Plug, piping structure, and plug installation method

Abstract

To provide a plug capable of sealing gas for back shield with the plug itself, a piping structure, and an installation method for the plug.SOLUTION: A plug 1 closes a through hole 51 formed on a pipe 50 from an outer peripheral surface side of the pipe 50 and includes: a columnar nozzle part 20 extending in an axis X direction; and a seal part 30 which is connected to the nozzle part 20 and defines a retention space S for retaining gas between itself and the nozzle part 20 in the through hole 51. The seal part 30 has: a shaft part 31 whose diameter is smaller than an inner diameter of the through hole 51 and whose base end is connected to the nozzle part 20; and a disc part 32 connected to an end of the shaft part 31 in accordance with an inner shape of the through hole 51.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a plug, a piping structure, and a method for installing the plug. [Background technology]

[0002] A large boiler used in a power plant or the like has a hollow furnace that is installed vertically, and a plurality of combustion burners are arranged on the furnace wall along the circumferential direction of the furnace. The boiler is connected to a flue vertically above the furnace, and a heat exchanger for generating steam is arranged in the flue. The combustion burner injects a mixture of fuel and air (oxidizing gas) into the furnace to form a flame, and combustion gas is generated and flows into the flue. A heat exchanger is installed in the area where the combustion gas flows, and water or steam flowing inside a heat transfer tube that constitutes the heat exchanger is heated to generate superheated steam.

[0003] Steam systems used in power plants with boilers are constructed by connecting multiple pipes together by welding. In this case, radiographic testing may be performed to check the soundness of the joints (presence or absence of defects). For this reason, through-holes are drilled near the joints to insert radiographic testing equipment (radiation sources) into the inside of the pipes. Radiographic testing is usually performed only once after welding, and the drilled through-holes must be sealed after the radiographic testing is completed.

[0004] As a method for closing a through hole, for example, a closing plug is disclosed in Patent Document 1. The closing plug in Patent Document 1 is fixed to the pipe by welding. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-158823 A Summary of the Invention [Problem to be solved by the invention]

[0006] When welding a plug to a pipe, back shielding may be performed to suppress oxidation of the inner surface of the weld and improve the quality of the weld. An example of a method for performing back shielding is to use a balloon to prevent the diffusion of the back shielding gas (e.g., an inert gas such as nitrogen or argon) inside the pipe. However, this method requires a lot of work to install and remove the balloon, so it is preferable to seal in the back shielding gas in the simplest possible way.

[0007] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a plug, a piping structure, and a method for installing a plug that is capable of sealing in a back shielding gas by the plug itself. [Means for solving the problem]

[0008] In order to solve the above problems, the plug, piping structure, and plug installation method of the present disclosure employ the following measures. That is, a plug according to one aspect of the present disclosure is a plug that closes a through hole formed in a piping from the outer peripheral surface side of the piping, and includes a columnar nozzle portion extending in the axial direction, and a sealing portion that is connected to the nozzle portion and defines a retention space for retaining gas between the nozzle portion and the sealing portion within the through hole.

[0009] A piping structure according to an embodiment of the present disclosure includes a piping having a through hole; the above and a plug, the sealing portion of the plug being inserted into the through hole.

[0010] Moreover, a method for installing a plug according to one aspect of the present disclosure is a plug that blocks a through hole formed in a piping from an outer peripheral surface side of the piping, the plug having a columnar nozzle portion extending in an axial direction and a sealing portion that is connected to the nozzle portion and defines a retention space for retaining gas between the nozzle portion and the through hole, the method including a step of supplying a gas used for back shielding during welding to the retention space. Effect of the Invention

[0011] According to the present disclosure, the gas for the back shield can be sealed in by the plug itself. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing a steam, condensate, and feedwater system in a boiler power plant. [Diagram 2] FIG. 2 is a side view of a plug according to an embodiment of the present disclosure. [Diagram 3] FIG. 2 is a longitudinal cross-sectional view of a plug according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is a plan view of a plug according to an embodiment of the present disclosure. [Diagram 5] FIG. 13 is a bottom view of a plug according to an embodiment of the present disclosure. [Figure 6] FIG. 2 is a longitudinal and circumferential cross-sectional view of a pipe with a plug installed according to an embodiment of the present disclosure. [Figure 7] 7 is a cross-sectional view taken along line VII-VII shown in FIG. 6. [Figure 8] 1 is a longitudinal and circumferential cross-sectional view of a pipe to which a plug is secured by welding according to an embodiment of the present disclosure. FIG. [Figure 9] FIG. 13 is a reference diagram illustrating the concept of a stress concentration portion. [Figure 10] FIG. [Figure 11] FIG. 13 is a diagram showing the relationship between the damage level Dc at the stress concentration portion and the weld toe and the protruding weld leg length Lw. [Figure 12] FIG. 1 is a diagram showing the relationship between the damage degree Dc at the stress concentration portion and the weld toe and the weld toe radius Rw. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] [About boiler power plants] First, a boiler power plant in which a plug according to an embodiment of the present disclosure is installed will be described with reference to FIG.

[0014] FIG. 1 is a schematic diagram showing the steam, condensate, and feedwater systems in a boiler power plant. The boiler power plant includes boiler heat exchangers 102, 103, and 104, a steam turbine 110 that is rotationally driven by steam generated by the boiler, and a generator 115 that is connected to the steam turbine 110 and generates electricity in response to the rotation of the steam turbine 110.

[0015] The steam turbine 110 is composed of, for example, a high-pressure turbine 111, an intermediate-pressure turbine 112, and a low-pressure turbine 113, and steam from reheaters 105 and 106 described below flows into the intermediate-pressure turbine 112 and then flows into the low-pressure turbine 113.

