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Acoustic Emission Testing Method

Questions & Answers Book Second Edition Supplement to Recommended Practice No. SNT-TC-1A Book G Levels I, II and Ill Review Questions

The American Society for Nondestructive Testing, Inc.

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Published by The American Society for Nondestructive Testing, Inc. 1711 Arlingate Lane PO Box 28518 Columbus, OH 43228-0518

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No part of this book may be reproduced or transmitted in any form, by means electronic or mechanical including photocopying, recording, or otherwise, without the expressed prior written permission of the publisher. Copyright© 2008 by The American Society for Nondestructive Testing, Inc. ASNT is not responsible for the authenticity or accuracy of information herein. Products or services that are advertised or mentioned do not carry the endorsement or recommendation of ASNT. IRRSP, NOT Handbook, The NOT Technician and www.asnt.org are trademarks of The American Society for Nondestructive Testing, Inc. ACCP, ASNT, Level Ill Study Guide, Materials Evaluation, Nondestructive Testing Handbook, Research in Nondestructive Evaluation and RNDE and are registered trademarks of The American Society for Nondestructive Testing, Inc. ASNT Mission Statement: ASNT exists to create a safer world by promoting the profession and technologies of nondestructive testing. ISBN-13: 978-1-57117-178-8 Printed in the United States of America Second Edition 05/08 first printing

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Contents Acknowledgments

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Recommended References

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Reference Usage

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Level I Questions

1

Level II Questions

5

Level Ill Questions

13

iv

Acknowledgments

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A special thank you to Ronnie K. Miller, who coordinated this edition of the Supplement to Recommended Practice SNT-TC-1A (Q&A Book): Acoustic Emission Testing, wrote many of the new questions, and recruited the volunteers who assisted with this update. Thank you also goes to the following contributors who assisted with the writing of new questions and review of this book: Gerry Hacker Jim Mitchell Richard Nordstrom Adrian Pollock Joel Whitaker The Publications Review Committee includes: Joseph L. Mackin, Chair Stephen P. Black Gary Heath

Cynthia M. Leeman Educational Materials Supervisor

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Recommended References Acoustic Emission Testing Method The following references were used in formulating the questions contained in this book. A. B. C.* D.*

E.* F.*

G. H.

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I.

J. K. L. M. N. 0.*

ASME, ASME Boiler and Pressure Vessel Code, Section V, Article 11, "Acoustic Emission Examination of Fiber Reinforced Plastic Vessels." New York, NY: American Society for Mechanical Engineers. Latest edition. ASME, ASME Boiler and Pressure Vessel Code, Section V, Article 12, "Acoustic Emission Examination of Metallic Vessels during Pressure Testing." New York, NY: American Society for Mechanical Engineers. Latest edition. Miller, Ronnie K. and Paul Mcintire, ed. Nondestructive Testing Handbook, second edition: Volume 5, Acoustic Emission Testing. Columbus, OH: The American Society for Nondestructive Testing, Inc. (1987). Nondestructive Evaluation and Quality Control: ASM Handbook, Volume 17, ninth edition. Metals Park, OH: ASM International (1989). Recommended Practice SNT-TC-1A (2006). Columbus, OH: The American Society for Nondestructive Testing, Inc. (2006). Moore, Harry D., ed. Materials and Processes for NOT Technology. Columbus, OH: The American Society for Nondestructive Testing, Inc. (1981). ASTM E 569-07, Standard Practice for Acoustic Emission Monitoring of Structures During Controlled Stimulation. West Conshohocken, PA: ASTM International (2007). ASTM E 750-04, Standard Practice for Characterizing Acoustic Emission Instrumentation. West Conshohocken, PA: ASTM International (2007). ASTM E 976-05, Standard Guide for Determining the Reproducibility of Acoustic Emission Sensor Response. West Conshohocken, PA: ASTM International (2007) . ASTM E 1067-39, Standard Practice for Acoustic Emission Examination of Fiberglass Reinforced Plastic Resin (FRP) TanksjVessels. West Conshohocken, PA: ASTM International (2007). ASTM E 1106-07, Standard Method for Primary Calibration of Acoustic Emission Sensors. West Conshohocken, PA: ASTM International (2007). ASTM E 1139-02, Standard Practice for Continuous Monitoring of Acoustic Emission from Metal Pressure Boundaries. West Conshohocken, PA: ASTM International (2007). ASTM E 1781-98, Standard Practice for Secondary Calibration of Acoustic Emission Sensors. West Conshohocken, PA: ASTM International (2007). ASTM E 1932-97, Standard Guide for Acoustic Emission Examination of Small Parts. West Conshohocken, PA: ASTM International (2007). Miller, Ronnie K., Eric v.K. Hill and Patrick 0. Moore, ed. Nondestructive Testing Handbook, third edition: Volume 6, Acoustic Emission Testing. Columbus, OH: The American Society for Nondestructive Testing, Inc. (2005).

