ACFM Inspection of Storage Tank Welds

A Strict Regulatory Framework for Storage Tanks

Storage tanks are major industrial assets. Their periodic inspection aims to ensure mechanical integrity, personnel safety, and the prevention of environmental risks.

The inspection program for a tank is defined by its construction standard — CODRES, EEMUA 159, or API 653 — as well as by French regulatory frameworks, particularly the Industrial Installations Modernization Plan (PM2I).

This plan relies on technical guidelines such as DT 94 or their industry-specific equivalents (for example, the Copacel Guide for paper mill sites).

These documents govern the implementation of Non-Destructive Testing (NDT) by requiring a high probability of detection and a high level of operator safety.

Within this framework, weld inspection represents a key step in periodic assessments.

The Limitations of Traditional Methods

Magnetic particle inspection has historically been the most widely used method for detecting surface cracks on tank welds.

While effective, it presents several limitations:

Extensive surface preparation (cleaning, degreasing, paint removal).
Use of aerosols and magnetic powders, generating waste and posing inhalation risks.
Low productivity: typically 5 to 10 m/h for thorough manual inspection.

To reduce inspection time and operator strain, the ACFM method (Alternating Current Field Measurement) offers a more suitable alternative for today’s industrial requirements.

Principle and Advantages of the ACFM Method

ACFM is an electromagnetic Non-Destructive Testing (NDT) technique used to detect surface-breaking cracks on metallic welds without requiring extensive surface preparation.

Principle

An alternating current is injected into the metal surface.
The presence of a crack disturbs the local electromagnetic field; this disturbance is measured by the ACFM sensors, which determine the position, length, and an estimated depth of the defect.

Advantages

Fast detection of longitudinal cracks on shell-to-bottom welds, vertical welds on the first shell course (V1), and the V1–V2 junction.
No need for full paint removal: ACFM operates through thin, non-conductive coatings or paint layers.
No aerosols or magnetic powder: the method minimizes chemical exposure risks.
High inspection speed: 60 to 80 m/h — nearly ten times faster than manual magnetic particle testing.

This rapid implementation, combined with excellent sensitivity to longitudinal cracking, makes ACFM a highly effective method for periodic inspection of atmospheric storage tanks.

Regulatory Framework: Integration into PM2I-DT94

The PM2I-DT94 framework specifies that weld inspections must ensure:

A high probability of detection,
A recognized and validated methodology,
A reduction of risks for inspection personnel.

The ACFM method meets these requirements:

When an indication is detected by ACFM on a weld:

Signal validation: the operator confirms signal consistency and rules out false positives.
Confirmation by magnetic particle inspection: the defect’s presence is verified according to the applicable procedure.
Repair: if a crack is confirmed, the weld must be repaired in compliance with current standards before the tank is returned to service.

Roboplanet: NDT Expertise and Technologies

Roboplanet is a French company specialized in automated Non-Destructive Testing (NDT).
We perform regulatory inspection services on storage tanks in full compliance with PM2I-DT94, CODRES, EEMUA 159, and API 653 standards.

Our Positioning

Automation of manual inspections through our proprietary robotic solutions.
Targeted interventions across France and international commercialization of our NDT technologies.
MASE safety approach, applied at every stage of the inspection process.

Roboplanet combines field expertise and innovation to reduce inspection time and enhance the safety of maintenance operations on industrial storage tanks.

ACFM is a proven method, used for many years and recognized in construction and maintenance codes.
Its contribution to periodic inspections is highly positive: faster than magnetic particle testing, it helps reduce downtime and operator strain, while maintaining a high level of reliability.

Our services are carried out within a MASE-certified safety framework, ensuring maximum protection for both our operators and your installations.

Also discover our robotized inspection and thickness measurement solutions, designed to optimize regulatory shutdowns — with no need for access scaffolding or confined entry.