[0016] A condenser 114 is connected to the low-pressure turbine 113, and the steam that rotates and drives the low-pressure turbine 113 is cooled by cooling water (e.g., seawater) in the condenser 114 to become condensed water. The condenser 114 is connected to the economizer 107 via a water supply system L1.

[0017] The feedwater system L1 is provided with, for example, a condensate pump (CP) 121, a low-pressure feedwater heater 122, a boiler feedwater pump (BFP) 123, and a high-pressure feedwater heater .

[0018] A portion of the steam that drives the steam turbine 110 is extracted and supplied to the high-pressure feedwater heater 124 and the low-pressure feedwater heater 122 as a heat source via an extraction system not shown, and the feedwater supplied to the coal economizer 107 is heated.

[0019] The following description will be given taking as an example a case where the boiler is a once-through boiler. The economizer 107 is connected to each evaporation tube of the furnace wall 101. The feed water heated by the economizer 107 is heated by radiation from the flame in the furnace when passing through the evaporation tube of the furnace wall 101, and is led to the steam separator 126. The steam separated in the steam separator 126 is supplied to the superheaters 102, 103, and 104, and the drain water separated in the steam separator 126 is led to the condenser 114 via the drain water system L2.

[0020] When the combustion gas flows through the combustion gas passage (flue) 13, heat of the combustion gas is recovered by the superheaters 102, 103, 104, the reheaters 105, 106, and the economizer 107. Meanwhile, the feed water supplied from the boiler feed pump (BFP) 123 is preheated by the economizer 107, and then heated as it passes through each evaporator tube of the furnace wall 101 to become steam, and is led to the steam separator 126.

[0021] The steam separated in the steam separator 126 is introduced into the superheaters 102, 103, and 104, and is superheated by the combustion gas.

[0022] The superheated steam generated in the superheaters 102, 103, and 104 is supplied to the high-pressure turbine 111 via a steam line L3, and drives the high-pressure turbine 111 to rotate.

[0023] The steam discharged from the high-pressure turbine 111 is introduced into the reheaters 105, 106 via a steam line L4 and is superheated again. The re-superheated steam is supplied to the low-pressure turbine 113 via the intermediate-pressure turbine 112 via a steam line L5, and drives the intermediate-pressure turbine 112 and the low-pressure turbine 113 to rotate.

[0024] The rotating shaft of each of the steam turbines 111, 112, 113 is connected to a generator 115. When the rotating shaft of each of the steam turbines 111, 112, 113 rotates, the generator 115 is rotated and electricity is generated. The steam discharged from the low-pressure turbine 113 is cooled in the condenser 114 to become condensed water, and is sent again to the economizer 107 via the water supply system L1.

[0025] In the piping 50 constituting each steam system of the boiler power plant as described above, plugs 1 for closing through holes 51 drilled for inserting a radiation source are installed at multiple locations. For example, in the figure, plugs are installed at location P on each steam system. Note that location P in the figure is merely an example and does not represent all installation locations.

[0026] [About the plug] Next, the plug 1 according to an embodiment of the present disclosure will be described with reference to FIGS. Fig. 2 is a side view of the plug 1. Fig. 3 is a vertical sectional view of the plug 1. Fig. 4 is a plan view of the plug 1. Fig. 5 is a bottom view of the plug 1.

[0027] The plug 1 is a metal member. Examples of the metal forming the plug 1 include chromium-containing alloy steels such as 12Cr steel, 9Cr steel, and 2Cr steel. Here, in consideration of ease of welding, it is preferable that the metal material forming the plug 1 is the same as or similar to the metal material forming the pipe 50 described below.

[0028] As shown in FIGS. 2 to 5, the plug 1 includes a nozzle portion 20, a sealing portion 30, and a groove portion 40.

[0029] The nozzle portion 20 is a cylindrical portion extending along the direction of the axis X. The nozzle portion 20 has a bottom surface 22. The bottom surface 22 is a surface facing the pipe 50 (specifically, the through hole 51) when the plug 1 is installed in the pipe 50 described later (see FIG. 6). The sealing portion 30 and the groove portion 40 are connected to the bottom surface 22. The diameter of the nozzle portion 20 is larger than the inner diameter of a through hole 51 formed in the pipe 50 described later (see FIG. 6), and is, for example, about φ100 mm to φ130 mm. The diameter of the nozzle portion 20 is also the maximum outer diameter of the plug 1.

[0030] The sealing portion 30 is a portion formed so as to extend from the bottom surface 22 of the nozzle portion 20 . When the plug 1 is installed in a pipe 50 described later, the sealing portion 30 is inserted into a through hole 51 formed in the pipe 50 described later (see FIG. 6). The sealing portion 30 has a shaft portion 31 and a disk portion 32 .

[0031] The shaft portion 31 is a columnar portion extending along the direction of the axis X, and has a base end connected to the bottom surface 22 of the nozzle stub portion 20 and integrated with the nozzle stub portion 20. In consideration of ease of manufacture, the shaft portion 31 is preferably cylindrical. The diameter of the shaft portion 31 is smaller than the inner diameter of a through hole 51 formed in a pipe 50 described later (see FIG. 6). For example, if the inner diameter of the through hole 51 is about φ50 mm, the diameter of the shaft portion 31 is about φ20 mm.

