AMS-STD-2154 is an Ultrasonic Testing (UT) specification that provides uniform methods for UT of wrought metals and wrought metal products.
Ultrasonic nondestructive testing (NDT) is a well-established technique that utilizes high frequency sound waves to locate cracks and other hidden flaws in metals, composites, and plastics. In the metals industry, ultrasonic inspection is not only used to inspect finished parts but also to inspect raw material in the form of bars, billets and plates supplied for further processing.
When employed appropriately by a qualified operator, ultrasonic NDT is quick and reliable, usually requires no test piece preparation other than wetting with ultrasonic couplant or water, and has no specific safety hazards or regulatory licensing requirements associated with its use.
Ultrasonic testing uses sound waves at frequencies commonly in the range of 2 MHz to 10MHz. Sound waves will travel through a medium like steel at a specific speed or velocity, in a predictable direction, and when they encounter a boundary with a different medium they will be reflected or transmitted according to simple rules. Thus ultrasonic waves will reflect from cracks, porosities, inclusions or other discontinuities in a test piece. The frequency and aperture of an ultrasonic transducer establishes the beam diameter and beam spread characteristics which factor into the ability to detect and size flaws. If flaws are larger than the beam diameter then comparative amplitude-based sizing techniques must be used.
Mechanical focusing with a fixed lens (conventional UT) or electronic focusing (phased array) can be used to establish tighter beam diameters and focal zones which in turn allow the edges of a defect to be better defined, resulting in improved dimensional analysis. The choice between inspection techniques is often a compromise between detection, sizing, throughput and documentation requirements.
Solid bars are commonly tested for cracks, piping voids, and inclusions. Tubular products that incorporate resistance welds or arc welds are tested for cracking and lack of penetration along the weld seam, as well as porosity and inclusions. Standards, codes and customer requirements typically set classification levels for acceptance based on critical defect location and size as related to the end use of product. Materials used in transportation, power generation and fluid/gas containment or distribution will typically require more stringent inspection than non-safety critical consumer goods.