Regulatory Guide 3.29

Preheat & Interpass Temperature Control for Welding of Low-Alloy Steel for Use in Fuel Reprocessing Plants & in Plutonium Processing & Fuel Fabrication Plants

ML003739381
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Issue date:	05/31/1975
From:	Office of Nuclear Regulatory Research
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RG-3.29
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'U.S. NUCLEAR REGULATORY COMMISSION May 1975 REGULATORY GUIDE

OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 3.29 PREHEAT AND INTERPASS TEMPERATURE CONTROL FOR THE

WELDING OF LOW-ALLOY STEEL FOR USE IN FUEL REPROCESSING PLANTS

AND IN PLUTONIUM PROCESSING AND FUEL FABRICATION PLANTS

A. INTRODUCTION

This guide describes a method acceptable to the NRC

staff for meeting these requirements with regard to the Section 50.34, "Contents of Applications; Technical control of welding of low-alloy steel components for Information," of 10 CFR Part 50, "Ucensing of Produc fuel reprocessing plants and for plutonium processing tion and Utilization Facilities," requires, among other and fuel fabrication plants.

things, that each application for a construction permit or operating license for a fuel reprocessing plant include a

B. DISCUSSION

discussion of how the applicable requirements of Appen dix B, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," to 10 CFR Part 50 The American Society of Mechanical Engineers Boiler will be satisfied. As used in Appendix B, "quality and Pressure Vessel Code* (ASME Code),Section III,

assurance" comprises all those planned and systematic "Nuclear Power Plant Components," and Section VIII,

actions necessary to provide adequate confidence that "Pressure Vessels," specify requirements for fabricating safety-related structures, systems, and components will components as indicated In the section titles. Many of perform Satisfactorily in service. Appendix B requires, in the requirements of this Code can also be applied to part, that measures be established to ensure that special safety-related structures, systems, and components of processes, including welding, are controlled and accomp fuel reprocessing plants and plutonium processing and lished by qualified personnel using qualified procedures, fuel fabrication plants. Specific portions of the ASME

and that proper process monitoring be performed. Para Code and of other applicable codes and standards have graph 70.22(f) of 10 CFR Part 70, "Special Nuclear been used for fabricating components for such plants.

Material," requires that each application for a license to Acceptable practices can differ significantly because possess and use special nuclear material in a plutonium there has not been sufficient guidance toward standard processing and fuel fabrication plant contain a des ization. In the interest of standardization, this guide cription of the quality assurance program to be applied specifies procedures acceptable to the NRC staff for the to the design, fabrication, construction, testing, and control of preheat and interpass temperatures for'

operation of the structures, systems, and components of welding of low alloy steels for use In the plants discussed the plant and that the description include a discussion of albove. These procedures, which draw on those used for how the criteria of Appendix B to Part 50 will be met. nuclear power plants, will provide a uniform quality Paragraph 70.23(b) of 10 CFR Part 70 provides that the level consistent with the function of safety-related Commission will approve construction of a plutonium structures, systems, and componentsiof fuel reprocessing processing and fuel fabrication plant when it has deter plants and of plutonium processing and fuel fabrication mined that the design bases and the quality assurance plants.

program provide reasonable assurance of protection against natural phenomena and the consequences of

• American Society of Mechanical Engineers 'Boiler and potential accidents, noting that the criteria in Appendix Pressure Vessel Code, 1974 Edition. AI references to the ASME

B to-0 CFR Part 50 will be used by the CommissionIn Code wre to the 1974 edition. Copies may be obtained from the determining the adequacy of the quality assurance pro American Society of Mechanical -Engineers, United Engineering gram- Center, 345 East 47th Street, New York, N.Y. 10017.

USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission. U.S Nuclear Regulatory Guides are issued to describe and make available to the public Regulatory rvKe. Gommisson. Washington. D.C. ttention: Docketing end methods acceptable to the NRC.staff of Implementing specific parts of the Commoilon's regulatlons. to delineate techniques used by the staff in eralu- The guideswe Issuedin the fo*owingon broad divisions:

ating specific problems or postulated accidents. or to provide guidance to appi cents. Regulatory Guides are not substitutes for regulations, and compliance 1. Power Reacto., S. Products with them Is not required. Methods end solutions different from thas 0ot mut in 2. Research and Test Reactors 7. Transportation the ugudes will be acceptable if they provide a basis for the findings requisite to $. Fuels and Matedria Facilties ,L Occupational fheath the Isauanc or continuance of a permit or license by the Commission. 4. Environmental and Sting 9. Antitrust Review Comments and suggestione for improvements in these guides am encouraged 5. Materials and Plant Protection 10. General at all times, and guides will be revised. es appropriate. to accommodate eam mants and to reflect now information or experlence. However. comments on Coies of published guides may be obtained by written request Indicating the this guide, If received within about two months after its issuance, will be par- divisions desired to the US. Nuclear Regulatory Commission. Washington. D.C.

ticularly useful in evaluating the need for an early revision. N05S. Attention: Director. Office of Standards Development.

