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Eddy Current Testing 8.1

Thermal Infrared Testing 9.1

Acoustic Emission Testing 10.1

CONTRIBUTORS

He holds an ASNT Level III Certificate in Electromagnetic and Ultrasonic Test Methods. Snell had the honor of becoming the first ASNT Level III certificate holder in thermography in the United States.

PREFACE

In addition to Mike and Sheryl and the contributing authors, the efforts of the following individuals have added so much: Alice Baldi (tables and word processing), Christina Hellier (word processing and much encouragement), Lynne Hopwood (graphic design and illustrations), and William Norton (text review ). Finally, this Manual would have taken much longer without the understanding, patience, and support of Rockwood Service Corporation management, especially Peter Scannell and James Treat.

HANDBOOK OF NONDESTRUCTIVE

EVALUATION

INTRODUCTION TO NONDESTRUCTIVE

TESTING

WHAT IS NONDESTRUCTIVE TESTING?

The human body has been described as one of the most unique non-destructive testing instruments ever created. But of all the human senses, sight provides us with the most versatile and unique non-destructive testing method.

CONCERNS REGARDING NDT

Another misconception involves the nature and characteristics of the part or object being examined. Again, this illustrates the need for some sort of monitoring or evaluation of the part or structure once it is operational.

HISTORY OF NONDESTRUCTIVE TESTING

In the early days of railroading, the precursor to today's penetrant test (PT), a technological Courtesy of the Library of Congress.). And there was also some basic electrical testing using some of the basic principles of eddy current testing (ET).

Table 1-1 lists some of the key events in the chronology of NDT and the individuals who were mostly responsible for these developments

NONDESTRUCTIVE VERSUS DESTRUCTIVE TESTS

The measurement of the material's resistance to impact (or notch toughness) is determined by the subsequent rise of the pendulum (see Figure 1-17). 앫 Every object or large part of the material can be examined without negative consequences.

FIGURE 1-16 Typical tensile testing machine. (Courtesy of J. Devis Collection.)

CONDITIONS FOR EFFECTIVE NONDESTRUCTIVE TESTING

앫 Some methods do not provide permanent records of the investigation 앫 NDT methods generally do not provide quantitative data. Since non-destructive testing is a hands-on technology and is highly dependent on the ability of the individuals performing the inspections, personnel must not only be trained but also properly certified.

PERSONNEL CONSIDERATIONS

It is expected that the Level II is also thoroughly familiar with the various aspects of the method for which they are qualified. The administration of this program is the responsibility of The Welding Institute (TWI) in England.

CERTIFICATION SUMMARY

Since 1985 it has replaced certification programs run by a number of other organizations and is now one of the most recognized schemes in the world. It began in 1960 as a centralized certification program and has remained a basically third-party program administered by the Ministry of the Federal Government of Canada (Natural Resources Canada).

Broad industry certification is offered in five methods (RT, UT, ET, MT and PT) at three levels. Some countries, including France (COFREND), Japan (JSNDI), and others, have centralized certification programs that comply with, or follow a pattern of, ISO 9712.

DISCONTINUITIES—

ORIGINS AND CLASSIFICATION

PRIMARY PRODUCTION OF METALS

The extraction of metals from ores requires processes that often transfer some of the mineral impurities from the rocks and the chemical additives used in the refining process. When steel is formed by deformation at relatively high temperatures, these incorporated particles will extend in the direction of flow of the steel.

FIGURE 2-1 Silicate stringer in cold drawn bar of steel (235X). [From The Making, Shaping and Treating of Steel, 10th Edition, US Steel (1985).]

CASTING

In the example, the solid is a lead-rich crystal structure with tin atoms replacing some of the lead atoms. In the mixture of the crystalline solid and the liquid alloy at point two, the liquid is richer in tin than the solid.

FIGURE 2-3 A cross section through a billet showing pipe from solidification shrinkage.

CRACKS

However, the sizes, shapes and distributions of the solid phases of the alloy characterize the microstructure, which is critical in determining the physical properties of the alloy. Additionally, gas evolution inside a casting at high temperatures can cause pressure that is sufficient to crack the interior of the casting.

