decomposition of the residual deposits on the inner surface of the pipe by heat treatment using a non-oxidizing gas containing a small amount of water vapor as the atmospheric gas ( In other words, it was found that it is possible to easily form an oxide film that suppresses the elution of metal ions from the surface of the tube while at the same time replacing the “contaminating gas” that causes contamination of substances passing through the tube with atmospheric gas. . That is, heat treatment of the steel pipe after cold working and treatment for forming an oxide film (hereinafter referred to as “coating treatment”) can be performed simultaneously while eliminating the contaminated gas.

This invention is made | formed based on the above-mentioned knowledge, and makes the summary the following film formation method.
“A method for forming an oxide film on a cold-worked metal tube, using a continuous heat treatment furnace in which the pressure changes in two or more stages in the furnace after degreasing, with a dew point of −50 ° C. to + 50 ° C. A film forming method, wherein an oxide film is formed by introducing a non-oxidizing gas adjusted within a range into a continuous heat treatment furnace. ]
In the film forming method, oil lubrication is performed, cold working is performed, degreasing is performed by immersing in alkali and washing with warm water, and then heat treatment is performed to form an oxide film. It is desirable that the coating does not deteriorate in roughness due to corrosion, and has a thin and tight coating without defects.

  In the film forming method, hydrogen or a gas containing hydrogen as a main component and containing at least one of nitrogen, helium, and argon can be used as the non-oxidizing gas.

  According to the coating film forming method of the present invention, heat treatment and elution of metal ions from the tube surface are performed on a metal tube after cold working while excluding gas generated from residual deposits on the inner surface of the tube. It is possible to simultaneously perform a film treatment for forming an oxide film for suppression. As a result, when used in various plants such as nuclear power generation facilities, it is possible to provide a metal tube that is free from metal elution and gas generation from residual deposits on the inner surface of the tube.

  As described above, the film forming method of the present invention is “a film forming method for forming an oxide film on a cold-worked metal tube, and after degreasing, the continuous heat treatment in which the pressure changes in two or more stages in the furnace. A method of forming an oxide film by introducing a non-oxidizing gas having a dew point adjusted within a range of −50 ° C. to + 50 ° C. into a continuous heat treatment furnace using a furnace ”. That is, a method of forming an oxide film using a continuous heat treatment furnace for a cold-worked metal tube, and simultaneously performing the film treatment and the heat treatment while eliminating the generated gas from the residual deposits on the inner surface of the tube. It can be carried out.

  FIG. 1 is a diagram showing an example of a general stainless steel pipe manufacturing process to which the coating film forming method of the present invention is applied. (A) is an example of a conventional heat treatment process, and (b) and (c) of FIG. It is an example of a process to which the film forming method of the invention is applied. (B) The figure shows the case of performing cold working for one pass, and (c) the figure shows the case of performing cold working for two or more passes.

  As shown in FIG. 1 (b) or (c), the stainless steel tube obtained by “hot pipe making” is subjected to “cold working” after being subjected to “chemical conversion film lubrication treatment or oil lubrication treatment”. Followed by “degreasing” (or “degreasing” followed by further “pickling”) treatment. The “degreasing” treatment is usually performed by immersing in an alkali and washing with warm water.

  The raw pipe after hot pipe making has a rough surface roughness due to the generation of scale, and has a large variation. In addition, the base material Cr is consumed for forming the scale layer, and the surface of the base material has a low Cr concentration. Since the crystal grain boundary has a high Cr diffusion rate, the Cr concentration is further lowered, and the influence extends deeply along the grain boundary.

  In order to smooth the surface of the raw tube and make the Cr concentration uniform, a “chemical conversion film lubrication treatment or an oil lubrication treatment” is performed, and a cold working with a cross-section reduction rate of a certain degree or more is performed.

  The chemical conversion film lubrication treatment is a lubrication method in which a chemical conversion film is formed by a chemical reaction to impart lubricity. That is, the surface is corroded and roughened, and the surface is covered with a corrosion product. The surface is covered with good adhesion, and lubricity is imparted. Since a film is interposed between the tool and the material surface during cold working, the frictional shear force is relatively weak and the surface recesses (pockets) in a state where the film is clogged are hardly crushed. Further, it is difficult to remove the lubricating film (chemical conversion film), and after cold working, in addition to alkali immersion and hot water cleaning, a film removal treatment by “pickling” is required (see FIG. 1A). Even after such treatment, there is a film residue on the surface recess, which causes an increase in gas generated by thermal decomposition during the heat treatment.

