Nondestructive Examination (NDE) Technology and …

[Pages:52]Nondestructive Examination (NDE) Technology and Codes Student Manual

Volume 1

Chapter 4.0

Introduction to Visual Examination

NDE Technology and Codes Student Manual

TABLE OF CONTENTS

Table of Contents

4.0 INTRODUCTION TO VISUAL EXAMINATION..................................................................... 1

Learning Objectives

4.1 History

...................................................................................................... 1

4.2 Personnel Qualification and Certification ........................................................................... 1

4.2.1 Visual Acuity ...................................................................................................... 2

4.2.2 Equipment ..............................................................................2

4.2.3 Experience and Training....................................................................................... 2

4.2.4 Procedures ------------------------------------------------------------------------------3

4.2.5 Certification ...................................................................................................... 3

4.3 Principles of Visual Testing ................................................................................................... 4

4.3.1 Applications ...................................................................................................... 4

4.3.2 Visual Factors ..............................................................................5

4.3.3

Human Eye ...................................................................................................... 5 4.3.3.1 Refractivity ............................................................................................... 6 4.3.3.2 Distance Judgment.................................................................................... 6 4.3.3.3 Mechanism of Vision................................................................................ 7 4.3.3.4 Light Receptors......................................................................................... 7

4.3.4

Color and Color Vision......................................................................................... 7 4.3.4.1 Color Characteristics ................................................................................ 7 4.3.4.2 Brightness Characteristics ........................................................................ 8 4.3.4.3 Spectrum Limits of Visibility ................................................................... 8

4.3.4.4 Color Changes .................................................................................... 8

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4.3.5 Observer Differences ............................................................................................ 9

4.3.6 Lighting

...................................................................................................... 9

4.3.7 Specific Lighting Devices .................................................................................. 10

4.4 Imaging Equipment

.................................................................................................... 10

4.4.1 Mirrors

.................................................................................................... 10

4.4.2 Magnification .................................................................................................... 10 4.4.2.1 Focal Length ........................................................................................... 11 4.4.2.2 Magnifying Devices ............................................................................... 11

4.4.3 Borescopes and Fiberscopes ............................................................................... 12 4.4.3.1 Borescopes.............................................................................................. 12 4.4.3.2 Fiberscopes ............................................................................................. 13

4.4.4

Electronic Imaging ............................................................................................. 13 4.4.4.1 Closed Circuit Television ....................................................................... 13 4.4.4.2 Cathode-ray Tube (Viewing).................................................................. 13 4.4.4.3 Digital Imaging....................................................................................... 14

4.4.5

Photographic Techniques ................................................................................... 15 4.4.5.1 Depth of Field ......................................................................................... 15 4.4.5.2 Lighting .................................................................................................. 16 4.4.5.3 Film .................................................................................................... 16

4.5 Measuring Equipment ............................................................................16

4.5.1 Linear Scales .................................................................................................... 16

4.5.2 Steel Rules .................................................................................................... 17

4.5.3 The Vernier Scale ............................................................................................... 17 4.5.4 Vernier Calipers.................................................................................................. 17

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4.5.5 Dial Calipers .................................................................................................... 18

4.5.6 Micrometer .................................................................................................... 18

4.5.7 Micrometer Depth Gages.................................................................................... 18

4.5.8 Dial Indicator .................................................................................................... 18

4.5.9 Balanced Dials .................................................................................................... 18

4.5.10 Combination Square Set ..................................................................................... 19

4.5.11 Thread Pitch Gages............................................................................................. 19

4.5.12 Thickness Gages ................................................................................................. 19

4.5.13 Levels

.................................................................................................... 19

4.6 Visual Examination of Welds............................................................................................... 19

4.6.1 Prior to Welding ................................................................................................. 19

4.6.2 During Welding .................................................................................................. 20

4.6.3 After Welding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.6.4

Weld Examination Gages ................................................................................... 20 4.6.4.1 Fillet Weld Gage..................................................................................... 20 4.6.4.2 Multipurpose Gage ................................................................................. 21 4.6.4.3 Taper Gage ............................................................................................. 21 4.6.4.4 Hi-Lo Gage ............................................................................................. 21 4.6.4.5 Ferrite Gages........................................................................................... 21

