GB2548910A

GB2548910A - Method of manufacture

Info

Publication number: GB2548910A
Application number: GB1605575.8A
Authority: GB
Inventors: Longfield Nicholas; Juffs Philip
Original assignee: Rolls Royce Power Engineering PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 2016-04-01
Filing date: 2016-04-01
Publication date: 2017-10-04

Abstract

A method of electron beam welding the full depth along a joint 29 between two components 24 having a front face and a rear face. The intensity of the electron beam 30 and/or the speed of travel of the electron beam along the joint is selected such that at the point of impact of the beam with the two components the keyhole structure (fig. 4, 50) consists of a liquid (fig. 4, 54) region extending from the front face to the rear face of the components and a vapour (fig 4, 52) region that extends from the front face to a position spaced from the rear face of the component. The method may be carried out in a local vacuum. The method may use a laser 32 to determine the depth, e.g. by an interferometry unit 36, with analysis, feedback and control involving a processor 40, memory storage 42, controller 38, input device 46, output device 48, circuitry, and/or a computer and programme 44.

Description

METHOD OF MANUFACTURE

TECHNICAL FIELD

The present disclosure concerns a method of electron beam welding two components and/or a method of manufacturing a component for a nuclear power plant.

BACKGROUND

Nuclear pressure vessels (e.g. reactor vessels) are generally large components, for example a typical pressure vessel would have a diameter in the region of at least 2 metres. The vessels are thick-walled components, e.g. greater than or equal to 200 mm thick, so as to meet process and regulatory requirements.

Nuclear pressure vessels (e.g. reactor vessels) are usually fabricated from a plurality of parts, e.g. multiple cylindrical central parts and two domed ends. Welding is used to join the parts of the vessel together. Due to the operating conditions of nuclear pressure vessels, and regulatory requirements, the welded joints need to have high integrity.

Another component of a nuclear power plant that requires welding is a fuel assembly. Components of the fuel assembly are generally thinner than pressure vessel components.

Electron beam welding is advantageous over other types of welding because it does not require a filler material (i.e. the process is autogenous in nature), so the chemical composition of the material of the weld is the material of the parent components. Further advantageously, electron beam welding offers the potential to weld thick sections of a pressure vessel in a single pass. Traditional welding processes in the nuclear industry require multiple passes of weld, requiring inter-stage examination, and warming of the component prior to each weld pass.

When electron beam welding it is common to use what is known in the art as a keyhole. When the electron beam impacts components for welding, the keyhole is where the component material vapourises so as to form a hole through the entire thickness of a component. To verify the integrity of the weld, as is particularly important in nuclear applications, a camera is used to visually detect whether the keyhole has gone through the entire thickness of the weld.

Manual control of the focus position is typically used to control the size and stability of the keyhole. Manual focus position control can also be used to control the penetration depth.

SUMMARY

According to a first aspect there is provided a method of electron beam welding two components along a joint there between, the two components having a front face and a rear face. The method comprises directing an electron beam at and moving the electron beam along the joint between the two components. The intensity of the electron beam and/or the speed of travel of the electron beam along the joint is selected such that at the point of impact of the beam with the two components a liquid region extends from the front face to the rear face of the components and a vapour region extends from the front face to a position spaced from the rear face of the component.

In this way, the components are welded along the full depth of the joint between the components without the electron beam penetrating the full depth of the components.

The liquid region may be considered to circumscribe the vapour region.

The formation of a vapour region that does not extend through the thickness of the components means that the electron beam does not penetrate through the full thickness of the components. This means that spatter from the rear of the weld can be eliminated, which can remove or significantly reduce the need for rework. Furthermore, because the electron beam does not penetrate the components the need for beam impingement shields is eliminated or significantly reduced. The blind keyhole full penetration weld will also reduce the root drop through.

The front face (or front weld face) is defined as the face of the components impacted by the electron beam. The rear face (or rear weld face) is defined as the face of the components opposite the front face.

The method may comprise directing a laser beam at and moving the laser beam along the joint between the two components; detecting reflections from the laser; and analysing the reflections to determine the depth of a weld formed along the joint.

Analysing the reflections may include using interferometry.

The depth of the weld may be monitored and compared to a predetermined required depth (including a predetermined depth range). In the event of the weld depth being below or optionally above the required depth, the intensity and/or speed of travel of the electron beam may be adapted.

The depth of the vapour region may be less than or equal to 99% of the thickness of the components. For example, less than or equal to 90% or less than or equal to 85% or 80% of the thickness of the components. The depth of the vapour region may be greater than or equal to 50% of the thickness of the components. For example, greater than or equal to 60% or 70% of the thickness of the components.

The depth of the vapour region may be equal to or between 50 and 99 % of the thickness of the components.

The two components may be components of a nuclear power plant, for example components of a pressure vessel (e.g. a reactor vessel) or components of a nuclear fuel assembly.

