Radiographic and Ultrasonic Weld Testing

29 March 2018

Straightforward visual testing methods hit a roadblock when weld flaws are concealed. Where does the NDT (Non-Destructive Testing) process go from here? Expanding to include electronic scanning instrumentation, the procedure recruits radiographic and ultrasonic weld testing, an approach that seeks hidden discontinuities. These internal flaws can’t be seen or felt, but they do interfere with the electromagnetic spectrum. Let’s put these bleeding-edge instruments to work.

Radiographic Weld Analysis

Non-destructive weld tests use the electromagnetic spectrum to seek out weld discontinuities. On the visible spectrum, the naked eye is good enough to get the job done. However, plain old eyesight can’t see the internal structure of a fused joint. So what does radiographic analysis do to “see” the obscured weld structure? It emits X-Rays or Gamma Rays, radiated waves that penetrate the metal. As the short wavelength emissions travel through the weld, they’re absorbed. Like a hospital X-Ray, the equipment film now develops to show what’s going on deep inside the obscured material joins.

Ultrasonic Test Technology

High-frequency sound waves replace the radioactive isotope. They create imperceptible vibrations in the weld, and those vibrations change when a material flaw is encountered. As the ultrasonic waves reflect back towards their origin point, they’re converted into usable data. An image is rendered on a screen or cathode-ray oscilloscope. Of course, this is a generalization. The instrument is far more intricate than we’ve described here. First of all, signal attenuation and signal reflectance principles rule this non-destructive test method. Transducer designs, couplant configurations, and pulse amplitude, all of these factors impact test interpretation.

Interpretating the Data

It’s not easy to read an ultrasonic test (UT), not when it’s rendering the data as a series of spiky waves. A trained inspector scrutinizes the amplitude of each wave peak, sees patterns, and translates the results into spatial information. Weld inclusions, voids, and hidden fractures are discovered when the readings are interpreted properly. In fact, those test results will quickly pinpoint the precise location of any material discontinuity so that the weld structure can be classed as a full-integrity join or a flawed creation that will require reworking.

Radiographic waves appear on X-Ray film as opaque and clear areas. As for ultrasonic testing, high-frequency vibrations penetrate weld surfaces and peer deep into their structural makeup. The filmed results and reflected sound waves create a picture, a detailed image of the welds internal anatomy. Clearly, these waves and images, X-Rays and electronically rendered impressions, require interpretation. That’s a job for an expertly trained weld testing professional.

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