Electromagnetic Inspection Method for Welding Imaging

  • Hanyang Xu

Student thesis: Phd


Weld inspection is significant in manufacturing to improve productivity and ensure safety. During the welding process, steel microstructures experience complex transformations depending on welding conditions. Examining weld microstructures can reveal valuable information on its metallurgical, mechanical and electromagnetic properties. In this research, a novel weld imaging method has been proposed based on EM testing. The newly designed electromagnetic (EM) sensor has a feature that at certain lift-off, the effect of a sample’s conductivity on the sensor’s response is reduced. Hence, the permeability can be estimated in a reasonable accuracy without the influence of its conductivity for dual phase steels. This sensor design enables better spatial resolution for weld imaging with reduced lift-off effect. A cross-section of an X70 steel submerged arc welding (SAW) sample has been imaged using impedance and a novel frequency feature in multi-frequency EM testing. It is derived that this frequency feature is closely related to the permeability of the sample. Therefore, the imaging results obtained from this feature reflects better permeability map of the sample. These images show good correlation with the hardness testing and metallurgical information of the weld sample. An approximate linear relationship was found between the EM signal and the hardness of the weld. The novel method significantly reduces scanning time with respect to hardness test and requires less surface preparation. And the operation frequency range can be adjusted to suit a particular instrument capability.
Date of Award1 Aug 2020
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorWuqiang Yang (Supervisor) & Wuliang Yin (Supervisor)


  • Microstructure
  • Weld Inspection
  • Eddy Current
  • Imaging
  • Non-destructive Testing
  • Electromagnetic Testing

Cite this