JP2006136911A - Tube welding method and tube welding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tube welding method and a tube welding device capable of enhancing the corrosion resistance by exerting the compressive residual stress in the axial direction in a weld metal portion on an inner face of a tube in the connection by welding tubes of large tube thickness to each other. <P>SOLUTION: After root passes of tubes are welded, the surface of the tubes is quenched by spraying cooling water in the stage of high temperature immediately after the molten metal is solidified behind a torch to perform the welding on the outer surface of the tubes while cooling the inner surface by allowing cooling water to flow on the inner surface of the tubes. The compressive stress is generated on the outer surface side of the tubes to suppress generation of shrink-deformation in the circumferential direction of the tubes, and generate the compressive residual stress as the residual stress in the axial direction of the inner surface of the tube. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pipe welding method and apparatus for connecting pipes with corrosion resistance on the inner surface of the pipe used in a corrosive environment.

  In welded parts of austenitic stainless steel and high nickel-base alloys, chromium carbide precipitates at the grain boundaries due to welding heat, resulting in the formation of a chromium-depleted layer in the immediate vicinity of the grain boundaries. That is, a phenomenon that becomes more sensitive to corrosion. Further, generally high tensile residual stress exists on the surface in the vicinity of the weld. When the material is sensitized, high tensile residual stresses are present, and stress corrosion cracking can occur when used in severe corrosive environments. That is, when the three factors of material sensitization, high tensile residual stress, and corrosive environment overlap, the risk of stress corrosion cracking increases.

  Conventionally, stress corrosion cracking of austenitic stainless steel was thought to occur in the weld heat affected zone of materials with high carbon content such as type 304 stainless steel. For this reason, in the part exposed to a corrosive environment in the welding part of type 304 stainless steel, improvement of a material factor has been aimed at among the factors which generate stress corrosion cracking. For example, measures have been taken to replace type 316L stainless steel with an element that has a low carbon content and is less susceptible to sensitization. Thereby, it was thought that stress corrosion cracking does not occur in the heat-affected zone of the pipe and the weld metal.

  However, in recent years, it has become clear that the possibility of stress corrosion cracking from the heat-affected zone of the type 316L stainless steel welded part cannot be denied. It is becoming clear that the improvement in material factors using type 316L is not necessarily sufficient. Furthermore, it is undeniable that stress corrosion cracking can occur even in stainless steel weld metal, which has been thought to fail in conventional knowledge. From such a possibility, in order to suppress stress corrosion cracking, it is important not only to improve material factors but also to improve residual stress and environmental factors.

  In order to suppress the occurrence of stress corrosion cracking, reduction of tensile residual stress in an area exposed to a corrosive environment can be cited as one countermeasure. When stress corrosion cracking is detected in the welded part of the existing pipe, the pipe is replaced. In the replacement work of the existing pipes in the plant, the “welding method for austenitic steel pipes” described in Patent Document 1 is used for the purpose of reducing the tensile residual stress generated on the inner surface of the pipes exposed to the corrosive environment. May be. This method is a method of welding in the circumferential direction while supplying cooling water over the entire outer circumference of the pipe before and after the pipe joint so as to sandwich the torch when the pipes are connected by welding.

  In Patent Document 2, when pipes are connected by welding, carbon dioxide is condensed on both the surface of the welded part immediately after the lamination welding and the first layer welding part on the back side at the time of lamination welding after the first layer welding. Techniques for cooling by spraying solid particles are disclosed.

Japanese Patent Publication No.52-18141 (Overall) JP-A-8-155650 (Overall)

  In the prior art of the above-mentioned Patent Document 1, no consideration is given to the case where the thickness of the pipe is large. Generally, if the outer surface is welded while cooling the inner surface of the pipe, a tensile yielding occurs on the inner surface of the pipe and a compressive yielding occurs on the outer surface of the pipe. By contraction, compressive residual stress can be applied to the inner surface of the pipe, which is convenient. However, as the thickness of the pipe increases, the distance from the cooling area on the inner surface of the pipe to the welding path increases, so the tensile stress on the inner surface of the pipe generated by the inner surface cooling decreases. In addition, the shrinkage deformation in the circumferential direction of the welded portion increases, and as described later, a deformation that protrudes inside the welded portion occurs. As a result, in pipes with a large thickness, in the weld metal part on the inner surface of the pipe, the residual stress in the circumferential direction is compressed due to the lamination of the weld path on the outer peripheral side, but the residual stress in the axial direction becomes tensile due to bending deformation. As a result, the corrosion resistance of the inner surface of the pipe is impaired.

  On the other hand, the technique of Patent Document 2 requires equipment for producing or storing carbon dioxide condensed solid particles, which makes the apparatus complicated and disadvantageous in terms of cost. In addition, in the replacement work for some of the existing pipes in the plant, it was impossible to apply the solid particles of carbon dioxide to the inside of the pipes, which could not be applied. Furthermore, even if it could be applied, the cooling effect of the solidified particles of carbon dioxide was weak, and it was difficult to obtain the desired corrosion resistance.

