nrc peening validation program · the nrc presentation states, ... aircraft landing gear, shot...

© 2016 Electric Power Research Institute, Inc. All rights reserved.

Paul Crooker (EPRI), Glenn White (DEI)

NRC Offices, RockvilleFebruary 28, 2017

NRC Peening Validation ProgramMRP Comments and

Questions

2© 2017 Electric Power Research Institute, Inc. All rights reserved.

Summary

Questions and comments on NRC peening validation program as described in NRC slides for the February 28, 2017, public meeting are organized by area discussed in the NRC presentation Validation Program

– X-Ray Diffraction Uncertainty [NRC Slides 3-4]– Stress Measurement Locations [5-7]– Non-Destructive Examination (DMWs) [8-9]– PWSCC Initiation [10-12]Optional Validation Work

– Optional Crack Arrest Program [16-18]– Optional WRS Measurement Validation [19-20]– Optional Validation Plan for CRDM Nozzles [21-22]– Optional CRDM NDE Validation Plan [23]


X-Ray Diffraction (XRD) Uncertainty The NRC presentation states, “X-ray diffraction reported to have high uncertainty,

especially on welds”– Please provide a reference– Section 2.3.6 of MRP-335 R3-A provides references for effective use of XRD for stress

measurements, including of welds Validation of XRD residual stress measurement uncertainty is specific to

measurement procedure and equipment– Will this validation be performed specific to a measurement procedure and equipment?– Different XRD measurement vendors may use different procedures and equipment

What approach/comparisons does NRC plan to assess the XRD stress measurement accuracy? Peening and XRD stress measurements vendors are in the best position to

provide data to NRC validating stress measurement uncertainty. If NRC proceeds with these XRD stress measurements, MRP suggests

consideration be given to measurements on annealed and actively loaded specimens. Through active loading a known stress could be applied to the specimen surface.


Stress Measurement Locations The pre-peening residual stress state is not important to qualification of the

peening process to prevent PWSCC initiation– The peening effect is self-normalizing (Section 3.3.3 of MRP-335 R3-A) The peening effect is enhanced for areas with relatively high tensile initial residual

stress state MRP does not understand the value of investigating the stress on un-peened

CRDM nozzles at areas identified by finite-element analysis to have high tensile weld residual stress Results of past studies measuring weld residual stress in CRDM nozzles and

associated welds are available in:– Pages 7-24 through 7-31 of PWSCC of Alloy 600 Materials in PWR Primary System

Penetrations, EPRI, Palo Alto, CA: 1994. TR-103696. [Freely Available at www.epri.com]

– J. Katsuyama, M. Udagawa, H. Nishikawa, M. Nakamura, and K. Onizawa, “Evaluation of weld residual stress near the cladding and J-weld in reactor pressure vessel head for the assessment of PWSCC behavior,” E-Journal of Advanced Maintenance, v. 2, pp. 50-64, 2010.


Non-Destructive Examination (DMWs)EPRI (3002008359) and peening vendors have performed tests

showing that UT and ET qualified for use on unmitigated DMWs are reliable for use on peened DMWsMRP and vendor testing have demonstrated that peening does

not adversely affect the component surface condition with regard to inspectabilityThe rigidity of the peened specimen should be representative of

the actual plant component so that the level of deformation upon peening is relevant to the plant application– The rigidity depends on the specimen thickness and geometryFlaw sizes should be relevant to the type of NDE performed

– For example, flaws at least 10% through-wall in the case of ultrasonic testing


PWSCC Initiation (1/3) As documented in MRP-267 R1 and R2, the effectiveness of peening to mitigate

PWSCC initiation has already been demonstrated through SCC testing, including testing in PWR primary water and independent testing sponsored by EPRI supplementing testing performed by the peening vendors Peening also has a long history of effectiveness in mitigating stress corrosion

cracking– “Improving Resistance to Stress Corrosion” under “Shot Peening” in 1982 and 1994 Editions of

Volume 5 of ASM Handbook– Examples cited in MRP-267 R1 and R2 including elimination of SCC in 300M steel used for

aircraft landing gear, shot peening of Alloy 600 PWR steam generator tubes, and shot peening of Alloy 600 pressurizer heater sheaths

What will be the uncertainty in the +10 ksi tensile stress at the test surface under operating conditions, including the possibility of changes over time during the test?– In this experimental approach, the stress must be precisely controlled to ensure that the actual

stress does not exceed +10 ksi The specimen yield strength is a relevant parameter as it affects the stress ratio

(applied tensile stress divided by yield strength)


PWSCC Initiation (2/3)What is the thickness of the planned 4-point bend bar specimen?

