HomeKnowledge CentreLatest News

All About Guided Wave Testing

Readily accepted as a superior method of NDT testing that detects corrosion under insulation in pipework, guided wave technology is commonly utilised within the oil and petrochemical industries.
Man guided wave testing

Readily accepted as a superior method of NDT testing that detects corrosion under insulation in pipework, guided wave technology is commonly utilised within the oil and petrochemical industries.

Whilst the torsional wave mode is readily in use, embracing the ability of longitudinal testing is often dismissed due to the perceived difficulties it represents. However, while no-one can deny that the use of longitudinal wave mode is more challenging, it brings about increased benefits.

To fully understand what these are it’s necessary to first compare how the two methods work.

Torsional Wave Testing

When testing for Long Range Ultrasonics the only wave mode that exists is that of T (0,1) within the frequency range. Torsional wave testing is relatively simple to carry out, thanks to users only needing to control the direction of the wave propagation. The frequency range doesn’t disperse, leading to constant velocity, and only two rings of transducers are necessary.

The technology is widely used as an effective method of pipe inspection in inaccessible areas, including jetty lines, refineries, power plant tubing and river crossings.

Longitudinal Wave Testing

 The biggest difference when it comes to longitudinal testing is that of having two waves – the first being dispersive, L (0,1) and the second nondispersive L (0,2). This requires an additional ring of transducers to effectively control the waves, as it’s necessary to suppress the dispersive (and therefore unwanted) portion of the former.

This, therefore, brings with it increased challenges, including:

  • More complex electronics and software
  • The likelihood of the longitudinal wave transmitting through liquids and causing reverberations
  • Interpretation of the returned results

While these are, indeed, issues that need to be overcome, the use of the two modes concurrently brings many advantages.

Benefits of combining torsional and longitudinal wave testing

When it comes to the testing of inaccessible applications where torsional testing alone would only provide partial inspection, a combination of the two provides operators with the to carry out a full survey in areas that would otherwise only be partially inspected. The longitudinal aspect overcomes issues such as complex geometry within pipes (for example, axially welded pipe supports), leading to accurate readings that extend significantly further along pipelines than that of torsional testing alone.

When it comes to accurate data and the ability for a more advanced and earlier detection of corrosion within such inaccessible assets, consideration of this dual testing provides operators with a distinct advantage.

The technology now exists that has overcome the perceived difficulties of such testing, and removed factors that led to the use of longitudinal testing being dismissed as too complicated. The Teletest Focus+ was the first commercially available system that effectively brought the dual technology of torsional and longitudinal testing to market, and offers unrivalled penetration and frequency.

Such advanced solutions are at the core of the philosophy brought to the clients of leading global equipment provider, Nexxis. Our team of industry professionals understand the need for operators to have access to flexible options, as requirements constantly evolve and the need for an adaptable provider is essential for productive, cost-effective resolutions.

This innovative approach has been a welcome change that allows forward-thinking companies to effectively reduce the cost of equipment outgoings while having access to the very latest technology. This effectively gives them a crucial advantage over its competitors.

To discover how this unique ‘Nexxis difference’ can benefit your operation, call 08 9418 4952 for an exploratory chat or visit

Join our mailing list // Discover a world of forward-looking solutions designed to shape the future. Ready?