CMI vs. ILI
What Is In-Line Inspection and Where Does It Apply
In-Line Inspection (ILI) uses instrumented devices — commonly known as pigs — that travel through the pipeline interior to measure wall condition. ILI tools typically rely on Magnetic Flux Leakage (MFL) or ultrasonic sensors to detect metal loss, cracks, and geometric anomalies from inside the pipe wall.
ILI is widely used in transmission pipelines that have pig launcher and receiver stations, consistent diameters, and predictable flow conditions. When these requirements are met, ILI delivers detailed internal wall data and is a well-established method in pipeline integrity management programs worldwide.
However, a significant portion of the global pipeline network cannot accommodate inline tools. Pipelines with tight bends, diameter changes, unbarred tees, or missing launcher stations are classified as unpiggable — and for these lines, ILI is simply not an option.
How CMI Inspects Pipelines from Above Ground
EMPIT’s patented Current Magnetometry Inspection (CMI) takes a fundamentally different approach. Instead of entering the pipeline, CMI applies a multi-frequency electrical current (2 Hz – 2 kHz) to the pipeline and measures the electromagnetic response from the surface — without excavation and without service interruption.
Through patented spectrum analysis, CMI distinguishes between active corrosion and coating defects — where bare steel is in direct soil contact and a corrosion cell is electrically active — and passivated corrosion, where a calcareous or oxide film has formed and the corrosion process has stopped. This distinction is critical: only active defects require excavation and repair, while passivated defects need only monitoring.
CMI is deployed via EMPIT’s carrier systems — the Current Mapper (handheld onshore), Yellowfin (offshore vessel), and Black Copter (drone) — equipped with up to 70 tri-axial sensors recording 20,000 data points per second. Defects are GPS-georeferenced with a precision better than 1 mm².
CMI and ILI — Key Differences at a Glance
CMI and ILI are not interchangeable — they differ in methodology, access requirements, and the type of information they deliver.
- Access: ILI requires physical access to the pipeline interior via launcher and receiver stations. CMI operates entirely from above ground — no excavation, no pipeline entry.
- Service interruption: ILI typically requires flow adjustments or temporary shutdowns. CMI inspects pipelines while they remain fully operational.
- Corrosion classification: ILI measures internal wall thickness and metal loss geometry. CMI classifies corrosion by electrochemical activity — distinguishing active from passivated defects.
- Applicability: ILI is limited to piggable pipelines with compatible geometry. CMI works on piggable and unpiggable pipelines alike, including steel, ductile iron, and grey iron — at depths up to 7 m onshore and 50 m offshore.
- Data output: ILI delivers a detailed internal profile of wall condition. CMI provides a surface-based corrosion activity map with georeferenced defect locations.
Important: CMI does not measure corrosion depth or wall thickness. The two technologies answer different questions — ILI asks “how much metal has been lost?”, while CMI asks “is corrosion actively progressing?”
When to Use CMI, ILI, or Both
The choice between CMI and ILI depends on pipeline accessibility, the information required, and the integrity management strategy in place.
- Unpiggable pipelines — CMI is often the only viable non-invasive inspection option for pipelines that cannot accept inline tools.
- Pre-ILI screening — CMI can identify critical zones before a full ILI campaign, helping operators focus resources where they matter most.
- Post-ILI validation — after an ILI run identifies metal loss, CMI can determine whether the corrosion is still active or has passivated — informing repair priority.
- Complementary data — combining ILI wall-thickness data with CMI activity classification gives operators a more complete picture of pipeline condition.
EMPIT’s CMI technology aligns with ISO 15589-1 and is ECDA-ready, making it suitable for integration into existing pipeline integrity management systems alongside non-invasive pipeline inspection services.
Talk to Our Team About Your Pipeline
Whether your pipeline is piggable, unpiggable, or somewhere in between — our team can help you determine the right inspection approach. Contact us to discuss your specific requirements.