ML20009G255

Reg Guide 1.150, Ultrasonic Testing of Reactor Vessel Welds During Preservice & Inservice Exams

ML20009G255
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Issue date:	06/30/1981
From:	NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
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ML20009G256	List: ML20009G255 ML20009G258
References
TASK-OS, TASK-SC-705-4 REGGD-01.150.00, REGGD-1.150.00, NUDOCS 8108040038
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U.S. NUCLEAR REGULATORY COMMISSION June 1981 o

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(&f; REGULATORY Glh h

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OFFICE OF NUCLEAR REGULATORY RESEARCH W d.J &be 3

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uL yg 15 M " h REGULATORY GUIDE 1.150 (Task SC 705 4)

ULTR ASONIC TESTING OF REACTOR VESSEL WELDS D f$G U

P3ESERVICE AND INSERVICE EXAMINATIONS T

N A

si3 A. INTRODUCTION Criterion XVil," Quality Assurance Records." of Appen-dix B requires,in part, that sufficient records be maintained Criterion I," Quality Standards and Records " of Appen-to furnish evidence of activities affectingquahty. Consistent da A, " General 1)esign Criteria for Nuclear Power Plants,"

with applicable regulatory requirements, the applicant is to 10 Cl R Part 50, " Domestic Licensing of Production and required to establish such requirements concerning record Utihtation Facihties,' requires, in part, that components retention es duration, location, and assigned responsibihty.

important to safety be tested to quality standards commen-sarate with the importance of the safety functions to be performed. Where generally recognized codes and standards This guide describes procedures acceptable to the NRC are used, these codes and standards must be evaluated to staff for implementing the above requirements with regard determine their adequacy and sufficiency and must be sup-to the prescrvice and inservice examinations of reactor plemented or modified as necessary to ensure a quality pro-vessel welds in light-water-cooled nuclear power plants by duct in keeping with the required safety function. Criterion I ultrasonic testing (UT). The scope of this guide is limited to further requires that a quality assurance program be imple-reactor vessel welds and does not apply to other structures mented in order to provide adequate assurance that these and components such as piping.

components will satisfactordy perform their safety functions and tLat appropriate records of the testing of components B. DISCUSSION important to safety be maintained by or under the control of the nuclear power unit licensee throughout the life of Reactor vessels must periodically be volumetrically the unit.

examined according to Section XI of the ASME Code.

Section So.55a, " Codes and Standards." of 10 CFR which is incorporated by reference, with NRC staff modifier Part 50 requires, in part, that structures, systems, and tions, in @ 50.55a of 10 CI R Part 50. The rules of Section XI components be designed, fabricated, erected, constructed, require a program of examinations, testing, and inspections tested, and inspected to quality standards commensurate to evidence adequate safety. To ensure the continued with the importance of the safety function to be performed.

structural integrity of reactor vessels, it is essential that Section 50.55a further requires that American Society of flaws be reliably detected and evaluated. It is desirable that Mechanical 1 ngineers Boiler and Pressure Vessel Code results from prior UT examinations be compared to results

( ASME B&PV Code) Class I components meet the require-from subsequent examinations so that flaw growth rates ments set forthin Section XI," Rules for Inservice inspection may be estimated. Lack of reliability of Ur examination of Nuclear Powe: Plant Components," of the ASME Code.

results is partly due to the reporting of ambiguous results, such a reporting the length of flaws to be shorter during Cnterion Xil,' Control of Measuring and Test Equipment,"

su bsequer,.xaminations. This lack of reproducibility arises of Appendix B, " Quality Assurance Criteria for Nuclear because the Code requirements are not specific about Power Plants and Fuel Reprocessing Plants," to 10 CIN many essentialvariablesin the UT procedures. Recommenda-Part 50 reluires, in part, that measures be established to tions of this guide provide guidance that would help to ensure that instruments used in activities affecting quality obtain reproducibility of results. Reporting of UTindications are ; operly controlled, calibrated, and adjusted at specified as recommended in this guide will help to prmide a means periods to maintain accuracy within necessary limit s.

for assessing the ambiguity of the reported data.

Z O Q b b USNRC REGULATORY GutOES Comments should be sent to the Secretary of the CwTilssion, U.S. Nuclear Regulatory Commission, Washington, O.C. 2055 5, d

O Regulatory Guides are issued to describe and make available to the Attention: Docketing and Service Granch.