  On the other hand, in the case of oil lubrication treatment, the lubricant (oil) is only physically attached to the surface of the tube, so there is no deterioration of the surface roughness, and the difficulty of removing the lubricant is the difficulty of the chemical conversion film. Compared with the case of removal, the process is greatly reduced, and the “pickling” step can be omitted.

  Therefore, the “chemical conversion film lubrication treatment or oil lubrication treatment” before the “cold working” in the process example shown in FIG. 1B is usually an oil lubrication treatment, and after cold working, it is immersed in an alkali. It is desirable to perform degreasing by washing with warm water (that is, “non-pickling degreasing” without pickling treatment). In addition, what is necessary is just to perform the degreasing | defatting by an alkali by the method used normally.

  Also, in the process example shown in FIG. 1C, it is desirable that the finishing pass is performed by oil lubrication and is non-pickled and degreased without pickling. Furthermore, all passes are performed by oil lubrication treatment, non-pickling degreasing is performed, and intermediate heat treatment is performed by applying a continuous heat treatment furnace in which the pressure described later changes in two or more stages in the furnace. More desirable.

  Cold work is performed at least once. The working rate of cold working is preferably 20% or more in terms of the cross-sectional reduction rate. As a result, a new surface is created on the inner and outer surfaces of the tube, the surface of the tube is smoothed, and the Cr concentration in the vicinity of the surface is made uniform.

  The processing method may be either drawing or rolling, and may be a combination of drawing and rolling. Pulling is performed with a cored bar that inserts a tool into the pipe. Emptying is not desirable because the generation of new surfaces on the inner surface is insufficient.

  In order to obtain a good new surface, it is desirable to perform rolling at least once so that the reduction rate of the cross section can be increased.

  After “cold processing”, “degreasing” is performed. When the lubrication treatment before the cold working is an oil lubrication treatment, the lubricant (oil) is only physically attached to the pipe surface, so that the lubricant is almost removed by “alkaline soaking → warm water washing”. Therefore, no “pickling” treatment is required. On the other hand, in the case of the chemical conversion film lubrication treatment, as described above, it is difficult to remove the lubricating film (chemical conversion film), and degreasing by “pickling” is necessary.

  When the pickling treatment is performed, the crystal grain boundary is particularly eroded, the surface roughness is deteriorated (see Invention Example 12 in Examples described later), and the reaction film formed by the reaction between the base material and the acid is a film. During processing, it adversely affects the formation of oxide films.

  Subsequent to the “lubricating treatment”, “cold working” and “degreasing”, a “coating treatment” is applied to the metal tube. In this treatment, “a non-oxidizing gas whose dew point is adjusted within the range of −50 ° C. to + 50 ° C. is introduced into the continuous heat treatment furnace using a continuous heat treatment furnace whose pressure changes in two or more stages in the furnace”. .

  “A continuous heat treatment furnace in which the pressure changes in two or more stages in the furnace” means, for example, a heat treatment furnace composed of an inlet zone, a heating zone, a cooling zone, and an outlet zone, where the internal pressure of the inlet zone is equal to or higher than the external pressure of the furnace. It is a heat treatment furnace set so as to be equal to or lower than the pressure of the heating zone (in this case, it changes in two stages).

  FIG. 2 (a) is a diagram schematically showing a cross-sectional configuration example of a continuous heat treatment furnace in which such pressure changes in two stages in the furnace, and (b), (c) and (d) of FIG. These are figures which show typically the discharge effect of the gas generated from the temperature pattern of a metal pipe (for example, stainless steel pipe), the pressure distribution in the furnace, and the residual deposit on the inner surface of the pipe when this heat treatment furnace is used. The lengths in the horizontal direction in (B) to (D) in FIG. 2 correspond to those in (A).

  The heat treatment furnace shown in FIG. 2 (a) has an inlet zone 1, a heating zone 2, a cooling zone 3 and an outlet zone 4, and an atmosphere gas is introduced into the heating zone 2 so that the metal tube is in the axial direction. Along with this, the furnace is continuously charged from the inlet zone 1 into the furnace, subjected to a predetermined heat treatment, and carried out from the outlet zone 4. A pipe feeding roller (not shown) for conveying the metal pipe is disposed on the hearth.

  Seal curtains 5a, 5b, and 5c are attached to the entrance side of the inlet zone 1, the vicinity of the entrance side of the heating zone 2, and the exit side of the exit zone 4, respectively.