WELDING DISCONTINUITIES

There is a state of stress that arises in welding operations due to the differential expansion and contraction of the base material. The weld toe is the edge of the fusion zone on the surface of a base material.

FIGURE 2-10 Undercut at the edges of weld beads in a multiple pass weld. (Courtesy of C.

DISCONTINUITIES RESULTING FROM PLASTIC DEFORMATION

CORROSION-INDUCED DISCONTINUITIES

These cracks will initiate at the surface and can be damaging, causing puncture of the component wall and serving as a site of fatigue propagation under conditions of cyclic tensile loading. This internal cracking can occur over significant areas of the component and cause the component to weaken and create initiation sites for fatigue crack propagation.

FIGURE 2-12 Corrosion pit that penetrated a pipe wall (5×). (Courtesy of R. B. Pond, Jr.)

OPERATIONALLY INDUCED

The hydrogen atom formed on the surface of alloys is small enough to dissolve in the alloy. In a similar manner to the embrittlement of high strength material welds, the hydrogen will form molecular hydrogen at inclusions and grain and phase boundaries.

OPERATIONALLY INDUCED DISCONTINUITIES—CREEP

OPERATIONALLY INDUCED

There are conditions of precipitation of phases at the grain boundaries of alloys that cause the grain boundaries to become brittle, and brittle fracture in those cases will tend to be confined to the shell of the grains. Fracture around grain boundaries has a characteristic appearance called a “rock-candy” fracture surface (Figure 2-16).

GEOMETRIC DISCONTINUITIES

The dimensions and slope transition of the notch sides are critical characteristics of the degree of stress concentration that will exist under the operating loads. Residues from surface interactions and oxidation products are embedded between the surfaces and act as a grinding medium.

FIGURE 2-17 Brittle fracture surface of fastener. Bright flecks are planar cleavage facets of ferrite in the steel

SUMMARY

Slippage is a surface condition caused by metallurgical bonding of surfaces under pressure and the local expulsion of surface material during movement between the surfaces. However, surface finish greatly influences the fatigue resistance of a material, and under given environmental conditions, smoother surfaces offer greater resistance to fatigue cracking.

GLOSSARY OF METALLURGY AND DISCONTINUITY TERMS

Cold Shut A discontinuity on the surface of a casting caused by the ingress of melt (without fusion) into part of a casting. Crater A localized depression in the surface of a part caused by excessive chip contact during machining or arc disruption of a weldment.

DISCONTINUITY GUIDE

Flat Fluorescent Visible Magnetic Magnetic Eddy Thermal Beam Non-Destructive Test Methods Visual Penetrant PenetrantParticleParticleParticleCurrentInfraredRadiographyUltrasonicsUltrazsonics Types of discontinuities Surface and near-surface methodsSubsurface Process Category Inherent LaminationsPUUUUUUUUA(1)c PipedU UUUUUUUA(2)A(1) SeamsPA(4)A(5)A(1)A (2) A(3)PPUU StringsUUUA(1)A(2)A(3)PUPP Mechanical forming processes Stretching or splitting UUUUUUUUUA(1) Forging Cracks PA(2)A(3)A(1)A(4)A (5)PPPP Forging LapsPA(2)A(3)A(1)PPPUUP Rolling Lap (seam)PA(2)A(3)A(1)PPPUUP Casting Process Cold ClosingPPPPPPPUA(1)P Casting Shrinkage CracksUUUPPUUUA(1) A(2 ) Gas porosityUUUPUUUA(1)A(2) Hot tearsUUUPPUUUA(1)A(2) ScabsPA(3)A(4)A(1)A(2)A(5)PPUU Shrinkage PorosityPePePeUUUUUA(1)A( 2) InclusionsUPePePePePeUUA (1)A(2) Grinding checks in the secondary processPA(2)A(3)A(1)PPPUUU Machining tearsPA(2)A(3)A(1)UUUUUU Coating cracksPA(2)eA(3) )eA(1) PPePUUU Quenching and heat cracksPA(2)A(3)A(1)A(4)A(5)Welding/joining crater cracks PPPUPA(2)A(3)A(1)PPPUUP Guest inclusionUUUUPUUUA(1)P.

