NDT Lesson 1 - 8. PDF
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PREPARED BY:
George L. Pherigo Director of Education American Society for Nondestructive Testing. Inc.
REVIEWED AND EDITED BY THE FOLLOWING MEMBERS OF THE EDUCATIONAL COUNCIL OF ASNT: Boyd W. Brown Argonne National Laboratory Kinney C. McKeel General Electric Co. W. C. Morrey Ebasco Services Phillip A. Olkle Yankee Atomic Electric Co. Allen Reynolds Stone & Webster Corp. Ward d. Rummel Martin Marietta Corp. A. J. Schwarber Lawrence Livermore Laboratories Albert L. Smith Westinghouse Hanford Co. John L. Summers Rockwell Int ernational Paul H. Todd Martin Marietta Corp. Published by The American Society for Nondestructive Testing 4153 Arlington Caller # 28518 Columbus. Ohio 43228 Copyright© by The American Society for Nondestructive Testing. Inc. All rights reserved. Portions of this manual have been taken from the General Dynamics Corporation’s Classroom Training Handbook CT 6-4, Ultrasonic Testing. And Programmed Instruction Handbooks PI-4-1, Introduction and PI-4-4, Ultrasonic Testing. These portions are subject to General Dynamics Cooperation’s copyright 1967.
Printed in the United State of America
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STUDENT’S GUIDE NDT TRAINING PROGRAM ULTRASONIC METHOD I
INTRODUCTION TO THE ULTRASONIC TRAINING PACKAGE The training materials in this package are designed to provide a basic knowledge of the fundamentals of ultrasonic testing. The training program that you are participating in will contain the following classroom hours of instruction to present the information as suggested in the ASNT publication SNT-IC-IA. Recommended Practice, June 1980 Edition. Level 1 Training will include lectures on all 14 lesson with approximately 2.9 hours per lesson. The student should assume the responsibility for reading all assignments, attending lectures, and participating in class discussions. Short exams will be administrated after each lesson to provide the student with a measure of progress and to stimulate study.
II
CONTENTS OF TRAINING PACKAGE Your training package contains the following materials with specific instructions and assignments to be given by the course instructor. 1. STUDENT PACKAGE A. Students’ Guide which outline the purpose, content and use of the training materials. B. 1 Classroom Training Handbook (CT-6.4) which serves as the major text for the training course. C. 1 set of individual lecture guide packets on the fundamentals of ultrasonic testing the lecture guide materials are provided with each lesson and are identical to the transparencies used by the instructor during the lecture. During the lecture, the student should use the guide to make additional notes. and the guide will then become valuable for future study . D. 1 packet of exams. The instructor may elect to remove the exams from your packet poor to starting the course and administer them as each lesson is completed. An exam will be furnished for each of the 14 lesson in the training course. 2. INSTRUCTOR PACKAGE A. The instructor’s package contains all of the information that you have with the addition of lecture guide transparencies and exam keys. B. At the option of the instructor a set of filmstrips may be used to provide additional depth and clanty . C. At the option of the instructor, the programmable instruction handbook may be used for additional assignments. D. Several types of certificates are available from ASNT and may be issued at the option of the instructor.
III
OUTLINE OF LESSONS AND RELATED READING ASSIGNMENTS The reading assignments will be made by the instructor and will correlate with the lectures the Classroom Training Handbook (CT-6-4) and programmed instruction Handbooks (PI4-4) follow the lesson in this training course in the following order.
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Lesson 1
Lesson 2
Lesson 3
Lesson 4
Lesson 5
Lesson 6
Lesson 7
Lesson 8
Lesson 9
Applications, Training, and Certification CT-6-4, Chapter 1 SNT-TC-1A
all all
Ultrasonic, Principles CT-6-4, Chapter 2 PI-4-4, Volume 1, Chapter 1 PI-4-4, Volume 1, Chapter 2
2-5 to 2-8 all 2-1 to 2-6
Equipment Controls CT-6-4, Chapter 2 PI-4-4, Volume 1, Chapter 5 PI-4-4, Volume 2, Chapter 4
2-8 to 2-16 all 4-1 to 4- 60
Wave Propagation, Reflection, and Refraction CT 6-4, Chapter 2 PI-4-4, Volume 1, Chapter 3
2-16 to 2-31 all
Couplants, Material Characteristics, Beam Spread CT-6-4, Chapter 2 PI-4-4, Volume 1, Chapter 6 PI-4-4, Volume 2, Chapter 2
2-26 to 2-36 all all
Attenuation, Impedance, and Resonance CT-6-4, Chapter 2 PI-4-4, Volume 1, Chapters 2 & 4 PI-4-4, Volume 2, Chapter 4
2-23 to end all 4-61 to end
Screen Presentations, Angle Beam Inspection With UT Calculator CT-6-4, Chapter 3 PI-4-4, Volume 1, Chapter 5 PI-4-4, Volume 2, Chapter 5 PI-4-4, Volume 3, Chapter 3
3-3 to 3-12 all all 3-60 to end
Transducers, Standard Reference Blocks CT-6-4, Chapter 3 PI-4-4, Volume 2, Chapters 1 & 3
3-3 to 3-12 all
Immersion Inspection CT-6-4, Chapter 4 PI-4-4, Volume 3, Chapters 4 & 5
4-1 to 4-18 all
Lesson 10
Contact Testing, Longitudinal & Shear Waves, Shell’s Law CT-6-4, Chapter 4 4-19 to 4-28 PI-4-4, Volume 3, Chapters 1 & 2 all
Lesson 11
Applications of Angle Beam Contact Testing CT-6-4, Chapter 4, PI-4-4, Volume 3, Chapter 3
4-19 to 4-31 all
Nonrelevant Ultrasonic Indications CT-6-4, Chapter 4 PI-4-4, Volume 3, Chapter 6
4-32 to end all
Classification of Discontinuities in UT CT-6-4, Chapter 7 PI-4-4, Chapters 1 through 7
7-1 to 7-7 all
Identification and Compensation of Discontinuities CT-6-4, Chapter 7
7-8 to end
Lesson 12
Lesson 13
Lesson 14
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Lesson 1 BASIC APPLICATIONS OF ULTRASONICS ULTRASONICS IS A VERSATILE INSPECTION TECHNIQUE, IT IS USED TO TEST A VARIETY OF BOTH METALLIC AND NON METALLIC PRODUCTS SUCH AS WELDS FORGINGS, CASTINGS, SHEET, TUBING, PLASTICS AND CERAMICS. ULTRASONICS HAS AN ADVANTAGE OF DETECTING SUBSURFACE DISCONTINUITIES WITH ACCESS TO ONLY ONE SIDE OF THE SPECIMEN. THE OBJECTIVE OF ULTRASONIC TESTING IS TO ENSURE PRODUCT RELIABILITY BY MEASNS OF: 1. OBTAINING INFORMATION RELATED TO DISCONTINUITIES 2. DISCLOSING THE NATURE OF THE DISCONTINUITY IMPAIRING THE USEFULNESS OF THE PART. 3. SEPARATING ACCEPTABLE AND UNACCEPTABLE MATERIALS IN ACORDANCE WITH PREDETERMINED STANDARDS TRAINING AND CERTIFICATION IT IS IMPORTANT THAT THE TECHNICIAN AND SUPERVISOR BE QUALIFIED IN THE ULTRASONIC METHOD BEFORE THE TECHNIQUE IS USED AND TEST RESULTS EVALUATED THE AMERICAN SOCIETY FOR NON DESTRUCTIVE TESTING RECOMMENDS THE USE OF THEIR DOCUMENT “RECOMMENDED PRACTICE NO. SNT-TC-1A.” THIS DOCUMENT PROVIDES THE EMPLOYER WITH THE NECESSARY GUIDE LINES TO PROPERLY QUALIFY AND CERTIFY THE NDT TECHNICIAN IN ALL METHODS. TO COMPLY WITH THIS DOCUMENT THE EMPLOYER MUST ESTABLISH A “WRIT TEN PRACTICE” WHICH DESCRIBES IN DETAIL HOW THE TECHNICIAN WILL BE TRAINED, EXAMINED AND CERTIFIED. THE STUDENT IS ADVISED TO STUDY THE CURRENT EDITION OF SNT-TC-1A TO DETERMINE THE RECOMMENDED INITIAL NUMBER OF HOURS OF CLASSROOM INSTRUCTION AND MONTHS OF EXPERIENCE NECESSARY TO BE CERTIFIED AS AN ULTRASONIC TESTING TECHNICIAN
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UT Lecture Guide Lesson 1 CERTIFICATION OF NDT PERSONNEL IS THE RESPONSIBILITY OF THE EMPLOYER AND IS USUALLYAT THREE LEVELS LEVEL I
PERFORM SPECIFIC CALIBRATIONS, SPECIFIC TESTS, AND S P E C I F I C E VA L U AT I O N S A C C O R D I N G TO W R I T T E N INSTRUCTIONS.
LEVEL II
SET UP AND CALIBRATE EQUIPMENT AND INTERPRET AND EVALUATE RESULTS WITH RESPECT TO CODES, STANDARDS AND SPECIFICATIONS. MUST BE ABLE TO PREPARE WRITTEN INSTRUCTIONS AND REPORT TEST RESULTS
LEVEL III
RESPONSIBLE FOR ESTABLISHING TECHNIQUES, INTERPRETING CODES, AND DESIGNATING THE TEST METHOD AND TECHNIQUE TO BE USED. MUST HAVE A PRACTICAL BACKGROUND IN THE TECHNOLOGY AND BE FAMILIAR WITH OTHER COMMONLY USED METHODS OF NDT.
THE SNT. TC. 1A DOCUMENT RECOMMENDS THAT LEVEL I AND II NDT TECHNICIANS BE EXAMINED IN THE FOLLOWING AREAS A. GENERAL EXAMINATION B. SPECIFIC EXAMINATION C. PRACTICAL EXAMINATION
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UT Lecture Guide Lesson 1 ASNT PROVIDES A SERVICE TO THE INDUSTRY BY PROVIDING LEVEL III EXAMINATIONS IN THE BASIC AND METHOD AREAS, BECAUSE OF THE INDIVIDUAL REQUIREMENTS OF THE MANY INDUSTRIES USING NDT, THE SPECIFIC EXAMINATION IS STILL THE RESPONSIBILITY OF THE EMPLOYER. THE FOLLOWING FLOW CHART INDICATES THE PATHS THAT CAN BE TAKEN TO C E RT I F I E D A C C O R D I N G TO T H E S N T- T C - 1 A D O C U M E N T.
ASNT CERTIFICATION WITHOUT EXAMINATION
ASNT CERTIFICATION BY EXAMINATION
Basic, Method LEVEL III CERTIFICATION PER RECOMMENDED PRACTICE SNT TC-1A June 1980 EDITION
QUALIFICATIONS FERIFIED AND DOCUMENTED PER THE EMPLOYERS WRITTEN PRACTICE
EXAMINATION BY THE EMPLOYER
LEVEL III CERTIFICATION ISSUED BY THE EMPLOYER
CUSTOMER ACCEPTANCE
Basic, Method, Specific 15 years Education/ Experience
EXAMINATION BY OUTSIDE AGENCY EMPLOYER WAIVES EXAMINATION
Notes : Certificate issued to individual This documentation as recommended in paragraph 5, 6-3.3, 6.3.4 and 9 of the SNT-TC- 1A 1980 edition
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Name
UT LESSON 1 QUIZ 1.
The selection of one test method over another is usually the decision of the Level I technician performing the test. 2. ASNT provides a service for examining Level I, II and III personnel in the General and specific areas. 3. The responsibility of issuing a certificate to the NDT technician is always retained by the employer in compliance with the SNT-TC-1A document. 4. If the SNT-TC-1A document is to be used as recommended guideline, the “written Practice” must be submitted to ASNT for approval. 5. If the SNT-TC-1A guidelines are followed, the Level III technician should have a knowledge of other commonly used methods of NDT even though certification is needed only in the ultrasonic area. 6. A Level I technician performing an ultrasonic test is permitted to accept or reject the part provided that written instructions or procedures are given to him by a Level II or Level III. (in accordance with SNT-TC-1A) 7. To comply with the guidelines of SNT-TC-1A all three levels of technicians must take a “General”, “Practical” and “Specific” test it examinations are used to determine certification. 8. The June 1980 Edition of SNT-TC-1A permits the employer to waive an examination for Level III personnel provided that documentation is on file showing the technician’s qualifications. 9. It is essential that every employer that uses the SNT-TC-1A document establish a “written Practice” 10. If an employer does not have a Level III in his company the services of an outside agency may be retained to perform these functions 11. An advantage of ultrasonics is that it reveals internal discontinuities with access to only one side of the part being inspected. 12. Ultrasonic inspection techniques can be used without impairing the future usefulness of the material
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Lesson 2 ULTRASONIC PRINCIPLES IN ULTRASONIC TESTING WE USE SOMETHING CALLED “ULTRASONIC VIBRATIONS.” WE MUST KNOW TWO FACTS ABOUTA VIBRATION 1. A VIBRATION IS A BACK AND FORTH MOVEMENT. 2. A VIBRATION IS ENERGY IN MOTION A DEPRESSION OF A SURFACE FROM ITS NORMAL POSITION IS CALLED A DISPLACEMENT.
RUBER BALL
VIBRATIONS PASS THROUGH A SOLID MATERIALAS A SUCCESSION OF PART I CLE DISPLACEMENTS. THIS CAN BE VISUALIZED AS SHOWN BELOW:
1
2
3
4
5
THE STRUCTURE OF A MATERIAL IS ACTUALLY MANY SMALL PARTICLES OR GROUPS OF ATOMS. THESE PARTICLES HAVE NORMAL OR REST POSITIONS, AND CAN BE DISPLACED FROM THESE POSITIONS BY SOME FORCE WHEN THE FORCE IS REMOVED, THE PARTICLES WILL TEND TO RETURN TO THEIR ORIGINAL POSITIONS.
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UT Lecture Guide Lesson 2 ENERGY IS TRANSMITTED THROUGH A SOLID MATERIAL BY A SERIES OF SMALL MATERIAL DISPLACEMENTS WITHIN THE MATERIAL. THE TRANSMISSION OF ULTRASONIC VIBRATIONS THROUGH A MATERIAL IS RELATED TO THE ELASTIC PROPERTIES OF THE MATERIAL. IF YOU TAP A METAL SURFACE, THE SURFACE MOVES INWARD, CAUSING A DISPLACEMENT.
PLATE STRUCK WITH HAMMER
THIN PLATE
SUPPORT VIEW A
SINCE THE METAL IS ELASTIC THE SURFACE WILL TEND TO MOVE BACK TO ITS ORIGINAL (REST) POSITION. THE SURFACE WILL ALSO MOVE THROUGH THE ORIGINAL POSITION AND MOVE TO A MAXIMUM DISTANCE IN THE OPPOSITE DIRECTION THIS COMPLETE SEQUENCE OF MOVEMENTS IS DEFINED AS A CYCLE.
STRING
DIRECTION OF BALL SWING
DIRECTION OF STRING TRAVEL
B STRING
BALL
BALL B A
PENCIL
A
C
E D
ONE CYCLE C
E
PENCIL
D
THE TIME REQUIRED FOR SOMETHING TO MOVE THROUGH ONE COMPLETE CYCLE IS CALLED THE PERIOD EXAMPLE : IF THE SWINGING BALL ABOVE MOVES OVER PATH ABCDE IN ONE SECOND, THEN THE PERIOD OF THE CYCLE IS ONE SECOND.
