ACFM Inspection of Storage Tank Welds
Storage tanks are critical industrial assets. Their periodic inspection is intended to ensure mechanical integrity, personnel safety, and the prevention of environmental risks. Within this framework, weld inspection is a key step in periodic inspection programs.
The inspection program for a tank is defined by its construction code â CODRES, EEMUA 159, or API 653 â as well as by French regulatory frameworks, especially PM2I, which relies on technical guidance documents including DT94.
The limitations of traditional methods
Magnetic particle inspection has historically been the most widely used method for detecting surface cracking on tank welds. Although effective, it has several constraints:
- Extensive surface preparation required (cleaning, degreasing, paint removal)
- Use of aerosols and magnetic powders â generating waste and inhalation risks
- Low productivity: typically 5 to 10 m/h for thorough manual inspection
Principle and advantages of the ACFM method
ACFM (Alternating Current Field Measurement) is an electromagnetic NDT technique used to detect surface-breaking cracks on metallic welds, without heavy surface preparation.
Principle. An alternating current is induced into the metal surface. The presence of a crack disturbs the local electromagnetic field; this disturbance is measured by ACFM sensors, which determine the position, length, and an estimate of the defect depth.
5 â 10 m/h
Full paint removal required
Aerosols and magnetic powders
Low productivity
60 â 80 m/h
Works through paint
No chemical products
10Ã faster
- Fast detection of longitudinal cracks on annular-to-shell welds, vertical V1 welds, and the V1-V2 junction
- No full paint removal: works through thin coatings or non-conductive paint
- No aerosols or powders: reduced risks related to chemical products
- 60 to 80 m/h: nearly ten times faster than manual magnetic particle inspection
Regulatory framework: integration into PM2I-DT94
PM2I-DT94 specifies that weld inspections must ensure a high probability of detection, a recognized methodology, and reduced exposure to risk for operators.
ACFM meets these requirements
The method is recognized by the regulations, notably in the PM2I technical guide DT75, which defines approved methods for finding indications.
It removes several hazardous preparation steps and reduces operator strain, particularly by avoiding aerosol inhalation and prolonged working positions that contribute to musculoskeletal disorders.
All detected indications are systematically confirmed by magnetic particle inspection.
Actions to take in case of an indication
Signal validation
The operator confirms the consistency of the signal and rules out false positives.
Magnetic particle confirmation
The presence of the defect is verified according to the applicable procedure.
Repair
If confirmed, the weld is repaired according to the applicable standards before return to service.
ROBOPLANET: NDT expertise and technologies
ROBOPLANET works on storage tanks to deliver regulatory inspection services compliant with PM2I-DT94, CODRES, EEMUA 159, and API 653.
- Automation of manual inspections through our proprietary robotic solutions
- Operations in France and international commercialization of our NDT technologies
- MASE safety approach applied at every stage of the inspection process
ACFM is a proven method recognized in construction and maintenance codes. Faster than magnetic particle inspection, it helps reduce downtime and operator strain while maintaining a high level of reliability.
10Ã faster, no paint removal, no aerosol â ACFM modernizes storage tank weld inspection while remaining fully compliant with regulatory requirements.
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