JP4847885B2 - Method for reducing residual stress in piping - Google Patents

Description

  The present invention relates to a heat treatment method for reducing the residual stress of a pipe generated by welding or bending, and particularly to a technique for a small diameter pipe.

  As typical methods for reducing the residual stress after pipe welding or bending, Patent Document 1 and Patent Document 2 can be cited. These patent documents describe a heat treatment method in which a refrigerant is preliminarily present on the inner surface of a pipe, the outer surface of the pipe is heated to generate a temperature difference between the inner and outer surfaces of the pipe, the inner surface is pulled to yield, and the outer surface is compressed to yield. Has been.

  Patent Document 3 discloses a heating / cooling process in which a refrigerant is not previously present on the inner surface of a pipe, and the inner surface of the pipe is heated for a predetermined time so as to be in the same temperature state in the creep temperature region, and then the inner surface of the pipe is cooled with the refrigerant. A heat treatment method is shown in which the residual stress in the vicinity of the welded portion or in the vicinity of the bending process can be changed into a compressive residual stress. The heat treatment method includes a heating source that heats an outer surface of a pipe, a heating source controller that controls heating of the pipe by the heating source in a creep temperature region for a predetermined time, and a refrigerant supply that supplies a refrigerant to the inner surface of the pipe And a heat treatment control device for supplying a refrigerant to the inner surface of the pipe after heating for the predetermined time.

  Further, Patent Document 4 mentions a method of heating the outer surface of the pipe to reduce the residual stress of the pipe, and has a feature that a laser is used as a means for heating the outer surface of the pipe.

JP-A-52-130409 JP-A-52-70914 Japanese Patent Laying-Open No. 2005-320626 JP 2006-37199 A

  Heat generated by welding, residual stress generated with processing history, or tensile residual stress generated by bending is a major factor in fatigue strength reduction, stress corrosion cracking, and progress. By compressing or reducing the tensile residual stress at a site where the above-mentioned damage is a concern, it is possible to suppress damage due to fatigue and stress corrosion cracking.

  The technique of performing heat treatment represented by Patent Document 1 and Patent Document 2 on the tensile residual stress acting on the inner surface of the pipe is a large pipe that allows the refrigerant to exist on the inner surface of the pipe in advance. It is effective for a piping system having a small diameter, but a thin-walled small-diameter piping cannot be expected to have a sufficient effect.

  When the inner surface of the pipe is cooled with cooling water while the pipe is kept at a high temperature in Patent Document 3, the amount of heat input to the cooling water is large in the case of a small diameter pipe with a small diameter and a small amount of cooling water supplied to the pipe. Therefore, the boiling state becomes film boiling, and the heat transfer rate may be drastically reduced. When the heat transfer rate decreases, the temperature difference between the inner and outer surfaces of the pipe becomes smaller, and the difference in thermal expansion between the inner and outer surfaces becomes smaller, so the effect of reducing the residual stress is reduced. In addition, in a pipe group in which pipes are installed adjacent to each other at a narrow interval (hereinafter referred to as a collecting pipe), it is difficult to uniformly install a band-type electric heater or the like at a target portion of each pipe, and temperature unevenness occurs. May occur and the residual stress reduction effect may vary.

  The method of reducing the residual stress by laser irradiation in Patent Document 4 may be difficult to apply in the pipe group (collecting pipe) as described above due to interference between adjacent pipes.

  In nuclear power plants, austenitic stainless steel piping is used for high-temperature piping around the nuclear reactor. In addition, piping around the reactor is often installed adjacent to each other with a narrow interval. The small-diameter pipe here has an outer diameter of 77 mm or less and a wall thickness of about 8 mm or less.

  The present invention has been made in view of the above situation, and its problem is to improve the residual stress reduction effect and reduce the variation in construction effect when performing a process for reducing the residual stress for small diameter pipes. There is to plan.

The present invention provides a procedure for heating a residual stress reduction target portion of a pipe to a desired temperature, a procedure for supplying pressurized gas to a sealed container containing cooling water and pressurizing the cooling water, and the desired temperature. A procedure for passing the pressurized cooling water through the heated piping target portion at a flow rate and pressure that does not cause film boiling at least at a location where the cooling water contacts the inner surface of the heated piping target portion. made has, to achieve the above object by a tensile residual stress reduction method distribution pipe surface.