  An object of the present invention is to improve the corrosion resistance on the inner surface of a pipe of a pipe welded joint and to suppress the occurrence of stress corrosion cracking.

  Another object of the present invention is to improve the corrosion resistance by reducing the tensile residual stress on the inner surface of the pipe of the pipe welded joint, desirably generating the compressive residual stress.

  In order to reduce the residual tensile stress on the inner surface of the pipe and preferably generate the residual compressive stress when the pipes are thick when the pipes are connected by welding, the circumferential shrinkage deformation generated by welding It is necessary to suppress.

  In one aspect of the present invention, after welding the root path, when welding the path after the root path, the inner surface of the pipe is allowed to flow with a liquid refrigerant to cool the inner surface, and the welding torch on the outer surface of the pipe passes to pass the molten metal. The plastic deformation (strain) on the tensile side is imparted to the surface of the welded portion immediately after solidification.

  In a desirable embodiment of the present invention, in order to give the plastic deformation on the tensile side, the lamination weld is performed while cooling the surface of the welded portion immediately after the molten metal after the lamination welding is solidified.

  In another preferred embodiment of the present invention, when the lamination of each welding pass is completed, a mechanical load is applied to the surface of the completed pass to generate tensile plastic deformation (strain) on the pass surface. Processing is performed, and subsequent passes are stacked.

  In another aspect of the present invention, welding is performed while cooling the inner surface of the pipe from the root pass welding to 3/4 of the pipe thickness, and in the pass from 3/4 of the thickness to the total thickness, In addition to cooling, laminating welding is continued while applying tensile plastic deformation to the outer surface.

  In a preferred embodiment of the present invention, the means for cooling the inner surface of the pipe is performed by passing a liquid refrigerant through the pipe, and the means for imparting tensile plastic deformation to the outer surface of the pipe is a liquid refrigerant on the pipe surface. This is done by spraying.

  In a desirable embodiment of the present invention, water is used as both the liquid refrigerant used for cooling the inner surface of the pipe and the refrigerant used for cooling the surface of the welded portion on the outer surface side of the pipe.

  In particular, when the pipe to be welded constitutes an existing plant, the liquid refrigerant used for cooling the inner surface of the pipe is a fluid that flows in the pipe in the existing plant, for example, cooling water.

  In a preferred embodiment of the present invention, the existing plant is a boiling water reactor, the pipe for welding is a recirculation pipe of the nuclear reactor, and the liquid refrigerant used for cooling the inner surface of the pipe passes through the pipe. Flowing reactor water.

  In a preferred embodiment of the present invention, when pipes are connected to each other by welding, after the root path is welded, the inner surface of the pipe is cooled by flowing a liquid refrigerant when the path after the root path is welded, and the pipe A welding device for laminating a welding pass while cooling the surface of the welded portion immediately after the weld torch on the outer surface passes and the molten metal solidifies, and a welding torch fixed to the jig and a cooling fixed to the jig A jet nozzle that supplies liquid to the surface of the welded portion, and a suction nozzle that collects the cooling liquid disposed around the jet nozzle, and jets the cooling liquid from the jet nozzle to a region through which a welding torch has passed, A welding device that welds the pipe in the circumferential direction while sucking the cooling liquid from the suction nozzle is used.

  According to the present invention, at the time of welding construction of butt joints between pipes, it is possible to suppress the occurrence of shrinkage deformation in the circumferential direction of the welded portion, reduce the tensile residual stress in the axial direction of the pipe inner surface, and improve its corrosion resistance. it can.

  According to a preferred embodiment of the present invention, water is used for the inner surface for cooling the pipe, and shower-like water is also used for the outer surface, thereby reducing the tensile residual stress of the welded portion efficiently at a low cost. The corrosion resistance of the inner surface can be improved and the occurrence of stress corrosion cracking can be suppressed.

  Other objects and features of the present invention will become apparent from the following description of embodiments.

  By using the welding method according to the present invention, a mechanism capable of reducing tensile stress as an axial residual stress and desirably applying compressive stress in the welded portion on the inner surface of the pipe will be described in detail with reference to FIGS.

  FIG. 1 is a perspective view schematically showing a pipe welding method according to the first embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view of the main part thereof. The state where the pipe 1 and the pipe 2 are abutted and connected by welding is shown. First, the root pass (first pass welding) 3 is welded. Thereby, it becomes possible to flow cooling water to the inner surface through the pipes 1 and 2. Therefore, the subsequent pass (lamination welding) 6 is welded while flowing the cooling water 5 to the pipe inner surface 4. At this time, it is a welding method in which the welding torch 7 is advanced in the circumferential direction while cooling the outer surface cooling region 8 of FIG. 1 consisting of the pipe outer surface immediately after the torch 7 and the surface of the weld metal part.

  FIG. 3 is a distribution diagram of residual stress generated by pipe welding for explaining the principle of the present invention. When the pipe thickness is thick, even if the inner surface only is cooled sufficiently effectively, tensile residual stress is generated on the inner surface, while cooling the inner and outer surfaces results in compressive residual stress on the inner surface. The mechanism that can be generated is schematically shown.

