JP2020082147A - Pipe material welding method - Google Patents

Abstract

To provide a pipe material welding method that can improve creep strength of a weld zone while maintaining a mounting dimension of a branch pipe with good accuracy.SOLUTION: A main pipe and a branch pipe made of high chrome steel are subjected to normalizing processing at temperatures of 1040°C or more (step S1), then executed beveling of the main pipe and the branch pipe (step S2), and while subjecting the main pipe and the branch pipe to preheat treatment at temperatures of 300°C or more (step S3), the main pipe and the branch pipe are welded (step S4). After welded, the main pipe and the branch pipe are conveyed to a heat treatment furnace (step S5) while keeping the main pipe and the branch pipe at temperatures of 200°C or more, and the main pipe and the branch pipe are annealed at temperatures of 730-780°C in the heat treatment furnace (step S6).SELECTED DRAWING: Figure 3

Description

The present invention relates to a welding method of a pipe material in which a large number of branch pipes are welded and joined to a mother pipe, such as a pipe side of a heat exchanger in a boiler apparatus, and in particular, a pipe material made of high chromium steel having high high temperature strength is used. Regarding the welding method.

Generally, in a boiler system, a pipe side and a manifold are housed in a penthouse provided above the furnace ceiling wall, and a heat exchanger (superheater or resuperheater) is configured in the furnace below the ceiling. It is configured to suspend the heat transfer tubes.

In recent years, especially in large-capacity power generation boiler devices, steam conditions are becoming higher in temperature and pressure in order to improve power generation efficiency, and along with this, high-temperature high-strength high-chromium steel is used as heat transfer tubes and pipe materials. Has been done. High-chromium steel is a ferritic steel material in which the content of chromium in the steel material is 9 to 12% by weight, and by performing normalizing at about 1050°C and tempering treatment at about 780°C, a tempered martensite structure or High temperature strength can be enhanced as a tempered bainite structure.

In order to construct a pipe stack using high chromium steel, it is necessary to weld a large number of heat transfer pipes as branch pipes to the mother pipe. However, in high-chromium steel, the metal structure of the base material changes due to heat during welding, so a heat-affected zone with low creep strength is formed, and this heat-affected zone becomes a weak point of the welded zone.

As a conventional technique for suppressing such a decrease in creep strength of a heat-affected zone, as disclosed in Patent Document 1, a mother pipe and a short pipe made of high chromium steel are welded with a welding material having the same composition as that of the high chromium steel. After welding using, normalize and temper the high chromium steel, and then weld the branch pipe of ferritic or austenitic heat resistant steel to the tip of the short pipe, and normalize the welded part. Welding methods are known in which the tempering and tempering processes are not performed.

In the method for welding a pipe material described in Patent Document 1, a short pipe made of high chromium steel is welded to a mother pipe by using a welding material having the same composition as that of high chromium steel, and then 730 to 730 after normalizing at 1040°C or higher. By performing heat treatment for tempering at 780° C., the metal structure of the heat-affected zone is made equal to that of the base material and the creep strength is improved. Further, since the normalizing and tempering processes are not performed on the welded portion of the short pipe and the branch pipe, it is not possible to recover the strength reduction of the welded portion, but there is a possibility that an excessive bending load acts. Since there is a welded portion between the short pipe and the mother pipe, the reduction in strength at the welded portion between the short pipe and the branch pipe is not a problem.

Japanese Patent No. 4015780

In the technique described in Patent Document 1, after welding a mother pipe made of high chromium steel and a short pipe, normalizing and tempering treatments are performed to improve creep strength, and then a branch pipe is provided at the tip of the short pipe. Since the welding is performed, a short pipe that connects the mother pipe and the branch pipe is required, and there is a problem that the entire working process including the welding process of the short pipe and the branch pipe becomes complicated.