*Available from The American Society for Nondestructive Testing, Inc.

Each question found in this book contains letter(s) and page number(s). paragraphs or sections in bold type immediately following the answers. For example, 2.

In acoustic emission testing per ASME Section V, Article 11, sensor spacing on fiberglass-reinforced pressure (FRP) pressure vessels is governed by: a. b. c. d.

the test article temperature sensor diameter attenuation the type of couplant A.90.15

In this example, the letter "A" refers to Reference A in the list provided above, and "90.15" is the specific page in Reference A where the answer to the question can be found. References may also indicate specific chapters, paragraphs and sections, and are indicated as such.

vi

Reference Usage Acoustic Emission Testing Method Reference A: Total = Levell Level II Level ill Reference B: Total = Levell Level II 'Level Ill

7 3 0

Reference 1: Total = Levell Levell I Level Ill

3 0 1 2

5 2 3 0

Reference J: Total = Levell Level II Level ill

0 0 0 0

Reference C: Total = 19 Levell 7 Level II 9 Level ill 3

Reference K: Total = Levell Level II Level Ill

4 0 0 4

Reference D: Total = Levell Level II Level ill

0 0

Reference L: Total = 12 Levell 2 Level II 8 Level Ill 2

Reference E: Total = Levell Level II Level Ill

0 0 0 0

Reference M: Total = 2 Levell 0 Levell I 0 Levell II 2

Reference F: Total = Levell Levell I Levell II

3 0 2 1

Reference N: Total= Levell Level II Level ill

Reference G: Total= Levell Level II Level ill

6 0 6 0

Reference 0: Total = 28 Levell 12 Level II 15 Level Ill 1

Reference H: Total = Levell Level II Level ill

3 0 0 3

4

1 1

3 1 2 0

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Level I Questions Acoustic Emission Testing Method 1.

Hold periods at high loads during fiberglass-reinforced pressure (FRP) vessel examinations using ASME Article 11 are necessary to: a. b. c. d.

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6.

attenuation the test article temperature sensor diameter the type of couplant

7.

a. apply extra couplant around the sensor b. use heavy-duty fasteners on sensors and cables c. measure the peak amplitude response from a simulated acoustic emission source d. use acoustic waveguides A.90.14-15

P8

The source of the energy of the acoustic emission wave during crack growth is the: acoustic emission sensor surface energy of the new crack elastic stress field in the structure power supply from the mainframe to the preamplifier C.64 qL

qg

pg

transformation acoustic emission brittle fracture isotrophy C.12; 0.32

How can an examiner be assured that proper contact has been made between the sensor and the vessel?

a. b. c. d.

The elastic energy that is released by materials when they m;dergo deformation . is called: a. b. c. d.

A.90.15

4.

in-rushing fluid wind radio transmissions all of the above 8.179

In acoustic emission testing per ASME Section V, Article 11, sensor spacing on fiberglass-reinforced pressure (FRP) vessels is governed by: a. c. c. d.

3.

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a. b. c. d.

calculate the felicity ratio check for leaks monitor continuing damage measure the kaiser ratio A.90.16

2.

Which of the following can be a significant source of background noise?

5.

op

os

During loading, a metallic structure emits throughout the test period. When the load is reduced and then reapplied, no emissions are noted until the previous stress level was exceeded. This phenomenon is an example of: a. the dunegan corollary b. the kaiser effect c. the felicity ratio d. a hsu-nielsen source C.16; 0.37

8.

The founder of modern acoustic emission technology was: a. Conrad Earl Krieder b. Professor Firestone c. james C. Bolling d. josef Kaiser C.17; 0.37

e;;

OT

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Supplement to Recommended Practice SNT-TC-1A (Q&A Book): Acoustic Emission Testing Method

9.

