WO2013044901A1 - Method for producing a joining seam at band ends of steel during the continuous production of welded pipes - Google Patents

Abstract

The invention relates to a method for producing a joining seam at band ends of steel during the continuous production of welded pipes, wherein in a multistage process comprising severing of the band ends and subsequent finish-welding, individual bands are welded to form a continuous band and said continuous band is moulded by means of a deformation unit to form a slot pipe and the converging band edges are welded together. According to the invention, the band ends are joined to one another in one layer, dispensing with a separate band edge preparation process and a stapling operation, by means of a method combination of a plasma arc and gas-shielded metal arc welding (GMAW) process acting simultaneously at the same welding joint.

Description

 Method for producing a seam at steel strip ends in the continuous production of welded tubes

 description

The invention relates to a method for producing a connection seam at steel strip ends in the continuous production of welded tubes according to claim 1.

In the following, welded tubes are understood to mean both threaded tubes (so-called spiral seam tubes) and longitudinally welded tubes.

For the transport of water, oil and gas as a rule underpulver (UP), high frequency induction welded (HFI) or electrically resistance welded (ERW) pipes are used, which preferably from hot strip (coils) or from steel sheet in thicknesses of about 10 to over 25 mm. In the following, the term "band" or "steel band" is used as a synonym for hot-rolled wide strip or sheet steel.

From the brochure "Spiral Welded Large Pipes - Product Information -" (Salzgitter Mannesmann Großrohr 3/08), it is known to form the hot strip into a slotted tube in spiral forming into an injection molding device and to weld it into a tube in a two-stage process Hot strip formed in a forming unit of a tube forming machine into a tube

Deformation unit consists of a 3-roller beam bending system with an outer roller support cage and a so-called offset roller. With the height adjustable offset roller any band edge offset of the slot tube can be compensated. In this manufacturing process known as "HTS process" (Helical Seam-Two-Step), the strip edges of the slot tube are welded by means of a protective gas tack welding at a high welding speed of up to 15 m / min in a first method step, whereby the strip edges only partially be connected to each other.

The pipe diameter is influenced by the inlet angle of the belt in the Deformation unit and the bandwidth of the input material used. By means of the height adjustable offset roller can also be influenced on the diameter of the tube.

The final welding with a complete welding of the strip edges with an inner and outer seam is then carried out in a second step on separate

Welding stands by submerged arc welding.

The advantage over the conventional single-stage process, in which directly in the tube forming machine and the submerged arc welding seams are performed and the tube is thus finished welded in one step, is that due to the high

Speed at the tack weld a higher performance of

Tube molding machine is achieved.

After welding, the pipes are tested for quality at several stations. For this purpose, the end faces of the tubes receive a machining process and then a

To be subjected to water pressure test.

After the water pressure test, a final ultrasonic test of the entire weld seam is carried out. Sites that have become noticeable during the automatic ultrasonic test as well as the welds at the pipe ends are X-rayed. In addition, all pipe ends are subjected to ultrasound testing for doubling.

As part of quality assurance, integrated destructive and non-destructive tests are carried out in the production process. After the pipes including all test stations

Have undergone dimensional control, they are submitted for final acceptance.

In addition to the advantages of the economy of this process (faster forming and tack welding), the division of the processes into the steps tube forming and welding also results in technical advantages, by allowing separate optimization of the sub-steps tube forming and UP welding.

Furthermore, the generated tube geometry in the tube forming machine is not adversely affected by the UP welding process, thus improving compliance with given tolerance values. In HFI or ERW welding, on the other hand, the strip formed by rolling mills into the slotted tube runs without contact through a coil through which high-frequency current flows. As a result, a high-frequency current is generated in the tube, which closes around the tube surface and the two band edges to the circle. The strip edges are heated to the welding temperature in a very short time. By pressure rollers, the band edges

pressed together and welded without additional materials homogeneously as a longitudinal seam.

The quality assurance measures are comparable to those of UP spiral-welded pipes.

In order to enable continuous tube molding and welding, it is necessary to weld together the ends of the individual bands to form an endless band. From the prior art, it is z. B. from the specifications JP 56141984 A and

JP 2000141034 A discloses the production of a band connection seam in several

To carry out work steps.

First, before the formation of the tape, the ends of the wound tapes are separated and the band edges are processed with a plasma torch so that it has a joint with a defined geometry, for. B. I-, Y- or V-shaped obtained as a weld preparation.

