ML22143A929

NRC Technical Assessment of Electron Beam Welding

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Issue date:	06/01/2022
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NRC Technical Assessment of Electron Beam Welding

1. Introduction and Purpose

This document provides a U.S. Nuclear Regulatory Commission (NRC) technical assessment of the process considerations and knowledge gaps related to the application of electron beam welding (EBW) in the nuclear power industry. This assessment is primarily based upon the technical information and gap analysis developed by Oak Ridge National Laboratory (ORNL) in technical letter report (TLR) entitled Review of Advanced Manufacturing Techniques and Qualification Processes for Light Water ReactorsElectron Beam Welding, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML22143A928)

(hereafter referred to as the ORNL TLR). This assessment, combined with the ORNL TLR, highlights key technical information related to the application of EBW in nuclear facilities and fulfills the deliverable for EBW under Subtask 1A of the Action Plan for Advanced Manufacturing Technologies (AMTs), Revision 1, dated June 23, 2020 (ADAMS Accession No. ML19333B973).

2. NRC Identification and Assessment of Differences

This section describes the differences between the EBW process and conventional arc welding, assesses the impact that the identified difference has on the performance of welded assemblies, and identifies specific technical considerations related to EBW assemblies. This assessment was conducted on the EBW process in general; however, it identified relevant material-specific impacts and considerations. The overall impact on plant safety (e.g., safety significance) is a function of component or assembly performance and the specific component or assembly application, such as its intended safety function. This report does not include the impact on plant safety, as such an assessment would not be possible without considering a specific component or assembly application.

The staff identified the differences between the EBW and conventional arc welding processes by reviewing the information and gap analysis rankings from the ORNL TLR and other relevant technical information (e.g., NRC regulatory and research experience, technical meetings and conferences, codes and standards activities, Electric Power Research Institute and U.S. Department of Energy products and activities). The identified differences and their significance originated either as important aspects of or gaps in the EBW process or component or assembly performance, as defined here:

important aspect: part of the AMT fabrication process or component or assembly performance that needs to be considered and carefully controlled during the process

gap: part of the AMT fabrication process or component or assembly performance that is not well known or understood due to limited information and data

The results of this technical assessment are provided in two tables. Table 1 contains the EBW process considerations. Table 2 compares the material properties and performance characteristics of an EBW assembly with those associated with a conventionally arc welded pressure vessel steel assembly. The results in Tables 1 and 2 are based on a generic EBW assembly; however, relevant material-specific technical information is also included. In general, any nuclear EBW assembly needs to have material-specific data for the proposed processing and post-processing parameters to ensure adequate component or assembly performance in its environment, including applicable properties (e.g., fracture toughness) and aging mechanisms (e.g., irradiation effects and stress corrosion cracking (SCC)).

The following columns in Tables 1 and 2 identify and provide technical information for the EBW process and the properties and performance characteristics for EBW assembly:

Difference: Identification of the corresponding gaps from Section 3.4 of the ORNL TLR.

Definition: Brief description of the difference with the EBW process.

NRC Ranking of Significance: Discussion of two considerations:

o Importance: Impact on final weld integrity, considering the likelihood of occurrence or magnitude of degradation in conjunction with the ease of detection or ability to mitigate.

A high ranking signifies that the difference has a significant impact on component performance.

A medium ranking signifies that the difference has a moderate impact on component performance.

A low ranking signifies that the difference has a minimal impact on component performance.

o Knowledge/Manageability: Description of how well understood and manageable the difference is.

Key Technical Information: Technical information for the consideration of EBW for use in nuclear power plants.

Discussion of the corresponding gaps can be found in Section 3.1 of the ORNL TLR.