  FIG. 2 (c) shows the pressure distribution in the furnace. By attaching the seal curtains 5a, 5b and 5c as described above, the pressure difference between the inlet zone 1 and the outside of the continuous heat treatment furnace with the seal curtain 5a interposed therebetween. And a pressure difference is generated between the heating zone 2 and the inlet zone 1 across the seal curtain 5b. That is, the internal pressure of the furnace can be changed in two stages with respect to the pressure outside the furnace, in the inlet zone 1 and the heating zone 2. Note that there is no pressure difference between the seal curtain 5b and the seal curtain 5c, and there is a pressure difference of the two stages between the outlet belt 4 and the outside of the furnace across the seal curtain 5c.

  FIG. 2B shows a temperature pattern of the metal tube. The metal tube is heated in the heating zone 2, reaches 500 ° C. before the seal curtain 5 b, further rises in temperature and is held at a solution heat treatment temperature for a predetermined time, and then cooled to a predetermined temperature in the cooling zone 6, After that, it is gradually cooled. The above-mentioned 500 ° C. is based on the investigation result (see FIG. 9) to be described later, and the generation of F, Cl and S-containing gas from the residual deposits is completed by this temperature. Temperature ".

  FIG. 2 (d) is a diagram for explaining the effect of discharging the gas generated from the residual deposits on the inner surface of the pipe, and the metal pipe charged in the continuous heat treatment furnace is moved from the position of the metal pipe 6a to the position of 6e. This shows a state in which the gas in the pipe is discharged out of the pipe while being transported in the furnace. The entire metal tube 6a or the light black portion such as the rear half of the tube 6b has not been completely discharged even if gas has not yet been generated from the residual deposits. It means that it stays in the pipe. Moreover, the light black arrow described at the front-end | tip and the rear end of the metal pipes 6a-6e has shown the direction of the flow of the atmospheric gas which flows through the inside of a pipe | tube.

  In FIG. 2 (d), the metal tube 6a is in a state immediately before its tip side 3/4 is inserted into the furnace and the tip of the tube reaches the seal curtain 5b. Most of the tube has not yet been heated, and the tip has not been heated to 500 ° C. Although there is a pressure difference between the outside of the furnace and the inlet zone 1, the atmospheric gas flows from the tip to the rear end of the tube, but gas generation from residual deposits on the inner surface of the tube is near the tip of the tube. It has just begun (as will be described later, gas generation from residual deposits is observed in the temperature range from 200 ° C. to 500 ° C.), and gas generation has not yet occurred in most of the tubes.

  In the metal tube 6b, the tip of the tube is in the heating zone 2 and the rear end of the tube is in the inlet zone 1, and the half on the tip side of the tube has already been heated to 500 ° C. or higher, and the gas from the residual deposits On the other hand, since there is a pressure difference between the tip and the rear end of the tube, the atmospheric gas flows from the tip of the tube toward the rear end, and the generated gas in the tip half of the tube is outside the tube. Is discharged. The metal pipe 6c shows a state where the discharge to the outside of the pipe has further progressed.

  The metal pipe 6d represents a state in which the entire pipe is heated to 500 ° C. or more and the gas generation from the residual deposits is finished, and the generated gas is discharged out of the pipe by the flow of the atmospheric gas from the front end to the rear end. ing. The metal tube 6e is in a state in which the tip of the tube is carried out of the furnace, and the pressure at the rear end side of the tube still in the furnace is higher, so the atmospheric gas flows from the rear end of the tube to the tip. (See light black arrow).

  FIG. 3 is a cross-sectional configuration example of another continuous heat treatment furnace in which the pressure changes in two stages in the furnace (FIG. 3 (a)), and the temperature pattern of the metal tube when this heat treatment furnace is used (same (b)). FIG. 3 is a diagram schematically showing the pressure distribution in the furnace (same (C)) and the effect of discharging the gas generated from the residual deposits on the inner surface of the pipe (same (D)). The lengths in the horizontal direction in (B) to (D) in FIG. 3 correspond to those in (A).

  The difference between the heat treatment furnace shown in FIG. 3 and the furnace shown in FIG. 2 is that, in the heat treatment furnace shown in FIG. 3, the entry side of the exit zone 4 (in other words, the exit side of the cooling zone 3). The point is that a seal curtain 5d is attached. For this reason, as shown in FIG. 3C, the pressure distribution in the furnace changes in two stages even on the outlet zone 4 side of the furnace.

  As shown in FIG. 3D, the effect of discharging the gas generated from the residual deposits on the inner surface of the tube is the same as that in the heat treatment furnace shown in FIG.

