This article reviews nondestructive testing (NDT) and inspection techniques, namely liquid penetrant, magnetic particle, ultrasonics, X-ray, eddy current, visual and radiography that are commonly used to detect and evaluate flaws or leaks in an engineering system. This article compares the merits and limitations of these techniques and describes the various uses of NDT, including leak detection, metrology, structure or microstructure characterization, stress-strain response determination, and rapid identification of metals and alloys.

Thermal nondestructive evaluation (TNDE) is an indirect process, so that regardless of the form of energy used to excite the sample, interaction with the internal structure of a part occurs through the process of heat conduction. This article discusses the steady-state configuration and selective excitation configuration of the signal-generation mechanisms in thermal nondestructive evaluation methods. The three widely used approaches to TNDE are surface-excited thermography, vibrothermography, and thermoelastic stress analysis. The article provides information on the common features, characteristics, and limitations of these approaches.

Nondestructive inspection (NDI) methods for cast iron are used to ensure that the parts supplied perform as required by the purchaser. This article focuses on the principal nondestructive methods used to inspect for anomalies in cast irons and to determine if the volume, shape, size, or number of these anomalies exceeds the maximum allowed by the purchaser. The nondestructive methods include visual inspection, dimensional inspection, liquid penetrant inspection, magnetic-particle inspection, eddy-current inspection, radiographic inspection, ultrasonic inspection, resonant testing, and leak testing. The technique, strengths, and weaknesses of each of the nondestructive methods are also discussed.

Of the many different nondestructive evaluation (NDE) techniques, ultrasonic inspection continues to be the leading nondestructive method for inspecting composite materials, because measurements can be quantitative and the typical defect geometries and orientations lend themselves to detection and characterization. This article focuses on the three common methods for ultrasonic nondestructive inspection of plastics, namely pitch-catch, through-transmission, and pulse-echo, as well as the three basic types of ultrasonic NDE scans: the A-scan, B-scan, and C-scan. The discussion includes the linear and phased array systems that are sometimes used for large-scale inspection tasks to reduce scan times, the various gating and image processing techniques, and how ultrasonic data are interpreted and presented. A brief section on future trends in ultrasonic inspection is presented at the end of the article.

Case depth is the normal distance from the surface of the steel to the start of the core. Measurement of case depth is highly sensitive to the type of case hardening, original steel composition, quenching condition, and even to the testing method. This article describes the various methods of measuring case depth in steels, including chemical methods such as the combustion analysis and spectrographic analysis, microhardness test method, macroscopic and microscopic visual methods, and nondestructive methods. It contains a table that provides approximate equivalent hardness numbers for steel.

Case hardening is defined as a process by which a ferrous material is hardened in such a manner that the surface layer, known as the case, becomes substantially harder than the remaining material, known as the core. This article discusses the equipment required, process variables, carbon and hardness gradients, and process procedures of different types of case hardening methods: carburizing (gas, pack, liquid, vacuum, and plasma), nitriding (gas, liquid, plasma), carbonitriding, cyaniding and ferritic nitrocarburizing. An accurate and repeatable method of measuring case depth is essential for quality control of the case hardening process and for evaluation of workpieces for conformance with specifications. The article also discusses various case depth measurement methods, including chemical, mechanical, visual, and nondestructive methods.

This article discusses the need of and the strain basis for residual stress measurements and describes the nature of residual stress fields. A generic destructive stress relief procedure is described along with the issues generally involved in each procedural step. The article presents the stress reconstruction equations to be used for computational reconstruction of the stress fields from the measured strains for the destructive methods. It provides information on the sectioning, material removal, strain measurement, and chemical methods of residual stress measurement. The article reviews the semidestructive methods of residual stress measurement: blind hole drilling and ring coring, spot annealing, and X-ray diffraction techniques. Nondestructive methods such as neutron diffraction, ultrasonic velocity, and magnetic Barkhausen noise techniques, are also discussed.

Measuring the thickness of thin films can be accomplished in many ways. This article focuses on the optical method of single-wavelength ellipsometry, two multiple-wavelength methods of reflectometry and spectroscopic ellipsometry for measuring the thickness of thin films. The general capabilities, principles and applications of ellipsometry and reflectometry are discussed in terms of nondestructive methods.

Ultrasonic inspection is a nondestructive method in which beams of high-frequency acoustic energy are introduced into a material to detect surface and subsurface flaws, to measure the thickness of the material, and to measure the distance to a flaw. This article provides a detailed account of ultrasonic flaw detectors, including ultrasonic transducers and types of search units and couplants. The article describes pulse-echo and transmission inspection methods and data interpretation. The general characteristics of ultrasonic waves and the factors influencing ultrasonic inspection are also addressed. The article concludes with a review of the advantages and disadvantages of ultrasonic inspection compared with other methods applications of the technique.