3. Codes and Standards

Section 3.2 of the ORNL TLR provides an overview of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (ASME Code) pertaining to EBW of nuclear components, including an analysis to identify any gaps. EBW is generally accepted across the ASME Code, given that the prescribed post weld heat treatment (PWHT), non-destructive testing, and destructive testing of weld joints requirements are followed. The ORNL TLR does note a few cases for which EBW is prohibited, such as the welding of instrument tubing, which is restricted to only gas-tungsten arc welding, as stated in ASME Code,Section III. For EBW, ASME Code,Section III, requires an ultrasonic examination in addition to radiographic examination. Therefore, the analysis found that there are no significant gaps in the codes and standards for EBW use, although there are a few current limitations.

4. Summary and Conclusion

In Tables 1 and 2 of this report, the staff identified and assessed the process considerations and differences associated with using EBW for nuclear applications, as well as the properties and performance characteristics of EBW assemblies. The staff also assessed existing codes and standards pertaining to EBW use in nuclear applications and found that there are no significant gaps for EBW use.

Table 1 Technical InformationEBW Process Considerations

Difference Definition NRC Ranking of Significance Key Technical Information

The addressing of High Because the welding process is typically used for deep defects that occur single-pass welds, defects that occur are typically not during the EBW Defects formed during EBW are typically near the surface of the weld when discovered. This may process to prevent not near the surface of the weld when require additional machining or grinding or both to reach them from discovered. Weld repairs can be difficult the defect depth.

impacting the to complete successfully and may require A re-weld may be required that consists of the repeated performance and additional machining or grinding or both to use of the fusion pass weld schedule over the previously integrity of the reach the defect depth. Weld repairs may welded section. This is often done in its entirety, re-weld. also require the use of filler metals, which welding the entire weld joint, not just the section with the Weld Repairs can negate some of the advantages of defect.

using EBW (e.g., removing sources of More difficult repairs may require the use of a qualified trace elements, which can result in procedure. Because qualifications are very expensive, improved materials properties). the fabricator may be limited to certain repair procedures or may need to request a deviation to a procedure to best serve the product.

Arc welding is typically used for weld repairs. Repairing an electron beam weld with an arc weld using filler metals requires careful consideration of the filler metal permitted and subsequent inspections.

Unintended Medium The EBW process is a highly reliable process. However, interruptions of the arc faults or shutdowns do occur for various reasons. Arc electron beam and Although EBW is a highly reliable faults are known to scrap small components due to the weld that occur process, arc faults or shutdowns can runaway energy that is sometimes produced.

mid-process. occur for various reasons, which can lead Welding amperage can spike suddenly, causing a large to termination of the weld and defects in increase in heat input at the location of the weld. This is Unexpected Arc the weld. These occurrences can be often followed by a fault and termination of the weld, Shut Down / minimized through quality assurance which may leave a hole in the weld.

Faults During (e.g., thorough cleanliness activities). Dirtier materials, such as plain carbon steels, may Welding Repairing electron beam welds can be release entrapped gases in the material due to the lower difficult if it is needed. vapor pressure of the substance and vacuum during welding. This release of entrapped gases can cause momentary spikes in the gun, which can terminate the weld.

A repair to address defects can be attempted in large components; however, it may be difficult to address a Difference Definition NRC Ranking of Significance Key Technical Information

loss of material at the joint through expulsion at the weld top surface or at the root of the weld.

The addition of filler metal can be used to repair the weld, using either EBW or traditional arc welding.

Addition of metal in Medium Advanced beam controls and additive manufacturing the making of a have revitalized the use of wire for EBW to the point of joint through EBW with filler metal additions has had practical use for certain applications.

welding, in EBW limited historical use. Filler metal can be - However, wire addition is still likely to remain in through wire-fed or used to address certain issues related to limited use.

preplaced filler EBW (e.g., porosity, excessive loss of Wire-fed EBW is completed by adding an alloy to material between material, difficulty of weld repair). improve the alloy composition of the weld. However, this the parts to be However, careful consideration is needed can be difficult or impossible to implement, depending on Addition of Filler welded. to determine the use of filler, as adding the geometry of the part and access to the weld pool.