  First, FIG. 3A shows a case where welding is performed while effectively cooling only the inner surface of the pipe. In FIG. 3, “+” means that an axial tensile residual stress is generated, and “−” means that an axial compressive residual stress is generated. T represents the thickness of the pipe.

  When welding is performed while the inner surface 4 of the pipe is effectively cooled, a temperature distribution occurs in which the inner surface is low temperature and the outer surface is high temperature. In such a temperature distribution state, tensile stress is applied to the inner surface as the outer surface expands, and compressive stress is applied to the outer surface. The inner surface undergoes tensile plastic deformation (strain), and the outer surface undergoes compressive plastic deformation. To do. As shown in (1) and (2) of FIG. 3 (A), the welding process is completed at the time when the welding of the welding path with the laminated thickness of the welding ranging from 0 to t / 2 and from t / 4 to 2t / 4 is completed. The tensile plastic deformation of the inner surface generated in (1) is constrained from the outer surface side due to the shrinkage due to cooling of the outer surface side. Therefore, the inner surface becomes compressive residual stress and the outer surface becomes tensile residual stress. Until the lamination of the welding paths becomes 1/2 of the pipe thickness, the distribution in which the inner surface is compressive residual stress and the outer surface is tensile residual stress continues as described above.

  On the other hand, when the weld stack exceeds 1/2 of the thickness, the outer surface 9 that has been heated during welding and yielded by compression contracts as it gradually cools, and the pipe shrinks in the circumferential direction. It becomes prominent, and the cross section of the pipe is deformed so as to have a convex shape on the inner surface side as shown in (3) of FIG. Such bending deformation has the property of making the axial stress on the inner surface of the pipe the tensile side. Due to the bending deformation of the pipe cross section caused by the circumferential shrinkage deformation of the welded portion, the axial residual stress of the pipe inner surface 4 becomes the compressive residual stress from the position where the welded laminate thickness exceeds 1/2 of the pipe thickness. The absolute value becomes smaller. Further, when passes are laminated, the axial residual stress of the pipe inner surface 4 becomes tensile stress as shown in FIG. 3A (4).

  On the other hand, the circumferential residual stress of the pipe inner surface 4 is subjected to a contraction force due to the contraction deformation of the outer surface side 9, and the circumferential residual stress of the inner surface 4 becomes the compression side. As a result, when welding is finished, the axial direction becomes tensile residual stress and the circumferential direction becomes compressive residual stress.

  Next, after root pass welding, the pipe inner surface 4 is effectively cooled to the laminated thickness t / 2, and the pipe inner surface 4 and the pipe outer surface 7 are cooled in the range of the laminated thickness from t / 2 to t. explain. The change in the stress distribution at this time follows the progress of (1) to (4) in FIG. As shown in (1) and (2) of FIG. 3 (B), when the stacking thickness is in the range of 0 to t / 2, only the inner surface 4 is effectively cooled during welding. The same result.

  By welding the outer surface side while effectively cooling the pipe inner surface 4 in the range of the stacking thickness from t / 2 to t, tensile stress is generated on the pipe inner surface 4 during welding. On the other hand, a compressive stress is generated at a portion receiving heat. When the pipe outer surface 9 is cooled after the torch passes, a temperature distribution is generated in which the surface of the welded portion is at a low temperature and the inside is at a high temperature. Accordingly, a stress distribution in which the surface of the welded portion on the outer surface side is tensile and the inside is compressed occurs, tensile plastic deformation (strain) occurs on the outer surface, and compressive plastic deformation (strain) occurs on the inside. As a result, after the inside is cooled, as shown in (3) of FIG. 3B, compressive residual stress is generated on the pipe inner surface 4 and the pipe outer surface 9, and tensile residual stress is generated inside the wall thickness. To do.

  The outer surface cooling immediately after the lamination welding causes a tensile plastic deformation (strain) on the outer surface side. Therefore, the shrinkage deformation in the circumferential direction of the pipe becomes smaller than that without the outer surface cooling, resulting in bending deformation of the weld. The occurrence of tensile stress due to is reduced. As a result, the compressive residual stress generated in the stacking up to ½ of the plate thickness can suppress the transition to the tensile side caused by the bending deformation generated in the subsequent stacking. It is possible to apply compressive residual stress as shown in (4) of FIG.

  Next, when there is no cooling, only the outer surface is cooled, only the inner surface is cooled, and when the inner and outer surfaces are cooled, the welding lamination and residual stress when the pipe thickness is thin and thick The relationship will be described with reference to FIG. 4 and FIG. 4 and 5, σy means the tensile yield stress, and −σy means the compressive yield stress.

FIG. 4 shows the relationship between the lamination thickness when the pipe is thin and the axial stress of the weld metal on the inner surface of the pipe. In the laminated thickness of the horizontal axis, t _thin means that the welding paths are laminated up to the thickness of the pipe, and the value of the axial stress corresponding thereto becomes the residual stress in the axial direction. Curve 10 in FIG. 4 is the case without cooling. As the weld metal is laminated, the axial stress becomes tensile. Curve 11 is the case where only the outer surface is cooled, and the absolute value of the tensile stress is smaller than curve 10. Curve 12 is the case where only the inner surface is cooled, and the axial stress is significantly compressed. A curve 13 is a case where the inner and outer surfaces are cooled, and an axial compressive stress having a larger absolute value is applied than when only the inner surface and only the outer surface are cooled.

