The Basics of Nondestructive Testing
Non-Destructive Testing (NDT) comprises a group of component testing methods to assess the serviceability of a part without compromising its integrity. END is frequently used in safety-critical industries such as oil and gas, offshore and marine, petrochemical, aerospace, power generation, and medical instruments and prosthetics. Due to the Non Destructive Inspection (NDI) ability to ensure exceptionally high levels of safety and quality, NDT plays a crucial role in both the original equipment manufacturer and in-service maintenance.
Virtually all materials contain microscopic pores, voids, and contaminants, which can melt or extrude into a material during primary fabrication or subsequent fabrication. These defects can spread when stressed, eventually leading to part failure. Because the cost of part failure is extraordinarily high in safety critical industries, it is of utmost importance to detect faults that effectively forecast part failure before it actually occurs. In principle, NDT attempts to locate surface faults on a part that predict future failures before the part fails in service and without compromising the part’s utility.
The most widely used NDT methods are: penetrating fluorescent liquid (LP), magnetic particles (MP), ultrasound (UT), X-rays and eddy current tests (ECT).
The Fluorescent Liquid Penetration Test employs a fluid tint that makes cracks visible under white or black light. Similar to fluorescent dyes, the magnetic particle test uses a layer of fine iron particles applied to a temporarily magnetized part. Because the defects alter the magnetic field, the iron particles conform to the shape of the defect. Although both liquid penetration and magnetic particle tests offer a quick and inexpensive means of detecting Nondestructive testing services defects, both are limited to detecting the length and width of a defect. Neither LP nor MP are capable of measuring the depth of a crack.
Ultrasound and X-ray tests are capable of detecting defects both on the surface and throughout the body of a part. While both UT and X-rays are capable of detecting flaws in non-metallic parts, both require the use of cumbersome procedures and materials, as well as the disposal of hazardous waste.
Eddy current testing avoids the problem of detecting the depth of surface defects while eliminating waste removal problems. Eddy current tests use the physical characteristics of electrical currents induced by an electrical coil in the metal part itself. Discontinuities in the metal disturb the eddy current that feeds back to the coil, then to the signal processor, where it is interpreted as a fault.
In summary, there are a variety of NDT methods that allow comprehensive inspections of metal components. These test solutions help maintain the newest product manufacturing quality standards, as well as the safety standards for older operating equipment and machinery. Effective NDT testing enables thousands of industries to maintain confidence in the quality of their products and services.