.4 pu blic metnons ac cept able to the NRC st a f f of implementing specific parts of the Commission's regulations, to delineate tech-The guides are issued in the following ten broad divisiom:

g niques used by the staf f in evaluating specific problems or postu-E lated accidents or to provide guidance to apolicants. Regulatory

1. Power Reactors

6. Products O

c.uides are noi substitutes for regulations, and compliance w th

2. Research and Test Reactors

7. Transportation (100 them is not reauneo. Methods and solutions dif ferent from those set

3. Fuels and Materials Facilities

8. Occupational Health oco out in tne guides wiu be acceptable if they provide a bases for the

4. Environmental and Siting

9. Antitrust and Financial Review

5. Materials and Plant Protection IO. General ticen'"se bytn"e' site to tne issuance or continuance of a permit or

ad 95 OO -

commission.

Copies of issued guides may be purchased at thecurrent Government WO Printing Of fice price. A subscription service for future guides in spe-OEn This guide was issued af ter consideration of comments received from cific divisions is available through the Government Printing Office.

(D the pubuc. Comments and suggestions for 6mprovements 6n these information on the subscription service and current GPO prices may guides are encouraged at all times, and guides wifi be revised, as be obtained by writing the J.S. Nuclear Regulatory Commission, og approonate, to accommodate comments and to reflect new informa-4g Washington, D.C. 20555, Attention Pubhcations Sales Manager.

tion of emperience.

Operating and beensing experience,2,3 and industry performance characteristics (amplitude linearity and l

tests" have indicated that UT procedures that have been amplitude controllinearity)is to be serified at the beginning used for examination of reactor vessel welds may not be of each day of examination. Requirements in Article 4, adequate to consistently detect and reliably characterize Section V,1977 edition, which is referenced by Section XI, flaws during inservice examination of reactors. This lack of for the periodic check of instrument characteristics (screen reproducibihty of location and characterization of flaws has height linearity, amplitude control linearity, and beam resulted in the need for additional examinations and spread measuremen ts) for UT examination of reactor esaluations with ' associated delays in the licensing process.

pressure sessels have i een relaxed. The interval between periodic checks has been extended from a period of I day

1. INSTRUMENT SYSTEM PERFORM ANCE CilECKS to a period of extended use or every 3 months, whichever is less. This change has not been justified on the basis of Instrument system performance checks to determine the statistically significant field data. Performance stability of characteristics of the'. U F system should be performed at automated electronic equipment is dependent on system intersals short enough to permit each UT examination to be performance parameters (essential variables), and the ASME correlated with particular system performance parameters to Code has no quality standards to control these performance help compare results. These determinations will help make it parameters. Until the performance stability of UT systems possible to judge whether differences in observations made can be ensured by the introduction of quality standards, at different times are due to changesin the instrument system it is not reasonable toincrease the period between calibration characteristics or are due to real changes in the flaw size and checks. Therefore, recommendations have been made to characteristics. Determinations for " Frequency-Amplitude check instrument performance parameters more frequently Curve" and " Pulse Shape" recommended in regulatory posi-than is specified in the ASME Code.

tions 1.4 and 1.5 may be made by the licensee's examination agent by using any of the common industry methods for Requirements of Appendix I, Article I,I-4230,Section XI measuring these parameters as !cng as these methods are of the ASME Code,1974 edition, state:

adequately documented in the examination record. These measurements may be performed in the laboratory before

" System calibration shall be checked by verifying the and after each examinati-m, provided the identical equip-distance-amphtude correction curve (I-4420 or I-4520) ment combination (i.e., instrumentation, cable, and search and the sweep range calibration (1-4410 or I-4510) at the unit! n used daring the examinition.

start and finish of cach examination, with any change in examination personnel, and at least every 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> during t hese determinations are to r.id third-party evaluations an examination."

when different equipment is used to record indications on subsequent examinations and are not intended to qualify in the 1977 edition, these requirements were changed, systems for use.

According to Article 4 (T-432.1.2),Section V of the ASME The intent of regulatory position 1.5 is to establish the I

mstrument pulse shape in a way that actual values of pulse length and voltages can be observed on an oscilloscope. The "A calibratidn check on at least one of the basic reflectors calibrated time base does not necessarily have to follow the n the basic calibration block or a check using a simulator time base of the distance-amplitude correctaxi(DAC) curve but shall be made at the finish of each examination, every may be chosen to suitably characterize the initial pulse.The 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> during the examination and wh:n examination pulse slupe record will assist in analyzing potential differences in flaw response between successive examinations (i.e.,is the diff erence due to flaw growth or system change).

This requirement has several minor deficiencies, including g ggg Pulse shape is best determined by using a high-impedance oscilloscope with the traasdue; disconnecte i from the

a. One-Point Check mstrument.