FIG. 5 shows the relationship between the lamination thickness when the pipe is thick and the axial stress at the center of the weld metal on the inner surface of the pipe. In the laminated thickness of the horizontal axis, t _thick means that the welding path is laminated to the thickness of the pipe, and the value of the axial stress corresponding thereto is the residual stress in the axial direction. Curve 14 in FIG. 5 is the case without cooling. When the weld metal is laminated, a compressive stress is generated up to t _thick / 2, which is ½ of the thickness, and the value corresponds to the yield stress. In the process in which the stack thickness is changed from t _thick / 2 to t _thick , the axial stress becomes the tensile side, and when the stack thickness is t _thick at the end of welding, tensile residual stress is generated. Curve 15 shows a case where cooling only the outer surface, the absolute value of the tensile stress in the process of becoming Compared to the curve 14 from _{t thick} / 2 to _{t thick} small. Curve 16 shows the case where only the inner surface is cooled, and the tensile stress is relaxed in the axial stress in the process from t _thick / 2 to t _thick as compared to the case where there is no cooling. A curve 17 is a case where the inner and outer surfaces are cooled, and compressive residual stress can be applied. Further, the curve 18 shows a case where only the inner surface is cooled before 3 t _thick / 4 and the inner and outer surfaces are cooled after 3 t _thick / 4. Further, when only the inner surface was cooled before t _thick / 2, and the inner and outer surfaces were cooled after t _thick / 2, the curve 17 was hardly changed.

  As described above, when the pipe thickness is thin due to effective inner surface cooling, the influence of compressive stress generated by inner surface cooling rather than the axial tensile stress generated by circumferential shrinkage deformation As a result, the inner surface of the pipe can be set to compressive residual stress. On the other hand, when the pipe is thick, the influence of the tensile stress generated by the circumferential shrinkage deformation in the vicinity of the final layer is larger than the influence of the compressive stress generated by cooling the inner surface. Liquid cooling alone results in tensile residual stress.

  On the other hand, even when the pipe is thick, it is possible to suppress the occurrence of shrinkage deformation in the circumferential direction of the pipe by adding the outer face cooling during the lamination welding in addition to the effective inner face liquid cooling. It became clear that it was possible. Further, it has been clarified that the shrinkage deformation in the circumferential direction of the pipe starts to occur at a portion where the welding exceeds 1/2 of the thickness of the piping, and becomes a tensile stress at the lamination of the portion exceeding 3/4. Thus, specifically, compressive residual stress is applied in the axial direction of the inner surface of the pipe by cooling the pass surface immediately after the lamination at the time of the lamination pass welding after the thickness (1/2 to 3/4). Can do.

  From the above knowledge, the residual stress on the inner surface of the pipe can be compressed by cooling the inner and outer surfaces after route pass welding. Furthermore, even if cooling of the outer surface is carried out after exceeding 1/2 of the thickness of the pipe, compressive residual stress can be applied. Furthermore, it has become clear that the tensile residual stress can be reduced even if the outer surface is cooled beyond 3/4 of the thickness of the pipe. For this reason, it is desirable to start the cooling of the outer surface as late as possible in order to save waste and reduce the work using the nerve of injecting cooling water in the immediate vicinity of the weld.

  Next, a method and apparatus for welding pipes while cooling the inner and outer surfaces after welding the route path will be described with reference to FIGS.

  FIG. 6 is a configuration diagram of a pipe welding apparatus according to an example embodying the first embodiment of the present invention described so far. Here, a pipe welding apparatus that uses a TIG welding torch as a welding torch and performs welding while supplying a weld metal is shown. In the figure, reference numeral 130 denotes a support mechanism upper support plate installed on the carriage, and the TIG welding torch 101 is a weaving device 111 installed on the support mechanism upper support board 130 on the carriage via the torch support mechanism 110. Is installed. Here, the weaving device 111 is a device that swings the support beam 112 protruding in the depth direction with respect to the paper surface in FIG. 6 in the vertical direction of the paper surface. Welding can be performed. A wire tip 104 is attached to the TIG welding torch 101 via a wire tip support mechanism 105. A weld metal wire 103 is supplied to the wire tip 104 from a wire supply device via a conduit cable 106. Here, the TIG welding torch 101 is a known one, and a current is supplied to the tungsten electrode 102 via the current torch cable 107. Further, argon gas is supplied through the argon gas torch cable 108 and is ejected from the gas nozzle 113. This argon gas becomes an atmosphere of an arc generated at the time of welding, and has an effect of preventing impurities in the surrounding atmosphere from entering the weld metal part. Further, in order to prevent the torch from being heated, cooling water circulates through the cooling water torch cable 109.