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UT Lecture Guide Lesson 2 THE NUMBER OF CYCLES IN A GIVEN PERIOD OF TIME IS CALLED THE FREQUENCY. EXAMPLE: IF THE BALL SWINGS THROUGH THREE COMPLETE CYCLES IN ONE SECOND, THEN THE FREQUENCY IS 3 CPS (CYCLES PER SECOND). IF YOU STRIKE A DRUM, IT HAS A FREQUENCY THAT IS LOW, APPROXIMATELY 50 CPS. THE TOP NOTE ON THE PIANO HAS A HIGHER FREQUENCY, APPROXIMATELY 4100 CPS. THE UNIT OF FREQUENCY USED TO DENOTE ONE CYCLE PER SECOND IS HERTZ (ABBREVIATED Hz). ONE CYCLE PER SECOND (CPS) IS EQUAL TO ONE HERTZ (Hz), 2 CPS = 2 Hz, ETC. SOUND TRAVELS IN METAL AS WELL AS IN AIR SOUND IS A VIBRATION AND HAS A RANGE OF FREQUENCIES MAN CAN ONLY HEAR VIBRATIONS (SOUND) UP TO ABOUT 20.000 Hz. HOWEVER. SOUND FROM AN ULTRASONIC TESTING UNIT IS ABOUT 5,000.000 Hz. (5 MEGAHERTZ) VIBRATIONS ABOVE THE HUMAN HEARING RANGE ARE CALLED ULTRASONIC VIBRATIONS. THE TWO TERMS. SOUND AND VIBRATIONS, AS WE WILL USE THEM WILL MEAN THE SAME THING. THE BEST WAY TO DEFINE SOUND IS TO SAY THAT IT IS A VIBRATION THAT TRANSMITS ENERGY BYA SERIES OF SMALL MATERIAL DISPLACEMENTS
JACK HAMMER
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UT Lecture Guide Lesson 2 ULTRASONIC TESTING IS THE PROCESS OF APPLYING ULTRASONIC SOUND TO A SPECIMEN AND DETERMINING ITS SOUNDNESS, THICKNESS, OR SOME PHYSICAL PROPERTY. THE ENERGY IS ORIGINATED IN SOMETHING CALLED A “TRANSDUCER” WHICH CAUSES MATERIAL DISPLACEMENT WITHIN THE SPECIMEN. A TRANSDUCER IS A DEVICE THAT CONVERTS ENERGY FROM ONE FROM TO ANOTHER. EXAMPLE : ELECTRICAL ENERGY TO MECHANICAL, OR MECHANICAL TO ELECTRICAL A SPEAKER IN A RADIO CONVERTS ELECTRICAL ENERGY TO A BACK AND FORTH MECHANICAL MOVEMENT VIEW “A” BELOW ILLUSTRATES THE “PIEZOELECTRIC EFFECT” ELECTRICAL ENERGY IS APPLIED THROUGH TWO WIRES CONNECTED TO A CRYSTAL, CAUSING THE CRYSTAL TO VIBRATE. THE TERMS CRYSTAL AND TRANSDUCER ARE USED INTERCHANGEABLY IN THIS LESSON. CRYSTAL
TRANSDUCER
WIRE
SOUND
VIBRATION ELECTRICAL ENERGY WIRE VIEW A
VIEW B
ELECTRICAL ENERGY CAUSES A PIEZOELECTRIC CRYSTAL TO EXPAND AND CONTRACT, FORMING MECHANICAL VIBRATIONS. A PIEZOELECTRIC TRANSDUCER CAN ALSO CONVERT MECHANICAL ENERGY TO ELECTRICAL ENERGY. THEREFOR, A TRANSDUCER CAN BOTH SEND AND RECEIVE ENERGY. SPECIMEN NOTE: SOUND IS REFLECTED WITHIN SPECIMEN AND RETURN TO TRANSDUCER
TRANSDUCER
VIEW B
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UT Lecture Guide Lesson 2 ENERGY TRANSMITTED BY A TRANSDUCER CAN BE EITHER PULSED OR CONTINUOUS. PULSED ULTRASOUND IS DEFINED AS SHORT GROUPS OF TRANSMITTED VIBRATIONS BEFORE AND AFTER WHICH THE TRANSDUCER CAN ACT AS A RECEIVER. STEEL, WATER AND OIL WILL TRANSMIT ULTRASOUND VERY WELL, BUT AIR PRESENTS A PROBLEM. TRANSDUCER OIL STEEL SPECIMEN
AIR IS A POOR TRANSMITTER OF ULTRASOUND BECAUSE THE PARTICLE DENSITY IS SO LOW THAT IT IS DIFFICULT TO TRANSMIT SOUND ENERGY FROM PARTICLE TO PARTICLE THAT IS WHY WE PUT OIL OR GREASE BETWEEN THE TRANSDUCER AND THE SPECIMEN. THE PARTICLE DENSITY OF A MATERIAL HELPS DETERMINE THE VELOCITY OF SOUND. THE VELOCITY OF SOUND WILL CHANGE AS IT MOVES FROM ONE MEDIUM TO ANOTHER AS SHOWN BELOW. THE ELASTICITY OF THE MATERIAL IS ALSO A FA CTOR.
1
2
3
4
5
6
7
8
9
10
11
12 13 14 15 16 17 18
0.33 KM/SEC
1.48 KM/SEC
5.9 KM/SEC
AIR
WATER
STEEL
VISUALIZE THAT THE BALLS SHOWN ABOVE REPRESENT THE INTERNAL STRUCTURE OF AIR, WATER AND STEEL. THE IMPULSE MOVING THROUGH THE ROW OF BALLS CAN BE COMPARED TO A PULSE OF ULTRASONIC SOUND
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UT Lecture Guide Lesson 2 A PRACTICAL EXAMPLE OF THE VELOCITY OF SOUND IN DIFFERENT MATERIALS IS SHOWN BELOW.
PISTON TRANSDUCER
WATER STEEL SPECIMEN
IT WILL TAKE LONGER FOR THE SOUND TO TRAVEL THROUGH THE WATER THAN THROUGH THE STEEL. THE SOUND VELOCITY IN STEEL IS APPROXIMATELY FOUR TIMES GREATER THAN IN WATER. A WAVELENGTH IS CONSIDERED TO BE THE DISTANCE BETWEEN TWO SUCCESSIVE DISPLACEMENTS. TRANSDUCER
WAVELENGTH
A
A
A
B
A
THE WAVELENGTH CAN ALSO BE DEFINED AS THE DISTANCE A WAVE TRAVELS DURING ONE COMPLETE CYCLE.
PISTON
TRANSDUCER A
B
1
4
VIEW A
THE SYMBOL “LAMBDA”
V
VELOCITY
SOUND WAVE
3
2
1
VIEW B
IS USED TO REPRESENT A WAVELENGTH AND IS CALLED
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UT Lecture Guide Lesson 2 THE ILLUSTRATION BELOW SHOWS A TRANSDUCER VIBRATING AT A FIXED FREQUENCY (f) AND TRANSMITTING SOUND WAVES INTO THE SPECIMEN. VELOCITY
TRANSDUCER
SOUND WAVES
THESE SOUND WAVES MOVE AT A FIXED VELOCITY (v) THROUGH THE SPECIMEN. THE WAVELENGTH CAN BE CHANGED IF THE FREQUENCY OF THE TRANSDUCER VIBRATION CHANGES. v
=
WAVELENGTH =
VELOCITY FREQUENCY
f
EXAMPLE: YOU CAN SHORTEN THE WAVELENGTH BY INCREASING THE FREQUENCY WAVELENGTH IS A RATIO OF A FIXED VALUE (VELOCITY) DIVIDED BY A VARIABLE (FREQUENCY). IN PRACTICAL SITUATIONS, THE SMALLEST DISCONTINUITY YOU CAN FIND WITH ULTRASONIC TESTING IS ABOUT ½ LAMBDA (WAVELENGTH) THEREFORE . TO DETECT SMALLER DEFECTS, YOU WILL NEED TRANSDUCERS THAT PRODUCE HIGHER FREQUENCIES. EXAMPLE: WHAT WOULD BE THE SMALLEST DISCONTINUITY THAT YOU COULD FIND IN A STEEL SPECIMEN WITH A VELOCITY OF 6KM/SEC USING A TRANSDUCER WITH A FREQUENCY OF 3 MEGAHERTZ (MHz). 5
=
6 X 10 CM/SEC
= 2 MILLIMETERS
3 Mhz IF THE SMALLEST DEFECT DETECTABLE IS ½ LAMBDA. THEN THE ANSWER IS 1 MILLIMETER OR 0.040 INCHES.
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UT LESSON 2 WORKSHEET
A B C
D
The distance between two displacements is called the WAVELENGTH. This is the distance a wave advances white a particle makes one complete cycle. The symbol used to represent a wavelength “ ” is called LAMBDA. The wavelength is a ratio of a fixed value (VELOCITY) divided by a variable (FREQUENCY). v VELOCITY WAVELENGTH = ------------------or = ---------FREQUENCY f
For the purpose of this exercise, consider that the smallest discontinuity detectable using pulse echo testing is one half lambda. 1. What is the smallest defect you can detect with a 2 Mhz probe inspecting a steel specimen with a velocity of 60 x 105 cm/sec? = (answer in inches) (1 mm equals . 040 )
2. What is the smallest detect could detect frequency to 5 Mhz? (Answer in inches)
if you increased the probe
3. What probe below would detect the smallest detect if you were inspecting a 5 steel specimen with a velocity of 5.9 x 10 cm/sec? What is the smallest each of the below would detect? (Answer in inches) ______ 2.5 Mhz ______ 5.0 Mhz ______ 10.0 Mhz 4. With everything else equal. Would a wavelength be longer in water or steel?
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UT LESSON 2 QUIZ
1. Relative to ultrasonic testing, air is considered a good conductor and for ths reason ultrasound will carry long distances in air. 2. Particle density of a material has a direct relationship to the velocity of sound in that material. 3. The symbol used to represent a wavelength is called “Shepda.” 4. With everything else equal, the wavelength in water would be shorter than a wavelength in steel. 5. To understand our definition of ultrasonics, a steel ball is considered to be more elastic than a lead ball 6. Man can hear sound up to approximately 5.000.000 Hz. 7. Vibration pass through a solid material as a series of particle displacements. 8. The velocity of sound is slower in steel than in water. 9. The number of cycles in a given period of time is called the frequency. 10. For the purposes of this lesson, ½ the wavelength is considered to be the smallest discontinuity that can be detected with ultrasonics. 5
11. If the longitudinal velocity in aluminum is 6.5 x 10 cm/sec and you are using a 2.5 MHz probe, what is the smallest discontinuity you can detect? (3 pts) 12. The ability of a transducer to convert mechanical energy to electrical and electrical energy to mechanical is due to the _______________ effect. 13. The distance that an ultrasonic pulse travels while a particle makes one complete cycle is called ______________
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LESSON 3
ULTRASONIC EQUIPMENT
CRT
TIMER (RATE GENERATION)
MARKER CIRCUIT
PULSER CIRCUIT
RECEIVER AMPLIFIER CIRCUIT
SWEEP CIRCUIT TRANSDUCER
TEST SPECIMEN POWER SUPPLY
(TO EACH CIRCUIT)
DISCONTINUITY
BACK REFLECTION THE ULTRASONIC PULSE ECHO INSTRUMENT GENERATES HIGH VOLTAGE ELETRICAL PULSES OF SHORT DURATION. THESE PUYLSES ARE APPLIED TO THE TRANSDUCER WHICH CONVERTS THEM INTO MECHANICAL VIBRATIONS THATARE APPLIED TO THE MATERIAL BEING INSPECTED. A LARGE PERCENTAGE OF THE SOUND IS REFLECTED FROM THE FRONT SURFACE OF THE TEST PART BACK TO THE TRANSDUCER. THE R E M A I N D E R I S R E F L E C T E D B Y T H E B A C K S U R FA C E O R DISCONTINUITIES. THE SOUND REFLECTED BACK TO THE TRANSDUCER IS CONVERTED BACK TO ELECTRICAL PULSES. WHICH ARE AMPLIPIED AND DISPLAYED ON THE CATHODE RAY TUBE (CRT) AS VERTICAL PULSES. THE A-SCAN DISPAY INDICATES THE DEPTH AND THE AMPLITUDE OF THE SOUND REFLECTIONS FROM A DISCONTINUITY. THE AMPLITUDE IS A RELATIVE MEASURE OF THE AMOUNT OF REFLECTED ENERGY.
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UT Lecture Guide Lesson 3 THERE ARE TWO BASIC ULTRASONIC TEST SYSTEMS: PULSE-ECHO
SPECIMEN CATHODE-RAY TUBE
COUPLANT
TRANSDUCER
DISCONTINUITY GENERATOR/INDICATOR INSTRUMENT
COAXIAL CABLE PULSE-ECHO SYSTEM
RECEIVING TRANSDUCER
SPECIMEN
THROUGH TRANSMISSION
COUPLANT
CATHODE-RAY TUBE
COUPLANT
TRANSMITTING TRANSDUCER
DISCONTINUITY GENERATOR/INDICATOR INSTRUMENT
COAXIAL CABLE THROUGH TRANSMISSION SYSTEM
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UT Lecture Guide Lesson 3 PULSE-ECHO IS THE MOST WIDELY USED ULTRASONIC SYSTEM. SHORT EVENLY TIMED PULSES OF ULTRASONIC WAVES ARE TRANSMITTED INTO THE M ATERIALS BEING TESTED. THESE PULSES REFLECT FROM DISCONTINUITIES IN THEIR PATH, OR FROM ANY BOUNDARY THAT THEY STRIKE. THE RECEIVED REFLECTIONS ARE THEN DISPLAYED ON A CATHODE RAY TUBE (CRT) THE SAME TRANSDUCER CAN BE USED TO TRANSMITAND RECEIVE. THROUGH TRANSMISSION REQUIRES THE USED OF TWO TRANSDUCERS, ONE FOR SENDING AND THE OTHER FOR RECEIVING. EITHER SHORT PULSES OR CONTINUOS WAVES ARE TRANSMITTED INTO THE MATERIAL. THE QUALITY OF THE MATERIAL BEING TESTED IS MEASURED IN TERMS OF ENERGY LOST BYA SOUND BEAM AS IT TRAVELS THROUGH THE MATERIAL THERE ARE TWO TEST METHODS NORMALLY USED IN ULTRASONIC TESTING "CONTACT TESTING" WHERE THE TRANSDUCER IS COUPLED TO THE MATERIAL THROUGH THIN LAYER OF COUPLANT. " IMMERSION TESTING ". BOTH THE MATERIAL AND THE TRANSDUCER ARE IMMERSED IN ATANK OF COUPLANT (USUALLY WATER).
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UT Lecture Guide Lesson 3 TO DETERMINE THE LOCATION OF DISCONTINUITIES WITHIN A TEST PART, THE CRT HORIZONTAL DISPAY IS DEVIDED INTO CONVENIENT INCREMENTS SUCH AS CENTIMETERS, INCHES, ETC.
A
1
2
3
B
1
4
2
3
4
4"
AT A GIVEN SESNSITIVITY (GAIN) SETTING. THE AMPLITUDE OF THE PIP IS DETERMINED BY THE STRENGTH OF THE SIGNAL GENERATED BY THE REFLECTED SOUND WAVE. THUS, THE CRT DISPLAYS TWO TYPES OF INFORMATION: 1. DISTANCE (TIME) OF THE DISCONTINUITY FROM THE TRANSDUCER 2. RELATIVE MAGNITUDE OF THE REFLECTED ENERGY FOCUS AND ASTIGMATISM COTROLS. ADJUST THE SHARPNESS OF THE DISPLAYED SIGNALS SENSITIVITY OR GAIN CONTROLS. DETERMINE THE AMOUNT OF AMPLIFICATION THE SIGNALS FROM THE DISCONTINUITY RECIEVED. INCREASING THE SENSITIVITY (GAIN) INCREASES THE AMPLITUDE OF THE PIPS ON THE CRT SCREEN.
