To　understand　the　influence　of　carbon　on　stress　corrosion　cracking　of　pipeline　steels,　a　carburization　treatment　was　applied　to　API　X80　steel.　Carbon-rich　structures　rather　than　ferrite　grains　remain　intact　and　act　as　cathode　during　immersion　in　the　acidic　environment.　Coalescence　of　micro-cracks　induced　by　galvanic　effect　and　higher　dissolution　inclination　of　ferrite　grains　lead　to　the　higher　driving　force　for　crack　growth　within　grains　in　the　low　pH　environment.　Higher　average　crack　velocity　at　grain　boundaries　and　passivation　of　ferrite　grains　provide　higher　driving　force　for　crack　propagates　along　grain　boundaries　in　the　high　pH　environment.　(C)　2013　Published　by　Elsevier　Ltd.