GB2258836A

GB2258836A - Improvements in or relating to weld-cladding.

Info

Publication number: GB2258836A
Application number: GB9118003A
Authority: GB
Inventors: Roy Mathers
Original assignee: Mixalloy Ltd
Current assignee: Mixalloy Ltd
Priority date: 1991-08-21
Filing date: 1991-08-21
Publication date: 1993-02-24
Also published as: GB9118003D0

Abstract

An apparatus for feeding an elongate flexible welding consumable 5 to the head of an automatic welding machine comprises transport means 7 for conveying a continuous strip of the consumable along a helical path from a source to the welding head. The transport means preferably comprises a mandrel 7 provided with guides 8 for containing travel of the strip to a helical path. A method of weld-cladding 3 the base-metal inner surface of a pipe or generally tubular vessel or body comprises feeding an elongate, flexible welding consumable from a source via the head of an automatic welding machine such that the depositing edge of the welding consumable 5 is aligned with a line along the surface substantially parallel to the longitudinal axis of the pipe or vessel. The welding consumable is conveyed from the welding head towards the surface along a path which forms an angle of less than 90 DEG with respect to said line. <IMAGE>

Description

Improvements in or Relating to Weld-Cladding This invention relates to apparatus and method for feeding an elongate flexible welding consumable to the head of an automatic welding machine, e.g. a machine used to deposit weld metal by a submerged arc or resistance heated electroslag cladding technique.

The technique of weld-cladding, wherein an item formed of a base metal such as mild steel is coated with another metal or an alloy in the form of a strip or sheet by means of a submerged arc or electroslag welding process, is well known. Weld-cladding is used to provide a surface having a desirable combination of properties which are absent from the base metal, for example improved resistance to corrosion and/or wear resistance at ambient or elevated temperatures. By using the technique of weldcladding to deposit a surface coating, it is thus not necessary to fabricate the entire item from the cladding alloy.As is generally known, typical applications for weld-cladding may be found in the oil, chemical and power generation industries for, amongst other things, the cladding of tubes, plates, valves, heat exchanger components, flue gas desulphurisation equipment and the sheathing of risers on oil platforms.

In recent years, an improved method of manufacturing weld-cladding strip has been developed which involves the preparation of the strip from metal powder. In this method, which is described in, for example, our European Patent Application No. 162555, metal powders are mixed with a binder to form a slurry which is then deposited in an accurately metered thickness and width onto a conveyor, e.g. a continuous band of stainless steel, and then heated to gel and dry the slurry. The resulting continuous self supporting web of metal powder/binder matrix is then removed from the conveyor, passed through a rolling mill to compact the particles of powder and then sintered.

Further compactions and sinters may be provided to achieve the finished weld cladding strip. This method is highly advantageous in that it enables weld-cladding strips to be produced to a variety of precise chemical and physical specifications and to high level of purity. However, a drawback with weld-cladding strips produced in this way is that they are relatively brittle compared to weldcladding strips produced by more conventional methods, i.e. wherein the metal is fully alloyed rather than in the form of metal particles sintered together such that alloying occurs usually only at the interfaces between the particles. For the great majority of applications, the brittleness of the aforesaid strips is not a significant problem and this disadvantage is generally outweighed by the many virtues of the sintered strip.However, the brittleness can be a problem when the strip is to be used for the weld-cladding of the internal surface of a pipe or vessel of relatively small diameter. It is conventional practice to present the metal strip from the welding head to the base metal surface such that it is generally perpendicular to the surface. In the case of a pipe, wherein the cladding strip would be fed along the interior of the pipe from a roll of the strip positioned outside the pipe, the general requirement for the strip to be presented perpendicularly to the surface during the weldcladding process means that it is necessary to twist the metal strip through 900 about the longitudinal axis of the pipe and also through 90o about an axis orthogonal to the longitudinal axis.When the pipe is of relatively large diameter, this does not give rise to a problem, but with pipes of small diameter the very tight turns necessary to avoid the strip coming into contact with the wall of the pipe can cause fracturing of the strip.

It is an object of the present invention to avoid the aforementioned problems sometimes encountered with weldcladding strips, and to provide a method and apparatus for feeding a welding strip to a welding head which is suitable for use in relatively small diameter pipes and tubular vessels.

In a first aspect, the invention provides apparatus for feeding an elongate flexible welding consumable to the head of an automatic welding machine, the apparatus comprising transport means for conveying a continuous strip of the consumable along a helical path from a source to the welding head.

In a further aspect, the invention provides welding apparatus comprising an automatic welding head, means for supplying power to the welding head, and transport means for conveying a continuous strip of a welding consumable along a helical path from a source of the strip to the welding head.

