GB2104106A - Heat treatment of weld seams - Google Patents

Abstract

The invention relates to the heat treatment of longitudinal weld seams in pipes, in particular large pipes. In order to provide more precise control of the area heated, and obtain a better energy efficiency than available in prior methods, the seam region is heated conductively by the passage of current between a plurality of contact points in the vicinity of or adjacent the seam, or on the seam itself with a spacing between adjacent contact points which corresponds to approximately 0.5 to 10.0 times the pipe wall thickness. <IMAGE>

Description

SPECIFICATION Method for the heating of longitudinal weld seams for the heat treatment of the seam region The invention relates to the heating of longitudinal weld seams in pipes, for example in the heat treatment, typically heat finishing treatment, of the seam region. The invention has particular application to longitudinal seams on large pipes with wall thicknesses of say 10 mm or more.

Heat treatment of the seam region on pipes has heretofore been accomplished using inductive heating (so-called line induction) or flame heating.

In these methods only a local heating takes place, and relative movement between pipe and heating apparatus (coil in the inductive heating, burner in the flame heating) must take place to heat a larger expanse of the seam. The simultaneous heating of the entire length of the seam, as is favourable for a heat treatment, is not possible. In addition, with either method, the introduction of heat takes place through the surface, and as a result of heat conduction, much of the heat generated is carried away. Both methods thus have the disadvantage of poor energy efficiency and the flame heating method in addition has that of burdening the environment with fumes.

The present invention seeks to provide a heating method in which the energy is concentrated along the pipe seam, enabling the material properties of this region to be substantially improved, while minimizing the affect on adjacent regions in the pipe. To this end the method of the invention comprises passing an electric current between contact points on or adjacent the seam, the spacing between adjacent contact points being 0.5 to 10.0 times the wall thickness of the pipe. The method of the invention is not restricted to steel pipes, but can be used for non-magnetic electrically conductive materials.

In one preferred arrangement according to the invention, the contact points are in two rows, one on either side of the seam. In the rows, which are normally substantially parallel, the contact points may be opposite one another or relatively offset.

In another arrangement, the contact points are on the weld seam in a single row, although this might be varied if the dimensions of the seam itself are large, or some additional body or component has to be incorporated in the treatment system.

The most substantial advantage of the method according to the invention lies in that the entire seam can be heated in one step. This means that also the entire longitudinal seam can be cooled in one operation. Through the penetration of the current into the pipe wall, the width of the heating zone can be considerably reduced in comparison with the known methods. The losses of energy are restricted, in contrast to the known methods, to the losses in the current supply cables.

Alteration of the contact spacing facilitates adaptation to other wall thicknesses and variation in such thickness and seam dimensions. Thus, local concentrations of material such as flanges and collars, can be heated evenly. Partial heatings of specific regions are also possible. Compared with the inductive method, the application of conductive heating is independent of frequency.

The invention will now be described by way of example and with reference to the accompanying diagrammatic drawing which illustrates various arrangements of contact points in methods according to the invention.

In the left part of the drawing a pipe 1 adjacent a weld seam 2 is provided a row of dot-shaped contact points 3. The contacts 3 are arranged parallel and lying opposite each other. In the middle part of the drawing, the contacts 4 are arranged on the weld seam and in the right part the contacts 5 are arranged parallel to the weld seam but staggered with respect to each other.

After pressing one of the contracts 3, 4 or 5 at the same time over the entire effective length of the seam, the supply of current is switched on.

The heating takes place in the region of the greatest current density; i.e., in the vicinity of the contact points and between the contacts.

Through alteration of the contact pressure during the heating process, locally differing heating speeds can be counterbalanced.

Claims

1. A method for heating a longitudinal weld seam on a pipe which method comprises passing an electric current between contact points on or adjacent the seam, the spacing between adjacent contact points being 0.5 to 10.0 times the wall thickness of the pipe.

2. A method according to Claim 1 wherein the contact points are arranged in two rows, one on either side of the seam.

3. A method according to Claim 2 wherein the rows are substantially parallel, the contact points thereof lying opposite one another.

