High resolution magnetic PIGs: What do they detect and when should they be used?

An unexpected leak in a pipeline rarely occurs without prior warning signs. The real problem is that these signals often remain hidden until the damage has already become critical. In this context, high-resolution magnetic PIGs have revolutionized the way the internal condition of pipelines is assessed, enabling the detection of corrosion, metal loss, and anomalies with a level of detail previously unthinkable. Thanks to advanced MFL Technology, these tools not only identify defects but also transform the way pipeline integrity and operational reliability are managed.

What are magnetic PIGs?

They are instrumented devices that travel inside pipelines propelled by the product flow. Their main objective is to perform pipeline inspection without interrupting operations.

These devices use magnetic sensors to identify changes in the magnetic field caused by wall thickness loss in the pipe. This technique allows the condition of the pipeline to be evaluated without excavations or operational shutdowns.

High-resolution magnetic PIGs represent a technological evolution that improves detection sensitivity, allowing smaller defects to be identified and improving the overall asset diagnosis.

In practice, magnetic PIGs are highly valuable for modern condition-based maintenance programs, especially in critical systems where pipeline integrity is a priority.

MFL Technology in Inline Inspection

The core technology behind these systems is Magnetic Flux Leakage (MFL), widely used in inline inspection (ILI) of metallic pipelines.

When a magnetic PIG travels through the pipeline, it magnetizes the pipe wall. If corrosion or metal loss is present, magnetic flux “leaks,” generating signals recorded by high-precision sensors.

MFL Technology therefore enables continuous reading of pipeline condition, providing valuable information for integrity analysis.

Modern high-resolution magnetic PIG systems incorporate dense sensor arrays, improving corrosion mapping quality and enabling detailed digital models of internal pipeline conditions.

This transforms inline inspection into a predictive tool rather than a purely reactive one.

What do magnetic PIGs detect?

Magnetic PIGs are designed to detect a wide range of anomalies in metallic pipelines.

Main detections include:

• Internal and external corrosion
• Wall thickness loss
• Pitting corrosion
• Mechanical damage due to pressure or impact

High-resolution magnetic PIGs significantly improve the detection of small discontinuities, enabling more precise pipeline inspection.

Thanks to MFL Technology, these systems can generate detailed corrosion maps, identifying even early-stage degradation zones.

In terms of inline inspection, this represents a strategic advantage, as it allows failures to be anticipated before they become leaks or ruptures.

Corrosion mapping and integrity data

Corrosion mapping is one of the most valuable outputs obtained through magnetic PIGs.

This process consists of generating digital representations of metal loss inside the pipeline, allowing visualization of critical zones and degradation trends.

High-resolution magnetic PIGs provide higher data density, resulting in more accurate and reliable corrosion mapping.

This enables engineers to make data-driven decisions when evaluating pipeline integrity.

Additionally, advanced software integration allows correlation of results with operating conditions, improving maintenance planning.

In this context, inline inspection becomes a key tool for predictive asset management.

Advantages over other ILI tools

Compared to other inline inspection tools, magnetic PIGs offer significant advantages:

• High precision in metal loss detection
• Wide coverage over long distances
• Capable of operating in pipelines without extensive prior cleaning
• Continuous monitoring without interrupting flow
• Excellent cost-benefit ratio

High-resolution magnetic PIGs outperform conventional technologies by providing better resolution in defect detection.

In addition, MFL technology provides more consistent data for pipeline integrity analysis, which is critical in hydrocarbon transportation systems.

Compared to ultrasonic or caliper tools, magnetic PIGs stand out for their operational robustness and versatility.

Limitations of magnetic PIGs

Although high-resolution magnetic PIGs provide excellent results for corrosion and metal loss detection, they also have limitations.

The main limitation is that MFL Technology has lower sensitivity for detecting very fine cracks or defects without significant thickness loss. Additionally, internal debris, speed variations, or complex geometries can affect inline inspection accuracy.

For this reason, they are often complemented with other specialized technologies.

Comparison with other technologies

There are different inspection tools used to evaluate pipeline integrity. Each has specific advantages depending on the type of damage expected.

