JP2019023332A - Tube end lid and manufacturing method of steel pipe using the same - Google Patents

Abstract

To provide a pipe end lid capable of being easily installed and prevented from falling out during heat treatment.SOLUTION: A pipe end lid 1 which is attached to a pipe end of a steel pipe P includes: an inner lid 11 disposed inside the steel pipe P; a heat insulating material 12 disposed inside the steel pipe P at a position closer to the pipe end of the steel pipe P than the inner lid 11; and a connecting member 13 connecting an end face of the steel pipe P and the inner lid 11 to hold them at a certain distance.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a tube end cap and a method for manufacturing a steel tube using the same.

The heat treatment of steel has been widely performed for a long time for the purpose of imparting desired characteristics and performance to machine parts and steel products, and the essence is adjustment of the metal structure. In particular, “quenching” accounts for the majority of heat treatment, and at room temperature, the heat-treated material, which is usually a ferrite and pearlite structure, is heated to a temperature higher than Ac ₃ point (austenite transformation end temperature) to become austenite and then rapidly cooled to martensite. It forms an organization. The martensite structure has the highest strength among all the structures of metal materials and is a very important structure used in all industrial fields.

  The most important point in quenching the tubular body is uniform cooling in the circumferential direction. When the circumferential cooling becomes uneven, the steel pipe is bent during cooling. This bending becomes larger as the length of the steel pipe becomes longer, which leads to undesirable situations such as troubles during line conveyance and the addition of a bending correction process. In quenching a steel pipe, it is preferable to cool the outer surface with water while passing the cooling zone while moving and conveying the steel pipe. Uniform outer surface water cooling can be achieved relatively easily by means such as evenly arranging cooling nozzles in the annular main pipe, but internal water cooling has many technical problems and may complicate the equipment configuration. That is why.

  Even if the coolant is sprayed only from the outer surface of the steel pipe, the coolant may enter the steel pipe from the end of the pipe. If the refrigerant enters the inside of the steel pipe, the inner surface of the steel pipe is cooled unevenly, which causes bending. When the steel pipe wall thickness is large, the adverse effect of bending is small, but even so, it causes various problems such as variation in hardness. Further, the refrigerant may flow into the heating furnace along the inner surface of the steel pipe and may damage the heating furnace.

  In Japanese Patent Laid-Open No. 58-27331, in a cooling device for injecting and cooling a refrigerant on a transported tubular object, an insertion cylinder for cooling water blocking is provided to prevent the refrigerant from entering the pipe from the rear end of the pipe. It is described to do. Japanese Patent No. 5252131 describes that a pipe end is air-cooled in a quenching method in which a steel pipe is cooled from the outside by water cooling. JP 2012-172173 A discloses a method of quenching a steel pipe by injecting quenching water to the outer peripheral surface of the steel pipe while inclining it with respect to the conveying direction while conveying the heated steel pipe along the longitudinal direction. It is described that a lid is attached to the rear end of the steel pipe in the conveying direction. Japanese Utility Model Laid-Open No. 61-77192 discloses an apparatus for continuously and automatically welding a pipe end cover to a plurality of steel pipes.

JP 58-27331 A Japanese Patent No. 5252131 JP 2012-172173 A Japanese Utility Model Publication No. 61-77192

  As a means for suppressing the penetration of the refrigerant into the steel pipe, it is simple and reliable to attach a lid to the pipe end. Generally, the lid is attached to the pipe end of the steel pipe all around the spot or spot welded, but an attachment process before processing and a pipe end cutting process including the lid after processing are required. Production efficiency and yield decrease. Further, in the case of attachment by simple insertion, the lid may fall off during the heat treatment.

  An object of the present invention is to provide a tube end lid that is easy to attach and can be prevented from falling off during heat treatment, and to provide a method of manufacturing a steel pipe using the same.

  A tube end cover according to an embodiment of the present invention is a tube end cover attached to a tube end of a steel pipe, and includes an inner lid disposed on the inner side of the steel pipe, an inner side of the steel pipe, and more than the inner lid. A heat insulating material disposed at a position close to a pipe end of the steel pipe, and a connection member that connects the end face of the steel pipe and the inner lid and holds the fixed distance.