A cahbration check is now required on only one of the

2. CAllBR AflON basic retlectors. As a result, the accuracy of only one point on the DAC curve, and not the accuracy of three points as Accordmg to Appendix 1, Article 1,1-4230,Section XI of previously required, is checked. This alteration would the ASMI: Code,1974 edition, instrument calibration for permit the instrument drift for other metal path distances to go unnoticed, which is not desirable.

I"ltitrasonic Reinspection of P Igrim i Reactor Vessel Nonle N 2 tl," John 11. Gieske, N U RFG-6 so2.

b. Secondary Reference 2" Summary ifarch Suclear Plant Unit i Reactor Pressure Vesset Repair," 197 2, Georgia Power Company.

1W d 2

a est dM h a whid 3"Sumr iry of the Detection and baluation of I'Itrasonic or electronic simulator instead of a check against (Fe basic In dica tipna F, twin llatch Unit 1 Reactor Pressure Vessel," Jan uary calibration block. A mechanical simulator could be a 1972, Georgia Power Company.

plastic, steel, or aluminum block with a single reference

,Round robin tests conducted by the Pressure Vessel Research Committee (PVRC) of the Welding Research Counci! for UT of reflector, which may be a hole or a notch. Without specified thid section stects.

details, the electronic simulator could be any device that 5.150-2

I provides an electrical signal. With the resulting uncertainty, dropped) during transport than those parameters that

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there may be errors in checking against the secondary served as a basis for defining the error band.

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reference (simulator), the magnitude of which is undefined Use of electronic simulators would be permissible if

\\g and unknown.

they can check the calibration of the UT system as a whole

c. Electronic Simulator and the error band introduced by their use can be relied on and ta',en into consideration.

Suharticle T-432.1.3 of Article 4,Section V of the ASME Code,1977 edition, allows the use of an electronic

d. Static Versus Dynamic Reflector Responses simulator and also permits the transducer sensitivity to be checked separately Both these provisions may introduce With some automated systems, the DAC curve is errors that will be very difficult to detect.

manually established. In these cases, the signal is maximized by optimizing the transducer orientation toward the To avoid the introduction of errors and to ensure calibration holes. Subsequently, detection and sizing of repeatability of examinations at a later date, it would be flaws are based on signals received from a moving transducer advisable to check the calibration of the entire system whcre no attempt is made (oritis not possible) to maximize rather than that of individual components. Checking system the signal even for significant flaws. This procedure neglects calibration without the transducer and the cable is not several sources of error introduced by the possible variation advisable because these tests do not detect possible leakage in signal strength caused by:

or resistance changes at the connectors. This is especially important when the UT examination is performed under (1) Differences between the maximized signal conditions of high humidity or under water and the connec-and the unmaximized signal.

tors may not be waterproof or moistureproof. Checking the transducer sensitivity separately (sometimes weeks in (2) Lossin signal strength due to the separation of advance) also neglects the effects of possible damage due to the transducer from the metalsurface because transport or use. The transducer characteristics may change of the viscosity of the coupling medium (plan-because of damage to or degradation of internal bonding ing effects).

agents or inadvertent damage to the transducer element.

Further the use of an electronic block simunator(EBS)as a (3) Variation in contact force and transducer m secondary standard introduces an error band in the calibra-coupling efficiency.

t I tion process. The error band may depend on, among others,

(_,/

the following factors:

(4) Loss in signal strength due to structural vibra-tion effects in the moving transducer mount (I) Drift due to ambient temperature change.

and other driving mechanisms.

(2) Drift due to high temperature storage.

(3) Drift due to high humidity storage.

(5) Loss in signal strength due to the tilting caused (4) Drift due to vibration and shock loading during by the mounting arrangement in some trans-shipment.

ducer mounts.

(5) Degradation of the memory device used to store the reference signal information due to vibra-Because of the above,it would be advisable to establish tion, shock, aging, or heat effects.

the DAC curve under the same conditions as those under which scanning is performed to obtain data for detection To ensure stability, ccmputer systems are generally and sizing. It would be acceptable to establish a DAC curve kept in an air conditioned environment; however, EBS by maximizing signal strength during manual scans when systems are not usually kept in a controlled environment.

signals are also maximized for flaw sizing. Ilowever, it would not be advisable to use manually maximized signals 5

Frror band for one particular type of instrument to establish the D AC curve when data are obtained later by was determined to be in the range of !6 percent. The error mechanized transducers (where signals cannot be maximized) band for other instruments may be in a different range and for the detection and sizing of flaws without adjustment for may vary for the same instrument if memory devices or the potential error introduced. In these situations, an components of different quality are used at a later date.

acceptable method would be to establish DAC curves using The error band is dependent on the temperature extremes, moving transducers or to establish correction factors that shock loedings, and vibrations suffered by the instrument.