The transport means conveniently takes the form of a mandrel provided with guides for constraining travel of the strip to a helical path. Such guides may take the form of grooves, channels or raised ledges in or on the surface of the mandrel. Advantageously, the pitch of the helix is selected such that for each 3600 turn about the longitudinal axis of the mandrel, the strip is advanced along the mandrel by a distance corresponding to the width of the strip.

A mechanism such as a pair of pinch rollers, e.g.

adjacent the welding head, may be employed to advance the strip along the helical path.

Instead of the mandrel, the strip may be conveyed towards the welding head in a helical path by means of an array of guides, e.g. rollers, arranged in an appropriate helical configuration, at least one of the guides being actuable to move the strip along its helical path.

Where a mandrel is employed, this may take the form of inner and outer tubular elements with the helical path being defined by a pair of helical guide walls linking the two tubular elements. The guide wall can be continuous or discontinuous, for example the guide wall may be defined as a series of discrete guide elements spanning the inner and outer tubular elements. Conveniently the bore of the inner tubular element can serve as a conduit for e.g. the power line to the welding head or a supply of flux granules or powder.

The invention also provides a method of depositing by welding a metal coating on a base metal surface, the method being characterised in that a continuous strip of a welding consumable is conveyed along a helical path from a source of the strip to a welding head, and thence towards the base metal surface.

In an alternative aspect of the invention, there is provided a method of weld-cladding the base-metal inner surface of a pipe or generally tubular vessel or body, the method comprising feeding an elongate flexible welding consumable from a source thereof via the head of an automatic welding machine such that the depositing edge of the welding consumable is aligned with a line along the surface which is substantially parallel to the longitudinal axis of the pipe or tubular vessel or body; characterised in that the welding consumable is conveyed from the welding head towards the surface along a path which forms an angle of less than 900 with respect to said surface line.

Conveniently the angle between the feed-path and the surface line is in the range from about 300 to 600.

The advantage of this arrangement is that it reduces the tightness of the turns in the consumable which are necessary in order to bring the consumable from its axial alignment, as it advances along the pipe or vessel from its source outside the said pipe or vessel, into the alignment necessary for correct presentation of the depositing edge of the consumable to the surface of the pipe or vessel. In consequence, any tendency of the consumable to fracture is minimised.

The invention also provides an apparatus for use in the method of weld cladding defined hereinabove, the apparatus comprising a welding head and means suitable for conveying an elongate, flexible welding consumable from a source thereof via the welding head towards the base-metal inner surface of a pipe or generally tubular vessel or body such that the depositing edge of the welding consumable is aligned with a line along the surface which is substantially parallel to the longitudinal axis of the pipe or tubular vessel or body; characterised in that the conveying means is adapted to direct the consumable from the welding head towards the surface along a path which forms an angle of less than 900 (e.g. in the range from about 300 to 600) with respect to said surface line.

The invention will now be illustrated in more detail by reference to the accompanying drawings in which: Figure 1 is a schematic representation of a side elevation of an apparatus according to one aspect of the invention; Figure 2 is a schematic representation of a side elevation of an apparatus according to another embodiment of the invention; and Figure 3 is a view in cross-section along the line A A shown in Figure 2.

Thus, in Figure 1, there is shown a metal tube 1 having a wall 2 which has been partially coated on its inner surface with a layer 3 of an alloy. The apparatus for weld-cladding the inner surface of the tube 1 comprises an automatic welding head of the type generally known for use in the deposition of metal layers through the submerged automatic welding technique. The automatic welding head, which is represented schematically by the box 4 shown in phantom, may comprise means for advancing a consumable welding strip 5 (for example a sintered consumable welding strip of the type produced by Mixalloy Limited) towards the surface of wall 2. The welding head 4 is connected to a power source via cable 6 which passes along the hollow centre of a cylindrical mandrel 7 upon which the welding strip 5 is wound.Cylindrical mandrel 7 is designed to feed the welding strip 5 from a source (not shown) located outside the pipe, to the welding head 4.

Mandrel 7 is provided with a pair of helical guides 8 which ensure that the welding strip is helically wound on the mandrel. The mandrel 7 may be rotatable about its longitudinal axis so as to advance the welding strip 5 inwardly towards the welding head 4, or it may be irrotatably mounted, in which case advancing/driving means such as appropriately located pinch rollers may be provided to cause the welding strip to advance along its helical path to the welding head 4.

During the welding-cladding process the welding head 4 (and mandrel) can be moved along the interior of the tube 1 in the direction of the arrow, in conventional fashion.

