ML20101N172

Preservice/Inservice Insp,Solution Heat Treated Corrosion Resistant Cladded Recirculating Piping, Progress Rept

ML20101N172
Person / Time
Site:	Hope Creek
Issue date:	12/18/1984
From:	Public Service Enterprise Group
To:
Shared Package
ML20101N164	List: ML20101N172
References
NUDOCS 8501030381
Download: ML20101N172 (20)

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4 Enclosure 3 9

PRESENTATION TO THE NUCLEAR REGULATORY COMMISSION MATERIALS ENGINEERING BRANCH PROGRESS REPORT HOPE CREEK UNIT 1 PRESERVICE/ INSERVICE INSPECTION SOLUTION HEAT TREATED CORROSION RESISTANT CLADDED RECIRCULATING PIPING B501030301 841218

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o Figure 1 PRESENTATION OBJECTIVES 1., Steps taken to mitigate IGSCC.

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2. Review of NDE considerations.

3.- Present the proposed ultrasonic technique.

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a 4. Demonstration of the technique.

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Steps Taken to Minimize IGSCC 4

Replacement and redesign of RPV safe-ends Minimize number of stagnant lines Application of CRC d

Solution Heat Treatment of shope welds i

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1. Steps Taken to Mitigate IGSCC In accordance with NUREG-0313, measures were taken to ~

mitigate intergranular stress corrosion cracking (IGSCC) of austenitic stainless steel piping.

The RPV nozzle safe-ends and extensions were replaced with corrosion resistant material and redesigned to eliminate crevices.

To minimize the number of stagnant lines, the recirculation system bypass lines and control rod drive return line were eliminated. Also, the stainless steel system piping in the core spray system and the residual ,

heat removal system was replaced with impact tested carbon steel.

• Corrosion resistant cladding (CRC) was applied to field weld connections of the Type 304 stainless steel recirculation system piping, and all shop welds were o.. solution heat treated before installation.

, By applying CRC and combining it with solution heat treatment of the weld joint-area, we have eliminated areas'around the weld joint where-IGSCC could form (see Figure 3).

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2. Review of NDE Considerations The application of CRC on the pipe ID and cladding on the OD presented problems with performing acceptable volumetric examinations when using standard ultrasonic techniques.

Working with EPRI and SWRI, the PSI /ISI inspection agency at Hope Creek, the development of an acceptable ultrasonic examination program was undertaken.

The inspectability by ultrasonic examination was considered in the CRC joint design at Hope Creek. The OD cladding is flush with the base material and the thickness has been kept to a minimum (Figure 3). This configuration is in contrast with cladded overlay (Belly Bands) being used as temporary fixes at some operating BWRs. The thickness of these belly bands is usually equal to the wall thickness of the base -

naterial making acceptable ultrasonic examinations very difficult.

We have been hampered in the qualification of the new techniques becausE a CRC test block with IGSCC has been unavailab'.e. Currently, the procedure has been demonstrated on a combination of test blocks. One is the Hope Creek

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calibration block that has CRC and a test block containing IGSCC obtained from EPRI and fabricated by IHI. The portion of this presentation given by SWRI wilU elaborate on this further.

Radiography was also considered in satisfying the volumetric examination' requirements on the Reactor Recirculation System piping. A field survey was conducted by J. A. Jones Applied Research Services Company to determine if the MINAC could be i

used for this purpose. The results of this survey indicated accessibility problems for the MINAC equipment, the MINAC technique would not be appropriate for certain thin wall and smaller diameter welds, and when in use the MINAC would restrict other work from going on inside the drywell. These disadvantages c.learly indicated radiography should not be used as the primary method for volumetric ~ examination and should only be considered to augment ultrasonic examination when necessary.