  A water ejection nozzle 121 is supplied with water from the cooling medium supply pipe 125 and is ejected from the perforated plate 122. Reference numeral 120 denotes a suction nozzle, which is installed so as to include the ejection nozzle 121 therein. A suction port 123 is formed between the ejection nozzle 121 and the suction nozzle 120 and is sucked into the cooling medium recovery pipe 126. The ejection nozzle 121 is fixed inside the suction nozzle 120 via a jig 128, and the suction nozzle 120 is fixed to the moving mechanism upper support plate 130 via a cooling device support mechanism 127. Therefore, the moving mechanism is configured by a carriage including the support plate 130 on the moving mechanism.

  A shield 119 is installed at a portion where the suction nozzle 120 is in contact with the pipe 140. Since the shape of the groove of the pipe 140 is followed, when the suction is performed by the suction nozzle, the disturbance of the air flow in the direction in which the TIG welding torch 101 is present is reduced, and an arc can be generated stably.

  FIG. 7 illustrates the injection nozzle 121 from the direction in which the perforated plate 122 can be seen. A holed plate 122 is attached to the injection nozzle 121, and a hole 129 for injecting a cooling medium is formed in the holed plate 122. The injection nozzle 121 is installed inside the suction nozzle 120. A gap between the ejection nozzle 121 and the suction nozzle 120 becomes a suction port 123. Water is supplied to the ejection nozzle 121 from a cooling medium supply pipe. Water is sprayed onto the welded structure via the hole 129 of the perforated plate 122. Part of the jetted water evaporates, and part of it is not evaporated and remains in the surface area of the weldment. Inside the suction nozzle 120, a negative pressure is generated via the cooling medium recovery pipe 126 shown in FIG. Therefore, the water remaining on the surface of the welded portion without being evaporated or evaporated is sucked from the suction port 123. Since the ejection nozzle 121 is included in the suction nozzle 120, the water ejected from the ejection nozzle 121 is recovered from the suction nozzle 120 even if it evaporates into water vapor or does not evaporate. It does not leak out of 120. Therefore, the water ejected for cooling does not scatter to the surroundings, and further does not enter the welding torch. This makes it possible to perform welding without containing impurities in the weld.

  FIG. 8 is a diagram showing an overall configuration of a pipe welding apparatus according to an embodiment of the present invention. Power is supplied to the TIG power supply 201 from the power supply panel 203 via the input cable 206. In addition, cooling water is supplied from the water cooling circulation device 204 through the water cooling hose 207. Further, argon gas is supplied from an argon gas cylinder 205 through a gas hose 208.

  The torch cable 209 is a cable that connects the TIG power source 201 and the TIG welding torch, and includes a current torch cable, an argon gas torch cable, and a cooling water torch cable. The current generated by the TIG welding power source 201 is supplied to the current torch cable. Argon gas supplied from an argon gas cylinder 205 is supplied to the argon gas torch cable. Cooling water supplied from the water-cooling circulation device 204 is fed to the cooling water torch cable.

  The pipe 140 is connected to a power source via the ground cable 211. A current detector 290 is attached to the ground cable 211, and a measured value of the current is taken into the control device 202. A welding power source remote controller 214 and a wire feeder remote controller 215 are attached to the controller 202 via a remote controller cable 213. A wire feeder 221 is attached via a control cable 217, and a torch switch 219 is attached from the wire feeder 221 via a torch switch cable 218. The wire 103 is fed from the wire feeding device 221 to the TIG welding torch 101 via the conduit cable 106.

  A weaving device 111 is installed on the carriage 131 and connected to the weaving control device 210 via a control cable. In addition, electric power is supplied to the weaving control device 210 via the input cable 206. A TIG welding torch is installed from the weaving device 111 through the torch support mechanism 110. The suction nozzle 120 is installed in the carriage 131 via the cooling device support mechanism 127. The carriage 131 is connected to the carriage moving mechanism remote controller 216 by a remote control cable 213. The carriage 131 travels on a track 299 installed over the entire circumference of the pipe.

  A cooling medium recovery pipe 126 is attached to the suction nozzle 120, and the cooling medium recovered by suction stays in the water tank 220. A suction pump 222 is installed to perform suction. An injection nozzle 121 is installed inside the suction nozzle 120, and a cooling medium is supplied via a cooling medium supply pipe 125.

  Next, the welding operation according to this embodiment will be described. First, the root path is welded. In the route path welding, the TIG welding torch 101 is installed at a position where the pipe 140 is welded in FIG. Current and voltage conditions corresponding to the welding conditions are set from the welding power source remote controller 214. Further, the wire feeding amount is set from the wire feeding device remote controller. The control device 202 is set to supply a current corresponding to the input from the welding power source remote controller 214 to the TIG welding torch 101. In addition, a setting for supplying a wire input from the wire feeder remote controller 215 is made. A weaving condition is input to the weaving control device 210 to start weaving. Further, the moving speed of the carriage 131 is input from the moving mechanism remote controller 216.

  When the above preparation is completed, the torch switch 219 is turned on. An electric current is supplied to the TIG welding torch to generate an arc. Further, the wire feeding device 221 is activated and the wire feeding is started. When the carriage 131 makes one round on the track 299, the welding of the route path of the piping is completed.