  A method of manufacturing a steel pipe according to an embodiment of the present invention includes a step of preparing a raw pipe, a step of attaching the pipe end lid to at least one of the pipe ends of the raw pipe, and a raw piece to which the pipe end lid is attached. Quenching the tube.

  According to the present invention, it is possible to obtain a tube end lid that can be easily attached and can be prevented from falling off during heat treatment. By manufacturing a steel pipe using this pipe end lid, bending of the steel pipe can be suppressed.

FIG. 1 is an exploded perspective view showing a configuration of a tube end cover according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a state in which the pipe end lid according to the first embodiment is attached to a steel pipe. FIG. 3 is a flowchart showing a method for manufacturing a steel pipe according to an embodiment of the present invention. FIG. 4 is a block diagram showing a functional configuration of an example of the heat treatment line. FIG. 5 is a temperature-elongation diagram of a general steel material that causes phase transformation. FIG. 6 is an exploded perspective view showing the configuration of the tube end cover according to the second embodiment of the present invention. FIG. 7 is a cross-sectional view showing a state in which the pipe end lid according to the second embodiment is attached to a steel pipe. FIG. 8 is an exploded perspective view showing the configuration of the tube end lid according to the third embodiment of the present invention. FIG. 9 is a cross-sectional view showing a state in which the pipe end lid according to the third embodiment is attached to a steel pipe. FIG. 10 is a graph showing the relationship between the heat transfer coefficient on the inner surface of the steel pipe and the residual tensile stress on the inner surface of the steel pipe. FIG. 11 is a diagram illustrating a state in which the refrigerant stays at the bottom of the steel pipe. FIG. 12 shows the stress distribution of the steel pipe when the refrigerant stays at the bottom. FIG. 13 shows a model used in the numerical calculation. FIG. 14 is a graph showing the change over time in the gap amount. FIG. 15 is a graph showing changes in temperature of the tube end and the lid over time. FIG. 16 is a diagram illustrating a state 25 seconds after the start of cooling in the absence of a heat insulating material. FIG. 17 is a diagram illustrating a state 100 seconds after the start of cooling in the case where there is a heat insulating material. FIG. 18 is a diagram showing an outline of the waterproof performance evaluation test. FIG. 19 is a diagram schematically showing the state of conveyance of the steel pipe.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated. The dimensional ratio between the constituent members shown in each drawing does not necessarily indicate the actual dimensional ratio.

[First Embodiment]
FIG. 1 is an exploded perspective view showing a configuration of a tube end lid 1 according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a state in which the pipe end lid 1 is attached to the steel pipe P. The pipe end lid 1 includes an inner lid 11 arranged inside the steel pipe P, a heat insulating material 12 arranged inside the steel pipe P and closer to the pipe end of the steel pipe P than the inner lid 11, and the steel pipe P. And a stay 13 which is a connecting member for connecting the end face and the inner lid 11. The tube end lid 1 further includes an outer lid 14 disposed so as to be adjacent to the end surface of the steel pipe P, a connection screw 15a for fixing the outer lid 14, and the like.

  The inner lid 11 has a disk shape whose outer diameter is slightly smaller than the inner diameter of the steel pipe P so that it can be arranged inside the steel pipe P. The inner lid 11 is preferably formed of a material having a linear expansion coefficient α larger than that of the steel pipe P. The material of the inner lid 11 is, for example, stainless steel. The inner lid 11 is preferably thin from the viewpoint of workability. The thickness of the inner lid 11 is preferably 20 mm or less, and more preferably 10 mm or less.

  Similarly to the inner lid 11, the heat insulating material 12 also has a disk shape whose outer diameter is slightly smaller than the inner diameter of the steel pipe P so that it can be disposed inside the steel pipe P. The heat insulating material 12 preferably has heat resistance, and for example, a ceramic molded body such as alumina can be used.