  After the residual stress reduction target location near the pipe weld is heated to a desired temperature, pressurized cooling water is passed through the pipe inner surface of the target location to cool the pipe inner surface of the target location. On the inner surface of the pipe at the target location, the cooling water is heated and boiled by the heat of the pipe, but the heat from the inner surface of the pipe to the cooling water is maintained by maintaining the flow rate and pressure of the cooling water so that the boiling state does not become film boiling. A decrease in transmission rate is avoided. Thus, the cooling efficiency of the inner surface of the pipe can be maintained at a high value, the temperature gradient of the inner and outer surfaces of the pipe can be increased, and the ability to reduce the tensile residual stress acting on the inner surface of the pipe can be improved.

  By using a sealed container that is pressurized inside with pressurized gas as the source of cooling water flowing through the piping, there is no need for a temporary pump for cooling water flow or power supply equipment for that purpose. The installation to the piping equipment becomes easy.

  In addition, when heating the pipe of the target location, an oil container is provided to immerse the pipe including the residual stress reduction target location, and the oil adjusted to the heating target temperature of the pipe is supplied to the oil container, so that Heat the pipe to the target temperature. Filling the heated oil with an oil container that surrounds the piping, even when the piping is arranged at narrow intervals, the circumference of each piping is covered with heated oil, and the whole is heated to a uniform temperature Is possible. After heating to a uniform temperature, the tensile residual stress acting on the pipe inner surface can be efficiently reduced by supplying cooling water into the pipe in the same manner as the method for reducing the tensile residual stress.

  According to the present invention, it becomes possible to cool the inner surface of the pipe as a boiling state with a high heat transfer rate in the cooling of the inner surface of the pipe at the construction site after heating the construction site near the pipe weld to a uniform temperature. . As a result, a temperature difference between the pipe inner surface and the outer surface can be efficiently created, and the tensile residual stress acting on the pipe inner surface of the collecting pipe can be reduced.

  Further, according to the present invention, it is possible to uniformly heat the pipe temperature at the construction site even in the heating of the collecting pipe where the pipes are adjacent to each other narrowly. Thereby, the dispersion | variation in a construction effect can be made small.

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

  FIG. 1 is a conceptual diagram illustrating an example of a configuration of a main part of an apparatus that performs a tensile residual stress reduction method according to Embodiment 1 of the present invention. The illustrated apparatus accommodates cooling water and seals an airtight container (hereinafter referred to as a pressurizer) 8 that pressurizes the cooling water, and an oil container 23 that is installed so as to accommodate and immerse a pipe 28 to be subjected to reduction of tensile residual stress. A heating oil supply device 22 connected to the oil container 23 by oil pipes 31 and 32 and supplying heated oil to the oil container 23; one end of the pressurizer 8 and the pipe 28 is connected to a header pipe 29; And a cooling water supply pipe 14 connected via the. In FIG. 1, details such as the control device and the power source are omitted. Further, although not shown in the drawing, a cooling water recovery pipe interposing a cooling water recovery valve is temporarily connected to the other end of the pipe 28.

  The pressurizer 8 is a cylindrical container configured to withstand internal pressure, and a compressed air supply pipe 34 for pressurization is connected to the upper part, and a pressurized valve 9 is interposed in the compressed air supply pipe 34. Yes. An air compressor 35 is connected to the compressed air supply pipe 34 via a pressure reducing valve so that compressed air can be supplied. An upper valve 10 for releasing compressed air to the atmosphere and a pressure gauge 13 for measuring and displaying the pressure inside the pressurizer 8 are connected to the upper portion of the pressurizer 8. In addition, a cooling water intake pipe 12 having a cooling water intake valve 36 interposed in the upper part of the pressurizer 8 and a cooling water supply pipe 14 having a cooling water supply valve 11 interposed in the bottom of the pressurizer 8. Are connected to each other. Further, a liquid level gauge (not shown) for displaying the liquid level inside the pressurizer is provided.

  The oil container 23 is installed so as to surround the lower side and the side of the pipe 28 to be subjected to tensile residual stress reduction, and is filled with heating oil. In the present embodiment, since the construction is performed on an existing pipe group, although the details are omitted, the container is an assembly-type container having an open upper surface. The oil container 23 is connected at one end to an oil pipe 31 for supplying oil at the upper part and an oil pipe 32 for taking out oil at the lower part. A thermometer (not shown) for measuring the oil temperature is also attached to the bottom of the oil container 23.