The welding process may be local vacuum electron beam welding.

The method may comprise selecting the intensity of an electron beam and/or the speed of travel of the electron beam along a joint such that at the point of impact of the beam with the two components a liquid region extends from the front face to the rear face of the components and a vapour region extends from the front face to a position spaced from the rear face of the component.

According to a second aspect there is provided a method of manufacturing an assembly, comprising at least two components welded together using the method according to the first aspect.

The assembly may be an assembly for a nuclear power plant. For example, the assembly may be a pressure vessel or a nuclear fuel assembly.

According to a third aspect there is provided an apparatus comprising at least one processor; and at least one memory comprising computer readable instructions; the at least one processor being configured to read the computer readable instructions to cause performance of the method according to the first aspect.

According to a fourth aspect there is provided an apparatus comprising a controller to perform the method according to the first aspect.

According to a fifth aspect there is provided an apparatus comprising control circuitry to perform the method according to the first aspect.

According to a sixth aspect there is provided a system comprising: the apparatus according to the third, fourth and/or fifth aspect; a welding gun; a laser; and an interferometry unit.

According to a seventh aspect there is provided a computer implemented method comprising selecting the intensity of an electron beam and/or the speed of travel of the electron beam along a joint such that at the point of impact of the beam with the two components a liquid region extends from the front face to the rear face of the components and a vapour region extends from the front face to a position spaced from the rear face of the component.

According to an eighth aspect there is provided a computer program that, when read by a computer, causes performance of the method according to the seventh aspect.

According to a ninth aspect there is provided a non-transitory computer readable storage medium comprising computer readable instructions that, when read by a computer, cause performance of the method according to the seventh aspect.

According to a tenth aspect there is provided a signal comprising computer readable instructions that, when read by a computer, cause performance of the method according to the seventh aspect.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein.

DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of example only, with reference to the Figures, in which:

Figure 1 is a schematic of a nuclear power plant;

Figure 2 is a schematic sectional view of a reactor vessel of the power plant of Figure 1;

Figure 3 is a schematic of equipment used to weld the reactor vessel of Figure 2; and

Figure 4 is a schematic of a cross section through a weld formed between two components.

DETAILED DESCRIPTION

In the following description, the terms ‘connected’ and ‘coupled’ mean operationally connected and coupled. It should be appreciated that there may be any number of intervening components between the mentioned features, including no intervening components.

Referring to Figure 1, a nuclear power plant is indicated generally at 10. The plant includes a nuclear reactor 12, a primary circuit 14, a heat exchanger 16, a secondary circuit 18 and a turbine 20. The primary fluid in the primary circuit is heated by the nuclear reactor. The primary fluid then flows to the heat exchanger, where it heats secondary fluid in the secondary circuit. The heated secondary fluid is then used to drive the turbine 20.

Referring to Figure 2, a pressure vessel for use in the nuclear reactor 12 or heat exchanger 16 is indicated generally at 22. The vessel 22 is fabricated from multiple parts individually manufactured; including a plurality of cylindrical sections 24, and two domes 26, one dome being provided at each longitudinal end of the vessel. The thickness of the cylindrical sections and the dome sections is greater than 200mm, for example 350mm. The parts 24, 26 of the vessel are joined together using welding, in this example using electron beam welding.

Although pressure vessels are provided as an example of vessel that can be welded, it will be appreciated that other components (e.g. fuel assemblies) can also be welded using this technique.

Referring to Figure 3, equipment for electron beam welding two cylindrical sections 24 together is shown. The equipment includes a welding gun 28 that directs an electron beam 30 along the joint 29 between the two sections 24. Apparatus is provided such that the gun 28 and/or the sections 24 are arranged to move, so that the electron beam moves along the joint to weld the two sections together. Such apparatus is known in the art so will not be described in more detail here.

The intensity of the electron beam 30 emitted from the gun 28 and the speed of movement of the beam along the joint 29 may be controlled by a controller 38. A user input device 46 and an output device 48 are coupled to the controller 38. The controller 38, the user input device, and the output device may be coupled to one another via a wireless link and may consequently comprise transceiver circuitry and one or more antennas. Additionally or alternatively, the controller, the user input device and the output device may be coupled to one another via a wired link and may consequently comprise interface circuitry (such as a Universal Serial Bus (USB) socket). It should be appreciated that the controller, the user input device, and the output device may be coupled to one another via any combination of wired and wireless links.

The controller 38 may comprise any suitable circuitry to cause performance of the methods described herein, e.g. as illustrated in Figure 5. The controller may comprise: control circuitry; and/or processor circuitry; and/or at least one application specific integrated circuit (ASIC); and/or at least one field programmable gate array (FPGA); and/or single or multi-processor architectures; and/or sequential/parallel architectures; and/or at least one programmable logic controllers (PLCs); and/or at least one microprocessor; and/or at least one microcontroller; and/or a central processing unit (CPU); and/or a graphics processing unit (GPU), to perform the methods.

