GB1579607A - Method for avoiding end defects in the multi-wire longitudinal seam welding of tubes - Google Patents

Description

(54) METHOD FOR AVOIDING END DEFECTS IN THE MULTI-WIRE LONGITUDINAL SEAM WELDING OF TUBES (71) We, MANNESMANN AKTIENGESELLSCHAFT, a joint stock company organised under the laws of Germany, of Mannesmannufer 2, 4 Dusseldorf 1, Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method for avoiding end defects in multi-wire longitudinal seam consumable electrode arc welding of tubes, particularly in submerged arc welding of tubes. The method includes the provision of run-out pieces on the workpiece blank and is especially applicable in welding processes using high welding speeds.

With the introduction of multi-wire welding, ie with three or four electrodes in line ahead a considerable increase in welding speed was possible, and this in turn led to end defects which do not occur with singlewire welding or when using a slower welding speed.

For example a concave-shaped recess in the form of the tail of a comet is produced behind the welding head, which does in fact fill up as welding proceeds, but results in defects at the tube end and these either make it necessary to have a subsequent welding operation or make it necessary to sever the tube end. Extending the run-out pieces is possible from the process point of view only by tolerating relatively large waste pieces or increasing the size of all installations, i.e. tolerating economic disadvantages: Simply slowing down the welding speed does not give satisfactory results, since then the risk of material being broken through cannot be excluded.

In addition to these disadvantags, rewelding increases the outlay on labour/time, slower welding takes more time, and cutting off the tube ends increases the outlay on labour and also on material and time.

We have sought to provide a method whereby the residual tail occurring when using a high welding speed with multi-wire longitudinal seam welding is reduced.

Accordingly the present invention provides a method for avoiding end defects in multi-wire consumable electrode arc welding of longitudinal seams in tubes wherein a workpiece blank is provided with run-out pieces and, when welding is carried out in the run-out pieces, the welding speed is reduced in a controlled fashion and as the welding speed is reduced the welding current supplied is also reduced.

The method is particularly applicable to submerged arc welding. Run-in as well as run-out pieces may be welded to the workpiece blank.

By the method of the present invention, it is possible to ensure that the residual tail projecting into the remaining weld seam is so small that the concave depression of the weld seam does not reduce the wall thickness of the tube.

The run-out pieces which amount to 50 to 500 mm depending on the process, are so arranged, before the bending of the blank, at the external corners, that the weld seam preparation at the blank edges of the nonbent blank also includes the run-out pieces, the length of the run-out pieces being kept as short as possible.

The invention is further illustrated in the accompanying Drawings, wherein; Figure 1 shows a workpiece blank with the welded-on run-in and run-out pieces; Figure 2 shows a finished tube section; and Figure 3 shows a cross-section through a weld seam at the level of the concave dip of the weld seam on an enlarged scale.

In Figure 1, metal workpiece blank 1 is provided with two run-in and two run-out pieces 2, which are welded to the blank and are provided, like the blank 1, with prepared welding edges 3 for the weld seam.

The finish welded tube section shown in Figure 2 shows residual tail 4 extending over the run-out pieces.

Figure 3 shows a cross-section of a concave-shaped dip of weld seam 5 in the residual tail 4.

When carrying out the method, the welding speed is reduced in controlled manner within the run-out pieces, and the welding current supplied is reduced either by switching-off individual welding heads independently of one another or by the simultaneous reduction of the current supplied to the individual welding heads.

WHAT WE CLAIM IS: 1. A method for avoiding end defects in multi-wire consumable electrode arc welding of longitudinal seams in tubes wherein a workpiece blank is provided with run-out pieces and, when welding is carried out in the run-out pieces, the welding speed is reduced in a controlled fashion and as the welding speed is reduced, the welding current supplied is also reduced.

2. A method as claimed in Claim 1, wherein the welding process is a submerged arc welding process.

3. A method as claimed in Claim 1 or 2, wherein run-in pieces as well as run-out pieces are welded to the workpiece blank.

4. A method as claimed in Claim 1, substantially as herein described and with reference to the accompanying Drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. pieces 2, which are welded to the blank and are provided, like the blank 1, with prepared welding edges 3 for the weld seam. The finish welded tube section shown in Figure 2 shows residual tail 4 extending over the run-out pieces. Figure 3 shows a cross-section of a concave-shaped dip of weld seam 5 in the residual tail 4. When carrying out the method, the welding speed is reduced in controlled manner within the run-out pieces, and the welding current supplied is reduced either by switching-off individual welding heads independently of one another or by the simultaneous reduction of the current supplied to the individual welding heads. WHAT WE CLAIM IS:

1. A method for avoiding end defects in multi-wire consumable electrode arc welding of longitudinal seams in tubes wherein a workpiece blank is provided with run-out pieces and, when welding is carried out in the run-out pieces, the welding speed is reduced in a controlled fashion and as the welding speed is reduced, the welding current supplied is also reduced.

2. A method as claimed in Claim 1, wherein the welding process is a submerged arc welding process.

3. A method as claimed in Claim 1 or 2, wherein run-in pieces as well as run-out pieces are welded to the workpiece blank.

4. A method as claimed in Claim 1, substantially as herein described and with reference to the accompanying Drawings.