ML12305A259

Safety Guide 31, Control of Stainless Steel Welding.

ML12305A259
Person / Time
Issue date:	08/11/1972
From:	Office of Nuclear Regulatory Research
To:
References
Safety Guide 31 RG-1.031
Download: ML12305A259 (4)

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August 11, 1972 SAFETY GUIDE 31 CONTROL OF STAINLESS STEEL WELDING A. Introduction supplementary requirements to assure adequate control of weld metal General Design Criterion 1, "Quality properties when welding austenitic Standards and Records," of Appendix A to 10 stainless steel. Specifically, the CFR Part 50, "General Design Criteria for assurance of satisfactory welds in Nuclear Power Plants," requires that structures, austenitic stainless steel of the AISI systems, and components important to safety be 3XX series can be increased designed, fabricated, erected, and tested to significantly and, in particular, the quality standards commensurate with the sensitivity to fissuring or hot cracking importance of the safety function to be can be reduced by maintaining the performed. Appendix B to 10 CFR Part 50, amount of delta-ferrite in the weld "Quality Assurance Criteria for Nuclear Power metal between 5 and 15 percent.

Plants and Fuel Reprocessing Plants," requires that measures be established to assure materials Experiments indicate that 5-10 percent control and control of special processes such as delta-ferrite in welds for austenitic welding, and that proper testing be performed. structures provides optimum resistance This guide describes an acceptable method of to fissuring or hot cracking. An implementing these requirements with regard to acceptable range of delta-ferrite for

.e control of welding when fabricating and welding wrought austenitic structures is

. ing austenitic stainless steel components and 5-12 percent. However, a higher ems. delta-ferrite range of 5-15 percent is acceptable for welding duplex cast B. Discussion structures.

The ASME Boiler and Pressure Vessel Code, Section IX acceptance standards for Section III, "Nuclear Power Plant fissures or cracks in transverse side Components,"' specifies certain requirements bend tests were not intended to cover associated with manufacturing Class 1, 2, and 3 microfissures as such; however, the components. Although welds fabricated for core subject is covered in specification support structures of austenitic stainless steel are MIL-E-0022200/2B (SHIPS), dated not presently within the scope of Section III, September 15, 1970, which states that they should meet Class 1 requirements. 3 fissures smaller than 1/ 16 inch (0.015 inch) need not be counted. Although

1. Procedure Qualifications the formation of microfissures in welds also depends on factors other than Section III requires adherence to ASME delta-ferrite content and heat input, it Boiler and Pressure Vessel Code, is generally agreed that there will be Section IX, "Welding Qualifications,"' few, if any, small fissures in a side bend one of the requirements being test of weld metal deposited with the procedure qualifications for welds. proper heat input and containing 5-15 Review of the requirements of percent delta-ferrite.

procedure qualifications stated in Section IX indicates the desirability of In addition to supplementing procedure qualification requirements of Section

... 1Copies may be obtained from American Society of

.]*lhanical Engineers, United Engineering Center, 345 IX by specifying acceptable 47th Street, New York, N.Y. 10017. delta-ferrite content in the weld metal, 31.1

tests and examinations should be made segregation and microfissuring will be to assure that this specification is met reduced.

and that unacceptable microfissures will not result. The use of chemical Control of both local and gross heat analysis of the undiluted weld deposit input is important in welding.

to determine key constituents Experience indicates that welds combined with the use of the produced manually are more likely to Schaeffler diagram to predict its be unacceptable than welds produced delta-ferrite content and a by automatic welding machines. This nondestructive examination of 1he weld results principally because local and using a magnetic measurement device, gross heat inputs are more controllable such as the Severn Ferrite indicator, are in automatic rather than manual weld available techniques to determine production. In order to control gross delta-ferrite content, and both should and local heat inputs during the be included in the procedure welding process (these cannot be qualifications. measured directly) and to assure a proper solidification rate of weld metal, Another important variable in the the variables of amperage, voltage, and control of weld metal is heat input. speed of travel should all be specified in Excessive heat input often results in a procedure qualifications. To provide large weld puddle and a slow cooling reasonable assurance that there will be rate of the weld metal. The resulting no unacceptable microfissures in weld slower solidification rate has a metal, macroscopic examination on a tendency to diminish ferrite retention guided transverse side bend test and to result in large grain size specimen should be included as part of microstructures, which in turn increase the procedure qualifications. All results of the above tests and examinations the tendency both for impurities to segregate at the grain boundaries and should be included in the certified for fissure formation. qualification test report required by Section IX.

