Regulatory Guide 1.31

Control of Ferrite Content in Statinless Steel Weld Metal

ML003739986
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Issue date:	04/30/1978
From:	Office of Nuclear Regulatory Research
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RG-1.031, Rev 3
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Revision 3 April 1978 U.S. NUCLEAR REGULATORY COMMISSION

REGULATORY GUIDE

OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 1.31 CONTROL OF FERRITE CONTENT IN

STAINLESS STEEL WELD METAL

presence of microfissures. Further investigations re

A. INTRODUCTION

lated the presence of the microfissures to the low General Design Criterion 1, "Quality Standards delta ferrite content of the deposited weld metal.

and Records," of Appendix A, "General Design Since microfissures in austenitic welds may have an Criteria for Nuclear Power Plants," to 10 CFR Part adverse effect on the integrity of components, the

50 requires that components- important to safety be control of weld deposits to ensure the presence of designed, fabricated, erected, and tested to quality delta ferrite in these welds is advisable.

standards commensurate with the importance of the As part of achieving this control, recommendations

• safety function to be performed. Criterion 14, "Reac to test production welds were made in the original tor Coolant Pressure Boundary," of Appendix A re version of this guide (Safety Guide 31, "Control of quires that the reactor coolant pressure boundary be Stainless Steel Welding"), and these recommenda designed, fabricated, erected, and tested so as to have tions were retained in Revision 1. Because licensees an extremely low probability of abnormal leakage, of and other representatives of the nuclear industry be rapidly propagating failure, and of gross rupture. Ap lieved that adequate control of filler metal ferrite con

"pendix B, "Quality Assurance Criteria for Nuclear tent would consistently provide sound weld deposits Power Plants and Fuel Processing Plants," to 10 CFR with an absence of microfissures, a cooperative study Part 50 requires that a quality assurance program be group was formed by ASME, ANSI, and NRC to in applied to the design, construction, and operation of vestigate the problem and the alternatives that would structures, systems, and components. Appendix B ensure adequate control of ferrite content. The study also requires that measures be established to ensure group analyzed data from welds prepared by eight that special processes, including welding, are con different procedures. About 1500 test results were trolled and accomplished by qualified personnel analyzed, and recommendations were made to both using qualified procedures and that proper process ASME and NRC on how testing of production welds monitoring be performed. could be reduced without sacrifice of ferrite content This guide describes a method acceptable to the control. Revision 2 and this Revision 3 are based on NRC staff for implementing these requirements with those recommendations. At present, the ASME

regard to the control of welding in fabricating and Code* provisions incorporated by reference into the joining safety-related austenitic stainless steel com NRC regulations require compliance with one of two ponents and systems in light-water-cooled nuclear alternative methods for control of delta ferrite in weld power plants. The Advisory Committee on Reactor metal filler materials; either a chemical analysis Safeguards has been consulted concerning this guide method or a magnetic measurement method. The and has concurred in the regulatory position. NRC staff does not consider either method adequate

B. DISCUSSION

Inspection of some welds in austenitic stainless

• Winter 1976 Addenda,Section III, "Nuclear Power Plant steel components of nuclear reactors has revealed the Components," ASME Boiler and Pressure Vessel Code. Copies may be obtained from the American Society of Mechanical En gineers, United Engineering Center, 345 East 47th Street, New York. New York 10017.

• Lines indicate substantive changes from previous issue.

Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regu.

USNRC REGULATORY GUIDES latory Commission. Washington. D.C. 20555. Attention Docketing and Service Regulatory Guides are issued to describe and make available to the public methods Branch.

acceptable to the NRC staff of implementing specific parts of the Commission's regulations. to delineate techniques used by the staff in evaluating specific problems The guides are issued in the following ten broad divisions or postulated accidents, or to provide guidance to applicants. Regulatory Guides

6. Products

1. Power Reactors are not substitutes for regulations. and compliance with them is not require

7. Transportation

2. Research and Test Reactors Methods and solutions different from those set out in the guides will be accept. 3. Fuelsand Materials Facilities 8. Occupational Health able if they provide a basis for the findings requisite to the issuance or continuance 4. Environmental and Siting 9 Antitrust Review of a permit or license by the Commitsion. 5. Materials and Plant Protection 10. General Comments and suggestions for improvements in these guides are encouraged at all Requests for single copies of issued guides (which may be reproducedI or for place ment on an automatic distribution list for single copies of future guides in specific times, and guides will be revised, as appropriate, to accommodate comments and to reflect new information or experience. This guide was revised as a result of divisions should be made in writing to the US. Nuclear Regulatory Commission.

