JP5621540B2 - Cage roll restraint method - Google Patents

Description

  The present invention manufactures a UOE steel pipe in which a steel sheet is press-formed into a “U” shape and then into an “O” shape, and then the butt portion is arc welded and then expanded (E) from the inside to finish to a predetermined size. The present invention relates to a cage roll restraining method for reducing a load on a welded part which becomes a problem when the butt part of a welded steel pipe original pipe after pressing is tack-welded from the outer surface in the process.

  The original pipe (pipe P) of the welded steel pipe after pressing is sent to the temporary welding machine WR on the conveying line and the butt portion is temporarily welded, and then inner and outer surface welding is performed. In the temporary welding of the original pipe, a load is generated in the welded portion when released from the restraint by the cage roll CR. This load is caused by the springback of the original pipe, and the larger the thickness of the steel pipe, the larger the load is generated (see FIG. 1).

  In the prior art, a restraining method and apparatus for eliminating the level difference in the butt portion of the steel pipe original pipe after pressing has been established (for example, see Patent Document 1). However, no measures are taken against the load generated in the pipe weld when released from the cage roll restraint.

Japanese Utility Model Publication No. 05-000211

  When producing a thicker and higher-strength pipe than that currently produced, it is predicted that the load generated in the welded part during temporary welding will be greater. However, the conventional method cannot cope with this load, and there is a risk of welding peeling at the weld when released from the cage roll restraint.

  An object of the present invention is to provide an advanced welding portion load reducing method that solves the above-described problems, and enables production of a thick high-strength pipe.

  In order to solve the above-mentioned problem, the cage roll restraining method of the present invention is such that the shape of the pipe (original steel pipe) when restrained by the cage roll (hereinafter referred to as “restraint shape”) is a welded portion after being released from the cage roll. The restraint position of the steel pipe original pipe by the cage roll is determined so that the shape of the steel pipe is minimized (hereinafter referred to as "ideal shape"). Specifically, the outer circumference of the steel pipe original pipe is surrounded. A cage of UOE steel pipe that eliminates a gap in a butt portion where continuous tack welding of the steel pipe original pipe is performed by applying a load while constraining the steel pipe original pipe with a plurality of cage rolls each arranged at a predetermined restraining angle In the roll restraint method, the loads and restraint angles of the plurality of cage rolls are determined so that the load generated in the steel pipe tack weld when released from the cage roll restraint is minimized. It is an. At the time of restraint, the restraint cannot be made unless the specific shape of the ideal shape is known. Even if the ideal shape is known, the constraint shape cannot be matched with the ideal shape without knowing how much the pipe is deformed with respect to the constraint force of the cage roll. That is, it is necessary to predict the ideal shape and the constraining shape. Therefore, in the present invention, based on the law of elasticity, the pipe is regarded as a “cantilever bending beam” and modeled, and a technology for theoretically obtaining the ideal shape and the constraining shape based on the relationship between the bending beam load and the bending is established. . Hereinafter, methods for deriving the ideal shape and the constraint shape will be described.

[Derivation of ideal shape]
FIG. 2 shows the stress generated in the welded portion after release for a steel pipe having a pipe outer diameter of 48 in (1219.2 mm), a wall thickness of 40 mm, and a seam gap of 150 mm by FEM (finite element method) analysis. In case 1, the pipe P is constrained in a perfect circle shape using the upper, lower, left, and right cage rolls CR, and in case 2, the pipe P is constrained in the vertical direction using the left and right cage rolls CR, and the stress of the welded portion after release is calculated. (Case 1 corresponds to the conventional restraint method). It can be seen that when constrained to a perfect circle shape, a bending moment is exerted on the welded part to return in the vertical direction, and when constrained longitudinally, a bending moment is exerted on the welded part to return to the lateral direction (the welded part in this case). The stress exceeds 1000 MPa, and there is a possibility of welding peeling). In case 1 and case 2, the direction of the bending moment is opposite, so by restraining the pipe P to cancel each other's bending moment with the upper, lower, left and right cage rolls CR, the stress generated in the weld after release is reduced. It is thought that it can be made.

  In case 3, as described above, the FEM analysis was performed by giving the pipe P a restraining force that cancels the bending moment with the upper, lower, left, and right cage rolls CR. The stress of the welded portion was greatly reduced to 15 MPa, and it was found that the risk of welding peeling could be avoided by devising a restraining method. From the results of the FEM analysis, it was found that the weld stress can be significantly reduced by restraining the bending moment from acting. Therefore, the pipe shape when restrained so that the bending moment does not work can be regarded as an ideal shape.

