WO2019083566A1

WO2019083566A1 - Method of temper bead welding using a conformal heat conductive material for stress reduction

Info

Publication number: WO2019083566A1
Application number: PCT/US2018/035255
Authority: WO
Inventors: Gerald J. Bruck
Original assignee: Siemens Aktiengesellschaft
Priority date: 2017-10-24
Filing date: 2018-05-31
Publication date: 2019-05-02

Abstract

A method of reducing stress of a weld in a gas turbine engine involves applying a temper bead weld heat application. A temper bead weld is applied by applying a conformal heat conductive material to a surface of a component having a weld. Heat is then applied to the conformal heat conductive material. The application of the heat tempers and reduces stress of the weld without re-melting of the weld.

Description

METHOD OF TEMPER BEAD WELDING USING A CONFORMAL HEAT CONDUCTIVE MATERIAL FOR STRESS REDUCTION

BACKGROUND

[0001] 1. Field

[0002] Disclosed embodiments are generally related to turbine engines, and in particular to temper bead welding.

[0003] 2. Description of the Related Art

[0004] Gas turbine engines typically comprise a casing or cylinder for housing a compressor section, a combustion section, and a turbine section. A supply of air is compressed in the compressor section and directed into the combustion section. The compressed air enters the combustion inlet and is mixed with fuel. The air/fuel mixture is then combusted to produce high temperature and high pressure (working) gas. This working gas then travels through the transition and into the turbine section of the turbine.

[0005] The turbine section typically comprises rows of vanes which direct the working gas to the airfoil portions of the turbine blades. The working gas travels through the turbine section, causing the turbine blades to rotate, thereby turning a rotor attached thereto. The rotor is also attached to the compressor section, thereby turning the compressor and also operatively connected to an electrical generator for producing electricity.

[0006] High efficiency of a combustion turbine is improved by heating the gas flowing through the combustion section to as high a temperature as is practical. However, the hot gas may degrade various metal turbine components, such as the combustor, transition ducts, vanes, ring segments, and turbine blades as it flows through the turbine.

[0007] With gas turbine engines and similar large sized structures (e.g. for power generation, oil refining and chemical processing), it is inconvenient or impractical to insert the structure in a furnace for heat treating after welding. Temper bead welding is a widely practiced alternative to such post weld heat treatments. These techniques are used to soften or temper hardened microstructures produced in underlying weld metal and weld heat affected zones. The heat from additional weld passes provides the heating instead of furnace, torch or localized electric resistance blanket heating. By its localized effect, temper bead welding is also useful to avoid distortions and unintended heating of heat-sensitive parts of a completed structure.

[0008] A potential benefit of temper bead welding is reduction in weld residual stresses, however, because the temper bead itself causes fusion to the substrate, it also introduces residual stresses upon its solidification and shrinkage. So the temper bead can result in no reduction or even net increases of residual stresses. Because of this temper welding is generally limited in application to carbon and alloy steels where tempering of martensite in weld heat affected zones is required and where residual stress reduction is not the primary objective. Also, the temper bead method is typically not useful for austenitic alloys and alloys where hardening transformations do not occur.

[0009] Therefore being able to expand the use of temper bead welding can help in achieving reduction in weld stresses.

SUMMARY

[0010] Briefly described, aspects of the present disclosure relate to a method for providing temper bead welding in systems.

[0011] An aspect of the present disclosure may be a method of reducing stress of a weld. The method may comprise applying a conformal heat conductive material to a surface of the component where the weld is located; and applying heat to the conformal heat conductive material, whereby the application of the heat reduces stress of the weld without re-melting of the weld.

[0012] Another aspect of the present invention may be a method of applying a temper bead weld to austenitic alloys. The method may comprise applying a conformal heat conductive material to a surface of a component; and applying heat to the conformal heat conductive material, whereby the application of the heat reduces stress of the weld without re-melting of the weld.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 is a schematic diagram illustrating a temper bead weld applied to a gas turbine engine component that uses a sacrificial layer. [0014] Fig. 2 is a flow chart of the method for applying the temper weld bead.

[0015] Fig. 3 is a schematic diagram illustrating a temper bead weld applied to a gas turbine engine component that directly applies heat to a conformal heat conductive material.

DETAILED DESCRIPTION

[0016] To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are disclosed hereinafter with reference to implementation in illustrative embodiments. Embodiments of the present disclosure, however, are not limited to use in the described systems or methods and may be utilized in other systems and methods as will be understood by those skilled in the art.

[0017] The components described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components that would perform the same or a similar function as the components described herein are intended to be embraced within the scope of embodiments of the present disclosure.