The use of a couplant between the

acoustic emission sensor arld the surface of the material being tested is to provide:

13. One of the major differences in the acoustic emission NDT method compared to most other NDT methods is that:

a. protection for the sensor b. ground loop elimination c. a medium through which elastic stress waves can excite an acoustic emission sensor d. none of the above

a. acoustic emission relies on visual interpretation of data b. computers are used exclusively for analysis c. acoustic emission directly detects the growth of flaws d. transducers are used to gather data

C.39; 0.53

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C.12 10. During a pressure vessel test, there is a rapidly (exponentially) increasing count rate. There are several possible causes. The opefator's first priority is to examine the possibility that:

14. The signal amplitude (in decibels) is given as: A = 20 log 10 (V/V0 )- Gp

a. the initial system calibration was invalid b. the vessel is undergoing local yielding due to high secondary stresses c. failure of the vessel is impending d. the level of background noise has increased

where: Signal Amplitude at the preamp output, in microvolts Vo = Reference Voltage= 1.0 !J.V Gp= Preamplifier Gain = 40 dB

v

What is the signal amplitude (in decibels) of an AE signal captured at the preamplifier output on an oscilloscope and measuring 1.0 V?

8.181 11. In order for an AE system to detect an active AE source in a material, the AE sensor must be placed: a. directly on the AE source b. anywhere in the general vicinity of the AE source c. as far from the AE source as possible d. at a standard distance from the AE source

a. b. c. d.

.)

55 dB 60 dB SO dB 120 dB

0.26 15. One microvolt is the same as:

C.12

a. b. c. d.

12. Which of the following is measured in meters per second (m/s)?

0.001 v 0.000001 v 10mV 0.1mV

0.27 a. the time required for a crack to grow b. the resonant frequency of a material c. the velocity of sound in a given material d. the rate of strain when a material is being deformed

0.233

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Level I Questions - Acoustic Emission Testing Method

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16. Raising the detection threshold (or lowering the gain) to reduce background noise is not desired because it can lead to: a. reduced genuine emissions b. changes in the value of the AE signal features c. fewer locatable AE events due to fewer hits being detected d. all of the above

20. The most common way of attaching AE sensors to carbon steel vessels that operate at low to medium temperatures is: a. with hot glue b. with duct tape and wax c. silicon based vacuum grease and magnetic hold downs d. permanent stick epoxy glue

0.271

0.41 17. The active element inside an AE sensor that senses surface displacements is usually: a. b. c. d.

a capacitor a piezoelectric crystal a strain gauge an inductive coil

0.51

21. The most common artificial source of AE used to verify sensor coupling is: a. a spring loaded center punch b. a handful of small rocks thrown at the vessel wall c. 0.3 mm, 2H mechanical pencil lead breaks d. 0. 7 mm, 2H mechanical pencil lead breaks

0.273

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18. When should a waveguide be used in place of an adhesive for coupling an AE transducer to a text object?

22. ASTM E 1139-02 applies to metal pressure boundaries in industrial systems

such as: a. when access to the surface of the test object is limited b. when surface temperatures start to reduce the coupling properties and bond strength of the adhesive c. both a and b d. none of the above

a. pressure vessels b. piping c. other system components which serve to contain system pressure d. all of the above

L.Para. 1.1

0.53 19. AE sensors may be mounted directly to painted surfaces if: a. the paint is smooth, not too thick and well bonded to the vessel surface b. the paint is oil based c. the paint is not lead based d. the paint has been adequately cured

0.271

23. What information should be recorded about background noise during a test? a. the magnitude of background noise at periodic intervals during the test, as the test circumstances allow b. the times of any specific noise incidents c. the effects of noise on the examination d. all of the above

L.Para. 5.4.2.2

t P£0

Pi:

7.

What is the main difference in testing

spheres as compared to bullets and drums?

a. the size and shape b. the liquid loading experienced by the sphere c. aandb d. spheres require minimal sensor placement 0.270

the kaiser effect the felicity effect the dunegan corollary

eg

0.221

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Supplement to Recommended Practice SNT-TC-1A (Q&A Book): Acoustic Emission Testing Method

8.

AE testing of inservice vessels is aimed primarily at detecting service related cracking. This cracking may be a result of: a. b. c. d.

12. During continuous monitoring of pressure boundaries, AE sources are stimulated by: a. b. c. d.

stress corrosion cracking (SCC) sulfide stress cracking (SSC) fatigue cracking all of the above

e

special cyclic loading normal system operating conditions over pressurization all of the above L.Para. 5.1

0.270

9.

