EDDYFI TECHNOLOGY develop an ACFM solution for underwater non-destructive inspections

What is ACFM?

It is a flourishing time for NDT, and ACFM (Alternating Current Field Measurement) in particular. The drive towards safer inspection operations in difficult environments is forcing change in the mechanisation of inspection deployment, and a technique such as ACFM is perfectly suited to provide a solution for some of these inspection challenges. ACFM is an electromagnetic inspection technique that introduces an alternating current into the surface of a component to detect surface-breaking cracks and then size them for length and depth.

How is ACFM suited for subsea inspections?

Prior to ACFM, the inspection methods for the subsea world were not so easy to carry out. Removal of all coating and a very high level of surface cleaning up to bare metal were required, and the surface length of indications could be measured, but could not give a measurement for defect depth, which is the most relevant parameter in determining the severity of a defect. As today’s industry is looking to scale the use of auditable NDT methods to all their assets, faster, more reliable, easier to deploy inspections and better reporting capabilities are required. With that in mind, we decided to elaborate on a product that would meet those new requirements: Eddyfi Technologies’ TSC’s U41.

U41, the ultimate ACFM solution for underwater non-destructive inspections

Following the success of the U31, our subsea inspection system, TSC developed an enhanced version of their subsea inspection instrument: a unit that can operate using divers as well as being deployed remotely with Remotely Operated Vehicle (ROV) systems. Recognised and approved by many certification bodies, including DNV, ABS and Lloyds, the ACFM technique has been successfully deployed by divers and ROV for the inspection of structural node welds on jackets, caisson inspection, pipeline damage, spudcans, welded plate structures, mooring systems, including chains, among others.

Dr. Michael Smith, Technical Director of TSC comments, “The U41 system has been completely redesigned with new electronics, which delivers the highest resolution for ACFM data the industry has seen.  New features include the ability to connect 3 probes simultaneously, which avoids frequent returns to the surface, and a diver array probe, which reduces the number of scans and allows for faster recognition and characterisation of defects. The umbilical reel is dramatically reduced in size, weighing one third less and taking one third less space. These features have been coupled with an innovative software package which continues the ease of use that past operators have become familiar with while adding many time saving features.”

Faster inspections

Inspection integrity and speed are improved with the support of the new mini-array probe. This allows faster recognition and characterisation of defect calls as the diver does not need to repeat parallel scans to distinguish a defect from a spurious signal. The new instrument electronics also acquires data 10 times faster than the previous generation.

Safer and more reliable

The U41 has an improved ACFM signal quality with 14 times the data resolution of the previous instrument. The new electronics allow for better signal filtering and the ability to inspect coating twice as thick as before. Probe configurations are now stored on the probe itself instead of on a remote PC, ensuring that the correct setup is used and enhances data storage security.

An adaptable system

Eddyfi Technologies have developed specific array probes and tooling which enable inspection by ROV through the use of crawlers and scanners, working with the U41R. Every inspection is different, and we focused on the development of custom tools and probes which are optimised for a variety of geometries and inspection environments, even the harshest ones.