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Innovative Sensors for Pipeline Crawlers to Assess Pipeline Defects and Conditions
Project Number

The goal of this project is to develop electromagnetic sensors (based on eddy current technology) that can be integrated with a robotic platform (crawler) to conduct internal natural gas pipeline inspections. Combinations of sensor types will be used to assess a wide range of pipeline conditions, including corrosion (pitting, localized, and extended), mechanical damage, cracking, and seam weld defects. Small physical size and weight, as well as low electrical power consumption, are the primary design constraints for the crawler systems.

Rotating permanent magnet inspection device for a twelve inch pipe
Rotating permanent magnet inspection device for a twelve inch pipe



Battelle Columbus Laboratories – research products and project management

Columbus, Ohio 43201


Internal inspection of pipelines is an important capability for ensuring safe and reliable delivery of fossil energy products. However, not all pipelines can be inspected with current systems that move inside the pipeline propelled by the product flow. Inspection platforms that crawl slowly inside a pipeline are being developed to maneuver past the physical barriers that limit inspection. Small physical size and weight, as well as low electrical power consumption, are the primary design targets for crawler sensor systems. Pipeline inspection equipment in commercial use today has not been designed to meet these goals, rather, most equipment focuses on high-speed, long distance inspection.

For this project, Battelle will develop innovative electromagnetic sensors for pipeline crawlers. The electromagnetic techniques will incorporate moving permanent magnets, either rotating (for the case of sinusoidal eddy currents) or translational (for pulsed eddy currents). Such magnets reduce power consumption and improve energy coupling into the pipe wall. The successful development of this concept will augment other eddy current technologies currently available or being developed.

Battelle will develop sensor prototypes for bench scale testing on a representative defect by evaluating defect detection characterization potential, as well as implementation considerations including power, size, and mass. Development will include four subtasks: (1) establish resolution requirements for the sensor systems by combining historical incident defect data assessment criteria, (2) review general physical constraints and obstructions that challenge current internal inspection methods and review current pipeline crawler platforms to assess preliminary specifications for the sensor systems, (3) design and develop sensors that efficiently induce strong electromagnetic signals in the pipe using high-strength permanent moving magnets, and (4) perform bench scale tests to assess the performance of the electromagnetic sensor systems and ensure that they can detect all significant defect types and magnitudes.

Battelle will then identify and select sensors to be hardened and mounted on test bed inspection equipment. Detection and characterization capability will be quantified on a full range of defects under unpressurized conditions, using the inspection vehicles, pull rigs, and defect sets available at Battelle’s Pipeline Safety and Reliability Center. Sensor systems will be optimized to achieve desired performance levels.

Finally, if a suitable crawler platform is available at a reasonable level of development, the sensors with the greatest potential for pipeline inspection will be combined with the crawler system and tested. Final testing will be performed at the pipeline test facility or, if available, on an operating pipeline.

Finite-element modeling results for a two-pole magnetizer
Finite-element modeling results for a two-pole magnetizer

The image on the left shows the logarithm of the magnitude of the currents at the inside pipe wall. The current is strongest at the magnetizer poles, but becomes uniform at a distance of about half a pipe diameter away. The image on the right shows the current flow in the pipe, the direction as indicated by the arrows. While the current flow is complex near the rotating magnet poles, the current at a pipe diameter or more away from the magnetizer is uniform and sinusoidal.


This combined inspection tool will provide a means of non-destructive natural gas pipeline examination and provide a technique for inspecting a large portion of the pipeline infrastructure that cannot be inspected with existing equipment (unpiggable pipelines).