may be used to adjust signal strength. It would be prudent Since the error band value depends on these parameters,it to use care and planning in establishing correction factors.

would be advisable to ensure, through recording instruments, For example, establishing a ratio between a dynamic and that the EBS was not subjected to higher temperatures static mode under laboratory conditions using a precision (container lying in the sun) and greater shock (container transducer drive and stiff mounting may have very little in common with the transducer mounting and traverse condi-

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tions of the actual examination setup. If correction factors

((j) 5"Calitiration venrication of Ultrasonic Etarnination Systerns with are to be used, it would be worthwhile to build either the Electronic Block Sirnulator." D.J. Boorngard et al., August t 979, full-scale mockups or consider the variation of all the Report No.% CAP-9545, westinghouse Electric Corporatian, Nuclear Senice Division, P.O. tu 2728, Pittsburgh. PA I 5230.

Important parameters in a suitable model takm.g mto 1.150-3

consideration scaling laws on variables such as mass, vibration, holes; however, if the block or these holes are polished, this and stiffness constants. It would be advisable toconfirm the fact should be recorded for consideration if a review of the scaling law assumptions and predictions for vibration and UT data becomes necessary at a later date.

viscosit).ffects before correction factors are used for setting scanning sensitivity levels.

3. NEAR-SURFACE EXA511 NATION AND SURFACE RESOLUTION Differences in the curvature and surface finish between cahbration blocks and vessel areas could change the dynamic Sound beam attenuation in any material follows a response, so it may be advisable to establish correction factors decaying curve (exponential function); howcVer, in some between dynamic and static responses from the indications cases the reflection from the nearest hole is smaller than the that are found during examination. This would avoid the reflection from a farther hole. This makes it difficult to difficulties associated with establishing a dynamic response draw a proper DAC curve. In such cases,it may be desirable DAC curve and still take all the factors into consideration.

to use a lower frequencv -r a smaller transducer for Daw detection near the beam-entry surface to overcome the

e. Secondary D AC difficulty of marginal detectability.

l During some manual scans, the end point of the DAC Near-field effects, decay time of pulse reflections, curve may fall below 20 percent of the full screen height.

shadow effects, restricted access, and other factors do not When this happens, it is difficult to evaluate Daws on the permit effective examination of certain volume areas in the 20 percent and 50 percent DAC basis in this region since component. To prnent a clear documentation and record the 20 percent and 50 percent DAC points may be too close of the volume of material that has not been effectively to the baseline. To overcome this difficulty, it is advisable examir ed. these volume areas need to be identified. Recom-that a secondary DAC curve using a higher-gain setting be mendations are provided to best estimate the volume in the developed so that 20 percent and 50 percent DAC points may region of interest that has not been effectively examined, be easily evaluated. For this purpose,it is advisable that the such as volumes of material near each surface (because of gain be increased sufficiently to keep the lowest point of near-field effects of the transducer and ring-down effects of the secondary DAC curve above 20 percent of screen height.

the pulse due toIN contaci surface), volumes near interfaces between cladding and parent metal, and volumes shadowed The secondary DAC curves need not be generated by laminar flaws.

unless they are required. If electronic DAC is used and amplitudes are maintained above 20 percent of full screen

4. BEA51 PROFILE height, a secondary DAC would not be necessary.

Beam profile is one of the main characteristics of a tiano

f. Component Substitution ducer. It helps to show the three-dimensionaldictribution 01 l

beam strength for comparing results between examinations A calibration check should be made each time a and also for characterizing flaws. The beam profile needs to component is put back into the system to ensure that such be determined and recorded so that comparisons may be components as transducers, pulsers, and receivers were not made with results of successive examinations.

damaged while they were in storage. This will ensure elimination of the error band and mistakes in resetting the

5. SCANNING WELD-SIETAL INTERFACE various control knobs.

The amount of energy reflected back from a flaw is

g. Calibration flotes dependent on its surface characteristics, crientation, and size. The present ASNIE Code procedures rely on the Comparison of results between examinations performed amplitude of the redected signal as a basis for judging flaws.

