Different Techniques in Testing Welds Using Non-Destructive Testing

26 April 2018

As we’re all taught in life, surface appearances can be deceiving. That proverb might as well be written on the front of every non-destructive weld testing instruction book, for even the best, most well-formed welds can hide a multitude of sins. Non-destructive testing techniques look past that surface. They don’t affect the weld’s part’s linking power in any way whatsoever. Let’s run through the different NDI techniques.

Apply Visual Acuity

A seasoned weld inspection technician analyzes welds with a critical eye. The shape and consistency of the HAZ (Heat-Affected Zone) is assessed in this manner. Of course, the human eye is fallible, and a simple pair of corrective lenses can only do so much. The tools of the profession come to the aid of the naked eye. There are micrometres and microscopes that aid visual tests. Borescopes, cameras with a flexible lens barrel, look even deeper so that a fused area receives the quality-assessing attention that’s required.

Dye Penetrant Tests 

Another member of the NDI arsenal, bottles of specially prepared dyes, are kept in the tech’s toolkit. They seep into impossibly narrow cracks and highlight those near invisible discontinuities until they’re easy to spot. Applied sometimes as a fluorescing colourant, this technique helps to identify weld issues when non-ferrous fusion sites are employed.

Perfectly Applied Electronic Solutions 

This is the upper echelon, the area of this professional field that calls upon special instrumentation. Ultrasonic testers and radiographic instruments send harmless waves of invisible sound or radio waves deep inside suspect welds. They bounce off of internal flaws or are absorbed into the material defects. As the reflected/absorbed energies are captured by an accompanying sensory mechanism, the scanning effect is rendered on a screen as a series of wave-captured data or even as a fully imaged picture.

Completing the non-destructive test toolkit, we arrive at magnetic particle testing. In plain English, a magnetic field flows through the weld. The generated field of magnetic energy flows unbroken, except at a point where a hidden continuity exists. Iron filings aid this technique, especially when the test is used alongside a visually conducted inspection. Expect a magnetic field generator of some type when this procedure is actioned. Otherwise, the weld characteristics and the test conditions determine the selected NDT analysis method. Magnetic instruments obviously work well when ferrous-heavy welds are in use. If this is a non-ferrous joint, a dye test may be in order. Ruling all of these instances, sensory instrumentation tests see far below surface obstacles and discover hidden weld discontinuities.


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