  In the present embodiment, the heat insulating material 12 is fixed to the inner lid 11. However, the heat insulating material 12 may be fixed to the stay 13, for example, or may be fixed to the outer lid 14. The heat insulating material 12 should just be arrange | positioned in the position nearer to the pipe end of the steel pipe P than the inner lid 11.

  The stay 13 connects the end surface of the steel pipe P and the inner lid 11. The stay 13 can prevent the inner lid 11 from moving in the axial direction of the steel pipe P. The material of the stay 13 is not specifically limited, For example, carbon steel may be sufficient and stainless steel may be sufficient.

  More specifically, each of the stays 13 includes a first portion 13a extending in a direction substantially perpendicular to the inner lid 11, and a second portion extending in a direction substantially parallel to the inner lid 11 and continuing to one end of the first portion 13a. Part 13b. Each of the stays 13 regulates the distance between the end surface of the steel pipe P and the inner lid 11 by the second portion 13b coming into contact with the end surface of the steel pipe P. In FIG. 1, eight stays 13 are arranged in the circumferential direction of the steel pipe, but the number of stays 13 is arbitrary.

  In the present embodiment, as shown in FIG. 2, each of the stays 13 is fixed to the inner lid 11 with screws 16. However, the fixing method of the stay 13 is arbitrary. For example, the stay 13 and the inner lid 11 may be connected by fixing the stay 13 to the heat insulating material 12. In addition, you may fix the stay 13 and the steel pipe P with a heat resistant adhesive material etc., for example.

  The stay 13 of this embodiment is an example of a connecting member, and the configuration of the connecting member is not limited to this. The connecting member may be any member that connects the end surface of the steel pipe P and the inner lid 11 and holds them at a certain distance.

  The outer lid 14 has a disk shape whose outer diameter is slightly larger than the inner diameter of the steel pipe P so as to close the opening of the steel pipe P. In order to suppress thermal deformation as much as possible, the outer lid 14 is preferably formed with a material amount having a small linear thermal expansion coefficient α. The material of the outer lid 14 is, for example, carbon steel. The outer lid 14 is preferably thin, mainly from the viewpoint of workability. The thickness of the outer lid 14 is preferably 20 mm or less, and more preferably 10 mm or less.

  In the present embodiment, the outer lid 14 is coupled to the inner lid 11 by a coupling screw 15a. The connecting screw 15a is welded to the inner lid 11a. The outer lid 14 has a through hole 14a through which the connecting screw 15a is passed. The outer lid 14 is held in contact with the end surface of the steel pipe P via the stay 13 by passing the connecting screw 15a through the through hole 14a and tightening the nut 15b. According to this configuration, the outer lid 14 can be easily attached and detached. However, the fixing method of the outer lid 14 is arbitrary. For example, a rod may be welded to the inner lid 11 instead of the connection screw 15a, and the outer lid 14 may be welded to the rod.

[Manufacturing method of steel pipe]
Next, the manufacturing method of the steel pipe using this pipe end cover 1 is demonstrated. Hereinafter, in the description related to the method of manufacturing a steel pipe, the steel pipe that is the target of heat treatment is referred to as a “base pipe”. In addition, the term “steel pipe” is used in the sense of a steel pipe manufactured by heat treatment in distinction from the “element pipe”.

  FIG. 3 is a flowchart showing a method for manufacturing a steel pipe according to an embodiment of the present invention. The method of manufacturing a steel pipe according to the present embodiment includes a step of preparing a raw pipe (step S1), a step of attaching a pipe end lid 1 to at least one of the pipe ends of the raw pipe (step S2), and the pipe end lid 1 being attached. And a step (step S3) of quenching the obtained raw pipe

  A raw tube to be heat-treated is prepared (step S1). Although the target pipe is not limited, the manufacturing method of the present embodiment is suitable for manufacturing a steel pipe having a high carbon material with a carbon content of 0.50 to 0.60% by mass, particularly high carbon. It is suitable for the production of oil well pipes of a system material amount. More specifically, the production method of the present embodiment is particularly suitable for production of oil well pipes of low alloy steel and high alloy steel having a carbon content of 0.50 to 0.60 mass%.