Metal using filler may also negate some of the Adding a wire feeder to the electron beam welder allows Conventional or advantages of using EBW (e.g., removing for gaps in the mating materials to be filled, thus Electron Beam sources of trace elements, which can reducing the amount of residual stress on the completed Methods result in improved materials properties). weld. This may be of particular interest for very thick welds or welds where a preferential filler alloy is beneficial because of its metallurgical or corrosion resistance properties.

Adding filler metal may reduce porosity levels in the weld.

Utilizing filler metal should be carefully decided upon as the addition of filler metals introduces a source of copper, which can impact fracture toughness of the weld, especially if the component is irradiated.

The availability and High In traditional EBW, the size of the welded assembly is reliability of limited by the size of the vacuum chamber.

systems that can EBW systems large enough to perform A reduced-pressure electron beam system has been Vendor/ perform EBW for girth welds for full-size reactor pressure developed for large component fabrication, eliminating Equipment girth welds, which vessels do not exist in the United States. the need for a large vacuum chamber. However, this Capability are necessary for Therefore, there are no current vendors technology is not currently being pursued in the full-size reactor that can perform all of the electron beam U.S. nuclear industry.

pressure vessels. welds for a fully assembled reactor Development of welding systems to accommodate the pressure vessel. welding of small modular reactor pressure vessels is Difference Definition NRC Ranking of Significance Key Technical Information

currently underway. Modular in-chamber EBW is being investigated for this effort.

The selection of Medium The application of EBW to pressure vessel girth welds alloys to construct may benefit from the use of supplemental chemistry reactor pressure Unlike many materials where a general requirements within existing specification limits, such as vessels or other understanding of weldability is sufficient, specifying limits of tramp elements.

components using EBW requires more attention to the Materials selected for EBW typically have fewer EBW. selection of base metals due to the impurities and are selected for their fast cooling rate unique aspects of EBW and because morphology upon welding.

cleaner steels are needed for EBW. - New materials may be sought to take advantage of However, materials that are more optimal EBW microstructure and process aspects.

for EBW may not have been previously A cleaner steel with lower amounts of trace element Electron-Beam-evaluated for environments and impurities can minimize radiation effects and may Specific Material degradation mechanisms applicable to improve the fracture toughness of electron beam welds.

Specifications nuclear power plant operation, such as Alloys with high thermal expansion coefficients, such as neutron degradation or SCC resistance. stainless steels and alloys with high solidification shrinkage (e.g., some aluminum alloys) add to the cracking susceptibility.

New material processing techniques such as powder metallurgy-hot isostatic pressing (PM-HIP) introduce higher levels of argon, oxygen, or nitrogen, depending on the technique used. In the case of PM-HIP, it may be beneficial to place limits on the amount of oxygen and nitrogen in the material.

- EBW of alloys with high gas content can result in excessive porosity and reduced fracture toughness.

The size, Low The vacuum environment used in EBW eliminates distribution, and uniform porosity in welds when materials are clean and total volume of Porosity formation has been studied to a free from entrapped gases. However, porosity can occur voids and pores in great extent in laser welding. Due to the due to the process development, material, or loss of the weld. high energy density common in EBW, the cleanliness of the piece parts.

Porosity two processes share many attributes. Entrapped oxygen and nitrogen in steels can contribute Welding in a vacuum environment helps to porosity formation, which may be an issue, particularly eliminate pores, although they can still for EBW of PM-HIP components.

occur. Residual magnetisms may cause the beam to deflect unexpectedly and develop root porosity in partial penetration welds.

Difference Definition NRC Ranking of Significance Key Technical Information

The weld schedule can be defocused to lessen the sharp intensity of the beam impingement area to reduce root porosity.

The best means of repairing pores is often to grind or machine the pore out of the weld and proceed with a repair procedure.

Adding filler metal may reduce porosity in the weld.

For aluminums, scraping the surfaces to remove the oxide layer before welding is a common technique to minimize porosity formation in the weld.