[0032] The disk portion 32 is a plate-shaped portion that is connected to the tip of the shaft portion 31 and is integrated with the shaft portion 31 . When the sealing portion 30 is inserted into the through hole 51, the disk portion 32 defines a space (retention space S) between the nozzle portion 20 and the sealing portion 30 (see FIG. 6). The shape of the disk portion 32 corresponds to the cross-sectional shape of the through hole 51 perpendicular to the axis X (see FIG. 6). Note that the corresponding shape does not mean a completely identical shape, but a shape with a gap that allows the disk portion 32 to be smoothly inserted into the through hole 51. For example, if the inner diameter of the through hole 51 is about φ50 mm, the diameter of the disk portion 32 is about φ49.8 mm. In other words, a gap of 0.1 mm is provided on both radial sides between the disk portion 32 and the through hole 51. This gap is not limited to 0.1 mm, but if it is too large, the gas for back shielding described later will be more likely to leak, and the steam flowing inside the pipe 50 and foreign matter contained in the steam will be more likely to penetrate. For this reason, the dimensions of the disk portion 32 must be set so that the gap is not too large. Specifically, in order to suppress the intrusion of steam and foreign matter contained in the steam, it is preferable that each of the gaps on both radial sides is 0.4 mm or less, and the closer to 0.1 mm the more preferable.

[0033] The groove portion 40 is a portion formed on the front end 11 side of the plug 1 so as to protrude from the bottom surface 22 of the nozzle portion 20 . The groove portion 40 has a groove surface 41 and a straight surface 42 .

[0034] The groove surface 41 is an inclined surface whose diameter decreases from the outer circumferential surface of the nozzle portion 20 toward the axis X in the direction from the base end 12 to the tip end 11 of the plug 1. The groove surface 41 is formed in an annular shape in the circumferential direction about the axis X.

[0035] The straight surface 42 is a surface connected to the tip (the end portion close to the axis X) of the groove surface 41 near the bottom surface 22 of the plug 1, and extends along the direction of the axis X in the direction from the tip 11 toward the base end 12 of the plug 1. The straight surface 42 is parallel or approximately parallel to the axis X. Similar to the groove surface 41, the straight surface 42 is formed in an annular shape in the circumferential direction about the axis X. The straight surface 42 preferably has a length in the direction of the axis X of 10 mm to 14 mm. If the length is 9 mm or less, welding defects may occur. If the length is 15 mm or more, machining of the straight surface 42 may become difficult.

[0036] The base end of the straight surface 42, the tip of which is connected to the groove surface 41, is connected to the bottom surface 22 via a quarter-circular round surface 44. For example, if the outer diameter of the plug 1 (i.e., the diameter of the nozzle stub portion 20) is 110 mm and the thickness dimension (the radial thickness from the straight surface 42 to the outermost peripheral surface of the nozzle stub portion 20) is 30 mm, the radius of the rounded surface 44 is preferably 4 mm or less. The value of 4 mm is the minimum value within the range of dimensions that can ensure the length of the straight surface 42 to eliminate defects during welding and satisfy the lifespan (e.g., 240,000 hours). The radius of the rounded surface 44 is determined within the above-mentioned range of dimensions so that the straight surface 42 is located radially outward of the inner diameter of a through hole 51 formed in a piping 50, which will be described later.

[0037] By the groove surface 41 and the straight surface 42 formed as described above, a groove portion 40 protruding so as to be pointed in a V shape is formed at the lower part of the plug 1. The groove portion 40 is formed in an annular shape in the circumferential direction about the axis X, similar to the groove surface 41 and the straight surface . The groove portion 40 is formed so as to protrude toward the pipe 50 when the plug 1 is installed in the pipe 50 described below. This can ensure good penetration of the molten metal when welding to the pipe 50, and can suppress the occurrence of unwelded parts in parts to be welded. At the tip of the groove portion 40, a root surface 43 may be formed between the groove surface 41 and the straight surface 42.

[0038] [About piping structures] Next, the structure of the pipe 50 in which the plug 1 is installed will be described with reference to FIGS. Fig. 6 is a longitudinal (right side of axis X in the figure) and circumferential (left side of axis X in the figure) cross-sectional view of a pipe 50 in which a plug 1 is installed. Fig. 7 is a cross-sectional view taken along line VII-VII shown in Fig. 6. Fig. 8 is a longitudinal and circumferential cross-sectional view of a pipe 50 to which a plug 1 is fixed by welding. Fig. 9 is a reference diagram illustrating the concept of a stress concentration portion. Although the pipe 50 shown in FIGS. 6 and 8 is a cross-sectional view, hatching is omitted in the drawings.

[0039] The pipe 50 constitutes a steam system (L3, L5 in FIG. 1), and high-temperature and high-pressure steam flows inside the pipe 50. The wall thickness of the pipe 50 is, for example, about 25 mm to 130 mm. A through hole 51 for inserting a radiation source for radiographic testing is formed in the piping 50. The through hole 51 is a straight hole that penetrates the wall of the piping 50 in the thickness direction, and communicates between the outside and the inside of the piping 50.

[0040] The radiographic test is carried out in the vicinity of the joint between the pipes 50. For this reason, the through hole 51 is preferably formed in the vicinity of the joint between the pipes 50. In addition, if appropriate inspection can be performed by the radiation source inserted into through hole 51, through hole 51 may be formed with a gap between the joints of pipes 50.

[0041] 6, the plug 1 is installed in the pipe 50 such that at least a part of the sealing portion 30 is inserted into the through hole 51 and the groove portion 40 is abutted against the outer circumferential surface of the pipe 50. At this time, the axis X of the plug 1 approximately coincides with the axis of the through hole 51.

[0042] At this time, in the through hole 51 into which the sealing portion 30 is inserted, a retention space S is defined by the bottom surface 22 of the pipe stub portion 20, the shaft portion 31, the disk portion 32, the straight surface 42 of the groove portion 40, the rounded surface 44, and the inner peripheral surface of the through hole 51. As shown in Fig. 7, the retention space S is annular about the axis X.

