A　finite　element　model　was　developed　to　evaluate　the　interaction　of　internal　and　external　defects　with　various　orientations　on　pipelines　and　its　effect　on　failure　pressure　in　this　work.　With　an　approximately　identical　geometry,　the　external　defect　is　associated　with　a　greater　maximum　von　Mises　stress　than　the　internal　defect.　The　longitudinal　limit　spacing,　below　which　the　interaction　occurs　between　defects,　for　a　defect　distribution　type　containing　external　defects　only　(SL,extLim)　is　larger　than　the　longitudinal　limit　spacing　for　a　defect　distribution　type　containing　both　external　and　internal　defects　(SL,intLim).　There　is　a　lower　failure　pressure　for　the　defect　type　with　all　external　defects.　When　both　external　and　internal　defects　are　present,　the　failure　pressure　of　a　pipeline　depends　on　both　the　longitudinal　spacing　between　internal　and　external　defects　(SL)　and　the　ratio　of　the　internal　defect　depth　to　pipe　wall　thickness　(rbB,int).　For　small　rbB,int,　the　failure　pressure　is　almost　independent　of　the　presence　of　the　internal　defect.　With　the　increase　of　the　rbB,int,　the　effect　of　the　internal　defect　on　failure　pressure　becomes　apparent　if　SL　smaller　than　SL,intLim.　When　the　rbB,int　is　so　large,　the　failure　pressure　decreases　rapidly.　Thus,　for　more　accurate　prediction　of　the　failure　pressure,　it　would　be　necessary　to　sufficiently　assess　the　interaction　between　the　internal　and　external　defects　on　the　pipelines　according　to　the　new　SL,intLim　rule.　©　2020