Some wondered NDT terms

ARRAY : A group of transducers for source location,

AUSTENITE : A solid solution with iron as the solvent in a face centered cubic structure formed by slow cooling of delta ferrit,

ASNT : American Society for Nondestructive Testing,

BEAD : A half-round cavity in a mold or a halh-round projection or molding on casting,

CHAPLET : A metal support used to hold a core in place on a mold.

CREEP : Gradual and permament change of shape in a metal under constant load, usually at elevated temperature,

LİFTOFF : Distance between the probe coil and the test object,

NULL : To adjust a bridge circuit so that the test sample and reference arms produce equal and opposite currents through the dedector,

PUPIL : Aperture in the center of an eye's iris, through which light focused by the lens passes.

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Introduction Ultrasonic Inspection

In ultrasonic nondestructive testing, ultrasound is used to nondestructively detect discontunities or estimate the phsical characteristics of a material. The most frequently used ultrasonic wave is longitudinal wave, due to the simplicity of generation and the ability to acustically couple the transducer to the test specimen. However, the other wave types have their merits. For instance, shear wave have a better resolution for detecting smal discontiuities tahn do longitudinal waves at the same frequency. Some kinds of discontinuities reflect shear waves much better than longitudinal waves and shear waves can also be used to test near vertical cracks

Nondestructive testing (NDT)

Nondestructive testing (NDT), also called nondestructive evaluation (NDE) and nondestructive inspection (NDI), is testing that does not destroy the test object. NDE is vital for constructing and maintaining all types of components and structures. To detect different defects such as cracking and corrosion, there are different methods of testing available, such as X-ray (where cracks show up on the film) and ultrasound (where cracks show up as an echo blip on the screen). This article is aimed mainly at industrial NDT, but many of the methods described here can be used to test the human body. In fact methods from the medical field have often been adapted for industrial use, as was the case with Phased array ultrasonics and Computed radiography.

While destructive testing usually provides a more reliable assessment of the state of the test object, destruction of the test object usually makes this type of test more costly to the test object's owner than nondestructive testing. Destructive testing is also inappropriate in many circumstances, such as forensic investigation. That there is a tradeoff between the cost of the test and its reliability favors a strategy in which most test objects are inspected nondestructively; destructive testing is performed on a sampling of test objects that is drawn randomly for the purpose of characterizing the testing reliability of the nondestructive test.