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UT Lecture Guide Lesson 3 TWO CONTROLS, THE "SWEEP LENGTH" AND "SWEEP DELAY" REGULATE HOW MUCH OF THE TEST PART IS DISPLAYED AT ONE TIME ON THE CRT, AND WHAT PORTION OF THE PART IS DISPLAYED. THE SWEEP LENGTH (MATERIAL CONTROL) EXPANDS OR COMPRESSES THE DISPLAY ON THE CRTAS SHOWN BELOW:
40 FT
1 IN.
EXPANDED SWEEP
COMPRESSED SWEEP
VIEW A
VIEW B
THE SWEEP DELAY CONTROLALLOWS ONE TO MOVE THE VIEWING SCREEN ALONG THE DEPTH OF THE TEST PART. IN IMMERSION TESTING, THE SWEEP DELAY CAN BE USED TO REMOVE THE INITIAL PULSE FROM THE CRT. A - INITIAL PULSE B - FRONT SURFACE PIP C - 1ST BACK SURFACE REFLECTION PIP
A
B
A
C
B
C
VIEW B
VIEW A A B C
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UT Lecture Guide Lesson 3 "PULSE REPETITION RATE" CONTROL REGULATES HOW OFTEN THE PULSE IS APPLIED. PULSE RATES VARY FROM 50 TO 1200 PULSES PER SECOND OR MORE. WHEN THE SWEEP IS LONG, THE PULSE RATE MUST BE LOWER TO ALLOW ENOUGH TIME FOR THE SWEEP TO BE DISPLAYED BEFORE ANOTHER PULSE IS TRANSMITTED. IN SOME INSTRUMENTS THE PULSE RATE IS ADJUSTED AUTOMATICALLY. INCREASING THE PULSE LENGTH INCREASES THE AMOUNT OF SOUND ENERGY APPLIED TO THE TEST PART. BUT DECREASES THE RESOLVING POWER OF THE EQUIPMENT. THE "PULSE ENERGY" MUST BE INCREASED TO OBTAIN DEEP PENETRATION OR TO PENETRATE COARSEGRAINED MATERIALS. THE "REJECT CONTROL" OR "SUPPRESSION CONTROL" IS USED TO ELIMINATE OR REDUCE "GRASS" OR VERY LOW AMPLITUDE PIPS ALONG THE BASE OF THE SWEEP LINE. THIS CONTROL MAY AFFECT THE VERTICAL LINEARITY OF THE PRESENTATION. A "FLAW ALARM" OR "GATING CIRCUIT" IS USED TO ESTABLISH ZONES ALONG THE SWEEP LINE WITHIN WHICH PIPS OF PREDETERMINED AMPLITUDE WILLACTIVATE EITHER AN ALARM OR A RECORDING SYSTEM.
ALARM AMPLITUDE
A B
START OF GATE
A
C
B
END OF GATE
VIEW A
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VIEW B
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UT Lecture Guide Lesson 3 “DISTANCE AMPLITUDE CONTROL” . ULTRASONIC TESTING THE AMPLITUDE OF THE PIP FROM A DISCONTINUITY OF A GIVEN SIZE DECREASES AS THE DEPTH INCREASES. TO COMPENSATE FOR THIS “ATTENUATION,” AN ELECTRONIC CONTROL HAS BEEN ADDED TO MANY ULTRASONIC UNITS. SOME OF THE COMMON NAMES FOR THIS CONTROL ARE: DAC - DISTANCE AMPLITUDE CORECTION TCD - TIME CORRECTED GAIN STC - SENSITIVITY TIME CONTROL THIS CONTROL IS VERY USEFUL WHEN USED IN CONDUCTION WITH THE FLAW ALARM AND WITH RECORDING SYSTEMS.
WITH DAC WITHOUT DAC
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UT LESSON 3 WORKSHEET #1
A.
As shown below, many ultrasonic units have 50 divisions along the base line of the CRT screen. By using the simple formula below, we can make the distance across the screen represent any distance we wish from about 5 inches to over 100 inches. The formula used to find the value of each division on the screen below is: Range x 2
Increment/Division =
100
0
1
2
5
4
3
-2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
6
7
8
9
10
EXAMPLE: If you wanted the entire screen to represent 10, we would find that by using the formula that, each division on the base line represents 0.2
Inc/Div =
B.
C. D.
10 x 2 100
=
20 100
= 02”
After you have selected a suitable screen range it is than possible to use the sweep controls and match the pulses on the CRT to a know thickness calibration block. This will be discussed in later lessons. Many Ultrasonic units have 100 divisions across the base line instead of 50 in this case simply divide the range by 100 to find the increment per division. On the next page rill in the CRT screens as instructed.
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UT LESSON 3 WORKSHEET #1
On the CRT screens below, draw in the left edge of the first back reflection and at least one multiple the back echo as if would appear using a normal beam transducer on a properly calibrated unit
0
1
2
5
4
3
0
1
2
5
4
3
A -2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
6
7
8
9
B
-2 -1 0 -1 -2
-2 -1 0 -1 -2
10
0
SCREEN RANGE - 1 inch PART THICKNESS - 0.49”
0
1
2
5
4
3
1
2
3
4
5
6
7
8
9
10
SCREEN RANGE - 25” PART THICKNESS -
0
1
2
5
4
3
C -2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
6
7
8
9
D
-2 -1 0 -1 -2
10
-2 -1 0 -1 -2
0
SCREEN RANGE - 20” PART THICKNESS - 6 0
E
1
2
5
4
3
-2 -1 0 -1 -2
1
2
3
4
5
6
7
8
9
10
SCREEN RANGE - 2.5” PART THICKNESS - .6B”
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2
3
4
5
6
7
8
9
10
SCREEN RANGE - 1” PART THICKNESS - 3/16”
-2 -1 0 -1 -2
0
1
0
F
1
2
-2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
6
7
SCREEN RANGE - 50” PART THICKNESS - 10
-25-
5
4
3
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8
9
10
Name _______________________________ UT LESSON 3 WORKSHEET #2
Calculate the depth to each pulse on the CRT screens below. Consider that a normal beam transducer was used on a properly calibrated unit. 0
1
2
5
4
3
0
A
1
2
5
4
3
B -2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
6
7
8
9
-2 -1 0 -1 -2
-2 -1 0 -1 -2
10
0
If The above CRT is calibrated to a 25° range, what is the distance to the pulse? ____________
0
1
2
2
3
4
5
6
7
8
9
10
If The above CRT is calibrated to a 25° range, what is the distance to the pulse? ____________
5
4
3
1
0
C
1
2
5
4
3
D -2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
6
7
8
9
-2 -1 0 -1 -2
10
0
If The above CRT is calibrated to a 2.5° range, what is the distance to the pulse? ____________
0
1
2
1
2
3
4
5
6
7
8
9
10
If The above CRT is calibrated to a 2.5° range, what is the distance to the pulse? ____________
5
4
3
-2 -1 0 -1 -2
E
F -2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
6
7
8
9
10
If The above CRT is calibrated to a 2.5° range, where would the pips for a two discontinuities and back cohoes shear as shown is Fig. 1?
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EACH SQUARE REPRESENTS 1/4° Fig. 1
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Name _______________________________ UT LESSON 3 QUIZ
________
1.
With “Through Transmission”, an increase in amplitude indicates the presence of a possible discontinuity. 2. The “Pulse Echo” system uses a continuous wave and a separate transducer receives the echo. 3. Both contact testing and immersion testing require the use of a coupling medium. 4. Typically, the “gain” control will determine the amount of amplification for a suspected discontinuity indication. 5. Sweep length and sweep delay are two names for the same control. 6. The sweep length control is often used to sweep the initial pulse off the CRT in immersion testing. 7. In the a-scan presentation used in contact testing, the height of the vertical deflection (pip) on the CRT represents: A. Velocity B. Elapsed time C. Distance D. Signal amplitude 8. The “distance amplitude correction” control has the ability to automatically increase the screen range when a thicker part is inspected. 9. On the CRT “A” below, draw in the pulse if a normal beam transducer were used to show a 9° deep continuity using a 15° screen range. How many division from the left? ___________ (3 pts) 10. On the CRT “B” below, what is the distance to the pulse if a 2.5° screen range were being used for the inspection? ___________ (3 pts)
________ ________ ________ ________ ________ ________
________ ________
________
0
A
2
1
3
5
4
0
B
-2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
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6
7
8
9
10
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2
1
3
5
4
-2 -1 0 -1 -2
-2 -1 0 -1 -2
0
1
2
3
4
5
6
7
8
9
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10
Lesson 4
MODES OF ULTRASONIC WAVEL TRAVEL VELOCITY CAN BE DEFINED AS THE DISTANCE A WAVE WILL PROPOGATE THROUGH A MEDIUM IN A GIVEN UNIT OF TIME, USUALLYA SECOND. THE WAVE SPEED REMAINS CONSTANT THROUGH A GIVEN MEDIUM.
TRANSOUCER STEEL
OIL COUPLANT
POINT A
PULSES POINT B
LISTED BELOW IS A TABLE OF IMPEDANCE, VELOCITY AND DENSITY VALUES. THIS INFORMATION WILL BE USEFUL LATER IN THIS LESSON FOR PERFORMING BASIC ULTRASONIC CALCULATIONS.
MATERIAL
ACOUSTIC
SOUND
IMPEDANCE
VELOCITY
2
(GRAM)CM - SEC
2
(CM /SEC)
DENSITY 3
(GRAM/CM )
AIR
0.000033 X 106
0.33 X 105
0.001
WATER
0.149 X 106
1.49 X 105
1.00
ALUMINUM
1.72 X 106
6.35 X 105
2.71
STEEL
4.56 X 106
5.85 X 105
7.8
ULTRASONIC WAVES ARE REFLECTED WHEN THEY ENCOUNTER A MEDIUM OF A DIFFERENT ACOUSTICAL IMPEDANCE. THE “SURFACE” AT WHICH THIS REFLECTION OCCURS IS CALLED AN “INTERFACE”. AN INTERFACE IS THE COMMON BOUNDARY BETWEEN TWO MATERIALS OR PHASES, SUCH AS ALUMINUM-TO-STEEL OR WATER-TO STELL.
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UT Lecture Guide Lesson 4
A BEAM OF ENERGY APPROACHING AN INTERFACE IS REFERRED TO AS AN “INCIDENT WAVE”. THE ANGLE AT WHICH THE WAVE STRIKES THE INTERFACE IS KNOW AS THE “ANGLE OF INCIDENT” AS SHOWN BELOW
IMAGINARY PERPENDICULAR LINE INCIDENT WAVE INTERFACE
THE INCIDENT WAVE IS SAID TO HAVE NORMAL INCIDENCE WHEN ITS DIRECTION OF PROPAGATION IS PERPENDICULAR TO AN INTERFACE. AS SHAWM BELOW THE ANGLE OF INCIDENCE IS ZERO.
INCIDENT WAVE INTERFACE
NORMAL INCIDENCE SOME OF THE WAVE ENERGY STRIKING AN INTERFACE WILL BE TRANSMITTED THROUGH THE INTERFACE, AND SOME WILL BE REFLECTED AT THE ANGLE OF INCIDENCE. THE AMOUNT OF REFLECTION DEPENDS ON THE ACOUSTIC IMPEDANCE RATIO BETWEEN THE TWO MEDIA INVOLVED THIS REFLECTANCE WILL FACTOR WILL BE DISCUSSED IN DETAIL IN THE NEXT LESSON.
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UT Lecture Guide Lesson 4
THE ANGLE OF REFLECTION AT AN INTERFACE OR BOUNDARY ALWAYS EQUALS THE ANGLE OF INCIDENCE ANGLE = ANGLE “B”
NORMAL INCIDENCE
B
A
INCIDENT WAVE
REFLECTED WAVE
INTERFACE
ANGLE OF REFLECTION
TRANSDUCER COUPLANT INCIDENT WAVE INTERFACE OR BOUNDARY A B
REFLECTED WAVE
IMAGINARY LINE
ULTRASONIC VIBRATIONS TRAVEL IN MANY MODES. AND THE MOST COMMON ARE: 1. LONGITUDINAL (COMPRESSION) 2. SHEAR (TRANSVERSE) 3. SURFACE (RAYLEIGH) 4. PLATE (LAMB) EACH WAVE MODE HAS A SPECIFIC FUNCTION IN ULTRASONIC INSPECTION AND IT IS IMPORTANT THAT EACH BE UNDERSTOOD COMPLETELY
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UT Lecture Guide Lesson 4
LONGITUDINAL (COMPRESSIONAL) WAVES HAVE PARTICLE VIBRATIONS IN A BACK AND FORTH MOTION IN THE DIRECTION OF WAVE PROPAGATION. CONSIDER THAT ALL MATERIALS ARE MADE UP OF ATOMS LINED UP IN STRAIGHT LINES TO FORM A LATTICE STRUCTURE. WHEN STRIKING THE SIDE OF THE LATTICE, A CHAIN REACTION OF PARTICLE MOVEMENT IS STARTED CAUSING THE LONGITUDINAL WAVE
MEDIUM
DIRECTION
OF
PROPAGATION
PARTICLE MOTION LONGITUDINAL WAVES
S H E A R ( T R A N S V E R S E ) WAV E S H AV E PA RT I C L E V I B R AT I O N S PERPENDICULAR TO THE DIRECTION OF WAVE MOTION. SHEAR WAVES WILL NOT TRAVEL THROUGH LIQUIDS OR GASSES. IN SOME MATERIALS, VELOCITY OF A SHEAR WAVE IS ABOUT ½ THAT OF LONGITUDINAL WAVES. THEREFORE, THE WAVELENGTH IS SHORTER (ABOUT ½)PERMTTING SMALLER DISCONTINUITIES TO BE LOCATED.
MEDIUM
DIRECTION
OF
PROPAGATION
PARTICLE MOTION
(SHEAR WAVES)
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UT Lecture Guide Lesson 4
MODE CONVERSION TAKES PLACE WHEN A SOUND BEAM HITS AN INTEFACE BETWEEN TWO DIFFERENT MEDIAATAN ANGLE OTHER THAN 90 DEGREES. MODE CONVERSION IN THE CASE PRESENTED BELOW PRODUCES TWO REFLECTED BEAM: ONE BEAM CONSISTS OF LONGITUDINAL WAVES. THE OTHER BEAM CONSISTS OF SHEAR WAVES.
TRANSDUCER GREASE COUPLANT
STEEL BLOCK
INCIDENT BEAM (LONGITUDINAL WAVES) AIR
REFLECTED BEAM (LONGITUDINAL WAVES)
REFLECTED BEAM (SHEAR WAVES)
THE ULTRASONIC ANGLE BEAM TRANSDUCER USES THE FOLLOWING EXAMPLE THE “REFRACTED” SHEAR WAVES ARE USEFUL IN MANY INSPECTION TECHNIQUES. THE “ANGLE OF REFRACTION” IS THE ANGLE FORMED BETWEEN A REFRACTED BEAM AS IT ENTERS THE SECOND MEDIUM AND A KLINE DRAWN PERPENDICULAR TO THE INTERFACE.