According to JP 56141984, the tape after applying a defined

Tape edge geometry first plasma-cut by means of metal inert gas welding (MIG) stapled and then welded by means of UP welding.

To increase performance in the production of the band connection seam, it is known from JP 2000141034 A to fill the joint between the band ends to be welded with iron powder and then to weld together by means of inert gas welding in 2-wire technology.

Also well-known is the production of the band connection seam in the following steps:

First, the most irregularly shaped band end located in the deformation unit is, for example, by means of a thermal method, such as the plasma method, separated. Subsequently, the welding of inlet and outlet plates on

Tape end. In parallel, z. B. also separated by means of a cutting shear the beginning of the tape from the new band. After attaching the inlet and outlet sheets, the ends of the strips to be welded are provided over the bandwidth by means of a milling with a defined geometry as a weld preparation.

After these steps, the tape ends are aligned with each other in height, collapsed on impact or with a small air gap, fixed and a

Welding fuse made of ceramic attached. Thereafter, the bands are first connected to each other with stitching seams as a root layer and completely welded by means of inert gas and / or UP welding depending on the sheet thickness in one or more layers.

Here, the band ends to be joined are first stapled at the top, the later inside of the molded tube, and welded UP-g. Thereafter, the tape or sheet is formed in the Rohrinformung to a slotted tube and to the

welded together converging longitudinal edges. Depending on the customer order, the band connection seam remains in the finished tube and it is either from the other, the

Outside of the tube, the root position grooved and the counterpart of the tube

Band connection seam usually welded by means of UP process and ground sheet metal or the pipe section with the band connection seam is, for example by means of a plasma section cut, separated from the finished tube.

Although high-quality band connection seams can be produced with these known methods, they nevertheless have several disadvantages.

The main problem of the known methods for producing a band connection seam is that a joining process by the multi-stage welding process, consisting of separating the strip ends, seam preparation, stitching and welding, with relatively slow welding process depending on the wall thickness can be up to 30 minutes. During this time, the production of spiral tubes stops, which leads to high production losses when no tape storage is available.

In addition, for the production of the complete band connection seam by the finished pipe still to be executed counter weld and the for the application of the Exact seam preparation by thermal or machining methods very cost-intensive.

In order to avoid the aforementioned disadvantages, it is an object of the invention to improve the production of band connection seams for the production of welded steel tubes in that the band connection seam can be produced significantly faster and more cost-effectively with consistently high quality. This object is achieved starting from the preamble in conjunction with the characterizing features of claim 1. Advantageous developments are part of subclaims.

According to the teachings of the invention, a method is proposed in which the tape ends are waived by dispensing with the separate tape edge preparation and the stapling process by means of a combination of a process simultaneously acting on the same weld plasma and metal inert gas (MSG) welding process in one layer.

The advantage over the known methods is that this procedure does not require separate seam preparation. Even a simple cut of the tape ends, for example, with a pair of shears, is sufficient. As has been shown in experiments, the geometry of the striking edge as a seam preparation for welding the

Band ends completely out. However, a thermal separation cut, z. B. by autogenous cutting, plasma or laser cutting applicable.

In addition to the saving of the production step of the separate strip edge preparation, another major advantage of the invention is that by using the combined plasma MSG process, the band connection seam due to the

process-specific lower seam volume can be created much faster and with less filler metal than with the known methods and thus can also be dispensed with a stitching.

The welds of the band connection seams can advantageously be designed as a butt joint in a single layer in the I joint.

Plasma MIG / MAG welding is a combination of plasma and MIG welding. By combining both processes very favorable conditions are created Combine the advantages of both processes, ie the high melting rate of the MSG process with good gas protection and deep penetration as well as pore safety and accuracy of the plasma process.

The basic principle of this combined welding process is that a MSG arc is concentrically surrounded by a stationary plasma arc at a consumable wire-fed continuous filler material or serially operated with the plasma arc in a process zone. The taphole effect characteristic of the plasma process makes it possible to combine the concentrated energy of the plasma arc during the plasma process

Welding of butt joints evenly into the material over the entire workpiece thickness and penetrate. This results in the formation of a weld eyelet, whereby the liquid weld metal forced in the eyelet flows together again by the burner movement and thus forms the weld in combination with the coupled MSG process.

The high thermal load of all components, such as the electrode of the

Power contact tube and the plasma nozzle, require a good water cooling.