In various examples, the controller 38 may comprise at least one processor 40 and at least one memory 42. The memory stores a computer program 44 comprising computer readable instructions that, when read by the processor, causes performance of the methods described herein, e.g. as illustrated in Figure 5. The computer program may be software or firmware, or may be a combination of software and firmware.

The processor 40 may include at least one microprocessor and may comprise a single core processor, may comprise multiple processor cores (such as a dual core processor or a quad core processor), or may comprise a plurality of processors (at least one of which may comprise multiple processor cores).

The memory 42 may be any suitable non-transitory computer readable storage medium, data storage device or devices, and may comprise a hard disk and/or solid state memory (such as flash memory). The memory may be permanent non-removable memory, or may be removable memory (such as a universal serial bus (USB) flash drive or a secure digital card). The memory may include: local memory employed during actual execution of the computer program; bulk storage; and cache memories which provide temporary storage of at least some computer readable or computer usable program code to reduce the number of times code may be retrieved from bulk storage during execution of the code.

The computer program 44 may be stored on a non-transitory computer readable storage medium. The computer program may be transferred from the non-transitory computer readable storage medium to the memory 42. The non-transitory computer readable storage medium may be, for example, a USB flash drive, a secure digital (SD) card, an optical disc (such as a compact disc (CD), a digital versatile disc (DVD) or a Blu-ray disc). In some examples, the computer program may be transferred to the memory via a wireless signal or via a wired signal.

Input/output devices 46, 48 may be coupled to the system either directly or through intervening input/output controllers. Various communication adaptors may also be coupled to the controller to enable the apparatus to become coupled to other apparatus or remote printers or storage devices through intervening private or public networks. Non-limiting examples include modems and network adaptors of such communication adaptors.

The user input device may comprise any suitable device for enabling an operator to at least partially control the apparatus. For example, the user input device may comprise one or more of a keyboard, a keypad, a touchpad, a touchscreen display, and a computer mouse. The controller is configured to receive signals from the user input device.

The output device 48 may be any suitable device for conveying information to a user. For example, the output device may be a display (such as a liquid crystal display, or a light emitting diode display, or an active matrix organic light emitting diode display, or a thin film transistor display, or a cathode ray tube display), and/or a loudspeaker, and/or a printer (such as an inkjet printer or a laser printer). The controller 38 is arranged to provide a signal to the output device to cause the output device to convey information to the user. A laser 32 is arranged adjacent to or in close proximity to the electron beam gun 28. The laser 32 is configured to emit a laser beam 34 to the joint 29 and reflections of the laser are received by a detection unit and/or a detection and analysis unit, e.g. an interferometry unit 36. The interferometry unit is connected to the controller 38.

The laser 32, interferometry unit 36, and the controller 38 may be configured as described in US8822875 incorporated herein by reference.

Referring to Figures 3 to 5, a method of welding the two sections 24 together will now be described. Firstly the sections are positioned adjacent to each other so as to define a joint 29 between the two sections. An electron beam 30 from gun 28 is directed towards the joint (as indicated in block 56). The electron beam 30 is moved along the joint at a desired speed and intensity so as to form a keyhole that does not extend through the thickness of the components (referred to from hereon in as a partial (or blind) keyhole) and weld along the joint (as indicated in block 58).

The structure of the keyhole 50 at a point in time the when the electron beam impacts the components 24 is illustrated in Figure 4. The partial keyhole includes a vapour region 52 and a liquid region 54. On impact, the electron beam vapourises material in the vapour region and melts material in the liquid region. The components have a front face 53 and a rear face 55. The liquid region surrounds the vapour region and extends through the thickness of the components from the front face to the rear face of the components. The liquid region forms a base of the keyhole such that on the rear face the material of the keyhole is liquid. The vapour region extends from the front face to a position spaced from the rear face. The vapour region is separated from the rear face by the liquid region. That is, a partial weld has a liquid region extending through the thickness of the component and a vapour region not extending the entire way through the thickness of the component, the liquid and vapour regions being such that the components are welded through the entire thickness.

It is important, particularly in nuclear applications, to ensure that the components are welded together through the entire thickness of the components. Accordingly, as the electron beam 30 moves along the joint, a laser beam 34 also moves along the joint. The laser 32 that produces the laser beam 34 may be provided on the same connector and/or end effector as the electron beam gun 28 or it may be provided on a separate connector and/or end effector. The laser beam 34 may move relatively around the joint at the same speed as the electron beam. The laser beam 34 may impact the components at substantially the same time as the electron beam impacts the components.

The laser beam 34 is reflected and the reflection is detected by the interferometry unit 36.