Can occur in Low A magnetic field generated by the parts to be welded, ferromagnetic fixturing, or nearby sources can influence the beam and materials Magnetism is a property that is normally have a deleterious effect on the weld.

containing iron, not measured or noticed until it is a A thermoelectric effect, in which a magnetic field is nickel, or cobalt problem. However, it can be addressed generated by the interaction of the beam with materials and can impact the appropriately through process of different thermal potentials, can cause a lack of EBW process. qualification, including developing a bonding in the electron beam weld.

procedure that involves measuring the When welding new components, magnetism can be magnetization during setup to determine difficult due to the material chemistry effects, installed whether the levels need to be addressed. ferritic components, or the magnetization of tooling Magnetism components.

Steels are generally avoided in tooling for EBW because of the eventual magnetization of the tooling.

- aluminum, stainless steel, and copper or brass are often used to avoid magnetization Demagnetization techniques currently used for EBW include the following:

- use of a slowly decreasing alternating current magnetic field

- use of a magnetic shield

- preheating above the curie temperature (i.e., the temperature above which certain materials lose their permanent magnetic properties)

Defects resulting Medium EBW of thick materials commonly have issues with Undercut from grooves in the undercutting on the top surface.

base metal along Undercutting can have a significant effect on fatigue life.

Difference Definition NRC Ranking of Significance Key Technical Information

edges of the weld Undercutting is a common problem in Locally to the undercut area, the material is under higher that are not EBW, particularly for deep welds, and can solidification stresses, which can initiate solidification completely filled increase the susceptibility for fatigue and cracks in sensitive materials.

during the welding solidification cracks. However, In some cases, the additional heat input needed to reflow process. undercutting can be addressed through a the top surface can be undesirable. However, in such cosmetic or defocused weld pass placed instances, the top surface can be ground flush or the joint on top of the penetrating pass. can be made with increased joint thickness that is later machined or ground off.

Traditional EBW Low (High if pursued in the United Removal of the large vacuum chamber allows immediate that is conducted States) improvements in application to large structures and using a local reduces the size of the pumps needed to provide the vacuum at the The size of some reactor pressure local vacuum around the weld area.

location of the weld vessels necessitates a large chamber or - The energy and time used to pump down a large as opposed to the advanced process to conduct EBW. chamber can be reduced significantly.

entire assembly These large chambers are not commonly Initial testing has shown that single-pass, Reduced within a vacuum available in the United States. Minimal reduced-pressure EBW results in higher as-welded Pressure chamber. information is available about the hardness through the fusion zone compared to arc Electron Beam reliability of reduced-pressure EBW, as welding. However, PWHT was shown to be effective in Welding this process has not been widely used in reducing hardness values.

nuclear industry. Current efforts in the Initial testing showed that, after PWHT, residual stress United States are focused on magnitudes can be comparable for reduced-pressure large-chamber EBW, which results in a EBW and arc welding, but the residual stress Low NRC Ranking of Significance. If this distributions were quite different between the welds.

technology is pursued in the future, the Limited information is available on the effect of these need for demonstration of this technology different residual stress distributions on weld integrity.

would be elevated to a High ranking.

Post weld surface Low The weld root in particular can have large amounts of conditions of the spatter present, although this is not expected to impact electron beam weld During full-penetration EBW, spatter can the integrity of the weld.

Weld and surrounding solidify on the inner and outer surfaces. The excess beam power and droplets of material can be Appearance surfaces. However, this can be successfully expelled from the root of the weld and adhere strongly to Including removed through mechanically assisted the opposite side of a vessel.

Spatter and tooling. Spatter and blow-through can The visual appearance of an electron beam weld will be Blow Through also be mitigated through other means, narrower and rougher than a typical arc weld and may such as sacrificial spatter shields or a include spatter, particularly on the interior of the beam impingement device that can be component. This could increase susceptibility to fatigue inserted on the backside of the weld. and SCC.

Difference Definition NRC Ranking of Significance Key Technical Information

For components fabricated using PM-HIP, a high amount of inherent dissolved gas in the components may cause fluctuations in the weld pool, resulting in increased spatter.

