Pitting Corrosion Behavior of S32101/ER2209 Duplex Stainless Steel Welded Plate Used for Spent Fuel Pool

The pitting corrosion behavior of S32101/ER2209 duplex stainless steel welded plate for liner of spent fuel pool of nuclear power plants in ferric chloride solution, 3.5% NaCl solution and boric acid aqueous solutions simulating the environments of spent fuel pool was studied by chemical immersion testing and electrochemical testing. The results show that the corrosion resistance ranking of the parts of the welded plate was weld metal > base metal > heat affected zone in experimental environments. The weld metal had the best pitting corrosion resistance mainly due to its high content of Cr, Mo and Ni. Imperfect microstructure was the reason for the heat affected zone having the worst pitting corrosion resistance. No apparent pitting was found in the parts of the weld even at high potentials in the electrochemical tests in pure boric acid solution at 30, 40 and 60℃, the nominal pitting potentials were above 1 000 mV (SCE). After adding 200 mg/L Cl^- in the pure boric acid solution, the pitting tendency increased significantly. The pitting sensitivity increased with the increase of temperature. The pure boric acid environment that meets the technical specifications is good enough for service, but when the solution contains corrosive Cl^-, the pitting corrosion resistance of welded parts will be greatly reduced. Therefore, during the service period of spent fuel pool, the water quality and water temperature should be monitored and controlled strictly to avoid pitting corrosion.