[0043] The retention space S is a space for retaining gas for back shielding when the plug 1 is connected to the pipe 50 by welding. Back shielding is the first layer welding. Bead The oxygen-containing gas such as air in the space adjacent to the back surface is replaced with an inert gas. Bead It is possible to suppress the oxidation of the back surface and the occurrence of defects such as pores and cracks due to oxidation. In addition, the first layer Bead If the space adjacent to the back side is an open space, an inert gas is evacuated. In between As a result, the inert gas will diffuse and lose its oxidation suppression effect. Therefore, as described above, it is generally necessary to define a space in which the inert gas is retained by using a sealing member such as a balloon. Examples of the gas for the back shield include inert gases such as nitrogen and argon.

[0044] Here, the disk portion 32 inserted into the through hole 51 is set so that the lower surface 32a is substantially flush with the inner circumferential surface of the pipe 50. This reduces the step between the lower surface 32a and the inner circumferential surface of the pipe 50, making it difficult for foreign matter contained in the steam to adhere. In addition, the disk portion 32 can be prevented from blocking the flow of steam flowing inside the pipe 50. Furthermore, by not blocking the flow of steam, turbulence of the steam flow near the disk portion 32 is suppressed, so that the amount of steam that enters the retention space S through the gap between the through hole 51 and the disk portion 32 and the amount of foreign matter contained in the steam can be reduced. In addition, since the disk portion 32 is brought closer to the inner circumferential surface of the pipe 50, the volume of the retention space S can be secured as large as possible. The lower surface 32a refers to the surface of the disk portion 32 facing the inside of the pipe 50 (the steam flow path).

[0045] By butting the groove portion 40 against the outer peripheral surface of the pipe 50, a groove for welding is formed between the groove portion 40 and the outer peripheral surface of the pipe 50. Here, a predetermined gap (root spacing) is secured and maintained between the groove portion 40 and the outer peripheral surface of the pipe 50. The root spacing is, for example, 2 mm to 7 mm.

[0046] At this time, since the straight surface 42 is located radially outward from the inner diameter of the through hole 51 in the direction of the axis X, the outer peripheral surface of the pipe 50 is located radially inward from the tip of the groove portion 40 (part A surrounded by a dotted square in Figure 6). The outer peripheral surface of the pipe 50 from the tip of the groove 40 to the through hole 51 functions as a receiving portion for the molten metal that flows out from the gap between the tip of the groove 40 and the outer peripheral surface of the pipe 50 at the start of welding. In addition, by welding the groove 40 by butting it against the outer peripheral surface of the pipe 50, the penetration of the molten metal at the start of welding can be improved. This can prevent the occurrence of unwelded parts in the parts to be welded, and prevent the occurrence of discontinuous weld penetration shapes.

[0047] When starting welding, a heat-resistant seal is applied between the groove surface 41 of the groove portion 40 or the outer peripheral surface of the pipe 50 and the outer peripheral surface of the pipe 50 so as to cover the first layer welded area between the groove portion 40 and the outer peripheral surface of the pipe 50, and gas for back shielding is supplied to the retention space S through a gap in the seal. The air originally present in the retention space S is discharged from the gap between the disk portion 32 and the inner peripheral surface of the through hole 51 as the gas for back shielding is supplied. When the air is discharged from the retention space S and the retention space S is filled with gas for back shielding, welding is started.

[0048] Specifically, first, a first layer of welding is performed around the entire circumference of the groove 40 while removing the seal, and then, as shown in Fig. 8, molten metal is deposited between the groove face 41 and the outer peripheral surface of the pipe 50 by welding to form a weld 60, thereby connecting the plug 1 and the pipe 50. This allows the through hole 51 to be closed by the plug 1.

[0049] When forming the welded portion 60, it is preferable to position the weld toe 61 at a position farther from the axis X than the outer circumferential surface of the nozzle portion 20, that is, radially outward than the outer circumferential surface of the nozzle portion 20. With this configuration, the weld toe 61 can be located away from the stress concentration portion 53 occurring inside the piping 50 (inside the pipe wall). The weld toe 61 is the end of the welded portion 60 that contacts the pipe 50 and is the end located radially outward.

[0050] The stress concentrating portion 53 will be described below with reference to FIG. It is assumed that a tensile stress σf is applied to the long side of a flat plate 70 extending in the longitudinal direction in which a through hole 71 is formed. At this time, as is known, the stress σy acting on the center line of the flat plate 70 generates a maximum stress σmax in the longitudinal vicinity of the through hole 71 (so-called stress concentration). The maximum stress σmax is approximately three times the stress generated at the through hole point 72.

[0051] In the pipe 50, a hoop stress acts in the circumferential direction of the through hole 51 due to the pressure of the steam flowing inside. When the above-mentioned stress concentration phenomenon is applied to the pipe 50, a stress concentration portion 53 is generated in the axial direction (longitudinal direction) of the pipe 50 near the through hole 51 inside the pipe 50 (inside the pipe wall), as shown in Fig. 8.

[0052] In this embodiment, a part of the stress at the stress concentration portion 53 caused by the hoop stress can be borne by the nozzle portion 20, and the weld toe 61 is located radially outward in the direction of the axis X from the stress concentration portion 53 generated inside the pipe 50. This alleviates the stress concentration caused by the hoop stress, thereby enabling the life span of the weld toe 61 and the pipe 50 to be extended.

[0053] [Details about weld toes] In detail, the position of the weld toe 61 of the weld 60 is preferably determined as follows.

[0054] 10, the weld leg length of the weld 60 protruding radially from the outer circumferential surface of the nozzle section 20 of the plug 1 is designated as Lw. In other words, the distance along the radial direction (the radial direction of the plug 1) from the outer circumferential surface of the plug 1 to the weld toe 61 is designated as Lw.

