SK8722000A3 - Process for producing pipe bends from straight, spiral-welded pipes - Google Patents

Abstract

The invention relates to a method for producing pipe bends from straight, spirally welded pipes. Said pipes are produced from steel band rolls that are welded together by a double-sided butt seam consisting of a filler material. The welding seam is configured in such a way that it exceeds the inner and/or outer surface of the pipe by max. 2 mm and in such a way that the tangent with its cross-section at the transition point between the welding seam and the base material of the pipe forms an angle of max. 45<o> with the pipe surface. Having been welded in this way, the pipe is then bent in the electro-induction bending machine with a water spray, at a pipe deforming temperature T that is selected from a field of overlap of the following temperature intervals: TGM = [AC3GM - (30 to 80<o>C)] and TZM = [AC3ZM - (30 to 80<o>C)], AC3GM meaning the temperature AC3 of the basic steel material and AC3ZM meaning the temperature AC3 of the added material, AC3 being given by the following: AC3 = 910 x (203)<1/2> x 30 Mn + 44.7 Si [<o>C].

Description

Technical field.

The invention relates to a process for the production of pipe bends from straight, spirally welded steel pipes, in particular for long-distance natural gas lines, which are bent into a corresponding bend with the desired bending radius in an electro-induction bender with a water shower. Such pipe bends must withstand an internal overpressure of the conveyed medium of up to 40 bar during operation.

BACKGROUND OF THE INVENTION.

Up to now, pipe bends for gas lines using steel pipes with nominal diameters of 300 to 700 mm have been produced by bending straight seamless pipes in an electro-induction bender at a forming temperature above Aci. Such pipe bends meet all the strength requirements placed on them, but their disadvantage is the relatively expensive production of seamless tubes.

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The bending of the longitudinally welded tubes, in which the longitudinal weld was in a neutral plane during the bending, so that the weld and the heat-affected zone of the base material of the tube during bending were as low as possible in tension or pressure, did not expand too much. This was due to the unstable quality of the weld and the large fluctuations in the values of notch toughness and strength as a result of welding and thermal deformation during bending. The strength properties of the weld joint are also influenced by the shape and quality of the weld surface as well as the passage of the weld into the base material of the pipe. If the transition is not gradual and smooth, there is an undesirably large concentration of stresses in the mechanical stress of the oven, resulting in cracks and / or cracks. cracking material. In operation, when the pressure of the conveyed medium in the pipe reaches values up to 40 bar, the longitudinal weld is stressed much more than the spiral weld would be stressed.

Spiral welded tubes, made of steels of C = 0,03 to 0,25% by weight, Mn = 0,5 to 1,7%, Ni = 0 to 0,5%, Si = 0,2 to 0 7%, Al = 0.001 to 0.035%, P = 0.0 to 0.03%, S = 0.0 to 0.035%, Cr = 0 to 0.25%, Mo = 0 to 0.1%, V = 0 to 0.08%, Nb = 0 to 0.05%, Ti = 0 to 0.06%, with Cr + Cu + Mo content of max. 0.45% and Nb + Ti + V content = max. 0.12%, the remainder being iron and process impurities, welded on both sides with butt weld, with an additive material with a chemical composition of C = 0.04 to 0.08%, Si = 0.3 to 0.7%, Mn = 0.9 to 1.7%, the remainder being iron and manufacturing impurities, have not yet bent in the electro-induction or other bender, although the internal pressure of the spiral weld is considerably more favorable than the longitudinal weld because of the risk of cracking with undefined weld joint requirements and bending temperature t

was significantly larger than longitudinally welded tubes.

SUMMARY OF THE INVENTION.