at different times may be facilitated if the same equipment This means that the sire estimation of a defect depends on e

is used and if the reflections from growing flaws can be the proportion of the ultrasonic beam reflected back to the compared to the same reference signal. Reference signals probe. The ref'ection behavior of a planar defect, which l

obtained from a calibration block depend on, among other largely depends on the incident beam angle when a single things, the surface roughness of the block and the reflector search unit is used to characterite the flaw, is thus a decisive holes. Therefore, these surfaces should be protected from factor in flaw estimation. The larger the size of a planar corrosion and mechanical damage and also should not be defect, the narrower is the reflected sound beam. The altered by mechanical or chemical means between successive narrow reflected sound beam makes the flaw very difficult examinations. If the reference reflector holes or the block to detect in most cases (unless the beam angle is right).O surface are given a high polish by any chemicalor mechanical means, the amplitude of the reflections obtained from these reDector holes may be altered. Polishing the holes or the 6"probat aity of Detecting 11anar Defec tsin IIeavy wall welds by block surface is not forbidden by the ASSIE Code. llowever, Ultras nic Tectiniqucs According to Existing Codes," Dr. Ing. Ilans-Jurgen Meyer, Quality Department of M.A.N., Nurnberg D 8s00 this possibly altered amplitude could affect the sizing of Nurnbcrg 115.

indications found during any examination. At this time, no 7

recommendations are being made to control the surface Lan[ ton cnIr"at $lectric$"b'en t$g rI,"tf.5.hsI)"Itep ri roughness of the block or the above-mentioned reflector Number RD 18/N4 t l5.

1.150-4

Therefore, the beam angles used to scan welds should be has to be considered in judging the significance of flaws.8 optimized and should be based on the geometry of the it is thert fore recommended that only signals with a total weld / parent-metal interface. At least one of these angles transducer travel movement greater than the beam spread should be such that the beam is almost perpendicular (115 should be considered significant.

degrees to the perpendicular) to the welrl/ parent-metal interface, unless it can be demonstrated that large (Code-

7. REPORTING OF RESULTS unacceptable) planar flaws unfavorably oriented, parallel to the weld-metal interface, can be detected by the UT tech-This guide gives recommendations for recording the charac-nique being used. In vessel construction, some weld preps are teristics of the UT examination system. This information essentially at right angles to the metal surface. In these cases, can be of significance in later analysis for determining the use of shear wave angles close to 75 degrees is not recom-location, dimensions, orientation, and growth rate of flaws.

mended. Two factors would make the use of shear wave angles close to 75 degrees inadvisable,- first, the test distances Records pertaining to UT examinations should be con-necessary become too large resulting in loss of signal, and sidered quality assurance records. Recommendations on the second, the generation of surface waves tends to confuse collection, storage, and maintenance of thest records are the interpretation of results. In these cases,use of alternative given in Regulatory Guide 1.88, "Comction, Storage, and volumetric nondestructive examination (NDE) techniques, Maintenance of Nuclear Power Plant Quality Assurance Re-as permitted by Subarticle IWA-2240,Section XI of the cords." Availability of these records at a later date will permit ASME Code, should be considered. Alternative NDE a review of the UT results from the data gathered during techniques to be considered may include high-intensity previous ultrasonic examinations.

radiograph or tandem-probe ultrasonic examination of the weld-metal interface. To avoid the possibility of missing When ultrasonic examination is performed, certain vol-targe flaws, particularly those that have an unfavorable umes of material such as the following are not effectively orientation, it is desirable that the back reflection amplitude, examined:

while scanning with a straight beam, be monitored over the entire volume of the weld and adjacent base metal. Any

a. Material volume near the front surface because of near-area where a reduction of the normal back-surface reflection field effects, cladding disturbance, or electronie gating.

amplitude exceeds 50 percent should be examined by angle beams in increments of 15 degrees until the reduction of

b. Material volume near the surface because of surface signal is explained. Where this additional angle beam roughness or unfavorable flaw orientations.

I examination is not practical,it may be advisable to consider examining the weld by a supplemenary vola netric NDE

c. Volumes shadowed by insulation or part geometry.

technique.

In some cases, as much as 1 inch (25.4 mm) or more

6. SIZING below the surface is not examined because of the electronic gate setting. This mear s that the unexamined volume may The depth or through-wall dimension of flaws is more contain flaws that unald be unacceptable accordir"- W significant than the length dimension, according to fracture Section XI, ASME Code, as follows:

mechanics analysis criteria. Using the single-probe pulse-echo technique, it is p,ssible, depending on f.aw orientation,

a. Without evaluarum (deeper than approximately 0.2 that some hrge flaws may not reflect much energy to the inch).

search unit.' Because of this possibility, the depth dimen-sion of the flaw should be conse:vatively sized unless there is

b. Even after evalt ation (deeper than approximately evidence to prove that the Saw orientation is at right angles 0.85 inch).

to Ihe beam.15 is recommended that indications that are asso-

isted with through-thickness flaws and do not meet Code-Assuming an aspect rato of 0.1, according to IWB-3510.1, allowable criteria or criteria recommended in this guide be Section XI, ASME CoJe, flaws 0.2 inch deep would be sized at 20 percent DAC as we!! as at 50 percent DAC.

unacceptable for a 9-inch wall thickness.