Technology	Operating Principle	Detected Defects	Advantages	Limitations
Magnetic PIGs (MFL)	Detect magnetic flux leakage due to metal loss	Corrosion, wall loss, pitting	High speed and excellent corrosion mapping	Lower sensitivity to fine cracks
Ultrasonic PIGs (UT)	Use ultrasonic waves to measure thickness	Localized corrosion and wall loss	High thickness accuracy	Usually require liquid medium
EMAT PIGs	Use electromagnetic acoustic waves	Cracks and SCC	Excellent crack detection	Higher complexity and cost
Geometric PIGs	Detect mechanical deformation	Dents and ovality	Internal geometry evaluation	Do not detect corrosion

EMAT technology (Electromagnetic Acoustic Transducer) uses electromagnetic acoustic waves to identify cracks associated with fatigue and stress corrosion cracking.

In many advanced pipeline inspection programs, multiple technologies are combined for more complete diagnostics.

When to use magnetic PIGs in pipelines

The use of magnetic PIGs is recommended under several operational conditions:

• When internal corrosion assessment is required
• In risk-based maintenance programs
• Before pipeline life extension projects
• In pipeline integrity audits

High-resolution magnetic PIGs are especially useful in aging pipelines or systems with a history of active corrosion.

Pipeline inspection using this technology is ideal when a balance between accuracy, cost, and operational continuity is required.

They are also key in periodic inline inspection strategies to monitor damage evolution.

How magnetic PIGs improve mapping

One of the greatest advantages of high-resolution magnetic PIGs is their ability to improve corrosion mapping.

Thanks to increased sensor density, higher diagnostic resolution is achieved, allowing smaller defects to be identified with greater accuracy.

Modern magnetic PIGs generate large volumes of data which, once processed, enable detailed models of pipeline internal condition.

This significantly improves decision-making in pipeline inspection, as engineers can prioritize repairs based on quantitative evidence.

Additionally, MFL Technology allows more accurate correlation between corrosion depth and extent.

Applications in corrosion and metal loss

The main applications of magnetic PIGs are related to corrosion and metal loss detection.

In the energy industry, these systems are essential for ensuring operational continuity and safety.

High-resolution magnetic PIGs enable more detailed evaluation of critical pipelines, especially in aggressive environments where corrosion is accelerated.

MFL-based inline inspection helps identify high-risk zones before structural failures occur.

Furthermore, the data obtained allows mitigation strategies based on real conditions, strengthening long-term pipeline integrity.

Pipeline integrity and decision-making

Pipeline integrity depends directly on the quality of information obtained from pipeline inspection.

Magnetic PIGs provide critical data for risk evaluation, repair prioritization, and asset life extension.

High-resolution magnetic PIGs offer a more complete view of the internal pipeline condition, enabling evidence-based decisions.

When integrated into integrity management systems, inline inspection results become strategic tools for operational planning.

This reduces the risk of catastrophic failures and optimizes maintenance costs.

Conclusion

High-resolution magnetic PIGs represent a major evolution in modern pipeline assessment. Their ability to detect corrosion, metal loss, and internal defects using MFL Technology makes them an essential tool for inline inspection. Additionally, they improve corrosion mapping and strengthen pipeline integrity through accurate and reliable data. Their use is fundamental in pipeline inspection programs focused on reliability, safety, and optimization of industrial maintenance.

References

1. American Petroleum Institute. (2021). API Recommended Practice 1160: Managing System Integrity for Hazardous Liquid Pipelines (5th ed.). American Petroleum Institute.
2. American Petroleum Institute. (2022). API 570: Piping Inspection Code: In-service Inspection, Rating, Repair, and Alteration of Piping Systems (5th ed.). American Petroleum Institute.
3. International Organization for Standardization. (2021). ISO 12747 Gas Industries — Pipeline Transportation Systems — Pipeline Integrity Management Systems. ISO.
4. NACE International. (2021). SP0206-2021: Internal Corrosion Direct Assessment Methodology for Pipelines Carrying Normally Dry Natural Gas (DG-ICDA). NACE International.