[0055] In this case, the relationship between the weld leg length Lw and the damage degree Dc in the stress concentration portion 53, and the relationship between the weld leg length Lw and the damage degree Dc in the weld toe 61 are as shown in the graph in Fig. 11. That is, as the weld leg length Lw increases, the damage degree Dc in the stress concentration portion 53 decreases. Also, as the weld leg length Lw increases, the damage degree Dc in the weld toe 61, particularly the weld toe 61 in the circumferential direction of the pipe 50 (see Fig. 8), increases. For this reason, it is preferable to determine a range of the weld leg length Lw such that the damage degrees of both the stress concentration portion 53 and the weld toe 61 are unlikely to exceed a predetermined amount that affects the material performance. Here, the damage level Dc indicates the effect of damage on the metal structure, and indicates the degree of effect on factors that deteriorate material performance such as mechanical strength.

[0056] 10, the weld 60 in the vicinity of the weld toe 61 is preferably formed into a smoothly curved round shape. This makes it possible to suppress stress concentration at the weld toe 61.

[0057] Here, the radius of the rounded weld toe 61 is Rw. In this case, the relationship between the radius Rw and the damage degree Dc in the stress concentration part 53, and the relationship between the radius Rw and the damage degree Dc in the weld toe 61 are as shown in the graph in Fig. 12. That is, as the radius Rw increases, the damage degree Dc in the stress concentration part 53 and the damage degree Dc in the weld toe 61 decrease. For this reason, it is preferable to set the radius Rw large.

[0058] However, because the through hole 51 is formed near the joint between the pipes 50, when the position of the through hole 51 is fixed, the larger the radius Rw is set, the closer the weld toe 61 is to the joint between the pipes 50. In this case, the thermal effect when forming the weld 60 may affect the joint between the pipes 50, which is not preferable. On the other hand, when the position of the weld toe 61 is fixed, the larger the radius Rw is set, the farther the position of the through hole 51 is from the welded joint between the pipes 50. In this case, the through hole 51 is farther away from the welded joint between the pipes 50, which may cause an obstacle to the operation of inserting a radiation source through the through hole 51 for radiographic testing, and is therefore undesirable. In view of the above, it is preferable to set the radius Rw of the welded portion 60 as large as possible within a range that does not thermally affect the joint between the pipes 50 during welding and does not interfere with the operation of inserting a radiation source for radiographic testing through the through hole 51. For example, it is preferable to set the radius Rw of the welded portion 60 within a range of 10 mm to 30 mm.

[0059] This embodiment provides the following advantages. Since the plug 1 is provided with the nozzle stub part 20, which is columnar and extends in the direction of the axis X, and the sealing part 30, which is connected to the nozzle stub part 20 and defines a retention space S for retaining gas between the nozzle stub part 20 and the through hole 51, it is possible to retain gas for back shielding in the retention space S when the plug 1 is connected to the piping 50 by welding. As a result, the gas for back shielding can be sealed in well by the simple operation of simply using the plug 1, and incidental operations associated with welding the plug 1 to the piping 50 can be reduced.

[0060] In addition, the sealing portion 30 has a shaft portion 31 whose base end is connected to the pipe support portion 20 and whose diameter is smaller than the inner diameter of the through hole 51, and a disk portion 32 connected to the tip of the shaft portion 31 and whose shape corresponds to the cross-sectional shape of the through hole 51 perpendicular to the axis X. Therefore, the pipe support portion 20, the shaft portion 31, the disk portion 32 and the through hole 51 define a retention space S, and the disk portion 32 can prevent foreign matter from entering the through hole 51. Furthermore, since the disk portion 32 functions as a guide for the through hole 51, positioning of the sealing portion 30 when inserting it into the through hole 51 can be easily performed.

[0061] In addition, since the lower surface 32a of the disk portion 32 is configured to be substantially flush with the inner peripheral surface of the piping 50, there is no step between the surface of the disk portion 32 and the inner peripheral surface of the piping 50, making it difficult for foreign matter to adhere. Also, it is possible to prevent the disk portion 32 from obstructing the flow of steam flowing inside the piping 50. Furthermore, by not obstructing the flow of steam, turbulence of the steam flow near the disk portion 32 is suppressed, so that the amount of steam that enters the retention space S through the gap between the through hole 51 and the disk portion 32 and the amount of foreign matter contained in the steam can be reduced. Furthermore, since the disk portion 32 is located as close as possible to the inner peripheral surface of the pipe 50, the volume of the retention space S capable of retaining a sufficient amount of gas can be secured.

[0062] In addition, since the plug 1 is provided with the groove portion 40 that is formed so as to protrude from the nozzle portion 20 and is abutted against the outer peripheral surface of the pipe 50, the plug 1 can be connected to the pipe 50 by welding using the groove portion 40.

[0063] In addition, since the groove portion 40 has a groove surface 41 and a straight surface 42, by butting the formed groove portion 40 against the outer peripheral surface of the pipe 50 and welding it, it is possible to ensure good penetration of the molten metal at the start of welding. In addition, when the groove portion 40 is butted against the pipe 50, the outer peripheral surface of the pipe 50 exists for the distance from the tip of the groove portion 40 formed by the straight surface 42 and the groove surface 41 to the through hole 51. As a result, the outer peripheral surface of the pipe 50 from the tip of the protruding groove portion 40 to the through hole 51 functions as a receiving portion for the molten metal flowing out from between the tip of the groove portion 40 and the outer peripheral surface of the pipe 50 at the start of welding, so that the penetration of the molten metal can be further improved and the occurrence of unwelded parts can be suppressed. By improving the penetration of the molten metal in this way, the occurrence of a discontinuous weld penetration shape in which there is an unwelded part in the part to be welded is suppressed. As a result, when a load is applied, the possibility that stress will concentrate on the welded part 60 and cause cracks can be reduced.