4.7 Remote Visual Inspection (RVI) .......................................................................................... 21

4.7.1 Fiber-optic Borescopes, Fiberscopes, and Video image scopes ......................... 21

4.7.2 Liquid Penetrant Examinations Combined with RVI......................................... 22

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4.7.3 Magnetic Particle Examinations Combined with RVI ....................................... 23

4.7.4 Ultrasonic Examinations Combined with RVI................................................... 23

4.7.5 Eddy Current Examinations Combined with RVI.............................................. 23

4.8 Specific Applications for Power Generation ........................................................................ 24

4.8.1 Steam Turbines ................................................................................................... 24

4.8.2 Surface Condensers and Heat Exchangers ......................................................... 24

4.9 Visual Examination Code Requirements.............................................................................. 25

4.9.1 ASME-Section V ................................................................................................ 25

4.9.2 ASME-Section XI............................................................................................... 25

4.9.2.1 Supplemental Qualifications of VT Examination Personnel............................................................... 27

4.9.3 AWS Certified Welding Inspector ..................................................................... 26

4.10 Records

.................................................................................................... 27

4.11 Advantages and Limitations of Visual Testing .............................................................. 27

4.11.1 Advantages .................................................................................................... 27

4.11.2 Limitations .................................................................................................... 28

LIST OF TABLES

4-1 Precision, Accuracy, and Reliability .......................................................................................... 29

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Table of Contents

4-1 Electromagnetic Spectrum.......................................................................................................... 30 4-2 Direction of View (DOV)........................................................................................................... 31 4-3 Typical Borescope ...................................................................................................................... 32 4-4 Fiberscope ...................................................................................................33 4-5 Halitation ...................................................................................................34 4-6 Vernier Caliper ........................................................................................................................... 35 4-7 Dial Indicating Calipers.............................................................................................................. 36 4-8 Micrometer ................................................................................................................................. 37 4-9 Dial Indicator .............................................................................................................................. 38 4-10 Combination Square Set ....................................................................................................... 39 4-11 Thread Pitch Gages............................................................................................................... 40 4-12 Measuring Convex Fillet Weld Size..................................................................................... 41 4-13 Measuring Concave Fillet Weld Size ................................................................................... 42 4-14 Palmgren Weld Gage............................................................................................................ 43 4-15 Weld Gages........................................................................................................................... 44

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Chapter 4.0 Introduction to Visual Examination

4.0 INTRODUCTION TO VISUAL EXAMINATION

Learning Objectives:

To enable the student to:

1. Understand the basic concepts and use of Visual Examination (VT) and the qualification/ certification of examiners.

or destroying the object being examined."

In VT the most important tools are the eyes. Visual acuity is of prime importance to the visual examiner. According to recent statistics, at least 50 percent of the American population over twenty years of age is required to wear some type of corrective lenses. However, in the early stages of eyesight failure, either many persons are not aware that they need corrective lenses or they just do not wear them.

2. Become familiar with general applications of VT.

3. Recognize the equipment used for VT.

4. Understand the processes and techniques by which VT is applied to the examination of materials, components, and structures.

5. Know the importance of the qualification and certification of personnel in VT.

6. Recognize the advantages and limitations of VT.

4.1 History

The oldest and most commonly used NDE method is Visual Examination (VT). It may also be the least understood and least effectively used of all methods. There is a difference between just looking at an object and really seeing it through a trained eye. VT may be defined as `an examination of an object using the naked eye, alone or in conjunction with various magnifying devices, without changing, altering,

As with any sensitive tool, the most important tools in VT must be checked for accuracy at regular intervals to ensure that they remain accurate and sensitive. Most codes require that VT examiners have annual eye tests to check:

? Near vision acuity, ? Far vision acuity, and ? Color perception.

Although the eyes are the most important tool, in many situations they are not sensitive enough, not accurate enough, or cannot get to the area to be examined. In those cases, the use of optical aids is necessary in order to complete the visual examination.

4.2 Personnel Qualification and Certification

The training and qualification requirements for VT were debated vigorously over many years within the NDE community. Many argued that SNT-TC-1A should not include VT, feeling it was not necessary and was being pushed on

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