  When cooling the inner and outer surfaces from the construction of the second pass, the cooling medium is allowed to exist on the inner surface of the pipe from the second pass to cool the inner surface of the pipe, and the cooling medium injection mechanism and the recovery mechanism are operated on the outer surface of the pipe. Thus, the region that has become hot due to welding is rapidly cooled. At the time of rapid cooling, the water of the cooling medium does not leak out of the suction nozzle, and even if suction is performed, the air flow in the vicinity of the electrode is not disturbed, so that high-quality welding can be performed. The second pass to the final pass are welded while cooling the inner and outer surfaces in this way.

  The inner surface of the pipe is cooled from the stack after the second pass, and in the first welding method of this embodiment, the outer surface is also cooled from the stack thickness of 1/2 of the thickness of the pipe. On the other hand, in the second welding method of this embodiment, the outer surface is cooled from 3/4 of the thickness of the pipe.

  When the groove is filled with weld metal and the welding is finished, the torch switch 219 is turned off to stop the arc. A stop signal is issued from the control device 202 to the wire feeding device 221 to stop the wire feeding. The carriage 131 is stopped. Further, the supply of the cooling medium is stopped, and finally the suction pump 222 is stopped. This is the end of the work.

  In the embodiment described above, as a liquid cooling method for the inner surface of the pipe, it is possible to use a method of spraying water with a water discharge gun or a method of circulating a cooling water by providing a water supply pump at an end portion sandwiching a welded portion. Moreover, in the piping replacement work of the existing plant, liquid refrigerant flowing through the piping in the plant can be used as cooling water. Next, a pipe welding method in the pipe replacement work of the existing plant will be described.

  First, the pipe welding apparatus described in FIGS. 6 to 8 is installed. In this embodiment, the pipe cooling water valves before and after the replacement pipe are closed until the route path is welded. Therefore, air is contained in the piping. In this state, the root path is welded by the welding apparatus without cooling the inner and outer surfaces. When the root path welding is completed and the medium in the pipe no longer leaks, the valve of the cooling water in the pipe is released. Next, the circulating pump of the plant is operated to circulate the cooling water on the inner surface of the pipe. Here, the welding apparatus is operated so that the inner surface of the pipe is cooled by cooling water, and the outer surface of the pipe is welded while cooling the rear of the torch as described above.

  In this embodiment, it is not necessary to set a water discharge gun for cooling the inner surface by using the liquid refrigerant circulating in the plant for cooling the inner surface of the pipe. Therefore, the number of steps required for cooling the inner surface of the pipe can be greatly reduced. In this method, the pipe replacement work can be performed in parallel with the periodic inspection of the plant.

  FIG. 9 is a configuration diagram in the case where the above embodiment is applied to replacement of the recirculation piping of the boiling water nuclear power plant. In the figure, 31 is a reactor pressure vessel and 32 is a recirculation pump. After stopping the plant by periodic inspection or the like, the valves 34 and 35 before and after the replacement part 33 on the piping are closed. Water remaining in the pipe of the replacement site 33 is drained, and the replacement site 33 is cut out. A groove is provided in the piping on the plant side. On the other hand, a new pipe 36 for replacement is installed. Further, the pipe welding apparatus described with reference to FIGS. 6 to 8 is installed in the pipe, and the welding head for TIG welding and the outer surface cooling mechanism are mounted on the track. The installation of these devices is as described in the previous embodiment.

  When the installation of these devices is completed, the route 34 of the welded portion 37 and the welded portion 38 is welded in the manner described above while the valve 34 and the valve 35 are closed. The reactor water will not leak even if the valve is released by root path welding. At this stage, the valves 34 and 35 before and after the replacement site are released, and the recirculation pump 32 is operated to circulate the reactor water through the piping. Further, the welding apparatus and the cooling mechanism are operated, and the inner surface of the pipe is cooled by the reactor water, and the outer surface of the pipe is laminated in the manner described above while the heat from the torch and the cooling immediately after the cooling are performed.

  Thus, by carrying out lamination | stacking to the thickness of piping, it becomes possible to provide a compressive residual stress to the welding part of piping inner surface. In particular, it is not necessary to set up an additional device for cooling the inner surface of the pipe, and recirculated water circulating in the pipe is used, and the recirculation pump installed in the plant is used for the circulation. Therefore, the equipment preparation process required for construction can be greatly reduced. In addition, the cooling of the inner surface of the pipe with this recirculated water is necessary and sufficient and appropriate as the cooling from the inner surface in the present invention, compared with the insufficient spraying of solid particles of carbon dioxide, which is insufficient, and the pipe welded joint. Compressive residual stress can be generated on the inner surface of the pipe to improve the corrosion resistance.

  Next, a second embodiment of the present invention will be described.

  In the first embodiment described so far, tensile plastic deformation (strain) is imparted to the surface of the weld zone from the temperature difference between the heat from the torch and the cooling immediately thereafter. On the other hand, in this embodiment, in order to suppress the shrinkage deformation in the circumferential direction of the pipe, a mechanical force is applied to the weld metal that has been laminated to impart tensile plastic deformation (strain). .