I I

Procedure Qualification In addition to the minimum preheat temperature, a maximum interpass temperature should be specified. If Section III and Section VIII require adherence to the weld metal should transform at too high a tempera Section IX, "Welding and Brazing Qualifications," of the ture, the required mechanical properties for the metal ASME Code, including the requirements governing pro may not be met. The maximum Interpass temperature cedure qualifications for welds. Review of the require varies for different steels, as does the minimum preheat ments of Section IX for procedure qualifications and the temperature, and should be selected on the basis of such fabrication requirements of Sections II and VIII influencing factors as the chemical composition of the indicates the desirability of supplementary requirements steel.

to ensure adequate control of welding variables in the production welding of low-alloy steels. Production Welds The assurance of satisfactory welds in low-alloy steels can be increased significantly and, in particular, the pro The procedure qualification by itself does not ensure pensity for cracks (cold cracks) or reheat cracks forming that the production welds will be made within the in underbead areas and heat-affected zones (HAZ) can specified preheat temperature range. To ensure that the be minimized by maintaining proper preheat tempera welds will be acceptable, the metal temperature should tures on the base metals concurrent with controls on be monitored during the welding process and through other welding variables. postweld heat treatment.

Cold cracking can occur when the steel is hardened;

i.e., undergoes a phase transformation to martensite in

C. REGULATORY POSITION

the HAZ and/or weld metal. The martensite exhibits brittle fracture tendencies, and it may not be able to Weld fabrlcation* for low-alloy steel components withstand rapid cooling and the volume change associ important to safety should comply with acceptable fab ated with the phase transformation without the occur rication requirements and should be performed by quali rence of local cracking. This susceptibility to cracking fled welders and welding procedures in accordance with increases with higher stresses, such as those experienced the requirements of Section IX of the ASME Code with increased thickness or welding under constraint of supplemented by the following:

the parts being welded, .and also increases with a de crease in welding energy input. In order to avoid or mini 1. The procedure qualification should require that:

mize the effects of hardening associated with phase transformation, a longer cooling time is needed for the a. A minimum preheat and a maximum interpass weld; in other words, the preheat temperature should be temperature be specified.

maintained high enough to achieve an acceptable con dition of the phase transformation. b. The welding procedure be qualified at the minimum preheat temperature.

It is generally recognized that atomic hydrogen absorption and diffusion into and through the region 2. For production welds, the preheat temperature being welded have an important influence an the should be maintained until a postweld heat treatment tendency to form cracks. While the level of hydrogen in has been performed.

weld filler metal is low enough to preclude adverse effects in the welds, greater quantities of hydrogen can 3. Production welding should be monitored to verify be present in the weld region from the dissociation of that the limits on preheat and Interpass temperatures are moisture in hygroscopic welding fluxes or adsorbed on maintained.

metal surfaces if the welding fluxes and surfaces have not been properly dried before weld deposition. Em 4. In the event that regulatory positions C.1, C.2, brittlement of metal in the weld area due to the presence and C.3 above are not met, the weld is subject to of hydrogen generally occurs at lower temperatures and rejection. However, the soundness of the weld may be may be prevented by prolonging the time the weldment verified by an acceptable examination procedure.

is maintained at preheating temperature or by per forming a postweld heat treatment. Prolonged time at preheating can prevent or interrupt local hardening and

D. IMPLEMENTATION

assist in reducing adverse effects of a potential hydrogen gradient. This gradient would disappear by means of The purpose of this section is to provide information diffusion of the hydrogen before the weldment Is to applicants and licensees regarding the NRC staff's returned to room temperature. Therefore, the minimum plans for utilizing this regulatory guide.

preheat temperature should be established to ensure a desirable cooling rate for the weld, and this temperature should be maintained until a postweld heat treatment

• Applies also to welding and weld repairs after Initial fabrica has been achieved. tion when a postweld stress-relieving heat treatment Is used.

3..9-2

Except in those cases in which the applicant proposes For 'those applications docketed on or before Novem an acceptable alternative method for complying with ber 3, 1975, the NRC staff may reevaluate the appli

2J specified portions of the Commission's regulations, the cation on a case-by-case basis to ensure that acceptable method described herein will be used in the evaluation weld qualification and production welding procedures of submittals in connection with applications for permits are being used.

and licenses docketed after November 3, 1975.

3.29-3

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