  FIG. 4 shows a cross-sectional configuration example of still another continuous heat treatment furnace (FIG. 4 (a)) in which the pressure changes in two stages in the furnace, and the temperature pattern of the metal tube when this heat treatment furnace is used (same (b)). ), The pressure distribution in the furnace (same (c)) and the exhaust effect of the gas generated from the residual deposits on the inner surface of the tube (same (d)), in the horizontal direction in (b) to (d) The length of each corresponds to that of (A).

  The difference between the heat treatment furnace shown in FIG. 4 and the furnace shown in FIG. 2 is the attachment position of the seal curtain in the inlet zone 1, and in the heat treatment furnace shown in FIG. A seal curtain 5a 'is attached to the end. Therefore, as shown in FIG. 4C, the pressure distribution in the furnace is slightly different, and the first-stage pressure range in the furnace is narrow.

  As shown in FIG. 4 (d), the effect of discharging the gas from the residual deposits on the inner surface of the tube is the same as in the case of the heat treatment furnace shown in FIG.

  FIG. 5 is a sectional configuration example of another continuous heat treatment furnace in which the pressure changes in two stages in the furnace (FIG. 5 (a)), and the temperature pattern of the metal tube when this heat treatment furnace is used (the same (b)). ), The pressure distribution in the furnace (same (c)) and the exhaust effect of the gas generated from the residual deposits on the inner surface of the tube (same (d)), in the horizontal direction in (b) to (d) The length of each corresponds to that of (A).

  The difference between the heat treatment furnace shown in FIG. 5 and the furnace shown in FIG. 2 is that a preheater 7 is provided in the inlet zone 1, the seal curtain 5 b of the heating zone 2 is removed, and the seal curtain at the rear end of the inlet zone 1. 5a 'is attached. Therefore, as shown in FIG. 5C, the region where the temperature of the metal tube reaches 500 ° C. moves to the inlet zone 1 side, and the range of the second-stage pressure in the furnace is widened.

  As a result, as shown in FIG. 4 (d), the gas generation effect from the residual deposit on the inner surface of the pipe is early because gas generation from the residual deposit occurs. Done quickly. This makes it possible to increase the pipe feeding speed into the heat treatment furnace.

  There are no particular limitations on the material, shape, etc. of the seal curtain, and conventionally used heat-resistant curtains can be used. If a plurality of sheets are stacked and further used in a plurality of sets, it is effective for maintaining a pressure difference before and after the seal curtain.

  Although the above description is an example in which the pressure in the furnace changes in two stages in the inlet zone and the heating zone, a furnace that changes in three stages or more may be used.

  In contrast, conventionally, a heat treatment furnace without a stepwise change in pressure in the furnace has been used, but here it will be described for comparison with a continuous heat treatment furnace used in the film forming method of the present invention. .

  FIG. 6 shows a cross-sectional configuration example (FIG. 6 (a)) of a conventionally used continuous heat treatment furnace, the temperature pattern of the metal pipe (same (b)), the pressure distribution in the furnace (same (c)), and the inner surface of the pipe. It is a figure which shows typically the discharge effect (the same (d)) of the gas which generate | occur | produces from a residual deposit, and all the horizontal length in (b)-(d) of FIG. It corresponds.

  The difference between the heat treatment furnace shown in FIG. 6 and the heat treatment furnace shown in FIGS. 2 to 5 is the presence or absence of the seal curtain 5 b in the heating zone 2 and the seal curtain 5 a ′ at the rear end of the inlet zone 1. That is, since the heat treatment furnace shown in FIGS. 2 to 5 includes the seal curtain 5b or the seal curtain 5a ′, the pressure in the furnace can be changed in two stages, but the conventional heat treatment furnace shown in FIG. In the heat treatment furnace, as shown in FIG. 6C, the pressure distribution in the furnace is one stage.

  Therefore, as shown in FIG. 6 (d), in the state where the entire metal tube is charged in the furnace (metal tubes 6b, 6c, 6d), the flow of the atmospheric gas from the furnace toward the rear end occurs. In addition, since the gas generated from the residual deposit remains in the pipe and is subjected to the coating treatment (solution heat treatment), a good coating is not formed.

  When the state of the metal tube 6e is reached, the tip portion of the tube is carried out of the furnace, so that an atmosphere gas flows from the rear end of the tube to the tip, but before the generated gas is completely discharged (removed), When the whole is carried out of the furnace, a part of the generated gas remains in the pipe, condenses and adheres to the inner surface of the pipe, and causes contamination of substances passing through the pipe when used as piping.

  In the film forming method of the present invention, as described above, the continuous heat treatment furnace in which the pressure changes in two or more stages in the furnace is used for the following reason.

