WO2019164488A1

WO2019164488A1 - Welding tool and methodology for forming welding joints free of notch-induced cracking

Info

Publication number: WO2019164488A1
Application number: PCT/US2018/019128
Authority: WO
Inventors: Gerald J. Bruck
Original assignee: Siemens Aktiengesellschaft
Priority date: 2018-02-22
Filing date: 2018-02-22
Publication date: 2019-08-29

Abstract

A welding tool and methodology for forming a welding joint with a weld backing member are provided. The tool may be in the form of a weld backing member (12) including a backing member surface positioned against a back side of a welding joint (14) for joining two workpieces (16). The backing member surface comprises at least one trench (20) disposed along a periphery of a root gap (22) in a joint root of the welding joint. The design of the weld backing member and methodology are effective to suppress formation of notches (e.g., stress risers) in the joint root of the welding joint and in turn effective to eliminate cracking.

Description

WELDING TOOL AND METHODOLOGY FOR FORMING WELDING JOINTS FREE OF NOTCH-INDUCED CRACKING

[0001] BACKGROUND

[0002] 1. Field

[0003] Disclosed embodiments are generally related to welding, and, more particularly, to a welding tool and methodology effective for suppressing formation of notch-induced cracking in welding joints.

[0004] 2. Description of the Related Art

[0005] Weld backing members serve as a welding tool to, for example, shield from atmospheric gases (and concomitant chemical reactions that could impair welding quality) a back side of a welding joint for joining two workpieces.

Additionally, weld backing members can provide some tolerance to variation in the configuration of a root gap in the joint root of the welding joint. Unfortunately, certain known weld backing members tend to form notches at the joint root that constitute stress raisers, and in turn can eventually lead to failure of the welding joint. See US patent 3,432,915 for one example of a weld backing member and method of forming welded joints in metallic workpieces or between metallic workpieces. This design involves the complexity of depositing on the contact area of the weld backing member a refractory oxide layer to purportedly eliminate the stress raisers. This design further presumes welding applications where the weld backing member can be removed after completion of the root run of the weld. This is not always the case since there are various welding applications where access to the weld backing member is not feasible. At least in view of the foregoing considerations, there is a need for an improved design and methodology involving weld backing members. [0006] BRIEF DESCRIPTION

[0007] One disclosed embodiment is directed to a welding tool including a backing member surface positioned against a back side of a welding joint for joining two workpieces. The backing member surface includes at least one trench disposed along a periphery of a root gap in a joint root of the welding joint.

[0008] In accordance with a further disclosed embodiment, a method for forming a welding joint with a weld backing member is disclosed. The method allows forming in a backing member surface of the weld backing member at least one trench, and positioning the backing member surface against a back side of the welding joint. The trench is disposed along a periphery of a root gap in a joint root of the welding joint.

[0009] The design of the weld backing member and methodology are effective to suppress formation of notches (e.g., stress risers) in the joint root of the welding joint and in turn effective to eliminate cracking, which otherwise could form.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a cross-sectional view of a disclosed welding tool involving a weld backing member that may be used for forming a welding joint for joining two workpieces.

[0012] FIG. 2 is a cross-sectional view of another disclosed weld backing member, as may include a protruding tongue.

[0013] FIG. 3 is a cross-sectional view of another disclosed weld backing member, as may include one or more inert gas feed channels. [0014] FIG. 4 is a cross-sectional view of still another disclosed weld backing member, as adapted for joining non-coplanar workpieces. [0015] DETAILED DESCRIPTION

[0016] The inventor of the present invention has recognized that a practical limitation of weld backing members, such as may be fused with a root pass, and may be left in place with a formed welding joint, is a tendency of notch formation in the joint root of the welding joint. As noted above, these notches constitute stress raisers (i.e., areas where stress may be substantially concentrated) that can lead to crack initiation and propagation.

[0017] In view of such recognition, the present inventor proposes an innovative design for weld backing members and methodology effective to suppress formation of notches in the joint root of the welding joint. Disclosed embodiments in a cost-effective manner make use of uncomplicated structural features in the weld backing member to avoid notch formation in the joint root, (e.g., stress raisers) and in turn avoid crack initiation and propagation, as commonly encountered in conventional weld backing members.

[0018] Without limitation, disclosed embodiments may be used in a variety of welding applications, as may be used to fabricate or repair metallic components, such as without limitation, combustor components, exhaust components, etc., for turbomachinery, such as gas turbine engines. Without limitation, welding

configurations that can benefit from disclosed embodiments may include: welding configurations substantially inaccessible to welding operations from both of the mutually opposed sides of the workpieces being joined; welding configurations where shielding with an inert gas on the back side of the welding joint may not be feasible or at least may be substantially burdensome; and welding configurations subject to large variation in the configuration of the root gap. [0019] In the following detailed description, various specific details are set forth in order to provide a thorough understanding of such embodiments. However, those skilled in the art will understand that embodiments of the present invention may be practiced without these specific details, that the present invention is not limited to the depicted embodiments, and that the present invention may be practiced in a variety of alternative embodiments. In other instances, methods, procedures, and components, which would be well-understood by one skilled in the art have not been described in detail to avoid unnecessary and burdensome explanation.