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PROCEIURE DEVELOPMENT POR ULTRASONIC EIAMINATION l OF CORROSION EL3ISTANT CLAD STAINLESS STEEL PIPING Intergranular Stress Corrosion Cracking (ICSCC) in nuclear power

. plant stainless steel piping has prompted the industry to develop measures to mitigate such problems. At the Hope Creek Generating Station- Corrosion Resistant Cladding (CRC) has been implemented for selected field welded circumferential butt velds. Due to deformation 4

of the material during the CRC process, outside surface cladding has also been deposited on the base material near the butt veld where CRC is used. It is the cladding layers which present problems when ettempting to perform a UT examination using standard shear-wave L techniques. These interfaces (the outside diameter overlay to the i base material and the base material to inside diameter clad

interface) tend to disperse and redirect the shear wave ultrasound signals which ultistately must be interpreted by the UT examiner. The problem of multiple reflectors and their interpretation is combined with the severe attenuation of ultrasonic shear / waves which further decrease the effectiveness of UT examination. Although radiography is considered an alternate method to satisfy the volumetric l requirements, the time, cost, and access considerations are not r

conducive to satisfying the volmetric examination requirement. The I

ultrasonic examination (UT) method has been selected by PSEM; to meet the Code requirement and extensive work hae hcen performed in i

development of a UT technique for examination of CRC piping. There

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were two basic ways to approach this problem.. One was to accept the i

. l low quality signals provided by conventional UT and work on )

high-level signal analysis / interpretation techniques using sophisticated equipment. The other was to try to enhanse the quality of the UT signal by optimizing the search unit design for the l

specific acoustic properties of the application. Our ultimate choice was to research the accoustic properties of the mock-up and develop J

UT transducers chat would provide a higher quality signal. What follows in this presentation is a summary of the research and davelopment that has been carried oct in an effort to develop a field applicable technique for the UT examination of stainless steel piping with CRC cladding and overlays.

4 SvRI performed its initial work in the development ' a technique for examination of CRC on a Susquehanna Nuclear Pcwer Plant reactor recirculation riser weld mockup in 1979. As detailed in the attached table, reflectors appeared to be from not only the known reflectors, but also from the clad interfaces. This presentation was considered unacceptable as geometric reflectors could be misinterpreted as flaws and, conversely, flaws could be interpreted as uoise or non-relevant indications. Based on this study, Sw11 concluded that with the use of conventional UT equipment, transducers and procedures, the resulting examinations were not acceptable. SwRI recommended RT as a more appropriate volumetric method where CRC had been applied.

In December,1983, SvRI performed an evaluation for inspectability of a CRC mockup provided by Public Service Electric & Gas Company ,

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(PSE&G). This mockup simulated the reactor recirculation 12-inch riser piping with the CRC condition. The evaluation was performed initially to determine whether SwtI'd conventional stainless steel l weld examination procedure, using the shear mode, provided an acceptabule screen presentation for examination. The results were similar to that of the study on the Susg*2ehanna recirculation mock

-up. All transducer and technique development since this time has been centered upon the mock-up. It van also agreed to expand the 1/3T examination volume to the extent required for coverage of the inside surface cladding.

More recently, at the request of PSE&G to develop a procedure for the examination of CRC, SwRI readdressed techniques for UT examination.

SvRI had concluded that the use of the shear mode was impractical due

. to previously mentioned problems and the angle changes encountered at the CRC interfaces. SwRI attempted to implement a single transducer,

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45-degree refracted longitudinal angle to satisfy the Code-required examination. The single element was selected to eliminate the need for various transducer wedge omnbinations which would be encountered with dual convergent been transducers. Such dual transducers are usable only on given thicknesses compatible with the transducer wedge ,

design. The single element transducer and wedge combination was found to be unac:eptable due to the continuing difficulties with the screen presentation and signal to noise ratio. Reflectors :ould be identified, however, the signal to noise ratio at scanning r

sensitivity resulting from CRC interface reflections remained a j i

confusing factor. This technique allowed the detection of Code )

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reflectors only with additional examiner training and the examiner confidence level was low.

In an effort to further refine the screen presentation, obtain better signal to noise ratios and maximize examiner confidence in the interpretation of signals, a dual transducer wedge combination was implemented. The wedges used were fabricated to produce pitch / catch 45-degree refracted longitudinal waves. These wore combined with off-the-shelf 1.5 MHz transducers. The wedge / transducer combination were designed to provide the 45-degree refracted longitudinal wave with a convergent crces-over depth at the approximate thickness of the 12-inch recirculation mockup. This combination provided a screen presentation with the signal to noise ratio enhanced over previous CRC examination techniques. There still remained, however, reflections from the clad interfaces which could be confused with readily identifiable relevant indications.

