Pitting Behavior of 304L/ER316L Austenitic Stainless Steel Welded Plate

Pitting behavior of the 304L/ER316L/304L austenitic stainless steel welded plate for the spent fuel pool cover of nuclear power plant was studied in the solution containing 3.5% (mass fraction) NaCl (No. 1 solution), containing 2 700 mg/L B³⁺ (No. 2 solution) and containing 2 700 mg/L B³⁺ + 200 mg/L Cl^- (No. 3 solution) by ferric chloride immersion test and electrochemical test. The results show that in the three solution environments, the pitting resistance of different areas of the welded plate was weld metal > base metal > heat affected zone. The main reason for the best pitting resistance of weld metal was that the Ni and Mo content were high, and the poor pitting resistance of the heat affected zone was caused by poor microstructure. In No. 2 solution at 30, 40, 60℃, no obvious pitting of the welded plate was observed even at high potential. After doping 200 mg/L Cl^- in solution No. 2, the pitting tendency of the welded plate increased remarkably, and the pitting sensitivity increased with the increase of temperature. A pure boric acid solution meeting the design parameters was a good service environment, but when Cl^- was added, the pitting resistance of the welded plate was greatly reduced. Therefore, during the service period of the spent fuel pool, the water temperature change should be strictly controlled and the water quality should be monitored to avoid excessive temperature and excessive erosive Cl^- content.