ASNT

the probe or probe medium to the object examined. Other factors limit the detection and/or character- ization of discontinuities, properties, and other attributes and limit interpretation of signals or images. Classification Relative to Test Object Nondestructive testing techniques may be classified according to how they detect indications relative to the surface of a test object. Surface methods include penetrant testing, visual testing, grid and moiré testing, holography, and shearography. Surface/ near-surface methods include tap, potential drop, magnetic particle, and electromagnetic testing. When surface or surface/near-surface methods are applied during manufacturing, they provide preliminary assurance that volumetric methods performed on the completed object or component

will reveal few, if any, rejectable discontinuities, that is, f laws. Volumetric methods include radiography, tomography, ultrasonic testing, bond testing, acoustic emission testing, certain infrared thermographic techniques, and less familiar methods such as acoustoultrasonic testing and magnetic resonance imaging. Through-boundary methods described include leak testing, some infrared thermographic techniques, airborne ultrasonic testing, and certain techniques of acoustic emission testing. Other less easily classified methods are material identification, vibration analysis, and strain gauging. No one nondestructive testing method is all revealing. That is not to say that one method or technique of a method cannot be adequate for a specific object or component. However, in most cases, it takes a series of test methods to do a

Table 1 Objectives of nondestructive testing methods Discontinuities and separations

Objectives

Attributes Measured or Detected

Surface anomalies

roughness; scratches; gouges; crazing; pitting; inclusions and imbedded foreign material

Surface connected anomalies

cracks; porosity; pinholes; laps; seams; folds; inclusions

Internal anomalies

cracks; separations; hot tears; cold shuts; shrinkage; voids; lack of fusion; pores; cavities; delaminations; disbonds; poor bonds; inclusions; segregations

Structure

Objectives

Attributes Measured or Detected

Microstructure

molecular structure; crystalline structure and/or strain; lattice structure; strain; dislocation; vacancy; deformation grain structure, size, orientation, and phase; sinter and porosity; impregnation; filler and/or reinforcement distribution; anisotropy; heterogeneity; segregation leaks (lack of seal or through-holes); poor fit; poor contact; loose parts; loose particles; foreign objects

Matrix structure

Small structural anomalies

Gross structural anomalies

assembly errors; misalignment; poor spacing or ordering; deformation; malformation; missing parts

Dimensions and metrology

Objectives

Attributes Measured or Detected

Displacement; position

linear measurement; separation; gap size; discontinuity size, depth, location, and orientation

Dimensional variations

unevenness; nonuniformity; eccentricity; shape and contour; size and mass variations

Thickness; density

film, coating, layer, plating, wall, and sheet thickness; density or thickness variations

CHAPTER 1

7

Part 1