Accomplishments (most recent listed first)

Battelle is developing a rotating permanent magnet inspection system where pairs of permanent magnets are rotated around the central axis. This alternative to the more common concentric coil method can be used to induce high current densities in the pipe. Along the pipe away from the magnets in either direction, the currents flow in the circumferential direction. Anomalies and wall thickness variations are detected with an array of sensors that measure local changes in the magnetic field produced by the current flowing in the pipe. The inspection methodology can be configured to pass tight restrictions and narrow openings such as plug valves. The separation between the magnets and the pipe wall is on the order of an inch (2.5cm). The strength of circumferential current produces signals on the order of a few gauss, which can be detected by hall effect sensors positioned between 8 and 40 inches (10 and 100 cm) away from the rotating magnets.

Accomplishments to date include:

  • Designed, fabricated, and evaluated a translating permanent magnet pulsed eddy current system that measures the decay of induced eddy currents – a technique used for measuring wall thickness.
  • Completed and posted a technology status assessment – “Implementing Current In-Line Inspection Technologies on Crawler Systems.”
  • Designed, fabricated, and tested/evaluated a rotating permanent eddy current exciter for the detection of pipeline defects.
  • Participated in testing the rotating permanent eddy current exciter at the DOE/NETL sponsored advanced sensor demonstrations (Battelle, Columbus, Ohio).
  • Based on the testing and evaluation, selected the rotating permanent eddy current exciter for further development and integration with a robotic platform.
  • Derived a closed form equation for designing rotating and positioning sensors from fundamental principles.
  • Developed preliminary mechanical designs for an operating rotating magnet internal pipeline inspection sensor.
  • Developed signal processing methods for detection and assessment of pipeline anamolies. A lock in amplifier was chosen as the best method for detection of the signals.
  • Developed mechanical implementations for passing tight restrictions, such as plug valves.
  • Submitted a U.S. Patent Application for the inspection concept.
  • Constructed a prototype of the rotating permanent eddy current exciter.
  • Participated in testing of the inspection tool at Battelle’s Pipeline Simulation Facility during a January 2006 benchmarking demonstration of a variety of pipeline inspection devices on test lines with a variety of defects. During this test the Rotating Permanent Magnet technology was able to continuously acquire data through each pipe sample taking approximately 10 to 15 minutes to scan a test line. During the demonstration Battelle processed signals and displayed inspection results in real-time. The Rotating Permanent Magnet technology detection rate was 100%, detecting all defect sites on each of three pipe samples. On average, Battelle located anomalies shy of the actual start of the defect location with a standard deviation of 2.05 inches. The device detected only one false positive signal.
  • Completed detailed design, fabrication and testing of a prototype system capable of collapsing to fit through a 50% diameter restriction and having a power draw of less than 50 watts. The design featured a hinged rotating magnet system designed to inspect 12 inch pipe.
Current Status

All work under this effort has been successfully completed demonstrating the feasibility of the use of a rotating permanent magnet system for inspection of unpiggable natural gas pipelines. The details of the project and its results can be found in the project final report. A link to the report is included in the "Additional Information" section below. 

Translational permanent magnetic pulsed eddy current method
Translational permanent magnetic pulsed eddy current method


Project Start
Project End
DOE Contribution


Performer Contribution


Contact Information

NETL – Richard Baker ( or 304-285-4714)
Battelle – Bruce Nestleroth ( or 614-424-3181)

Additional Information

Final Project Report [PDF-4.46MB]

April, 2006: Pipeline Inspection Technologies Demonstration Report [PDF-7.29MB]

Project Report 2006: Rotating Permanent Magnet Exciter for Pipeline Inspections [PDF-3.14MB]

Status Assessment [PDF-397KB]

Pipeline Inspection Technologies – Demonstration Report [PDF-7327KB] – participant in the sensor tests.
Topical Report - April 2004: "Gas Pipeline Pigability" [PDF-54KB] 

Presentation and Proceedings Publication – “Rotating Permanent Magnet Exciter for Pipeline Inspection” – Natural Gas Technologies 2005, Orlando, Florida, February 2005.

Illustration of the Rotating Magnet Exciter and Sensor
Illustration of the Rotating Magnet Exciter and Sensor
Rotating permanent magnet remote field technique
Rotating permanent magnet remote field technique