[0020] Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent, unless otherwise indicated. Moreover, repeated usage of the phrase "in one embodiment" does not necessarily refer to the same embodiment, although it may. It is noted that disclosed embodiments need not be construed as mutually exclusive embodiments, since aspects of such disclosed embodiments may be appropriately combined by one skilled in the art depending on the needs of a given application.

[0021] The terms "comprising", "including", "having", and the like, as used in the present application, are intended to be synonymous unless otherwise indicated. Lastly, as used herein, the phrases“configured to” or“arranged to” embrace the concept that the feature preceding the phrases“configured to” or“arranged to” is intentionally and specifically designed or made to act or function in a specific way and should not be construed to mean that the feature just has a capability or suitability to act or function in the specified way, unless so indicated. [0022] FIG. 1. is a cross-sectional view of a disclosed welding tool 10 involving a disclosed weld backing member 12, such as a bar, plate, ring, strip, etc., that may be used for forming a welding joint 14 for joining two metallic workpieces 16. Weld backing member 12 includes a backing member surface 18 positioned against a back side of welding joint 14 for joining workpieces 16. Backing member surface 18 includes at least one trench 20 disposed along a periphery of a root gap 22 in a joint root 24 of welding joint 14. Trench 20 may be made up of a trench pair, where each trench 20 is arranged on a respective side of root gap 22. This trench arrangement is effective to receive molten root pass when the welding joint is formed, and in turn this is effective to suppress formation of notches in the joint root 24 of welding joint 14.

[0023] Without limitation, as shown in FIG. 2, weld backing member 12 may optionally include a tongue 25 disposed between the respective trench pair 20. A tip 26 of tongue 25 may be arranged to protrude beyond backing member surface 18. Tongue 25 may be used for aligning the respective trench pair 20 relative to root gap 22 (FIG. 1) by way of the protruding tip 26 of tongue 25. Additionally tongue 25 may serve to set the separation between workpieces 16 and to contribute material to the weld root pass. A base 28 of tongue 25 may be configured to define a portion of a wall 30 of the respective trench pair 20.

[0024] FIG. 3 is a cross-sectional view of another disclosed weld backing member 40, as may optionally involve one or more inert gas feed channels 42 in fluid communication with trench/es 20. Without limitation, when forming the welding joint, an inert gas may be conveyed into trench/es 20 through inert gas feed channel/s 42, and this is effective for shielding, for example, a back side of the joint root pass.

[0025] A non-limiting alternative technique may be, prior to forming the welding joint, coating (e.g., painting) with a temporarily liquid fluxing agent (upon drying leaving solid residue of flux) surfaces in the weld backing member and the involved workpieces that could melt while forming the welding joint, and

consequently can benefit from shielding provided by the fluxing agent. Without limitation, such surfaces may include trench/es 20, tongue 25, and neighboring substrate back surfaces. Non limiting examples of this fluxing agent may be Solar flux, Superior flux, etc. [0026] Another non-limiting alternative technique for shielding the back side of the joint root pass may be, prior to forming the welding joint, filling trench/es 20 with a granulated (e.g., powdered) flux, such as would be packed against the molten metal and form a slag, e.g., initially a molten slag and eventually becoming a solidified slag. As would be appreciated by those skilled in the art, this powdered flux would be similar to fluxes used in submerged arc welding or electroslag welding. In this application, the grains forming this powdered flux would be sufficiently fine to provide and maintain appropriate contact with the molten metal.

[0027] It will be appreciated that the disclosed embodiments respectively illustrated in FIGs. 1-3 are embodiments representative of arrangements where the respective sides of root gap 22 are formed by workpieces 16 that share a common plane 50 (FIG. 1), and the respective longitudinal (or circumferential) axes

(represented by dots 52) of the respective trench pair 20 may be parallel relative to common plane 50. [0028] FIG. 4. is a cross-sectional view of still another disclosed weld backing member 70, as may be adapted for joining non-coplanar workpieces 72. In this embodiment respective sides of the root gap are formed by non-coplanar workpieces 72 and the respective trench pair 20 may be arranged between tongue 25 and respective support portions 74 that in this embodiment constitute the backing member surface of weld backing member 70. Without limitation, the respective support portions 74 are arranged to provide support against a corresponding back surface of the non-coplanar workpieces 72.