In certain cases, it is possible for various reasons that a Typically a BWR reactor pressure vessel (RPV) wall in flaw weald not reflect enough energy to the search unit to the beltline region is 6 inches thick and a PWR-RPV wallis make the indication height 50 percent of the DAC curve 8.5 inches thick. During flaw evaluation, where the wall height. Ilowever, if such a flaw were largc, a persistent temperature is high and the available toughness is high, and signal could be obtained over a large area. It is therefore the calculated critical surface flaw depth (a ) exceeds the wall c

recommended that all continuous signals that are 20 percent thickness (t), a is taken' as the wall thickness. According to c

of DAC with transducer travel movement of more than is B-3600,Section XI, the allowable end-of-life size is ag =

I inch plus the beam spread (as defined in Article 4, non-0.la. Flaws exceeding this allowable value, which would c

f mandatory Appendix B,Section V of the ASME Code, s"Ultramnic Examination con arison aIndication and Actunt flaw g

1977 edition) should be considered significant and should in RPV," Ishi Kawajima Harima Industries Co., Ltd., January 1976.

V be recorded and investigated further. The beam spread effect in some cases can make very small flaws appear to be

9. flaw Evaluation Pnredures: ASME Section XI-EPRI,* NP 719-SR, large when judged at 20 percent DAC; hence, beam spread special report, August 1978.

1.150-5

l be 0.85 inch for a PWR and 0.65 im.h for a BWR, will have 1.3 Amplitude Control Linearity to be repaired. The above example illustrates theimportance of blanking out the electrome indication signals and not Amplitude controllinearity should be determined according examining the surface volume to a depth of 1 inch. Since to the mandatory Appendix 11 of Article 4, Sectior ' of the the Gaws that can be missed because of electronic gating may ASME Code,1977 edition, within the time limits specified in be largt r than the flaws permitted with or without evaluation, regulatory position 1.1.

this unexamined volunt is important and needs to be identified.

In certain specific cases, areas were not examined 1.4 Frequency Amplitude Curve because insulation was in the way and the transducer could not scan the volume of interest. NRC was not informed of A photographic record of the frequency-amplitude curse this situation untd much later. In view of the above and to should be obtained. This record should be available for asoid licensing delays,it is advisable that the volume of areas comparison at the inspection site for the next two successive not examined for any or all of the abose reasons be reported.

inspections of the same volume. The reflector used in generating the frequency-amplitude curves as well as the

~lhe 5olumes of material that are not effectively examined electronic system (i.e., the basic ultrasonic instrument, depend on the particular part geometry and unique situa-gating, form of gated signal, and spectrum analysis equip-tions associated with each RPV. During identification of ment) and how it is used to capture the frequency-amplitude the material volurres that have not been examined, considera-iniormation should be documented.

tion should be given to the types of flaws that are currently being reported in some of the operating plants. These include stress corrosion cracks in the heat-affected ione,

'.5 Pulse Shape fatigue cracks, and cracks that are close to the surface and sometimes penetrate the surface. These volumes of A photographic record of the unloaded initial pulse material should be idenntied and reported to NRC along against a calibrated time base should be obtained. The time with the report of welding and material defectsin accordance base and voltage values should be identified and recorded with the recommendation of regulatory position 2.a(3) of on the narizontaland verticalaxisof the above photographic Regubtory Guide 1.16, " Reporting of Operating Informa-racord of the initial pulse. The method used in obtaining tion-Appendix A Technical Specifications.'

the pulse shape photograph, including the test point at which it is obtained, should be documented.

C REGULATORY POSITION

2. CAllBRATION Ultrasonie examination of reactor vessel welds should be performed according to the requirements of Section XI of System calibration should be checked to verify the DAC the ASME B&PV Code, as referenced in the Safety Analysis curve and the sweep range calibration per nonmandatory Report (SAR) and its amendments, supplemented by the Appendix B, Article 4,Section V of the ASME Code, as a following:

minimum, before and after each RPV examination (or each week in which it is in use, whichever is less)or each time any

1. INSTRUMENT PERFORMANCE CIIECKS component (e.g., transducer, cabb, connector, pulser, or receiver)in the examination system is changed. Where possible, The checks described in paragraphs 1.2 through 1.5 should

'he same calibration block should be used for successive in-be made for any UT system used for the recording and sizing service examinations of the same RPV. The calibration side of reflectors in accordance with regulatory position 6 and holes in the basic calibration block and the block surface shouki for reflectors that exceed the Code-allowable criteria.

be protected so that theircharacteristics do not changeduring storage. These side holes or the block surface should not be modified in any way (e.g., by polishing) between successive 1.1 Frequency of Checks examinations. If the block surface or the calibration reflector holes have been pohded by any chemical or mechanical means, As a minimum, these checks should be verified within I day this fact should be recorded.

before and within I day after examining all the welds that need to be eumined in a reactor pressure vessel during one outage.

