JP2005088048A - Flange for absorbing welding deformation for piping joint, and piping joint using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To dispense with useless correction of deformation in welding a flange to piping, to eliminate press equipment as well as training or the like that requires skill, and to attain improved quality and large reduction in manufacturing cost. <P>SOLUTION: This is a circular flange for piping joint, a flange which has a hole opening 12 for inserting piping in the center and which is welded to the tip end of the piping 13 inserted in the opening. In the direction opposite to the welding deformation which is assumed to be generated at the time of welding of the flange to the piping 13, counter deformation is provided in the same quantity as the assumed welding deformation. As a result, in a pre-welding state, flange planes 11a, 11b are formed that are not vertical to the axial center of the piping. In the actual welding, the counter deformation is negated by the welding deformation, making the flange plane vertical to the axial center of the piping 13. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a flange for a pipe joint applied to various industrial plants such as a power plant and a chemical plant, and in particular, improves the quality by absorbing the weld distortion generated at the time of welding with the pipe by the reverse distortion applied before welding. The present invention relates to a welded joint that absorbs a weld strain and a pipe joint using the flange.

  The prior art will be described with reference to FIGS. FIG. 6 is a cross-sectional view showing a conventional welded joint flange and a pipe to which the flange is welded before welding, and FIG. 6 is a right side view of the flange shown in FIG. FIG. 8 is a cross-sectional view showing a joined state between the pipe and the flange immediately after welding.

  As shown in FIGS. 6 and 7, the conventional JIS standardized flange 1 applied as a joint for plant piping has a disk shape, and the flat flanges 1a and 1b on both sides are parallel and have no distortion. There is no. An opening hole 2 for inserting the pipe 3 is formed in the center of the flange 1.

  At the time of manufacturing the pipe joint, as shown in FIG. 8, the distal end portion of the pipe 3 is inserted into the opening hole 2 of the flange 1 to the non-penetrating position, and the outer periphery of the distal end surface of the pipe 3 is used as the first welded portion 4. The vicinity and the inner peripheral surface of the opening hole 2 of the flange 1 are welded along the circumferential direction. As the second welded portion 5, an outer peripheral surface near the line end of the pipe 3 and one flange surface 1a of the flange 1 Are welded along the circumferential direction.

  In such a conventional pipe joint 6, the first welded portion 4 is located in the inner peripheral surface of the opening hole 2 of the flange 1, and the second welded portion 5 is one flange surface 1 a of the flange 1. Since it is located on the side, a large amount of welding heat is supplied to one flange surface 1a, and the amount of heat given to the other flange surface 1b on the opposite side is relatively small.

  Therefore, in this pipe joint 6, shrinkage due to cooling on the one flange surface 1a side to which a large amount of heat is supplied during welding increases, and welding distortion occurs. Due to this welding distortion, the flange 1 is deformed in a bow shape such that one flange surface 1a side on the pipe insertion side is concave and the other flange surface (seal surface) 1b side is convex. That is, in the prior art, as the welding operation is completed and naturally cooled to room temperature, welding distortion occurs due to thermal contraction in the welded portions 4 and 5, and the welded flange 1 is deformed.

  In addition, as a flange joint welding method, the TIG welding method, the MAG / MIG welding method, or the covering arc welding method is applied, and it is performed by these welding methods. Deformation phenomenon due to weld distortion. In addition, this weld distortion (deformation) tends to be particularly large in the case of a stainless steel material that has a small thermal conductivity and tends to accumulate heat, but is not limited to the stainless steel material and also occurs in almost all carbon steel materials.

  As a method for preventing the occurrence of this welding distortion, until now, a deformation preventing disk in the thickness direction is tangled on one side (the other flange surface 1b) side which becomes the joint surface (seal surface) of the flange 1, and each other. A method in which the outer periphery of the steel plate is temporarily welded and flange joint welding is performed, or a disk of several millimeters is sandwiched between the contact surfaces of the paired flange joints 6 and the flanges are tightened with bolts to reverse strain (expected A method of performing flange joint welding in a state in which deformation before welding toward the opposite side of the weld deformation side is performed.

  However, these methods often do not allow sufficient prevention of deformation for the time required to manufacture jigs, and require a technique for achieving uniform welding heat input. Furthermore, the base metal is a factor that causes an increase in residual stress due to forced restraint, a decrease in quality such as an increase in hardness, and an increase in manufacturing cost.