  It is judged that the degreasing agent (lubricating oil used in the oil lubrication treatment) is apparently removed on the inner and outer surfaces of the metal tube after cold working and degreasing (non-pickling degreasing) treatment. The However, a slight amount remains (attaches), and when heated, gas is generated from the remaining deposits.

  Lubricating oils for metal processing generally contain oils and fats, and extreme pressure additives added to them contain compounds such as F, Cl, S, and P. A small amount of residual lubricating oil that has not been removed after degreasing adheres to the inner and outer surfaces of the pipe, but during coating treatment, the gas generated from the deposit on the outer surface of the pipe scatters into the furnace and is supplied continuously. Since it is diluted with atmospheric gas, it has little effect. However, the gas generated from the residual deposits on the inner surface of the pipe tends to stay in the pipe and is an amount that cannot be ignored with respect to the internal volume in the pipe.

In a conventional hydrogen furnace that uses hydrogen as the atmospheric gas (also called “bright furnace”), the gas in the pipe when heat-treating the stainless steel pipe was collected and analyzed, and as a result, the pipe was sufficiently replaced with hydrogen, and the material to be treated In the furnace, the gas mainly composed of hydrocarbons, CO, CO ₂ , N ₂ , and O ₂ is 6 to 10% by volume (the balance is atmospheric gas) H ₂ ) was found to be included. Hydrocarbon, CO, and CO ₂ are gases generated from residual deposits after degreasing, and N ₂ and O ₂ are considered to be derived from the air that was present in the pipe before charging. Furthermore, from this result, it is also predicted that a gas component containing F, Cl, S, etc. contained in the extreme pressure material is generated from the residual deposits and stays in the pipe although it is in a very small amount. Note that these components are problematic even in a minute amount from the viewpoint of contamination of substances passing through the pipe.

  Therefore, as shown in FIG. 7, a cylindrical heating furnace 8 is used to heat the stainless steel tube 9 after cold working and degreasing (non-pickling degreasing) treatment, and F, Cl, S from the residual deposits. The generation characteristics of gas containing etc. were investigated.

  FIG. 8 is a diagram schematically showing the heat pattern used in the experiment. (A) shows a case where the temperature in the heating furnace is raised stepwise (heat pattern A), and (b) shows a sudden increase to 500 ° C. After heating, the temperature is lowered to room temperature and then raised stepwise (heat pattern B).

Table 1 shows the experimental conditions. “Yes” in the column “Hydrogen hydrogen flow” in Table 1 means that the hydrogen flow is approximately the same as the normal flow rate (0.5 Nm ³ / h) in the actual furnace during the heating of the stainless steel pipe 9. “None” means that no hydrogen was sent.

FIG. 9 shows the survey results. Test 1 (◯ mark), test 2 (● mark), and test 3 (x mark) in FIG. 9 correspond to test 1, test 2 and test 3 in Table 1, respectively. The generated gas was introduced and dissolved in pure water together with hydrogen sent into the pipe, and then quantified as F ⁻ , Cl ⁻ or SO ₄ ²⁻ by the method used in the examples, and the vertical direction of FIG. The total amount of them is displayed on the axis.

  Test 1 in FIG. 9 is a result of increasing the temperature in the heating furnace step by step and examining the generation amount of gas containing F, Cl and S at each temperature. It can be seen that gas generation from the kimono is observed, and the generated amount gradually decreases when the temperature exceeds 300 ° C., and hardly occurs at 500 ° C. or higher. When these gases are mixed in the atmosphere gas, they adversely affect the formation of the oxide film. Therefore, the atmosphere gas in the furnace is passed through the tube at 500 ° C or higher, and the tube is completely discharged from the tube before the tube temperature reaches the film processing temperature. It is necessary to discharge.

  Test 3 was performed in order to confirm that the generated gas reattached due to a decrease in temperature. As shown in FIG. 8B, even when the gas was generated by heating to 500 ° C., Since the gas generation characteristics similar to those in the test 1 are shown by the stepwise temperature increase after the temperature is lowered, it can be seen that the generated gas adheres again due to the temperature decrease. When such a steel pipe is used for piping, gas is generated again when the temperature rises, resulting in contamination.

  Therefore, if the continuous heat treatment furnace illustrated in FIG. 2 to FIG. 5 is used, a flow of atmospheric gas from the front end to the rear end of the pipe can be naturally generated in the steel pipe, and residual deposits inside the pipe can be generated. The coating treatment and the heat treatment (in this example, the solution heat treatment) can be performed simultaneously while replacing or removing the generated gas with the atmospheric gas. In Test 2 shown in FIG. 9, an oxide film was formed in a continuous heat treatment furnace in which the pressure changed in two stages in the furnace in order to confirm the effect when the film forming method of the present invention was applied. As a result of performing the heat treatment on the stainless steel pipe, the gas generated from the residual deposits in the pipe was completely eliminated, and no re-adhesion accompanying cooling of the pipe occurred, so no gas generation was observed.

