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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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