Pulse shape and noise suppressbn controls should remain at 2.1 Calibration for Manual Scanning the same setting during examindan and calibration.

For manual scanning for the sizing of flaws, static calibra-1.2 Screen lleight Linearity tion may be used if sizing is performed using a static trans-ducer. When signals are maximized during calibration, they Screen height linearity of the ultrasonic instrument should also be maximized during sizing. For manual scanning should be determined according to the mandatory Appen-for the detection of flaws, reference hele detection should be dix ! to Article 4,Section V of the ASME Code, within the shown at scanning speed and detectio? level set accordingly time limits specified in regulatory position 1.1.

(from the dynamic DAC).

1.150 6

2.2 Calibration for Mechanized Scanning

d. When a universal calibration block is used and some or all of the reierence holes are larger than the reflector

[ ])

When flaw detection and sizing are to be done by holes at comparable depths recommended bv Article 4, Sec-(b/

mechanized equipment, the calibration should be performed tioa V, of the ASME Code,1980 edition,a correction factor should be used to adjust the DAC level to compensate fcr using the following guidelines:

the larger reflector holes. Also,if the reactor pressure vessel

a. Calibration speed should be at or higher than the has been previously examined by using h conventional block, a ratio between the DAC curves obtained from the two scanning speed.

blocks should be noted (for reference) with the significant

b. The direction of transducer movement during calibra-indicctions data.

tion should be the same as the direction during scanning unless(l)it can be showa that the change in scanning direction

3. NEAR-SURFACE EXAMINATION AND SURFACE does not make a difference in the sensitivity and vibration RESOLUTION background noise received from the search unit or(2) these differences are taken into account by a correction factor.

The capability to effectively detect defects near the front and back surfaces of the actual component should be

c. For mechanized scanning, signals should not be estimated. The results shodd be reported with the report of maximized during the establishment of the DAC curve.

abnormal degradation of reactor pressure boundary in accordance with the recommendation of regulatory posi-

d. One of the following alternative guidelines sliould be tion 2.a(3) of Regulatory Gide 1.16. In determining this followsd for establishing the DAC curve:

capability, the effect of the fellowing facters should also be considered:

(1) The DAC curve should be established using a moving transducer mounted on the mechanism that will be

a. If an electronic gate is used, the time of start and stop of the control points of the electronic gate should be used for examination of the component.

related to the volume of mate-ial near each surface that is (2) Correction factors between dynamic and static not being examined.

response should be established using full-scale mockups.

b. The decay time, in terms of metal path distance, of

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(3) Correction factors should be established using the initial pulse and of the pulse reflections at the front and models and taking scaling factors into consideration (assumed back surface should be considered.

5 j

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scaling relationship should be verified).

c. The disturbance created by the clad-weld-metal (4) Correction factors between dynamic and static interface with the parent metal at the front or the back response should be established from the indications that are surface should be related to the volume of material near the found durmg examination for sizing. For detection of flaws interface that is not being examined.

during the initial scan, correction factors may be assumed based on engineering judgment. If assumed correction

d. The disturbance created by front and back metal factors are used for detection, these factors should later be surface roughness should be reiated to the volume of confirmed on indications from flaws in the vessel during the material near each surface that is not being examined.

examination. Deviation from the assumed value may

4. BEAM PROFILE suggest reexamining the data.

The beam profile should be determined if any recordable 2.3 Calibration Checks flaws are detected. This should be done for each search unit if an EBS is used for calibration check, the following used during the examination by a procedure similar to that

(.utlined in the nonmandatory Appendix B(B-60), Article 4, should apply:

Section V of the ASME Code,1980 edition, for determining

a. The significant DAC percentage level used for the beam spread. Beam profile curves should be determined for detection and sizing of indications should be reduced to each of the holes in the basic calibration block. Interpola-take into account the maximum error that could be introduced tion may be used to obtain beam profile correction for assess-in the system by the variation of resistance or leakage in ing flaws at intermediate depths for which the beam profile the connectors or other causes.

has not been determinet

b. Calibration checks should be performed on the

5. SCANNING WELD-METAL INTERFACE complete connected system (e.g., transducer and cables should not be checked separately).