  On the other hand, there is also known a method of performing flange joint welding without pressurizing such a distortion prevention method and correcting the generated welding distortion by press, or a method of heating by a gas burner and correcting by a so-called “saddle method”. Yes. However, the former method of press correction is limited by the piping shape and size, and the latter method of correction has a problem that it cannot be applied to austenitic stainless steel or the like.

  For this reason, the most frequently used method so far is a method of removing the deformed portion by machining (ie, a crushing method). However, this method requires skilled skills for correction processing, and increases the number of processing steps due to unnecessary additional steps.

  In technical fields other than pipe joints, for example, in the manufacturing technical field of square steel pipes that weld U-shaped materials and lid plates, bow deformation, which is distortion in the direction perpendicular to the axis of the steel pipe, is prevented by lid plate welding. For the purpose of manufacturing a straight square steel pipe, before welding the cover plate to the U-shaped material, the U-shaped material is preliminarily subjected to reverse distortion corresponding to the welding deformation, and heat absorption during the cover plate welding is performed. It has been proposed to cancel the amount (see Patent Document 1).

However, this method merely prevents the simple bow-shaped deformation of the square steel pipe along the longitudinal direction as a whole, and cannot be applied to prevent the deformation of the partial and complicated flange welding.
JP-A-7-314171

  As described above, the conventional technique requires a technique for obtaining a uniform welding heat input amount and a skill for performing a correction process, and the number of processing steps increases due to useless additional steps. Furthermore, the base metal is a factor that causes an increase in residual stress due to forced restraint, a decrease in quality such as an increase in hardness, and an increase in manufacturing cost.

  The present invention has been made in view of such circumstances, and eliminates the above-mentioned factors, and at the same time as improving quality, reduces manufacturing costs and effectively absorbs welding distortion. An object is to provide a weld strain absorbing flange.

  Another object of the present invention is to provide a high-quality pipe joint with a small residual stress in the flange portion.

  In order to achieve the above object, in the invention according to claim 1, for a disk-shaped pipe joint having an opening hole for pipe insertion at the center and welded to the tip of the pipe inserted into the opening hole. The flange is subjected to reverse strain of the same amount as the assumed welding strain in a direction opposite to the direction of the welding strain assumed to occur during welding with the pipe, and thereby the pipe in the pre-weld state. A flange surface that is non-perpendicular to the axial center of the pipe is formed, and the reverse strain is canceled by welding strain during actual welding, and the flange surface is perpendicular to the axial center of the pipe. A weld strain absorbing flange for a pipe joint is provided.

  That is, the direction and amount of welding distortion that is assumed to occur during welding can be specified by the welding location between the pipe and the flange and the amount of welding heat. When the end of the pipe is joined from one flange surface side of the flange, as explained in the above-mentioned conventional example, the amount of heat input to one flange surface side is large. Is one flange surface side on which contraction during cooling acts greatly. Therefore, deformation occurs such that one flange surface side is concave in the vicinity of the weld. Therefore, in the present invention, as the reverse strain, an inclined deformation is performed in advance so that the other flange surface side is concave with the vicinity of the welded portion as a boundary.

  Further, as a result of many tests, it was confirmed that the weld distortion was generated with the base point being approximately one place in the radial direction of the flange. This welding strain generation base point is a position on the diameter side several mm larger than the diameter of the opening hole for pipe insertion. Therefore, it is not necessary to apply reverse strain to the portion of the flange surface on the inner diameter side of the weld strain generation base point in the flange. Therefore, the portion where deformation is caused by reverse strain is a range on the outer diameter side from the welding strain generation base point.

  In view of this point, in the invention according to claim 2, the reverse strain is a plate thickness direction in which a welding strain generation starting point that is generated at a position several mm larger than the diameter of the opening hole of the flange is a bending point. The flange surface on the inner diameter side from the welding strain generation base point is a vertical surface with respect to the axis of the pipe, and the flange surface on the outer diameter side from the welding strain generation point is the axis of the pipe. The weld strain absorbing flange for a pipe joint according to claim 1, wherein the weld strain absorbing flange is inclined with respect to the center.

  Depending on the plant, stainless steel, carbon steel, or the like is applied as the material for the flange for the pipe joint. And since the magnitude | size of the inclination angle by the welding distortion of the flange which generate | occur | produces at the time of joint welding changes with materials, it is desirable to specify the angle of reverse distortion according to a material.