Therefore, by omitting the short pipe, a branch pipe made of high-chromium steel was directly welded to the mother pipe, and after the welding, normalizing at 1040° C. or more and then performing heat treatment of tempering at 730 to 780° C., the welding deteriorated. It is considered to recover the creep strength. However, in the structure in which a large number of branch pipes are welded to the mother pipe, the strength of the high chromium steel at the normalizing temperature (1040°C or higher) is low, so the branch pipes bend due to their own weight, and the mounting dimensions of the branch pipes are small. The problem of going crazy arises.

The present invention has been made in view of the circumstances of the prior art as described above, and an object thereof is to provide a welding method of a pipe material capable of improving the creep strength of a welded portion while maintaining the installation dimension of the branch pipe with high accuracy. To do.

In order to achieve the above object, a typical method of welding a pipe material according to the present invention is to perform normalizing only a mother pipe and a branch pipe made of high-chromium steel at a temperature of 1040° C. or higher, and then to form the mother pipe. The branch pipe is preheated at a temperature of 300° C. or higher, welded between them, and then subjected to cold cracking prevention treatment, and then the mother pipe and the branch pipe are heated at a temperature of 730 to 780° C. Characterized by tempering.

According to the method for welding a pipe material of the present invention, it is possible to improve the creep strength of the welded portion while accurately maintaining the attachment dimension of the branch pipe. Problems, configurations and effects other than those described above will be clarified by the description of the embodiments described below.

It is a whole block diagram of a boiler device. It is an explanatory view showing a welding structure of a mother pipe and a branch pipe to which the present invention is applied. It is explanatory drawing which shows the work procedure of the welding method which concerns on 1st Embodiment. It is explanatory drawing which shows the relationship between time and temperature in each process of 1st Embodiment. It is explanatory drawing which shows the work procedure of the welding method which concerns on 2nd Embodiment. It is explanatory drawing which shows the relationship between time and temperature in each process of 2nd Embodiment. It is explanatory drawing which shows the work procedure of the welding method which concerns on 3rd Embodiment. It is explanatory drawing which shows the relationship between time and temperature in each process of 3rd Embodiment. It is explanatory drawing which shows the work procedure of the welding method which concerns on 4th Embodiment. It is explanatory drawing which shows the relationship between time and temperature in each process of 4th Embodiment. It is explanatory drawing which shows the welding structure of the mother pipe and branch pipe to which 4th Embodiment is applied.

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 1 is an overall configuration diagram of a boiler apparatus. The boiler apparatus includes a furnace 1 for burning fuel, a combustion gas passage 2 which is a passage for combustion gas generated in the furnace 1, the furnace 1 and the combustion gas passage. 2 and the penthouse 3 provided on the ceiling part. In the combustion gas passage 2 connected to the upper part of the furnace 1, a primary superheater 4, a secondary superheater 5, a tertiary superheater 6, and a quaternary superheater are provided as heat exchangers for recovering heat of the combustion gas. A reactor 7, a primary reheater 8, a secondary reheater 9, and a economizer (not shown) are provided, and between the combustion gas generated in the furnace 1 and the boiler feed water flowing through the heat exchanger. Heat exchange takes place. The boiler feedwater supplied from the feedwater pump to the heat exchanger is preheated by the economizer and then heated while being supplied to the water pipe of the furnace wall to become saturated steam.

The superheated steam heated in the furnace 1 is introduced to the inlet side of the primary superheater 4, then superheated to some extent in the primary superheater 4, and then introduced into the secondary superheater 5. The superheated steam introduced into the secondary superheater 5 is further superheated in the secondary superheater 5 and the tertiary superheater 6 and introduced into the final quaternary superheater 7, and is heated to a predetermined temperature in the quaternary superheater 7. After that, it is discharged from the outlet side of the fourth superheater 7 and supplied to a high pressure turbine (not shown). Then, the high-pressure turbine is rotationally driven by the superheated steam that has exited the fourth superheater 7, and the steam that has worked in the high-pressure turbine is introduced to the inlet side of the primary reheater 8. The steam introduced into the primary reheater 8 from the high-pressure turbine is superheated in the primary reheater 8 and then introduced into the secondary reheater 9 and is heated to a predetermined temperature in the secondary reheater 9. , Is discharged from the outlet side of the secondary reheater 9 and supplied to a low pressure turbine (not shown).

