A novel non-contact, magnetic-based stress inspection technology and its application to stress concentration zone diagnosis in pipelines

Abstract During their construction and long-term operation, stress concentration zones (SCZs) will inevitably occur in buried pipelines. This may cause pipe leakage or fracture failures. Therefore, it is essential to inspect and identify the precise position and stress damage degree of SCZs. Non-contact pipeline magnetic-based stress inspection (PMSI) is an important topic in the field of oil and gas pipeline stress inspection. In order to determine the response of a non-contact magnetic gradient signal to the stress damage of SCZs, we establish a PMSI model to analyze the three-dimensional magnetic signals of SCZs. The effects of changes to the axial stress value, the stress concentration length, the detection height and the gradiometer jitter are also studied. In addition, the PMSI is carried out on a 10.3 km liquefied natural gas buried pipeline, which is validated by the excavation inspection results. The results indicate that the x component of the magnetic gradient signal, G x , shows sinusoidal fluctuation near a SCZ, and the y and z components, G y and G z, each reach a peak value. The G max value, the maximal magnetic gradient modulus, increases with the severity and length of the SCZs. As a result, two level-II SCZs and two level-III SCZs are identified.