  The tube end lid 1 is attached to at least one of the tube ends of the raw tube (step S2). The tube end lid 1 is preferably attached to both of the tube ends of the raw tube. However, depending on the angle at which the refrigerant is blown or the like, the refrigerant can be prevented from entering even if it is attached only to the front or the rear.

The raw tube to which the tube end lid 1 is attached is quenched (Step S3). Specifically, after heating the raw tube to which the tube end cap 1 is attached to a temperature of Ac ₃ point or higher to austenite transformation, it cools to a temperature lower than the martensitic transformation end temperature to cause martensitic transformation. At this time, if the cooling rate is too low, an isothermal transformation occurs at an intermediate temperature and a structure having a high martensite ratio cannot be obtained. On the other hand, if the cooling rate is too high, bending and cracking occur. Therefore, it is necessary to appropriately control the cooling rate. Preferably, the cooling rate is increased as much as possible up to the martensite transformation start temperature, and the cooling rate is decreased as much as possible from the martensite transformation start temperature to the cooling end temperature (martensite transformation end temperature or room temperature).

  FIG. 4 is a block diagram showing a functional configuration of a heat treatment line 100 which is an example of the heat treatment line. The heat treatment line 100 includes a quenching device 20 and a tempering device 30. The quenching device 20 includes a heating device 21, a cooling device 22, and an immersion bath 23. A conveyance roller 40 (conveyance device) is disposed between the devices.

  The conveyance roller 40 sequentially conveys the raw tube from the heating device 21 to the cooling device 22, from the cooling device 22 to the immersion bath 23, and from the immersion bath 23 to the tempering device 30. The raw tube is heated by the heating device 21 and cooled by the cooling device 22 and / or the immersion bath 23. The blank tube is then heated again by the tempering device 30.

According to the configuration of the heat treatment line 100, after heating the raw tube to Ac ₃ points or more by the heating device 21, the raw tube is quenched by cooling the raw tube with the cooling device 22 and / or the immersion bath 23. it can. Furthermore, the raw pipe can be tempered by heating the raw pipe to a predetermined temperature by the tempering device 30. The tempered tube is cooled by a cooling device (not shown) and then transferred to a flaw detection device or the like.

  According to the configuration of the heat treatment line 100, the base pipe can be continuously subjected to quenching and tempering heat treatment. However, quenching and tempering may not be performed continuously. In this case, the heat treatment line 100 may not include the tempering device 30.

  Although the detailed structure is not illustrated, the cooling device 22 includes a plurality of cooling rings. Each of the plurality of cooling rings is provided with a plurality of nozzles, and is configured such that a refrigerant can be sprayed from each of the plurality of nozzles to the outer surface of the raw tube passing through the inside of the cooling ring. The amount of the refrigerant is configured to be controlled for each cooling ring, and the raw pipe can be cooled at an optimum speed by adjusting the refrigerant amount for each cooling ring and the conveying speed of the raw pipe.

  The immersion tank 23 is filled with a refrigerant, and can be rapidly cooled from the inner and outer surfaces by immersing the raw tube. When the raw pipe to be heat-treated is a low-medium carbon steel (C content less than 0.30%) with low susceptibility to fire cracking, the cooling pipe 22 is not used, and the raw pipe is cooled using only the immersion bath 23. You can also. In this case, the processing speed can be increased. On the other hand, even when the pipe to be heat-treated is a pipe with a high susceptibility to fire cracking, if the steel pipe is sufficiently cooled by the cooling device 22, bending or fire cracking may occur even if it is immersed in the immersion bath 23. Absent.

  That is, according to the configuration of the quenching device 20, the cooling by the cooling device 22 and the cooling by the immersion bath 23 can be selectively performed according to the properties of the target raw pipe. On the other hand, in the case where only an elementary tube having high susceptibility to burning cracks is targeted, the heat treatment line 100 may not include the immersion bath 23.