The unit 36 sends a signal to the controller 38. The controller 38 may output an indication via output 48 to indicate that the depth of the weld is sufficient. For example, indicate that the liquid region extends to the rear face 55 and/or that the vapour region does not extend through the entire thickness of the components. The controller may send a signal to the gun 28 to adjust the speed and/or intensity of the electron beam if it is detected that the depth of the weld is not within a specified range, e.g. if the liquid region of the partial keyhole has not penetrated the full depth of the components. The controller may send a signal to move the gun 28 so as to rectify a portion of the weld, in the event the liquid region of the partial keyhole does not extend through the thickness of the weld.

The desired depth of the weld may be calculated by the controller, e.g. based on inputs via input device 46 in relation to the material and/or geometry of the component, or the desired depth may be inputted directly via the input device.

In conventional electron beam welding techniques, particularly in the nuclear industry, the keyhole (i.e. the vapour region) is designed to extend through the entire thickness of the components. A camera is used to indicate that the keyhole has penetrated the full depth of the components. However, using this technique means that there is a large amount of spatter from the rear of the weld, which requires substantial rework. Furthermore, the electron beam goes through and past the thickness of the components which means that in some cases shielding is required.

The formation of a partial keyhole in the presently disclosed method means that the electron beam does not penetrate through the thickness of the components. This means that spatter from the rear of the weld is significantly reduced, which can remove or significantly reduce the need for rework. Furthermore, because the electron beam does not penetrate the components the need for shielding is eliminated or significantly reduced.

The feedback mechanism provided by the described arrangement means that the integrity of the weld can be monitored and parameters of welding can be adapted in process to ensure that weld integrity is maintained.

In the present example conventional electron beam welding is used, but in alternative embodiments localised vacuum electron beam welding may be used, for example using similar equipment as described in US5491316 which is incorporated herein by reference.

It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and subcombinations of one or more features described herein.

Claims

1. A method of electron beam welding two components along a joint there between, the two components having a front face and a rear face, the method comprising: directing an electron beam at and moving the electron beam along the joint between the two components; wherein the intensity of the electron beam and/or the speed of travel of the electron beam along the joint is selected such that at the point of impact of the beam with the two components a liquid region extends from the front face to the rear face of the components and a vapour region extends from the front face to a position spaced from the rear face of the component, such that the components are welded along the full depth of the joint between the components without the electron beam penetrating the full depth of the components.

2. The method according to claim 1 further comprising directing a laser beam at and moving the laser beam along the joint between the two components; detecting reflections from the laser; and analysing the reflections to determine the depth of a weld formed along the joint.

3. The method according to claim 2, wherein analysing the reflections includes using interferometry.

4. The method according to any one of the previous claims, wherein the depth of the weld is monitored and compared to a predetermined required depth, and in the event of the weld depth being below or optionally above the required depth, the intensity and/or speed of travel of the electron beam is adapted.

5. The method according to any one of the previous claims, wherein the depth of the vapour region is equal to or between 50 and 99 % of the thickness of the components.

6. The method according to any one of the previous claims, wherein the two components are components of a nuclear power plant, for example components of a pressure vessel or fuel assembly.

7. The method according to any one of the previous claims, wherein the welding process is local vacuum electron beam welding.

8. A method of manufacturing an assembly, the method including providing at least two components, and welding the two components along a joint there between using the method according to any one of claims 1 to 7.

9. A method of controlling a welding process, the method comprising selecting the intensity of an electron beam and/or the speed of travel of the electron beam along a joint such that at the point of impact of the beam with the two components a liquid region extends from the front face to the rear face of the components and a vapour region extends from the front face to a position spaced from the rear face of the component, such that the components are welded along the full depth of the joint between the components without the electron beam penetrating the full depth of the components.

10. An apparatus comprising: at least one processor; at least one memory comprising computer readable instructions; the at least one processor being configured to read the computer readable instructions to cause performance of the method according to claim 9.

11. An apparatus comprising a controller to perform the method according to claim 9.

12. An apparatus comprising control circuitry to perform the method according to claim 9.

13. A system comprising: the apparatus according to any one of claims 10 to 12; a welding gun; a laser; and an interferometry unit.

14. A computer implemented method comprising selecting the intensity of an electron beam and/or the speed of travel of the electron beam along a joint such that at the point of impact of the beam with the two components a liquid region extends from the front face to the rear face of the components and a vapour region extends from the front face to a position spaced from the rear face of the component.

15. A computer program that, when read by a computer, causes performance of the method as claimed in claim 14.

16. A non-transitory computer readable storage medium comprising computer readable instructions that, when read by a computer, cause performance of the method as claimed in claim 14.

17. A signal comprising computer readable instructions that, when read by a computer, cause performance of the method as claimed in claim 14.

18. A method substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.