NORMAL INCIDENCE INCIDENT BEAM (LONGITUDINAL)
LE ANG OF CE IDEN INC INTERFACE
PLASTIC STEEL
ANGLE OF REFLECTION (LONGITUDINAL)
REFLECTED BEAM (LONGITUDINAL WAVES) REFRECTED BEAM (SHEAR WAVES) ANGLE OF REFRECTION (SHEAR)
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UT Lecture Guide Lesson 4
SNELL’S LAW CAN BE USED TO DETERMINE ANGULAR RELATIONSHIPS BETWEEN MEDIA FOR BOTH LONGITUDINALAND SHEAR WAVES. = V1 = 2 = V2 = 1
SIN SIN
1
=
2
V1 V2
ANGLE OF INCIDENCE VELOCITY IN FIRST MEDIUM ANGLE OF REFRACTION VELOCITY IN SECOND MEDIUM
THE FOLLOWING EXAMPLE CALCULATES THE ANGLE OF REFRACTION 2 FOR A LONGITUDINAL WAVE PASSING THROUGH A WATER TO-STEEL INTERFACE. 10 DEGREES = ANGLE OF INCIDENCE 2 1.49 KM/SEC = LONGITUDINAL VELOCITY IN WATER (V1) 5.85 KM/SEC = LONGITUDINAL VELOCITY IN STEEL (V2)
sin sin sin
sin sin
V1 = V 2 2 V2 (sin = 2 V1
1
2 2 2
=
1
1)
1 . 012 1 . 49
V1
FIRST MEDIUM (WATER) SECOND MEDIUM (STEEL)
V2
2
= 0 . 6791 = 42o 46'
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UT Lecture Guide Lesson 4
AS THE ANGLE OF INCIDENCE INCREASES, THE ANGLE OF REFRACTION INCREASES. WHEN THE REFRACTION ANGLE OF A LONGITUDINAL WAVE REACHES 90 DEGREES, THE WAVE EMERGES FROM THE SECOND MEDIUM AND TRAVELS PARALLEL TO THE INTERFACE OR SURFACE. THIS IS CALLED ITS FIRST OR LOWER "CRITICAL ANGLE" ABOVE APPROXIMATELY 28 DEGREES WITH A PLASTIC-TO-STEEL INTERFACE, ONLY SHEAR WAVES ARE GENERATED IN THE PART.
ANGLE OF INCIDENCE
28
O
REFRACTED LONGITUDINAL WAVE
PLASTIC STEEL 9 0O
REFRACTED SHEAR WAVE
IF THE ANGLE OF INCIDENCE IS INCREASED PAST THE FIRST CRITICAL ANGLE, ONLY A SHEAR WAVE IS GENERATED IN THE PART. WHEN THE ANGLE OF REFRACTION FOR THE SHEAR WAVE IS 90 DEGREES, THEN WE HAVE REACHED THE UPPER OR SECOND CRITICAL ANGLE WHICH PRODUCES SURFACE WAVES, AS SHOWN BELOW, THERE IS THEN TOTAL REFLECTION FOR BOTH LONGITUDINALAND SHEAR WAVES. WITH A PLASTIC-TO-STEEL INTERFACE. THIS HAPPENS AT APPROXIMATELY 58 DEGREES
REFLECTED LONGITUDINAL WAVE
O
28 ANGLE OF INCIDENCE
PLASTIC
REFRACTED SHEAR WAVE
STEEL
(SURFACE WAVE)
9 0O
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UT Lecture Guide Lesson 4
WHEN THE INCIDENT BEAM IS AT ITS SECOND CRTITICAL ANGLE, A THIRD TYPE OF WAVE IS DEVELOPED, CALLED A RAYLEIGH OR SURFACE WAVE. AS SHOWN BELOW, THE WAVE TRAVELS WITH AN ELLIPTICAL PARTICEL MOTION. SURFACE WAVES ARE USEFUL IN DETECTING SURFACE CRACKS, BUT ONLY PENETRATE ABOUT ONE WAVELENGTH.
PARTICLE MEDIUM'S SURFACE DIRECTION
OF
PROPAGATION
PARTICLE MOTION
SURFACE WAVES
AS SHOWN, SURFACE WAVES HAVE THE ABILITY TO FOLLOW THE SURFACE CONTOUR AS LONG AS THE CONTOUR DOES NOT SHARPLY CHANGE. HOWEVER, THE SURFACE WAVE CAN BE ALMOST COMPLETELY ABSORBED BY EXCESS COUPLANT OR BY TOUCHING YOUR FINGER TO THE SURFACE OF THE PARTAHEAD OF THE TRANSDUCER. TRANSDUCER
DISCONTINUITY WEDGE
TEST SPECIMEN
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UT Lecture Guide Lesson 4
PLATE WAVES OR LAMB WAVES HAVE THE ABILITY TO PROPAGATE THROUGH THIN PLATES IN A VARIETY OF WAVE MODES DEPENDING ON PLATE THICKNESS, TRANSDUCER. FREQUENCYAND INCIDENTANGLE. PLATE WAVES ARE GENERATED BY USING LONGITUDINAL WAVES WHICH DEVELOP EITHER SYMMETRICAL OR ASYMMETRICAL WAVES AS SHOWN BELOW. PLATE WAVES OCCUPY THE ENTIRE THICKNESS OF THE PART. WITHOUT "SATURATING" THE PART, THE WAVE CANNOT EXIST.
THIN SHEET OR PLATE
THIN SHEET OR PLATE
DIRECTION OF PROPAGATION PARTICLE
DIRECTION OF PROPAGATION
MOTION
PARTICLE
SYMMETRICAL
MOTION
ASYMMETRICAL PLATE
WAVES
TO GENERATED PLATE WAVES, YOU ADJUST THE INCIDENT ANGLE TO THE POINT THAT MAXIMUM REFLECTIONS ARE OBSERVED ON THE CRT SCREEN FROM A KNOWN REFLECTOR. IT IS NOT POSSIBLE TO GENERATE SHEAR OR SURFACE WAVES ON MATERIALS THINNER THAN ONE-HALF WAVELENGTH. THEREFORE, PLATE WAVE ARE USEFULAS SHOWN BELOW.
TRANSDUCER
HOLLOW EXTRUSION
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Name _______________________________ UT LESSON 4 WORKSHEET #1
A. Using snell’s Law and the attached Sine table, calculate the following refraction problems, using the information in the sketch below.
1
LUCITE (long. Velocity 2.73 x 105 cm/sec)
2
STEEL
( long. Velocity 5.9 x 105 cm/sec) ( shear velocity 3.23 x 105 cm/sec)
________
1.
Find the refracted longitudinal wave if the incident angle Ø1 is 25 degrees. (SHOW WORK) (2 pts)
________
2.
Find the refracted shear wave angle if the incidence angle is 45 degrees. (SHOW WORK) (2 pts)
________
3.
If you wanted a shear wave to travel into the steel at 70 degrees, what would the incident angle through the lucite be? (SHOW WORK) (2 pts)
________
4.
If Ø1 = 18º, is it possible to have a refracted longitudinal wave? If yes, what is it? (SHOW WORK) (2 pts) If no, why not?
________
5.
If Ø1 = 36°, is it possible to have a refracted longitudinal wave? If yes. what is it? If no. Why not?
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UT LESSON 4 WORKSHEET #1 Angle
1* 2* 3* 4* 5* 6* 7* 8* 9* 10* 11* 12* 13* 14* 15* 16* 17* 18* 19* 20* 21* 22* 23* 24* 25* 26* 27* 28* 29* 30* 31* 32* 33* 34* 35* 36* 37* 38* 39* 40* 41* 42* 43* 45*
.0175 .0349 .0523 .0698 .0872 .1045 .1219 .1392 .1564 .1736 .1908 .2079 .2250 .2419 .2588 .2756 .2924 .3090 .3256 .3420 .3584 .3746 .3907 .4067 .4226 .4384 .4540 .4695 .4848 .5000 .5150 .5299 .5446 .5592 .5736 .5878 .6018 .6157 .6293 .6428 .8561 .6691 .6820 6947 .7071
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Cos
Tan
Angle
Sin
Cos
Tan
.9998 .9994 .9986 .9976 .9962 .9945 .9925 .9903 .9877 .9848 .9816 .9781 .9744 .9703 .9659 .9613 .9563 .9511 .9455 .9397 .9336 .9272 .9205 .9135 .9063 .8988 .8910 .8829 .8746 .8660 .8572 .8480 .8387 .8290 .8192 .8090 .7986 .7880 .7771 .7660 .7547 .7231 .7314 7193 .7071
.0175 .0349 .0524 .0699 .0875 .1051 .1228 .1405 .1584 .1763 .1944 .2126 .2309 .2493 .2679 .2867 .3057 .3249 .3443 .3640 .3839 .4040 .4245 .4452 .4663 .4877 .5095 .5317 .5543 .5774 .6009 .6249 .6494 .6745 .7002 .7265 .7536 .7813 .8098 .8391 .8893 .9004 .9325 .9657 1.0000
46* 47* 48* 49* 50* 51* 52* 53* 54* 55* 56* 57* 58* 59* 60* 61* 62* 63* 64* 65* 66* 67* 68* 69* 70* 71* 72* 73* 74* 75* 76* 77* 78* 79* 80* 81* 82* 83* 84* 85* 86* 87* 88* 89* 90*
.7193 .7314 .7431 .7547 .7660 .7771 .7880 .7986 .8090 .8192 .8290 .8387 .8480 .8572 .8660 .8740 .8829 .8910 .8988 .9063 .9135 .9205 .9272 .9336 .9397 .9455 .9511 .9563 .9613 .9659 .9703 .9744 .9788 .9816 .9848 .9877 .9900 .9925 .9945 .9962 .9976 .9986 .9994 .9898 1.0000
.6947 .6820 .6691 .6561 .6428 .6293 .6157 .6018 .5878 .5736 .5992 .5446 .5299 .5150 .5000 .4848 .4695 .4540 .4384 .4226 .4067 .3907 .3746 .3584 .3420 .3256 .3090 .2924 .2757 .2588 .2419 .2250 .2079 .1908 .1736 .1564 .1392 .1219 .1045 .0872 .0698 .0523 .0349 .0175 .0000
1.0355 1.0724 1.1108 1.1504 1.1918 1.2349 1.2799 1.3270 1.3764 1.4281 1.4826 1.5399 1.6013 1.6643 1.7321 1.8040 1.8807 1.9626 2.0503 2.1445 2.2460 2.3559 2.4751 2.6051 2.7475 2.9042 3.0777 3.2709 3.4874 3.7321 4.0108 4.3315 4.7046 5.1446 5.6713 6.3138 7.1154 8.1443 9.5144 11.4301 14.3007 19.0811 28.6363 57.2900
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Name _______________________________ UT LESSON 4 QUIZ
________ ________ ________ ________ ________ ________
1. 2. 3. 4. 5. 6.
________
7.
________ ________
8. 9.
An “ultrasonic beam” travels trough a medium as waves of sound energy. Normal incidence is when the incident beam is parallel to the interface. The reflection of an incident beam at an interface is equal to its angle of reflection. Particle vibration in a longitudinal wave is in the direction of wave propagation. Shear wave velocity is approximately twice the velocity of longitudinal waves. Mode conversion occurs when a sound beam strikes an interface between two media of different velocities at an angle. The bending of an incident beam as it passes through an interface is called refraction. Longitudinal waves will propagate through both solids and liquids. Both plate waves and surface waves can follow the part contour.
Sin O
V 1
5
Shear velocity in steel = 3.23 x 10 cm/sec 5 = Long. Velocity in steel = 5.85 x 10 cm/sec. 5 V Long. Velocity in water = 1.49 x 10 cm/sec Sin O 2 2 5 Long. Velocity in lucite = 2.73 x 10 cm/sec USING THE ABOVE INFORMATION, SOLVE THE FOLLOWING PROBLEMS. INDICATE THE APPROXIMATE ANGLES ON THE SKETCH AND LABEL EACH. ________
1
10. If you wanted a shear wave to travel into steel at 60 degrees, what would be the incident angle on the lucite wedge? (SHOW WORK) (3 pts)
60
________
11. What would be the refracted longitudinal wave if the angle of incidence through a water to steel interface is 12 degrees? (SHOW WORK) (3 pts)
0
12
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UT LESSON 4 QUIZ Angle
1* 2* 3* 4* 5* 6* 7* 8* 9* 10* 11* 12* 13* 14* 15* 16* 17* 18* 19* 20* 21* 22* 23* 24* 25* 26* 27* 28* 29* 30* 31* 32* 33* 34* 35* 36* 37* 38* 39* 40* 41* 42* 43* 45*
.0175 .0349 .0523 .0698 .0872 .1045 .1219 .1392 .1564 .1736 .1908 .2079 .2250 .2419 .2588 .2756 .2924 .3090 .3256 .3420 .3584 .3746 .3907 .4067 .4226 .4384 .4540 .4695 .4848 .5000 .5150 .5299 .5446 .5592 .5736 .5878 .6018 .6157 .6293 .6428 .8561 .6691 .6820 6947 .7071
Non Destructive Testing (NDT)
Cos
Tan
Angle
Sin
Cos
Tan
.9998 .9994 .9986 .9976 .9962 .9945 .9925 .9903 .9877 .9848 .9816 .9781 .9744 .9703 .9659 .9613 .9563 .9511 .9455 .9397 .9336 .9272 .9205 .9135 .9063 .8988 .8910 .8829 .8746 .8660 .8572 .8480 .8387 .8290 .8192 .8090 .7986 .7880 .7771 .7660 .7547 .7231 .7314 7193 .7071
.0175 .0349 .0524 .0699 .0875 .1051 .1228 .1405 .1584 .1763 .1944 .2126 .2309 .2493 .2679 .2867 .3057 .3249 .3443 .3640 .3839 .4040 .4245 .4452 .4663 .4877 .5095 .5317 .5543 .5774 .6009 .6249 .6494 .6745 .7002 .7265 .7536 .7813 .8098 .8391 .8893 .9004 .9325 .9657 1.0000
46* 47* 48* 49* 50* 51* 52* 53* 54* 55* 56* 57* 58* 59* 60* 61* 62* 63* 64* 65* 66* 67* 68* 69* 70* 71* 72* 73* 74* 75* 76* 77* 78* 79* 80* 81* 82* 83* 84* 85* 86* 87* 88* 89* 90*
.7193 .7314 .7431 .7547 .7660 .7771 .7880 .7986 .8090 .8192 .8290 .8387 .8480 .8572 .8660 .8740 .8829 .8910 .8988 .9063 .9135 .9205 .9272 .9336 .9397 .9455 .9511 .9563 .9613 .9659 .9703 .9744 .9788 .9816 .9848 .9877 .9900 .9925 .9945 .9962 .9976 .9986 .9994 .9898 1.0000
.6947 .6820 .6691 .6561 .6428 .6293 .6157 .6018 .5878 .5736 .5992 .5446 .5299 .5150 .5000 .4848 .4695 .4540 .4384 .4226 .4067 .3907 .3746 .3584 .3420 .3256 .3090 .2924 .2757 .2588 .2419 .2250 .2079 .1908 .1736 .1564 .1392 .1219 .1045 .0872 .0698 .0523 .0349 .0175 .0000
1.0355 1.0724 1.1108 1.1504 1.1918 1.2349 1.2799 1.3270 1.3764 1.4281 1.4826 1.5399 1.6013 1.6643 1.7321 1.8040 1.8807 1.9626 2.0503 2.1445 2.2460 2.3559 2.4751 2.6051 2.7475 2.9042 3.0777 3.2709 3.4874 3.7321 4.0108 4.3315 4.7046 5.1446 5.6713 6.3138 7.1154 8.1443 9.5144 11.4301 14.3007 19.0811 28.6363 57.2900
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Lesson 5 COUPLANTS AND ULTRASONIC SOUND ENERGY THE PRIMARY PURPOSE OF A COUPLANT IS TO PROVIDE A SUITABLE SOUND PATH BETWEEN THE TRANSDUCER AND THE TEST SURFACE. A COUPLANT MUST EFFECTIVELY WET OR TOTALLY CONTACT BOTH SURFACES OF THE TRANSDUCER AND TEST PART. 1. THE COUPLANT MUST EXCLUDE ALL AIR FROM BETWEEN THE SURFACES AS AIR IS A VERY POOR CONDUCTOR OF SOUND. 2. THE COUPLANT FILLS IN AND SMOOTHS OUT IRREGULARITIES ON THE SURFACE OF THE TEST PART. 3. THE COUPLANT AIDS IN THE MOVEMENT OF THE TRANSDUCER OVER THE SURFACE IN CONTACT TESTING. 4. A PRACTICAL COUPLANT MUST BE AESY TO APPLY AND EASY TO REMOVE IT MUSTALSO BE HARMLESS TO THE PART SURFACE.
