Effects of Copper and Nickel Compounds on the Corrosion of Pressurized Water Reactor Steam Generator Materials

Pot boiler tests have been conducted to study the effects of copper and nickel compounds on the tube wastage and support plate denting phenomena observed in steam generators of pressurized water reactors. The results of these tests revealed that copper compounds produced denting when chloride was present, but were not a necessary ingredient since NiCl₂ produced even more severe denting in the absence of copper. The pot boiler consisted of seven steel umbrellas mounted on a heated Inconel Alloy 600 tube under boiling conditions at 288°C. Six tests, each of 30-days duration, were conducted with all volatile treatment (morpholine at pH 9.0 to 9.2) in each test. Water chemistry of 50 ppm phosphate (as Na₂HPO₄) to 15 ppm chlorine (as NaCl) produced wastage on the Inconel tube but no denting (fast linear magnetite growth) of the steel umbrellas. Adding CuO sludge and substituting CuCl for NaCl in the phosphate system reduced the wastage attack on the tubing and produced only incipient denting on the steel umbrellas. Water chemistries of CuO sludge-CuCl (15 ppm chloride) or Fe₃O₄ sludge-NiCl₂ (15 ppm chloride) produced extensive denting, but no wastage, with the attack by NiCl₂ being more severe. The NaCl alone or American Society for Testing and Materials sea salt plus NiFe₂O₄ sludge (15 ppm chloride in both tests) produced no denting of steel umbrellas nor wastage of Inconel tubes, perhaps because tests were not conducted for sufficient time to develop acid-chloride conditions beneath the umbrellas. Microprobe examination revealed that the chloride concentrated at the steel surface in the umbrella-tube crevices of those specimens that exhibited denting. For the most part, nickel (but not copper) was associated with the chloride except at the steel surface