  The heating oil supply device 22 includes a heater 24 that heats oil, an oil supply pipe 30 that has one end connected to the heater 24, an oil supply pipe 30, and a discharge side facing the heater 24. An oil supply pump 25 mounted, an oil valve 26d interposed in an oil supply pipe 30 on the downstream side of the oil supply pump 25, oil pipes 31 and 32 connecting the heater 24 and the oil container 23, and An oil valve 26 a interposed in the oil pipe 31, an oil circulation pump 27 interposed in the oil pipe 32 with the discharge side facing the heater 24, and an oil circulation pump 27 downstream of the oil pipe 32. The oil valve 26 b, one end of which is branched and connected between the oil circulation pump 27 of the oil pipe 32 and the oil valve 26 b, and the oil valve 26 c interposed in the oil drain pipe 33. And.

  The heater 24 is a hermetically sealed casing with a heating source inside, and the oil supply pipe 30 and the oil pipes 31 and 32 are connected to the casing. The other ends of the oil supply pipe 30 and the oil extraction pipe 33 are connected to an oil tank (not shown).

  Hereinafter, a procedure for reducing the tensile residual stress of the target pipe using the apparatus configured as described above will be described.

  As initial conditions, the pressurizing valve 9 is fully closed, the opening valve 10 and the cooling water recovery valve are fully opened, and the cooling water supply valve 11 and the cooling water intake valve 36 are fully closed. The oil valves 26a, 26b, 26c, and 26d are fully closed. The open / closed state of the valve shown in FIG. 1 is the state at this point.

  First, the cooling water intake valve 36 is opened, and cooling water is taken in until the liquid level inside the pressurizer 8 reaches a predetermined position. When the liquid level inside the pressurizer 8 reaches a predetermined position, the cooling water intake valve 36 is closed, and then the release valve 10 is closed.

  Next, the pressurized valve 9 is opened, and the compressed air reduced to a predetermined pressure is sent into the pressurizer 8. In this state, the cooling water inside the pressurizer 8 is pressurized to a predetermined pressure, and when the cooling water supply valve 11 is opened, the cooling water is fed into the pipe 28.

  Next, the piping 28 is heated with oil. First, the oil valves 26 a, 26 b and 26 d are opened, the oil supply pump 25 is driven, and heating oil is supplied to the oil container 23 via the heater 24 and the oil pipe 31. At the same time, the heater 24 is activated and the passing oil is heated. When the oil level in the oil container 23 is a desired oil level, that is, the pipe 28 to be treated is covered with oil, the oil supply pump 25 is stopped, the oil valve 26d is closed, and the oil circulation pump 27 Is activated.

  The oil in the oil container 23 is driven by the oil circulation pump 27 and circulates through the oil pipe 32, the heater 24, the oil pipe 31, and the oil container 23, and is heated by the heater 24 in the process to be heated. . The heating amount of the heater 24 is controlled so that the temperature detected by the oil thermometer maintains a desired temperature. Heating is continued until the outer surface temperature of the pipe 28 reaches a desired temperature by the high-temperature oil supplied into the oil container 23. It is desirable to provide a means for measuring the outer surface temperature of the pipe 28 in advance so that it can be confirmed that the outer surface temperature of the pipe 28 has reached a desired temperature.

  When the outer surface temperature of the pipe 28 reaches a desired uniform temperature, or when a predetermined time elapses after the display temperature of the oil thermometer reaches the desired temperature, the cooling water supply valve 11 is opened. When the cooling water supply valve 11 is opened, the cooling water in the pressurizer 8 is pressurized to the pressure of the compressed air, and thus flows into the pipe 28 through the cooling water supply pipe 14 and the header pipe 29 at the normal temperature. Then, it passes through the pipe 28 and flows out from the cooling water recovery pipe. At this time, the gas pressure in the pressurizer 8 decreases as the cooling water in the pressurizer 8 flows out. However, as the gas pressure decreases, the pressure reducing valve operates and compressed air is supplied from the air compressor 35 to the pressurizer 8. Flow into. Therefore, the cooling water always flows out at the same pressure.

  In the pipe 28 that is heated with oil from the outer surface side of the pipe and the outer surface side is maintained at a desired temperature, the inner surface side is cooled by the cooling water flowing through the inner surface of the pipe. At this time, the inner surface of the pipe is cooled while boiling the cooling water. However, when the boiling state becomes a film boiling state, the heat transfer rate from the inner surface of the pipe to the cooling water is reduced, and cooling is not effectively performed. In the present embodiment, the internal pressure of the pressurizer 8 is set so that the cooling water flow rate becomes a flow rate and pressure so that the boiling state of the inner surface of the pipe does not become a film boiling state. At this time, the flow rate and pressure of the cooling water flowing through the pipe 28 may be adjusted by adjusting the opening of the cooling water recovery valve.

