INVESTIGATION OF THE POTENTIAL FOR CAUSTIC STRESS CORROSION CRACKING OF A537 CARBON STEEL NUCLEAR WASTE TANKS

Lam, P.

Savannah River Site (S.C.)

关键词: Corrosion;    Evaporators;    Carbon Steels;    Testing;    Hydroxides;   

DOI  :  10.2172/966687
RP-ID  :  SRNS-STI-2009-00564
RP-ID  :  DE-AC09-08SR22470
RP-ID  :  966687

美国|英语

来源: UNT Digital Library

【 摘 要 】

The evaporator recycle streams contain waste in a chemistry and temperature regime that may be outside of the current waste tank corrosion control program, which imposes temperature limits to mitigate caustic stress corrosion cracking (CSCC). A review of the recent service history (1998-2008) of Tanks 30 and 32 showed that these tanks were operated in highly concentrated hydroxide solution at high temperature. Visual inspections, experimental testing, and a review of the tank service history have shown that CSCC has occurred in uncooled/un-stress relieved F-Area tanks. Therefore, for the Type III/IIIA waste tanks the efficacy of the stress relief of welding residual stress is the only corrosion-limiting mechanism. The objective of this experimental program is to test carbon steel small scale welded U-bend specimens and large welded plates (12 x 12 x 1 in.) in a caustic solution with upper bound chemistry (12 M hydroxide and 1 M each of nitrate, nitrite, and aluminate) and temperature (125 C). These conditions simulate worst-case situations in Tanks 30 and 32. Both as-welded and stress-relieved specimens have been tested. No evidence of stress corrosion cracking was found in the U-bend specimens after 21 days of testing. The large plate test is currently in progress, but no cracking has been observed after 9 weeks of immersion. Based on the preliminary results, it appears that the environmental conditions of the tests are unable to develop stress corrosion cracking within the duration of these tests.