In order to obtain the ideal shape theoretically, the pipe was modeled by a “cantilever beam” (see FIG. 3). The ξη coordinate with the center fixed end on the pipe circumference as the origin O is defined, the coordinate of the pipe tip is Q (ξ ₁ , η ₁ ), and the coordinate of an arbitrary point on the pipe circumference is R (ξ ₂ , η ₂ ). The center of the pipe is a point M, and ∠RMO = α and ∠QMO = θ. Further E the modulus of elasticity of the pipe, the second moment I, the pipe radius state with no added weight was R _m. Thereby, the one side of the pipe which has a seam gap in the upper part can be expressed by a curved beam. The released pipe can be regarded as a state where the seam gap is closed by applying a bending moment M and a radial tensile load F to the tip Q. If the bending moment distribution of the beam is illustrated on the assumption that the bending moments M1, M2, M3 and the radial tensile loads F1, F2, F3 are respectively applied to the tip portion Q with respect to case 1 to case 3, FIGS. (M1 and M2 have opposite signs and M3 = 0). Thereby, the ideal shape that minimizes the stress in the welded portion can be regarded as “a shape when the seam gap is closed by applying only the radial tensile load F to the tip portion Q”.

Here, the ideal shape is expressed by a mathematical expression. As shown in FIG. 7, it is assumed that an arbitrary point R (ξ ₂ , η ₂ ) on the pipe circumference is moved to a point R ′ (ξ ′ ₂ , η ′ ₂ ) by the load F. Further, the pipe center before deformation is defined as point M, and the pipe center after deformation is defined as point M ′, which is defined as ∠R′M′O = α ′. However, the point M ′ is defined as the intersection of the normal line of the curve indicating the pipe shape at the point R ′ and the ξ axis. Assuming that the amount of change at an arbitrary point R caused by the load F is δR (δ _h , δ _v ), δ _h and δ _v are defined as in Equation 1 below.

The angle variation [delta] _alpha is defined as δ α = _α'-α. If δ _h , δ _v and δ _α are obtained, it is possible to calculate the bent beam shape when the tip load is applied. δ _h , δ _v and δ _α can be calculated from a “relational expression of bending beam load and deflection” based on the law of elasticity, and the derivation result is as shown in Expression 2 below. However, E, respectively I and R _m, the modulus of elasticity of the pipe, a second moment and before restraint pipe radius.

  Considering that the magnitude of the load F is such that the seam gap is deformed until it closes, the following formula 3 is obtained.

但し、Ｒ_０はパイプを真円形状に拘束し、ギャップを閉じたときのパイプ半径である。これにより、任意のサイズ、材質、シームギャップのパイプに対して、理想形状を導出することができる。なお、Ｒ_ｍおよびＲ_０におけるパイプ「半径」は、パイプ肉厚の中央での値すなわち（内径＋外径）／４とする。

However, _R0 is a pipe radius when the pipe is constrained to a perfect circle shape and the gap is closed. Thereby, an ideal shape can be derived for a pipe having an arbitrary size, material, and seam gap. The pipe “radius” at R _m and R ₀ is a value at the center of the pipe thickness, that is, (inner diameter + outer diameter) / 4.

[Derivation of constraint shape]
In order to investigate the pipe shape when the cage roll is restrained, the pipe at the restraint is expressed using a bending beam as shown in FIG. FIG. 8 shows a state in which the bending beam is bent and the gap is closed by four concentrated loads in the radial direction. If the position change amount of an arbitrary point R generated when the load W _n of the n-th cage roll is added as the constraint angle θ _n is δR _n (h _n , v _n ) and the angle change amount is δα _n , h _n, v _n and δα _n than the "expression of the deflection and the load of the curved beam", is derived as shown in equation 4 below.

Assuming that the position change amount of the point R caused by the four cage roll loads is δR _k (Δh, Δv) and the angle change amount w is Δα, the following equation 5 is established according to the principle of superposition.

  Thereby, it is possible to derive a constraining shape when an arbitrary load is applied to a pipe having an arbitrary size, material, and seam gap. By constraining the pipe so that the constrained shape matches the ideal shape, it is possible to minimize the weld stress after release from the constrained state.

Actually, it is not necessary to make the pipe shape completely coincide with the ideal shape, and it is sufficient if the angle change amounts of the tip portions coincide. Therefore, the load W _n and the restraint angle θ _n are adjusted and restrained so that the following expression 6 holds, and this is referred to as “a restraint method that minimizes the weld stress after release”.