Size, shape and orientation of defects detected by AE testing, is usually determined by:

13. During continuous monitoring of pressure boundaries per ASTM E 1139,AE system operation and data interpretation should be verified by a qualified AE specialist:

a. size is estimated by the number of

a. b. c. d.

ringdown counts b. orientation can be assumed to be

normal to the hoop direction c. shape can always be assumed to be like a "half penny" d. follow-up nondestructive testing 0.270 10. When testing inservice pressure vessels, the maximum test load is commonly

once a month once a year every six months

only when there are signs of the system malfunctioning

L.Para. 7.7

14. During continuous monitoring of pressure boundaries per ASTM E 1139, a 0.3 mrn, 2H pencil lead break at a distance of 300 mm (12 in.) should produce a signal

based on the maximum operating

to noise ratio of

pressure experienced: a. b. c. d.

a. in the last one or tvvo months of operation b. in the last six or 12 months of

1 to I 2 to 1 3 to I 4 to I

.l

L.Para. 8.1.2

operation c. in the last 10 years of operation d. over the life of the vessel

15. During continuous monitoring of pressure 0.274

boundaries, signal detection sensitivity

should be evaluated during normal 11. Why is it wise to start an AE test for an

operation:

inservice pressure vessel at a load lower

then required?

a. by using a spring loaded center punch b. by tapping the pressure boundary with a light hammer c. by using pencil lead breaks as a signal

a. to determine that the loading rate is sufficient

b. to verify that the AE instrument is operating satisfactorily c. the maximum operating pressure may be uncertain and AE from SCC occurs within a few percent of this value d. all of the above 0.271

09]:

Pt>l:

source

d. by using a 7 mm pencil lead break 3.05 m (10ft) from the sensor L.Para. 8.1.2

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qn

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Level II Questions - Acoustic Emission Testing Method

16. During continuous monitoring of pressure boundaries, the distance at which an AE source can be detected is maximized by using a recommended low monitoring frequency of: a. b. c. d.

10kHz to 20kHz 20 kHz to 60kHz 50 kHz to 100 kHz 200 kHz to 400 kHz

L.Para. 8.1.4 17. During continuous monitoring of pressure boundaries, an AE system can perform leak detection if: a. it can measure the average signal level and/or AE rms voltage at each channel b. it can measure ring.down counts c. it can measure hit rate d. it can measure signal duration above 500KHz

20. What characteristic of a part best determines whether a test piece should be considered a large part or small part for AE testing purposes? a. a part is considered small when one load parameter will characterize the whole part b. a part is considered small when attenuation factors do not need to be considered c. if a waveguide is required to access the part, the part is considered small d. a part is considered small if all pencil lead breaks made at any and all positions on the part can still be detected by a single sensor N.Section 1 21. Of the following situations, which is the most appropriate for using only a single AEsensor?

L.Para. 12.1.2; Para. 8.1. 7.2

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18. For continuous monitoring of pressure boundaries, source location can be performed using:

a. difference in Time Of Arrival for multiple sensors b. a "look up" table of L',t's c. signal difference d. all of the above

L.Para. 12.1.6; Para. 8.1.7.2 19. During continuous monitoring of pressure boundaries, leaks are indicated by

a. a sudden increase in the AE rms signal level and a return back to the normal signal level b. a 6 dB change in the average signal level lasting more than 5 seconds c. a sustained increase in the AE rms signal level from one or more sensors in a given sensor array d. an increase in the noise level lasting more than 5 seconds

L.Para. 12.1.6

a. in a small part where the sensor can be placed near the expected source of AE and where one or two known noises occur b. in a large part where a single sensor can be used to locate AE sources because of the separation of fast and slow wave modes c. in a small part with no known noise sources and where the sensor can be placed next to the expected source of AE d. near multiple expected sources of AE, provided there is no background noise present N.Sections 1 and 5 22. For checking zonal location sensitivity, what is the minimum number of AE sensors that shall detect a simulated source at any given position on the structure?

a. b. c. d.

none one two three or more G.Section 8.3.2.1

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061

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Supplement to Recommended Practice SNT-TC-1A (Q&A Book): Acoustic Emission Testing Method

23. When monitoring a source of AE, the acoustic activity (as measured by event count or emission count) does not increase with increasing stimuli. Which of the following classifications apply to this source? a. inactive b. active c. critically active d. intense

G.Para. 11.1.2 24. According to Table T-1121 of ASME Section V,Article 11 (below), how much time must a pressure vessel, normally operated at 414 kPa ( 60 psig), be operated at 207 kPa (30 psig) before acoustic emission examination? a. b. c. d.

