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NDE Technology and CodesStudent ManualChapter 8.0 Introduction toUltrasonic Examinationber that the requirements of CP-189 (1995 Editions) are minimum for Section XI. The specificand practical examinations must be directed at thespecific techniques an examiner will use in thefield. To have examiners spend 80 percent oftheir time doing erosion/corrosion (straight beam)examinations and then administer a simple anglebeam practical examination is not adequate for theperformance of ISI weld examinations.The requirements of Appendix VII are:ClassroomSection XI requires that personnel performingNDE be qualified and certified using a writtenpractice prepared in accordance with ANSI/ASNTCP-189 as amended by Section XI. IWA 2314states that the possession of an ASNT Level IIICertificate, which is required by CP-189, is notrequired by Section XI. Section XI also states thatcertifications to SNT-TC-1A or earlier editions ofCP-189 will remain valid until recertification atwhich time CP-189 (1995 Edition) must be met.ExperienceLevel I4040250 hoursLevel II4040800 hoursLevel III40-Options-see belowOption I - Graduate of a 4 year accreditedengineering or science college or university with adegree in engineering or science, plus 2 yearsexperience in NDE in an assignment comparable tothat of an NDE Level II in the ultrasonic examination method. At least 1 year of this experienceshall be in nuclear applications and shall includethe actual performance of examinations andevaluation of examination results. Also, it requires 4,200 hours of total experience with 2,100hours in nuclear applications.To assure that an examiner performing ISIultrasonic examinations is properly qualified,ASME Section XI has added extensive requirements above the minimums as outlined in CP-189.Specifically, Appendix VII was added to SectionXI. The following section outlines basic requirements for ASME Section XI. (Refer to ASMESection XI, Appendix VII for detailed information.)Option 2 - Completion with a passing grade ofat least the equivalent of 2 full years of engineering or science study at a university, college, ortechnical school, plus 3 years experience in anassignment comparable to that of a Level II in theultrasonic examination method. At least 2 yearsof this experience shall be in nuclear applicationsand shall include the actual performance ofexaminations and evaluation of examinationresults.Also, it requires 6,300 hours ofexperience with 4,200 hours in nuclearapplications.The 2007 edition with 2008 addenda of SectionXI, requires certification to CP-189 - 1995 asmodified in ASME Section XI MandatoryAppendix VII article VII 4000.USNRC Technical Training CenterLaboratory8 3Rev 0409

NDE Technology and CodesStudent ManualChapter 8.0 Introduction toUltrasonic Examination"hertz" units as follows:Option 3 - High school graduate, or equivalent, plus 4 years experience in an assignmentcomparable to that of a Level II in the ultrasonicexamination method. Also, it requires 8,400hours of experience with 4,200 hours in nuclearapplications. Appendix VII also addresses NDE InstructorQualification, Annual Training (minimum of 10hours per year), Examinations (with much emphasis on performance demonstration), andQualification Records.The audible range, which is the range of humanhearing, is 20 Hz to 20 KHz. Ultrasoundencompasses all frequencies higher than 20 KHz.UT utilizes only a portion of the ultrasonic range.Most commercial UT is performed within therange of 100 KHz to 25 MHz; a few applicationsare performed both above and below thisfrequency band. Actual examination frequencydepends on the frequency of the transducerselected.Appendix VII Supplement 1 contains theminimum content for initial training courses.8.3 PrinciplesSound is the transmission of mechanicalenergy, in the form of vibrations, through a material. Although sound can be propagated in allthree states of matter; solids, liquids, and gases,factors such as type of sound wave, materialcomposition, and wavelength can make propagation difficult or impossible in a given situation.8.3.18.3.2 VelocityVelocity is the speed at which sound travels.It is expressed as distance traveled per unit time.The most common units of time in UT are thesecond and microsecond (μsec). A microsecondis one millionth of a second.FrequencyThe velocity of sound depends upon:Frequency is the rate of vibration or the number of vibrations per second. Because soundwaves are in motion, frequency can also be viewedas the number of complete waves which pass agiven point during 1 second. One complete unitof vibration is called a cycle. A cycle isgraphically represented by a sine curve andconsists of two opposing motions, such as forwardand backward, or up and down. The rate ofvibration, or cycles per second, is expressed inUSNRC Technical Training CenterHertz (Hz) cycles per second,Kilohertz (KHz) one thousand cycles persecond, andMegahertz (MHz) one million cycles persecond. Density and elasticity of the material throughwhich sound is traveling, Wave mode (the manner in which materialparticles vibrate as sound travels through thematerial), and Material temperature, which has a minor effecton sound velocity for temperatures greater than150 F.8 4Rev 0409