  In the invention according to claim 3, the flange is made of stainless steel, and the inclination angle of the flange surface at the welding strain starting point is set to 90.5 ° to 93 ° with respect to the axis of the pipe. A weld strain absorbing flange for a pipe joint according to 2, is provided.

  In the invention according to claim 4, the flange is made of carbon steel, and the inclination angle of the flange surface at the welding strain occurrence starting point is set to 90.5 ° to 92 ° with respect to the axis of the pipe. A weld strain absorbing flange for a pipe joint as described is provided.

  When the reverse strain applied in the above inventions of claims 2 to 4 is canceled by the weld strain at the time of actual welding and all flange surfaces are perpendicular to the axis of the pipe, the results of many tests It was confirmed that a deformation such that a part of the flat surface was raised at the starting point of the welding strain on the flange surface which was a concave side surface before welding. If this raised deformation remains, when joining with other joint flanges that form a pair, there is a possibility that the sealing performance may deteriorate due to the joining of the raised deformed parts. In this case, if the deformed portion is removed by subsequent machining or the like, an extra additional step is required. Therefore, by forming a ring-shaped concave groove on the flange surface where the bulging deformation occurs in advance, it is possible to prevent the bulging deformation from occurring over the entire circumferential direction of the flange. By performing such treatment, a flange having excellent sealing performance can be obtained, and an additional process is not required. Further, by forming the ring-shaped concave groove at the welding strain generation starting point, the bending stress generated during actual welding becomes a diffusion state in the surface portion of the concave groove, and the one-point concentration state of the stress is eliminated. As a result, the bending action of the flange material is uniformly performed when the reverse distortion applied in advance is canceled and the flange surface becomes flat. As a result, the perpendicularity of the flange surface after welding with respect to the pipe axis can be set with high accuracy and the residual stress can be reduced.

  Therefore, in the invention according to claim 5, a ring-shaped concave groove is formed on the flange surface in the inclined direction of the flange so as to pass through the welding strain starting point and along a concentric circle with the center of the flange. A weld strain absorbing flange for a pipe joint according to any one of claims 2 to 4 is provided.

  By applying the flange described above, it is possible to configure a high-quality pipe joint with a small residual stress.

  In view of this, the invention according to claim 6 provides a pipe joint configured by using the weld strain absorbing flange for pipe joint according to any one of claims 1 to 4.

  According to the present invention, the partial reverse strain preliminarily applied to the flange cancels out the weld strain generated in a part of the flange during actual welding, and the flange is axially centered without any distortion after cooling. Is perpendicularly bonded. Therefore, there is no need for skills to make uniform welding heat input, skilled skills for correction processing, etc., and there is no increase in processing steps due to unnecessary additional steps, and due to forced restraint on the base material. It is possible to absorb welding distortion without causing an increase in residual stress or a decrease in quality such as an increase in hardness and an increase in manufacturing cost, and at the same time as improving the quality of the pipe joint, the manufacturing cost can be reduced.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an enlarged cross-sectional view of a central portion of a welded strain absorbing flange for a pipe joint according to the present embodiment. FIG. 2 is a partial cross-sectional view showing the flange and a pipe welded thereto, and FIG. 3 is a right side view of the flange shown in FIG. FIG. 4 is a cross-sectional view showing a state immediately after welding of the flange and the pipe (a state configured as a pipe joint).

  As shown in FIG. 1 to FIG. 3, the flange 11 of the present embodiment is basically disc-shaped and has an opening hole 12 for inserting a pipe 13 in the center as in the conventional case. However, unlike the conventional generally flat structure, the flange 11 of the present embodiment has the same amount as the assumed welding strain in the direction opposite to the direction of the welding strain that is assumed to occur during welding with the pipe 13. The reverse strain is applied in advance, and the reverse strain is canceled by the weld strain during actual welding so that the flange surface is perpendicular to the axis of the pipe.

  The reverse distortion of the flange 11 is determined based on the observation result of the welding distortion generated in the conventional JIS standardized flange. In the present embodiment, a part of the flange 11 in the radial direction is specifically described. The base point is applied by inclining a portion on the outer diameter side of the base point by a predetermined angle θ in the plate thickness direction.

