Ultrasonic Inspection is a non-destructive method in which beams of high-frequency sound waves are introduced into materials for the detection of surface and subsurface flaws in the material. The sound waves travel through the material with some attendant loss of energy (attenuation) and are reflected at interfaces. The reflected beam is displayed and then analyzed to define the presence and location of flaws or discontinuities.

Cracks, laminations, shrinkage cavities, bursts, flakes, pores, disbands and other discontinuities that produce reflective interfaces can be easily detected. Inclusions and other inhomogeneities can also be detected by causing partial reflection or scattering of the ultrasonic waves or by producing some other detectable effect on the ultrasonic waves.

The ultrasonic inspection of metal is principally conducted for the detection of discontinuities. This method can be used to detect internal flaws in most engineering metals and alloys. Bonds produced by welding, brazing, soldering and adhesive bonding can also be ultrasonically inspected. In-line techniques have been developed for monitoring and classifying material as acceptable, salvageable or scrap and for process control. Both line-powered and battery-operated commercial equipment is available, permitting inspection in shop, laboratory, warehouse or field.

Ultrasonic inspection is used for quality control and materials inspection in all major industries. This includes electrical and electronic component manufacturing; production of metallic and composite materials; and fabrication of structures such as airframes, piping and pressure vessels, ships, bridges, motor vehicles, machinery and jet engines. In-service ultrasonic inspection for preventive maintenance is used for detecting the impending failure of railroad - rolling - stock axles, press columns, earthmoving equipment, mill rolls, mining equipment, nuclear systems, and other machines and components.

Some of the major types of equipment that are ultrasonically inspected for the presence of flaws are:

• Mill components: rolls, shafts, drives and press columns.

• Power equipment: turbine forgings, generator rotors, pressure piping, weldments , pressure vessels, nuclear fuel elements and other reactor components.

• Jet engine parts: turbine and compressor forgings and gear blanks.

• Aircraft components: forging stock, frame section and honeycomb sandwich assemblies.

• Machinery materials: die blocks, tool steels and drill pipe.

• Railroad parts: axles, wheels, track and welded rail.

• Automotive parts: forgings, ductile castings and brazed and welded components.

The flaws to be detected include voids, cracks, inclusions, pipe, laminations, debonding, bursts and flakes. They may be inherent in the raw materials, may result from fabrication and heat treatment, or may occur in service from fatigue, impact, abrasion, corrosion, or other causes.

Government agencies and standardsmaking organizations have issued inspection procedures, acceptance standards and related documentation. These documents are mainly concerned with the detection of flaws in specific manufactured products, but they also can serve as the basis for characterizing flaws in many other applications.

Ultrasonic inspection can also be used to measure the thickness of metal sections. Thickness measurements are made on refinery and chemical-processing equipment, shop plate, steel castings, submarine hulls, aircraft sections and pressure vessels

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