Regulatory Guide 1.34

Control of Electroslag Weld Properties

ML101670357
Person / Time
Issue date:	03/31/2011
From:	Stevens G NRC/RES/DE/CIB
To:
Bayssie Mekonen/RES 251-7489
Shared Package
ML101670354	List: ML101670369 Regulatory Guide 1.34
References
DG-1223 RG 1.034, Rev. 1
Download: ML101670357 (6)

The NRC issues regulatory guides to describe and make available to the public methods that the NRC staff considers acceptable for use in implementing specific parts of the agency's regulations, techniques that the staff uses in evaluating specific problems or postulated accidents, and data that the staff needs in reviewing applications for permits and license Regulatory guides are not substitutes for regulations, and compliance with them is not require Methods and solutions that differ from those set forth in regulatory guides will be deemed acceptable if they provide a basis for the findings required for the issuance or continuance of a permit or license by the Commissio This guide was issued after consideration of comments received from the publi Regulatory guides are issued in 10 broad divisions: 1, Power Reactors; 2, Research and Test Reactors; 3, Fuels and Materials Facilities; 4, Environmental and Siting; 5, Materials and Plant Protection; 6, Products; 7, Transportation; 8, Occupational Health; 9, Antitrust and Financial Review; and 10, Genera Electronic copies of this guide and other recently issued guides are available through the NRC's public Web site under the Regulatory Guides document collection of the NRC's Electronic Reading Room at http://www.nrc.gov/reading-rm/doc-collections/ and through the NRC's Agencywide Documents Access and Management System (ADAMS) at http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML10167035 The regulatory analysis may be found in ADAMS under Accession No. ML10167036 U.S. NUCLEAR REGULATORY COMMISSION March 2011 Revision 1 REGULATORY GUIDE OFFICE OF NUCLEAR REGULATORY RESEARCH REGULATORY GUIDE 1.34 (Draft was issued as DG-1223, dated June 2009) CONTROL OF ELECTROSLAG WELD PROPERTIES INTRODUCTION This guide describes methods that the staff of the U.S. Nuclear Regulatory Commission (NRC) considers acceptable for implementing requirements about the control of weld properties when fabricating electroslag welds for nuclear components made of ferritic or austenitic material This guide applies to light-water reactor General Design Criterion 1, "Quality Standards and Records," as set forth in Appendix A, "General Design Criteria for Nuclear Power Plants," to Title 10, of the Code of Federal Regulations, Part 50, "Domestic Licensing of Production and Utilization Facilities" (10 CFR Part 50) (Ref. 1), requires that structures, systems, and components important to safety be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety function to be performe Appendix B, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," to 10 CFR Part 50 requires the establishment of measures to ensure materials control and the control of special processes, such as welding, and the performance of proper testin This regulatory guide contains information collection requirements covered by 10 CFR Part 50 that the Office of Management and Budget (OMB) approved under OMB control number 3150-001 The NRC may neither conduct nor sponsor, and a person is not required to respond to, an information collection request or requirement unless the requesting document displays a currently valid OMB control Rev. 1 of RG 1.34, Page 2 numbe This Regulatory Guide is a rule as designated in the Congressional Review Act (5 U.S.C. 801-808). However, the NRC has determined this Regulatory Guide is not a major rule as designated by the Congressional Review Act and has verified this determination with the OM DISCUSSION Background The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section III, "Nuclear Power Plant Components" (Ref. 2), specifies certain requirements associated with manufacturing Class 1 and 2 component Procedure QualificationsSection III requires adherence to ASME Boiler and Pressure Vessel Code,Section IX, "Welding Qualifications," which includes the welding procedure qualification requirement Review of the requirements of the procedure qualification stated in Section IX indicates that supplementary requirements are desirable to provide assurance of adequate weld metal properties when the electroslag welding process is used for joinin The qualification of electroslag welding process for purposes of cladding is not addresse The assurance of satisfactory electroslag welds for low-alloy steel and stainless steel can be increased by maintaining a weld metal solidification (dendritic) pattern with a strong intergranular bond in the center of the wel A number of electroslag welding process variables, such as slag pool depth, electrode feed rate and oscillation, current, voltage, and slag conductivity, have been shown to influence the weld metal solidification patter If the combination of process variables results in a deep pool of molten weld metal, the crystalline (dendritic) growth direction from the pool sides will join at an obtuse angle in the center of the weld, and cracks may develop because of the weaker centerline bond between dendrite Figure A of this guide illustrates the dendritic growth patter A combination of process variables resulting in a shallow pool of molten weld metal will promote a dendritic growth pattern with an acute joining angle and will result in a strong centerline bon Acceptable welds should show a dendritic freezing pattern with a joining angle of less than 90 degrees in the weld cente Tests should be conducted to ensure that the acceptable weld metal solidification pattern specified above is obtained and that unacceptable patterns will not resul The use of a macro-etch examination is a satisfactory technique to determine the weld solidification pattern, and the procedure qualification should include i Production Welds The procedure qualification by itself does not ensure that low-alloy steel production welds will meet the weld solidification pattern and mechanical property requirements specified in the procedure qualificatio To ensure that welds do comply, the production welds themselves must be examine Where the electroslag welding process is used for longitudinal welds in low-alloy steel vessels, it is customary to continue the welding process into prolongations to the base meta These prolongations contain both base metal and weld metal and provide representative samples for testing the mechanical properties of the base metal