  More specifically, as shown in the above-described conventional example, the weld distortion is the first welded portion where the vicinity of the outer periphery of the front end surface of the pipe and the inner peripheral surface of the opening hole of the flange are welded along the circumferential direction. It is generated based on the second welded portion in which the outer peripheral surface of the portion of the pipe that protrudes to the outside and the flange surface that is one side surface of the flange are welded along the circumferential direction. And since these welding parts supply much welding heat to the one side surface side of a flange, the calorie | heat amount given to each flange surface was unevenly distributed, and the deformation | transformation by the welding distortion had arisen in the flange. As a result, a bow-like deformation is generated in the flange so as to be inclined toward one flange surface on the pipe insertion side.

  Therefore, in this embodiment, as a reverse strain of such welding strain, the flange surface 11a, 11b on the outer diameter side from the one point in the radial direction of the flange 11 is the side where the pipe 13 is inserted. Toward the opposite side, an inclination of a certain angle θ is given to the axis O of the pipe 13 as a reverse strain having the same amount as the welding strain.

  In this embodiment, the “welding strain generation starting point P” of the flange 11 is obtained as the base point of this inclination based on the result of the test. That is, as a result of many tests, it has been found that the flange 11 has a base point at which welding distortion occurs at a substantially constant radial position according to the diameter. The starting point at which this welding distortion occurs was present at a position on the large-diameter side having a fixed length δ (several mm (3 to 8 mm)) from the diameter D0 of the opening hole 12 for pipe insertion. The base point P at which this welding strain occurs is hereinafter referred to as “welding strain generation starting point P”.

  By setting a reverse strain in which the flange surfaces 11a and 11b on the outer diameter side from the welding strain generation starting point P are inclined by a certain angle θ with respect to the axis O of the pipe, the welding strain at the time of actual welding can be canceled. all right. Based on this result, the flange 11 of the present embodiment has a welding strain generation starting point P at a position larger than the diameter D0 of the opening hole 12 for pipe insertion by a fixed length δ, and this weld strain generation. The flange surfaces 11c and 11d on the inner diameter side from the starting point P are perpendicular to the axis O of the piping, and the flange surfaces 11a and 11b on the outer diameter side from the welding strain generation starting point P are on the axis O of the piping 11. On the other hand, it is assumed that it is inclined by a certain angle θ. Various means such as an NC lathe and a machining center can be applied to such reverse strain machining.

  FIG. 5 shows a graph for each material regarding the strain angle for applying reverse strain and the diameter of the pipe 13 in this embodiment, and the strain angle (vertical axis) and the diameter for stainless steel and carbon steel. (Horizontal axis) is changed.

  As shown in FIG. 5, in the case of the stainless steel flange 11, the welding strain generation starting point of 90.5 ° to 93 ° with respect to the corresponding pipe diameter standard 100A to 400A (opening hole diameter of the flange 100 mm to 400 mm). The change of the welding distortion angle of the flange surface was observed. Further, in the case of the flange 11 made of carbon steel, the welding strain of the flange surface at the origin of welding strain generation of 90.5 ° to 92 ° for the corresponding pipe diameter standards 100A to 400A (flange opening hole diameter 100 mm to 400 mm). A change in angle was observed. That is, it can be seen that the change in the welding strain angle of the stainless steel flange 11 is larger than that of the carbon steel.

  Correspondingly, in the present embodiment, when the flange 11 is made of stainless steel, the inclination angle θ of the flange surface at the welding strain generation point P is 90.5 ° to 93 ° with respect to the axis O of the pipe. Is set to Further, when the flange is made of carbon steel, the inclination angle θ of the flange surface at the welding strain starting point P is set to 90.5 ° to 92 ° with respect to the axis O of the pipe.

Next, in the present embodiment, the ring-shaped concave groove 14 is formed on the flange surface 11b in the inclination direction of the flange 11 so as to pass through the welding strain starting point P and along a concentric circle with the center of the flange. As shown in FIG. 1, the cross-sectional shape of the concave groove 14 is preferably a gentle curved surface by R processing (circular processing) in which stress is relaxed. However, although not shown, a groove having a square cross section may be used as long as it is a gentle curved surface.

  FIG. 4 shows a state after the flange 1 and the pipe 2 are welded by the welded portions 15 and 16. As shown in FIG. 4, in the pipe joint 17 after welding, the reverse strain was canceled by the actual welding strain, and the inclination of the flange 11 was returned, so that substantially vertical flange surfaces 11a and 11b were obtained. That is, no bowing deformation occurs such that one side (non-welded end face side) of the flange becomes a convex side due to cooling after welding of the welded portion as in the conventional example. In this case, in the flange joint welding process, the pipe 13 is inserted into the opening hole 12 of the flange 11 and welded. After natural cooling, the paired flanges have parallel angles due to welding distortion, and the distortion correction process is performed. It became unnecessary.

