Evaluation of Circumferential Magnetic Flux for In-Line Detection of Stress Corrosion Cracks and Selective Seam Weld Corrosion

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Abstract:

Need: Longitudinal defects, including stress-corrosion cracking (SCC) and selective seam weld corrosion, can occur in natural gas transmission pipelines. Previously developed nondestructive testing techniques (including angle beam ultrasonics, electromagnetic acoustic transducers (EMATs), and remote field eddy current) are capable of detecting longitudinal defects. Two angle beam ultrasonic syatems are commercially available, and an EMAT system is being commercialized. But there are factors that limit the applicability of these techniques, such as minimum pipe diameter and maximum inspection speed. A new more cost effective nondeastructive testing technique for pipeline inspection is needed to identify and evaluate the potential hazards from SCC.

Benefits: The complexity of angle beam ultrasonics and EMAT's and others makes the cost of inspection higher than MFL corrosion inspection. Circumferential MFL is more economical has the potential to to more accurately size axially oriented corrosion than the more common axial implementation. Though at present the method contained within this study has some deficiencies, a circumferential MFL in-line inspection tool could serve as a screening tool to determine whether a pipeline has cracks and seam weld defects as well as other longitudinal defects such as third-party mechanical damage.

Result: Circumferential magnetic flux leakage (MFL), a new implementation of a commonly used technology, was investigated as an alternative to other nondestructive testing techniques and hydrostatic proof testing. The results of this study show that both cracks and seam weld defects can be detected with circumferential MFL. However, many small cracks with lengths less than 1 inch and depth of less than 20 percent of the wall thickness were not detectable. Since the initial publication of this work in 1996, two implementations of circumferential MFL have been used to inspect pipelines for axially oriented corrosion and stress corrosion cracking. Both implementations were considered successful since they produced new information on defects that could affect the servicability of the pipeline.

Price: $495.00

L51811 is included in the Ultrasonic Pipeline Reports Compendium
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