Relationship Between Acid Intergranular Corrosion and Caustic Stress Corrosion Cracking of Alloy 600

Abstract

Modified Streicher and 288 C (550 F) electrochemical caustic stress corrosion tests were performed on Alloy 600 to determine the relationship between acid intergranular attack susceptibility and caustic stress corrosion cracking (SCC) susceptibility. Mill annealed and solution annealed materials with and without a subsequent 621 C (1150 F) heat treatment (simulated stress relief) were evaluated. Susceptibility to attack in the Streicher test was greatest for material that had received a 621 C (1150 F) heat treatment, whereas this heat treatment caused the same material to be least susceptible to cracking in the electrochemical tests. The conclusions drawn from these results are: (1) stress relieving Alloy 600 does improve its resistance to caustic SCC, and (2) resistance of Alloy 600 to acid intergranular attack does not imply resistance of Alloy 600 to caustic SCC. Therefore, the results demonstrate the need for selecting corrosion qualification tests which are relevant to service conditions.

Corrosion in bioprocessing applications

“…Examples of the impact of various heat treatments on subsequent corrosion are: (1) decreased pitting resistance when holding types 304 and 316 SS in the sensitizing temperature range (950-1,450°F) [35], (2) greatest pitting resistance for austenitic SS when solution quenched above 1,800°F [35], (3) increased resistance of Alloy 600 to SCC by 620°C (1,150°F) heat treatment, producing ''carbide decorated'' grain boundaries [32], (4) significantly improved caustic SCC resistance of Inconel 600 steam generator tubing using thermal treatment in the carbide precipitation regime (649-704°C), (5) increased number of SCC cracks in Alloy 600 from higher annealing temperature (760-1,093°C, 1,400-2,000°F) [32], and (6) stress relieving heat treatment of Alloy 600 (593-621°C for 10 h) improved resistance to IGSCC from caustic but increased IGC in acidic ferric sulfate solutions (vs. nonstress-relieved material) [93]. Thus, not only the alloy composition but also its fabrication specifications must be specified during design.…”

“…Many of the more reliable tests are destructive in nature, requiring a commitment to replace the corroded metal that is sampled. For new materials being considered for fabrication, corrosion qualification tests must reflect proposed service conditions [93].…”

On the Use of NaOH Solution to Simulate the Crevice Conditions of a Nuclear Steam Generator

“…[ 9 , 10 , 13 , 14 , 15 , 16 ]. Accordingly, the following solutions have been widely used: solutions containing sodium hydroxide (NaOH) [ 17 , 18 , 19 , 20 , 21 , 22 ], sodium chloride (NaCl) [ 23 , 24 , 25 ], sulfate (SO 4 2− ), sulfite (SO 3 2− ), tetrathionate (S 4 O 6 2− ) and thiosulfate (S 2 O 3 2− ) [ 26 , 27 , 28 , 29 ], lead oxide (PbO) [ 30 , 31 , 32 ], and silicone compounds (SiO 2 , Na 2 SiO 3 ) [ 33 , 34 , 35 ]. Among them, NaOH solution has been frequently used to investigate the performance of SG tubing under impurity-concentrated crevice conditions.…”

Prediction of Corrosion of Advanced Materials and Fabricated Components

“…Quantitative modeling of the sensitization process has been well understood for simple alloy systems such as alloy 600 McIlree and Michels, 1977;Was and Kruger, 1985;Kruger et al, 1988;Wilson and Aspden, 1976). A substantial body of work exists regarding the effects of grain-boundary precipitation on stress corrosion cracking (SCC) of alloy 600 (McIlree and Michels, 1977;Wilson and Aspden, 1976;Weeks, 1974;Theus, 1977;Brown, 1969;Airey, 1979;Airey and Pement, 1983;Bandy and Van Rooyen, 1984), since cracking of nuclear steam generator piping accounts for a significant portion of all material failures for these systems (Weeks, 1974). For alloy 690, Kay et al (1989)demonstrated the minimum Cr at the grain boundary was observed after 5 hours of aging at 700 o C, and recovered after approximately 100 hours.…”

“…Work performed to understand the effect of sensitization on the occurrence of intergranular corrosion has focused on accelerated test techniques (Airey et al, 1981;Scarberry et al 1976;Hall and Briant, 1985;Theus, 1977;Brown, 1969;Airey, 1979;Airey and Pement, 1983;Bandy and Van Rooyen, 1984) that directly exploit the effect of microchemical segregations of the alloy on corrosion in severely oxidizing, acidic environments or on the electrochemical polarization behavior. In the latter case, electrochemical potentiodynamic reactivation (EPR) test has been used to characterize the degree of passive film stability in an acidic environment that exhibits active-passive behavior.…”