The preparation Low Most electron beam welds are completed without the and set up of the addition of filler material. This requires that the mating Joint EBW joint. The machining of weld joints is simplified components are tight fitting with minimal gaps.

Preparation, for EBW; however, the joint preparation Larger gaps reduce the amount of weld reinforcement Fit-Up, and for EBW and tolerancing of mating and may result in a concave weld surface, which can Gaps components are critical for EBW without increase solidification cracking susceptibility.

wire additions. EBW does not have the flexibility that exists in traditional arc welding processes to accommodate variations in the bevel angle or joint gaps.

The fluidity and Low Loss of material due to fluid flow is usually more severe propensity of on the beam side (hot end) of the weld; therefore, material to flow The potential for loss of material in the support structures are typically used on the beam side away from the weld weld joint should be identified early in the and not the root side of the weld. Very hot, deep, or joint. procedure development process. It can high-energy welds may also need root-side support.

be addressed appropriately through The effects of using an off-axis weld depend on the process qualification, including adding material being welded, as molten pool fluidity has a great Fluidity of the material to support the molten weld bead effect on the surface tension of the pool and the ability to Molten Pool during welding. create a weld without losing molten material due to the combination of surface tension, gravity, and fluid flow.

Larger welds are therefore more susceptible to fluid material loss.

Material can be tack welded to the weld joint (e.g., support bars) to help resist the fluid puddle from falling out of the joint. These can be used on the outer and inner surfaces of the weld, depending upon internal access and weld parameter settings.

Methods that High ASME Code,Section III, requires PWHT of all carbon involve elevated steel and low-alloy welds. Some exemptions to these Post Weld Heat temperatures to PWHT should make material properties requirements are provided in the ASME Code based on Treatment1 reduce internal and performance more homogeneous material type, carbon content, thickness, and the residual stresses in and similar to those of the arc welding application of a specified preheat. However, none of the material and process and may significantly impact these exemptions can be applied to heavy section welds.

improve material considerations related to the other EBW Difference Definition NRC Ranking of Significance Key Technical Information

properties in the differences presented in Tables 1 and 2. PWHT may be beneficial in reducing hardness, yield weld. Conversely, weld integrity may be strength, and residual stress and in increasing impact degraded if adequate PWHT is not used. toughness.

PWHT is required by ASME Code, - In terms of these properties, PWHT can result in Section III, for carbon steel and low-alloy electron beam weld properties that are more welds. The adequacy of these comparable to conventional arc welds.

requirements for thick-section EBW is still The use of a solution heat treatment is being investigated being demonstrated. specifically for electron beam welds. Because the electron beam weld does not add filler metal, the chemical composition of the weld is nearly identical to the base material. The heat treatment is intended to homogenize the weld and base metal microstructures and return the weld fusion zone to near base metal properties.

- Because the heat treatment would be completed on final assemblies after welding and machining, distortion caused by the heat treatment is a concern.

Parameters at the Medium Slope out parameters need to be developed end of a weld cycle appropriately to minimize or eliminate defects at the to be adjusted to Improper control of slope out parameters termination of the weld.

minimize or can adversely affect properties and Work has been done to identify and optimize parameters Slope Out eliminate defects at performance of the electron beam weld. such as section length, beam power, welding defocus, Parameters the stoppage point However, work has been done to identify and beam oscillation.

in circumferential and optimize these parameters and can Improper slope out parameters can lead to increased welds. be addressed appropriately through root porosity and keyhole collapses at the root of the process qualification. partially penetrating electron beam weld.

Note 1: Difference does not correspond to an ORNL gap from Section 3.1 of the ORNL TLR.

Table 2 Technical InformationEBW Assembly Properties and Performance Characteristics

Difference Definition NRC Ranking of Significance Key Technical Information

EBW of High Early testing demonstrated that a forged plate to components that PM-HIP plate weld behaved similarly to the join forged material Differences have been seen in the few tests wrought product with no significant difference in to PM-HIP completed on deep-penetrating electron beam weld fusion zone or heat-affected zone (HAZ)

Welding of fabricated materials welds on reactor pressure vessel steels when width.

