Cathodic Protection Effect of Sacrificial Anode on Internal Corrosion of 20 Pipeline Steel and Its Influencing Factors

Due to the high possibility of internal corrosion occurring in gathering pipelines and outlet pipelines of oilfield, and lack of practical anti-corrosion measures such as internal penetration or extrusion coating for internal corrosion protection in field, the protection effects of different sacrificial anodes on 20 pipeline steel internal corrosion were investigated, including strap zinc alloy, ring and stick shapes of aluminum alloy. The results show that the protection of sacrificial anode for internal wall of pipeline decreased with the increase of distance from sacrificial anode. For the pipes in diameter from 159 mm to 308 mm and without internal coatings, the protection range on one side of anode could reach 3.10 m to 3.45 m. Every shape of anode presented a limit current; the predicted lifetime of the anodes in a ring shape and a stick shape could meet the design lifetime of 5 years. Experimental results show a good agreement with simulation results, also indicating that the anode output current decayed with time because of calcareous deposit, and the anode in field should be expected to have a longer lifetime than the predicted one from simulation.