In-line inspection device to detect and size stress corrosion cracks utilizing low frequency eddy currents in combination with magnetic saturation of the pipe wall in natural gas pipelines
- American Gas Association, Inc., Arlington, VA (United States). Pipeline Research Committee
In two earlier research programs conducted for the NDT Supervisory Committee, Battelle developed low-frequency eddy current equipment for detecting and characterizing stress corrosion cracks from the outside of gas transmission pipelines without requiring the removal of the protective coating. In this program, Battelle examined the possibility of using this or similar equipment to detect stress corrosion cracks from the interior of the pipeline by magnetically saturating the pipeline to reduce the permeability of the pipeline material and thereby increase the penetration of eddy current fields into the pipeline. The study was divided into two parts, an analytical study to determine how well eddy currents could be used to detect cracks if the permeability of the pipeline material is reduced by using magnetic saturation and an experimental study to verify the results of the analytical study and to determine how much the permeability could be reduced using a large magnetizing field. The analytical study indicated that significant improvements could be made in the defect sensitivity of eddy current probes to external cracks even if the pipeline is not completely saturated; reducing the permeability to a value as high as 10 would be sufficient. However, the experimental study showed just how difficult it is to reduce the permeability of the pipeline to such a low value. The power required to reduce the permeability to 33 was about 5 kilowatts, which we believe is excessive for an internal inspection device; however, this power requirement may be reduced by a better design. With a transverse permeability of 33, we believe that defects which are 70 percent or more of the pipe wall in depth would be detectable with an eddy current device.
- Research Organization:
- American Gas Association, Inc., Arlington, VA (United States). Pipeline Research Committee; Battelle, Columbus, OH (United States)
- Sponsoring Organization:
- American Gas Association, Inc., Arlington, VA (United States)
- OSTI ID:
- 10195059
- Report Number(s):
- AGA-94003340; ON: UN94003340; CNN: PR3-025
- Resource Relation:
- Other Information: PBD: 21 Dec 1992
- Country of Publication:
- United States
- Language:
- English
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