The plasma MSG process takes place in three consecutive basic phases. In the first phase, the ignition of the plasma arc takes place. In the second process section, the preheating phase, only the plasma arc burns without the feed motion being activated. In the third phase, the MSG arc and the feed motion are switched on. In this section, the actual Abschmelzvorgang takes place.

In test series with the combined plasma MSG process, various welding parameter settings were also different

Weld preparation (I, Y joint preparation) and combined

Suture configurations (HY and HV configuration) investigated on different sheet wall thicknesses. Based on these extensive studies, the following findings can be summarized:

Due to the large penetration depth of this high-performance process (plasma MSG torches with currents up to 500 A in plasma welding), even with sheet metal wall thicknesses> 10 mm, a separate weld seam preparation for producing a high-quality weld seam can be dispensed with, so that a simple I joint is sufficient. The quickly adjustable process stability of the plasma MSG process in the start and end phase of the weld by means of suitable parameter settings enables the elimination of inlet and outlet sheets even with larger wall thicknesses.

Destructive examination of the weld seams showed that the mechanical welding properties of the plasma MSG welds also in the use of various shielding gases and wire electrodes and in various

Combinations are at least as good as the welded joints produced by the known methods.

Since it is for the use of the plasma MSG process for the production of

Bandverbindungsnähten still gives no experience, have been extensive

Welding tests with different seam configurations as well as with different ones

Protective gases and filler materials performed. For the investigations were

Hot strips with wall thicknesses of 12.7 and 15.1 mm used. For the welding experiments, the shielding gases used were the mixed gas M21, which is composed of argon (Ar) and carbon dioxide (C02), and the protective gas C1, consisting of pure carbon dioxide (C02).

Welding wire electrodes with the designations EN

ISO 14341-A G42 2 C G3Si1 and EN ISO 16834-A G Mn3Ni1 Mo used. All

Ribbon joints were welded in one layer in the I joint.

In FIGS. 1 and 2, macrosections of the welded connections and, in Tables 1 and 2, essential welding parameters for these strip thicknesses are listed, with which perfect welded connections can be achieved.

By the inventively combined welding process is at the I-shock of the

Band ends reaches a Y-shaped seam formation.

With strip thicknesses of about 10 to more than 25 mm, welding speeds of 30 to 100 cm / min are achieved. The welding parameters of the plasma jet source are included

Amperages between 100 and 500 A (corresponding voltage values between 22 and 35 V) and the shielding gas welding source between 150 and 600 A (corresponding voltage values between 19 and 38 V). 10

Table 1

Table 2

 Welding parameters 15.1 mm wall thickness

Welding speed 45 -50 cm / min

Gas flow rate plasma 3 - 4 l / min

 Gas flow rate MSG 9 - 10 l / min

Seam configuration I or Y seam

Air gap approx. 1 mm

 Plasma welding current 250 - 350 A

MSG welding current 400 - 500 A

Claims

8 claims 1. A method for producing a seam at steel strip ends in the continuous production of welded tubes, wherein in a multi-stage process consisting of separating the strip ends and subsequent finish welding, individual bands are welded to form an endless belt and this by means of a Deforming unit is formed into a slotted tube and the converging band edges are welded together characterized, the strip ends are connected to each other in a single layer by dispensing with a separate strip edge preparation and a stapling operation by means of a combination of methods from a plasma and metal inert gas (MSG) welding process acting simultaneously on the same welding point. 2. The method according to claim 1 characterized, that the severing of the tape ends is effected by a thermal and / or mechanical separation cut. 3. The method according to claim 2 characterized, that the thermal separation cut is a plasma, laser or autogenous flame cutting. 4. The method according to claim 2 characterized, that the mechanical separation cut is a shearing off. 5. The method according to at least one of claims 1 - 4 characterized, that steel strips with thicknesses of more than 10 mm are used for welding. 6. The method according to at least one of claims 1-5 9 characterized, that steel strips with thicknesses of up to 30 mm are used for welding. 7. The method according to any one of claims 1-6 characterized, that the band ends to be joined are welded together in the I-joint. 8. The method according to any one of claims 1-7 characterized, that the welding of the tape ends at a speed of 30 cm / min up to 100 cm / min, with currents of plasma jet source between 100 and 500 A at Voltage values between 22 and 35 V and currents of inert gas welding source between 150 and 600 A at voltage values between 19 and 38 V.