  In FIG. 1B and FIG. 1C, the heat treatment that also serves as the coating treatment is indicated as “bright heat treatment with atmospheric gas aeration in the tube”. In addition, in the conventional process example shown in FIG. 1A, “atmospheric furnace heat treatment” is performed, but this is a heat treatment performed in an air atmosphere without a stepwise change in the furnace pressure. . The “bright heat treatment” of “atmospheric furnace heat treatment or bright heat treatment” performed in the first pass of the process example of the present invention shown in FIG. This is a heat treatment performed in a main atmosphere. In the process example shown in FIG. 1 (c), heat treatment using a continuous heat treatment furnace in which the pressure changes in two or more stages in the furnace in the finishing pass, that is, “bright heat treatment with atmospheric gas ventilation in the tube” is performed. However, as mentioned above, it is more desirable to perform this bright heat treatment not only in the finishing pass but in all passes.

  Thus, in the film forming method of the present invention, a continuous heat treatment furnace in which the pressure changes in two or more stages in the furnace is used. At this time, “the dew point was adjusted within the range of −50 ° C. to + 50 ° C. Introduce non-oxidizing gas into continuous heat treatment furnace. That is, a furnace in which an appropriate oxide film (a close-contact oxide film without defects) can be obtained under the heat treatment conditions (that is, heating temperature and time) determined in operation so that the film treatment and the heat treatment can be performed simultaneously. The inside atmosphere. Specifically, a non-oxidizing gas atmosphere is used to suppress excessive oxidation on the surface of the metal tube, and water vapor is added thereto to obtain an appropriate oxide film.

  The mixing amount of water vapor is controlled by the dew point, and is adjusted so that the dew point is in the range of −50 ° C. to + 50 ° C. In accordance with the shape of the object to be processed, the heat treatment temperature and the heating time in the heat treatment furnace are taken into consideration, and the conditions under which a predetermined oxide film is obtained within this range. For example, in heat treatment of stainless steel pipes, the heating temperature rise time and cooling time differ depending on the outer diameter and wall thickness. In the case of small diameter thin-walled pipes, the heating temperature rise time is short and the feed rate of the pipe is large. Since the time is shortened, the dew point of the atmospheric gas is set on the high temperature side (+ 50 ° C. side) where the oxidizing atmosphere is strong. Conversely, in the case of a thick material with a long in-furnace time, it is preferable to set the dew point on the low temperature side where the oxidizing atmosphere is weak. The thickness of the oxide film is not particularly limited. An oxide film having no defects, thin adhesion, and little surface color unevenness is effective in suppressing elution of metal ions from the surface of the tube and preventing contamination associated with elution.

  As the non-oxidizing gas, hydrogen is generally used, but it is also possible to use a gas mainly composed of hydrogen and an inert gas (including nitrogen). For example, a gas mainly containing hydrogen and containing at least one of nitrogen, helium, and argon.

  Nitrogen is an inexpensive gas and is advantageous in terms of cost. However, for example, depending on the nitrogen content level of the stainless steel pipe, penetration (nitriding) or denitrification occurs in the base material, and therefore it is preferable to adjust in the range of 0 to 10% by volume according to the nitrogen content of the base material. .

  After finishing the treatment in the continuous heat treatment furnace in which the pressure is changed in two stages in the furnace, which combines the heat treatment and the film treatment, and forming the oxide film on the inner and outer surfaces of the metal tube, as shown in FIG. In the "preparation" process and "inspection" process, "rectification" and "inspection" such as bending correction, cutting and pipe end finishing are performed according to conventional methods, and further, U-bend processing and finishing inspection are performed as necessary. .

  As mentioned above, although the stainless steel pipe was mainly demonstrated, the film formation method of this invention is applicable also to manufacture of the metal pipe which uses other alloy steel, Ni base alloy, and another nonferrous metal as a raw material.

  Stainless steel pipe or nickel chrome iron alloy pipe (hereinafter referred to as SUS304 (austenite stainless steel), SUS444 (ferritic stainless steel) and NCF690 (nickel chrome iron alloy, Ni: 60 mass%, Cr: 30 mass%), respectively. , Which is also simply referred to as “pipe”), is manufactured in accordance with the pipe making process illustrated in FIG. 1 (b) or (c), and the surface roughness, metal elution amount, coating variation and deposits (salts) And sulfide) were investigated.

