Regulatory Guide 1.34
| 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: |
| References | |
| DG-1223 RG 1.034, Rev. 1 | |
| Download: ML101670357 (6) | |
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
A. 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 materials. This guide applies to light-water reactors.
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 performed.
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 testing.
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 3150-0011.
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 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 agencys 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 licenses. Regulatory guides are not substitutes for regulations, and compliance with them is not required. 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 Commission.
This guide was issued after consideration of comments received from the public.
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, General.
Electronic copies of this guide and other recently issued guides are available through the NRCs public Web site under the Regulatory Guides document collection of the NRCs Electronic Reading Room at http://www.nrc.gov/reading-rm/doc-collections/ and through the NRCs Agencywide Documents Access and Management System (ADAMS) at http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML101670357. The regulatory analysis may be found in ADAMS under Accession No. ML101670363.
number. 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 OMB.
B. 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 components.
Procedure QualificationsSection III requires adherence to ASME Boiler and Pressure Vessel Code,Section IX, Welding Qualifications, which includes the welding procedure qualification requirements. 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 joining. The qualification of electroslag welding process for purposes of cladding is not addressed. 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 weld. 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 pattern. 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 dendrites. Figure A of this guide illustrates the dendritic growth pattern. 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 bond. Acceptable welds should show a dendritic freezing pattern with a joining angle of less than 90 degrees in the weld center.
Tests should be conducted to ensure that the acceptable weld metal solidification pattern specified above is obtained and that unacceptable patterns will not result. The use of a macro-etch examination is a satisfactory technique to determine the weld solidification pattern, and the procedure qualification should include it.
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 qualification. To ensure that welds do comply, the production welds themselves must be examined.
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 metal. 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 metal. The weld solidification pattern can be determined from weld samples taken from these prolongations. 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 made. An acceptable alternative to the macro-etch test for ensuring the Rev. 1 of RG 1.34, Page 2
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 A.
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 treatment. 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 metal. For Class 2 vessels, testing all electroslag weld seams would not be necessary, but at least one weld should be tested for each shell course.
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 controlled.
In addition, the weld metal structure and mechanical properties are generally acceptable. To ensure that the production welds are satisfactory, the welding process variables specified in the procedure qualification should be monitored during the welding process.
C. 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 below.
1. 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 center.
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 guide. 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 cracks.
2. The welding procedure qualification record should include the results of the tests specified in Regulatory Position 1 above.
3. 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 metal.
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 3
(2) impact testing with the specimen notch located at the weld center as shown in Figure A of this guide.
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 Charpy specimen,Section III
location and orientation Charpy specimen, center Weld centerlines location and orientation Base metal
1/4T
I I
T - section thickness
1/2T
1/4T
WELD CROSS-SECTION
CL
Welding direction Weld prolongation or test section Acute joining angle of dendrites LONGITUDINAL SECTION I-I
Rev. 1 of RG 1.34, Page 4
(1) each of the welds for Class 1 vessels, and
(2) one weld per shell course for Class 2 vessels.
4. 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 qualification.
5. If properties obtained from tests or limits are not acceptable, or there is a specific reason to question the welders 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 above.
D. IMPLEMENTATION
The purpose of this section is to provide information to applicants and licensees regarding the NRCs plans for using this regulatory guide. The NRC does not intend or approve any imposition or backfit in connection with its issuance.
In some cases, applicants or licensees may propose or use a previously established acceptable alternative method for complying with specified portions of the NRCs regulations. 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 requests.
Rev. 1 of RG 1.34, Page 5
REFERENCES
1. 10 CFR Part 50, Domestic Licensing of Production and Utilization Facilities,
1 U.S. Nuclear Regulatory Commission, Washington, DC.
2. ASME Boiler and Pressure Vessel Code, American Society of Mechanical Engineers, New York, NY.2
1 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 NRCs 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 NRCs 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.gov.
2 Copies of American Society of Mechanical Engineers (ASME) standards may be purchased from ASME, Three Park Avenue, New York, NY 10016-5990; telephone (800) 843-2763. Purchase information is available through the ASME
Web-based store at http://www.asme.org/Codes/Publications/.
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