Washington. D.C. 20555, Attention Director. Division of Document Control.

substantive comments received from the public and additional staff review.

by itself to ensure controlled delta ferrite in produc Chromium and Chromium-Nickel Steel Covered tion welds. The recommendations of this guide are Welding Electrodes,"* which describes a procedure intended to supplement the ASME Code requirements for pad preparation and ferrite measurement. The to ensure control of delta ferrite in welds in austenitic NRC staff considers this procedure acceptable for use stainless steel core support structures and Class 1 and with covered electrodes.

2 components. 3. Instrumentation The recommendations for testing of production The weld pad should be examined for ferrite con welds in Revision 1 of this guide have been replaced tent by a magnetic measuring instrument which has by recommendations for process control by testing of been calibrated against a Magnegage in accordance weld test pads. These changes will considerably re with American Welding Society Specification AWS

duce the testing effort needed to control delta ferrite A4.2-74, "Procedures for Calibrating Magnetic In in welds. struments to Measure the Delta Ferrite Content of The staff recommends that ferrite content in the Austenitic Stainless Steel Weld Metal."'** The Mag weld filler metal as depicted by a ferrite number (FN) negage should have been previously calibrated in ac be between 5 and 20. This lower limit provides suffi cordance with AWS A4.2-74 using primary standards cient ferrite to avoid microfissuring in welds, as defined therein.

whereas the upper limit provides a ferrite content 4. Acceptability of Test Results adequate to offset dilution. Weld pad test results showing an average Ferrite Number from 5 to 20 indicate that the filler metal is

C. REGULATORY POSITION

acceptable for production welding of Class 1 and 2

1. Verification of Delta Ferrite Content of Filler austenitic stainless steel components and core support Materials structures.

Prior to production usage, the delta ferrite content The upper limit of 20 may be waived for (a) welds of test weld deposits from each lot and each heat of that do not receive postweld stress relief heat treat weld filler metal procured for the welding of austeni ment or welds for which such postweld stress relief tic stainless steel core support structures and Class 1 treatment is conducted at temperatures less than and 2 components should be verified for each process 900'F, (b) welds that are given a solution annealing to be used in production. heat treatment, and (c) welds that employ consuma ble inserts.

It is not necessary to make delta ferrite determina

5. Quality Assurance tions for SFA-5.4 type 16-8-2 weld metal or for filler The applicable provisions of 10 CFR Part 50, Ap metal used for weld metal cladding. Delta ferrite de terminations for consumable inserts, electrodes, rod pendix B, should be used in verifying compliance or wire filler metal used with the gas tungsten arc with requirements for delta ferrite as described herein.

welding process, and deposits made with the plasma arc welding process may be predicted from their chemical composition using an applicable constitu

D. IMPLEMENTATION

tional diagram to demonstrate compliance. Delta fer rite verification should be made for all other proc The purpose of this section is to provide informa esses by tests using magnetic measuring devices on tion to applicants regarding the NRC staff's plans for undiluted weld deposits. For submerged arc welding using this regulatory guide.

processes, the verification tests for each wire and Except in those cases in which the applicant pro flux combination may be made on a production weld poses an acceptable alternative method for complying or simulated production weld. All other delta ferrite with specified portions of the Commission's regula weld filler verification tests should be made on weld tions, the method described herein will be used in the pads that contain undiluted layers of weld metal. evaluation of submittals in connection with construc tion permit applications docketed after October 1,

2. Ferrite Measurement

1978.

Appendix A to this guide contains extracts from a If an applicant wishes to use this regulatory guide future edition of the American Welding Society's in developing submittals for applications docketed on AWS A5.4, "Specification for Corrosion-Resisting or before October 1, 1978, the pertinent portions of

• This specification has been recommended by the Subcommit the application will be evaluated on the basis of this tee on Welding of Stainless Steels of the High Alloys Committee guide.

of the Welding Research Council and has been approved by the American Welding Society (AWS). It is expected to be pub **Copies may be obtained from the American Welding Society, lished as AWS A5.4-78. 2501 N.W. 7th Street, Miami, Florida 33125.

1.31-2

APPENDIX A

The following is mainly extracted from a future A4.10.3 The welding current used for the size of edition of the American Welding Society's (AWS) the electrode being tested may be as specified in Fig

"Specification for Corrosion-Resisting Chromium ure 4 and the arc length shall be as short as practica and Chromium-Nickel Steel Covered Welding Elec ble. The weld bead layers may be deposited with a trodes," which the AWS plans to publish as AWS weave, if 'necessary, to fill the space between the A5.4-78.* This material describes a procedure for copper bars. The arc shall not be allowed to impinge weld pad preparation and ferrite measurement of cov on the copper bars. The welding direction for each ered electrode** deposits. pass shall be alternated and the weld stops and starts shall be located at the ends of the weld buildup. Each EXTRACT: pass shall be cleaned prior to depositing the next A4. 10 When it is desired to measure ferrite con weld bead. The maximum interpass temperature shall tent, the following procedure is recommended: be 95'C (200°F).** Between passes, the weld pad A4.10.1 Weld pads as detailed in Figure 4 are may be cooled by quenching in water not sooner than prepared as prescribed in paragraphs A4.10.2 20 seconds after the completion of each pass. The through A4.10.4. last pass shall be air-cooled to below 430'C (800'F)