  As a result, the inner surface of the pipe is cooled to room temperature by the cooling water, and a temperature difference is generated between the inner surface and the outer surface of the pipe.

  The pressurizer 8 stocked with a sufficient amount of cooling water to cool the inner surface of the pipe to the normal temperature supplies the cooling water until the inner surface of the collecting pipe reaches the normal temperature, and further maintains the state at the normal temperature in advance. After holding for a predetermined time, heating of the oil by the heater 24 is stopped. The state of the temperature of the inner surface of the collecting pipe can be known, for example, by measuring the temperature of the cooling water flowing into the cooling water recovery pipe.

  At the same time as the heating of the oil by the heater 24 is stopped, the cooling water supply valve 11 is closed to stop the supply of cooling water, and the cooling process ends. By generating a temperature difference between the outer surface and the inner surface of the pipe 28, the tensile residual stress acting on the inner surface in the vicinity of the welded portion of the pipe 28 is reduced.

  The temperature gradient between the inner and outer surfaces of the pipe is determined by the temperature difference between the inner and outer surfaces of the pipe and the thickness of the pipe. Since the temperature gradient necessary for reducing the tensile stress is known, the necessary temperature gradient can be obtained by setting the desired temperature according to the thickness of the pipe 28.

  When the work of reducing the tensile residual stress is completed, the oil valve 26b is closed, the oil valve 26c is opened, and the oil in the oil container 23 is passed through the oil extraction pipe 33 by the oil circulation pump 27 to the oil tank (not shown). It is taken out.

  3 and 4 are flowcharts showing the above procedure. Here, a case where tensile stress reduction is performed on the installed pipe 28 shown in FIG. 1 will be described.

  First, the oil container 23 surrounding the pipe 28 is installed (procedure 1). The oil container 23 is an assembly type that combines a plurality of panels.

  The pressurizer 8 is installed and related piping is connected (procedure 2). That is, a cooling water intake pipe 12 that connects the cooling water source and the pressurizer 8 via the cooling water intake valve 36, and a cooling water supply pipe 14 that connects the header pipe 29 and the pressurizer 8 via the cooling water supply valve 11 respectively. Install. A cooling water recovery pipe having a cooling water recovery valve interposed is connected to the end of the pipe 28 opposite to the header pipe 29. Also, an air compressor 35 is installed, and a compressed air supply pipe 34 that connects the air compressor 35 and the pressurizer 8 via the pressure reducing valve and the pressure valve 9 is installed.

  Next, the heating oil supply device 22 is installed, and the oil pipes 31 and 32 are connected to the oil container 23 (procedure 3). An oil tank containing heating oil is installed, and the oil tank and the heating oil supply device 22 are connected by an oil supply pipe 30 and an oil extraction pipe 33 (procedure 4). Further, a power source for driving the pump, a power source for the heater 24, and a necessary control device are installed (procedure 5).

  The open / close state of each valve is set to a predetermined initial condition (procedure 6). Cooling water is supplied to the pressurizer 8 to pressurize it (procedure 7). The oil supply pump 25 is activated to supply oil for heating the oil tank to the oil container 23 via the heater 24, and at the same time, the heater 24 is operated to heat the passing oil (procedure 8). When it is confirmed that the oil level in the oil container 23 is at a desired position, that is, the position where the pipe 28 to be treated is covered with oil (procedure 9), the oil supply is stopped and the oil is circulated. (Step 10). That is, the oil supply pump 25 is stopped, the oil valve 26d is closed, and the oil circulation pump 27 is activated.

  When the oil thermometer indicates a desired temperature (procedure 11), the heater 24 is controlled to maintain the temperature (procedure 12). When a preset time has elapsed (procedure 13), the cooling water supply valve 11 is opened, and the cooling water is passed through the pipe 28 (procedure 14). The pressurizer 8 stocked with a sufficient amount of cooling water to cool the inner surface of the pipe to room temperature supplies the cooling water to the pipe 28 until the inner surface of the pipe 28 reaches room temperature and a predetermined time elapses. , Let it flow.

