ACFM – Alternating Current Field Measurement
ACFM – Alternating Current Field Measurement
Alternating Current Field Measurement (ACFM®) is an advanced Non-Destructive Testing (NDT) technique designed to detect and size surface-breaking cracks in metals through coatings with an excellent surface tolerance compared to Eddy Current (EC).
For 30 years, ACFM electromagnetic inspection technology has been the method of choice for detecting and sizing subsea surface-breaking cracks. Recognised and approved by many certification bodies, including DNV, ABS and Lloyds, the technique has been used successfully to supersede traditional non-computerised and more user-dependent methods, such as magnetic particle inspection (MPI). As today’s industry is looking to scale the use of auditable NDT methods to all their assets, faster, more flexible, remotely deployed inspections and better reporting capabilities are required.
TSC Subsea’s ACFM technology was initially designed to assist divers in identifying and sizing fatigue cracking in jacket structures. Consequently, it is no surprise that this NDT technique has evolved into a standard for detecting and defect sizing of subsea cracks.
Our approach involves the utilisation of the U41 true subsea inspection system, acknowledged as the industry benchmark for inspections conducted by both divers and remotely operated vehicles (ROVs). In scenarios where achieving a high Probability of Detection (PoD) and minimising false calls are critical for determining offshore asset integrity, the U41 system excels. The system’s precision in accurately sizing defects provides essential information, enabling engineering decisions that safeguard and prolong the lifespan of these valuable assets.
Why use ACFM for Subsea Weld Inspection
Immediate defect sizing and recording is a major benefit compared to other NDT methods. Results from independent testing show that ACFM matches MPI performance when inspecting underwater structural welds. The amount of missed and spurious signals is significantly lower with ACFM compared to MPI and conventional eddy current testing. And, with ACFM’s lower cleaning requirements and fewer false calls, inspections are significantly shorter, maximising inspection campaigns.
Only Trust True ACFM
The True Alternating Current Field Measurement (ACFM) is described in the original patents and described in many technical papers from the origin of the technique at University College London.
Only the True ACFM Technique has been recognized over the years by authorization bodies.
- No on-site calibration – sizing is based on a mathematical solution of the field crack indication.
- A uniform field inducer.
- A constant current field drive.
- Orthogonal sensors in the Bx and Bz axes.
- Ability to sample the sensors at a discrete phase relative to the field inducer.
- Large inducer surface height compared with sensor surface height.
DNV Approved Service Supplier
Independent Approvals
Non-Destructive Testing of Hull Welds, February 2014. Section 6, ACFM Technique.
ASME V Article 15: ACFM Technique, 2006
Standard Practice for Examination of Welds using the ACFM Technique (E2261-03), latest revision E2261-12.
Standard Practice for Examination of Drill String Threads using the ACFM Technique (E2928-13)
Accepted for in-service examination of structural welds. TSC is also an LR-certified ACFM Inspection Services Provider.
Classification Note No. 7, March 2012. Section 2.1, Detection of Surface-Breaking Cracks.
BS EN ISO 19902: Petroleum and natural gas industries. Fixed steel offshore structures.
Approved technique for surface-breaking crack detection
North Sea standards (NS-2), 2012 revision: Accepted alternative to MPI for drill string thread inspection