Olsson Associates

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Non-destructive Testing 101

Wednesday, August 14, 2013

Sarah Ferdico, Communications

Liquid Penetrant Testing - An NDT testing methodFrom our bridges to our Tilt-o-Whirl carnival rides, sound construction must be monitored not only by the naked eye but also through careful testing to observe what our eyes can’t see. Olsson’s Non-destructive Testing (NDT) staff members understand that not all can be observed just by visually inspecting the structures we use, walk, or drive upon. Often, we must be able to see through structures to determine they are safe. Such a practice requires much time and skill, and it is what Olsson’s NDT staff members excel at.

NDT is the science of examining material properties for potential “subsurface discontinuities” without causing any damage to the material. These subsurface “defects” typically are not visually apparent. Materials that appear sound upon visual examination may actually be nonconforming to a specification or be unsuitable for the intended use. By detecting unseen defects and taking timely corrective actions, Olsson’s NDT inspectors give clients assurance that the structure or component being built will provide reliable and safe service. 

NDT is commonly used for commercial and industrial applications. Airplane engines, bridges, pipes, boilers, railcar wheels, and the like all undergo various levels of NDT inspections to ensure their safety.

NDT Testing Methods

So, how does an NDT technician determine if a structure is sound? Several methods are available and are described in detail below.

Visual

Method: The visual method is a practical quality control inspection, which is relatively quick and inexpensive. It requires no special equipment.

The objective of the visual method is to observe any discontinuities, cracks, porosity, undercut, or overlap in the structure. The visual method also looks at the structure’s dimensions and profile to determine its soundness.

Ultrasonic

Method: Ultrasonic pulses are directed into the test object. Ultrasonic echoes and reflections indicate the absence, presence, and location of flaws. It also can detect interfaces and/or discontinuities.

When using the ultrasonic method, technicians are looking for discontinuities, separations, cracks, voids, laminations, inclusions, lack of fusion/penetration, and the structure’s regulated thickness to ensure it is structurally sound.

Magnetic Particle

Method: The test object or part is magnetized. Magnetic powder is applied to the surface and accumulates over regions where the magnetic field reveals surface flaws.

When using this method, technicians are looking for discontinuities, separations, cracks, seams, pores, and inclusions to determine if it is constructed according to regulations.

Liquid Penetrant

Method: The test surface is covered with penetrating liquid that seeks open-to-the-surface discontinuities. Liquid in cracks bleeds out to stain powder-coating applied to the surface after removing excess liquid film from the surface of the test object.

With this method, technicians are look for discontinuities that are open to the surface of solid and nonporous materials.

Radiography

Radiography testingMethod: A photographic image is produced by passing x-rays and/or electrons through a test object onto a film.

The radiography method allows technicians to detect discontinuities and separations, cracks, inclusions, porosity, voids, and the lack of fusion/ penetration.

For more information on NDT methods and how NDT can assist with your project, please contact Eric Nordhues at 402.827.7220 or enordhues@olssonassociates.com.

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