The above disadvantages are substantially eliminated by the method of manufacturing pipe bends from straight, spirally welded tubes made of coil-shaped steel strips having a chemical weight composition: C = 0.03 to 0.25%, Mn = 0.5 to 1.7%, Ni = 0 to 0.5%, Si = 0.2 to 0.7%, Al = 0.001 to 0.035%, P = 0.0 to 0.03%, S = 0.0 to 0.035%, Cr = 0 up to 0.25%, Mo = 0 to 0.1%, V = 0 to 0.08%, Nb = 0 to 0.05%, Ti = 0 to 0.06%, with Cr + Cu + Mo content of max. 0.45% and Nb + Ti + V content = max. 0.12%, the remainder being iron and process impurities welded on both sides with butt weld with an additive material with a chemical composition of C = 0.04 to 0.08%, Si = 0.3 to 0.7%, Mn = 0.9 to 1.7%, the remainder being iron and process impurities, the principle of which is that the weld is made in such a way that the superelevation of the weld over the outer and / or inner surface of the pipe is not more than 2 mm and tangent to its cross-section at the transition point weld to the base material of the animal with its flat angle max. 45 °, whereby the spirally welded tube is bent in an electro-induction bender with a water spray at a forming temperature of T ° C, which is selected at the intersection or inlet. overlapping temperature intervals [A _C 3zm - (30 to 80)] ° C and [Ac3pm - (30 to 80)] ° C, where Ac3zm is the temperature A _C 3 of the base steel material and A _C 3pm is the temperature A _C 3 of the additive material where:

C _c3 = [910 - (203.C) ¹ ' ² - 30.Mn + 44.7.Si] ° C.

This method allows bending spirally welded pipes without causing cracks or cracking in the weld and in the heat affected zone along the weld, while maintaining the required strength parameters, ie the yield point R _c , the yield strength R _m , the notch toughness KCV and the required maximum permissible ovality values O of the cross-section of the arc.

The manufacture of these pipe bends is considerably cheaper than the production of pipe bends from seamless tubes having comparable mechanical properties.

Preferably, the weld is made on the outside and / or inside of the butt weld by two beadlets, the second bead covering at least partially the first bead.

In this way, in which the steel coils are welded at a lower heat input Q, there will be less thermal influence on the material in the heat affected area along the weld, while the heat input Q when boiling the second bead causes a post-welding annealing process to reduce stresses and texture the weld and the heat affected area along the weld.

BRIEF DESCRIPTION OF THE DRAWINGS.

1 is a view of a spirally welded straight pipe, FIG. 2 is a section A-A of FIG. 1, and FIG. 3 schematically illustrates the bending of a pipe in an electro-induction water spray bender.

DETAILED DESCRIPTION OF THE INVENTION.

A straight, spirally welded pipe, schematically shown in FIG. 1, is produced by welding the coils of a steel strip of thickness t = about 6 to 10 mm to the desired nominal diameter D, which ranges from 300 to 700 mm. The welding is performed by a double-sided butt weld, the cross-section of which is shown in FIG. 2. The superelevation of hi, h _{2 of} the weld surface above the surrounding surface of the pipe shall not exceed 2 mm and the angle of penetration of the weld into the surface of the pipe shall not exceed 45 °. The pipe thus produced is then bent in the electro-induction bender to the desired arcs. As shown in FIG. 3, a straight, spirally welded tube 4 is inserted into the bending guide rollers 1 and is displaced in the axial direction by the force Fi and the speed y into the bending rollers 2, which are adjustable according to the desired radius R of the arc. The curvature of the straight pipe takes place in the region of the inductor loop 3, in which the pipe or pipe is arranged. pipe material heated by electro-induction heat to a forming temperature T at which it is bent. In bending, the intended sheath fibers of the tube are elongated on the outside of the neutral arc plane and compressed on the inside of the arc. The molding temperature T has a significant influence both on the mechanical and strength properties and on the resulting oval roundness. Immediately after bending the oven, the oven, respectively. its material is cooled by a water spray 5 placed downstream of the inductor in order to avoid undesirable changes in the mechanical properties of the material and to ensure the desired ovality values.

Example 1

Edges of coils of steel strip thickness 7 mm of steel ČSN 41 1378 with chemical composition C = 0.1%, Mn = 0.6%, Si = 0.3%, Al = 0.02, P = 0.03%, S = 0,02%, the remainder being iron and process impurities having a yield strength R _e in the range of 305 to 319 MPa, a yield strength R _m in the range of 405 - 460 MPa (see Table 1 - lines 1) is adjusted for double-sided butt weld and automatic welding with filler material with chemical composition C = 0,06%, Si = 0,5%, Mn = 1,2%, the remainder being iron and manufacturing impurities, into a spiral tube of nominal diameter 324 mm, when the outer weld is made by one hen senica and the inner weld is made by two overlapping caterpillars. Notch toughness values of KCV are given in Tab. no. 3 - on lines 1.