[0064] In addition, since the straight surface 42 is located radially outboard of the through hole 51 when the groove portion 40 is butted against the pipe 50, the outer peripheral surface of the pipe 50 exists for the distance from the tip of the groove portion 40 formed by the straight surface 42 and the groove surface 41 to the through hole 51. The outer peripheral surface of the pipe 50 from the tip of the groove portion 40 to the through hole 51 functions as a receiving portion for the molten metal that flows out from between the tip of the groove portion 40 and the outer peripheral surface of the pipe 50 at the start of welding, so that the penetration of the molten metal can be further improved and the occurrence of a discontinuous weld penetration shape in which there is an unwelded portion in the part to be welded can be suppressed.

[0065] Moreover, because the sealing portion 30 of the plug 1 is inserted into the through hole 51, it is possible to retain the gas for back shielding in the retention space S when the plug 1 is connected to the piping 50 by welding. As a result, the gas for back shielding can be sealed in well by the simple operation of simply using the plug 1, and the burden of incidental operations accompanying welding the plug 1 and the piping 50 can be reduced.

[0066] Furthermore, the plug 1 is connected to the pipe 50 with the groove portion 40 butted against the outer peripheral surface of the pipe 50 and the welded portion 60 formed between the groove surface 41 of the groove portion 40 and the outer peripheral surface of the pipe 50, so that the entire welded portion 60 can be formed on the outer peripheral surface of the pipe 50. This allows the presence or absence of defects in the welded portion 60 to be inspected by a non-destructive method, so that the inspection of the welded portion 60 can be easily performed. Furthermore, since the entire welded portion 60 to be inspected is formed on the outer peripheral surface of the pipe 50, the accuracy of the inspection is improved.

[0067] Furthermore, since the weld toe 61 of the welded portion 60 is farther from the axis X than the outer circumferential surface of the nozzle portion 20, the weld toe 61 can be positioned radially outward of the stress concentration portion that occurs inside the pipe material of the piping 50 and in the vicinity of the through hole 51. This allows the nozzle portion 20 to bear part of the stress that occurs in the stress concentration portion. This makes it possible to improve the yield strength of the piping 50. Furthermore, the stress concentration that occurs in the welded portion 60 can be mitigated, ensuring the strength of the welded portion 60 and extending its lifespan. The term "stress concentration portion" used herein refers to a peak portion of stress generated in the vicinity of through hole 51 due to hoop stress acting on pipe 50 and its vicinity.

[0068] In addition, the position of the weld toe 61 is determined by comparing the degree of damage of the stress concentration portion and the degree of damage of the weld toe 61, so that the weld toe 61 can be set at a position where both the stress concentration portion and the weld toe 61 are unlikely to be damaged.

[0069] In addition, since the welded portion 60 is formed in a round shape that is concavely curved relative to the outer circumferential surface of the piping 50, it is possible to suppress stress concentration at the welded toe 61. As a result, even if the nozzle portion 20 bears part of the stress generated in the stress concentration portion of the piping 50, it is possible to suppress damage to the welded portion 60 due to the stress.

[0070] The embodiments described above can be understood, for example, as follows. That is, the plug (1) according to one embodiment of the present disclosure is a plug (1) that closes a through hole (51) formed in a pipe (50) from the outer peripheral surface side of the pipe (50), and includes a columnar nozzle support portion (20) extending in an axial direction (X) and a sealing portion (30) that is connected to the nozzle support portion (20) and defines a retention space (S) for retaining gas between the nozzle support portion (20) and the through hole (51).

[0071] The plug (1) according to this embodiment includes a columnar nozzle stub part (20) extending in the axial direction (X) and a sealing part (30) connected to the nozzle stub part (20) and defining a retention space (S) for retaining gas between the nozzle stub part (20) and the sealing part (30) in the through hole (51), so that backshielding gas can be retained in the retention space (S) when the plug (1) is connected to the piping (50) by welding. This makes it possible to seal in a good backshielding gas with a simple operation of just using the plug (1), and reduces the burden of incidental operations associated with welding the plug 1 and the piping 50.

[0072] In addition, in the plug (1) according to one embodiment of the present disclosure, the sealing portion (30) has an axial portion (31) having a diameter smaller than the inner diameter of the through hole (51) and a base end connected to the pipe base portion (20), and a disk portion (32) connected to a tip of the axial portion (31) in correspondence with the inner shape of the through hole (51).

[0073] According to the plug (1) of this embodiment, the sealing portion (30) has a shaft portion (31) having a diameter smaller than the inner diameter of the through hole (51) and a base end connected to the pipe support portion (20), and a disc portion (32) connected to the tip of the shaft portion (31) in correspondence with the inner shape of the through hole (51). Therefore, the pipe support portion (20), the shaft portion (31), the disc portion (32), and the through hole (51) define a retention space (S), and the disc portion (32) can suppress the intrusion of foreign matter into the through hole (51). Furthermore, since the disk portion (32) functions as a guide for the through hole (51), positioning of the sealing portion (30) when it is inserted into the through hole (51) can be easily performed.

[0074] In the plug (1) according to one aspect of the present disclosure, the surface (32a) of the disc portion (32) facing the inside of the pipe (50) is configured to be substantially flush with the inner circumferential surface of the pipe (50).

[0075] According to the plug (1) of this embodiment, the surface (32a) of the disc portion (32) facing the inside of the pipe (50) is configured to be substantially flush with the inner peripheral surface of the pipe (50), so that there is no step between the surface of the disc portion (32) and the inner peripheral surface of the pipe (50), and foreign matter is less likely to adhere to the surface. In addition, the disc portion (32) can be prevented from blocking the flow of steam flowing inside the pipe (50). Furthermore, by not blocking the flow of steam, disturbance of the steam flow near the disc portion (32) is suppressed, so that the amount of steam that enters the retention space (S) through the gap between the through hole (51) and the disc portion (32) and the amount of foreign matter contained in the steam can be reduced. In addition, since the disk portion (32) is located as close as possible to the inner peripheral surface of the pipe (50), a volume of the retention space (S) capable of retaining a sufficient amount of gas can be ensured.

