JP6859886B2 - Pipe end lid and method of manufacturing steel pipe using it - Google Patents

Description

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

Heat treatment of steel materials has been widely used for a long time for the purpose of imparting desired properties and performance to mechanical parts and steel products, and its essence is the adjustment of metallographic structure. Of these, "quenching" accounts for most of the heat treatment. At room temperature, the material to be heat-treated, which usually has a ferrite pearlite structure, is _{heated to a high temperature of 3} points (austenite transformation end temperature) or higher to austenite, and then rapidly cooled to martensite. It forms a tissue. The martensite structure has the highest strength of all the structures of metallic materials and is a very important structure form used in all industrial fields.

The most important point to keep in mind when quenching a tubular body is uniform cooling in the circumferential direction. If the cooling in the circumferential direction becomes non-uniform, the steel pipe during cooling will bend. This bending becomes larger as the steel pipe becomes longer, which causes unfavorable situations such as troubles during line transportation and addition of a bending straightening process. In quenching of steel pipes, it is preferable to water-cool the outer surface while moving and transporting the steel pipes and passing them through a cooling zone. Uniformity of outer surface water cooling can be achieved relatively easily by means such as evenly arranging cooling nozzles on the annular main pipe, but inner surface water cooling has many technical problems and complicates the equipment configuration. That's the reason.

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

Japanese Patent Application Laid-Open No. 58-27331 provides a cooling water blocking insertion cylinder in a cooling device that injects and cools a tubular object to be conveyed to prevent the refrigerant from entering the pipe from the rear end of the pipe. It is stated that it should be done. Japanese Patent No. 5252131 describes that the end of a pipe is air-cooled in a quenching method in which a steel pipe is water-cooled from the outer surface and then hardened. Japanese Patent Laying-Open No. 2012-172173 describes a method of quenching a steel pipe by injecting hardened water at an angle with respect to the transport direction on the outer peripheral surface of the steel pipe while transporting 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 transport direction. Japanese Patent Application Laid-Open No. 61-77192 describes a device for continuously and automatically welding pipe end lids to a plurality of steel pipes.

Japanese Unexamined Patent Publication No. 58-27331 Japanese Patent No. 5252131 Japanese Unexamined Patent Publication No. 2012-172173 Jikkai Sho 61-77192

As a means for suppressing the infiltration of the refrigerant into the inside of the steel pipe, it is convenient and reliable to attach a lid to the end of the pipe. To attach the lid, it is common to weld the lid to the end of the steel pipe all around or by spot welding, but the attachment process before the treatment and the cutting off process of the pipe end including the lid after the treatment are required. Production efficiency and yield are reduced. Further, in the case of mounting by simple insertion, the lid may fall off during the heat treatment.

An object of the present invention is to provide a pipe end lid which is easy to attach and can prevent falling off during heat treatment, and to provide a method for manufacturing a steel pipe using the pipe end lid.

The pipe end lid according to one embodiment of the present invention is a pipe end lid attached to the pipe end of a steel pipe, and has an inner lid arranged inside the steel pipe and an inner lid inside the steel pipe, which is more than the inner lid. A heat insulating material arranged at a position close to the pipe end of the steel pipe and a connecting member for connecting the end face of the steel pipe and the inner lid and holding the inner lid at a certain distance are provided.

The method for 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 base to which the pipe end lid is attached. It includes a step of quenching the pipe.

According to the present invention, a pipe end lid that is easy to install and can be prevented from falling off during heat treatment can be obtained. 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 pipe end lid 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 according to the first embodiment is attached to a steel pipe. FIG. 3 is a flow chart 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 a heat treatment line. FIG. 5 is a temperature-elongation diagram of a general steel material that undergoes phase transformation. FIG. 6 is an exploded perspective view showing the configuration of the pipe end lid 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 the steel pipe. FIG. 8 is an exploded perspective view showing the configuration of the pipe 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 the steel pipe. FIG. 10 is a graph showing the relationship between the heat transfer coefficient of the inner surface of the steel pipe and the residual tensile stress of the inner surface of the steel pipe. FIG. 11 is a diagram showing a state in which the refrigerant is retained at the bottom of the steel pipe. FIG. 12 shows the stress distribution of the steel pipe when the refrigerant is retained at the bottom. FIG. 13 is a model used in the numerical calculation. FIG. 14 is a graph showing the time change of the gap amount. FIG. 15 is a graph showing the time change of the temperature of the pipe end and the lid. FIG. 16 is a diagram showing a state 25 seconds after the start of cooling when there is no heat insulating material. FIG. 17 is a diagram showing a state 100 seconds after the start of cooling when 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 a state of transportation of steel pipes.