NDE Technology and CodesStudent ManualChapter 8.0 Introduction toUltrasonic Examinationmaterial offers to the passage of sound. It is theproduct of the material's velocity and density. Asthe impedance ratio increases between theinterfaces of two materials the greater the soundreflection at this interface boundary and hence lesssound is transmitted into the second material. Thepercentage of sound reflected from an interface,where Z1 is the acoustic impedance of the mediumthrough which the sound is initially traveling, andZ2 is the acoustic impedance of the medium thatthe sound meets at the interface and is reflected, iscalculated as follows:Several formulas used in UT employ materialvelocity as a variable. The most convenient unitfor calculating these formulas is kilometers persecond (km/sec), although inches per second andcentimeters per microsecond are sometimesencountered.8.3.3 WavelengthA vibration in motion is often called a soundwave. A series of sound waves sent into an objectis often called a pulse.(8-2)% Sound reflected (Z1-Z2)2/(Z1 Z2)2 x 100Wavelength is an important variable in UT andis defined as the distance from one point on anultrasonic wave train to the next identical point(e.g., from trough to trough or peak to peak)(Figure 8-1).Material discontinuities reflect sound becausethey have an acoustic impedance different from thematerial being examined (Figure 8-2). In additionto acoustic impedance, a number of other factorsreduce the amplitude of the echo that thetransducer receives from a discontinuity. Thesize, shape, and orientation of the reflector allaffect its echo response. Position of a reflector isparticularly important due to the effects of soundbeam geometry and material properties. Themore the sound beam has spread at the point ofreflector interception, the less will be the reflectedsound pressure per unit area. In addition, assound travels through test material, increasedscattering and absorption of the sound by thematerial's own structure is experienced. Whenexamining thick sections, some type ofdistance/amplitude correction (DAC) must beconsidered to compensate for amplitude lossescaused by the sound beam and test material.It is also defined as the distance sound travelswithin the duration of one complete cycle.Wavelength (represented by λ, the Greek letterlambda) is calculated by dividing velocity (V) byfrequency (f), as follows:λ(8-1)(mm) V(km/sec)/f8.3.4Transmission/Reflection(MHz).Sound reflects when it strikes a surface calledan acoustic interface. An echo is thereforedefined as a reflection from an acoustic interface.An acoustic interface is the boundary between twomaterials with different acoustic impedances.Acoustic impedance is defined as the opposition aUSNRC Technical Training Center8 5Rev 0409

NDE Technology and CodesStudent ManualChapter 8.0 Introduction toUltrasonic Examination8.3.5 Attenuation8.3.7 Ultrasonic Wave PropagationSound amplitude decreases (as it propagates inthe material) are called sound attenuation. Attenuation is due to several factors:Sound waves travel through materials bydisplacing tiny particles of the material, generallyat the molecular level. Depending on the mannerin which vibrations are introduced, the particledisplacements exhibit certain behaviors, calledwave modes, as the vibrations travel.Absorption - Sound is absorbed by the brakingeffect on the particle motion. Lost energy isconverted to heat.There are two basic wave modes, which differfrom each other depending on how materialparticles move relative to the direction oftransmitted energy. Longitudinal waves (alsoknown as compressional waves) are characterizedby the particle motion being parallel to thedirection of wave travel (Figure 8-4). Transversewaves (also known as shear waves), are defined byparticle motion perpendicular to wave travel(Figure 8-5). The difference in wave motion causesthese wave modes to also differ from each other intheir relative velocity as well as in their ability topropagate in the various states of matter.Scatter - Grain boundaries of the materialcause the sound to scatter.The amount of sound attenuation within amaterial is governed by the density, elasticity,grain size, and grain structure of the material.These factors are affected by alloying, heattreatment, working, etc.8.3.6Instrumentation and ControlFigure 8-3 shows a block diagram of a typicalultrasonic flaw detection instrument. The pulsegenerator (trigger, clock) transmits an electricalpulse simultaneously to the transducer (searchunit) and the time base of the cathode ray tube(CRT). The transducer converts the electrical pulseinto sound which is transmitted into the material.The time base (sweep generator) generates the Xsweep across the CRT. When the sound pulse isreflected back to the transducer, it is convertedback into an electrical pulse and is amplifiedbefore being fed to the Y axis of the CRT. Thispulse deflects the time base vertically and producesa peak.USNRC Technical Training CenterUltrasonic energy propagates throughmaterials in several different ways depending uponthe manner in which the particles within thecarrying medium move relative to the direction ofwave propagation.There are four forms of wave propagationthrough materials:8 6 Compression (or longitudinal), Shear (or transverse), Surface (or Rayleigh), and Plate (or Lamb).Rev 0409

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Student Manual Ultrasonic Examination USNRC Technical Training Center Rev 04098 1 8.0 INTRODUCTION TO ULTRASONIC EXAMINATION Learning Objectives: To enable the student to: 1. Understand the basic principles of the genera-tion, transmission, and reflection of ultra-sound. 2. Know the pe