What is Ultrasonic Testing?

Ultrasonic Testing (famously known as U.T.) is one of the most important methods in non-destructive testing. It is mainly used to detect defects in parts and materials and determine material’s thickness. The ultrasonic testing equipment is quite portable therefore making it suitable for inspecting large, irregularly shaped, or heavy stationary parts.

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What is the purpose of Ultrasonic Testing?

Ultrasonic Testing (UT) uses high frequency sound energy to conduct examinations and make measurements. It can be used for flaw detection or evaluation, dimensional measurements, material characterization, and more. 

How Do You Conduct An Ultrasonic Test?

Firstly, we need to know what is ultrasound. Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. It is not different from “normal” (audible) sound in its physical properties, except that humans cannot hear it.

This limit varies from person to person and it is approximately 20 kilohertz (20,000 hertz) in healthy young adults. Ultrasound devices operate with frequencies from 20 kHz up to several gigahertz.

The velocity of ultrasound in any material is constant, and in homogeneous materials, ultrasonic beams travel in straight lines. When ultrasonic waves pass through a material with a given sound velocity, to a second material with a different velocity, refraction and reflection of the sound beam will occur at the boundary between the two materials. This is similar to the light waves’ behavior.

Ultrasonic waves are deflected at a boundary between twomaterials with different acoustic properties. Therefore, probe which can beam sound into a material at any given angle (within certain limits) can be built makingit a useful tool for the detection of weld defects.

With the right equipment, ultrasound can also be used togive accurate positional information about a given reflector since velocity is a constant for any given material and sound travels in a straight line.

As the ultrasonic probe is moved together with the positional information obtained above and knowledge of the component history, careful observation of the echo pattern of a given reflector and its behavior enables the experienced ultrasonic operator to classify the reflector as slag, lack of fusion or a crack.

The Equipment for Ultrasonic Testing

The equipment for manual ultrasonic testing consists of:

A flaw detector:

• Pulse generator.
• Adjustable time base generator with an adjustable delay control.
• Cathode ray tube with a fully rectified display.
• Calibrated amplifier with a graduated gain control or attenuator.

An ultrasonic probe:

• Piezo-electric crystal element capable of converting electrical vibrations into mechanical vibrations and vice versa.
• Probe shoe, normally a Perspex block to which the crystal is firmly attached using suitable adhesive.
• Electrical and/or mechanical crystal which the to prevent excessive ringing.
• Electrical and/or mechanical crystal damping facilities to prevent excessive ringing.

The equipment is lightweight and extremely portable. Automated or semi-automated systems for ultrasonic testing use the same basic equipment, although it is bulkier and less portable since generally they are multi-channel.

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Probes for automated systems are set in arrays and some form of a manipulator is necessary to feed the positional information about them to the computer.

Automated systems generate huge amounts of data and burden the computer RAM. Recent advances in automated UT have led to a reduced amount of data being recorded for a given length of weld.

Simplified probe arrays with frequencies reduced the complexity of setting up the automated system to carry out and is a particular task. Nowadays, UT systems provide an alternative to radiography on pipelines constructions where a large number of similar inspections allow the unit cost of system development to be reduced to know what level.

Ultrasonic Testing Advantages and Limitations

The advantages of Ultrasonic testing are;

• Portable (no mains power) battery
• Direct location of defect (3 dimensional)
• Good for complex geometry
• Safe operation (can be done next to someone)
• Instant results
• High penetrating capability
• Can be done from one side only
• Good for finding planar defects

The limitations are;

• No permanent record
• Only ferritic materials (mainly)
• High level of operator skill required
• Calibration of equipment required
• Special calibration blocks required
• No good for pinpointing porosity
• Critical of surface conditions (clean smooth)
• Will not detect surface defects
• Material thickness >8mm due to the dead zone

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There you have it, a short info about ultrasonic testing. If you have anything to add, please let us know in in the comment section below.

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