JP2004001011A - Method for executing butt welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve welding workability and cost effectiveness by avoiding the occurrence of welding defects such as weld crack or the like under low temperature environment. <P>SOLUTION: This method for executing butt welding comprises a positioning step A for positioning each welding zone of a welding base material to a butting position, a primary pre-heating step B for preheating the welding zone to a specified temperature, a temporary welding step C for temporarily welding the welding zone, a secondary preheating step D for preheating the welding zone again to the specified temperature, a regular welding step E for regularly welding the welding zone, and a slow cooling step F for slowly cooling the welded zone after welding. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to butt welding of metal piping materials such as outdoor boiler tubes, metal plate materials, and the like, and particularly to a butt welding method for avoiding poor welding in a low-temperature environment such as a cold region.
[0002]
[Prior art]
Usually, it is considered that it is desirable to weld a carbon steel material having a tensile strength of 400 N / mm2 class used for a boiler tube or the like under a temperature environment of at least 5 ° C. This is because when welding is performed in a low temperature environment of 5 ° C. or less, rapid heating and rapid cooling of the welded portion easily cause welding defects such as cracks in the welded portion. For this reason, at present, almost no welding work for boiler tubes and the like outdoors in the cold season of 5 ° C. or less is performed.
[0003]
[Problems to be solved by the invention]
As described above, when welding a boiler tube or the like in a low-temperature environment (particularly -20 ° C to 5 ° C), the main cause of poor welding such as cracks in the welded portion is the rapid occurrence of the welding base metal. However, if hydrogen enters the molten zone during welding, the molten zone is rapidly cooled and hydrogen accumulates in the weld zone. As a result, a weld crack called hydrogen embrittlement occurs.
[0004]
The present invention has been made in view of the above problems, and a butt welding construction method capable of avoiding the occurrence of welding defects such as welding cracks in a low-temperature environment and improving the welding operation efficiency and economy. The purpose is to provide.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a butt welding method according to the present invention includes, as described in claim 1, a positioning step of positioning welded portions of a welding base material at a butt position, A primary preheating step of preheating the welded portion, a temporary welding step of temporarily welding the welded portion, a secondary preheating step of reheating the welded portion to a predetermined temperature, a main welding step of fully welding the welded portion, and welding after welding. And a gradual cooling step of gradually cooling the part.
[0006]
As described above, the primary preheating step and the secondary preheating step of preheating the welded portion before the temporary welding and the main welding are provided, and the slow cooling step of gradually cooling the welded portion after the main welding is provided. Since the welded portion is not rapidly heated and cooled during the welding below, the occurrence of welding defects such as welding cracks is avoided.
[0007]
In the butt welding method according to the present invention, as set forth in claim 2, the preheating temperature in the primary preheating step and the secondary preheating step is set in a range of 20 ° C to 100 ° C. If the preheating temperature is set in the range of 20 ° C. to 100 ° C., the energy consumption by the preheating can be minimized and the economy can be improved.
[0008]
Furthermore, in the butt welding method according to the present invention, as described in claim 3, when the welding base material is a tubular material, the temporary welding length in the temporary welding step is set to 20 mm or more, and The present invention is characterized in that two welding locations are arranged at opposing positions. By setting the temporary welding length as long as 20 mm or more in this manner, the heat input per one temporary welding portion is increased, rapid cooling after the temporary welding is prevented, and welding defects such as welding cracks are avoided. Can be.
[0009]
The butt welding method according to the present invention, as described in claim 4, maintains the temperature of the welded portion after welding at 100 ° C. or more in the slow cooling step, and maintains this state for 10 minutes or more. Features. Thus, cracks due to rapid cooling of the welded portion can be prevented, and the separation of hydrogen mixed during welding can be promoted to effectively avoid hydrogen embrittlement.
[0010]
In the butt welding method according to the present invention, the preheating of the welded portion in the primary preheating step and the secondary preheating step is performed by covering the welded portion with a preheating jacket with an electric heater, as described in claim 5. It is characterized by performing. This makes it possible to economically prevent the occurrence of welding defects such as welding cracks in a low-temperature environment with a simple configuration.
