In　this　work,　the　effects　of　stray　alternating　current　(AC)　on　the　corrosion　of　coated　X70　pipeline　steel　and　the　delamination　of　3-layer　polyethylene　(3PE)　coatings　with　defects　were　investigated　using　COMSOL　Multiphysics　simulation,　electrochemical　impedance　spectroscopy　and　three-dimensional　(3D)　digital　microscope　techniques.　The　results　showed　that　under　the　same　level　of　AC　interference,　pits　with　deeper　maximum　pit　depth　were　observed　at　the　smaller　defect　areas　than　those　at　larger　defect　areas.　It　was　consistent　with　the　simulation　results　that　a　greater　corrosion　current　density　was　accompanied　on　samples　with　smaller　defects.　According　to　3D　digital　images,　the　larger　delamination　of　3PE　coatings　was　found　on　samples　with　smaller　defects.　With　the　increase　of　current　density,　the　impedance　of　samples　with　small　defects　decreased,　while　that　of　samples　with　large　defects　increased.　Additionally,　with　the　same　defect　size,　the　maximum　pit　depth　became　deeper　and　the　corrosion　was　more　severe.