Comparison of corrosion behavior of X۷۰ welded specimens byusing modified and commertail E۸۰۱۸-G in۳.۵% NaCl corrosive medium

Corrosion is one of the problems of various industries, including oil and gas industries.API X۷۰ steel pipes are one of the most widely used steels in oil, gas and watertransmission lines due to their good toughness and suitable welding properties. Thepassage of gas accompanied by moisture inside the pipes may cause corrosion on theinner surface of the steel, especially in the weld areas. Therefore, in this research, threetypes of E۸۰۱۸-G electrodes were produced by different contents of Ni coded as Ni.۰,Ni.۰.۷ and Ni.۲.۹, and then welding was carried out on X۷۰ steel, and the corrosion ofthe base areas, HAZ and weld metals in the ۳.۵% NaCl corrosive environment wasinvestigated. The results of the TOEFL diagram showed that with the increase of Ni, thecurrent of corrosion decreases and corrosion resistance of weld metal increases. The CRand Rp of Ni.۲.۹ samples were ۰.۳۲mpy and ۱ ۶۳۲۰.۰۹Ω cm۲ respectively that waslowest corrosion rate compared to Ni.۰ and Ni.۰.۷ weld metals. The microstructure ofthesamples shows the weld metal sample with small amounts of nickel (Ni.۰) including bulkferrite (α), Widmannstein ferrite and martensite (M). With increasing the nickel contentin Ni.۰.۷ the austenite areas (γ) in weld metal increased and α become slightly coarser. Inthe Ni.۲.۹ sample, the structure is mainly of acicular ferrite (αA) type and blocky,therefore, the increase of nickel in the weld metal causes a more homogeneous structureand an increase in acicular ferrite and finally increases its corrosion resistance.

کلیدواژه ها:

E۸۰۱۸-G ، X۷۰ Tube ، Weld Corrosion ، Ni ، Polarization ، Microstructure.