[0076] Moreover, the plug (1) according to one aspect of the present disclosure includes a groove portion (40) that is formed to protrude from the nozzle portion (20) and is abutted against the outer circumferential surface of the pipe (50).

[0077] The plug (1) according to this embodiment is provided with the groove portion (40) that is formed so as to protrude from the pipe stub portion (20) and is butted against the outer peripheral surface of the pipe (50). Therefore, the plug (1) can be connected to the pipe (50) by welding using the groove portion (40).

[0078] In the plug (1) according to one aspect of the present disclosure, the groove portion (40) is contracted from the outer circumferential side in a radial direction perpendicular to the axial direction (X) in a direction from the base end (12) toward the tip end (11). Diameter and a straight surface (42) extending from an end of the groove surface (41) along the axis (X) direction from the tip end (11) side toward the base end (12) side.

[0079] According to the plug (1) of this embodiment, the groove portion (40) is contracted from the outer circumferential side in the radial direction perpendicular to the axial direction (X) in the direction from the base end (12) toward the tip end (11). Diameter The groove (40) has a groove surface (41) that forms a groove along the axis (X) direction and a straight surface (42) that extends from the end of the groove surface (41) from the tip end (11) side toward the base end (12) side. Therefore, by butting the formed groove portion (40) against the outer peripheral surface of the pipe (50) and welding it, it is possible to ensure good penetration of the molten metal at the start of welding. In addition, when the groove portion (40) is butted against the pipe (50), the groove portion (40) formed by the straight surface (42) and the groove surface (41) Tip The outer peripheral surface of the pipe (50) exists for the distance from the tip of the protruding groove portion (40) to the through hole (51). As a result, the outer peripheral surface of the pipe (50) from the tip of the protruding groove portion (40) to the through hole (51) functions as a receiving portion for the molten metal that flows out from between the tip of the groove portion (40) and the outer peripheral surface of the pipe (50) at the start of welding, so that the penetration of the molten metal can be further improved and the occurrence of unwelded parts can be suppressed. By improving the penetration of the molten metal in this way, the occurrence of a discontinuous weld penetration shape in which there is an unwelded part in a part to be welded can be suppressed. This reduces the possibility that stress will concentrate on the welded part (60) and cause cracks when a load is applied.

[0080] Moreover, in the plug (1) according to one aspect of the present disclosure, when the groove portion (40) is butted against the outer circumferential surface of the pipe (50), the straight surface (42) is located outer than the through hole (51) in the radial direction.

[0081] According to the plug (1) of this embodiment, when the groove portion (40) is butted against the pipe (50), the straight surface (42) is located radially outboard of the through hole (51), so that the outer peripheral surface of the pipe (50) exists for a distance from the tip of the groove portion (40) formed by the straight surface (42) and the groove surface (41) to the through hole (51). The outer peripheral surface of the pipe (50) from the tip of the groove portion (40) to the through hole (51) functions as a receiving portion for the molten metal that flows out from between the tip of the groove portion (40) and the outer peripheral surface of the pipe (50) at the start of welding, so that the penetration of the molten metal can be further improved and the occurrence of a discontinuous weld penetration shape in which there is an unwelded portion in a portion to be welded can be suppressed.

[0082] Moreover, a piping structure according to one embodiment of the present disclosure includes a piping (50) having a through hole (51) formed therein, and the above-mentioned plug (1), and the plug (1) has the sealing portion (30) inserted into the through hole (51).

[0083] According to the piping structure of this embodiment, the plug (1) has the sealing portion (30) inserted into the through hole (51), so that when the plug (1) is connected to the piping (50) by welding, the back shielding gas can be retained in the retention space (S). This makes it possible to seal in the back shielding gas well by a simple operation of just using the plug (1), and reduces the burden of incidental operations associated with welding the plug 1 and the piping 50.

[0084] Moreover, a piping structure according to one embodiment of the present disclosure includes a pipe (50) having a through hole (51) formed therein, and the above-mentioned plug (1), and the plug (1) is connected to the pipe (50) by having the groove portion (40) abut against the outer peripheral surface of the pipe (50) and a weld portion (60) formed between the groove portion (40) and the outer peripheral surface of the pipe (50).

[0085] According to the piping structure of this embodiment, the plug (1) is connected to the pipe (50) by having the groove portion (40) butted against the outer peripheral surface of the pipe (50) and a weld portion (60) formed between the groove portion (40) and the outer peripheral surface of the pipe (50), so that the entire weld portion (60) can be formed on the outer peripheral surface of the pipe (50). This allows the presence or absence of defects in the weld portion (60) to be inspected by a non-destructive method, so that the inspection of the weld portion (60) can be easily performed. In addition, the inspection accuracy is improved because the entire weld portion (60) to be inspected is formed on the outer peripheral surface of the pipe (50).

[0086] In addition, in a piping structure according to one embodiment of the present disclosure, the end (61) of the welded portion (60) that contacts the piping (50) is farther away from the axis (X) than the outer peripheral surface of the pipe support portion (20).

[0087] According to the piping structure of this embodiment, the end (61) of the welded portion (60) that contacts the pipe (50) is farther from the axis (X) than the outer circumferential surface of the nozzle stub (20), so that the end (61) of the welded portion (60) can be positioned radially outward of the stress concentration portion that occurs inside the pipe material of the pipe (50) and near the through hole (51). This allows the nozzle stub (20) to bear part of the stress that occurs in the stress concentration portion. This improves the strength of the pipe (50). In addition, the stress concentration that occurs in the welded portion (60) can be alleviated, ensuring the strength of the welded portion (60) and extending its life. The term "stress concentration portion" used herein refers to a peak portion of stress generated in the vicinity of the through hole (51) due to a hoop stress acting on the pipe (50) and its vicinity.