[0018] Fig. 1 is a schematic diagram illustrating a temper bead weld 14 applied to a gas turbine engine component 8 that uses a sacrificial layer 12. In this embodiment the weld 10 is covered by a conformal heat conductive material 11. Placed on top of the conformal heat conductive material 11 is a sacrificial layer 12. It should be understood that depending on the material used for the conformal heat conductive material 11 a sacrificial layer 12 may not be used. The temper bead weld 14 is applied via a heat source 15.

[0019] The gas turbine engine component 8 may be any component within the gas turbine engine that may require a weld. For example the gas turbine engine component 8 may be a blade, vane, basket, transition, exhaust component or the like. Additionally, while discussion of the inventive method is directed to gas turbine engines the method discussed herein may be used with components for other types of devices that may have a need for a method that can reduce stress on a weld.

[0020] In the embodiment disclosed the conformal heat conductive material 11, may be copper, aluminium or graphite. The materials may be used as a single blanket, multiple layers of material or as a powdered material. These materials have a heat conductivity λ that is sufficient to temper and stress reduce the weld 10. Such effective stress reduction may be pre-qualified and quantified by welding mockups of the joint without and with conformal material temper bead welding and measuring the stress reduction by, for example, hole drilling and strain gage assessment of stress reduction, x-ray diffraction, ultrasonics and magnetic domain change measurement. Such stress reduction is also possible to model, for example, by Sysweld. The heat conductivity of copper is λ=401 W/mK, the heat conductivity of aluminium is λ =205 W/mK. The heat conductivity of graphite is λ =168 W/mK. Beyond these materials additional metals such as, gold λ=315 W/mK and silver λ=407 W/mK may be effective conformal materials as they are very soft and readily conformed.

[0021] Having a high heat conductivity λ permits the transfer of heat to the underlying weld 10 in an efficient manner. It prevents the conformal heat conductive material 11 from having to undergo substantial heating for a long period of time that may overheat and cause fusion to the underlying weld 10.

[0022] While the materials discussed above may be used it should be understood that other materials may be used so long as the heat conductivity is at a sufficient level. For example, it is preferable that the heat conductivity of the material is at level of at least 150 W/mK, preferably greater than 165 W/mK. It is possible that a lower thermal conductivity may be tolerated if advantage is gained in conformance. For example, in unique situations a liquid could be applied as a material of exceptional conformance. For example, NaK which is liquid at room temperature but only has a thermal conductivity of about 22 W/mK. The heat conductivity of the conformal heat conductive material 11 and thickness of sacrificial material 12 should be such that heat applied to it should be sufficient to heat the weld 10 but not to cause re-melting or fusion of the underlying weld 10.

[0023] In addition to the materials discussed above, carbon nanotubes may be used for the conformal heat conductive material 11. Carbon nanotubes may have a heat conductivity λ of 600 W/mK or greater. Carbon nanotubes may be preferable to the materials discussed above due to their greater heat conductivity λ. Also, such small particles may conform well to the complex (possibly indeterminant) surface geometry of a weld crown. [0024] The sacrificial layer 12 may be made of a metallic material that is preferably sufficiently low cost so that after application of the temper bead weld 14 the sacrificial layer 12 may be discarded. Some examples of materials that may comprise the sacrificial layer 12 are carbon steel, alloy steels, aluminium alloys, and copper alloys. The sacrificial layer 12 operates as an additional barrier separating substrate from the welding arc and that can prevent any potential fusion or stress introduction to the underlying component 8.

[0025] The heat source 15 may be a beam source or an arc welding device. The beam source may be a plasma arc, and electron beam or a laser beam. The arc welding device may be for example a gas tungsten arc welder, a plasma welder a gas metal arc welder or a submerged metal arc welder. Other types of heat sources 15 may be resistance welders or ion beams. The heat source 15 applies heat to the sacrificial layer 12 in a manner to produce the temper bead 14, which will result in residual stress reduction to the underlying weld 10.

[0026] Fig. 2 is a flow chart setting forth the method of applying the temper bead weld 14. In step 102 the conformal heat conductive material 11 is placed over the weld 10 to be treated. The conformal heat conductive material 11 may be secured to the surface of the component 8 in some manner during the process. If a fine powder is used as the conformal heat conductive material it would readily conform to the underlying shape but it would just need to be held in place by gravity. If malleable such as soft silver sheet or copper powder laden putty it could be pressed or pounded to the underlying shape and held by temporary fastening clips.

[0027] In step 104, a sacrificial layer 12 is placed over the conformal heat conductive material 11. The sacrificial layer 12 may be secured to the conformal conductive material 11 during the application of heat from the heat source 15.

[0028] In step 106, heat is applied to the areas of the sacrificial layer 12 with magnitude and duration sufficient to temper and stress reduce the underlying weld 10. This produces the temper bead weld 14. After the application of the heat the sacrificial layer 12 may be discarded.

