Study On The Corrosion Behavior Of The Weld Area Of X80Pipeline Steel

The corrosion behavior of the weld area of X80pipeline steel was studied by weight-lossmethod、electrochemical experiment、pitting corrosion and SEM、XRD spectrum analysis, inorder to make clear the corrosion performance of the each welding area of X80pipeline. Andthen it was analysed of the microstructure, corrosion time, corrosion products on the corrosionproperties of X80pipeline steel.The results showed that in X80pipeline steel welding joint, the base metal and weldorganization are both composed of acicular iron chain and the low bainite. Because theacicular ferrite and bainite has small size, cross distribution, large Angle grain boundary andsubstructure and high-density movable dislocation, the crack initiation in corrosion mediumneed high energy, making the weld and base metal have a stronger ability to resist corrosion.Coarse grain group of heat affected zone is given priority to with granular bainite and has asmall amount of lath bainite+multilateral ferrite, the embrittlement phenomenon、higherhardness、plasticity decreased and badly resistant to corrosion are appared in this areaobviously, becoming the weak link of corrosion under the service condition. As the extensionof corrosion time, corrosion rate of X80steel decreased; XRD analysis shows that thecorrosion products is mainly composed of FeOOH (surface) and Fe3O4(inner) in5%NaCl+0.5%CH3COOH solution. At the same time, groove corrosion was occurred duringthe immersion experiment. But the result showed than groove corrosion of welding area ofX80pipeline was insensitivity. Polarization curves show that as the extension of corrosiontime, the corrosion potential Ecorr elevated, namely corrosion trend decreases, and thecorrosion current density is reduced, the corrosion rate is reduced.Through the experiment with the base metal of steel X80pipeline steel group inFeCl36H2O solution, including slightly0.05mol/L HCl solution acidification, continuoussoaking24h and48h of microstructure observation, as well as the measurement of corrosionrate by weight-loss method, using polarization curve analysis corrosion trend. The mainexperimental conclusion as follows:Corrosion48h was smaller1g than the sample quality corrosion after24h and there are corrosion products generated, the average corrosion rate decreases about20g/(m2·h). Pittingcorrosion pore density and pore size after corrosion48h is generally greater than corrosion24h. after corrosion and reduced the rate of corrosion pit depth, but the corrosion depth of holeare increased. Heat affected zone (HAZ) had higher corrosion sensitivity than base material.As the extension of corrosion time, corrosion products increased and became dense, resultingin HAZ compared with base material higher pitting corrosion sensitivity. The pitting holes ofbase material, compared with HAZ, is relatively uniform, but the HAZ produced corrosionproducts earlier. The welding area has corrosion holes unobviously, but its thickness obviouslythinning...