Recognizing the dual 45 refracted longitudinal wave technique as being most suitable for CRC examination, one further step has been taken to optimize techniques for the examination of CRC. This optimisation was the design of a unique transducer assembly for the i

given thicknesses of material being examined. The end result is a combination transducer / technique and procedure providing optimum examination of CRC piping.

This transducer-is a special pitch catch unit designed to alleviate I the particular accoustic problems presented by the UT examination of j r

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4 CRC. It is capable of providing a screen presentation without large amounts of interface interference. The signal to noise ratio has been greatly enhanced, thus, maximizing the examiner confidence in the procedure.It has been qualified on Code Reflectors in the Hope Creek CRC mock-up and has shown a minimal 3dB decrease in response between clad and unclad areas of the mock-up.

In comparison, it has yielded equivalent results to the SLIC-40 which will be used in conjunction with this technique for evaluation of indications.

What follows today is the presentation by Mr. Ed Ruescher of SwRI, demonstrating this technique.

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1 HOPE G EEK PRO DURE DEVELOPENT UT Instriment Transducers Frenumncv Sngla Size fin.) Ranarkn Sonic Mark I 2.5 mz 45R. (New Design) Dual Element (One Piece)

SUMARY 45R. provides a specific focal depth of .58" providing optimum response f ran ID notches in material .653" thick. The screen presentation is distinct and essentially free of misinterpretable signal s.

CDNCLUSION Technique / procedure (800-100/0) meets Code requirements, require limited special training.

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SUSluEHANNA RECIRC RISER WELD K)CK-UP UT Instrianent Transducers Freauencv Anale Size (In. ) Renarks USIPII Krautkramer 2.25 Miz 45R. 1/2 x 1/2 Single Element Sonic Mark I 1 Miz 45S 1/2 Single Element Sonic Mark I 1 Miz 45S 1/2 Single Element SlPMARY

. Reflectors appeared at the clad interface - could be misinterpreted as IGSCC and, conversely, IGSCC could be interpreted as noise.

GNC1.USION Techniques are - questionable - RT recommended.

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HOPE CREEK MCK-UP EV ALUATIONS 1

l UT Instrument Transdumrs Fran uenev, Anglg Size (In. ) Remarks 1 Sonic Mark I 1.5 Miz 45S 3/8 Single Element Sonic Mark I 1.5 Miz 60S 3/8 Single Element SU M Y Reflectors appeared at the clad interfaces - could be misinterpreted as IGSCC and, conversely, IGSCC could be interpreted as noise. _

Evaluated to 600-31 Procedure.

UT Instriment Transducers Fran uancv Angl.g Size (In. ) Remarks Sonic Mark I Unknown 45R. Unknown Single Element SU N Y 45R. was performed but found to be a problem in that the shear mode appeared on tne screen, complicating interpretations.

CDNCLUSION Technique is questionable.

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HOPE MEEK PRO &DLlRE DEVELOPENT UT Instrument Transducers Freauency Angig Size (In.) Remarks Sonic Mark I 2.5 Miz 45R. Single Element SLlW4ARY 45R. was used in the development of the procedure. The signal-to-noise ratto fran the interface was confusing to the untrained examiner but could be used when complemented with training.

CDNO.USION Technique / procedure (800-36/0) meets Code requirments; however, requires trained individual to imp 1 ment.

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I HOPE GEEK PRO DURE REFINEENT UT Instrtment Transducers Fren uencv Angl3 Sfra (In.) Ramarks Sonic Mark I 1.5 Wz 45R. Dual Element (Conven- (Repl aceable tional) Shoes) 3dG4ARY 45R. P/C was used to refine and improve the screen presentation for signal more closely resembling conventional presentations; however, there restain reflections f ran the clad interf aces, thus not providing readily identifiable relevant reflections.