A heat input that gives an acceptable 2. Production Welds solidification rate (temperature gradient) in a heavy weld cross section Procedure qualification by itself does may not be acceptable for a thinner not assure that production welds will weld cross section because of the meet the delta-ferrite and heat input smaller heat sink. Control of only the requirements specified in the procedure maximum interpass temperature, used qualification.Section III specifies to assure a satisfactory temperature requirements for welding materials. In gradient in a heavy, cross section, may addition to meeting these requirements, not be sufficient to control each Lot and Heat of welding material microfissuring in thinner sections and, for production welds should be shown consequently, control of heat input to be satisfactory by analysis to predict should also be utilized. Heat input, the delta-ferrite level. In order to assure measured in kilojoules per lineal inch that production welds are satisfactory, (kJ/in) of weld, is considered low when it is desirable that the production welds less than 25 kJ/in, intermediate in the themselves be examined range 25 to 50 kJ/in, and high above 50 nondestructively using a magnetic kJ/in. Microfissuring in weld thickness measurement device such as the Severn of 1 to 2 inches has been observed in ferrite indicator. Since such devices manual arc welded joints which were have limitations regarding the physical deposited with an intermediate heat depth to which they can examine weld input of about 40 kJ/in. If a low heat material, it may be necessary to input of about 25 kJ/in is utilized, the perform several examinations for each assurance of a satisfactory weld will be weld. The number of examinations to enhanced, regardless of thickness and, be conducted for each weld should in particular, the probability of reflect the thickness of the weld metal 31.2

pass, the number of passes ,per joint, delta-ferrite content be predicted the capability of 'the instrument used, by using the Schaeffler diagram 3 and the heats of the weld materials. or its equivalent, Sufficient examinations should be c. delta-ferrite content in weld metal conducted through the thickness of the be determined using magnetic weld to provide reasonable assurance measurement devices 4 such as the that the delta-ferrite content is within Severn ferrite indicator, the specified limits (the number of d. heat input during welding be examinations required for each weld specified in terms of amperage, will vary from weld to weld and is voltage, speed of travel, and dependent upon the factors interpass temperature limits (all enumerated above). In the event the values being selected to promote a examination indicates that the rapid cooling rate across the delta-ferite in the production weld is weldment),

not within the specified, range, e. macroscopic examination be macroscopic examinations should be performed on transverse side bend performed on transverse side bend test specimens to determine specimens from the welds to determine fissures or cracks (or absence of if cracks or fissures exist. Since high same) in weld metal.

reliance is placed on procedure qualifications, instruments used in examining production welds should be calibrated against the same standard as 2. The results of the destructive and that used when developing procedure nondestructive tests required in qualifications. In addition to regulatory position 1. above should be monitoring the normal welding included in the certified qualification variables during performance of test report. 2 production welds, the voltage, amperage, and speed of travel should be

3. The welding materials used for periodically monitored to verify production welds should meet the compliance with those included in requirements of Section III of the procedure qualifications.

ASME B&PV Code. In addition, each C. Regulatory Position Lot or Heat of welding material should meet the requirements of regulatory position L.a. and 1.b. above.

Welds for austenitic stainless steel core support structures should comply with the fabrication requirements specified in the 4. Production welds should be examined ASME Boiler and Pressure Vessel Code to verify that delta-ferrite level is (ASME B&PV Code) for Section III, Class 1 between 5 and 12-15 percent in weld components. Weld fabrications for metal. The number of examinations to austenitic stainless steel core support assure compliance with delta-ferrite structures and Class 1, 2, and 3 components level should be based on the thickness should comply with Section III and Section of weld metal per pass, the number of IX of the ASME B&PV Code supplemented passes per joint, the instruments used, by the following: and heats of materials. Instruments used should be calibrated against the

1. The procedure qualification 2 should same standard as that used when require that: developing procedure qualifications.

a. weld deposits contain between 5 and 12-15 percent delta-ferrite,

.3American Society for Metals Handbook, Vol. 6, at

b. chemical analysis be performed on 246-47.

undiluted weld deposits and that 4 Welding Research Council Bull. No. 132, The 2

ASME Boiler and Pressure Vessel Code, Section Measurement of Delta-Ferrite in Austenitic Stainless Ix. Steels (August 1968).

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V

5. In the event that requirements of 6. Production welding should be regulatory position 4. above are not monitored, to verify compliance with met, additional examinations should be the requirements in regulatory position performed in accordance with 1. above for amperage, voltage, speed regulatory position 1.e. above. of travel, and other essential variables.

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