The Benefits of Immersion Ultrasonic Inspection of Composites

Ultrasonic testing (UT) uses sound waves to detect cracks and defects in materials, including composites. Its ability to produce clearly defined images and indicate characteristics deeper than surface-level make it a highly regarded non-destructive test (NDT) method for industries such as Oil & Gas, Aerospace, and Power Generation.

When any new composite material is developed, the properties of the composite need to be carefully determined through qualification testing involving multiple specimens. Ultrasonic inspection uses electronic transducers to transmit high-frequency sound waves through the material. These sound waves bounce back signals which can reveal key characteristics of the material’s properties and indicate issues such as cracks, inclusions, and other subsurface defects. UT can also be used to measure a material’s thickness, such as the wall of a pipe.

There are two key methods of ultrasonic inspection, contact, and immersion ultrasonic testing (IUT), the latter being particularly applicable for the examination and qualification of composites.

Especially useful for the detection of smaller defects

A laboratory-based inspection, IUT is especially useful for detecting smaller defects, from cracking to porosity. By submersing the composite, sound travel from the transducer is enhanced, providing more accurate reporting of sub-surface irregularities and flaws.

IUT can support a broad range of requirements as it can be applied to many composite materials. IUT services can identify cracking, porosity, inclusions, and delaminations. It is especially useful for the oil and gas industry to identify incomplete penetration, lack of sidewall fusion, and other weld strength defects.

Element’s global testing laboratories are home to some of the world’s most cutting-edge IUT equipment. The laboratories house a bespoke combined immersion and jet probe system which has the option of using standard pulse-echo immersion techniques or through-transmission. The highly versatile system can inspect composite materials with flat and curved surfaces as well as varying geometries. The system’s evaluation software automatically records the results, which readily converts the ultrasound responses into A, B, and C scan images offering cross-sectional and plan views of the results.

Conventional immersion inspection

The system carries out conventional immersion inspection utilizing an immersion manipulator with the composite located above a glass reflector plate mounted on a leveling table. This technique is ideal for thin monolithic components where sufficient signal is available to pass through the component twice.

Water jet through-transmission inspection

Dense materials and those that dissipate sound to a large degree, such as glass fiber composites, are more suited to the system’s ability to offer water jet through transmission inspection. This has become the industry-standard method of inspection for such composites. It is also the most suitable technique for inspecting buoyant composites and those which have been used in components subject to water ingress, where immersion would cause problems.

Previously, Element’s IUT specialists were asked to meet with a composite manufacturer that was producing a composite designed for a specific aerospace component for a leading aerospace manufacturer.

The manufacturer brought a reference panel – a known defect sample with seeded defects — with them to the meeting at Element’s laboratories. Element offered to inspect the panel on its immersion ultrasonic system, which immediately picked up all the known defects.

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