[Effect of tube end cap 1]
Hereinafter, the effect of the tube end lid 1 will be described. FIG. 5 is a temperature-elongation diagram of a general steel material that causes phase transformation. As shown in FIG. 5, this steel thermally expands with increasing temperature from room temperature to Ac ₁ point, but shrinks by austenite transformation (Austenite transformation shrinkage) when Ac ₁ point is exceeded. Then, it expands again at the linear expansion coefficient of austenite and reaches the maximum temperature (Tmax). In the cooling process, since it is supercooled in the austenite state until martensitic transformation starts, it contracts with the linear expansion coefficient of austenite, and starts to expand when it reaches the martensitic transformation start temperature Ms (about 300 ° C. in the amount of the material). (Α transformation expansion).

  Also in the heat treatment of a steel pipe, the expansion and contraction shown in FIG. Therefore, it is difficult to fix the lid to the steel pipe before and after the heat treatment by simple mechanical means. For example, when the lid is fixed by a fixing means (a stick rod) that makes close contact with the inner surface of the steel pipe using the reaction force of the screw, even if it can be firmly fixed at room temperature, loosening occurs due to heating and cooling. In particular, the tension rod cannot follow the α transformation expansion in the cooling process, and loosening occurs.

  The pipe end lid 1 (FIG. 2) of the present embodiment is arranged at an inner lid 11 disposed inside the steel pipe P, and at a position closer to the pipe end of the steel pipe P than the inner lid 11 inside the steel pipe P. The heat insulating material 12 is provided. According to this configuration, in the cooling process, the temperature decrease of the inner lid 11 is delayed by the heat insulating material 12 than the temperature decrease of the steel pipe P. Therefore, the shrinkage of the inner lid 11 is slower than the shrinkage of the steel pipe P, and an effect similar to so-called “shrink fitting” in which the inner lid 11 is tightened by the steel pipe P is obtained. When the steel pipe P reaches the martensite transformation start temperature, it expands by α transformation expansion, but the inner lid 11 in the shrink-fitted state follows the expansion of the steel pipe P while weakening its reaction force. Therefore, it is possible to suppress the intrusion of the refrigerant without dropping to the cooling end temperature (martensite transformation end temperature or room temperature).

  If the outer diameter of the inner lid 11 is too small with respect to the inner diameter of the steel pipe P, the above effects cannot be obtained sufficiently. The lower limit of the outer diameter of the inner lid 11 is preferably 99% of the inner diameter of the steel pipe P, and more preferably 99.5% of the inner diameter of the steel pipe P. The upper limit of the outer diameter of the inner lid 11 is preferably 99.7% of the inner diameter of the steel pipe P.

  The inner lid 11 is preferably formed of a material having a linear expansion coefficient α larger than that of the steel pipe P. In this case, since the thermal expansion of the inner lid 11 is larger than the thermal expansion of the steel pipe P even in the heating process, the inner lid 11 can be kept in close contact with the inner surface of the steel pipe P.

  The outer lid 14 prevents the refrigerant from coming into direct contact with the inner lid 11 and the heat insulating material 12. Since the outer lid 14 is in direct contact with the refrigerant, it may be largely thermally deformed. However, even if the refrigerant enters from the gap generated by the deformation, the inner lid 11 is further suppressed from entering the inside. Moreover, if the heat insulating material 12 is a porous body or a fiber, a small amount of refrigerant can be absorbed. The tube end lid 1 may not include the outer lid 14 depending on the angle at which the coolant is blown.

  The method for manufacturing a steel pipe according to the present embodiment can also be applied when the steel pipe is a square steel pipe. In this case, the planar shape of the inner lid 11, the heat insulating material 12, and the outer lid 14 may be rectangular.

  In the above, the pipe end cover 1 by the primary embodiment of this invention and the manufacturing method of the steel pipe using the pipe end cover 1 were demonstrated. According to this embodiment, a tube end lid that can be easily attached and can be prevented from falling off during heat treatment is obtained. Moreover, the bending of a steel pipe can be suppressed by manufacturing a steel pipe using this pipe end cover.