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

[First Embodiment]
FIG. 1 is an exploded perspective view showing the configuration of the pipe 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 inside the steel pipe P and located closer to the pipe end of the steel pipe P than the inner lid 11, and the steel pipe P. It is provided with a stay 13 which is a connecting member for connecting the end face of the steel pipe and the inner lid 11. The pipe end lid 1 further includes an outer lid 14 arranged so as to be adjacent to the end surface of the steel pipe P, a connecting screw 15a for fixing the outer lid 14, and the like.

The inner lid 11 has a disk shape having an outer diameter 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 made of a material having a coefficient of linear expansion 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, mainly from the viewpoint of workability. The thickness of the inner lid 11 is preferably 20 mm or less, more preferably 10 mm or less.

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

In this embodiment, the heat insulating material 12 is fixed to the inner lid 11. However, the heat insulating material 12 may be fixed to, for example, the stay 13 or the outer lid 14. The heat insulating material 12 may be arranged at a position closer to the pipe end of the steel pipe P than the inner lid 11.

The stay 13 connects the end face 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 particularly limited, and may be, for example, carbon steel or stainless steel.

More specifically, each of the stays 13 has a first portion 13a extending in a direction substantially perpendicular to the inner lid 11, and a second portion 13a continuous with one end of the first portion 13a and extending in a direction substantially parallel to the inner lid 11. Includes portion 13b. Each of the stays 13 regulates the distance between the end face of the steel pipe P and the inner lid 11 by contacting the second portion 13b with the end face 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 this embodiment, as shown in FIG. 2, each of the stays 13 is fixed to the inner lid 11 by screws 16. However, the method of fixing 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. The stay 13 and the steel pipe P may be fixed with, for example, a heat-resistant adhesive.

The stay 13 of the present 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 one that connects the end face of the steel pipe P and the inner lid 11 and holds them at a constant distance.

The outer lid 14 has a disk shape having an outer diameter slightly larger than the inner diameter of the steel pipe P so as to close the opening of the steel pipe P. The outer lid 14 is preferably formed of a material having a small coefficient of linear thermal expansion α in order to suppress thermal deformation as much as possible. 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, more preferably 10 mm or less.

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

[Manufacturing method of steel pipe]
Next, a method of manufacturing a steel pipe using the pipe end lid 1 will be described. Hereinafter, in the description of the method for manufacturing a steel pipe, the steel pipe to be heat-treated is referred to as a "bare pipe". In addition, the term "steel pipe" is used to mean a steel pipe manufactured by heat treatment to distinguish it from "bare pipe".

FIG. 3 is a flow chart showing a method for manufacturing a steel pipe according to an embodiment of the present invention. The method for 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 attaching the pipe end lid 1. It is provided with a step (step S3) of quenching the obtained raw pipe.

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

The pipe end lid 1 is attached to at least one of the pipe ends of the raw pipe (step S2). The pipe end lid 1 is preferably attached to both the pipe ends of the raw pipe, but depending on the angle at which the refrigerant is sprayed or the like, it is possible to suppress the infiltration of the refrigerant by attaching it to only one of the front and the rear.

The bare pipe to which the pipe end lid 1 is attached is hardened (step S3). Specifically, the raw tube to which the tube end lid 1 is attached is _{heated to a temperature of 3} points or more to perform austenitic transformation, and then cooled to a temperature below the martensitic transformation end temperature to undergo martensitic transformation. At this time, if the cooling rate is too low, 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 burning cracks will occur. Therefore, it is necessary to appropriately control the cooling rate. Preferably, the cooling rate is increased as much as possible up to the martensitic transformation start temperature, and the cooling rate is decreased as much as possible from the martensitic transformation start temperature to the cooling end temperature (maltensite transformation end temperature or room temperature).