[0011]
Further, the butt welding method according to the present invention is characterized in that, as described in claim 6, the portion to be preheated by the preheating jacket is separated from the weld by about 50 mm. Thereby, preheating and welding can be advanced simultaneously, and welding efficiency is improved.
[0012]
In the butt welding method according to the present invention, as described in claim 7, the positioning of the welded portion in the positioning step is performed by a clamp-shaped positioning jig for temporarily fixing the welded portions of the opposing welding base materials. The preheating of the welding portion in the primary preheating step is performed by covering the welding portion with a preheating jacket with an electric heater, and the length of the positioning jig along the welding base metal axis direction is set by installing the preheating jacket. Set to the same size as the position inside dimension. Thereby, the positioning jig also functions as a positioning jig for the preheating jacket, and the positioning of the preheating jacket can be easily performed, thereby improving welding efficiency.
[0013]
Further, the butt welding method according to the present invention is characterized in that the gradual cooling of the welded portion in the gradual cooling step is performed by a heat retaining jacket covering the welded portion. Also in this case, it is possible to economically prevent the occurrence of welding defects such as welding cracks in a low-temperature environment with a simple configuration.
[0014]
Further, the butt welding method according to the present invention, as described in claim 9, the preheating of the weld in the primary preheating step and the secondary preheating step is performed by a preheating jacket with an electric heater covering the weld, The gradual cooling of the welded portion in the gradual cooling step is performed by covering the welded portion with the preheating jacket. As a result, the preheating jacket can be used also as a heat retaining jacket, so that the economical efficiency in equipment can be improved.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a butt welding method according to the present invention will be described with reference to the drawings.
[0016]
FIG. 1 is a flowchart showing an embodiment of a butt welding method according to the present invention. As shown here, the butt welding method according to the present invention includes a positioning step A, a primary preheating step B, a temporary welding step C, a secondary preheating step D, a main welding step E, and a slow cooling step F. And characterized in that:
[0017]
FIG. 2 is a side view showing a butt welding situation between boiler tubes (metal piping materials) as an example of butt welding. As shown here, a plurality of boiler tubes 2, 2 extending from upper and lower boiler walls 1, 1 are abutted and welded. First, in the positioning step A, the welding portions 3 (ends) of the boiler tubes 2, 2 serving as welding base materials are positioned at the butting position using the positioning jig 4.
[0018]
The welding portion 3 of the boiler tubes 2 and 2 has a chamfer (groove surface) 5 formed in advance to form a groove shape, and the welding portions 3 have a predetermined groove gap (4.0 mm to 4.5 mm). Then, they are fixed by the positioning jig 4 so that they face each other and their cores coincide with each other. The positioning jig 4 is provided with, for example, two clamps 6 and 6 as shown in the cross section in FIG. 3, and the four ends of the boiler tubes 2 and 2 are coaxial by tightening four bolts 7. Fixed.
[0019]
Subsequent to the positioning step A, a primary preheating step B for preheating the welded portion 3 to a predetermined temperature is executed. In the primary preheating step B, the welding portion 3 is first heated by a gas burner or the like in order to remove moisture or the like, and then while the remaining heat remains, the preheating jackets 10, 10 with an electric heater are used to raise and lower the welding portion 3. To preheat the weld 3.
[0020]
As shown in FIG. 4, the preheating jacket 10 is provided with an electric heater 13 on the inner periphery of a flexible tubular insulating pad 12 having a cut 11, for example, and a fastening band with a hook-and-loop fastener 14 on the outer periphery of the insulating pad 12. Reference numeral 15 denotes a simple configuration wound. The inner diameter of the preheating jacket 10 is set to a diameter at which the electric heater 13 comes into close contact with the outer diameter of the boiler tubes 2 and 2. Then, a lead wire 16 extending from the electric heater 13 is connected to a power supply.
[0021]
The portion to be preheated by the preheating jacket 10 is positioned at a distance of about 50 mm from the weld 3. Here, the length H (see FIG. 2) of the positioning jig 4 along the boiler tubes 2 and the two axial directions is set to the same size as the inner size of the installation position of the preheating jacket 10. That is, H is set to 100 mm, which is the distance between the inner surfaces of the upper and lower preheating jackets 10 and 10 that are fixed at a distance of 50 mm from the welded portion 3.