  By adjusting the restraining force of each cage roll and determining the value of Δα so that Equation 6 is satisfied, “restraint that minimizes the weld zone stress after release” can be realized. However, even if restrained as described above, the stress of the welded portion does not become zero. This is because a circumferential tensile load F acts on the upper end portion. Therefore, the welding material and the welding throat thickness must be selected so as to withstand the load F shown in Equation 3.

  According to the present invention, since the relationship between the cage roll restraining method of the steel pipe at the time of temporary welding and the load generated in the welded portion has been clarified, it is possible to temporarily weld the steel pipe having a larger thickness without causing welding peeling. It can be performed.

It is explanatory drawing which shows the load which arises in the welding part of a steel pipe by springback after cage roll release. (A), (b), (c) are welded parts after releasing the cage roll for case 1 (restrained to a perfect circle shape), case 2 (restrained to a vertically long shape), and case 3 (restrained to a shape that reduces stress) It is explanatory drawing which shows the load which arises. It is explanatory drawing which shows the pipe modeled with the cantilever bending beam of the no-load state. It is explanatory drawing which shows the bending moment which acts on a pipe in case1 (restraint to a perfect circle shape). It is explanatory drawing which shows the bending moment which acts on a pipe in case2 (restraint in a vertically long shape). It is explanatory drawing which shows the bending moment which acts on a pipe in case3 (restraint to the shape which reduces stress). (A), (b) is explanatory drawing which shows the ideal shape by the cantilever beam shape and circumferential direction tensile load of a no-load state, respectively. It is explanatory drawing which shows the pipe modeled with the cantilever bend beam at the time of radial direction load load. It is explanatory drawing which expands and shows the welding part of a pipe. It is explanatory drawing which shows the definition of front-end | tip part angle variation | change_quantity.

  The cage roll restraining method of the present invention has a plurality of restraint angles arranged around the outer peripheral surface of the steel pipe original pipe P formed in a substantially O shape, for example, as shown in the center of FIG. 1 and the left end of FIG. While restraining the steel pipe original pipe P with the individual cage roll CR, a load is applied to the steel pipe original pipe P by applying pressure to the cage roll CR with, for example, a hydraulic cylinder, and the steel pipe original pipe P is continuously attached. When eliminating the gap at the butt portion where welding is performed, as described above, a load is applied and restrained so that the tube cross-sectional shape does not change when released, so the bending moment does not act on the weld and the weld The generated load can be reduced.

As described in the means for solving the problem, in order to constrain the stress to be minimized, it is sufficient to constrain Equation 6 to hold. That is, if there is a large difference between the ideal shape contact portion angle change amount δα | _{α = θ} and the constrained shape contact portion angle change amount Δα, weld peeling occurs. If the difference is small, weld peeling does not occur. It can be said. Therefore, a range in which no welding peeling occurs is introduced below.

The temporary welding of the contact part has a shape as shown in FIG. When Δα is greatly different from δα | _{α = θ} , a large load is applied to the welded portion, but no welding peeling occurs immediately. First, the welded material is stretched, and the contact portion angle change amount δα | _{α = θ of the} ideal shape Try to get closer to. If the amount of change in angle caused by the extension of the welding material is Δθ, Δθ can be defined as in the following Expression 7 using the coordinates x and y shown in FIG. However, t, a, and ε are the welding throat thickness, the welding width, and the distortion of the welding material, respectively. Further, ρ is a radius of curvature generated by bending at an arbitrary point x.

Accordingly, the maximum value Δθ _m of Δθ is a value of the following equation 8 in which the elongation ε _{m of the} welding material is substituted for the strain ε of the above equation 7. When an angle change larger than Δθ _m occurs, the strain ε exceeds the elongation of the welding material, and welding peeling occurs.

Therefore, if the difference between the ideal shape contact portion angle change amount δα | _{α = θ} and the constrained shape contact portion angle change amount Δα is smaller than Δθ _m , welding peeling does not occur. That is, welding peeling due to bending does not occur in the range represented by the following Expression 9.

However, the welding material of the welded portion is subjected not only to the bending moment of the welded portion but also to the pipe circumferential direction tensile load F. That is, if the pipe length of the pipe is l and the welding material allowable stress is σ _y , the following equation 10 must be established.

Solving the above equation 10 with respect to the tread thickness t, the following equation 11 is obtained. However, the wall thickness of the pipe as a t _p.