12 hours 30 hours 2 days 4days

25. When monitoring a source of AE, the acoustic activity (as measured by event count or emission count) increases with increasing stimuli. Which of the following classifications apply to this source? Note: for this question, the rate of acoustic activity is not increasing with increasing stimuli.

a. inactive b. active c. critically active d. intense

G.Para. 11.1.2 26. When monitoring a source of AE, the rate of acoustic activity (as measured by event count or emission count) increases with increasing stimuli. Which of the following classifications apply to this source? a. inactive

b. active c. critically active

A.90.13-14

d. intense G.Para. 11.1.2

Table T-1121 Requirements for Reduced Operating Levels Immediately Prior to Examination Percent of Operating Maximum Pressure and/or Load

10 or less 20 30 40 50

60

Time Spent at Percent of Maximum Pressure and/or Load

12 hr 18 hr 30 hr 2 days 4 days 7 days

Example: For an inservice vessel, two factors must be known prior to making

27. When monitoring a source of AE, both of the following are found to be true: the acoustic activity (as measured by event count or emission count) increases with increasing stimuli; the intensity (as measured by average energy per event or average emission count per event or average amplitude per event) exceeds the average intensity by a fixed level. Whicb of the following classifications should be used to describe this source?

a. b. c. d.

inactive active critically active intense

G.Para. 11.1.2

a test: (1) the maximum operating pressure or load during the past year;

(2) the test pressure.

PLC:

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Level II Questions - Acoustic Emission Testing Method

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28. While there is no set criteria for acceptable limits on sensor degradation, what levels of discrepancy warrant further action?

33. A major benefit of the acoustic emission

method is that it: a. finds smaller cracks than any other method b. is readily repeatable c. produces superior images of defects in thick-section steels

a. sensors that demonstrate loss of

response of greater than 4 dB b. sensors that demonstrate loss of response of greater than 6 dB

d. requires access to the structure only at

c. sensors that demonstrate loss of response of greater than 8 dB

the sensor locations

d. sensors that demonstrate loss of response of greater than 10 dB !.Section 6 29. High amplitude events during the

examination of fiberglass-reinforced pressure (FRP) vessels usually indicates: a. fiber breakage b. debonding c. fiber pullout

C.13 34. MARSE is:

a. the Mean Acoustic Ringdown Signal Envelope b. useful as a measure of continuous noise c. often observed to increase with

increasing load in tests of damaged structures

d. all of the above

d. microcracking

A.90.16

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35. The concept that all, or nearly all, materials are capable of generating acoustic emission was first set forth in 1950 by:

30. When an elastic material is stretched

elastically, the stress is: a. b. c. d.

8.181

greater than the strain less than the strain

proportional to the strain equal to the strain

a. Dunegan

b. Parry

F.19-20

c. Kaiser

d. johnson C.17

31. Which of the following terms means a material's ability to resist crack growth?

36. A typical source mechanism of acoustic emission is:

a. ductility b. toughness c. hardness

a. crack growth

d. resistance

F.21

b. movement of dislocations c. matrix cracking in fiber-reinforced

plastics d. all of the above

32. A limitation of the acoustic emission

C.12

method applied to metals is that it: a. is not immediately repeatable b. can only find defects that break the

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surface c. requires vessels to be taken out of service for the test d. requires personnel to be close to

vessels at high pressures

0.13

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Ptt

008

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Supplement to Recommended Practice SNT-TC-1A (Q&A Book): Acoustic Emission Testing Method

37. The felicity ratio is a quantitative measure best used to evaluate: a. b. c. d.

carbon steel reactors stainless steel piping fiberglass vessels and storage tanks 7075 aluminum aircraft structures C.18

41. Of the following components, which one is not considered to be part of a typical acoustic emission sensor? a. b. c. d.