[0022]
For this reason, it is possible to accurately position the preheating jackets 10, 10 at a distance of 50 mm from the welded portion 3 only by bringing the upper and lower preheating jackets 10, 10 into contact with the positioning jig 4. Positioning can be facilitated and welding work efficiency can be improved.
[0023]
As described above, if the preheating is performed by covering the welded portion 3 with the preheating jacket 10 having the electric heater 13, the preheating operation in a low-temperature environment can be performed economically with a simple configuration.
[0024]
The preheating temperature by the preheating jacket 10 is set in the range of 20C to 100C. This makes it possible to minimize the energy consumption due to the preheating and to simplify the configuration of the preheating jacket 10 to further improve the economic efficiency.
[0025]
Subsequent to the primary preheating step B, a temporary welding step C for temporarily welding the welded portion 3 of the boiler tubes 2 and 2 is executed. At that time, the preheating jackets 10, 10 may be left wound around the boiler tubes 2, 2. Since the preheating jackets 10 and 10 are separated from the welding portion 3 by about 50 mm, the preliminary welding can be simultaneously performed while performing preheating by the preheating jackets 10 and 10, and the welding operation efficiency is good.
[0026]
When the welding base material (boiler tubes 2 and 2) is a tubular material as in this embodiment, as shown in FIGS. 5A and 5B, the welding length W of the temporary welding portion 20 is set to 20 mm or more. And temporary welding is performed by arranging the temporary welding portion 20 at two locations at opposing positions.
[0027]
In such a case, the temporary welding length is longer than when the temporary welding portions 21 having a temporary welding length of about 5 mm are provided in about four places as in the conventional example shown in FIGS. 6A and 6B. The amount of heat input per weld is increased, and rapid cooling after temporary welding can be prevented to prevent welding defects such as welding cracks.
[0028]
When the temporary welding is completed, the positioning jig 4 is removed, and a secondary preheating step D for preheating the welded portion 3 again to a predetermined temperature is executed. Here, as shown in FIG. 7, the preheating jackets 10, 10 used in the primary preheating step B are shifted to the position of the welding portion 3 to preheat the welding portion 3. The preheating temperature at this time is also set in the range of 20 ° C. to 100 ° C. as in the primary preheating step B.
[0029]
When the preheating in the secondary preheating step D is completed, the process proceeds to the main welding step E. As shown in FIG. 8, in the main welding step E, the preheating jackets 10, 10 covering the welding part 3 in the secondary preheating step D are shifted up and down to expose the welding part 3, and are welded by TIG welding, MIG welding, or the like. The part 3 is entirely welded. At this time, the heating by the preheating jackets 10, 10 may be continued.
[0030]
When the main welding step E is completed, the process immediately proceeds to the slow cooling step F for gradually cooling the welded portion 3. In the slow cooling step F, as shown in FIG. 9, the welded portion 3 immediately after welding is covered by the heat retaining jacket 24. As shown in FIG. 10, the heat retaining jacket 24 has a configuration in which a fastening band 28 with a hook-and-loop fastener 27 is wound around the outer periphery of a flexible tubular heat retaining pad 26 having a cut 25. The heat insulation performance of the heat insulation jacket 24 is such that the temperature of the welded portion 3 is maintained at 100 ° C. or higher, and this state can be maintained for 10 minutes or more.
[0031]
In this butt welding method, a primary preheating step B and a secondary preheating step D for preheating the welded portion 3 are provided before the temporary welding step C and the main welding step E, respectively. Since the step F is provided, the welding portion 3 is not rapidly heated and cooled even during welding in a low temperature environment, thereby effectively avoiding occurrence of welding defects such as welding cracks. Can be.
[0032]
In the slow cooling step F, since the welded portion 3 after welding is maintained at a temperature of 100 ° C. or more for 10 minutes or more, cracks due to rapid cooling of the welded portion 3 are reliably prevented, and desorption of hydrogen mixed during welding is performed. And the hydrogen embrittlement of the welded portion 3 can be effectively avoided.
[0033]
In addition, since the preheating of the welded portion 3 in the primary preheating step B and the secondary preheating step D is performed by the preheating jacket 10 and the gradual cooling of the welded portion 3 in the gradual cooling step F is performed by the heat retaining jacket 24, the simple configuration is economical. Preheating and slow cooling work can be performed to prevent the occurrence of welding defects such as welding cracks in a low temperature environment.