TRANSDUCER COUPLANT TEST MATERIAL
OIL OR WATER MIXED WITH GLYCERINE (2 PARTS WATER AND 1 PART GLYCERINE) ARE COMMONLY USED COUPLANTS. EVEN WALLPAPER PASTE HAS ADVANTAGES AS A COUPLANT. HEAVER COUPLANTS, SUCH S GREASE OR HEAVY OIL CAN BE USED ON ROUGH OR VERTICAL SURFACES. SPECIALLY FORMULATED LIQUID AND PASTE COUPLANTS ARE ALSO AVAILABLE FROM ULTRASONIC EQUIPMENT MANUFACTURERS. IN CIRCUMSTANCES WHERE THE USE OF LIQUIDS OR PASTE IS UNDESIRABLE, THIN RUBBER OR RUBBER-LIKE MATERIALS MAY BE USED. IN ALL CASES THE COUPLANT SHOULD BE AS THIN AS POSSIBLE IF THE COUPLANT IS EXCESSIVE, IT MAY ACT AS A WEDGE AND ALTER THE DIRECTION OF THE SOUND BEAM.
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UT Lecture Guide Lesson 5
THE SURFACE OF A TEST SPECIMEN CAN GREATLY AFFECT ULTRASONIC WAVE PROPAGATION. ROUGH SURFACE CAN CAUSE UNDESIRABLE EFFECTS SUCH AS REDUCTION OF DISCONTINUITY AND BACK SURFACE AMPLITUDES DUE TO DISTORTION OF WAVE DIRECTIVITY. COUPLANT
COUPLANT
UNEVEN BUT CONSISTANT SURFACE
FLAT SMOOTH SURFACE
ROUGH AND IRREGULAR SURFACE
TEST
POOR
FAIR
FRONT SURFACE (INITIAL PULSE) WIDE FRONT SURFACE
BACK SURFACE
DISCONTINUITY
REDUCED AMPLITUDE
MARKERS
CRT INDICATIONS
FLAT SMOOTH SURFACE - GOOD RESPONSE
ROUGH AND IRREGULAR SURFACE-POOR RESPONSE A-SCAN PRESENTATION (PULSE-ECHO)
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UT Lecture Guide Lesson 5
A GOOD BACK SURFACE REFLECTION INDICATES A GOOD RESPONSE FROM THE MATERIAL BEING TESTED. IT IS REFLECTED BACK TO ITS SOURCES SIMILAR TO LIGHT STRIKING A MIRROR. IF THE SURFACES ARE NOT PARALLEL, THE REFLECTED ENERGY WILL BE DIRECTED AWAY FROM THE TRANSDUCER SIMILAR TO LIGHT FALLING ON A MIRROR ATAN ANGLE. TRANSDUCER
FRONT SURFACE (INITIAL PULSE)
FRONT SURFACE
REDUCED BACK SURFACE INDICATION
SPECIMEN CROSS-SECTION REFLECTION CRT INDICATIONS
BACK SURFACE
THE PHYSICAL SHAPE OR CONTOUR OF A PART MUST BE CONSIDERED WHEN ATTEMPTING TO DISCERN WHETHER A DISCONTINUITY INDICATION IS REAL OR FALSE.
EXAMPLES OF SOUND PATHS LEADING TO SPURIOUS INDICATIONS
IN TESTING LONG SPECIMENS, REFLECTION F A SPREADING BEAM CAN PRODUCE FALSE INDICATIONS ON THE CRTAS SHOWN BELOW A SHEAR WAVE MAY BE GENERATED WHICH IS REFLECTED AT A STEEP ANGLE TO THE OPPOSITE SIDE, WHERE MODE CONVERSION TAKES PLACE. MODE CONVERSION WILL BE DISCUSSED IN A LATER LESSON. HOWEVER, THIS TYPE OF FALSE SIGNAL WILL APPEAR ON THE RIGHT SIDE OF THE FIRST BACK ECHO.
LONGITUDINAL WAVE
FIRST BACK
SHEAR WAVE
LONGITUDINAL WAVE
TRANSDUCER SPECIMEN DIAMETER
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UT Lecture Guide Lesson 5
GRAIN STRUCTURE HAS A GREAT INFLUENCE ON THE ACOUSTICAL PROPERTIES OF A MATERIAL A STEEL FORGING GENERALLY HAS A FINE GRAIN STRUCTURE AND HAS A LOW DAMPING EFFECT ON THE SOUND BEM. HOWEVER, A CASTING GENERALLY HAS A COARSER GRAIN STRUCTURE WHICH IS MOE DIFFICULT TO GET SOUND THROUGH.
DISCONTINUITY
FRONT SURFACE
FRONT SURFACE BACK SURFCE REFLECTION LOST OR REDUCED
BACK SURFACE REFLECTION
COARSE GRAIN
FINE GRAIN
WHEN A DISCONTINUITY IS NOT NORMAL (AT 90 DEGREES) TO THE INCIDENT WAVE THE REFLECTED WAVE WILL BE ATAN ANGLE. AS SHOWN BELOW, THE RESULT IS A REDUCTION IN THE AMPLITUDE OF THE DISCONTINUITY INDICATION DISPLAYED ON THE CRT. POSITION C POSITION B CRACK CYLINDRICAL SPECIMEN
POSITION A
POSITION A
POSITION B
POSITION C
AT POSITION “A” ABOVE, THERE IS A SHARP DISCONTINUITY INDICATION AND LITTLE BACK SURFACE INDICATION. AT POSITION “C” THE DISCONTINUITY S AT MINIMUM, OR MAY NOT BE SEEN ATALL.
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UT Lecture Guide Lesson 5
TWO BASIC TECHNIQUES ARE USED IN LOCATING AND EVALUATING ANGULAR FLAWS. 1. 2.
CONTACT TESTING UTILIZES AN “ANGLE BEAM” TRANSDUCER WITH A PLASTIC WEDGE TO CHANGES THE DIRECTION OF WAVE PROPAGATION. IMMERSION TESTING USES WATER AS A COUPLANT, TILTING THE TRANSDUCER TO ACHIEVE THE NECESSARY DIRECTIONALITY.
ANGLE BEAM TRANSDUCER
PROBE
TRANSDUCER
PLASTIC WEDGE
WATER TANK
SPECIMEN SPECIMEN CONTACT TESTING
IMMERSION TESTING
THE SHAPE OR SURFACE CONDITION OF A DISCONTINUITY INFLUENCES THE INDICATION ON THE CRT. A DISCONTINUITY HAVING A ROUGH SURFACE WILL TEND TO SCATTER THE REFLECTION AS COMPARED TO A SMOOTH FLAW. NONMETALLIC INCLUSIONS ARE TYPICAL ROUGH AND WOULD SCATTER THE SOUND MORE THAN A CRACK-LIKE DISCONTINUITY.
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UT Lecture Guide Lesson 5
AIR IS A POOR MEDIUM FOR TRANSFERRING ULTRASONIC VIBRATIONS INTO LIQUIDS OR SOLIDS. THEREFORE, A COUPLANT MUST BE USED TO TRANSFER ENERGY FROM HE TRANSDUCER TO THE TEST MATERIAL. WATER IS A COMMONLY USED COPLANTAS SHOWN BELOW:
WATER
SECODARY LOBER TRANSDUCER
PRINCIPAL DIRECTION OF SOUND BEAM
SECODARY LOBER
MOST OF THE ULTRASONIC ENERGY IS CONCENTRATED ALONG THE CENTERLINE OF THE BEAM. THE SECONDARY OR SIDE LOBES FROM AT THE TRANSDUCER FACE AND RADIATE AWAY FROM THE PRINCIPLE DIRECTION OF SOUND TRAVEL. THESE SECONDARY LOBES REPRESENT AREAS OF HIGH AND LOW INTENSITIES AT THE EDGE OF THE BEAM. BECAUSE OF THE SECONDARY LOBES, THE USEFUL WIDTH OF A TRANSDUCER BEAM IS-LESS THAN THE TRANSDUCER’S PHYSICAL WIDTH. TRANSDUCER DIAMETER HAS A DEFINITE INFLUENCE ON THE SOUND BEAM TRANSMITTED THROUGH A MEDIUM. FOR A GIVEN FREQUENCY, A SMALLER TRANSDUCER HAS A GREATER BEAM SPREAD ANGLE THAN A LARGER DIAMETER TRANSDUCER AS SHOWN BELOW: SMALL DIAMETER TRANSDUCER
MEDIUM
LARGE DIAMETER TRANSDUCER
BEAM CONSTANT
BEAM DIVERGES
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MEDIUM
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UT Lecture Guide Lesson 5
CHANGING THE TRANSDUCER’S VIBRATING FREQUENCY WILL ALSO CHANGE THE BEAM SPREAD. DIVERGENCE IS INVERSELY PROPORTIONAL TO FREQUENCY. THEREFORE, A HIGH FREQUENCY TRANSDUCER HAS A MORE CONSTANT DIAMETER SOUND BEAM THAN A LOW FREQUENCY TRANSDUCER. FREQUENCY OR BY USING A LARGER DIAMETER TRANSDUCER. THE AMOUNT OF BEAM SPREAD IS DETERMINED BY THE FOLLOWING EQUATION:
SIN O = 1.22
WHERE
D
= WAVELENGTH D = DIAMETER O = HALF-ANGLE OF = BEAM SPREAD TO = HALF-POWER POINT
HALF POWER POINT (. 707 OF INTENSITY)
THE BEAM SPREAD OF A ½ INCH DIAMETER, 1 Mhz TRANSDUCER IS SHOWN TO BE 34 DEGREES. REMEMBER THAT WAVELENGTH ( ) IS DETERMINED BY DIVIDING THE VELOCITY BY THE FREQUENCY. TO CHANGE INCHES TO CENTIMETERS. MULTIPLY BY 2.54.
0O
0 = 34
O
SECONDARY LOBES
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Name _______________________________ UT LESSON 5 WORKSHEET #1
Understanding “Beam Spread” will help point out importance of selecting the proper frequency and size transducer. The length of the ultrasonic wave and the diameter of the transducer are often critical in the determination of flaw size and location. Using the information given below, determine the “Beam Spread” for the conditions listed. (a) Velocity in steel = .585 x 10º cm/sec (b) Velocity in aluminum = .625 x 10º cm/sec (c) One inch = 2.54 centimeters
(D)
Wavelength (
(E)
Sin O = 1.22
y ) = Velocity Frequency y D
________
1.
What would be the beam spread using a 1” diameter, 2.25 MHz transducer on an aluminum test part? (SHOW WORK) (3 pts)
________
2.
What would be the beam spread using a 1” diameter, one MHZ transducer on an aluminum test part? (SHOW WORK) (3 pts)
________
3.
What would be the beam spread using a one half inch diameter, 2.25 MHz transducer on a steel test part? (SHOW WORK) (3 pts)
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UT LESSON 5 WORKSHEET #1 Angle
1* 2* 3* 4* 5* 6* 7* 8* 9* 10* 11* 12* 13* 14* 15* 16* 17* 18* 19* 20* 21* 22* 23* 24* 25* 26* 27* 28* 29* 30* 31* 32* 33* 34* 35* 36* 37* 38* 39* 40* 41* 42* 43* 45*
.0175 .0349 .0523 .0698 .0872 .1045 .1219 .1392 .1564 .1736 .1908 .2079 .2250 .2419 .2588 .2756 .2924 .3090 .3256 .3420 .3584 .3746 .3907 .4067 .4226 .4384 .4540 .4695 .4848 .5000 .5150 .5299 .5446 .5592 .5736 .5878 .6018 .6157 .6293 .6428 .8561 .6691 .6820 6947 .7071
Non Destructive Testing (NDT)
Cos
Tan
Angle
Sin
Cos
Tan
.9998 .9994 .9986 .9976 .9962 .9945 .9925 .9903 .9877 .9848 .9816 .9781 .9744 .9703 .9659 .9613 .9563 .9511 .9455 .9397 .9336 .9272 .9205 .9135 .9063 .8988 .8910 .8829 .8746 .8660 .8572 .8480 .8387 .8290 .8192 .8090 .7986 .7880 .7771 .7660 .7547 .7231 .7314 7193 .7071
.0175 .0349 .0524 .0699 .0875 .1051 .1228 .1405 .1584 .1763 .1944 .2126 .2309 .2493 .2679 .2867 .3057 .3249 .3443 .3640 .3839 .4040 .4245 .4452 .4663 .4877 .5095 .5317 .5543 .5774 .6009 .6249 .6494 .6745 .7002 .7265 .7536 .7813 .8098 .8391 .8893 .9004 .9325 .9657 1.0000
46* 47* 48* 49* 50* 51* 52* 53* 54* 55* 56* 57* 58* 59* 60* 61* 62* 63* 64* 65* 66* 67* 68* 69* 70* 71* 72* 73* 74* 75* 76* 77* 78* 79* 80* 81* 82* 83* 84* 85* 86* 87* 88* 89* 90*
.7193 .7314 .7431 .7547 .7660 .7771 .7880 .7986 .8090 .8192 .8290 .8387 .8480 .8572 .8660 .8740 .8829 .8910 .8988 .9063 .9135 .9205 .9272 .9336 .9397 .9455 .9511 .9563 .9613 .9659 .9703 .9744 .9788 .9816 .9848 .9877 .9900 .9925 .9945 .9962 .9976 .9986 .9994 .9898 1.0000
.6947 .6820 .6691 .6561 .6428 .6293 .6157 .6018 .5878 .5736 .5992 .5446 .5299 .5150 .5000 .4848 .4695 .4540 .4384 .4226 .4067 .3907 .3746 .3584 .3420 .3256 .3090 .2924 .2757 .2588 .2419 .2250 .2079 .1908 .1736 .1564 .1392 .1219 .1045 .0872 .0698 .0523 .0349 .0175 .0000
1.0355 1.0724 1.1108 1.1504 1.1918 1.2349 1.2799 1.3270 1.3764 1.4281 1.4826 1.5399 1.6013 1.6643 1.7321 1.8040 1.8807 1.9626 2.0503 2.1445 2.2460 2.3559 2.4751 2.6051 2.7475 2.9042 3.0777 3.2709 3.4874 3.7321 4.0108 4.3315 4.7046 5.1446 5.6713 6.3138 7.1154 8.1443 9.5144 11.4301 14.3007 19.0811 28.6363 57.2900
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Name _______________________________ UT LESSON 5 QUIZ
________ ________ ________ ________ ________ ________ ________ ________ ________ ________ ________ ________
1.
Higher frequency transducer have less beam spread than low frequency transducers. 2. Lower frequency transducers are usually used to find the smaller defects. y 3. The longer the wavelength ( ). The greater the beam spread and better ability to locate small discontinuities. 4. When comparing two transducer of the same frequency, the larger transducer will have the greatest beam spread. 5. A rough surface on the test specimen may cause a loss in amplitude on the CRT screen. 6. If the front and back surface of a test part are not parallel, there will be a greatly reduced signal amplitude from any discontinuity in the part. 7. Long or thin specimens may cause false indications due to mode conversion of the longitudinal beam. 8. A smooth discontinuity (crack) will reflect more energy than a discontinuity will a rough surface (inclusion) 9. Both contact and immersion testing techniques can be used for performing an “angle beam” examination of a part. 10. The couplant used in ultrasonic inspection should be as thick as possible to properly direct the sound beam. 11. Where a liquid or paste couplant cannot be used, a rubber sheet may sometimes be used by placing it between the transducer and test part. 12. What would be the “Beam Spread” if the following conditions existed? A. 1” Diameter, 5 MHz transducer. B. Velocity in steel = .585 x 10 cm/sec
y
C.
Sin O = 1.22
D.