Forgings to and join two using PM-HIP base materials. The development This early testing also showed notable differences PM-HIP and PM-HIP fabricated of EBW of PM-HIP components will need to in the fusion zone and HAZ width for PM-HIP to PM-HIP to materials. continue to address these issues in parallel with PM-HIP welds.

PM-HIP the development of fabricating PM-HIP reactor The development of EBW of PM-HIP components pressure vessel components. is occurring in parallel with the development of the fabrication process of PM-HIP components for the reactor pressure vessel; refinements in both processes may be needed to ensure acceptable weld joint performance.

Formation process Medium The fast welding speeds that are unique to EBW of shrinkage cracks as compared to arc welding processes produce a during the Base metals that are generally considered to be fast solidification rate that may increase the solidification period weldable by arc fusion processes may be susceptibility to solidification cracking.

of a weld metal. susceptible to cracking during EBW due to the EBW, with its high energy density, results in high faster cooling and solidification rates. Austenitic temperature gradients and elevated stress levels stainless steels such as 304L and 316L are well that may enhance the crack sensitivity of some researched due to crack sensitivity as a result of materials.

changes in solidification modes. Work has been The residual stresses on the electron beam weld Solidification done to decrease cooling rates and modify weld may be higher than for arc welding depending Cracking pool shapes, but further research is needed to upon joint configuration, restraint conditions, heat confirm these capabilities. input, and final bead profile. This may increase susceptibility to solidification cracking.

EBW without filler metal may cause a concave weld bead profile, which may be more susceptible to cracking.

Manufacturers have developed multibeam electron optics that raster the beam to multiple positions at extremely fast speeds. This technology has been used to decrease cooling rates, modify weld pool shapes, and deliver Difference Definition NRC Ranking of Significance Key Technical Information

PWHT during the completion of the welding pass.

Further research is needed to prove its capabilities.

SCC initiation and LowLow-Alloy Steels Data in representative environments are growth of important to demonstrate that weld integrity will susceptible MediumStainless Steels and Nickel-Based not be degraded due to SCC to a greater degree materials under Alloys in electron beam welds than arc welding.

roughly constant Electron beam welds are generally expected stress operating SCC can lead to degraded weld integrity if not perform better than arc welding due to the conditions in a adequately managed and is one of the most inherently clean environment, lower overall heat corrosive common failure modes in nuclear power plants. input, and resulting smaller grain structure of the environment. Local material characteristics (i.e., grain boundary weld.

chemistry and microstructure) may amplify PWHT has been shown to reduce hardness differences with conventional arc welds not values and residual stress levels in the weld apparent in other tests (e.g., tensile). Electron metal and HAZ of electron beam welds, largely Stress Corrosion beam welds may be less susceptible to SCC than mitigating SCC susceptibility.

Cracking arc welds, and low-alloy steels are generally PWHT would be expected to make electron beam resistant to SCC under normal operating weld properties and performance more similar to conditions. However, there are limited data to those of arc welding processes.

demonstrate SCC resistance in electron beam Low-alloy steels are generally resistant to SCC welds of stainless steels and nickel-based alloys. under normal operating conditions when sulfur content and hardness levels are appropriately controlled.

- SCC susceptibility is more pronounced in austenitic stainless steels and nickel-based alloys than low-alloy steels.

SCC of reactor pressure vessel materials is of higher concern in areas of dissimilar metal combinations, particularly those containing nickel-based alloys.

The initiation and Low Data in representative environments are propagation of important to support fatigue calculations for cracks due to cyclic Fatigue is a common concern in nuclear power electron beam welds, including for Fatigue loading with or plants and can lead to component failure. environmentally assisted fatigue.

without Fatigue information on the reactor pressure PWHT is expected to make electron beam weld environmental vessel steel electron beam weld metal properties properties and performance more similar to those effects playing a is limited. However, fatigue life is not expected to of arc welding processes.