[0029] Performing temper bead welding in the manner discussed above avoids fusion to the underlying component 8, which would reintroduce residual stresses to the component 8. Furthermore, the underlying weld 10 is not physically changed in such a way that it produces an improper or undesirable crown on the weld 10. Additionally, this method may be applied to final machined parts, such as weld crowns ground flat or flush flange faces without requiring a post temper welding treatment.

[0030] Another benefit of performing the temper bead welding in this manner is that it can be applied to components 8 made of materials that typically do not lend themselves to temper bead welding. For example the temper beam welding may be done to austenitic stainless steel. Austenitic stainless steel has austenite as its primary phase (face centered cubic crystal structure). These are alloys containing chromium and nickel, and sometimes molybdenum and nitrogen, staictured around a Type 302 composition of iron, 18% chromium, and 8% nickel. Other candidate materials include nickel based, cobalt based and aluminium based alloys.

[0031] Fig. 3 is a schematic diagram illustrating a temper bead weld heat application directed to a gas turbine engine component 8 wherein the heat is directly applied to heat the conformal heat conductive material 11. This is an alternative embodiment of the process discussed above and it should be understood that previous steps and materials are intended to be the same save for those aspects of the present embodiment impacted by the removal of the sacrificial layer 12.

[0032] The conformal heat conductive material 11 may be secured to the gas turbine engine component 8 during the performance of the process. The heat source 15 (for example a laser beam) heats the conformal heat conductive material 11 to a heating point just below the melting point of conformal heat conductive material 11. The heat (energy and travel speed) is regulated to avoid melting of the conformal material and underlying substrate. The conformal material in such case represents effective heat transfer to the substrate, while at the same time providing shielding from melting of the substrate.

[0033] In this manner the temper bead heat application is delivered for stress reduction without melting.

[0034] Performing the method without the use of the sacrificial layer 12 can provide a benefit in that resources do not have to be spent on the sacrificial layer 12. However, the heat source 15 and the underlying properties of the conformal heat conductive material 11 must be carefully controlled so as to prevent any incidental stresses from being introduced to the underlying component 8 and the weld 10. For example, a broad application of heat may be necessary to avoid localized differential thermal expansion of the underlying component 8 that could itself introduce stresses. Depending on the conformal heat conductive material 11 the heat applied may be less than that which is applied when using a sacrificial layer 12.

[0035] 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 spirit and scope of the invention and its equivalents, as set forth in the following claims.

Claims

What is claimed is:

1. A method of reducing residual stress of a weld or of transforming hardened weld and weld heat affected zone microstructure comprising; applying a conformal heat conductive material to a surface of the component where the weld is located; and

applying heat to the conformal heat conductive material, whereby the application of the heat reduces stress of the weld without re-melting of the weld.

2. The method of claim 1, wherein the conformal heat conductive material comprises carbon nanotubes.

3. The method of claim 2, wherein the thermal conductivity of the carbon

nanotubes is greater than 600 W/mK.

4. The method of claim 1, wherein the conformal heat conductive material is selected from a group consisting of copper, aluminum and graphite.

5. The method of claim 1, wherein the thermal conductivity of the conformal heat conductive material is greater than 150 W/mK.

6. The method of claim 1, wherein the application heat is applied by a heat source, wherein the heat source is a beam source.

7. The method of claim 1, wherein the application of heat is applied by a heat source, wherein the heat source is an arc welding source.

8. The method of claim 1, further comprising placing a sacrificial layer on the conformal heat conductive material prior to the application of heat, wherein the application of heat is provided to both the sacrificial layer and the conformal heat conductive material.

9. A method of applying a temper bead weld heat application to austenitic alloys comprising:

applying a conformal heat conductive material to a surface of a component; and

10. The method of claim 9, wherein the conformal heat conductive material

comprises carbon nanotubes of high thermal conductivity.

11. The method of claim 10, wherein the thermal conductivity of the carbon

nanotubes is greater than 600 W/mK.

12. The method of claim 9, wherein the conformal heat conductive material is selected from a group consisting of copper, aluminum and graphite.

13. The method of claim 9, wherein the thermal conductivity of the conformal heat conductive material is greater than 150 W/mK.

14. The method of claim 9, wherein application of heat is applied by a heat source, wherein the heat source is a beam source.

15. The method of claim 9, wherein the application of heat is applied by a heat source, wherein the heat is applied by an arc welding source.

16. The method of claim 9, further comprising placing a sacrificial layer on the conformal heat conductive material prior to the application of heat, wherein the application of heat is provided to both the sacrificial layer wherein melting may occur and the conformal heat conductive material wherein melting should be avoided.