and the weld meta The weld solidification pattern can be determined from weld samples taken from these prolongation A macro-etch test on a weld center sample taken across the weld from base metal to base metal in the direction of the weld progression, as shown in Figure A of this guide, would be an acceptable method of verifying that the specified solidification pattern has been obtained, and this test should be mad An acceptable alternative to the macro-etch test for ensuring the Rev. 1 of RG 1.34, Page 3 soundness of the center weld metal would be to perform an impact test with the specimen notch located at the weld center as shown in Figure Section III of the ASME Boiler and Pressure Vessel Code requires that material having its mechanical properties enhanced by a heat treatment must subsequently be tested to ensure the effectiveness of the heat treatmen To provide this assurance for low-alloy steel electroslag production welds, the mechanical properties of the weld metal should be determined from the weld prolongation by tests similar to those required for the quenched and tempered base meta For Class 2 vessels, testing all electroslag weld seams would not be necessary, but at least one weld should be tested for each shell cours Industry experience with electroslag welded stainless steel components has shown that cracking in the weld solidification region is not a problem when the process is properly qualified and controlle In addition, the weld metal structure and mechanical properties are generally acceptabl To ensure that the production welds are satisfactory, the welding process variables specified in the procedure qualification should be monitored during the welding proces REGULATORY POSITION Electroslag weld fabrication for core support structures and Class 1 and 2 vessels and components should comply with Sections III and IX of the ASME Boiler and Pressure Vessel Code, supplemented by the regulatory positions belo . The procedure qualification for low-alloy steel and stainless steel welding should include the following: a. Process variables such as slag pool depth, electrode feed rate and oscillation, current, voltage, and slag conductivity should be selected to produce a solidification pattern (dendritic grain pattern) with a joining angle of less than 90 degrees in the weld cente b. A macro-etch test should be performed in the longitudinal weld direction of the center plane across the weld from base metal to base metal as shown in Figure A of this guid The test should verify that the desired solidification pattern resulting from Regulatory Position l.a above has been obtained and that the weld is free of unacceptable fissures or crack . The welding procedure qualification record should include the results of the tests specified in Regulatory Position 1 abov . For longitudinal production welds of low-alloy steel vessels, material containing base metal and weld metal taken from weld prolongations should be tested as follows: a. Tensile and impact tests similar to those required for the base metal by Article NB-2000 of Section III of the ASME Boiler and Pressure Vessel Code should be made on the weld prolongation to determine the mechanical properties of the quenched and tempered weld meta b. To verify that the specified weld solidification pattern has been obtained and that the weld center is sound, one of the following methods should be used: (1) a macro-etch test similar to that described in Regulatory Position 1.b above, or Rev. 1 of RG 1.34, Page 4 I IWeld centerlines T - section thicknessBase metal 1/2 T1/4 T1/4 TCharpy specimen, center location and orientation Charpy specimen,Section III location and orientation WELD CROSS-SECTION Welding direction Weld prolongation or test section CL Acute joining angle of dendrites LONGITUDINAL SECTION I-I (2) impact testing with the specimen notch located at the weld center as shown in Figure A of this guid c. The tests specified in Regulatory Positions 3.a and 3.b above should be applied to the following: Figure A: Weld cross-section showing solidification pattern and Charpy test specimen Rev. 1 of RG 1.34, Page 5 (1) each of the welds for Class 1 vessels, and (2) one weld per shell course for Class 2 vessel . For production welds for austenitic stainless steel core support structures and fluid system components, the production welding should be monitored to verify compliance with the limits for the process variables listed in the procedure qualificatio . If properties obtained from tests or limits are not acceptable, or there is a specific reason to question the welder's ability to make production welds that meet the approved procedure as identified in Regulatory Positions 3 and 4 above, then the production weld is unacceptable and additional procedure qualifications should be performed in accordance with Regulatory Position 1 abov IMPLEMENTATION The purpose of this section is to provide information to applicants and licensees regarding the NRC's plans for using this regulatory guid The NRC does not intend or approve any imposition or backfit in connection with its issuanc In some cases, applicants or licensees may propose or use a previously established acceptable alternative method for complying with specified portions of the NRC's regulation Otherwise, the methods described in this guide will be used in evaluating compliance with the applicable regulations for license applications, license amendment applications, and amendment request Rev. 1 of RG 1.34, Page 6 REFERENCES 1. 10 CFR Part 50, "Domestic Licensing of Production and Utilization Facilities," U.S. Nuclear Regulatory Commission, Washington, D . ASME Boiler and Pressure Vessel Code, American Society of Mechanical Engineers, New York, N Publicly available NRC published documents such as Regulations, Regulatory Guides, NUREGs, and Generic Letters listed herein are available electronically through the Electronic Reading room on the NRC's public Web site at: http://www.nrc.gov/reading-rm/doc-collections/. Copies are also available for inspection or copying for a fee from the NRC's Public Document Room (PDR) at 11555 Rockville Pike, Rockville, MD; the mailing address is USNRC PDR, Washington, DC 20555; telephone 301-415-4737 or (800) 397-4209; fax (301) 415-3548; and e-mail PDR.Resource@nrc.go Copies of American Society of Mechanical Engineers (ASME) standards may be purchased from ASME, Three Park Avenue, New York, NY 10016-5990; telephone (800) 843-276 Purchase information is available through the ASME Web-based store at http://www.asme.org/Codes/Publications/.