As indicated above, the mandrel may be hollow, in which case its interior can serve as a conduit through which power lines and/or flux granules or powder (not shown) can be passed. By feeding the welding strip to the welding head along a helical path, the problem of the fracturing of the welding strip, which can occur when the strip is bent in too tight a curve, is avoided.

It will be appreciated that the mandrel 7 will be appropriately mounted on a suitable housing or mounting (not shown), which typically will be located outside the pipe, although a part of parts of any housing or mounting may extend into the pipe.

Figures 2 and 3 illustrate an alternative aspect of the invention. Thus, the welding strip 5 is fed along the inside of pipe 8 from a source (not shown) outside of the pipe 1 in such a way that the strip is initially substantially parallel to the walls of the pipe 8. The strip 5 passes through a welding head, generally designated 9, which is provided with guide means for twisting and advancing the strip towards the surface 10 of the pipe 8 such that leading edge 11 of the strip 5 lies along a line substantially parallel to the longitudinal axis of the pipe 8.The guide means associated with the welding head differs from conventional guide means in that rather than aligning the edges 12 and 13 of the strip 5 such that they are normal to the surface of the pipe 8, the said means guide the strip 5 such that edge 12 is at an angle of less than 900, e.g. 300 to 600 with respect to the surface 10 of the pipe.

Such an arrangement is advantageous in that it enables sintered weld-cladding strips to be used in the cladding of much smaller diameter pipes and tubes than has hitherto been possible, since the tight turns previously found necessary in order to bring the welding strip from an axial alignment through two 900 twists into an alignment normal to the surface of the pipe or tube, are avoided.

It will be readily apparent that the foregoing embodiments are described by way of illustration only and numerous modifications may be made without departing from the spirit of the invention.

Claims

CLAIMS:

1. Apparatus for feeding an elongate flexible welding consumable to the head of an automatic welding machine, the apparatus comprising transport means for conveying a continuous strip of the consumable along a helical path from a source to the welding head.

2. Apparatus according to Claim 1 wherein the transport means takes the form of a mandrel provided with guides for constraining travel of the strip to a helical path.

3. Apparatus according to Claim 2 wherein the guides take the form of grooves, channels or raised ledges in or on the surface of the mandrel.

4. Apparatus according to Claim 2 or Claim 3 wherein the pitch of the helix is selected such that for each 3600 turn about the longitudinal axis of the mandrel, the strip is advanced along the mandrel by a distance corresponding to the width of the strip.

5. Apparatus according to Claim 1 wherein the strip is conveyed towards the welding head in a helical path by means of an array of guides arranged in an appropriate helical configuration, at least one of the guides being actuable to move the strip along its helical path.

6. Apparatus according to any one of Claims 2 to 4, wherein the mandrel takes the form of inner and outer tubular elements with the helical path defined by a pair of helical guide walls linking the two tubular elements.

7. Apparatus according to Claim 6 wherein the guide walls are continuous.

8. Apparatus according to any one of Claims 2 to 4 or 6 and 7, wherein the mandrel has an inner bore which defines a service conduit, eg for the power line to the welding head and/or a supply of flux granules or powder.

9. Welding apparatus comprising a welding head, means for supplying power to the welding head, and transport means for conveying a continuous strip of a welding consumable along a helical path from a source of the strip to the welding head, said transport means being as defined in any one of Claims 1 to 8.

10. A method of weld-cladding the base-metal inner surface of a pipe or generally tubular vessel or body, the method comprising feeding an elongate, flexible welding consumable from a source thereof via the head of an automatic welding machine such that the depositing edge of the welding consumable is aligned with a line along the surface, which line is substantially parallel to the longitudinal axis-of the pipe or tubular vessel or body; characterised in that the welding consumable is conveyed from the welding head towards the surface along a path which forms an angle of less than 900 with respect to said line.

11. A method according to Claim 10 wherein the angle between the feed path and the surface line is in the range from about 300 to about 600.

12. Apparatus for use in the method defined in Claim 10 or Claim 11, the apparatus comprising an automatic welding head and means suitable for conveying an elongate, flexible welding consumable from the source thereof via the welding head towards the base-metal inner surface of a pipe or generally tubular vessel or body such that the depositing edge of the welding consumable is aligned with a line along the surface, which line is substantially parallel to the longitudinal axis of the pipe or tubular vessel or body; characterised in that the conveying means are adapted to direct the consumable from the welding head towards the surface along a path which forms an angle of less than 900 (e.g. in the range from about 300 to 600) with respect to said surface line.

13. Apparatus substantially as described herein with reference to the accompanying drawings Figures 1 to 3.

14. A method of welding-cladding a surface substantially as described herein with reference to Figures 1 to 3.