  Therefore, if the contact portion angle change amount Δα and the node thickness t of the constrained shape are determined within a range satisfying these equations (9) and (11), it is possible to prevent the occurrence of welding peeling after temporary welding. it can.

  As an embodiment of the present invention, the weld throat thickness t and the range of the contact portion angle variation Δα of the constrained shape are shown for the pipes of the two types of conditions shown in Table 1 below.

When Expression 9 and Expression 11 are applied to Example 1, the following conditions are obtained.
(Formula 12)
t ≧ 1.6 [mm]
(Formula 13)
1.8 [°] ≦ Δα ≦ 13.0 [°]

  Since the welding throat thickness is 7 mm, the condition related to the above equation 12 is satisfied. Therefore, by restraining the pipe with a plurality of cage rolls so as to satisfy Equation 13, it is possible to prevent the occurrence of weld peeling after temporary welding.

When Expression 9 and Expression 11 are applied to Example 2, the following condition is obtained.
(Formula 14)
t ≧ 0.8 [mm]
(Formula 15)
0.9 [°] ≦ Δα ≦ 6.6 [°]

  Since the welding throat thickness is 7 mm, the condition relating to the above-mentioned formula 14 is satisfied. Therefore, by restraining the pipe with a plurality of cage rolls so as to satisfy Formula 15, it is possible to prevent the occurrence of weld peeling after temporary welding.

  As mentioned above, although demonstrated based on the Example, this invention is not limited to the above-mentioned example, For example, it is not restricted to a hydraulic cylinder to pressurize the cage roll for applying a load to a steel pipe original pipe, for example, An electric drive mechanism or the like that obtains a propulsive force by rotating a screw shaft or a nut screwed therein by a motor may be used. Further, according to the present invention, it is possible to obtain the welding throat thickness t and the contact portion angle change amount Δα that do not cause welding peeling even for pipes of other sizes and materials by the same procedure.

  Thus, according to the cage roll restraining method of the present invention, the relationship between the cage roll restraining method of the steel pipe during temporary welding and the load generated in the welded portion has been clarified. Temporary welding can be performed without performing.

CR Cage Roll P Pipe WM Welding Material WR Temporary Welding Machine

Claims (2)

A butt where continuous tack welding of the steel pipe original pipe is performed by applying a load while restraining the steel pipe original pipe with a plurality of cage rolls arranged at a predetermined restraining angle so as to surround the outer peripheral surface of the steel pipe original pipe. In the cage roll restraining method of UOE steel pipe that eliminates the gap of the part,
The shape of the steel pipe original pipe, which is derived by calculation as the ideal shape of the steel pipe original pipe constrained so that a bending moment does not act on the steel pipe tack welded portion, and is loaded with the plurality of cage rolls Is derived as a constraint shape by calculation,
The plurality of cages such that a difference between an angle change amount of the tip end portion of the steel pipe original pipe in the ideal shape and an angle change amount of the tip end portion of the steel pipe original pipe in the constrained shape is smaller than Δθ _m. By determining the load and restraint angle of the roll, the load and restraint angle of the plurality of cage rolls are determined so that the load generated in the steel pipe tack weld when released from the cage roll restraint is minimized. A cage roll restraining method for a UOE steel pipe, which is characterized.
However,

ε _m : Elongation of welding material
a: welding width
t: welding throat thickness
It is. Using the thickness, pipe diameter, material, and seam gap of the steel pipe original pipe as parameters, a cage roll restraining position that minimizes the load on the steel pipe tack welded portion is calculated by the following formulas 9 and 11, and the calculation is performed. 2. The cage roll restraint method for a UOE steel pipe according to claim 1, wherein a load and a restraint angle of the plurality of cage rolls are determined according to positions.

However,
Δα: Contact portion angle change amount of constrained shape θ: ∠QMO when the center fixed end on the circumference of the steel pipe raw tube before restraint is point O, the tip is point Q, and the center is point M
E: Elastic modulus of the steel pipe original pipe R _m : Radius of the steel pipe original pipe before restraint R ₀ : Radius of the steel pipe original pipe when the steel pipe raw pipe is constrained in a perfect circle shape and the seam gap is closed ε _m : Welding material Elongation a: Weld width t: Weld throat thickness σ _y : Welding material allowable stress t _p : Thickness of the steel pipe original pipe, and “radius” in R _m and R ₀ is (inner diameter + outer diameter) / 4 To do.

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