Drill-string liner element furnished with an improved hardbanding layer

1. A drill-string liner element comprising:

at least one hardbanding layer;

wherein the hardbanding layer comprises one or more strands of filler metal, each having a width between 1 and 5 millimeters and deposited in adjacent manner to form a substantially continuous layer over a zone of the element,

wherein hardness in the thickness of the layer varies by less than 10 HRC over the zone.

2. An element according to claim 1 , further comprising a heat-affected zone underneath the zone, wherein the heat-affected zone extends at most to 2millimeters of depth.

3. An element according to claim 1 , wherein at least some of the strands extend at least partly in a helicoidal manner around the zone.

4. An element according to claim 1 , wherein each strand has a thickness greater than 2.4 millimeters.

5. An element according to claim 1 , further comprising a tubular part forming a pipe body, wherein the hardbanding layer is deposited over at least part of the body of the pipe.

6. An element according to claim 1 , wherein the zone is situated over a tubular portion of the element of thickness smaller than approximately 20 millimeters.

7. An element according to claim 1 , wherein the hardness for a given local radial thickness of the hard banding layer varies by less than 10 HRC in the local radial thickness.

8. An element according to claim 1 , wherein the hardness in the thickness of the layer varies monotonically in the thickness of the layer.

9. An element according to claim 1 , further comprising one or more open recesses on its exterior surface, wherein at least one of the hardbanding layers overlaps the recesses at least partly.

10. A method for hardbanding a metal piece with filler metal, wherein a welding installation including a torch of MIG/MAG type, a tool holder on which the torch is mounted, and a piece support are used, the method comprising:

a) placing a metal piece comprising a peripheral surface to be hardbanded at least partly on the piece support;

b) bringing the tool holder together with the torch and the piece support into an initial relative position in which the torch is directed at a first place of the peripheral surface;

c) displacing the tool holder and the piece support relative to one another up to a final position, in which the torch is directed at a second place of the peripheral surface, axially removed from the first place;

d) operating the torch in cold-welding mode during at least part of the relative displacement of the tool holder and piece support to deposit one or more strands of filler metal in adjacent manner while forming a substantially continuous layer over at least part of the peripheral surface extending from the first to the second place, the torch being operated in a cold-welding mode during at least part of simultaneous displacement in translation and rotation.

11. A method according to claim 10 , wherein the peripheral surface has a general shape generated by revolution, and the displacing c) comprises:

c1) displacing the tool holder and the piece support in relative translation such that the tool holder advances toward the final relative position; and

c2) displacing the tool holder and the piece support during at least part of their relative translation such that the tool holder turns around the peripheral surface at a same time.

12. A method according to claim 11 , wherein the operating d) comprises:

d1) operating the torch in the cold-welding mode during at least part of the simultaneous displacement in translation and rotation;

d2) immobilizing the torch relative to the tool holder at least during its operation in the cold-welding mode.

13. A method according to claim 12 , wherein the displacing c2) comprises:

c21) synchronizing the relative rotation of the tool holder and of the support with their relative translation during at least part of their relative translation such that the tool holder describes at least a portion of a helix relative to the peripheral surface; and

wherein the operating d1) comprises:

d11) operating the torch in cold-welding mode over at least part of the portion of a helix.

14. A method according to claim 12 , wherein the displacing c2) comprises:

c21) displacing the tool holder and the piece support in relative rotation such that the tool holder executes plural revolutions around the peripheral surface at the same time as the relative translation of the tool holder and of the piece support;

wherein the operating d 1) comprises:

d11) operating the torch in cold-welding mode during at least part of each revolution to deposit a strand of weld on the peripheral surface each time; and

wherein the immobilizing d2) comprises:

d21) maintaining the torch inclined relative to the tool holder, such that it is pointed during each revolution at the root of a weld strand deposited during the preceding revolution.

15. A method according to claim 13 , wherein the synchronization is such that a portion of a helix has joined turns, at least in part.

16. A method according to claim 10 , wherein the deposited strands each have a width between 1 and 5 millimeters.

17. A method according to claim 10 , wherein the torch is immobilized relative to the tool holder, at least during its operation in cold-welding mode.

18. A method according to claim 11 , wherein the tool holder and the support piece are translated relative to one another at a speed between 0 and 30 millimeters per minute during the displacing c1).

19. A method according to claim 11 , wherein the tool holder and the piece support are moved in rotation relative to one another at a speed between 0 and 10revolutions per minute during the displacing c2).

20. A method according to claim 10 , further comprising:

e) maintaining the piece at ambient temperature, at least until operation of the torch.

21. A method according to claim 10 , wherein the deposited strand or strands straddle one another over part of their length between 10 and 30%.