Difference Definition NRC Ranking of Significance Key Technical Information

significant role in be detrimentally affected by EBW of the reactor Because fatigue is heavily reliant on the weld the process. pressure vessel steel if similar microstructures microstructure, a significant change in fatigue life can be achieved. This has been seen in initial is not expected if similar microstructures of (albeit limited) evaluations. Furthermore, activities conventional arc welds are achieved.

can be conducted to address issues that Undercutting, a common problem for EBW, can adversely affect fatigue life (e.g., undercutting). have a significant effect on fatigue life; however, undercutting of the top surface can be remedied through a cosmetic or defocused weld pass placed on top of the penetrating pass.

A property that Medium Data in representative environments are describes the important to demonstrate that fracture toughness ability of a material Loss of fracture toughness can lead to brittle does not degrade excessively and will be containing a crack failure if not adequately managed. Fracture adequate to meet component design to resist further toughness of electron beam welds is expected to assumptions.

fracture. be comparable, if not superior, to conventional arc Fracture toughness of electron beam welds for welds for wrought alloys given appropriate PWHT. wrought alloys may be comparable to that of However, additional data are needed to conventional arc welds because of the use of Fracture demonstrate the fracture toughness behavior of cleaner steels with lower trace elements and the Toughness electron beam welds such that component reduction of copper due to the absence of filler integrity will be maintained throughout the design materials.

life. PWHT is expected to make electron beam weld properties and performance more similar to those of arc welding processes for wrought alloys.

More information on fracture toughness is needed for PM-HIP steels as the PM-HIP process matures for thick-section, low-alloy steels.

Aging, or thermal High Data in representative environments are aging, refers to the important to demonstrate that thermal aging or reduction in Thermal and irradiation embrittlement, particularly irradiation effects will not be significantly greater Aging and fracture toughness loss of fracture toughness, are concerns in in electron beam welds than in arc welding.

Irradiation after significant nuclear power plant applications. Local material EBW removes a source of the copper from the Degradation time at elevated characteristics (i.e., grain boundary chemistry and filler materials added through arc welding, which temperatures. microstructure) may amplify differences with can minimize radiation effects in welds.

Irradiation conventional arc welds not apparent in other tests degradation refers (e.g., tensile). PWHT is expected to make Difference Definition NRC Ranking of Significance Key Technical Information

to the impact of electron beam weld properties and performance PWHT is expected to make electron beam weld neutron irradiation more similar to those of arc welding processes. properties and performance similar to those of on various aspects However, no published articles could be found arc welding processes.

of material that discuss the effects of long-term exposure to properties and elevated temperatures or radiation-specific performance, electron beam girth welds on reactor pressure including, but not vessel steels.

limited to, loss of fracture toughness, irradiation assisted SCC, and void swelling.

Residual stresses Medium High residual stress can degrade weld integrity that remain in the (e.g., increase cracking susceptibility, impact electron beam weld Residual stress in the electron beam weld can irradiation behavior).

can affect negatively impact the mechanical properties of PWHT with appropriate parameters is expected important the materials if not properly managed. PWHT has to relieve residual stress in the weld metal and properties of the been demonstrated to significantly reduce peak HAZ.

weld. residual stress in electron beam welds. However, EBW of dissimilar welds results in high residual no published articles could be found that discuss stresses due to difference in melting Residual Stress the effects of residual stress on the structural temperatures and coefficients of thermal integrity of large-thickness EBW in reactor expansion. However, certain process variables pressure vessel materials. can be adjusted to help manage residuals stresses, such as directing more of the beam energy into the material with the higher melting temperatures.

Although the use of wire addition with EBW is limited, the filler metal can reduce the amount of residual stress on the completed weld.

22143A927; ML22143A929 OFFICE RES/DE/CIB RES/DE/CMB RES/DE NAME MYoo MY MHiser MH LLund JMcKirgan for JM DATE May 24, 2022 May 25, 2022 May 25, 2022