In the early 21^st century, a team of researchers in DNV (Norway) developed an ultrasonic technology for the inline inspection of gas pipelines without using a liquid batch. The technology has subsequently been used to inspect more than 15,000 kilometers of operational gas and liquid pipelines around the world.

The authors are presenting a review of lessons learned during the deployment of this new technology and reflecting on the advantages and limitations.

A summary is presented of validation work completed, both through pull testing and field excavations.

Several different use cases are considered; one being deployment of acoustic resonance ILI for the base line inspection of newly constructed gas pipelines. In particular, the others will highlight a number of long distance gas transmission pipelines that have been inspected using acoustic resonance ILI, and highlight the benefits of ultrasonic baseline for pipelines.

Furthermore, the tools have shown notable flexibility in the field of difficult-to-inspect gas and liquid pipelines. Notably, large diameter variations have been traverse, and bidirectional inspections have been performed, as well as extremely long duration runs.

A summary of completed work will be of value to all pipeline operators of challenging pipelines, in particular offshore, demonstrating challenging pipeline inspection projects which have been completed successfully.