In the thus constructed boiler apparatus, the ceiling portion 10 of the furnace 1 and the combustion gas passage 2 is manufactured by alternately connecting a plurality of heat transfer tubes and the heat transfer tubes. Then, in the penthouse 3 provided at the upper part of the ceiling part 10, the upper part of the heat transfer tube group constituting the superheaters 4, 5, 6, 7 and the reheaters 8, 9 which are hanging heat exchangers. A pipe side and a manifold connected by welding to these heat transfer pipe groups are arranged. A plurality of tubes are installed at a predetermined interval in the axial direction of the manifold, and a heat transfer tube group is hung from each tube.

Since the above-described boiler device is a supercritical pressure boiler device having a steam temperature of 600° C. class, high-chromium steel having high high-temperature strength is used as a pipe material such as a heat transfer pipe and a pipe side. FIG. 2 is an explanatory view of a pipe side and a heat transfer pipe installed in the penthouse 3. As shown in FIG. 2, a large number of heat transfer pipes are welded as branch pipes 12 to a mother pipe 11 which is a pipe side. There is. The mother pipe 11 and the branch pipe 12 are made of high chromium steel in which the content of chromium in the steel material is 9 to 12% by weight, and are joined by the welding method described below.

FIG. 3 is an explanatory diagram showing a work procedure of the welding method according to the first embodiment of the present invention, and FIG. 4 is an explanatory diagram showing a relationship between time and temperature in each step of the first embodiment.

As shown in FIGS. 3 and 4, in the welding method according to the first embodiment, first, a mother pipe and a branch pipe made of high chromium steel are normalized at a temperature of 1040° C. or higher (step S1). .. In this step S1, since the high chromium steel is not tempered but only normalized, the creep strength can be improved. However, the high chrome steel after normalizing is hard (hardness: about 400 HV) and brittle (absorbed energy: about 15 J), so if it is welded as it is, cold cracking will occur after welding. Therefore, after the normalizing process, after the groove processing of the mother pipe and the branch pipe is performed (step S2), a preheat treatment is performed to heat the mother pipe and the branch pipe to a temperature of 300°C or higher (300 to 400°C). Then, the mother pipe and the branch pipe are welded while being maintained at 300° C. or higher (step S3) (step S4). Then, after welding, the mother pipe and the branch pipe are conveyed to a heat treatment furnace while being maintained at 200° C. or higher (step S5), and the mother pipe and the branch pipe are tempered in the heat treatment furnace at a temperature of 730 to 780° C. (step S6). ..

As described above, in the welding method according to the first embodiment, after the normalizing treatment of the mother pipe and the branch pipe at 1040° C. or higher, the welding is performed while preheated at a temperature higher than normal (200 to 300° C.), Since the preheating range was maintained at 200°C or higher until the tempering process even after welding, hydrogen in the material, which is a factor of cold cracking, was reduced, and the welded part was maintained without cold cracking even in the normalized state. In addition to being manufactured, since normalization is not performed after welding, deformation of the branch pipe can be suppressed and creep strength of the welded portion can be improved. That is, the cold cracking is generated by the tensile residual stress generated by the welding heat and hydrogen in the material after the welded part is cooled, and the amount of hydrogen in the material, which is one of the factors of occurrence, is calculated in step S3. The low temperature cracking is prevented by reducing it by the preheat treatment in step S5 and maintaining it in a temperature range (200° C. or higher) in which low temperature cracking does not easily occur in step S5. This corresponds to the low temperature crack inhibiting process of the invention.
In addition, also in the second to fourth embodiments described below, the effect of the preheat treatment at 300° C. or higher before welding is similarly obtained.