The beam angles used to scan welds should be based on

[h the geometry of the weld / parent-metal interface. At least

(

)

c. Measures should be taken to ensure that the different one of these angles should be such that the beam is almost variables such as temperature, vibration, and shoci. limits perpendicular (tl5 degrees to the perpendicular) to the for which the EBS error band is determined are not exceeded weld / parent-metal interface unless it can be demonstrated during t'ransport. use, storage, etc.

that unfavorably oriented planar flaws can be detected by 1.150-7 I

)

the UT technique being used. Otherwise, use of alternative the site for examination by the NRC staff. If the size of volumetric NDE techniques, as permitted by the ASSIE aa indication, as determined in regulatory positions 6.1 or Code, shouM be considered. Alternative NDE techniques 6.2, equals or exceeds the allowable hmits of Section XI of may be considered to include high-intensity radiography or the ASN!E Code, the indications should be reported as tandem-probe ultrasonic examination of the weld-metal abnormal degradation of reactor pressure boundary in interface, accordance with the recommendation of regulatory posi-tion 2.a(3) of Regulatory Guide 1.16.

6. SIZING Along with the report of ultrasonic examination test Indications f:cm geometric sources need not be recorded.

results, the following information should also be included:

6.1 Traveling Indications

a. The best estimate of the error band in siring the flaws and the basis for this estimate should be given.

Indicat;ons that travel on the horizontal baseline of the scope for a distance greater than indications from the

b. The best estimate of the portion of the volume calibration holes (at 20 percent DAC amplitude) should be required to be examined by the ASNIF Code that has not recorded. Indications that travel should be recorded and beer, effective!y examined such as volumes of material near sized at 20 percent DAC. Where the indication is sized at each surface because of near-field or other effects, volumes 20 percent DAC, this size may be corrected by subtracting near interfaces between cladding and parent metal, volumes for the beam width in the through-thickness direction shadowed by laminar material defr:ts, volumes shadowed obtained from the calibration hole (between 20 percent by part geometry, volumes inaccessible to the transducer, DAC points) that is at a depth similar to the flaw depth. If volumes affected by electronic gating, and volumes near the the indication exceeds 50 percent DAC, the size should be surface opposite the transducer.8 0 recorded by measuring the distance between 50 percent D AC levels without using the beam-width corre-tion. The

c. The material volume that has not been effectively determined size should be the larger of the two.

examined by the use of the above procedures may be examined by alternative effective volumetric NDE techniques.

6.2 Nontraveling Indications if one of these alternative NDE techniques is a variation of UT, recommendations of regulatory positions I and 3 Nontraveling indications above 20 percent DAC level should apply. A description of the techniques used should l

i that persist for a scanning distance of more than I inch plus be included in the report. If other volumetric techniques or l

the beam spread between 20 percent DAC points (as variations of UT are used as indicated in regulatory pow defined by nonmandatory Appendix B, Article 4 Section V tion 5, the effectiveness af these techniques shouhl be l

of the ASME Code, 19 '7 edition) should be considered demonstrated and the procedures reporteJ for review by significant. The size of these flaws should be determined by the NRC staff.

measuring the distance between points at 50 percent DAC and between points at 20 percent DAC where the t'eam-D. IMPLEMENTATION width correction is made only for the 20 percent DAC size.

The recorded size of the flaw would be the larger of the Except in those cases in which an applicant proposes an two determinations. If it can be adequately demonstrated acceptable alternative method for complying with specified that a nontraveling indication is from a geometric source portions of the Commission's regulations, the method (and not a flaw), there is no need to record that indication.

described herein will be used in the evaluation of (1) the results ofinservice examination programs of all operating The following information should also be recorded for reactors after July 15,1981, and(2)the resultsof preserviec indications that are reportable according to this regulatory examination programs of all reactors under construction position:

performed after January 15,1982.

a. Indications should be recorded at scan intervals no The recommendations of this guide are not intended to greater than one-fourth inch.

apply to preservice examinations that have already been completed.

b. The recorded information should include the indica-tion travel (metal path length) and the transducer position The NRC staff intends to recommend that all licensees for 10 percent, 20 percent, 50 percent, and 100 percent modify their technical specifications to make them consistent DAC and the maximum amplitude of the signal.

with the recommendations contained herein.

7. REPORTING OF RESULTS

'O Records obtained while followmg the recommendations lt should be noted th the licensee is required to apply for relief from impractical ASMECode requirements according to 6 50.5sa of of regulatory positions 1.2, 3, 5' and 6, along with discus-10 CFR. If the licensee is committed to examine a weld as per the sions and explanations, if any, should be kept available at inspection plan m the plant SAR, the licensee is required to file an amendment when the commitments made in the SAR cannot he met.

1 l

1.150-8

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