– It appears that the specimen may not be sufficiently thick to retain the stress effect that would be retained for thicker and more rigid plant components considering a nominal 1-millimeter depth of compression

– Appendix C of MRP-335 R3-A presents results illustrating the effect of component thickness and geometry on the level of retained compression (surface stress magnitude and depth of compression) for a given peening intensity

How long will specimens be tested to obtain the relevant factors of improvement (if no initiation in peened specimens)?Will the weld specimens be checked for pre-existing flaws not

representative of inspected plant components?Why is the 4-point bend bar specimen labeled as “crack arrest

specimen” on Slide 12? MRP-335 R3-A does not credit any benefit for peening to arrest flaws


PWSCC Initiation (3/3)

Has NRC considered the “massive-bend” specimen design?– Pages A-115 and A-116 of MRP-267 R2 (EPRI 3002008083) describe this

specimen type, which results in massive mechanical behavior Is the material to be cold worked before being peened? What is the

planned cold work level and the basis for this choice?Who will perform and control the peening, and will the peening be

representative of the peening now being performed in PWRs?How will the initiation testing system be commissioned, calibrated,

and monitored to ensure loads are within expected limits and to quantify load transients?


Optional Crack Arrest Program (1/2)

MRP is unclear regarding the objective of this optional scope as MRP-335 R3-A does not credit any benefit for peening to arrest flaws Is the concern for relatively fast or relatively slow crack growth?

– Fast: cracks become more readily detectable at a sooner time, but will also grow through-wall more quickly

– Slow: cracks take longer to become reliably detectable, but also require a longer time to grow through-wall

– The crack growth rate varies by material heat and weld Testing in MRP-267 R1/R2 and analysis in MRP-335 R3-A show that

flaws extending a modest distance beyond the zone of compression grow at rates close to that for the un-peened situation


Optional Crack Arrest Program (2/2)

The thickness of the specimen affects the level of retained compressive stress (surface magnitude and depth) and the through-wall distribution of balancing residual tensile stress– The specimen thickness should be sufficient to result in a through-wall stress

profile representative of the plant componentHow will pre-peening weld residual stress and operational loads be

handled?


Optional WRS Measurement Validation

Section 2.3.6 of MRP-335 R3 lists methods that are generally applied for measuring residual stress– As stated in Section 2.3.6, XRD has commonly been applied for peening

qualification work– Relatively few methods, including XRD, are expected to be applied in peening

qualification workWhat is the specific NRC concern regarding the need for an in-situ

exam method to assure peening coverage?– Existing processes, equipment, controls, and verifications already provide high

confidence of full peening coverage– In some cases, there are visual changes to the surface in the peened area– What level of volumetric and visual inspection relief is not being credited for

cold leg temperature components due to this concern?


Optional Validation Plan for CRDM Nozzles

What peening method will be applied, and how will the critical peening parameters be determined?– The critical peening parameters are determined based on those

parameter values that result in a stress effect meeting the performance criteria for representative geometries and materials

What is the effect of the concern raised on the slide titled “Draft Initial Pre-Peened Weld Residual Stress Results”?– Where was measurement #1 made?– The pre-peening residual stress state is not important to

qualification of the peening process to prevent PWSCC initiation


Optional CRDM NDE Validation Plan In the case of peening mitigation, the initial flaw size of the

deterministic flaw evaluations is not based on the minimum flaw size that is detectable 10 CFR 50.55a(g)(6)(ii)(D)(4) and the MRP-335 R3-A performance

criteria (4.3.8.3 and 4.3.8.5) require that the ultrasonic testing be qualified and that the capability to perform ultrasonic exams of the relevant volume of the component not be adversely affected by the peening– These requirements are satisfied on a basis specific to the peening and

inspection vendorsPlant owners find eddy current surface examinations of J-groove

welds to be impractical considering the potential for false calls, detection of acceptable fabrication flaws, and high radiation worker dose associated with supplemental penetrant testing exams to characterize eddy current indications


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