Corrosive　failure　is　frequently　found　in　petrochemical　pipelines　which　may　lead　to　the　leakage　of　the　pipes　and　even　the　shutdown　of　the　system.　However,　the　corrosion　mechanism　is　still　not　well　understood　due　to　the　complex　service　environment,　e.　g.　the　corrosive　fluids　and　the　long　term　operation　at　higher　temperature.　The　corrosion　behaviour　of　a　petrochemical　pipe　elbow　was　evaluated　via　visual　examination　and　microanalysis　with　optical　microscope　and　scanning　electron　microscope(SEM)　together　with　energy　dispersive　analysis　X-ray(EDAX).　The　corresponding　corrosion　mechanisms,　the　combination　of　grain　boundary　attach　and　the　crevice　attach　together　with　the　flow-accelerated　corrosion,　were　proposed　consequently.