Effect Of Al And Cu Elements On Microstructure And Properties Of X80 Pipeline Steel Welded Joints

X80steel is widely used in oil and gas pipelines, the construction of long-distance pipeline depend on welding, and the welding joints usually failure to crack due to the extreme environment. In this paper, we make welding consumables by design the electrode coating with alloy elements Al and Cu for the SMAW welding of X80steel, composition analysis, metallographic observation, hardness test, tensile test, impact test, electrochemical test and soak corrosion test in the environment of H2S, and HIC test was used to study how the alloy element Al and Cu in the welding materials affect the organization, composition, mechanical properties and corrosion resistance in the environment of H2S of X80steel welding joint.Microstructure and component analysis showed that, the content of Al and Cu elements in the weld increase along it’s in the electrode coating, they respectively reached0.83%and1.16%while they are both8%in the drug skin; the weld organization was mainly acicular ferrite, polygonal ferrite and granular bainite, with the increase of Al and Cu, the content of acicular ferrite increased first and then decreased, big block eutectoid ferrite appear and uneven distribute while the Al and Cu content was excessive.Mechanical tests showed that, when there only exist element Al in the drug skin, with the increase of Al content in the welding consumables, the hardness and tensile strength of X80steel welding joint gradually increased while the impact toughness increased first and then decreased, the highest toughness was got when the Al content is0.27%in the deposited metal while it’s4%in the welding material; when there only exist element Cu in the drug skin, with the increase of Cu content in the welding consumables, the hardness and toughness strength of X80steel welding joint increased first and then decreased while the tensile strength gradually increased, the highest toughness was got when the Cu content is0.95%in the deposited metal while it’s6%in the welding material; when there exist8%of Al and Cu in the electrode coating containing, in the case of2%of Al and6%of Cu, the strength and toughness of welded joints have reached the highest value, and the weld metal containing0.17%of Al and0.94%of Cu.Corrosion tests in H2S environment showed that, in the environment of elctrochemical corrosion, if there only exist Al in the the drug skin, the welding joints got the lowest corrosion tendency when the Al content was6%, and got the lowest corrosion rate while it’s4%, if there only exist Cu in the the drug skin, the welding joints got the lowest corrosion tendency when the Cu content was2%, and got the lowest corrosion rate while it’s6%, if the drug skin contain8%of Al and Cu alloy element, the combination of2%Al and6%Cu could lower both the electrochemical corrosion tendency and rate; in the environment of hydrogen sulfide uniform corrosion, the corrosion rate reduce first and then raised along the increase of Al and Cu content, the corrosion rate reached the lowest value of0.4843mm/a when the Al content was2%, and it’s0.4895mm/a when the Cu content was4%, if the drug skin contain8%of Al and Cu alloy element, the combination of2%Al and6%Cu could get a lower corrosion rate; the crack not appeared in all of the samples in the HIC test, even the samples with holes,which showed that the material has excellent HIC resistance. When the Al or Cu content reached8%in drug skin or they are respectively0.84%and1.16%, the HIC resistance would not decreased much.