Ultrasonic inspection is a family of nondestructive methods in which beams of high-frequency mechanical waves are introduced into materials, using transducers, for the detection and characterization of both surface and subsurface anomalies and flaws in the material. This article describes the basic equipment in ultrasonic inspection systems, and lists the advantages and disadvantages of these systems. It discusses the applications of ultrasonic inspection and also the general characteristics of ultrasonic waves in terms of wave propagation, longitudinal waves, transverse waves, surface waves, and lamb waves. The article reviews the major variables in ultrasonic inspection, including frequency, acoustic impedance, angle of incidence, and beam intensity. It discusses the attenuation of ultrasonic beams and provides information on the pulse-echo and transmission methods for implementing ultrasonic inspection.

Liquid penetrant inspection is a nondestructive method of revealing discontinuities that are open to the surfaces of solid and essentially nonporous materials. This article provides information on physical principles, evolution, description, and processing parameters of liquid penetrant inspection as well as materials used. It discusses some of the more generally used types of equipment used in penetrant inspection and their requirements. The article describes various penetrant methods and their selection criteria and provides information on precleaning and postcleaning of workpieces before and after penetrant inspection. The quality assurance and maintenance of penetrant inspection materials are also discussed. The article concludes with information on specifications and standards applicable to penetrant inspection.

Liquid-penetrant inspection is a nondestructive method used to find discontinuities that are open to the surface of solid, essentially nonporous materials. This article describes the physical principles and the process of liquid-penetrant inspection. It also describes the basic penetrant systems, such as the water-washable system, the post-emulsifiable system, and the solvent-removable system. The article provides information on the liquid-penetrant materials, emulsifiers, solvent cleaners, and developers. It details the equipment requirements, selection of penetrant system, and specifications and standards for the liquid-penetrant inspection.

This article outlines the requirements and methods associated with the inspection of brazements. It emphasizes the incorporation of these requirements into the overall quality system. The article reviews the acceptance limits, design limitations, and nondestructive and destructive inspection techniques involved in the brazement inspection. Selected case studies are also provided for further reference.

This article provides information on the application of nondestructive examination (NDE) technologies to tube and pipe products. These include modeling and simulation methods, eddy-current methods, magnetic methods, acoustic methods, and physical methods. A summary of nondestructive examination methods based on flaw type and product stage is presented in a table. The article also discusses in-service inspection of tubular products and presents an example that illustrates the importance of nondestructive testing (NDT) for welds in austenitic stainless steel tubing.

Repair welding is a necessary operation for most fabricators and can cost more than the price of the original component if performed improperly. This article provides a discussion on the repair welding of castings for ferrous and nonferrous materials. The discussion focuses on the surface preparation, weld repair process selection, joint selection, filler metal selection, weld repair considerations, deposition techniques, postweld heat treatment, and verification of weld repair quality.

This article covers defect formation and classification, followed by a brief description of the most common nondestructive testing (NDT) methods used for postbuild inspection. Descriptions of the established and emerging NDT techniques for in-process monitoring (IPM) and in-process inspection (IPI) in additive manufacturing (AM) also are provided, highlighting the advantages and limitations. The article concludes with a list of the main NDT methods and techniques used. As qualification and certification of AM parts is an urgent matter for the AM industry, a description of the current work carried out for developing standards is also included.

This article discusses the standard test methods that can be applied to many types of welds: tension, bending, impact, and toughness testing. It provides information on four qualification stages, namely, the weld material qualification, base material qualification, the weld procedure qualification, and the weld service assessment. The article describes two general types of measurements for residual stress in welds: locally destructive techniques and nondestructive techniques. Locally destructive techniques include hole drilling, chip machining, and block sectioning. Nondestructive techniques include X-ray diffraction, neutron diffraction, Barkhausen noise analysis, and ultrasonic propagation analysis. The article concludes with an overview of weldability testing.

Nondestructive testing (NDT), also known as nondestructive evaluation (NDE), includes various techniques to characterize materials without damage. This article focuses on the typical NDE techniques that may be considered when conducting a failure investigation. The article begins with discussion about the concept of the probability of detection (POD), on which the statistical reliability of crack detection is based. The coverage includes the various methods of surface inspection, including visual-examination tools, scanning technology in dimensional metrology, and the common methods of detecting surface discontinuities by magnetic-particle inspection, liquid penetrant inspection, and eddy-current testing. The major NDE methods for internal (volumetric) inspection in failure analysis also are described.

Both nondestructive testing (NDT) and nondestructive evaluation (NDE) use noninvasive measurement techniques to gain information about defects and various properties of materials, components, and structures. This article begins with a discussion on the historical development of quantitative measurement techniques, evaluation reliability, and quantitative interpretation of nondestructive inspection methods. The common nondestructive evaluation methods, along with their uses and limitations, are summarized in a table. The article conceptually illustrates the interplay of NDE and fracture mechanics in the damage tolerant approach. It concludes with information on pressure vessel applications that can be separated into three protocols used by military nuclear power, commercial nuclear power, and non-nuclear pressure vessels and/or fired boilers.