Abstract: In response to the technical requirements for nondestructive testing of defects in small pipeline weld zones, a simulation of ACFM for small pipeline weld defects was conducted. Based on the simulation results, a detection probe and signal processing circuit for alternating current electromagnetic field detection were designed, and the tests were carried out on small pipelines specimens defects. The results showed that the ACFM technology could detect defects with a length of 5 mm in small pipeline welds, which was beneficial for the safety inspection and maintenance of small pipelines.