FIG. 4 is a block diagram showing a functional configuration of the 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 a dipping tank 23. A transport roller 40 (convey device) is arranged between the devices.

The transfer roller 40 sequentially conveys the raw pipe from the heating device 21 to the cooling device 22, from the cooling device 22 to the immersion tank 23, and from the immersion tank 23 to the tempering device 30. The raw pipe is heated by the heating device 21 and cooled by the cooling device 22 and / or the immersion tank 23. The raw tube is then reheated by the tempering device 30.

According to the configuration of the heat treatment line 100 _{, the raw pipe can be quenched by heating the raw pipe to three} or more points of Ac by the heating device 21 and then cooling the raw pipe by the cooling device 22 and / or the immersion tank 23. it can. Further, the raw tube can be tempered by heating the raw tube to a predetermined temperature by the tempering device 30. The tempered raw tube is cooled by, for example, a cooling device (not shown) and then transported to a flaw detector or the like.

According to the configuration of the heat treatment line 100, the heat treatment of quenching and tempering can be continuously performed on the raw pipe. However, quenching and tempering do not have to be carried out continuously. In this case, the heat treatment line 100 does not have to include the tempering device 30.

Although the detailed configuration is not shown, 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 the refrigerant can be blown from each of the plurality of nozzles to the outer surface of the raw pipe passing through the inside of the cooling ring. The amount of the refrigerant is configured to be controllable for each cooling ring, and the raw pipe can be cooled at an optimum speed by adjusting the amount of the refrigerant for each cooling ring and the transport 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 pipe. When the raw pipe to be heat-treated is low-medium carbon steel (C content less than 0.30%) with low crack sensitivity, the raw pipe is cooled using only the immersion tank 23 without using the cooling device 22. You can also. In this case, the processing speed can be increased. On the other hand, even if the raw pipe to be heat-treated is a raw pipe that is highly susceptible to shrinkage, if the steel pipe is sufficiently cooled by the cooling device 22, bending or shrinkage may occur even if the steel pipe is immersed in the immersion tank 23. Absent.

That is, according to the configuration of the quenching device 20, cooling by the cooling device 22 and cooling by the immersion tank 23 can be selectively performed according to the properties of the target raw pipe. On the other hand, the heat treatment line 100 does not have to include the immersion tank 23 when only the raw pipe having high crack sensitivity is targeted.

[Effect of tube end lid 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 undergoes phase transformation. As shown in FIG. 5, this steel _{thermally expands from room temperature to one} point of Ac with an increase in temperature, but when _{it exceeds one} point of Ac, it shrinks by austenite transformation (austenite transformation contraction). After that, it expands again with the coefficient of linear expansion of austenite and reaches the maximum temperature (Tmax). In the cooling process, it is supercooled in the state of austenite until the martensitic transformation starts, so it contracts with the linear expansion coefficient of austenite and starts expanding when the martensitic transformation start temperature Ms (around 300 ° C for the relevant material amount) is reached. (Α transformation expansion).

Even in the heat treatment of steel pipes, expansion and contraction as shown in FIG. 5 occur due to heating and cooling. 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 (tension rod) that is brought into close contact with the inner surface of the steel pipe by using the reaction force of the screw, even if the lid 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, resulting in loosening.

The pipe end lid 1 (FIG. 2) of the present embodiment is arranged at a position inside the steel pipe P and closer to the pipe end of the steel pipe P than the inner lid 11 with the inner lid 11 arranged inside the steel pipe P. It is provided with a heat insulating material 12. According to this configuration, in the cooling process, the temperature drop of the inner lid 11 is slower than the temperature drop of the steel pipe P due to the heat insulating material 12. Therefore, the contraction of the inner lid 11 is slower than the contraction of the steel pipe P, and the inner lid 11 is tightened by the steel pipe P, which is similar to the so-called “shrink fit” effect. When the steel pipe P reaches the martensitic transformation start temperature, it expands due to the 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, the infiltration of the refrigerant can be suppressed 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 effect cannot be sufficiently obtained. 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 made of a material having a coefficient of linear expansion α larger than that of the steel pipe P. In this case, even in the heating process, the thermal expansion of the inner lid 11 is larger than the thermal expansion of the steel pipe P, so that the inner lid 11 can be kept in close contact with the inner surface of the steel pipe P.

