RU2412032C1 - Method of welding butts of longitudinal welded tubes from high-strength steels - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention may be used for welding longitudinal seams of large-diametre tubes from high-strength steels in construction of main pipelines, field and sea pipelines of oil and gas industry. X-grooved outer seam is laser-arc welded by consumable electrode in pulse-intermittent conditions. Arc pulsation frequency coincides with laser pulse frequency and makes 380-420 Hz. Thereafter, inner seam is welded in one pass in atmosphere of protective gas or under flux layer.

EFFECT: possibility to weld thick-wall tubes with high strength and quality properties.

2 dwg, 2 tbl

Description

The invention relates to methods for welding a longitudinal seam of large diameter pipes and can be used both in the production of welded pipes in electric welding units, and in the construction of trunk, field and offshore pipelines in the oil and gas industry.

A known method for the production of longitudinal welded pipes [RF patent No. 2296023]. The method includes forming a strip into a tube stock, heating the edges to be welded during transportation through a high-frequency inductor with a cylindrical ferromagnetic core installed inside the tube stock along its axis, subsequent rapprochement and compression of the edges by the rolls of the welding stand.

The disadvantage of this method is the need for plastic deformation of the welded edges, which requires the creation of large mechanical forces. The disadvantage is the need to remove the burr formed as a result of plastic deformation of the welded edges, which leads to an increase in the complexity of manufacturing pipes.

A known method of laser-arc welding, see patent [application WO No. 2006129024]. The method is characterized in that they create a single liquid weld pool of metal with the simultaneous exposure to a laser beam transmitted by an optical fiber, and act on an electric arc with a melting electrode in a protective gas environment. An electric arc provides melting of the filler material, and a laser beam stabilizes the combustion of the arc at high welding speeds and provides deep penetration of the welded edges. Welding by this method is performed to the full depth in one pass. The invention is mainly used for welding pipelines.

The disadvantage of this method is the low quality of the weld, since the laser-arc action described in the method is characterized by high welding and cooling rates, which cause the formation of a martensitic structure of the weld metal. As a result, this method does not provide the required mechanical properties of the weld metal when welding new high-strength pipe steels.

A known method of welding joints of longitudinal steel pipes, selected for the prototype [application JP No. 2007283356]. The welding method is implemented by performing an X-shaped cutting, the cutting angle from the outside is from 20 to 40 degrees. The external seam of the X-shaped groove is welded using laser-arc welding with a consumable electrode, namely a combination of an electric arc in a protective gas and a laser with an output power of 1 to 20 kW. After that, the inner seam is welded in one pass by an electric arc.

The disadvantage of this method is the inability to provide the required mechanical properties, i.e. poor quality of the welded joint when welding pipes with increased wall thickness.

The objective of the present invention is to increase the strength and quality of the weld of pipe joints with increased wall thickness.

A method is proposed for welding joints of longitudinal welded pipes of high-strength steels, including X-shaped cutting, then laser-arc welding is performed by a consumable electrode in a pulse-periodic mode of the X-shaped external weld, and the arc pulsation frequency coincides with the frequency of laser pulses and is 380-420 Hz. After that, the weld is welded in one pass with an electric arc in a shielding gas or under a flux layer. When welding in a pulsed-periodic mode, both a laser and an arc power source work. The simultaneous use of a pulsed-periodic mode of the laser and the arc source contributes to the organization of droplet transfer of the filler material - the melting electrode into the weld pool. The pulse frequency is determined by the time of formation of the droplet at the end of the consumable electrode. The use of a pulse-periodic mode, which determines, along with the chemical composition of the weld metal, the crystallization nature, allows to obtain a finely dispersed structure of the weld metal and contributes to the growth of its tensile strength and impact strength, which increases the strength and quality of the weld.

Metal filler wire is used as the filler material, the chemical composition of which provides the required chemical composition of the weld metal.

The method was tested on welding joints of longitudinal pipes from high-strength steels 10G2FBY with a thickness s = 22 mm. Initially, an X-shaped groove was performed, where α _o = 20 °, α _i = 60 °, d _o = 14 mm, d _f = 4 mm, d _i = 4 mm. (Figure 1)

Laser-arc welding was performed on a fiber laser LS-15 using a pulse welding arc power source EWM Phoenix 500 Expert Plus. Laser-arc welding with a consumable electrode was performed at an average laser power of 12.5 kW.

The pulse repetition rate was 380-420 Hz. As a consumable electrode, POWER BRIDGE 60M metal powder wire (TU 1274-021-11143754-2005) with a diameter of 1.2 mm was used, with a wire feed speed of 15 m / min, arc current 250-280 A, voltage 27.5 V, welding speed 1.5 m / min, shielding gas - 75% CO ₂ + 25% Ar. Got a weld with a depth of 14 mm. (Figure 2). Then, automatic arc welding of the inner seam was carried out according to the known technology of automatic welding in shielding gases by POWER BRIDGE 60M metal cored wire with a diameter of 1.2 mm at a wire feed speed of 9 m / min, arc current 290 A, voltage 24 V, welding speed 0.4 m / min , shielding gas - 75% CO ₂ + 25% Ar. A similar result will be obtained with automatic arc welding under a flux layer.

Macro section of a one-sided welded joint made with a laser radiation power of 12.5 kW and the use of POWER BRIDGE 60M metal-cored wire with a diameter of 1.2 mm (Figure 2).

To analyze the uniformity of filling the welded joint of the joints of straight-line pipes in the central part of the welded joint with weld metal, an analysis of the content of alloying elements contained in the metal-cored wire was performed at the X-ray microanalysis unit. The results of the analysis of the metal of the laser-arc seam at three points, as well as the typical composition of the deposited metal during arc surfacing are shown in table 1.

Point 1 is the top of the seam.

Point 2 is the middle of the seam.

Point 3 - the lower part of the seam.

Table 1. The chemical composition of the weld metal. Chemical composition by points Ni Mn Ti Si Fe Point 1 0.248 1,656 0.003 0.60 97,230 Point 2 0.154 1.51 0.006 0.317 98.47 Point 3 0.157 1,482 0.015 0.405 97,706 Typical composition of deposited metal for arc surfacing with POWER BRIDGE 60M wire 0.3-0.5 1.3-1.5 0.05-0.03 0.5-0.7 Ost.

During the laser-arc welding process, the penetration of the electrode deposited metal occurs along the entire height of the deep weld seam. Manganese undergoes the smallest burn-out, nickel and titanium undergo the greatest, however, the content of these elements is sufficient to stabilize the mechanical properties of the weld. When testing the toughness of the weld metal at a test temperature of -40 ° C, the results are shown in table 2.

Table 2. frequency Hz 380 400 420 Impact strength, J / cm ² 250 290 275

Impact strength characterizes the strength properties of a welded joint, the higher the viscosity, the higher the strength properties, which characterizes the quality of the weld of joints of longitudinal joints of high-strength steels.

Claims (1)

A method of welding joints of longitudinal welded pipes made of high-strength steels, including performing an X-shaped cutting, welding the external seam of the X-shaped cutting by laser-arc welding with a consumable electrode, welding the internal seam in one pass with an electric arc in a protective gas or under a flux layer, characterized in that laser-arc welding is carried out in a pulsed-periodic mode, and the frequency of the arc pulsations coincides with the frequency of the laser pulses and is 380-420 Hz.

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