Aboveground Pipeline Inspection for Unpiggable Pipelines
Why Many Pipelines Cannot Be Inspected with Inline Tools
A large portion of the global pipeline network cannot be inspected using conventional in-line inspection (ILI) tools — commonly known as pigs. Pipelines are classified as unpiggable when they contain tight bends, diameter changes, unbarred tees, or lack launcher and receiver stations. In many cases, pipelines in urban areas, industrial facilities, or environmentally sensitive zones are simply inaccessible for traditional methods.
This creates a significant gap in pipeline integrity management. Without reliable inspection data, operators face increased risk of undetected corrosion, coating degradation, and potential failures — particularly on aging infrastructure where the remaining service life is uncertain.
The challenge is compounded by the fact that many unpiggable pipelines carry critical media — natural gas, crude oil, hydrogen, or industrial chemicals — where failure consequences are severe.
How Aboveground Inspection Works with CMI Technology
EMPIT’s patented Current Magnetometry Inspection (CMI) technology addresses the unpiggable pipeline challenge by inspecting buried pipelines entirely from above ground. Unlike ILI tools, CMI does not require physical access to the pipeline interior. Instead, the system applies a multi-frequency electrical current (2 Hz – 2 kHz) to the pipeline and measures the resulting electromagnetic response from the surface.
Through patented spectrum analysis, CMI distinguishes between active corrosion — where bare steel is in direct contact with soil and a corrosion cell is electrically active — and passivated corrosion, where a calcareous or oxide film has formed and the corrosion process has stopped.
Key capabilities of CMI for unpiggable pipeline inspection:
- No excavation required — inspection is performed from the surface, even at depths up to 7 meters onshore and 50 meters offshore
- No service interruption — pipelines remain fully operational during inspection
- GPS-georeferenced defect localization — precision better than 1 mm² for individual defect mapping
- Active vs. passive defect classification — only active defects require excavation and repair, reducing unnecessary interventions
- Applicable to multiple materials — steel, ductile iron, and grey iron pipelines
The technology is deployed via EMPIT’s carrier systems: the Current Mapper (handheld onshore device), Yellowfin (offshore vessel), and Black Copter (drone-based system), equipped with up to 70 tri-axial sensors recording 20,000 data points per second.
Where Aboveground Inspection Replaces or Complements ILI
CMI-based aboveground inspection is not limited to pipelines that are technically unpiggable. It is also used in situations where ILI is possible but impractical, too costly, or where operators seek a complementary data source.
Typical use cases for aboveground pipeline inspection with CMI include:
- Unpiggable transmission and distribution pipelines — including gas distribution networks with multiple diameter reductions, bends, and branch connections
- Complex industrial facilities — refineries, chemical plants, LNG terminals, and airport fuel systems where pipeline routing prevents pig launching
- Urban and road-crossing pipelines — where excavation is restricted and above-ground access is the only viable option
- Pre-ILI screening — identifying critical zones before committing to a full ILI campaign, reducing overall inspection costs
- Post-repair verification — confirming that a repair or recoating intervention was successful without re-excavating
EMPIT’s inspection approach aligns with ISO 15589-1 and is ECDA-ready, making it suitable for integration into existing pipeline integrity management systems.
Request an Inspection for Your Unpiggable Pipeline
Whether you operate a gas distribution network, an industrial facility pipeline, or a cross-country transmission line — if your pipeline cannot be pigged, EMPIT can inspect it from above ground. Contact our team to discuss your specific inspection requirements.