FIG. 5: is explanatory drawing which shows the work procedure of the welding method which concerns on the 2nd Embodiment of this invention, and FIG. 6 is explanatory drawing which shows the relationship of the time and temperature in each process of 2nd Embodiment.

As shown in FIGS. 5 and 6, in the welding method according to the second embodiment, first, the mother pipe and the branch pipe made of high-chromium steel are only normalized at a temperature of 1040° C. or higher (step S10). ). Next, after the groove processing of the mother pipe and the branch pipe is performed (step S11), a preheat treatment for heating the mother pipe and the branch pipe to a temperature of 300° C. or higher is performed (step S12), and the mother pipe and the branch pipe are performed. Are welded in a state of being preheated to 300° C. or higher (step S13). The steps up to here are the same as those in the first embodiment, but after the heat treatment is performed immediately after welding at 300° C. or higher (step S14), the mother pipe and the branch pipe are heated at a temperature of 730 to 780° C. in the heat treatment furnace. Temper (step S15).

As described above, in the welding method according to the second embodiment, the amount of hydrogen in the material that causes cold cracking due to the immediate heat is reduced even if it cannot be conveyed to the heat treatment furnace while maintaining the temperature in the preheating range after welding. Since it can be reduced, the deformation of the branch pipe can be suppressed and the creep strength can be improved without causing cold cracking after welding, as in the first embodiment. In the second embodiment, the process of step S13 of performing the heat treatment immediately after welding at 300° C. or higher corresponds to the low temperature crack suppression process of the present invention.

FIG. 7 is an explanatory diagram showing the work procedure of the welding method according to the third embodiment of the present invention, and FIG. 8 is an explanatory diagram showing the relationship between time and temperature in each step of the third embodiment.

As shown in FIGS. 7 and 8, in the welding method according to the third embodiment, first, the mother pipe and the branch pipe made of high chromium steel are only normalized at a temperature of 1040° C. or higher (step S20). ). Next, after the groove processing of the mother pipe and the branch pipe is performed (step S21), a preheat treatment for heating the mother pipe and the branch pipe to a temperature of 300° C. or higher is performed (step S22), and the mother pipe and the branch pipe are performed. Are welded in a state of being preheated to 300° C. or higher (step S23). The steps up to this point are the same as those in the first embodiment, but after the welding toe portion is subjected to peening treatment at a temperature of 200° C. or higher after welding (step S24), the mother pipe and the branch pipe are formed in the heat treatment furnace. Tempering is performed at a temperature of 730 to 780°C (step S25). Hammer peening and ultrasonic peening are used as the peening processing in step S24.

As described above, in the welding method according to the third embodiment, after normalizing the mother pipe and the branch pipe made of high chromium steel at a temperature of 1040° C. or higher, the temperature is higher than normal (200 to 300° C.). Pre-heat treatment reduces hydrogen in the material, which is a cause of cold cracking, and even if it cannot be transported to the heat treatment furnace while maintaining the temperature in the pre-heating range after welding, stress concentration before the temperature decreases. Since the tensile residual stress, which is also a factor of cold cracking, can be reduced by subjecting the weld toe portion, which is the welded portion, to the peening treatment to give the compressive stress, as in the first embodiment, The deformation can be suppressed, and the creep strength can be improved without causing cold cracking after welding. That is, in the third embodiment, the process of step S23 of performing peening treatment on the weld toe portion at a temperature of 200° C. or higher after welding corresponds to the cold crack prevention treatment of the present invention.

FIG. 9 is an explanatory diagram showing the work procedure of the welding method according to the fourth embodiment of the present invention, and FIG. 10 is an explanatory diagram showing the relationship between time and temperature in each step of the fourth embodiment. In addition, FIG. 11 is an explanatory view showing a welding structure of a mother pipe and a branch pipe to which the fourth embodiment is applied, and a welding method according to the fourth embodiment is applied to an existing pipe side (mother pipe) 11. It is applied when the attached branch pipe 12 is partially replaced with a new one.