Wavelength (
D Y) =
Velocity frequency
E. One inch
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UT LESSON 5 QUIZ Angl
1* 2* 3* 4* 5* 6* 7* 8* 9* 10* 11* 12* 13* 14* 15* 16* 17* 18* 19* 20* 21* 22* 23* 24* 25* 26* 27* 28* 29* 30* 31* 32* 33* 34* 35* 36* 37* 38* 39* 40* 41* 42* 43* 45*
.0175 .0349 .0523 .0698 .0872 .1045 .1219 .1392 .1564 .1736 .1908 .2079 .2250 .2419 .2588 .2756 .2924 .3090 .3256 .3420 .3584 .3746 .3907 .4067 .4226 .4384 .4540 .4695 .4848 .5000 .5150 .5299 .5446 .5592 .5736 .5878 .6018 .6157 .6293 .6428 .8561 .6691 .6820 6947 .7071
Non Destructive Testing (NDT)
.9998 .9994 .9986 .9976 .9962 .9945 .9925 .9903 .9877 .9848 .9816 .9781 .9744 .9703 .9659 .9613 .9563 .9511 .9455 .9397 .9336 .9272 .9205 .9135 .9063 .8988 .8910 .8829 .8746 .8660 .8572 .8480 .8387 .8290 .8192 .8090 .7986 .7880 .7771 .7660 .7547 .7231 .7314 7193 .7071
Tan
Angl
.0175 .0349 .0524 .0699 .0875 .1051 .1228 .1405 .1584 .1763 .1944 .2126 .2309 .2493 .2679 .2867 .3057 .3249 .3443 .3640 .3839 .4040 .4245 .4452 .4663 .4877 .5095 .5317 .5543 .5774 .6009 .6249 .6494 .6745 .7002 .7265 .7536 .7813 .8098 .8391 .8893 .9004 .9325 .9657 1.0000
46* 47* 48* 49* 50* 51* 52* 53* 54* 55* 56* 57* 58* 59* 60* 61* 62* 63* 64* 65* 66* 67* 68* 69* 70* 71* 72* 73* 74* 75* 76* 77* 78* 79* 80* 81* 82* 83* 84* 85* 86* 87* 88* 89* 90*
-51-
.7193 .7314 .7431 .7547 .7660 .7771 .7880 .7986 .8090 .8192 .8290 .8387 .8480 .8572 .8660 .8740 .8829 .8910 .8988 .9063 .9135 .9205 .9272 .9336 .9397 .9455 .9511 .9563 .9613 .9659 .9703 .9744 .9788 .9816 .9848 .9877 .9900 .9925 .9945 .9962 .9976 .9986 .9994 .9898 1.0000
Cos
Tan
.6947 .6820 .6691 .6561 .6428 .6293 .6157 .6018 .5878 .5736 .5992 .5446 .5299 .5150 .5000 .4848 .4695 .4540 .4384 .4226 .4067 .3907 .3746 .3584 .3420 .3256 .3090 .2924 .2757 .2588 .2419 .2250 .2079 .1908 .1736 .1564 .1392 .1219 .1045 .0872 .0698 .0523 .0349 .0175 .0000
1.0355 1.0724 1.1108 1.1504 1.1918 1.2349 1.2799 1.3270 1.3764 1.4281 1.4826 1.5399 1.6013 1.6643 1.7321 1.8040 1.8807 1.9626 2.0503 2.1445 2.2460 2.3559 2.4751 2.6051 2.7475 2.9042 3.0777 3.2709 3.4874 3.7321 4.0108 4.3315 4.7046 5.1446 5.6713 6.3138 7.1154 8.1443 9.5144 11.4301 14.3007 19.0811 28.6363 57.2900
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Lesson 6 ATTENUATION, ACOUSTIC IMPEDANCE, AND RESONANCE AS SHOWN BELOW, A BEAM OF SOUND ENERGY WILL SPREADS OUT (DIVERGE) AS IT MOVES THROUGH THE SPECIMEN, AND THE INTENSITY (ENERGY) DECREASES WITH DISTANCE AWAY FROM THE TRANSDUCER AND AWAY FROM THE CENTER OF THE BEAM.
SPECIMENT
NEAR ZONE TRANSDUCER 12
O
4O
FOR A GIVEN SIZE TRANSDUCER HIGH FREQUENCY TRANSDUCERS PRODUCE NARROWER SOUND BEAMS THAN LOW FREQUENCY TRANSDUCERS. FOR THE PURPOSE OF ILLUSTRATION, ULTRASONIC SOUND CAN BE VIEWED AS A NARROW CONE-SHAPED BEAM WHICH IS DIVIDED INTO TWO ZONES. THE INTENSITY IN THE NEAR ZONE VARIES IRREGULARLY DUE TO SOUND WAVE INTERACTION CLOSE TO THE TRANSDUCER. THIS PREVENTS RELIABLE DETECTION OF DISCONTINUITIES CLOSE TO THE SURFACE. IN THE FAR ZONE, THE INTENSITY (ENERGY) DECREASES STEADILY DUE TO BOTH ATTENUATION AND BEAM SPREAD SPECIMEN (MATERIAL)
TRANSDUCER (TRANSMITTER)
X
NEAR ZONE
Y
FAR
TRANSDUCER (RECEIVER)
ZONE
THE INTENSITY AT POINT “Y” ABOVE IS LESS THAN AT POINT “X”. ATTENUATION IS THE TERM USED TO DESCRIBE THIS CONDITION OF ENERGY LOSS. ATTENUATION MEANS THE PROCESS OF LESSENING THE AMOUNT. THE PRIMARY REASONS FOR ATTENUATION ARE ABSORPTION AND SCATTERING OF THE ULTRASONIC ENERGY.
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UT Lecture Guide Lesson 6
ATTENUATION IS DIFFERENT IN DIFFERENT MATERIALS, DEPENDING ON THE ABSORPTION AND SCATTERING OF THE SOUND ENERGY, ANOTHER PHENOMENON WHICH PERTAINS TO THE INTERRELATIONSHIP OF THE SOUND AND MATERIAL PROPERTIES (S “ACOUSTIC IMPEDANCE.” THIS TERM SHOULD NOT BE CONFUSED WITH “ATTENUATION.” “ACOUSTICAL IMPEDANCE” (Z) IS DEFINED AS THE PRODUCT OF THE DENSITY ( ) AND SOUND VELOCITY (V) WITHIN A GIVEN MATERIAL IMPEDANCE = DENSITY X VELOCITY, OR Z = V IMPEDANCE VALUES FOR TYPICAL MATERIALS ARE SHOWN BELOW:
IMPEDANCE MATERIAL
(GRAM/CM2 - SEC)
AIR
0.000033 X 10
WATER
0.149 X 10
ALUMINUM
1.72 X 10
STEEL
4.56 X 10
6
6
VELOCITY
DENSITY
(CM/SEC)
(GRAM/CM3)
0.33 X 10
5
1. 49 X 10
6
6.35 X 10
6
5.85 X 10
5
0.001 1.00
5
2.71
5
7.8
ATTENUATION IS DEFINED AS THE LOSS OF ENERGY (ACOUSTIC) PER UNIT OF DISTANCE. FOR ULTRASONIC WAVE PROPAGATION, THE ATTENUATION CONSTANT IS GIVEN BY: I2 I1
= e-2
WHERE I2 I1
=
= ATTENUATION CONSTANT RATIO OF INTENSITIES AT TWO POINTS A UNIT DISTANCE APART
I1 > I2
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UT Lecture Guide Lesson 6
IF ACOUSTIC ENERGY IS TRANSMITTED INTO TWO PICES OF PERFECTLY BONDED INDENTICAL STEEL, WE FIND THE SOUND HAS THE SAME VELOCITY THROUGH BOTH, WITH AN IMPEDANCE RATIO OF 1 TO 1.
STEEL
STEEL
TRANSDUCER SOUND BEAM
VELOCITY REMAINS CONSTANT
AN IMPEDANCE RATIO OF ANYTHING LESS OR GREATER THAN 1 TO 1 IS LESS THAN IDEAL. AS SHOWN BELOW A LARGE PORTION OF THE SOUND BEAM FROM A WATER TO STEEK INTERFACE WILL REFLECT BACK TOWARDS THE TRANSDUCER AND NEVER ENTER THE PART.
WATER TRANSDUCER
SOUND BEAM STEEL
TO DETERMINE HOW MUCH OF THE ENERGY IS REFLECTED YOU CAN USE 2 THE FOLLOWING FORMULA: Z - Z 1 2 REFLECTION FACTOR (R) = Z + Z 1 2 Z = ACOUSTICAL IMPEDANCE IN THE ILLUSTRATION ABOVE , HOW MUCH OF THE SOUND ENERGY IS REFLECTED FROM THE WATER TO STEEL INTERFAACE? 2 2 4.411 4. 56 .149 = = 88 PERCENT REFLECTED R =
4. 56 + .149
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UT Lecture Guide Lesson 6
RESONANCE CAN BE DEFINED AS THE CHARACTERISTIC OF A VIBRATING BODY TO RESONATE OR VIBRATE IN SYMPATHY WITH A VIBRATION SOURCE. AS SHOWN BELOW, A RESONANT CONDITION WILL EXIST ANY TIME A CONTINOUS LONGITUDINAL WAVE IS INTRODUCED INTO A SPECIMEN AND REFLECTED "IN PHASE" WITH THE INCOMING WAVE. COUPLANT
TRANSDUCER
STANDING WAVE
RESONANCE WILL OCUR ONLY WHEN THE THICKNESS OF A SPECIMEN IS EQUAL TO A HALF-WAVELENGTH OR AN EXACT MULTIPLE OF A HALFWAVELENGTH. SHOWN BELOW IS A "FUNDAMENTAL FREQUENCY" AND MULTIPLES CALLED "HARMONICS"
TEST SPECIMEN
REFLECTED WAVE
TRANSDUCER
1
INCIDENT WAVE
MHz (FUNDAMENTAL FREQUENCY)
THICKNESS = 1/2 WAVELENGTH
2
MHz (2ND HARMONIC)
THICKNESS = 1 WAVELENGTH
3
MHz (3RD HARMONIC)
THICKNESS = 1-1/2 WAVELENGTH
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UT Lecture Guide Lesson 6
ULTRASONIC UNITS USING THE PRINCIPLE OF RESONANCE WERE COMMONLY USED FOR THICKNESS MEASUREMENT AND BOND OR LAMINATION INSPECTION. HOWEVER, PULSE-ECHO UNITS HAVE BEEN REFINED TO PERFORM MOST OF THESE FUNCTIONS AND RESONANT INSTRUMENTS ARE RARELY USED. RESONANCE OCCURS WHEN THE MATERIAL THICKNESS IS EQUAL TO A HALF-WAVENGTH OR EXACT MULTIPLES. THE WAVELENGTH CAN BE CHANGED BY VARYING THE FREQUENCY THE FUNDAMENTAL RESONANT FREQUENCY IS THE FREQUENCY AT WHICH A SPECIMEN WILL RESONATE. HARMONICS ARE EXACT MULTIPLES OF THE FUNDAMENTAL (MINIMUM) RESONANT FREQUENCY. THE FUNDAMENTAL RESONANT FREQUENCY CAN BE FOUND BY: V
F =
F = FUNDAMENTAL RESONANT FREQUENCY V = VELOCITY OF LONGITUDINAL WAVE T = THICKNESS OF MATERIAL
2T
TRANSDUCER
MATERIAL
DISCONTINUITY
"B"
"A" STANDING WAVE
AS SHOWWN ABOVE IN "A" THE FREQUENCY HAS BEEN ADJUSTED UNTIL A STANDING WAVE "RESONANCE" HAS BEEN ESTABLISHED. IF THE TRANSDUCER IS MOVED TO POSITION "B" THE MATERIAL WILL STOP RESONATING UNTIL THE FREQUENCY (WAVELENGTH) IS ADJUSTED TO AGAIN ESTABLISH RESONANCE AS SHOWN.
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Name _______________________________ UT LESSON 6 WORKSHEET #1
A. B.
Using the information given below, solve the problems relating to “reflection factors”. The chart below lists the common impedance values.
(IMPEDANCE = VELOCITY X DENSITY) MATERIAL AIR
IMPEDANCE 2 (GRAM/CM - SEC) 0.000033 X 106 6
DENSITY 3 (GRAM / CM )
VELOCITY (CM / SEC) 0.33 X 105
0.001
5
1.00
WATER
0.149 X 10
ALUMINUM
1.72 X 106
6.35 X 105
2.71
STEEL
4.56 X 106
5.85 X 105
7.8
Z C. Reflection factor =
Z 1 - 2 Z1 + Z2
1.49 X 10
2
Z. = Acoustic Impedance Water
Z1 Aluminum Z2
________
1.
What percentage of the original sound energy will be reflected back to the probe at the water to aluminum interface? (SHOW WORK) (3 pts)
________
2.
What percentage of the original sound energy will finally enter the water on its way back to the transducer from the back surface of the aluminum part? (SHOW WORK) (3 pts). Only consider the reflection factors, do not consider the normal attenuation that would occur in the material it self.
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Name _______________________________ UT LESSON 6 WORKSHEET #1 (continued)
________
3.
A clad material is to be tested for bond defects. One material has a thickness of 2 2 0.3 inches and an acoustic impedance of 5.0 x 10 gram/cm - second and the 2 other material is 4.0 inches thick and has an acoustic impedance of 4.5 x 10 2 gram/cm - second. If the bond is perfect and acceptable, what percentage of sound would you expect to be reflected from the interface? (SHOW WORK) (3 pts)
________
4.
Would you inspect the bonded material through the thick side or through the thin side? Why? (2 pts)
________
5.
On the CRT screen below, using a 5 inch screen range, sketch the approximate location and amplitude of the pips from an acceptable bond condition. (2 pts)
2
1
0
3
5
4
-2 -1 0 -1 -2
-2 -1 0 -1 -2
0
•
1
2
3
4
5
6
7
8
9
10
As a general rule, “R” should be less than 20% for adequate bond inspection.
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Name _______________________________ UT LESSON 6 QUIZ
________ ________ ________ ________ ________ ________ ________ ________ ________ ________
1.
The gradual loss of energy as a sound beam travels through a material is called attenuation. 2. Whenever possible, the UT inspection should be done in the “near zone” before the sound can spread out and attenuated. 3. “Acoustic Impedance” refers to resistance of sound propagation through a part. 4. Compared to steel, air has a very high acoustic impedance value. 5. The original ultrasonic velocity remains the same regardless of the media it is passing through. 6. A sound beam with a given energy will travel farther in aluminum than in steel before it is attenuated by the same amount. 7. A fine grained material will usually caused less attenuation than a coarse grained material. 8. The terms “Intensity” and Impendence” mean the same thing. 9. In immersion testing, it is typical that less than 1% of the original sound energy is returned to the transducer. 10. Using the information given below, what would be the reflection Factor at the interface shown between the water (Z1) and steel (Z2)? (SHOW WORK) (3 pts)
2
Z1 - Z2
Reflection Facto (R) =
Z1 + Z2
=
Z = Acoustic Impedence
TRANSDUCER
WATER
Z1
Z2
STEEL
CRACK BEAM
MATERIAL AIR
IMPEDANCE 2 (GRAM/CM - SEC) 0.000033 X 106 6
DENSITY 3 (GRAM / CM )
VELOCITY (CM / SEC) 0.33 X 105
0.001
5
1.00
WATER
0.149 X 10
ALUMINUM
1.72 X 106
6.35 X 105
2.71
STEEL
4.56 X 106
5.85 X 105
7.8
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Lesson 7 DISPLAYING ULTRASONIC INDICATIONS THERE ARE THERE BASIC TYPES OF VISUAL DISPLAYS WHICH ARE COMMONLY USED TO EVALUATE THE SOUNDNESS OR QUALITY OF A MATERIAL BEING TESTED; A-SCAN, B-SCAN AND C-SCAN. A-SCAN IS A "TIME VERSUS AMPLITUDE" DISPLAY WHICH REVEALS A DISCONTINUITY USING A "PIP" ON A CATHODE-RAY TUBE (CRT).