  Although the flange processing angle in this embodiment changes with pipe diameters, materials, and plate thicknesses, the angle and range that should be given in advance by a welding test can be determined.

  As described above, according to the present embodiment, reverse strain is applied in the direction opposite to the expected strain generation direction of the flange 11, and the inclination as reverse strain is canceled by the weld strain generated during actual welding. The vertical flange surfaces 11a and 11b are obtained. The vertical plane extends from the center of the flange 11 to a range of several mm on the seal surface, and a reverse strain angle is applied to the outer peripheral range where deformation is assumed. By forming the ring-shaped concave groove 14 at the position where the strain generation starting point P is formed, the shape is restored using welding strain generated during actual welding so that the flange surfaces 11a and 11b after welding are in a vertical state. As a result, unnecessary distortion correction, which has been conventionally performed, is no longer necessary. This eliminates the need for press facilities and skill-intensive repairs, thereby improving quality and significantly reducing manufacturing costs.

  Moreover, the pipe joint 17 comprised using the welding distortion absorption flange for pipe joints of this embodiment reduced the residual stress at the time of welding, and became very high quality.

  As described above, according to the present invention, the flange surface is subjected to reverse distortion for each size from the test data predicted in advance, and the shape is restored using the welding distortion generated during actual welding, and the flange surface after welding It is possible to manufacture a welded flange with reverse strain by making the state close to vertical. Therefore, since unnecessary distortion correction is not required, press facilities and skill-intensive repairs are not required, and quality can be improved and manufacturing costs can be greatly reduced.

The expanded sectional view which shows the flange shape before welding by one Embodiment of this invention. Sectional drawing which shows the state before welding of the flange before welding by one Embodiment of this invention, and piping. The right view of the flange shown in FIG. Sectional drawing which shows the flange shape after the welding by one Embodiment of this invention. The distortion according to one embodiment of the present invention, and a graph according to material of a diameter. Sectional drawing which shows the flange shape before welding by a prior art example. The right view of the flange shown in FIG. Sectional drawing which shows the flange shape after the welding by a prior art example.

Explanation of symbols

11 Flange 11a, 11b Flange surface 12 Opening hole 13 Pipe 14 Ring-shaped concave groove 15 Welded portion 16 Welded portion 17 Pipe joint O Pipe shaft center P Welding strain starting point

Claims (6)

A disc-shaped flange for a pipe joint that has an opening hole for pipe insertion in the center and is welded to the tip of the pipe inserted into the opening hole, and is assumed to occur during welding with the pipe The reverse strain of the same amount as the assumed welding strain is applied in the direction opposite to the direction of the strain, thereby forming a flange surface that is non-perpendicular to the axis of the pipe in the pre-weld state. A welding strain absorbing flange for a pipe joint, characterized in that the reverse strain is sometimes canceled by welding strain and the flange surface is perpendicular to the axis of the pipe. The reverse strain is an inclination of a constant angle along the plate thickness direction with a bending strain starting point generated at a position several mm larger than the diameter of the opening hole of the flange as a bending point. The flange surface on the inner diameter side from the base point is a vertical surface with respect to the axis of the pipe, and the flange surface on the outer diameter side from the welding strain generation point is an inclined surface with respect to the axis of the pipe. Welding strain absorbing flange for pipe joints. 3. The weld distortion for a pipe joint according to claim 2, wherein the flange is made of stainless steel, and an inclination angle of the flange surface at the welding strain starting point is set to 90.5 ° to 93 ° with respect to the axis of the pipe. Absorption flange. 3. The weld strain absorption for pipe joints according to claim 2, wherein the flange is made of carbon steel, and an inclination angle of the flange surface at the welding strain generation starting point is set to 90.5 ° to 92 ° with respect to the axis of the pipe. Flange. 5. The ring-shaped concave groove is formed on the flange surface in the inclined direction of the flange so as to pass through the welding strain starting point and along a concentric circle with the center of the flange. A weld strain absorbing flange for pipe joints as described in 1. A pipe joint constituted by using the welded strain absorbing flange for a pipe joint according to any one of claims 1 to 5.

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