4. A method according to Claim 2 wherein the rows are substantially parallel, contact points on either side of the seam being offset relative to one another.

5. A method according to Claim 1 wherein the contact points are arranged on the weld seam.

6. A method for heating a longitudinal weld seam on a pipe substantially as described herein with reference to the accompanying drawing.

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

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method for the heating of longitudinal weld seams for the heat treatment of the seam region The invention relates to the heating of longitudinal weld seams in pipes, for example in the heat treatment, typically heat finishing treatment, of the seam region. The invention has particular application to longitudinal seams on large pipes with wall thicknesses of say 10 mm or more. Heat treatment of the seam region on pipes has heretofore been accomplished using inductive heating (so-called line induction) or flame heating. In these methods only a local heating takes place, and relative movement between pipe and heating apparatus (coil in the inductive heating, burner in the flame heating) must take place to heat a larger expanse of the seam. The simultaneous heating of the entire length of the seam, as is favourable for a heat treatment, is not possible. In addition, with either method, the introduction of heat takes place through the surface, and as a result of heat conduction, much of the heat generated is carried away. Both methods thus have the disadvantage of poor energy efficiency and the flame heating method in addition has that of burdening the environment with fumes. The present invention seeks to provide a heating method in which the energy is concentrated along the pipe seam, enabling the material properties of this region to be substantially improved, while minimizing the affect on adjacent regions in the pipe. To this end the method of the invention comprises passing an electric current between contact points on or adjacent the seam, the spacing between adjacent contact points being 0.5 to 10.0 times the wall thickness of the pipe. The method of the invention is not restricted to steel pipes, but can be used for non-magnetic electrically conductive materials. In one preferred arrangement according to the invention, the contact points are in two rows, one on either side of the seam. In the rows, which are normally substantially parallel, the contact points may be opposite one another or relatively offset. In another arrangement, the contact points are on the weld seam in a single row, although this might be varied if the dimensions of the seam itself are large, or some additional body or component has to be incorporated in the treatment system. The most substantial advantage of the method according to the invention lies in that the entire seam can be heated in one step. This means that also the entire longitudinal seam can be cooled in one operation. Through the penetration of the current into the pipe wall, the width of the heating zone can be considerably reduced in comparison with the known methods. The losses of energy are restricted, in contrast to the known methods, to the losses in the current supply cables. Alteration of the contact spacing facilitates adaptation to other wall thicknesses and variation in such thickness and seam dimensions. Thus, local concentrations of material such as flanges and collars, can be heated evenly. Partial heatings of specific regions are also possible. Compared with the inductive method, the application of conductive heating is independent of frequency. The invention will now be described by way of example and with reference to the accompanying diagrammatic drawing which illustrates various arrangements of contact points in methods according to the invention. In the left part of the drawing a pipe 1 adjacent a weld seam 2 is provided a row of dot-shaped contact points 3. The contacts 3 are arranged parallel and lying opposite each other. In the middle part of the drawing, the contacts 4 are arranged on the weld seam and in the right part the contacts 5 are arranged parallel to the weld seam but staggered with respect to each other. After pressing one of the contracts 3, 4 or 5 at the same time over the entire effective length of the seam, the supply of current is switched on. The heating takes place in the region of the greatest current density; i.e., in the vicinity of the contact points and between the contacts. Through alteration of the contact pressure during the heating process, locally differing heating speeds can be counterbalanced. Claims

1. A method for heating a longitudinal weld seam on a pipe which method comprises passing an electric current between contact points on or adjacent the seam, the spacing between adjacent contact points being 0.5 to 10.0 times the wall thickness of the pipe.

2. A method according to Claim 1 wherein the contact points are arranged in two rows, one on either side of the seam.

3. A method according to Claim 2 wherein the rows are substantially parallel, the contact points thereof lying opposite one another.

4. A method according to Claim 2 wherein the rows are substantially parallel, contact points on either side of the seam being offset relative to one another.

5. A method according to Claim 1 wherein the contact points are arranged on the weld seam.

6. A method for heating a longitudinal weld seam on a pipe substantially as described herein with reference to the accompanying drawing.