The outer lid 14 suppresses the direct contact of the refrigerant with the inner lid 11 and the heat insulating material 12. Since the outer lid 14 comes into direct contact with the refrigerant, it may be significantly thermally deformed. However, even if the refrigerant invades through the gap created by the deformation, the infiltration into the inside is further suppressed by the inner lid 11. Further, if the heat insulating material 12 is a porous body or a fiber, a small amount of refrigerant can be absorbed. The pipe end lid 1 may not be provided with the outer lid 14 depending on the angle at which the refrigerant is sprayed.

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

The method for manufacturing the pipe end lid 1 and the steel pipe using the pipe end lid 1 according to the primary embodiment of the present invention has been described above. According to this embodiment, a pipe end lid that is easy to install and can be prevented from falling off during heat treatment can be obtained. Further, by manufacturing a steel pipe using this pipe end lid, bending of the steel pipe can be suppressed.

[Second Embodiment]
FIG. 6 is an exploded perspective view showing the configuration of the pipe 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 configuration of the pipe end lid 1, the pipe end lid 2 is arranged at a position inside the steel pipe P and closer to the pipe end of the steel pipe P than the inner lid 11, and the inner lid 17 is connected to the inner lid 11. Is further equipped.

The inner lid 17 has a disk shape having an outer diameter slightly smaller than the inner diameter of the steel pipe P so that the inner lid 17 can be arranged inside the steel pipe P. The inner lid 17 is preferably made of a material having a coefficient of linear expansion α larger than that of the steel pipe P. The material of the inner lid 17 is, for example, stainless steel. 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, more preferably 10 mm or less.

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

The pipe end lid 2 is further configured so that the stay 13 expands radially outward of the steel pipe P by moving the inner lid 17 toward the inner lid 11. 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 facing the first portion 13a. It is configured in.

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

The inner lid 17 also plays a role of preventing the refrigerant that has entered through the gap between the steel pipe P and the outer lid 14 from further entering the inside.

The inner lid 17 is preferably made of a material having a coefficient of linear expansion α larger than that of the steel pipe P. In this case, even in the heating process, the thermal expansion of the inner lid 17 is larger than the thermal expansion of the steel pipe P, so that 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 arranged between the heat insulating material 12 and the outer lid 14. However, the inner lid 17 may be arranged between the inner lid 11 and the heat insulating material 12. That is, the pipe end lid 2 may have a configuration in which the heat insulating material 12 is fixed after the inner lid 17 is attached.

Also in this embodiment, the pipe end lid 2 may not include the outer lid 14 depending on the angle at which the refrigerant is sprayed and the like. Further, 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.

[Third Embodiment]
FIG. 8 is an exploded perspective view showing the configuration of the pipe 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 pipe end lid 2, the pipe end lid 3 is further provided with a tapered member 18 which is fixed to each of the stays 13 and whose thickness increases toward the inner lid 11.

More specifically, the tapered member 18 of the present embodiment has the shape of a triangular prism having a vertical triangular cross section, and the surface opposite to the tapered surface is welded to the stay 13. The specific shape of the tapered member 18 is not limited to that shown in FIGS. 8 and 9. The tapered member may have, for example, a curved surface on which the taper is provided.

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

Also in this embodiment, the pipe end lid 3 may not include the outer lid 14 depending on the angle at which the refrigerant is sprayed and the like. Further, 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.

Hereinafter, the present invention will be described in more detail based on Examples. It should be noted that this example does not limit the present invention.

[Investigation of the effect of internal cooling]
The effect of cooling the inner surface of the steel pipe was investigated by numerical analysis by 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, when the heat transfer coefficient of the inner surface is 50% of the heat transfer coefficient of the outer surface, the highest tensile stress is generated. When the heat transfer coefficient of the inner surface is made equal to that of the outer surface (100%), the stress becomes compressed, which is a result under the condition that the inner surface of the steel pipe is uniformly cooled.

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

[Examination of welding lid]
Next, the effect of welding the lid to the end of the pipe was also investigated by numerical analysis. In the numerical analysis, the welding joint was simulated by binding and restraining the node near the outer surface of the steel pipe and the node of the lid at the same position. The generated stress in this case was 369 MPa. On the other hand, when the coupling restraint 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 the fragile weld metal is the starting point for cracking.