[Second Embodiment]
FIG. 6 is an exploded perspective view showing the configuration of the tube end lid 2 according to the second embodiment of the present invention. FIG. 7 is a cross-sectional view showing a state in which the pipe end lid 2 is attached to the steel pipe P. In addition to the structure of the tube end lid 1, the tube end lid 2 is disposed inside the steel pipe P and at a position closer to the tube end of the steel pipe P than the inner lid 11, and is connected to the inner lid 11. Is further provided.

  The inner lid 17 has a disk shape whose outer diameter is slightly smaller than the inner diameter of the steel pipe P so that it can be arranged inside the steel pipe P. The inner lid 17 is preferably formed of a material having a linear expansion coefficient α larger than that of the steel pipe P. The material of the inner lid 17 is stainless steel, for example. The inner lid 17 is preferably thin, mainly from the viewpoint of workability. The thickness of the inner lid 17 is preferably 20 mm or less, and more preferably 10 mm or less.

  The inner lid 17 has a through hole 17a through which the connecting screw 15a is passed. The inner lid 17 has a shape in which the outer diameter on the side close to the inner lid is smaller than the outer diameter on the side near the pipe end. By passing the connecting screw 15 a through the through hole 17 a and tightening the nut 15 c, the inner lid 17 moves in a direction approaching the inner lid 11.

  Further, the tube end lid 2 is configured such that the stay 13 extends outward in the radial direction of the steel pipe P by moving the inner lid 17 to the inner lid 11 side. In the present embodiment, specifically, the outer diameter of the inner lid 17 is larger than the distance between the first portion 13a of one stay 13 and the first portion 13a of the stay 13 opposed thereto. It is configured.

  According to this configuration, by tightening the nut 15 c, the inner lid 17 moves in a direction approaching the inner lid 11, and the stay 13 extends outward in the radial direction of the steel pipe P, and between the stay 13 and the inner surface of the steel pipe P. Contact reaction force is generated. Thereby, the steel pipe P and the pipe end lid 2 can be more firmly fixed.

  The inner lid 17 also serves to prevent the refrigerant that has entered from the gap between the steel pipe P and the outer lid 14 from entering further inside.

  The inner lid 17 is preferably formed of a material having a linear expansion coefficient α larger than that of the steel pipe P. In this case, since the thermal expansion of the inner lid 17 is larger than the thermal expansion of the steel pipe P even in the heating process, a contact reaction force can be generated between the stay 13 and the inner surface of the steel pipe P.

  In the present embodiment, the inner lid 17 is disposed between the heat insulating material 12 and the outer lid 14. However, the inner lid 17 may be disposed between the inner lid 11 and the heat insulating material 12. That is, the tube end lid 2 may be configured to fix the heat insulating material 12 after the inner lid 17 is attached.

  Also in the present embodiment, the tube end lid 2 may not include the outer lid 14 depending on the angle at which the refrigerant is blown. Moreover, the manufacturing method of the steel pipe by this embodiment is applicable also when a steel pipe is a square steel pipe.

[Third Embodiment]
FIG. 8 is an exploded perspective view showing the configuration of the tube end lid 3 according to the third embodiment of the present invention. FIG. 9 is a cross-sectional view showing a state in which the pipe end lid 3 is attached to the steel pipe P. In addition to the configuration of the tube end lid 2, the tube end lid 3 is further provided with a taper member 18 that is fixed to each of the stays 13 and increases in thickness in a direction approaching the inner lid 11.

  More specifically, the taper member 18 of the present embodiment has a triangular prism shape whose section is a vertical triangle, and the surface opposite to the surface on which the taper is provided is welded to the stay 13. The specific shape of the taper member 18 is not limited to that shown in FIGS. For example, the tapered member may have a curved surface.

  According to the present embodiment, the contact reaction force generated between the stay 13 and the inner surface of the steel pipe P can be further increased by the taper member 18. Thereby, the steel pipe P and the pipe end lid 3 can be more firmly fixed.

