Ultrasonic Testing Method
An ultrasound probe connected to an ultrasonic testing machine transmits high frequency sound waves along the exterior of the test material or part. These sound waves are then reflected from the interior surface back to the probe. When there is a change in material structure, such as a flaw or defect in the wave path, part of the energy will be reflected back from this surface. The reflected wave signal is transformed into an electrical signal by the probe and is displayed on a screen.
Ultrasonic testing immersion method
As reflected signals are processed by the ultrasonic testing machine, they provide useful information about the condition which caused the reflection. Changes in the reflected energy from the sound waves can identify location and size of defects or inconsistencies in the material or part. The signals also produce precise measurements of wall thickness along the length of tubular products or at the designated test location on other products. For example, an instrument display with a time base shows the time it takes for an ultrasonic pulse to travel to a flaw or the interior surface, which can be directly converted to a thickness reading. The height of the reflected pulse is related to the flaw size as seen from the transmitter probe.
In most cases, reference standards are required to establish the sensitivity of the ultrasonic testing system. A reference standard is a manufactured flat bottom hole or set of precise notches used for both equipment calibration and the characterization of flaws. The dimensions of these holes or notches are typically given in the codes and/or standards which apply to the material.
Types of Ultrasonic Testing
Ultrasonic testing is performed either by the immersion or contact method. Immersion inspections take place in a liquid which conducts the beam of sound between the probe and test material. With the contact method, an ultrasonic testing probe is run over the surface of the test piece while emitting sound waves through a thin layer of gel couplant. Immersion ultrasonic inspection is preferred in many applications because it is generally faster, more accurate and eliminates the need for direct contact with the test item.
Ultrasonic Testing at Laboratory Testing Inc.
Laboratory Testing offers both immersion and contact ultrasonic testing for tubing, pipe, bar, plate and a wide-variety of metal parts in all shapes and sizes. Materials up to 18 ft. by 5 ft. in size or round stock up to 70 ft. long with a diameter between 1/8 in. and 6 5/8 in. can be tested by the immersion method, depending on weight. At LTI, all immersion UT inspections include chart recording and file maintenance. All immersion ultrasonic testing equipment is computerized for optimum test accuracy and continuous collection of test results for evaluation and archiving. Other products in various shapes and sizes can be tested by the contact method. Large materials and products are safely handled in a 26,000 sq. ft. nondestructive testing and receiving area using 3-ton cranes and heavy-duty forklifts.
Laboratory Testing has an extensive library of tube, pipe, bar and plate ultrasonic reference standards available for UT inspection. All reference standards are manufactured by LTI or by an LTI approved vendor, so we can readily obtain additional reference standards in nearly any configuration.
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