[Examination of the effect of heat insulating material]
Assuming the configuration of the pipe end lid (excluding the outer surface lid 14) according to the pipe end lid 1 of the first embodiment, numerical analysis by FEM is performed, and it occurs between the steel pipe and the pipe end lid in the cooling process. The size of the gap was calculated. FIG. 13 shows a model used in the numerical calculation. For the analysis, a two-dimensional target 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 the initial temperature of 900 ° C. The conditions are as follows. As a comparative example, the calculation was carried out when the heat insulating material was not 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: Φ366 mm x t10 mm (same material as steel pipe)
-Insulation material: Φ366mm x t10mm (ceramic heat-resistant insulation material)
-Initial temperature: 900 ° C (heating furnace set temperature)
・ Water cooling time: Water cooling of steel pipe outer surface and heat insulating material outer surface ・ Cooling heat transfer coefficient: Identified from measured values

FIG. 14 is a graph showing the time change of the gap amount. FIG. 15 is a graph showing the time change of the temperature of the pipe end and the lid. If there is no heat insulating material, a gap starts to be generated at the same time as the start of cooling, and the opening is 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 thin inner lid cools in a short time and shrinks heat.

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

From this result, it was confirmed that the use of the heat insulating material can prevent the inner lid from falling off and prevent the cooling water from entering the inner surface to suppress bending and burning cracks. In this study, the thickness of the inner lid and the heat insulating material were both set to 10 mm, but if these thicknesses and the dimensions of the steel pipe are different, the timing at which gaps are generated and the amount of gaps also change. The optimum inner lid thickness and heat insulating material thickness can be obtained by numerical calculation.

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

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

[Impact resistance test]
The steel pipe is conveyed from the previous process on the production line and reaches the heating furnace insertion port. FIG. 19 is a diagram schematically showing a state of transportation of steel pipes. In the process of transportation, the steel pipe P is lifted by the kicker K, then rolls on the inclined rail L, and is stopped by the stopper S. A pipe end lid 3 was attached to the pipe end of a steel pipe having a diameter of 356 mm × t21 mm × L12000 mm, and the impact resistance performance during steel pipe transportation was confirmed on an actual transfer line. As a result of several impact tests, it was confirmed that the tube end lid 3 did not fall off. It is at this stage that the largest impact is applied to the steel pipe in the heat treatment line, and no impact is applied in the subsequent processing process.

The embodiments of the present invention have been described above. The above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

1,2,3 Pipe end lid 11 Inner lid 12 Insulation material 13 Stay (connecting member)
14 Outer lid 15a Connecting screw 15b, 15c Nut 16 Screw 17 Inner lid 18 Taper member

Claims (6)

A pipe end lid that is attached to at least one of the pipe ends of the steel pipe when quenching the steel pipe.
An inner lid arranged inside the steel pipe and
A heat insulating material arranged inside the steel pipe at a position closer to the pipe end of the steel pipe than the inner lid.
E Bei a connecting member for holding a constant distance by connecting the inner lid with the end face of the steel tube,
The material of the inner lid is stainless steel.
The lower limit of the outer diameter of the inner lid is 99% of the inner diameter of the steel pipe . The pipe end lid according to claim 1.
An inner lid arranged inside the steel pipe and closer to the pipe end of the steel pipe than the inner lid and connected to the inner lid is further provided.
A pipe end lid configured such that the connecting member expands radially outward of the steel pipe by moving the inner lid in a direction approaching the inner lid. The pipe end lid according to claim 2.
A pipe end lid further comprising a tapered member that is fixed to the connecting member and increases in thickness toward the inner lid. The pipe end lid according to any one of claims 1 to 3.
A pipe end lid further comprising an outer lid arranged adjacent to the end face of the steel pipe. The process of preparing the raw pipe and
The step 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.
A method for manufacturing a steel pipe, which comprises a step of quenching a raw pipe to which the pipe end lid is attached. The method for manufacturing a steel pipe according to claim 5.
A method for manufacturing a steel pipe, wherein the coefficient of linear expansion of the inner lid is larger than the coefficient of linear expansion of the steel pipe.

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