FIGURE 2-18 Lamination in plate edge.

VISUAL TESTING

HISTORY AND DEVELOPMENT

Development of the endoscope continued as the eye fatigue problems associated with the use of endoscopes and fiberscopes led to the development of various "add-ons". The physical size of the CCD as well as its ability to allow electronic image processing and its other advantages expand the range of applications.

FIGURE 3-2 Rigid borescope. (Courtesy of Olympus Industrial, with permission.)FIGURE 3-1Minimum angle for typical visual testing.

THEORY AND PRINCIPLES

The amount of light that reaches the eye from an object is dependent on the cleanliness of the reflecting surface. Excessive rust or roughness can cause diffusion of the light and limit the light returning to the eye.

FIGURE 3-4 How charge coupling works.

EQUIPMENT AND ACCESSORIES

It is a measurement of the refractive power of lenses equal to the reciprocal of the focal length in meters. The Electronics Industries Association (EIA) standard measures the apparent resolution on a monitor using the Standardized EIA Resolution Test Pattern (see Figure 3-14).

FIGURE 3-8 Various measuring gauges.

APPLICATIONS AND TECHNIQUES

Non-metallic inclusions commonly referred to as slag (burnt flux in the case of welding processes) can be collected internally or on the surface of the weld face. If access to the bottom of the tank is possible, it may be placed on the floor.

FIGURE 3-16 Submerged arc welding process (SAW).

EVALUATION AND REPORTING OF TEST RESULTS

Product shapes should be specified in order to reduce the number of different visual procedures needed. Ball joints (if any) should be checked on bearing surfaces and stop positions for wear.

ADVANTAGES AND LIMITATIONS

Limitations may occur when multiple changes of direction are required; this means that the push rod soon becomes stuck at several bends in the pipe, shaft or opening. The challenge remains to fully understand "what" the inspector is inspecting and "how" the image appears to the eye.

TABLE 3-2 Comparative Color Film Speeds

GLOSSARY OF KEY TERMS

Visual Angle: The angle subtended by an object or detail at the point of observation. Visual field – the location of objects or points in space that can be perceived when the head and eyes are held fixed.

PENETRANT TESTING

• INTRODUCTION
• HISTORY AND DEVELOPMENT
• THEORY AND PRINCIPLES
• PENETRANT EQUIPMENT AND MATERIALS
• PENETRANT PROCEDURES
• TECHNIQUES AND VARIABLES

See Figure 4-7) After pre-cleaning, it is important that the pre-cleaners evaporate and that the test surface is completely dry before applying the penetrant. This will prevent contamination or dilution of the penetrant in the event that it interacts and becomes mixed with the precleaner.

FIGURE 4-1 Demonstration of capillary action. (All illustrations in this chapter courtesy C.

Process B (Lipophilic) and Process D (Hydrophilic) , Processes B and D use a fluorescent postemulsifiable penetrant, a lipophilic

It is not as effective for parts with complex shapes (eg threads) or rough surfaces as Technique I-A is. This process is generally used when removal with water is not desirable due to part size, weight, surface condition, water availability, or when a heat source is not readily available for drying.

FIGURE 4-14 Water-removable technique (Process I-A or II-A).

Process A (II-A)

Process B (II-B)

• EVALUATION AND DISPOSITION
• PENETRANT TESTING APPLICATIONS
• QUALITY CONTROL CONSIDERATIONS
• ADVANTAGES AND LIMITATIONS The major advantages of penetrant testing include
• GLOSSARY OF PENETRANT TESTING TERMS

Contrast ratio—The ratio of the amount of light reflected or emitted between a penetrant and a background (usually the test surface). Development Time - The time elapsed between application of the developer and examination of the part.

FIGURE 4-19 Comparator block.

MAGNETIC PARTICLE TESTING

When the magnetizing force is stopped, some domains spin back to a random orientation. We can see that in the center of the loop the current is essentially linear.

FIGURE 5-1 Magnetograph.