  The mechanism for compressing the residual stress on the inner surface of the pipe is as follows: (3) and (4) shown in FIG. 3 (B), where tensile plastic deformation occurs due to temperature distribution (compression residual stress generation) A compressive residual stress is given to the area | region) by generating the plastic deformation of the tension | tensile_strength generate | occur | produced resulting from a mechanical load. As a method of applying a mechanical load, a method of applying a load in a direction in which the laminated weld metal is crushed is necessary. As an example, application of wire peening can be cited.

  The implementation procedure of this method is shown below. First, the root path is welded while cooling the inner surface. When the root pass is welded, the outer surface is wire peened to impart tensile plastic deformation to the outer surface, and subsequent passes are laminated. By this method, it becomes possible to alleviate the shrinkage deformation in the circumferential direction caused by welding of each pass by wire peening for each pass.

  Next, a third embodiment of the present invention will be described.

  This embodiment is a combination of the first and second embodiments described above, and is intended to increase the absolute value of the compressive residual stress applied to the inner surface of the pipe. The devices required in this embodiment are the welding device of the first embodiment in which a cooling mechanism behind the torch is provided on the outer surface side, and the wire peening device which is one of the second embodiments.

  First, the root path is welded with air inside. Next, the subsequent passes are laminated while flowing cooling water on the inner surface of the pipe. At this time, welding is performed while the rear of the torch on the outer surface of the pipe is cooled by a cooling mechanism. After one pass of welding is finished, peening is performed on the surface of the weld metal laminated by the wire peening apparatus. It should be noted that the path for cooling the outer surface of the pipe to the rear of the torch, when there is a restriction in the process, etc., when it is performed from 1/2 of the pipe thickness to the final, and 3 / of the pipe thickness It is also possible to select as appropriate in the case of carrying out from 4 to the last. Also, with respect to the path for performing wire peening, the path to be started can be appropriately selected if there are restrictions on the process or the like.

  According to this embodiment, the occurrence of shrinkage deformation in the circumferential direction of the pipe can be suppressed by cooling the outer surface, and further, the suppression effect can be further increased by adding wire peening, which is a problem when the pipe thickness is large. It is possible to suppress the occurrence of axial tensile residual stress on the inner surface of the pipe.

  As a modified example of this embodiment, a wire peening apparatus is attached to the rear of the torch, and a cooling mechanism is attached to the rear of the torch, so that welding paths are stacked, tensile plastic deformation (strain) is imparted by wire peening, and rapid cooling is performed. It is also possible to sequentially apply the tensile plastic deformation (strain) by welding during welding. In this method, since the three steps of welding, peening, and rapid cooling are performed simultaneously, the number of man-hours can be reduced.

The perspective view which represents typically the welding method of piping by the 1st Embodiment of this invention. Sectional drawing which expands and shows the principal part of FIG. The residual stress distribution figure of piping which arises by welding explaining the principle of the present invention. The relationship figure of lamination | stacking thickness and axial direction stress when pipes with thin thickness are butt-welded. The relationship figure of lamination | stacking thickness when a pipe with thick thickness is butt-welded and axial stress. The block diagram of the torch and outer surface cooling mechanism of the welding apparatus by one Example of this invention. 1 is a structural diagram of a nozzle of a cooling mechanism of a welding apparatus according to an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The block diagram of the whole piping welding apparatus by one Example of this invention. The figure which shows the pipe replacement welding method of the boiling water nuclear power plant by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 2 ... Piping, 3 ... Root pass (first layer welding), 4 ... Inner surface of piping, 5 ... Cooling water, 6 ... Subsequent pass (lamination welding), 7, 101 ... Torch for TIG welding, 8 ... Outer surface Cooling region, 9 ... outer pipe surface, 102 ... tungsten electrode, 103 ... wire, 104 ... wire tip, 105 ... wire tip support mechanism, 106 ... conduit cable, 107 ... current torch cable, 108 ... argon gas torch cable, 109 ... cooling water torch cable, 110 ... torch support mechanism, 111 ... weaving device, 112 ... support beam, 113 ... gas nozzle, 119 ... shield, 120 ... suction nozzle, 121 ... injection nozzle, 122 ... perforated plate, 123 ... Suction port, 125 ... cooling medium supply pipe, 126 ... cooling medium recovery pipe, 127 ... cooling device support mechanism, 128 ... jig, 129 Hole: 130 ... Support plate on support mechanism, 131 ... Carriage moving mechanism, 132 ... Remote control for moving mechanism, 140 ... Piping, 201 ... TIG power source, 202 ... Control device, 203 ... Power supply panel, 204 ... Water-cooled circulation device, 205 ... Argon gas, 206 ... input cable, 207 ... water cooling hose, 208 ... gas hose, 209 ... torch cable, 210 ... weaving control device, 211 ... ground cable, 290 ... current detector, 213 ... remote control cable, 214 ... welding power source remote control, 215: Wire feeding device remote control, 216: Movement mechanism remote control, 217 ... Control cable, 218 ... Torch switch cable, 219 ... Torch switch, 220 ... Water tank, 221 ... Wire feeding device, 222 ... Suction pump.

