AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.1Presentation title

– Presenter/ref. - 04 August 2011 - p.1

Phased Array and Nonlinear Resonance Testing of Reactor Internals Bolts

Presenter:Dr. Jeremy RenshawAREVA NDE-Solutions

R&D Project Leader / Engineer IVBlacksburg, VA 6/21/2011

For External Use

By:

J. Renshaw A. Bleuze

B. Thigpen O. Burat S.W. Glass

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.3

Background

With the advent of the Materials Reliability Program (MRP 227/228), inspecting nuclear reactor internals has become a primary focusThe events at Fukushima have placed increased scrutiny on nuclear reactors worldwide

For more information, go to www.nei.org

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.4

Introduction

One primary component set to be inspected is bolting

Most bolts can be easily inspected via conventional UT

Some bolt geometries are difficult to inspect with UT

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.5

Phased Array Testing

Phased array UT was evaluated firstPhased array has many advantages over conventional UT

Beam steering

Numerous focal laws

Real time imaging

Phased array was only able to find defects in the head to shank region

Varying (uncontrolled) bolt geometries were to blame

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.6

Influential Geometry variables

Several uncontrolled geometrical variables were problematic

Variable angle of bottom of hex

Variable depth of hex head

Presence/absence of drilling in hex head

Depth of drilling in hex head

Angle Depth of Internal Hex

Drill Bit Depth

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.7

Subsequent Testing

Due to the failure of UT and Phased array, alternative techniques were evaluated

Guided Waves

Nonlinear Wave Modulation Spectroscopy (NWMS)

Nonlinear Resonant Ultrasound Spectroscopy (NRUS)

Nonlinear Resonance Testing (NRT)

Other

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.8

TheoryAll structures have natural resonances

These resonances can be represented in the frequency domain via a (temporal or spatial) Fourier transform

Frequency, Hz

Fourier Transform

Time, s

Am

plitu

de

Am

plitu

de

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.9

TheoryThe presence of a crack

changes a structure

Crack

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.10

When vibrated, crack faces hammer together

Hammering generates additional (nonlinear) vibrations in the structure

Imagine thousands of tiny hammers ( ) hitting together as the crack opens and closes

Theory

Crack

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.11

TheoryHammering actions generate additional resonances

+With CrackCrack

No Crack

Single resonance (or set of resonances)

Original plus additional

resonances

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.12

Uses a high freq. probing signal and low freq. pump signal. Cracked samples generate sidebands, uncracked

samples do not.

NWMS (Nonlinear Wave Modulation

Spectroscopy)

With CrackCrack

No Crack

Defect Defect SignalSignal

Frequency, Hz

Am

plitu

de

Frequency, Hz

Am

plitu

de

High Frequency Signal

Low Frequency Signal

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.13

Resonances are easily observed in the frequency domain, especially for complex waveforms

NRUS (Nonlinear Resonant Ultrasound

Spectroscopy)

With CrackCrack

No Crack

Higher Higher ΔΔf f

Defect presentDefect present

Frequency, Hz

Am

plitu

de

Frequency, Hz

Am

plitu

de

Less Δf No defect

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.14

Resonances are easily observed in the frequency domain, especially for complex waveforms

NRT (Nonlinear Resonant Testing)

With CrackCrack

No Crack

Defect Defect SignalSignal

Frequency, Hz

Am

plitu

de

Frequency, Hz

Am

plitu

de

Band of Observed Frequencies

Excited Frequencies

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.15

TheoryLoose bolts can be distinguished by their lack of resonances, or the presence of only noise in the frequency signal.

Loose Bolt

Tight Bolt

Loose Loose BoltBolt

Frequency, Hz

Am

plitu

de

Frequency, Hz

Am

plitu

de

Band of Observed Frequencies

Excited Frequencies

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.16

Good Bolt

Bolt 15-3, bolt holder, 1-5 kHz, 32 dB (max amplitude), note very small peaks at 6.6, 9.4, and 10.6 kHz.

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.17

Cracked Bolt (28% CSA)

20-11, bolt holder, 1-5 kHz, max 32 dB gain, note large peaks at 6.9 and 10.2 kHz.

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.18

Loose Bolt

Bolt 35-13 LOOSE, bolt holder, 1-5 kHz, 32 dB gain, note that the high noise, no structure in the excited spectrum, and a high peak at 10 kHz.

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.19

Preliminary results showed excellent defect detection capability

(11

out o

f 11)

(8 o

ut o

f 8)

(7 o

ut o

f 8)

(0 o

ut o

f 3)

The one false call appeared to be a result of a poorly executed test

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.20

Cracked Bolt (28% CSA) Load vs. No Load

20-11 comparison, 1-5 kHz, max 32 dB gain.

20-11 in Bolt Holder Mockup, in air, no tensile load

20-11 in Bolt Holder Mockup, in air with tensile load

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.21

Tensile loads mask the presence of defects

Cracked Bolt, in air, no tensile load

Cracked Bolt, in air, with tensile load

Good Bolt, in air, with tensile load

Good Bolt, in air, loose

No difference

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.22

Basic Physics of NRT Technique

Crack

1. Crack faces in contact 1. Crack faces not in contact

2. Crack faces hammer together, generating nonlinear resonances

2. Crack faces don’t hammer together; no nonlinear resonances

Frequency, Hz

Am

plitu

de

Frequency, Hz

Am

plitu

de

Defect Defect SignalSignal

No Defect No Defect SignalSignal

Result: NRT finds a closed crack Result: NRT misses an open crack

A –

Crack under low tensile stress B –

Crack under high tensile stress

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.23

Tensile Stresses in Reactor Internals Bolts

Reactor Internals Bolts have high torques, ~109 Nm (80 ft-lbs)According to Shigley’s

Machine Design, we can use the following equation to calculate the pre-load in these bolts

F = Force (bolt pre-load), N

T = Bolt Torque, Nm

d = Bolt Diameter, m

This leads to a relationship between Torque and tensile stress

This gives a static tensile stress of 318 MPa

in the baffle bolts, at or near the yield stress of stainless steel (300-450 MPa)

dTF 5

32

2054dT

dT

dAF

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.24

Conclusions

For this application

Phased Array testing did not work

Nonlinear methods did not work

The potential exists to use nonlinear methods for alternate applicationsThe end of the story: AREVA has developed a solution for this problem which has been successfully deployed, but cannot disclose these details until the appropriate IP is in place

AREVA NDE-Solutions

Limited distribution to AREVAPhased array and nonlinear resonant testing of reactor internals bolts – J. Renshaw -04 August 2011 - p.25

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