  Also in the present embodiment, the tube end lid 3 may not include the outer lid 14 depending on the angle at which the coolant is blown. Moreover, the manufacturing method of the steel pipe by this embodiment is applicable also when a steel pipe is a square steel pipe.

  Hereinafter, based on an Example, this invention is demonstrated more concretely. In addition, this Example does not limit this invention.

[Investigation of the effect of internal cooling]
The effect of cooling the inner surface of the steel pipe was investigated by numerical analysis using the finite element method (FEM). FIG. 10 is a graph showing the relationship between the heat transfer coefficient of the inner surface of the steel pipe (ratio to the heat transfer coefficient h of the outer surface) and the residual tensile stress of the inner surface of the steel pipe. As shown in FIG. 10, the highest tensile stress is generated when the heat transfer coefficient of the inner surface is 50% of the heat transfer coefficient of the outer surface. When the heat transfer coefficient of the inner surface is equal to that of the outer surface (100%), the stress becomes compressive, but this is a result of cooling the inner surface of the steel pipe uniformly.

  As shown in FIG. 11, it is considered that the refrigerant C actually stays at the bottom of the steel pipe P, and uneven thermal stress is generated in the circumferential direction. Therefore, the steel pipe cross section was modeled, and the residual stress was calculated under the condition that the heat transfer coefficient of the portion where the refrigerant stays is equal to the outer surface and the other portions are air-cooled. The results are shown in FIG. As shown in FIG. 12, it was found that high tensile stress was generated at the boundary portion with or without the refrigerant.

[Examination of welding lid]
Next, the effect of welding a lid to the pipe end was also investigated by numerical analysis. In the numerical analysis, welding joint was simulated by constraining the joint near the outer surface of the steel pipe and the joint of the lid at the same position. The generated stress in this case was 369 MPa. On the other hand, when the binding constraint condition was released, the stress decreased to 344 MPa. From this, it was found that the restraint by welding acts in the direction of increasing the stress. Furthermore, when the material properties of the weld metal were given as parameters, the stress increased to 422 MPa. This suggests that fragile weld metal is the starting point for cracking.

[Examination of the effect of insulation]
Assuming the configuration of a tube end lid (excluding the outer surface lid 14) according to the tube end lid 1 of the first embodiment, a numerical analysis is performed by FEM, and occurs between the steel pipe and the tube end lid in the cooling process. The size of the gap was calculated. FIG. 13 shows a model used in the numerical calculation. In the analysis, a two-dimensional object model composed of a steel pipe, an inner lid, and a heat insulating material was applied, and the temperature and deformation within a predetermined time were calculated from an initial temperature of 900 ° C. The conditions are as follows. As a comparative example, calculation was performed when no heat insulating material was used.
Steel pipe material: 0.5% C-1.0% Cr-0.7% Mo-0.015% Ti-0.002% B steel Steel pipe dimensions: Φ426mm x t30mm x L2000mm
・ Lid dimensions: Φ366mm × t10mm (same material as steel pipe)
・ Insulating material: Φ366mm × t10mm (ceramic heat-resistant insulating material)
-Initial temperature: 900 ° C (heating furnace set temperature)
・ Water cooling time: Water cooling / cooling heat transfer coefficient of steel pipe outer surface and heat insulating material outer surface: identified from measured values

  FIG. 14 is a graph showing the change over time in the gap amount. FIG. 15 is a graph showing changes in temperature of the tube end and the lid over time. When there is no heat insulating material, a gap begins to be generated simultaneously with the start of cooling, and opens 1.6 mm 25 seconds after the start of cooling. The state at this time is shown in FIG. 16 together with the temperature distribution. This is because the inner cover with a small thickness drops in temperature in a short time and heat shrinks.