A4.10.2 The weld pad shall be built up between prior to quenching in water.

two copper bars laid parallel on the base plate by de A4.10.4 The completed weld pad shall be draw positing single weld bead layers, one on top of the filed, machined, or surface ground to provide suffi other, to a minimum height of 13 mm (1/2in.). The cient finished surface to make the required ferrite spacing between the copper bars for the size of the readings. Draw filing or its equivalent filing method electrode being tested shall be as specified in Figure shall be performed with a 360 mm (14 in.)** mill

4. An optional welding fixture is shown in Figure 5. bastard file held on both sides of the weld with the If carbon steel is used as the base plate, the weld pad long axis of the file perpendicular to the long axis of shall be built up to a minimum height of 16 mm (5 the weld. The file should preferably not have been in.). previously used on ferritic material and should be

• When published, copies of AWS A5.4-78 may be purchased free from loosely adhering materials if previously from the American Welding Society, 2501 N.W. 7th Street, used. Draw filing shall be accomplished by smooth Miami, Florida 33125. forward and backward strokes along the length of the

• • Note: The U.S. customary units in this specification are weld while applying a firm downward pressure.

given as equivalent values to the SI units. The standard sizes and dimensions used in the two systems are not identical and for Crossfiling shall not be permitted. The finished this reason conversion from a standard size of dimension in one machined, ground, or filed surface shall be smooth system will not always coincide with the standard size of dimen with all traces of weld ripple removed and shall be sion in the other. Suitable conversions encompassing standard continuous in the length where measurements are to sizes of both can be made if appropriate tolerances are applied in be taken. The width of the prepared surface shall not each case. The SI values (including tolerances) given here for filler metal diameter, length, and package size were selected to be less than 3 mm (1/8in.).**

fit the product sizes which presently are U.S. standards. Toler A4.10.5 A total of six ferrite readings shall be ances are used in some cases in this specification but not in taken on the prepared surface along the longitudinal others. In those cases where no tolerances are given, the values axis of the weld pad with an instrument calibrated in are those that would be obtained if the measurements were taken in SI units. In this specification, a covered electrode is defined accordance with the procedures specified in AWS

as follows: Covered Electrode-A composite filler-metal elec A4.2, "Standard Procedures for Calibrating Magnetic trode consisting of a core of a bare electrode or metal cored Instruments to Measure the Delta Ferrite Content of electrode to which a covering sufficient to provide a slag layer Austenitic Stainless Steel Weld Metal" (latest edition).

on the weld metal has been applied. The covering may contain A4.10.6 The six readings 'obtained shall be aver materials providing such functions as shielding from the atmos phere, deoxidation, and arc stabilization and can serve as a aged to a single value for conversion to Ferrite source of metallic additions to the weld. Number.

1.31-3

- LL

Ferrite shall be measured in this area free of arc

-H starts and craters 1 Copper bar I

I

I

25x25x75 BASE PLATE

1465 min .

1 40 -25 min o I

All dimensions in millimetres, U.S. EQUIVALENTS*

mm in.

1.6 1/16

2.0 5/64

2.4 3/32

3.2 1/8

4.0 5/32

4.8 3/16 Electrode Welding In drawing above 6.4 1/4 diameter current (approx. mm) 6 0.25 (mm) (amperes) W L 8 0.3

9.5 3/8

1.6 35-45 6 30 10 0.4

2.0 45-55 6 30 13 0.5

2.4 65-75 8 40 15 0.6

3.2 90-100 10 40 18 0.7

4.0 120-140 13 40 25 1

4.8 165-185 15 40 30 1-1/4

240-260 18 40 40 1-1/2

65 2-1/2

75 3 See Editor's Note on Page 1.31-3.

Fig 4 - Details of Weld Pad for Ferrite Test

1.31-4

Copper bars 85 long of cross section as shown in A-A' below.

Copper bar 16 high x

9.5 thick x 70 lon

g. Copper bar same

-as shown at opposite end A

I

Type 1 For 4.0 dia. Electrodes and smaller Note: All dimensions are in millimetres.

COPPER

16 BAR

U.S. EQUIVALENTS*

MM in.

T Cross Section A-A'

4.0 5/32 This design allows increased visibility,

4.8 3/16 making it easier to hold a short arc length.

9.5 3/8

16 5/8

25 1 COPPEIR COPPER

BAR BAR

70 2-3/4 25 square

85 3-3/8 Type 2

• See Editor's Note on Page 1.31-3.

For 4.8 & larger welding electrodes and for any pads on carbon steel base plate Fig. 5 - Optional Welding Fixture for Welding Ferrite Test Pads

1.31-5