INITIAL PULSE BACK SURFACE REFLECTION AMPLITUDE DISCONTINUITY HORIZONTAL SWEEP
TIME
THE A-SCAN PRESENTATION, AS HAS BEEN DISCUSSED, IS READ FROM LEFT TO RIGHT. THE HEIHT OF A PIP CAN BE COMPARED TO THE HEIHT OF A PIP FROM A KNOWN REFERENCE REFLECTOR TO GIVE AN INDICATION OF RELATIVE DISCONTINUITY SIZE. A-SCAN PRESENTATION
AMPLITUDE
HORIZONTAL SWEEP
DISCONTINUITY INDICATION
INITIAL PULSE TRANSDUCER
BACK SURFACE REFLECTION
DISCONTINUITY
MATERIAL
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UT Lecture Guide Lesson 7 B-SCAN PRESENTATION, AS SHOWN BELOW, TYPICALLY USES AN OSCILLOSCOPE SCREEN TO DISPLAY A CROSS-SECTIONAL VIEW OF THE MATERIAL BEING TESTED. THE IMAGE IS RETAINED ON THE CRT LONG ENOUGH TO EVALUATE THE SAMPLE AND TO PHOTOGRAPH THE SCREEN FOR A A PERMANENT RECORD.
FRONT SURFACE DISCONTINUITIES
THICKNESS OF TEST MATERIAL
BACK SURFACE B-SCAN PRESENTATION
C-SCAN IS A "PLAN VIEW" PRESENTATION SIMILAR TO AN X-RAY PICTURE. AS SHOWN BELOW, THE C-SCAN SHOWNS THE SHAPE AND LOCATION OF THE DISCONTINUITY, BUT DOES NOT SHOW THE DEPTH.
DISCONTINUITIES
C-SCAN PRESENTATION
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UT Lecture Guide Lesson 7 HIGH SPEED ULTRASONIC SCANNING GENERALLY UTILIZES THE C-SCAN PRESENTATION. AS SHOWN BELOW, SOME RECORDERS USE A CHEMICALLY TREATED PAPER. THE PAPER MOVEMENT IS SYNCHRONIZED WITH THE MOVEMENT OF THE TRANSDUCER ACROSS THE TEST SURFACE.
RECORDING PAPER FEED
MOTION OF TRANSDUCER
PRINT BAR
SCAN LINES
HELIX DRUM DISCONTINUITY
DISCONTINUITY
THE ADNANTAGE OF THE C-SCAN IS ITS SPEED AND ABILITY TO PRODUCE A PERMANENT RECORD. HOWEVER, THE SCAN SHOWS ONLY LENGTH AND WIDTH, BUT NOT DEPTH.
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UT Lecture Guide Lesson 7 A TYPICAL BRIDGE/MANIPULATOR IS SHOWN FOR A BASIC ULTRASONIC IMMERSION TEST. WHEN A C-SCAN IS TO BE MADE, ELECTRIC MOTORS ARE UTILIZED TO ACTIVATE THE TRAVELING MECHANISMS AND THE UP AND DOWN MOVEMENT OF THE SEARCH TUBE.
TANK WITH MOTORIZED BRIDGE
SCANNER TURBE MANIPULATOR TRANSDUCER
CARRIACE OR BRIDGE
TEST SPECIMEN SUPPORT FOR TEST SPECIMEN
A TYPICAL A-SCAN PRESENTATION IS SHOWN BELOW USING CONTACT TESTING WITH AN ANGLE BEAM TRANSDUCER THE PROCEDURE USED TO CALIBRATE THE UT UNIT IS SIMILAR TO NORMAL BEAM TESTING AND REQUIRES A CALIBRATION BLOCK WITH A KNOWN SIZE REFLECTION SURFACE ATA KNOWN METAL TRAVEL
ANGLE BEAM TRANSDUCER
A A
B
SHEAR WAVES
CRT
B
DISCONTINIUTY
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UT Lecture Guide Lesson 7 A CALIBRATION BLOCK (IIW TEST BLOCK FURTHER DISCUSSED IN LESSON 8) IS SHOWN BELOW WITH A KNOW DISTANCE OF A INCHES TO THE CURVED SURFACE. USING THE SWEEP AND DELAY CONTROLS, THE PIPS ARE ADJUSTED TO SHOWN MULTIPLES OF 4 INCHES ON THE CRT.
NOTCH
4“
0
2
4
6
8
IF THE MINATURE ANGLE BEAM CALIBRATION BLOCK SHOWN BELOW WERE USED TO CALIBRATE THE ABOVE CRT SCREEN, WHERE WOULD THE PIPS APPEAR?
2”
1”
MINIATURE ANGLE BEAM
DEPENDING ON THE DIRECTION OF THE ANGLE BEAM PROBE, THE PIPS WOULD EITHER APPEAR AT ONE, FOUR, AND SEVEN INCHES OR TWO, FIVE, AND EIGHT INCHES.
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UT Lecture Guide Lesson 7 THE ANGLE BEAM TECHNIQUE IS OFTEN USED FOR WELD INSPECTION AS SHOWN BELOW.
2nd LEG
4th LEG
3rd LEG
1st LEG
1 st skip distance (”V” PATH)
2 nd skip distance (”V” PATH)
TYPICALLY, THE WELD SHOULD BE INSPECTED IN THE 1 ST OR 2 ND LEG WHENEVER POSSIBLE AS SHOWN BELOW.
SKIP DISTANCE
VIEW A
VIEW C
VIEW B
TO ASSIST IN EVALUATING THE RESULTS OF ANGLE BEAM INSPECTION, A DIRECT READING ULTRASONIC CALCULATOR IS COMMONLY USED.
0
1
3
2
5
4
6
7
8
9
10
80 1
1
70 60
2
2
50 40
THE HORIZONTAL SCALE ACROSS THE TOP OF THE CARD REPRESENTS THE NUMBER OF INCHES BETWEEN THE TRANSDUCER AND THE CENTER OF THE WELD. THE VERTICAL SCALE REPRESENTS SPECIMEN THICKNESS AND THE ARC SHOWN THE ANGLE OF THE SOUND BEAM. Non Destructive Testing (NDT)
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UT Lecture Guide Lesson 7 THE FOLLOWING IS AN EXAMPLE OF A TYPICAL ANGLE BEAM INSPECTION USING THE ULTRASONIC CALCULATOR. A DOUBLE VEE WELD WITH AN OPENING OF 30 DEGREES IN A 2” STEEL PLATE USING A 60 DEGREE SHEAR WAVE IN THE SPECIMEN.
POINT OF INCIDENCE 1 2
3
DASHED LINE 4
B 5
6
7
8
9
10
0 7 80
1
6
1 70
2
1 DISCONTINUITY
5 3
2 40
50
60
4
2 A
THE FOLLOWING PROCEDURE SHOULD BE USED IN SETTING UP THE CALCULATOR: 1. DRAW A LINE REPRESENTING THE SOUND PATH FROM THE UPPER LEFT CORNER THROUGH THE 60 DEGREE MARK ON THE ARC, EXTENDING TO THE 2 - POINT REPRESENTING THE PLATE THICKNESS. CALIBRATE THE HORIZONTAL SWEEP OF THE CRT TO REPRESENT BEAM TRAVEL DISTANCE IN THE MATERIAL BEING TESTED. 2. TO SHOW THE FULL SKIP DISTANCE OF THE SOUND BEAM, YOU THEN DOUBLE THE 3 7/16” AND MARK THAT POINT AT APPROXIMATELY 6 7/8” (POINT “B” ABOVE) 3. NEXT, DRAW THE 30 DEGREE FEE WELD ON THE PLASTIC SLIDE OR TRANSPARENT PAPER THAT SLIDES BACK AND FORTH OVER THE CALCULATOR. 4. AS SHOWN ABOVE, A DISCONTINUITY IS DISPLAYED ON THE CRT SCREEN AT 5.5”.THE OPERATOR THEN MEASURES THE DISTANCE BETWEEN THE CENTER OF THE TRANSDUCER (EXIT POINT) AND THE CENTER OF THE WELDMENT (4 5/8”) AND SLIDES THE TRANSPARENT PAPER TO THE SAME DISTANCE. 5. THE POSITION OF THE DISCONTINUITY IS INDICATED AND CAN BE EVALUATED.
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Name _______________________________ LESSON 7 WORKSHEET #1
Angle beam inspection requires that the operator understand how the sound beam is reflected within the specimen. On the CRT screen provided, indicate the location of each pip based on the sound path distances shown. (3 pts each)
0
1
A
5
4
3
15 INCH SCREEN RANGE
-2 -1 0 -1 -2
3”
3”
2
-2 -1 0 -1 -2
0
0
1
B
2
3
1
4
5
2
6
7
8
9
5
4
3
10
20 INCH SCREEN RANGE
2”
8”
-2 -1 0 -1 -2
-2 -1 0 -1 -2
0
0
2”
C
2
3
1
4
5
2
6
7
8
9
8”
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10
5
4
3
12 INCH SCREEN RANGE
-2 -1 0 -1 -2
-2 -1 0 -1 -2
0
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10
Name _______________________________ UT LESSON 7 QUIZ
________
1.
On a typical B-Scan, the horizontal sweep represents time and the vertical deflection represents amplitude. 2. The B-Scan can display how deep the discontinuity is below surface of the specimen. 3. The typical A-Scan is the display commonly used for recording a permanent record with the immersion inspection technique. 4. The vertical pip on an A-Scan can be used to compare the relative size of a discontinuity. 5. The C-Scan display will indicate length and width of a discontinuity, but it cannot show death. 6. To obtain an A-Scan display with ultrasonic immersion testing, it is necessary to auto mate the bridge/manipulator with electric motors. 7. The “Ultrasonic Calculator” can be used in weld inspection to indicate the location of a discontinuity in the weldment. 8. Whenever possible, the weld should be inspected in the “2nd Skip Distance.” 9. The calibration of a UT instrument for sound path distance can be performed using the curved surface of the “IIW Block” 10. To accurately utilize the “Ultrasonic Calculator” it is necessary to accurately measure the distance from center line of the weld to the exist point of the transducer. 11. Using an E-Screen range on the CRT below, indicate where the “pips” should appear if the instrument is to be properly calibrated for sound path distance in the block shown (SHOW WORK) (3 pts).
________ ________ ________ ________ ________ ________ ________ ________ ________
________
1”
2
1
0
3
5
4
2”
MINIATURE ANGLE BEAM
0
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-2 -1 0 -1 -2
-2 -1 0 -1 -2
1
2
3
4
5
6
7
8
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10
Lesson 8 ULTRASONIC TRANSDUCERS AND STANDARD REFERENCE BLOCKS THE ULTRASONIC TRANSDUCER IS THE HEART OF THE UT TEST SYSTEM.
SEALED CASE
SIGNAL CONNECTOR BACKING
GROUND CONNECTOR ELECTRODES
CRYSTAL
THE CRYSTAL MATERIAL IN AN ULTRASONIC TRANSDUCER IS MADE OF PIEZOELECTRIC MATERIAL SUCH AS QUARTZ, LITHIUM SULFATE AND POLARIZED CERAMICS. 1. QUARTZ WAS THE FIRST MATERIAL USED. IT HAS VERY STABLE FREQUENCY CHARACTERISTICS. HOWEVER, QUARTZ IS A POOR GENERATOR OF ACOUSTIC ENERGY AND HAS GENERALLY BEEN REPLACED BY MORE EFFICIENT MATERIALS. 2. LITHIUM SULFATE IS A VERY EFFICIENT RECEIVER OF ACOUSTIC ENERGY, BUT IS FRAGILE, SOLUBLE IN WATER AND LIMITED TO USE AT TEMPERATURES BELOW 165OF. 3. POLARIZED CERAMICS PRODUCE THE MOST EFFICIENT GENERATORS OF ACOUSTICS ENERGY BUT THEY DO HAVE A TENDENCY TO WEAR. COMMON POLARIZED CERAMICS INCLUDE B A R I U M T I TA N AT E , L E A D M E TA N I O B AT E , A N D L E A D ZIRCONATE/TITANATE. THE CAPABILITY OF ATRANSDUCER IS DESCRIBED BY THREE TERMS: 1. SENSITIVITY. THE ABILITY TO DETECT SMALL DISCONTINUITIES. 2. RESOLUTION. THE ABILITY TO SEPARATE THE SOUND REFLECTIONS FROM TWO DISCONTINUITIES CLOSE TOGETHER IN DEPTH OR TIME. 3. EFFICIENCY. ENERGY CONVERSION EFFECTIVENESS.
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UT Lecture Guide Lesson 8 SENSITIVITY OF A TRANSDUCER IS RATED BY ITS ABILITY TO DETECT A CERTAIN SIZE FLAT-BOTTOM HOLE, AT A SPECIFIED DEPTH, IN A STANDARD REFERENCE BLOCK. THE SMALLER THE DETECTABLE HOLE, THE GREATER THE SENSITIVITY. TRANSDUCER SENSITIVITY IS MEASURED BY THE AMPLITUDE OF ITS RESPONSE FROM AN ARTIFICIAL DISCONTINUITY IN A STANDARD REFERENCE BLOCK THE REFERENCE BLOCK IS NECESSARY, BECAUSE EVEN TRANSDUCERS OF THE SAME SIZE, FREQUENCY AND MATERIAL DO NOT ALWAYS PRODUCE THE SAME AMPLITUDE SIGNAL FROM A GIVEN REFLECTOR. TRANSDUCER
REFERENCE BLOCK
FLAT BOTTOMED HOLE
RESOLUTION IS THE ABILITY TO SEPARATE (DISTINGUISH BETWEEN) THE SOUND REFLECTIONS FROM A DISCONTINUITY CLOSE TO A BOUNDARY OR TWO DISCONTINUITIES CLOSE TOGETHER IN DEPTH OR TIME.
POOR RESOLUTION
GOOD RESOLUTION
INITIAL PULSE
INITIAL PULSE BACK SURFACE REFLECTION
BACK SURFACE REFLECTION
DISCONTINUITY
DISCONTINUITY
TIME
TIME
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UT Lecture Guide Lesson 8 TRANSDUCER MATERIALARE USUALLY CUT IN TWO WAYS: 1. CRYSTALS CUT PERPENDICULAR TO THE X-AXIS PRODUCE LONGITUDINAL WAVES. 2. CRYSTALS CUT PERPENDICULAR TO THE Y-AXIS PRODUCE SHEAR WAVES. AS SHOWN BELOW, MOST CRYSTALS USED FOR UT ARE CUT PERPENDICULAR TO THE X-AXIS. CRYSTAL DEFORMATION AXIS
X-AXIS
Y-AXIS
Z-AXIS
SIZE IS A CONTRIBUTING FACTOR IN PERFORMANCE OF ATRANSDUCER. 1. THE LARGER DIAMETER THE TRANSDUCER, THE LESS THE SOUND BEAM WILL SPREAD FOR A GIVEN FREQUENCY. 2. HOWEVER, THE SMALL, HIGH FREQUENCY TRANSDUCER ARE BETTER ABLE TO DETECT VERY SMALL DISCONTINUITIES. 3. THE LARGER THE TRANSDUCER, THE MORE SOUND ENERGY IT TRANSMITS INTO THE TEST PART. LARGE LOW FREQUENCY TRANSDUCERS ARE OFTEN USED TO GET MORE PENETRATION. 4. LARGE SINGLE CRYSTAL TRANSDUCERS ARE GENERALLY LIMITED TO THE LOWER FREQUENCIES. HIGH FREQUENCY CRYSTALS ARE SUSCEPTIBLE TO DAMAGE BECAUSE THEYARE VERY THIN.