A 'W1

electrodes active element acoustic waveguide backing material

C.123 38. When selecting the best sensor frequency for a particular acoustic emission test, it is important to consider all of the following except: a. attenuation characteristics of the

42. When performing source location, which of the following most directly affects the accuracy of computed location? a. b. c. d.

material b. frequency spectrum and level of background noise c. cable length d. sensor spacing

accuracy of sensor placement physical size of a sensor sensor frequency sensor couplant

C.150 8.191

39. After an initial proof test, a defect grows during a year in service. Acoustic emission can often detect this defect during a second proof test. Dunegan's reasoning for this phenomena is that the: a. second proof test will be done at a higher load b. kaiser effect will disappear after one year c. local stress field around the defect will be higher during the second proof test d. kaiser effect does not apply to flawed materials 0.37 40. The positioning of sensors for acoustic emission testing of metal pressure vessels is commonly based on: a. the measured attenuation in the structure b. the need to detect structural flaws at

43. In acoustic emission testing of fiberglass-reinforced pressure (FRP) tanks and pressure vessels. significant activity on low frequency sensors and very little activity on high frequency sensors normally indicates:

a. need to relocate high frequency sensors b. high amplitude, low frequency emissions c. fiber breakage d. crazing A.90.16 44. In acoustic emission testing of fiberglass-reinforced pressure (FRP) tanks and pressure vessels, low frequency sensors are used for: a. eliminating spurious noise sources b. low temperature environments c. examinations using cables over 91 m (300ft) d. backing up the high frequency sensors

A.90.14

critical locations c. the velocity of sound in the structure d. both a and b

R179

Pvv

POt

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Level II Questions -Acoustic Emission lesting Method

t

45. Which of the following factors tend to increase the amplitude of the acoustic emission response?

a. low strength material b. small grain size c. absence of discontinuities d. high strain rates

a. b. c. d.

C.13 46. One of the two major differences in the acoustic emission method from other forms of NOT is that:

a. acoustic emission relies on visual interpretation of data b. computers are used exclusively for analysis c. the energy detected is radiated from the defect itself d. transducers are used to gather data

C.12; 0.32

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47. One advantage of using acoustic emission over other forms of NOT is that acoustic emission can:

a. be used to evaluate an entire structure during one test b. be used to "size" a discontinuity in a material c. determine material thicknesses d. measure thermal gradients within a material

0.13

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~617

48. Which of the following facilitates the transmissio~ of acoustic waves into a typical sensor?

PS17

couplant active element surface of the test object damping material

C.124: 0.53 49. When should a system performance evaluation* be performed? (*)A performance evaluation in this case is a simulated AE, such as a pencil lead break, in the test structure to verify that the AE system registers the appropriate level of AE. a. before testing b. after testing c. at random and unscheduled intervals, as deemed necessary by the AE inspector d. all of the above G.Para. 8.3

11

12

Supplement to Recommended Practice SNT-TC-1A (Q&A Book): Acoustic Emission Testing Method

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Level Ill Questions Acoustic Emission Testing I.

The hoop stress in a thin-walled pressure vessel is given by pr/t, where pis the internal pressure, r is the radius of the vessel, and tis the wall thickness. The axial stress is: a. b. c. d.

4.

Yielding is a common source of acoustic emission in metals, for example A515 grade 70. At what stress levels do significant emissions generally begin? a. b. c. d.

twice the hoop stress the same as the hoop stress half of the hoop stress not directly related to the hoop stress

50-60 percent of the yield point 60-70 percent of the yield point 70-80 percent of the yield point 80-90 percent of the yield point

C.156

F.17 5.

2.

The phrase c'stress intensity factor" refers to the: a. stress in the neighborhood of a crack b. stress concentration produced by a hole c. stress needed to break a tensile specimen d. ratio of hoop stress to axial stress in a pressure vessel

•

C.46 3.

In order to use the signal-amplitude measurement method to locate a continuous signal source, which of the following should be known?

a. measured location of the sensors b. signal levels at sensor outputs c. attenuation characteristics of the structure d. all of the above

C.138

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pg

q-v

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Which of the following can be used to measure the operating characteristics of acoustic emission instrumentation?

a. b. c. d.

aRMS voltmeter a variable decibel attenuator a tone burst generator all of the above H.Section 4.0

14

Supplement to Recommended Practice SNT-TC-1A (Q&A Book): Acoustic Emission Testing Method

6.

Conventional source location, using time-of-arrival and triangulation, has proven to be unsatisfactory for fiber-reinforced pressure (FRP) equipment. Which item listed below is not one of the three main problems with source location in FRP equipment? a. Severe attenuation prohibits the multiple sensor hits that are required for triangulation. b. Triangulation assumes constant stress wave velocities in all directions. Since most FRP structures are anisotropic, this is rarely the case. c. Sensors resonant at 60 kHz are typically used for acoustic emission tests on FRP equipment. Time-of-arrival is generally not measured with these sensors. d. High event rates from single sources are typical in FRP material. Attenu