[0088] In addition, in a piping structure according to one embodiment of the present disclosure, the position of the end (61) of the welded portion (60) is determined by comparing the degree of damage of the stress concentration portion with the degree of damage of the end (61) of the welded portion (60).

[0089] In the piping structure of this embodiment, the position of the end (61) of the welded portion (60) is determined by comparing the degree of damage of the stress concentration portion and the degree of damage of the end (61) of the welded portion (60). Therefore, the end (61) of the welded portion (60) can be set at a position where both the stress concentration portion and the end (61) of the welded portion (60) are less likely to be damaged.

[0090] In the piping structure according to the aspect of the present disclosure, the welded portion (60) is formed in a round shape that is curved concavely with respect to the outer circumferential surface of the pipe (50).

[0091] In the piping structure according to this aspect, the welded portion (60) is formed in a round shape that is concavely curved relative to the outer circumferential surface of the pipe (50), so that it is possible to suppress stress concentration at the end (61) of the welded portion (60). As a result, even if the pipe stub portion (20) bears part of the stress generated in the stress concentration portion of the pipe (50), it is possible to suppress damage to the welded portion (60) due to the stress.

[0092] Moreover, a method for installing a plug (1) according to one aspect of the present disclosure is a method for installing a plug (1) that closes a through hole (51) formed in a pipe (50) from an outer peripheral surface side of the pipe (50), the plug (1) including a columnar nozzle support portion (20) extending in an axial direction (X) and a sealing portion (30) that is connected to the nozzle support portion (20) and defines a retention space (S) for retaining gas between the nozzle support portion (20) and the through hole (51), the method including a step of supplying a gas used for back shielding during welding to the retention space (S). [Explanation of symbols]

[0093] 1 Plug 11 Tip 12 Proximal end 20 Pipe support section 22 Bottom 30 Sealing part 31 Shaft 32 Disc section 32a Bottom side 40 Bevel 41 Bevel surface 42 Straight surface 43 Root surface 44 Round Surface 50 Piping 51 Through hole 53 Stress concentration area 60 Welding 61 Weld Toe 70 flat plate 71 Through hole 72 Through hole point 101 Furnace wall (heat transfer tube) 102 1st superheater (heat exchanger) 103 Second superheater (heat exchanger) 104 Third superheater (heat exchanger) 105 1st reheater (heat exchanger) 106 Second reheater (heat exchanger) 107 Energy saver (heat exchanger) 111 High Pressure Turbine 112 Intermediate Pressure Turbine 113 Low Pressure Turbine 114 Condenser 121 Condensate pump (CP) 122 Low pressure water heater 123 Boiler Feed Pump (BFP) 124 High pressure water heater 126 Brackish water separator L1 water supply system L2 Drain water system L3~L5 Steam system

Claims

1. A plug that closes a through hole formed in a pipe from an outer peripheral surface side of the pipe, a columnar pipe stub portion extending in an axial direction and protruding out of the through hole when the plug is installed in the piping; a sealing portion connected to the nozzle portion and defining a retention space for retaining a gas for back shielding between the sealing portion and the nozzle portion within the through hole; A plug that is equipped with

2. The sealing portion is a shaft portion having a diameter smaller than an inner diameter of the through hole and a base end connected to the nozzle portion; a disk portion connected to a tip of the shaft portion in correspondence with an inner shape of the through hole; 2. The plug of claim 1, comprising:

3. 3. The plug according to claim 2, wherein a surface of the disk portion facing the inside of the pipe is configured to be substantially flush with an inner circumferential surface of the pipe.

4. 4. The plug according to claim 1, further comprising a groove portion formed so as to protrude from the nozzle portion and abutted against the outer circumferential surface of the pipe.

5. The groove portion is A groove surface that reduces in diameter from the outer periphery side in a radial direction perpendicular to the axial direction in a direction from the base end to the tip end; A straight surface extending from an end of the groove surface along the axial direction from the tip side to the base end side; 5. The plug of claim 4, further comprising:

6. 6. The plug according to claim 5, wherein the straight surface is located outwardly of the through hole in the radial direction when the groove portion is butted against the outer circumferential surface of the pipe.

7. A pipe having a through hole formed therein; A plug according to any one of claims 1 to 6; Equipped with The plug is a piping structure in which the sealing portion is inserted into the through hole.

8. A pipe having a through hole formed therein; A plug according to any one of claims 4 to 6, Equipped with The plug is a piping structure in which the groove portion is butted against the outer peripheral surface of the pipe and a weld is formed between the groove portion and the outer peripheral surface of the pipe, and the plug is connected to the pipe.

9. The piping structure according to claim 8 , wherein an end of the welded portion that contacts the pipe is spaced further from the axis than an outer circumferential surface of the pipe stub portion.

10. 10. The piping structure according to claim 9, wherein the position of the end of the weld is determined by comparing a damage degree of a stress concentration portion with a damage degree of the end of the weld.

11. The piping structure according to claim 9 or 10, wherein the welded portion is formed in a round shape that is concavely curved with respect to the outer circumferential surface of the pipe.

12. A plug that closes a through hole formed in a pipe from an outer peripheral surface side of the pipe, A columnar nozzle portion extending in an axial direction; a sealing portion connected to the nozzle portion and defining a retention space for retaining a gas for back shielding between the sealing portion and the nozzle portion within the through hole; A method of installing a plug comprising: A plug installation method comprising the step of supplying a gas used for back shielding during welding to the retention space.

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