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Nondestructive Evaluation


Gas Pipeline Corrosion Characterization


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  image produced by software of adjacent scans of pipe strength and how they are stitched together to form one large image
  image of close-up view of image produced by software of adjacent scans of pipe strength and how they are stitched together to form one large image

If corrosion areas are larger than the array, the software provides the capability of stitching adjacent scans together to form one large image. Analysis software can evaluate the remaining pipe strength according to ASME B31G or an RSTRENG type algorithm. The array is flexible and therefore usable on any pipe diameter. Since the sensing mechanism is electromagnetic, measurement is not affected by non-ferrous material in the pits, giving this technique advantages over laser and ultrasonic measurements.

A two-phase gas pipeline corrosion characterization program was designed by Southwest Research Institute (SwRI) to:

  • Determine the feasibility of using an array of eddy current coils to map the depth profiles of corrosion pits on the outside of pipelines

  • Design, fabricate, and test a prototype corrosion measuring system using a flexible printed array of eddy current coil pairs.

Corrosion in gas transmission pipelines occurs primarily (though not exclusively) on the external surface of the pipe. When such corrosion has been detected by an in-line inspection (ILI), the common procedure, if significant corrosion depths are suspected, is to unearth the pipe and examine the corroded area to determine its depth and other dimensions.


Assessment algorithms such as B31G and RSTRENG require corrosion dimensions including, primarily, the maximum depth and length of the corrosion patch.


A flexible array was designed at SwRI to map a 150-mm square area of a corroded surface. The photos to the right show the 16 × 16 element array and a close-up with the details of individual coil pairs.


image of a large (12-inch x 24-inch) corrosion patch

image of color map of corrosion pit depth

A large (12-inch x 24-inch) corrosion patch and the resulting color map of pit depth.



For more information about our nondestructive evaluation (NDE) capabilities, gas pipeline corrosion characterization, or how you can contract with SwRI, please contact Clinton J. Thwing, at or (210) 522-3989.


Contact Information

Clinton J. Thwing

Nondestructive Evaluation

(210) 522-3989

Related Terminology

nondestructive evaluation


steel pipe inspection



pipe wall thinning

gas transmission pipelines

pipe surface corrosion

corroded pipe surface

conformable array

corrosion profile mapping

eddy current coils

corrosion measuring system

corroded surface

| Sensor Systems and Nondestructive Evaluation (NDE) Technology Department | Mechanical Engineering Division | SwRI Home |

Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.