The superelevation of the weld on the outer and inner surface of the pipe (see Fig. 2) at a pipe wall thickness of 7 mm does not exceed 2 mm and the tangent to its cross-section at the weld passage into the pipe base material has an angle of 31 °.

The pipe manufactured in this way is placed in an electro-induction bender with a water shower (see Fig. 3) and bent at a forming temperature T, which is selected on the basis of the following calculated values according to the chemical composition of the base and filler material:

A _C3 change = [910 - (203 ° C) ¹ ' ² - 30 Mn + 44.7 Si] ° C = 910 - (203.0.1) ^1/2 - 30.0.6 + 44.7. 0.3 = 900.9 ° C

T _ZM = A _{C 3} m - (30 to 80) ° C = 901 - (30 to 80) ° C = 871 to 821 ° C

Acspm = [910 - (203 ° C) ^1/2 - 30 Mn + 44.7 Si] ° C = 910 - (203.0.06) ^1/2 - 30.1.2 + 44.7. 0.5 = 892.9 ° C

Tp _M = Acspm - (30-80) ° C = 893- (30-80) ° C = 863-813 ° C

From the calculated forming temperatures of the base material Tzm and the additive material Tp _M , the temperature at the intersection of the intervals is 863 to 821 ° C, e.g. Mp: 840 ° C.

After bending this tube at a forming temperature of 90 ° at the above forming temperature, at a radius R = 6.D = 6 .324 = 1944 mm, the tube had the mechanical properties shown in Tables no. 2 and no. 4 on rows 1 and ovality shown in table no. 5 on line 1.

By comparing them together, it is found that the pipe bend had a slightly increased yield strength R _e and a yield strength R _m , only a very slightly increased ratio R _e / R _m and a very slightly reduced ductility A _s and more increased values of notch toughness in weld and heat affected zone.

A pipe bend with the above parameters meets all the requirements for a gas pipe, i.e. the oval cross-sectional area is 5.3% in the middle of the arc and 1.8% at the arc edges, which meets the required values - see Tab. 5th

The arc produced under these defined conditions corresponds to the required parameters placed on the pipe bend stressed by 40 bar internal pressure, ie yield strength R _e = min 240 MPa, strength limit R _m = 370 to 490 MPa, ratio R _e / R _m = max. 0.85, elongation A _s = min 24%, notch toughness KCV 0 ° C min 24 J / cm ² according to measuring point and ovality in the middle of the arc max. 6%, and 3% at the arc.

Example 2

The same tube made of the same materials and with the same mechanical properties before bending as in the previous example (see Table 1) was also bent to a 90 ° arc, at a radius R = 6.D, but at the selected forming temperature T = 760 ° C, which is about 50 to 60 ° C below the lower limit of the forming temperature range determined by the invention.

After bending, the tubular arc exhibited the mechanical and strength properties shown in Tables. 2 and no. When compared to the mechanical and strength properties before bending (see Tables 1 and 3, lines 2), it is found that they have not changed too much and the pipe complies with the strength. However, the ovality of the arc in the middle of the arc failed where it reached 13.6%, instead of the prescribed 6% (see Table 5).

Example 3

A tube of exactly the same mechanical properties before bending as in the previous examples 1 and 2 (see Table 1) was also bent to a 90 ° arc at a radius R = 6.D, but at the selected forming temperature T = 920 ° C which is about 50 to 60 ° C above the upper limit of the forming temperature range determined by the invention.

In this case, the bend wall of the elongated fiber side ruptured during bending, as the bending of the material coarsened as a result of exceeding the inventive ductile bending temperature, while significantly increasing the yield point Re and significantly reducing the ductility As and notch toughness KCV. 1 and 2, lines 3).

Example 4

A straight spiral welded pipe was made of the same material and welded with the same filler material as in the previous examples 1 to 3, but with the weld area exceeding the surrounding area by 3 mm and the tangent to the cross section of the inner weld seam clamped an angle of 82 ° to the base material.

The bending of the tube at a forming temperature T = 840 ° C, i.e. within the range of one of the inventive conditions, tore the wall of the tube on the pulled fiber side, with the crack initiating being at the point where the weld passes into the base material. The arc wall ruptured as a result of not complying with the other conditions laid down by the invention, namely the weld did not exceed the surrounding tube surface by more than 2 mm and the weld surface penetrated into the tube base material at an angle greater than 45 °.