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UT Lecture Guide Lesson 8 THE FREQUENCY OF A TRANSDUCER IS AN IMPORTANT FACTOR IN ITS APPLICATION. 1. THE HIGHER THE FREQUENCY OF A TRANSDUCER, THE LESS THE SOUND BEAM WILL SPREAD AND THE GREATER THE SENSITIVITY AND RESOLUTION. WHEN THE SOUND BEAM IS SPREAD AS SHOWN BELOW, LESS SOUND IS LIKELY TO BE REFLECTED FROM A SMALL DISCONTINUITY HIGH FREQUENCY TRANSDUCER
LOW FREQUENCY TRANSDUCER
DISCONTINUITY
FIG. 1B
FIG. 1A
2. THE LOWER THE FREQUENCY, THE DEEPER THE SOUND PENETRATION AND THE LESS SCATTER. THE GREATER BEAM SPREAD AIDS IN DETECTING REFLECTORS WHICH ARE NOT PERPENDICULAR TO THE AXIS OF THE SOUND BEAM. 3. CRYSTALS THICKNESS IS ALSO RELATED TO TRANSDUCER FREQUENCY. THE HIGHER THE FREQUENCY OF THE TRANSDUCER, THE THINNER THE CRYSTAL WILL BE. MOST ULTRASONIC TESTING IS DONE BETWEEN 0.2 MHz AND 25 Mhz AND CRYSTALS CUT FOR USE ABOVE 10 MHz ARE TO THIN AND FRAGILE FOR CONTACT TESTING. THEREFORE, TRANSDUCERS WITH OPERATING FREQUENCIES ABOVE 10 MHz ARE USED PRIMARILY FOR IMMERSION TESTING.
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UT Lecture Guide Lesson 8 TRANSDUCERS FOR CONTACT TESTING AND IMMERSION TESTING ARE ESSENTIALLY THE SAME BUT USUALLYARE NOT INTERCHANGEABLE. MOST CONTACT TESTING TRANSDUCERS HAVE WEAR PLATES IN FRONT OF THE PIEZOELECTRIC ELEMENT TO PROTECT IT. THE EXCEPTION TO THIS IS A QUARTZ TRANSDUCER. AS SHOWN BELOW, CONTACT TRANSDUCERS CAN BE EITHER “STRAIGHT BEAM” OR “ANGLE BEAM.” TRANSDUCER B
TRANSDUCER A LUCITE
CERAMIC
STRAIGHT BEAM TRANSDUCERS USUALLY HAVE A LUCITE, CERAMIC, OR QUARTZ WEAR PLATE IN FRONT OF THE CRYSTAL. ANGLE BEAM TRANSDUCERS HAVE THE WEAR PLATE WEDGE-SHAPED TO PRODUCE THE DESIRED REFRACTED ANGLE. AS SHOWN ABOVE, THE LUCITE WEDGE PROTECTS THE FACE OF THE CRYSTAL AND DETERMINES THE ANGLE OF INCIDENCE OF THE SOUND BEAM ON THE TEST PART. AS HAS BEEN DISCUSSED, WHEN SOUND WAVES ARE DIRECTED INTO THE TEST PART AT AN ANGLE, THEY ARE DIVIDED INTO LONGITUDINAL AND SHEAR WAVES BY REFRACTION. MOSTANGLE BEAM TESTING IS DONE WITH SHEAR WAVES.
STRAIGHT BEAM TRANSDUCER
ANGLE BEAM TRANSDUCER
LONGITUDINAL WAVES
SHEAR WAVES
DISCONTINUITY
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UT Lecture Guide Lesson 8 THE ANGLE BEAM PROBE CAN ALSO BE USED TO GENERATE SURFACE WAVES. AS WE HAVE DISCUSSED, SURFACE WAVES ARE GENERATED WHEN THE INCIDENT ANGLE OF THE SOUND BEAM REACHES THE SECOND OR UPPER CRITICALANGLE. MOST ANGLE BEAM CONTACT TRANSDUCERS ARE IDENTIFIED. BY THE REFRACTED SHEAR WAVE PRODUCED (70O, 60O, ETC.), IN A SPECIFIC MATERIAL, USUALLY STEELAND ALUMINUM. SPHERICALLY GROUND AND CYLINDRICALLY GROUND ACOUSTICAL LENSES ARE COMMONLY ADDED TO IMMERSION TYPE TRANSDUCERS. THEYARE USED TO: 1. IMPROVE SENSITIVITYAND RESOLUTION. 2. COMPENSATE FOR TEST PART CONTOURS. 3. EXAMINE A GIVEN DEPTH OF THE TEST PART MORE CAREFULLY. AS SHOWN BELOW, CYLINDRICALLY GROUND LENSES FOCUS THE SOUND ENERGY TO A LINE. SPHERICALLY GROUND LENSES FOCUS THE SOUND ENERGY TO A POINT.
WATER
TRANSDUCER
BEAM
ACOUSTICAL LENS
METAL
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UT Lecture Guide Lesson 8 CYLINDRICAL LENSES ARE USED IN TWO WAYS: 1. TO INCREASE THE SENSITIVITYAND RESOLUTION OF EQUIPMENT. 2. FOR CONTOUR CORRECTION AS SHOWN BELOW. THE LENS CAN BE GROUND SPECIALLY TO DIRECT THE SOUND ENERGY NORMAL (PERPENDICULAR) TO A CURVED SURFACE ATALL POINTS.
CONTOUR CORRECTION LENS
FLAT SHOE
CRT SCREEN DISPLAY
TUBING
TUBING VIEW A
VIEW B
SPHERICAL LENSES CONCENTRATE THE SOUND ENERGY INTO A CONE SHAPED BEAM. 1. THE FOCUSING INCREASES ITS INTENSITY, BUT SHORTENS ITS USEFUL RANGE. 2. WHILE THE CYLINDERICAL LENS ABOVE HAS A GREATER WIDTH, THE SPHERICAL LENS HAS THE GREATEST SENSITIVITY. 3. THE SPHERICAL LENS IS OFTEN USED WHEN IMMERSION TESTING PARTS HAVING A ROUGH SURFACE. FOCUSED TRANSDUCERS ARE DESCRIBED BY THEIR FOCAL LENGTH. THE SHORT FOCAL LENGTHS ARE FOR EXAMINING AREAS OF THE SPECIMEN CLOSE TO THE SURFACE. LONGER FOCAL LENGTHS ARE FOR INCREASINGLY DEEPER AREAS.
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UT Lecture Guide Lesson 8 TRANSDUCERS COME IN MANY SHAPES, SIZES AND PHYSICAL CHARACTERISTICS. SOME COMMON TYPES INCLUDE PAINT-BRUSH, DUAL ELEMENT, SINGLE ELEMENT, ANGLE BEAM, FOCUSED, MOSAIC, CONTACT, AND IMMERSION. SINGLE ELEMENT TRANSDUCERS MAY BE TRANSMITTERS ONLY, RECEIVERS ONLY, OR BUT TRANSMITTER AND RECEIVER. DOUBLE ELEMENT TRANSDUCERS (AS SHOWN BELOW) MAY BE EITHER SINGLE TRANSDUCERS MOUNTED SIDE BY SIDE OR STAKED. IN A DOUBLE ELEMENT TRANSDUCER, ONE IS A TRANSMITTER AND THE OTHER A RECEIVER. TRANSMITTER
RECEIVER TRANSMITTER
RECEIVER SOUND BARRIER
SOUND BARRIER
SIDE BY SIDE
STACKED
DOUBLE ELEMENT TRANSDUCERS HAVE BETTER NEAR SURFACE RESOLUTION BECAUSE THE RECEIVER CAN RECEIVER DISCONTINUITY SIGNALS BEFORE THE TRANSMITTER COMPLETES ITS TRANSMISSION. DISCONTINUITY OBSCURED BY INITIAL PULSE
COAXIAL CABLE TRANSDUCER
DISCONTINUITY SWEEP TEST SPECIMEN
MARKER
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UT Lecture Guide Lesson 8 STANDARD REFERENCE BLOCKS IN ULTRASONIC TESTING, DISCONTINUITIES ARE USUALLY COMPARED TO A REFERENCE STANDARD. THE STANDARD MY BE ONE OF MANY REFERENCE BLOCKS OR SETS OF BLOCKS SPECIFIED FOR A GIVEN TEST. REFERENCE BLOCKS COME IN MANY DIFFERENT SHAPES AND SIZES AND THIS LESSON WILL DISCUSS ONLY A FEW OF THOSE COMMONLY USED. A TYPICAL BLOCKS IS SHOWN BELOW
TEST SURFACE
B C A FLAT-BOTTOM HOLE
A = DIAMETER OF FBH B = METAL DISTANCE FROM TEST SURFACE TO FBH C = METAL DISTANCE FROM TEST SURFACE TO BOTTOM OF BLOCK
MOST REFERENCE BLOCKS HAVE THE FOLLOWING IN COMMON: 1. THEYARE MADE FROM CAREFULLY SELECTED MATERIAL 2. THE MATERIAL MUST HAVE THE PROPER ATTENUATION, GRAIN SIZE, HEAT TREATMENTAND BE FREE OF DISCONTINUITIES. 3. ALL DIMENSIONS MUST BE PRECISELY MACHINED. 4. ALL HOLES MUST BE FLAT-BOTTOMED AND HAVE A SPECIFIED DIAMETER TO BE AN IDEAL REFLECTOR. 5. SIDE DRILLED HOLE DIAMETER MUST BE CAREFULLY CONTROLLED. THREE COMMONLY USED SETS OF STANDARD REFERENCE BLOCKS ARE: 1. ARE AMPLITUDE BLOCKS 2. DISTANCE AMPLITUDE BLOCKS 3. ASTM BASIC SET OF ARE AND DISTANCE AMPLITUDE BLOCKS. AREAAMPLITUDE BLOCKS PROVIDE STANDARDS FOR DISCONTINUITIES OF DIFFERENT SIZES, AT THE SAME DEPTH. D I S TA N C E A M P L I T U D E B L O C K S P R O V I D E S TA N D A R D S F O R DISCONTINUITIES OF THE SAME SIZE AT DIFFERENT DEPTHS.
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UT Lecture Guide Lesson 8 THE ASTM BASIC SET OF AREA/DISTANCE AMPLITUDE BLOCKS CONSISTS OF TEN, TWO INCH DIAMETER BLOCKS AS SHOWN BELOW:
FLAT-BOTTOM HOLE (FB) DIA (SEE TABLE)
TEST TARGET SURFACE
METAL DISTANCE (SEE TABLE)
3/4 INCH
METAL DISTANCE, INCHES
1/8
1/4
1/2
3/4
1-1/2
3
3
3
6
6
FBH DIA IN 64 THS INCH
5
5
5
5
5
3
5
8
5
8
ANOTHER TYPE OF CALIBRATION BLOCK IS THE IIW BLOCK (INTERNATIONAL INSTITUTE OF WELDING). IT PROVIDES THE FOLLOWING: VERIFICATION OF DISTANCE KNOWN DISTANCES & ANGULAR RELATIONSHIPS, VERIFIES TRANSDUCER ANGLE AND BEAM EXIT POINT AND CHECKS TRANSDUCER RESOLUTION.
8”
0.125” 0.25”
40”
50”
60”
0.06” HOLE 4”
3.64”
2” DIAMETER HOLE
70”
75”
60”
FOCAL POINT
4”
12”
1” PLASTIC INSERT
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UT Lecture Guide Lesson 8 IN CONTACT ANGLE BEAM TESTING, THE BEAM EXIT POINT OF THE TRANSDUCER MUST BE KNOWN TO ACCURATELY DETERMINE THE LOCATION OF THE DISCONTINUITY. AS SHOWN BELOW, THE TRANSDUCER IS MOVED BACK AND FORTH UNTIL THE PIP ON THE CRT REACHES MAXIMUM AMPLITUDE. THE FOCAL POINT ON THE IIW BLOCK THEN CORRESPONDS WITH THE BEAM EXIT POINT OF THE TRANSDUCER. ANGLE BEAM TRANSDUCER BEAM EXIT POINT
FOCAL POINT
70”
60”
40”
50”
75”
60”
SPECIAL CALIBRATION STANDARDS SPECIAL STANDARDS ARE OFTEN USED FOR ITEMS SUCH AS WELDMENT, CASTINGS, AND PIPING. THE STANDARDS ARE NORMALLY OF THE SAME MATERIAL AND PRODUCT FROM TO BE TESTED. REFERENCE REFLECTORS SUCH AS NOTCHES OR HOLES ARE ARTIFICIALLYADDED TO THE STANDARD.
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UT Lecture Guide Lesson 8 VERIFICATION OF THE TRANSDUCER ANGLE IS ACCOMPLISHED AS SHOWN BELOW: THE PLASTIC WEDGE OF THE ANGLE BEAM TRANSDUCER IS SUBJECT TO WEAR IN NORMAL USE. THIS WEAR CAN CHANGE THE BEAM EXIT POINT AND THE ANGLE OF THE SOUND BEAM. BEAM EXIT POINT 60 DEGREE TRANSDUCER
40”
50”
60”
2” DIAMETER HOLE
75”
70”
60”
FROM THE POSITION SHOWN ABOVE, THE TRANSDUCER IS MOVED BACK AND FORTH UNTIL THE REFLECTION FROM THE 2 INCH HOLE SHOWS MAXIMUM AMPLITUDE ON THE CRT. THE ANGLE OF SOUND BEAM CAN THEN BE READ FROM WHERE THE EXIT POINT ON THE TRANSDUCER MATCHES THE DEGREES STAMPED ON THE SIDE OF THE BLOCK. THE TRANSDUCER SOUND BEAM EXIT POINT SHOULD ALWAYS BE CHECKED FIRST. IF THE EXIT POINT MARKING IS NOT CORRECT, THEN THE ANGLE CHEXK WILL NOT BE ACCURATE.
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UT Lecture Guide Lesson 8 THE FAR FIELD RESOLVING POWER OF THE TEST EQUIPMENT CAN BE ESTIMATED BY PLACING A NORMAL BEAM TRANSDUCER ON THE IIW BLOCK AS SHOWN. GOOD RESOLUTION WILL BE INDICATED IF THE INSTRUMENT CAN SATISFACTORILY SEPARATE THE PIPS FROM ALL THREE REFLECTORS
TRANSDUCER
BAD
COOD
IIW BLOCK
CRT DISPLAY
THE MINIATURE ANGLE BEAM BLOCK CAN ALSO BE USED TO CALIBRATE THE INSTRUMENT FOR ANGLE BEAM INSPECTION. THE MINIATURE BLOCK IS INTENDED FOR FIELD WORK AND IS NOT AS COMPREHENSIVE AS THE LARGER IIW BLOCK.
3” FOCAL POINT
0. 750” 1”
45o
2”
60o
0. 750”
70
o
1.75” MINIATURE ANGLE BEAM BLOCK
0.060” HOLE
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The term “resolution” refers to the ability of a transducer to detect a very small discontinuity. Quartz is the only transducer material commonly used that is not a piezoelectric material. If the frequency of a transducer is raised then the beam spread is reduced. The polarized ceramic transducer is considered to be a very good generator of ultrasonic energy. Quartz is a type of polarized ceramic transducer material. A transducer that can defect a discontinuity close to the surface is saint to have a good resolving power. Larger transducer usually have a higher frequency because they are more fragile. The higher the frequency of a transducer, the smaller the sound cone (i.a. Less beam spread). Immersion testing is always done with transducer that have a frequency between 2.5 and 5.0 MHz. Angle beam testing is usually done with longitudinal waves. Angle beam probes may be used to generate surface waves. A spherical focusing lens will usually have the ability to provide better sensitivity as compared to a cylinderical lens. Focused transducers are often used for shear wave inspection of welded plate due to the increased penetration. A double or dual element transducer can only be used in the longitudinal wave mode. With a double element transducer, the sensitivity is increased because both elements are receiving and sending sound energy. Acoustical tenses increases transducer sensitivity and resolution, but decreases their useful range. A reference block should be made from the same basic material as the part being tested. Blocks which provide a size reference and are used to check the systems linearity are known as area amplitude blocks. The exist point of an angle beam transducer should always be determined before the angle of the transducer is checked. Both the iiw block and miniature block will check the test system resolution.
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