[0029] It will be appreciated that the trench/es 22 formed in disclosed weld backing member may comprise longitudinally-extending trench/es, such as may be used without limitation for forming linearly-extending welding joints. One non limiting application may be linear welding joints involved in an exhaust of a gas turbine engine, such as linear welding joints between an internal stiffener and a strut shield in the exhaust of the gas turbine engine. [0030] It will be further appreciated that the trench/es 22 formed in disclosed weld backing member may additionally comprise circumferentially-extending trench/es, as may be used without limitation for forming curving (e.g., circular) welding joints. One non-limiting application may be circular welding joints that may be additionally involved in the exhaust of the gas turbine engine, such as between a standoff and the strut shield in the exhaust of the gas turbine engine. A standoff is a structural component that separates a strut from the strut shield. Both types of joints involve welding from outside of the gas turbine component as there is no access from inside of the gas turbine component. As will be appreciated by one skilled in the art, gas turbine components are commonly subject to substantial fatigue loadings, such as in the hot temperature environment of the exhaust of the gas turbine engine, and, consequently, suppression of formation of notches in the joint root is a significant practical benefit provided by disclosed weld backing members.

[0031] Disclosed embodiments in a cost-effective manner make use of uncomplicated structural features—such as trenches, alone or in combination with inert gas feed channels— formed in the weld backing member to avoid notch formation in the joint root, (e.g., stress raisers) and in turn avoid crack initiation and propagation, as commonly encountered in conventional weld backing members.

[0032] While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many

modifications, additions, and deletions can be made therein without departing from the scope of the invention and its equivalents, as set forth in the following claims.

Claims

What is claimed is:

1. A welding tool comprising:

a weld backing member (12, 40, 70) including a backing member surface (18) positioned against a back side of a welding joint (14) for joining two workpieces (16), wherein the backing member surface comprises at least one trench (20) disposed along a periphery of a root gap (22) in a joint root (24) of the welding joint.

2. The welding tool of claim 1, wherein the at least one trench comprises a respective trench pair (20), wherein each respective trench of the respective trench pair is arranged on a respective side of the root gap.

3. The welding tool of claim 2, wherein the weld backing member further comprises a tongue (25) disposed between the respective trench pair, a tip (26) of the tongue arranged to protrude beyond the backing member surface.

4. The welding tool of claim 3, wherein a base (28) of the tongue is configured to define a portion of a wall (30) of the respective trench pair.

5. The welding tool of claim 1, further comprising at least one inert gas feed channel (42) in fluid communication with the at least one trench (20) when the welding joint is formed.

6. The welding tool of claim 1, wherein each respective trench of the at least one trench comprises a longitudinally-extending trench.

7. The welding tool of claim 1, wherein each respective trench of the at least one trench comprises a circumferentially-extending trench.

8. The welding tool of claim 2, wherein respective sides of the root gap are formed by workpieces that share a common plane (50), and respective longitudinally or circumferentially-extending axes of the respective trench pair are parallel relative to the common plane.

9. The welding tool of claim 3, wherein respective sides of the root gap are formed by non-coplanar workpieces (72) and the respective trench pair is arranged between the tongue and respective support portions (74) that constitute the backing member surface, wherein the respective support portions are arranged to provide support against a corresponding back surface of the non-coplanar workpieces.

10. The welding tool of claim 1, wherein the at least one trench is arranged to receive molten root pass when the welding joint is formed, the molten root pass received in the at least one trench effective to suppress formation of notches in the joint root.

11. A method for forming a welding joint with a weld backing member, the method comprising:

forming in a backing member surface of the weld backing member at least one trench; and

positioning the backing member surface against a back side of the welding joint, wherein the at least one trench is disposed along a periphery of a root gap in a joint root of the welding joint.

12. The method of claim 11, wherein the at least one trench formed in the backing member surface of the weld backing member comprises a respective trench pair, and the method further comprises arranging each trench of the respective trench pair on a respective side of the root gap.

13. The method of claim 12, forming in the weld backing member a tongue disposed between the respective trench pair, and arranging a tip of the tongue to protrude beyond the backing member surface.

14. The method of claim 13, wherein the forming of the tongue in the weld backing member comprises configuring a base of the tongue to define a portion of a wall of the respective trench pair.

15. The method of claim 11, further comprising forming in the weld backing member at least one inert gas feed channel arranged to provide fluid communication with the at least one trench.

16. The method of claim 15, when forming the welding joint, conveying an inert gas into the at least one trench through the at least one inert gas feed channel.

17. The method of claim 13, prior to forming the welding joint, coating the at least one trench, tongue, and neighboring substrate back surfaces with a liquid fluxing agent.

18. The method of claim 11, receiving molten root pass in the at least one trench when the welding joint is formed, the molten root pass received in the trench effective to suppress formation of notches in the joint root.

19. The method of claim 13, further comprising aligning the respective trench pair relative to the root gap by way of the protruding tip of the tongue.

20. The method of claim 11, prior to forming the welding joint, filling the at least one trench with a granulated flux.