Design of the Detection Probe Based on ACFM

To ensure the safety of oil and gas pipelines, the key point is the effective detection of defects, and to make an accurate assessment of their damage. The technology of alternating current field measurement (ACFM) is one kind of non-contact measurement technologies, especially for the detection of surface defects such as cracks. And its test results would be not affected by the media of the pipeline or the coating of inner surface like paint or wax layer. However, the conventional research on ACFM does not point at inner-detection of pipeline. The detection sets based on ACFM have a resolution that is still low. And it has not been applied to the using of long-distance oil and gas pipeline. Based on technical characteristics of ACFM, a practical inner-detection device has been designed, in view of the current working condition for in-service pipeline. The detection probe uses pairs of coils in parallel arrange as the excitation coil. The mathematical model is used to derive the electromagnetic field distribution. Simulations in the computer and experiments on the physical pipeline are carried out to prove the effectiveness of this probe and to analyze the relevant factors that affects the detection. The device has the ability of quantitative detection of defects in the pipeline, and effectively achieves high detection sensitivity as the minimal identifiable defect has a dimension with a 1mm in depth and 3mm in length.