  It is confirmed whether or not the temperature of the inner surface of the pipe has reached a desired temperature condition (procedure 15), and after the set time has elapsed since the desired temperature condition was reached (procedure 16), oil heating by the heater 24 is stopped. The cooling water supply valve 11 and the cooling water recovery valve are closed (procedure 17). Next, oil is extracted from the oil container and transferred to the oil tank (procedure 18), and temporary facilities such as the pressurizer 8, the oil container 23, and the heating oil supply device 22 are removed (procedure 19).

  In the present embodiment, it is possible to uniformly heat the pipe temperature at the construction site even in the heating of the pipe where the pipes are narrowly adjacent to each other. Thereby, the dispersion | variation in a construction effect can be made small.

  Next, a second embodiment of the residual tensile stress reduction method according to the present invention will be described with reference to FIG. The present embodiment is different from the first embodiment in that the target small-diameter pipes are collecting pipes arranged in parallel at a narrow interval, and the other configurations are the same. About the structure, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  In the present embodiment, the pipe immersed in the heating oil filled in the oil container 23 is a small diameter pipe connected to the core of the nuclear power plant, and the small diameter pipe is a pair of header pipes 29. Is a collecting pipe arranged so as to be connected through a pressure pipe of the core. The other header tube corresponding to the header tube shown is behind the header tube shown. That is, FIG. 2 shows a collecting pipe provided with two pairs of header pipes, and the oil container 23 is installed so as to surround the entire collecting pipe shown in the figure. A cooling water supply pipe 14 is connected to one of the header pipes 29 shown in the upper part of the collecting pipe, and a cooling water recovery pipe is provided on the other side of the header pipe 29 with a cooling water recovery valve not shown. Is connected. The small diameter pipe constituting the collecting pipe is an austenitic stainless steel pipe having an outer diameter of 77 mm or less and a wall thickness of 8 mm or less.

  FIG. 2 shows a case where processing is performed on small-diameter pipes connected to the header pipes shown on the left side of the two pairs of header pipes 9 in the drawing. The work procedure is the same as that described in the first embodiment, and a description thereof will be omitted.

  In the present embodiment, it is possible to reduce the residual tensile stress acting on the inner surface of the pipe at the construction target location of a large number of collecting pipes with a single construction for the collecting pipe connecting the two header pipes. .

It is a conceptual diagram which shows the principal part structure of Example 1 of the apparatus which implements the tensile residual stress reduction method which concerns on embodiment of this invention. It is a conceptual diagram which shows the principal part structure of Example 2 of the apparatus which implements the tensile residual stress reduction method which concerns on embodiment of this invention. It is a flowchart which shows the example of the procedure of the tension | pulling residual stress reduction method which concerns on embodiment of this invention. It is a flowchart which shows the example of the procedure of the tension | pulling residual stress reduction method which concerns on embodiment of this invention.

Explanation of symbols

8 Pressurizer 9 Pressurizing valve 10 Opening valve 11 Cooling water supply valve 12 Cooling water intake piping 13 Pressure gauge 14 Cooling water supply piping 22 Heating oil supply device 23 Oil container 24 Heater 25 Oil supply pumps 26a, 26b, 26c, 26d Oil valve 27 Oil circulation pump 28 Pipe 29 Header pipe 30 Oil supply pipe 31, 32 Oil pipe 33 Oil extraction pipe 34 Compressed air supply pipe 35 Air compressor 36 Cooling water intake valve

Claims (3)

A procedure for heating the target portion for reducing the residual stress of the piping from the outer surface side to a desired temperature, a procedure for supplying pressurized gas to a sealed container containing cooling water and pressurizing the cooling water, and heating to the desired temperature A procedure for passing the pressurized cooling water through the residual stress reduction target portion at a flow rate and pressure that does not cause film boiling at least at a location where the cooling water contacts the inner surface of the heated pipe target portion. tensile residual stress reduction method distribution pipe surface ing a and. In tensile residual stress reduction method distribution pipe surface according to claim 1, wherein, when heating the residual stress reduction target portion of the pipe from the outer surface side to the desired temperature, lower and side of the pipe containing the residual stress reduction target portion the oil container surrounding provided, by supplying the oil heated to at least the desired temperature to the oil container, tensile distribution pipe surface you characterized by heating the pipe containing the residual stress reduction target portion remaining Stress reduction method. In tensile residual stress reduction method as claimed in claim 1 or 2 distribution pipe surface according, before Sharing, ABS pipe, a collecting pipe comprising a plurality of tubes communicating between the two header pipes, the cooling water, the header tensile residual stress reduction method distribution pipe surface you characterized in that it is supplied to the collecting pipe via a tube.

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