Claims (20)

  In a pipe welding method for connecting two pipes to each other and connecting them, a root pass welding step for welding a root path, which is the inner periphery of the butt pipe, and inner surface liquid cooling for supplying a liquid refrigerant to the inner face of the pipe after the root pass welding. A step of laminating and welding the outer surface of the route path in multiple layers in the circumferential direction during the liquid cooling of the inner surface, and immediately after the molten metal after the laminating welding is solidified during the laminating welding A pipe welding method comprising: a tensile side plastic deformation imparting step for imparting a tensile side plastic deformation to a surface of a welded portion.   2. The pipe welding method according to claim 1, wherein the tensile side plastic deformation applying step is started after the lamination welding is performed to ½ the pipe thickness.   2. The pipe welding method according to claim 1, wherein the tensile side plastic deformation applying step is started after the lamination welding is performed to 3/4 of the pipe thickness.   The pipe welding method according to claim 1, wherein the pipe to be welded has a thickness of 20 mm or more.   The pipe welding method according to claim 1, wherein the pipe includes a component of an existing plant, and the liquid refrigerant that flows through the inner surface of the pipe is a fluid that flows through the pipe in the existing plant.   6. The piping according to claim 5, wherein the existing plant is a boiling water reactor, the piping is a recirculation piping of the reactor, and the refrigerant flowing on the inner surface of the piping is reactor water. Welding method.   2. The pipe welding method according to claim 1, wherein the tensile side plastic deformation imparting step includes a surface cooling step of cooling the surface of the welded portion immediately after the molten metal after the lamination welding is solidified.   8. The pipe welding method according to claim 7, wherein the surface cooling step includes a step of bringing a solid refrigerant into contact with the surface.   9. The pipe welding method according to claim 8, wherein the solid refrigerant is ice.   8. The pipe welding method according to claim 7, wherein the liquid refrigerant on the inner surface of the pipe and the refrigerant in the surface cooling step are both water.   2. The tensile side plastic deformation applying step according to claim 1, further comprising a tensile load applying step of applying a dynamic tensile load to the surface of the preceding pass in the middle of the lamination welding of the outer surface of the pipe. Pipe welding method.   12. The pipe welding method according to claim 11, wherein the tensile load applying step includes a step of applying a mechanical tensile load to the pass surface for each round of the lamination welding of the outer surface of the pipe.   12. The pipe welding method according to claim 11, wherein the tensile load applying step includes a step of continuously abutting a welded portion at a tip of a bundled wire and applying plastic deformation to a surface layer of the welded portion.   Root path welding means to weld two root pipes and weld the root path which is the innermost circumference of the butt pipe (first layer welding), and after this root path welding, the outer surface of the root path is laminated and welded in multiple layers in the circumferential direction A pipe welding apparatus for connecting two pipes, wherein an inner surface liquid cooling device for flowing a liquid refrigerant to the inner surface of the pipe and a molten metal after the lamination welding of the outer surface of the pipe are provided. A pipe welding apparatus comprising: a tensile-side plastic deformation imparting means for imparting a tensile-side plastic deformation to a surface of a welded portion immediately after solidification.   15. The pipe welding apparatus according to claim 14, wherein the tensile side plastic deformation imparting means includes a surface cooling device for cooling the surface of the welded portion immediately after the molten metal after the lamination welding is solidified.   16. The inner surface liquid cooling device according to claim 15, further comprising a water distribution device for flowing cooling water to the inner surface of the pipe, and the surface cooling device supplies cooling water to the surface of the welded portion immediately after the molten metal after the lamination welding is solidified. A pipe welding apparatus comprising a water cooling device for jetting.   In Claim 15, one of the two pipes is a water distribution pipe of an existing plant, the other is a water pipe for replacement, and the inner surface liquid cooling device uses water distribution by the water distribution device of the plant. The surface cooling device is provided with a water cooling device for injecting cooling water onto the surface of the welded portion immediately after the molten metal after lamination welding is solidified.   15. The tension-side plastic deformation imparting means according to claim 14, further comprising a tensile load imparting means for imparting a mechanical tensile load to the surface of the preceding pass in the middle of the lamination welding of the outer surface of the pipe. Pipe welding equipment.   15. The pipe welding apparatus according to claim 14, wherein the tensile side plastic deformation imparting means is configured to start operation after being laminated and welded to the vicinity of 3/4 of the pipe thickness. In a pipe welding apparatus that butts two pipes together and connects them, means for welding a route path that is the inner periphery of the butt pipe, an inner surface cooling device that flows cooling water to the inner surface of the pipe after route path welding, and this inner surface cooling Laminating welding means for laminating and welding the outer surface of the root path across a plurality of layers in the circumferential direction, and an outer surface cooling device for cooling the surface of the welded portion immediately after the welding torch passes and the molten metal solidifies The outer surface cooling device is fixed to a jig together with a welding torch, and a jet nozzle that supplies the coolant to the surface of the welded portion, and is arranged around the jet nozzle to supply the coolant. A pipe welding apparatus comprising a suction nozzle for recovery.

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