As can be seen from Tables no. 2 and no. 4, lines 4, the bending strength and plastic properties of the pipe did not deviate from their same bending properties.

Tab. no. 1

Example Place of measurement Mechanical properties before bending together the Re [MPa] Rm [MPa] Re / Rm A _s [%] 1 perpendicular to the pipe axis 309 414 0.75 32.3 2 311 405 0.77 32.2 3 305 410 0.74 31.8 4 309 411 0.75 33.4 1 parallel to the pipe axis 315 422 0.75 27.8 2 311 418 0.74 29.2 3 309 415 0.74 27.6 4 319 420 0.76 29.7 1 weld 348 458 0.76 28.3 2 352 452 0.78 28.9 3 353 459 0.77 28.8 4 359 460 0.78 29.1

Tab. no. 2

Example Place of measurement Mechanical properties after bending Re [MPa] Rm [MPa] Re / Rm A ₅ [%] 1 perpendicular to the pipe axis 331 434 0.76 30.0 2 305 425 0.72 29.5 3 402 467 0.86 18.8 4 335 434 0.77 30.2 1 parallelepiped. with the axis of the pipe 332 420 0.80 32.8 2 311 418 0.74 33.7 3 423 481 0.88 17.3 4 339 430 0.78 32.6 1 weld 352 445 0.79 28.6 2 358 448 0.80 28.8 3 454 511 0.89 16.8 4 344 441 0.78 29.6

Tab. no. 3

Example Place of measurement Notch toughness before bending ° C [° C] [J / cm ² ] 1 perpendicular to the pipe axis 62 2 68 3 89 4 64 1 the center of the weld 149 2 138 3 145 4 151 1 heat affected zone 203 2 218 3 233 4 211

Tab. no. 4

Example Place of measurement Notched toughness after bending ° C [° C] [J / cm ² ] 1 perpendicular to the pipe axis 246 2 240 3 84 4 245 1 the center of the weld 242 2 239 3 41 4 245 1 heat affected zone 252 2 256 3 24 4 253

Tab. no. 5

Example roundness [%] in the middle of the arc (max. 6%) arc region (max. 2%) 1 5.3 1.8 2 13.6 4.9 3 5.2 1.7 4 5.6 1.9

Industrial usability

The method for producing pipe bends from straight spirally welded pipes can be used in the production of pipe bends with nominal diameters of 300 to 700 mm, wall thickness of 6 to 10 mm, for long-distance natural gas lines. The use of this method is also not excluded for the production of arches of other power or industrial distribution systems.

Claims (2)

PATENT CLAIMS Method for producing pipe elbows from straight spiral welded tubes made of coil-shaped steel strips, with a chemical composition by weight: C = 0.03 to 0.25%, Mn = 0.5 to 1.7%, Ni = 0 to 0.5%, Si = 0.2 to 0.7%, Al = 0.001 to 0.035%, P = 0.0 to 0.03%, S = 0.0 to 0.035%, Cr = 0 to 0.25 %, Mo = 0 to 0.1%, V = 0 to 0.08%, Nb = 0 to 0.05%, Ti = 0 to 0.06%, with Cr + Cu + Mo content of max. 0.45% and Nb + Ti + V content = max. 0.12%, the remainder being iron and process impurities, welded on both sides with butt weld, with an additive material with a chemical composition of C = 0.04 to 0.08%, Si = 0.3 to 0.7%, Mn = 0.9 to 1.7%, the remainder being iron and process impurities, characterized in that the weld is made so that it does not exceed the inner and / or outer surface of the pipe by more than 2 mm and the tangent to its cross-section at the weld animal with flat tube angle max. 45 °, whereby the spirally welded tube is bent in an electro-induction bender with a water spray at a forming temperature T, which is selected at the penetration or overlap of the temperature intervals [Ac3zm - (30 to 80 ° C)] and [A _C3 Pm - (30 to 80 ° C)], where Ac.3ZMis the temperature A _C 3 of the basic steel material and A _C 3pm is the temperature A _C 3 of the additive material, where Ac3 = 910 - (203 C) ¹ ' ² - 30 Mn + 44.7 Si [° C] Method for producing pipe bends according to claim 1, characterized in that at least the weld on the inside of the butt weld is made with two beadlets, the second bead overlapping at least partially the first bead. Fig. 1