[0034]
By the way, the preheating jacket 10 may be used in a state where the power is turned off or in an energized state instead of the heat retaining jacket 24. In this case, the preheating jacket 10 can also be used as the heat retaining jacket 24, so that the economical efficiency in equipment can be improved.
[0035]
Further, in this embodiment, the preheating jacket 10 is of an electric type, but is not limited to the electric type, and the preheating jacket 10 may be configured to generate heat by combustion, a chemical reaction, hot water, or the like.
[0036]
【The invention's effect】
As described above, according to the butt welding method according to the present invention, during welding in a low-temperature environment, the welding portion is prevented from being rapidly heated and cooled, and welding defects such as welding cracks in the welding portion are prevented. Can be effectively avoided.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an embodiment of a butt welding method according to the present invention.
FIG. 2 is a side view showing a butt welding situation between boiler tubes as an example of butt welding.
FIG. 3 is a transverse sectional view taken along the line III-III of FIG. 2;
FIG. 4 is a perspective view of a preheating jacket.
5A is a side view showing a temporary welded portion of the present invention, and FIG. 5B is a cross-sectional view taken along line Vb-Vb in FIG.
FIG. 6A is a side view showing a temporary welding portion according to the related art, and FIG. 6B is a cross-sectional view taken along a line VIb-VIb in FIG.
FIG. 7 is a side view showing a pattern of a secondary preheating step.
FIG. 8 is a side view showing the pattern of the main welding step.
FIG. 9 is a side view showing a pattern of a slow cooling step.
FIG. 10 is a perspective view of a thermal insulation jacket.
[Explanation of symbols]
2 Boiler tube 3 serving as welding base material 3 Welding part 4 Positioning jig 6 Clamp 10 Preheating jacket 13 Electric heater 20 Temporary welding part 24 Heat insulation jacket A Positioning step B Primary preheating step C Temporary welding step D Secondary preheating step E Main welding step F Slow cooling step H Length of positioning jig along the axis of welding base metal W Weld length of temporary weld

Claims (9)

A positioning step of positioning the welded portions of the welding base metal at abutting positions; a primary preheating step of preheating the welded portion to a predetermined temperature; a temporary welding step of temporarily welding the welded portion; A butt welding method, comprising: a secondary preheating step of preheating again, a main welding step of main welding the welded portion, and a slow cooling step of gradually cooling the welded portion after welding. The butt welding method according to claim 1, wherein a preheating temperature in the primary preheating step and the secondary preheating step is set in a range of 20C to 100C. The said welding base material is a tubular material, The temporary welding length in the said temporary welding step is set to 20 mm or more, and it arrange | positions at a facing position as two temporary welding places. Butt welding construction method. The butt welding method according to claim 1, wherein in the annealing step, the temperature of the welded portion after welding is maintained at 100 ° C or higher, and this state is maintained for 10 minutes or longer. The butt welding method according to claim 1, wherein the preheating of the welded portion in the primary preheating step and the secondary preheating step is performed by covering the welded portion with a preheating jacket provided with an electric heater. The butt welding method according to claim 5, wherein a portion to be preheated by the preheating jacket is separated from the weld by about 50 mm. The positioning of the welded portion in the positioning step is performed by a clamp-shaped positioning jig for temporarily fixing the welded portions of the opposing welding base materials, and the preheating of the welded portion in the primary preheating step is performed by a preheating jacket with an electric heater. 2. The butt welding method according to claim 1, wherein the butt welding is performed by covering a welded portion, and a length of the positioning jig along the axial direction of the welding base metal is set to be the same as an inner dimension of an installation position of the preheating jacket. The butt welding method according to claim 1, wherein the gradual cooling of the welded portion in the gradual cooling step is performed by a heat retaining jacket covering the welded portion. Preheating the welded portion in the primary preheating step and the secondary preheating step is performed by a preheating jacket with an electric heater covering the welded portion, and gradually cooling the welded portion in the slow cooling step is to cover the welded portion with the preheating jacket. The butt welding method according to claim 1, wherein the butt welding is performed.

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