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Introduction: Subsea & Offshore Service (SOS) Magazine picks the brains of Dr Michael Smith, Technical Director at TSC Inspection Systems – a global provider of high-performance NDT solutions for the inspection of critical components and assets in such major industries as oil & gas, nuclear, power generation and transportation.

Dr. Michael Smith, Technical Director at TSC Inspection Systems.


Welcome to SOS Magazine, so first up please introduce yourself and TSC Inspection Systems offering...

Hi, I am Mike Smith, the Technical Director at TSC, mainly working with the Alternating Current Field Measurement (ACFM) nondestructive inspection technique. 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.

Prior to Alternating Current Field Measurement (ACFM) Testing, what was the preferred method for NDT and what were its setbacks?...

Prior to ACFM, in the subsea world, Magnetic Particle Inspection (MPI or MT) was typically used to locate surface-breaking defects in structural welds. The drawbacks with this particular method were that it required a very high level of surface cleaning, back to bare metal, and the removal of any coating present. The surface length of any indications could be measured but it could not give a measurement for defect depth, which is the most relevant parameter in determining the severity of a defect and how it impacts the remaining life of the structure. Alternating Current Potential Drop (ACPD) was sometimes used to predict the depth but this was very difficult to conduct underwater due to the need to maintain good electrical contact between the voltage probe and the steel surface. Conventional Eddy Current Testing (ET) was also employed, however it struggled to reliably detect some flaws in carbon steel welds due to their electromagnetic complexity and was limited to predicting a maximum crack depth of about 5mm (0.2 in).

How is ACFM different to previous methodologies used?...

ACFM was designed so that it doesn’t require extensive cleaning or bare metal on which to operate which dramatically reduces the preparation time and cost. ACFM is designed around a uniform field input which leads to some important advantages over some other techniques: the probes don’t require on-site calibration, the probe scan patterns are simple as the probe is scanned along the line of the weld and the lift-off response is reduced so that the inspection is relatively insensitive to changes in probe handling and surface irregularities. Another important advantage is that ACFM can size much deeper defects, up to 25mm (1 in) in depth, which can be valuable information in thick walled structures. All ACFM data is stored electronically meaning that it is available for later evaluation or audit purposes.

Is there a general acceptance in the sector for ACFM and are there any certifications/standard practices in place?...

ACFM is a widely accepted inspection technique in the fields of oil and gas, petrochemical industry, and marine industries by bodies such as ABS, Lloyds Register, DNV-GL and BV. Standards featuring ACFM are also published by ASTM, ASME, and COFREND. Training is offered for technicians under schemes run by PCS, CSWIP, ASNT and ABENDI.

What challenges has TSC Inspection Systems / Eddyfi encountered in the development of ACFM equipment?...

One of the challenges has been to keep aligned with the trends and forces which change the way in which inspections are carried out. An example of this is the move towards using remote deployment devices, such as ROVs, to carry out inspection work that previously would have been done by divers. Also, operations in deeper waters mandate the use of remote intervention.

How have you overcome those challenges in your latest generation of ACFM equipment?...

TSC Inspection Systems / Eddyfi Technologies have developed specific array probes and tooling which enable inspection by ROV through the use of crawlers and scanners. Our new subsea instrument, the U41, is now available configured either for diver use or for integration onto an ROV. 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.

What do you think the future holds for NDT/ACFM?...

It is an exciting time for NDT generally and ACFM in particular. The market is demanding greater performance from its NDT solutions and advanced techniques, like ACFM, can leverage advances in electronics, software and new materials to tackle new and challenging inspection problems. 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 ideally placed to provide a solution for some of these inspections.

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