  The dimensions of the manufactured pipes are as follows. For each pipe, the outer diameter is 34 mm and the thickness is 4.0 mm (hereinafter referred to as dimension “A”), or the outer diameter is 16 mm and the thickness is 1.2 mm (hereinafter referred to as dimension “B”). ")".

The evaluation method is as follows.
〔Surface roughness〕
The surface roughness of the three inner surfaces of the tube is indicated by the centerline average roughness Ra (μm). If the average value is 0.5 μm or less, “◎ (very good)”, 0.5 μm to 1 μm or less If there was “◯ mark (good)”, if it exceeded 1 μm, it was marked “x mark (defect)”.

[Elution amount of metal]
Non-degassed pure water is sealed in the tube and held at 215 ° C. for 100 hours, and then the amounts of Fe, Cr, and Ni in the sealed water are quantified with an inductively coupled plasma emission spectrometer (ICP-MS). The elution amount per unit surface area (mg / m ² ) was calculated from the surface area in the tube.

If the total elution amount of Fe, Cr and Ni is 5 mg / m ² or less, “◎”, if it exceeds 5 mg / m ^{2 and} 10 mg / m ² or less, “◯”, if it exceeds 10 mg / m ² It was set as “x mark”.

[Coating variation]
The tube after coating treatment (heat treatment) was sampled from a total of 9 locations, 3 locations in the furnace width direction (both ends and center in the diameter direction of the tube) and 3 locations in the length direction (end, center and rear end of the tube). The color of was observed visually.

  First, the presence or absence of an oxide film was investigated, and if no oxide film was observed in the majority of the nine samples, “no film” was determined. Subsequently, when a film was observed, it was evaluated whether it was a thinly adhered oxide film, and in one or more samples, when a thinly adhered oxide film was not recognized, it was determined as “defective”. . When it was determined that there was no defect, color variation on the surface of the oxide film was further evaluated. If the surface color unevenness was small, “◯” was indicated, and if the surface color unevenness was large, “X” was indicated.

[Amount of deposit (amount of chloride and sulfide)]
After the pure water is sealed in the tube and the deposits on the inner surface are eluted, the concentration of Cl ion and SO ₄ ion in the sealed water is obtained by ion chromatography, and the amount of chloride per unit surface area is determined from the amount of sealed water and the surface area in the tube ( mg / m ² ) and the amount of sulfide (mg / m ² ) were calculated. When the total amount of chloride and sulfide was 1 mg / m ² or less, “◯” was indicated, and when exceeding 1 mg / m ² , “X” was indicated.

  The pipe making conditions are shown in Table 2, and the survey results are shown in Table 3.

  In Table 2, “alkali” in the column of “degreasing method” means “alkali soaking → hot water washing” treatment, and “pickling” means “pickling → water washing”.

“Two-stage furnace pressure 1” in the column of “Type of furnace” in Table 2 is a furnace in which the furnace pressure has a distribution as shown in FIG. Similarly, (c) in FIG. 3 and “two-stage furnace pressure 3” are the same as (c) in FIG. 4 and “two-stage furnace pressure 4” are the furnace pressures as in (c) of FIG. It is a furnace showing the distribution. In addition, the “conventional hydrogen furnace” of the comparative example is a hydrogen furnace (bright furnace) in which the pressure in the furnace does not change stepwise. Further, “hydrogen” in the “atmosphere gas” column means that H ₂ is substantially 100% by volume.

  As is clear from Tables 2 and 3, Invention Examples 1-11, 13 and Inventive Examples 1 to 11, 13 in which the dew point of the atmospheric gas was adjusted within a specified range using a heat treatment furnace (bright furnace) in which the pressure changed in two stages in the furnace. In No. 14, the surface roughness Ra, the metal elution amount, the amount of deposits, and the coating variation were all good. In Example 12 of the present invention, the surface roughness Ra was large because the chemical conversion film lubrication treatment was performed on the lubrication treatment before cold working. However, good results were obtained with respect to other metal elution amounts, deposit amounts, and coating variations.

  On the other hand, in Comparative Examples 1 and 3 using the “conventional hydrogen furnace”, the gas generated from the residual deposits on the inner surface of the pipe cannot be completely discharged, and the deposits are recognized in the pipe. Due to the influence of the generated gas in the atmosphere gas, a uniform oxide film was not formed over the entire length on the inner surface of the tube, and the coating varied greatly. On the other hand, in Comparative Examples 2 and 4 in which the dew point of the atmospheric gas deviates from the range defined in the present invention, no deposits were observed in the pipe because a heat treatment furnace having a “two-stage furnace internal pressure 4” was used. The state was worse compared to Comparative Examples 1 and 3. In all of Comparative Examples 1 to 4, the metal elution amount was large.