  On the other hand, when there is a heat insulating material, no gap occurs until 100 seconds after the start of cooling. The state at this time is shown in FIG. 17 together with the temperature distribution. Even when there is a heat insulating material, the steel pipe expands due to the martensitic transformation, so that a gap occurs after 100 seconds. However, at this time, the temperature at the end of the tube, which is likely to be the starting point of fire cracking, has dropped to 180 ° C. and is below the martensite transformation end temperature (about 200 ° C. for the material), so that fire cracking occurs. Absent.

  From this result, it was confirmed that by using the heat insulating material, it is possible to prevent the inner lid from falling off and to prevent the cooling water from entering the inner surface and to suppress the bending and the cracking. In the examination here, the thickness of the inner lid and the heat insulating material are both 10 mm. However, if the thickness and the dimensions of the steel pipe are different, the timing and the amount of the gap are also changed. The optimum thickness of the inner lid and the thickness of the heat insulating material can be obtained by numerical calculation.

[Waterproof performance evaluation test]
A tube end lid having a configuration similar to that of the tube end lid 3 of the third embodiment was produced, and a waterproof performance evaluation test was performed using a laboratory test facility. As the target steel pipe, a carbon steel pipe of Φ356 mm × t21 mm × L2000 mm was used.

The outline of the test is shown in FIG. A pipe end lid 3 is attached to the tip side of the steel pipe P, heated and soaked to 950 ° C. in the heating furnace Q, quickly transported to the installation position of the water cooling ring R, and kept in place, and the lid attachment part is water cooled for 170 seconds. did. The amount of refrigerant supplied from the water-cooled ring R was 50 m ³ / hr. If cooling water enters at the front end of the steel pipe P to which the pipe end lid 3 is attached, the steel pipe P flows out from the rear end. In this test, it was confirmed that water leakage did not occur within the cooling time and the waterproof function of the tube end lid 3 was satisfactory.

[Shock resistance test]
The steel pipe is conveyed through the production line from the previous process and reaches the heating furnace insertion port. FIG. 19 is a diagram schematically showing the state of conveyance of the steel pipe. In the process of conveyance, after the steel pipe P is lifted by the kicker K, it rolls on the inclined rail L and stops at the stopper S. The pipe end lid 3 was attached to the pipe end of a steel pipe of Φ356 mm × t21 mm × L12000 mm, and the impact resistance performance at the time of carrying the steel pipe was confirmed with an actual carrying line. As a result of several impact tests, it was confirmed that the tube end cap 3 did not fall off. It is at this stage that the greatest impact is applied to the steel pipe in the heat treatment line, and no impact is applied in the subsequent processing.

  The embodiment of the present invention has been described above. The above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

1, 2, 3 Tube end cover 11 Inner cover 12 Heat insulation material 13 Stay (connection member)
14 outer lid 15a connecting screw 15b, 15c nut 16 screw 17 inner lid 18 taper member

Claims (6)

A pipe end lid attached to the pipe end of a steel pipe,
An inner lid disposed inside the steel pipe;
A heat insulating material disposed inside the steel pipe and at a position closer to the pipe end of the steel pipe than the inner lid;
A pipe end cover, comprising: a connection member that connects an end surface of the steel pipe and the inner lid and holds the steel pipe at a predetermined distance. The tube end cap according to claim 1,
An inner lid connected to the inner lid, the inner lid being disposed at a position closer to the pipe end of the steel pipe than the inner lid inside the steel pipe;
A tube end cover configured to move the inner lid in a direction approaching the inner lid so that the connection member extends radially outward of the steel pipe. The tube end cap according to claim 2,
A tube end lid, further comprising a taper member fixed to the connection member and having a thickness that increases in a direction approaching the inner lid. The tube end cap according to any one of claims 1 to 3,
A tube end lid further comprising an outer lid disposed so as to be adjacent to an end surface of the steel pipe. Preparing a tube;
The process of attaching the pipe end lid according to any one of claims 1 to 4 to at least one of the pipe ends of the raw pipe;
Quenching the raw pipe to which the pipe end lid is attached. It is a manufacturing method of the steel pipe according to claim 5,
A method for producing a steel pipe, wherein the inner cover has a linear expansion coefficient larger than that of the steel pipe.

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