CDNQ.USION Technique / procedure (800-90/0) meets Code requirements; however, requires training for sir,nal interpretation.

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'insida surfcce chile maintaining adequato ocasitivity of th2 crecin:tica

volume as required by the Code as shown in Figure 3.

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!' To provide a comparison of sensitivity, the refracted longitudinal l

technique was campared to the refracted shear wave technique which as been i qualified and proven to be capable of reliable detection of IGSCC in unclad pipe. This comparison showed that the refracted inngitudinal technique was essentially equivalent for IGSCC detection in non CRC pipe.

Amplitude comparison of the notch in the clad and unclad portions of the CRC mock-up showed no discernable amplitude difference, therefore, it is felt that the technique developed by SwRI will be effective in the detection of IGSCC in the 12" diameter CkC piping at Hope Creek. This technique will be tested on mock-ups of other diameters and thicknesses of CRC piping to determine its acceptability for other applications.

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DEVELOPMENT OF ULTRASONIC TECHNIQUE FOR HOPE GEEK 12" CRC PIPING Southwest Research Institute's (SvRI) primary emphasis has been to develop a technique that was field usable, reliable and would require a minimum of instruction for the average technicians. In other words, keep it as simple as possible. J The development effort included the review of available data (including EPRI Research Program T101-5) which pointed cut the unreliability of shear '

wave examination through overlaid material. Accirding to literature and emperical testing, shear waves as an inspection medium through overlay cre not reliable due to the redirection, scattering (attenuation) and spurrous

reflections caused by the large grain and dendritic structure of stainless '

a steel weld overlay material. This literature review also indicated that longitudinal wave examination techniques showed promise as longitudinal waves are not as readily affected by the grain structure.

The use of refracted longitudinal wave techniques are not without problems in that there is a simultaneously amount of shear wave to be contended with. In addition there is a significant amount of longitudinal-to-shear energy conversion at a reflective interface. As shown by Figure 1, a significant percentage of longitudinal wave energy is converted to shear wave energy at the angles typically used for examination. This results in, the need for additional gain to compensate for this energy loss. This is not the case with shear waves. As shown by Figure 2, there is total shear l wave reflection at the angles typically used for examination.

t As previously stated by Mr. Richter, various refracted longitudinal wave techniques were evaluated, including the SwtI Slic 40 module. The Slic 40 module performed well when scanning was done in the axial direction.

However, when_ scanning in the circumferential direction, the long contact surface of the Slic 40 presented difficulty in maintaining adequate ultrasonic coupling to the pipe. The use of the Slic 40 for circumferential scanning would require extreme care and would result in significant additional time for scanning to maintain the proper angles in the material. Dr. Gruber compared the performance of the Slic 40 to that of the dual refracted longitudinal technique ultimately developed. Dr.

Gruber found that the performance of the dual refracted longitudinal technique was equal to the Slic 40 performance. Thetechniqueult[mately developed relies on special pitch catch 45 degree refracted longitrdinal search units developed by SwRI.

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It is still intended that the Slic 40 vill be used as a supplementary i examination technique to further evaluate any guestionable ultrasonic

[ reflectors. These search units utilize transducers that have been l designed fer the intended use and contain accoustical matching plates to minimize insertion losses as well as an electronic impedance and frequency matching network to optimize performance. The roof angle of the -

j- transducers is carefully controlled to provide optimum sensitivity at the r

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The progress made with the new transducers developed by SWRI and the demonstration of the technique on cup ently available n i(

l 1 test blocks, gives us';cenfidence that we will be succetsful in developing an approved technique.

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Our plans are to ' continue development by obtaining addi'ttonal 4 test blocks that,have IGSCC coupled with cladd overlay and will work on the development of a CRC test block with indications rep'esentative r of IGSCC. Our goal is to qualify

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'h the new technique 6o the intent of NRC Bulletin 83-02 and

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t will continue to keep the NRC staff informed of our progress.

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In addition to this program, PSE&G, as a member of the BWR owners group, will continue c' monitor the development of other new techniques.  !

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