  According to the coating film forming method of the present invention, heat treatment and coating treatment are simultaneously performed on the inner and outer surfaces of the tube while excluding gas generated from the residual deposits on the inner surface of the tube after subjecting the metal tube after cold working. A uniform oxide film can be formed. Therefore, the metal pipe to which the coating film forming method of the present invention is applied does not cause metal elution or gas generation from the residual deposit on the inner surface of the pipe, and can be used in various plants including nuclear power generation facilities.

It is a figure which shows the example of a pipe making process of the general stainless steel pipe to which the film formation method of this invention is applied, (a) is a process example which performs the heat processing of a conventional system, (b) and (c) are the film formation of this invention. It is an example of a process to which the method is applied. Cross-sectional configuration example (Fig. 2 (a)) of a continuous heat treatment furnace in which the pressure changes in two stages in the furnace, the temperature pattern of the metal tube (same (b)), the pressure distribution in the furnace (same (c)) and the inner surface of the tube It is a figure which shows typically the discharge effect (the same (d)) of the gas which generate | occur | produces from the residual deposit of this. Cross-sectional configuration example of another continuous heat treatment furnace in which the pressure changes in two stages in the furnace (Fig. 3 (a)), metal tube temperature pattern (same (b)), furnace pressure distribution (same (c)) and It is a figure which shows typically the discharge effect (the same (d)) of the gas which generate | occur | produces from the residual deposit | attachment of a pipe inner surface. Cross-sectional configuration example of another continuous heat treatment furnace in which the pressure changes in two stages in the furnace (FIG. 4 (a)), metal tube temperature pattern (same (b)), furnace pressure distribution (same (c)) It is a figure which shows typically the discharge effect (the same (d)) of the gas which generate | occur | produces from the residue deposit | attachment of a pipe inner surface. Cross-sectional configuration example of another continuous heat treatment furnace in which the pressure changes in two stages in the furnace (FIG. 5 (a)), metal tube temperature pattern (same (b)), furnace pressure distribution (same (c)) It is a figure which shows typically the discharge effect (the same (d)) of the gas which generate | occur | produces from the residue deposit | attachment of a pipe inner surface. From the cross-sectional configuration example of a continuous heat treatment furnace that has been used in the past (Fig. 6 (a)), the temperature pattern of the metal tube (same (b)), the pressure distribution in the furnace (same (c)) and the residual deposits on the inner surface of the tube It is a figure which shows typically the discharge effect (the same (d)) of the generated gas. It is a figure which shows schematic structure of the principal part of the experimental apparatus used for the examination of the generation | occurrence | production characteristic of the gas containing F, Cl, S, etc. from the residual deposit in a pipe | tube. It is a figure which shows typically the heat pattern used in the investigation of the generation characteristic of the gas containing F, Cl, S, etc. from the residual deposit in a pipe, and (a) raises the temperature in a heating furnace in steps. (Battery pattern A) and (b) are cases where the temperature is rapidly heated to 500 ° C., lowered to room temperature, and then raised stepwise (heat pattern B). F from the residual deposits in the tube, Cl, in findings occurred properties of gas containing S or the like, the heating temperature and F ^-, Cl ^- is a diagram showing the relationship between and SO ₄ ^2-of the total amount.

Explanation of symbols

1: Inlet zone 2: Heating zone 3: Cooling zone 4: Outlet zone 5a, 5a ', 5b, 5c, 5d: Seal curtain 6a, 6b, 6c, 6d, 6e: Metal pipe 7: Preheater 8: Cylindrical heating Furnace 9: Stainless steel pipe

Claims (4)

  A film forming method for forming an oxide film on a cold-worked metal tube using a continuous heat treatment furnace in which the pressure changes in two or more stages in the furnace after degreasing, and the dew point is in the range of −50 ° C. to + 50 ° C. A non-oxidizing gas adjusted inside is introduced into a continuous heat treatment furnace to form an oxide film.   The film forming method according to claim 1, wherein the film is cold-worked by oil lubrication, degreased by being immersed in an alkali and washed with warm water, and then heat-treated to form an oxide film.   The film forming method according to claim 1, wherein the non-oxidizing gas is hydrogen. The film forming method according to claim 3, wherein the non-oxidizing gas contains hydrogen as a main component and contains at least one of nitrogen, helium, and argon.

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