As shown in FIGS. 9 and 10, in the welding method according to the fourth embodiment, first, a high-chromium steel pipe having the same shape as the replacement portion of the branch pipe 12 is normalized at a temperature of 1040° C. or higher (hereinafter, This is called a normalizing tube 13) (step S30). Next, groove processing is performed on the pipe material to be joined and the normalizing pipe 13 (step S31). In this case, the pipe materials to be joined are both the pipe side 11 and the existing branch pipe 12. Thereafter, pre-heat treatment for heating the normalizing pipe 13 to a temperature of 300° C. or higher is performed (step S32), and in this state, both ends of the normalizing pipe 13 are respectively connected to the pipe side 11 and the branch pipe 12 to be joined. Welding (step S33). Then, after welding, both welding toes are subjected to peening treatment at a temperature of 200° C. or higher (step S34), and then the range surrounded by the welds at both ends of the normalizing pipe 13 is heated to a temperature of 730 to 780° C. And temper (step S35). The pipe side 11 and the branch pipe 12, which are joint partners of the normalizing pipe 13, may be the same material as or different materials from the normalizing pipe 13.

As described above, in the welding method according to the fourth embodiment, the normalizing pipe that has been subjected to the normalizing treatment at 1040° C. or higher is preheated at a temperature higher than normal (200 to 300° C.), which causes a factor of low temperature cracking. The tensile residual stress, which is also a factor of cold cracking, is reduced by reducing the hydrogen in the material and applying compressive stress to the weld toe of the normalizing pipe that becomes the stress concentration part after welding by peening treatment. Can be reduced. This makes it possible to improve the creep strength even in a partially welded portion such as a normalizing pipe without causing cold cracking after welding.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention, and all the technical matters included in the technical idea described in the claims are It is the subject of the present invention. Although the above-described embodiment shows a suitable example, those skilled in the art can implement various alternatives, modifications, variations, or improvements from the contents disclosed in this specification. These are included in the technical scope described in the appended claims.

1 furnace 2 combustion gas passage 3 penthouse 4 primary superheater 5 secondary superheater 6 tertiary superheater 7 quaternary superheater 8 primary reheater 9 secondary reheater 10 ceiling 11 mother pipe
12 Branch tubes (heat transfer tubes)
13 Normalizing tube

Claims (5)

After only normalizing the mother pipe and the branch pipe made of high chromium steel at a temperature of 1040°C or higher, the mother pipe and the branch pipe are preheated at a temperature of 300°C or higher before Welded, and then subjected to cold crack prevention treatment, and then tempering the mother pipe and the branch pipe at a temperature of 730 to 780°C. The method for welding a pipe material according to claim 1,
The method for welding a pipe material, wherein the cold crack prevention treatment is a preheat treatment for maintaining the mother pipe and the branch pipe after welding at 200° C. or higher until a heat treatment furnace. The method for welding a pipe material according to claim 1,
The method for welding a pipe material, wherein the cold crack prevention treatment is a treatment in which the mother pipe and the branch pipe after welding are immediately heat-treated at a temperature of 300° C. or higher. The method for welding a pipe material according to claim 1,
A method for welding a pipe material, wherein the cold crack prevention treatment is a treatment of performing a peening treatment on a welded portion while maintaining the mother pipe and the branch pipe after welding at 200°C or higher. After forming a normalizing tube by normalizing a tube material made of high chromium steel at a temperature of 1040°C or higher, a preheat treatment is performed at a temperature of 300°C or higher for the normalizing tube and the pipe material of the joining partner. After performing the welding between the two, then, after the peening treatment on the welded portion while maintaining the preheating range at 200 ℃ or more, temper the region surrounded by the welded portion at a temperature of 730 ~ 780 ℃. Welding method for pipe materials.

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