Stress Corrosion Cracking Response of 304 Stainless Steel in ASerated and Dearated Water
Scoping stress corrosion cracking (SCC) tests of 304 stainless steel (SS) were performed in 75 C and 250 C aerated pressurized water (APW) and 250 C deaerated pressurized water (DPW). The 250 C APW environment was used to initiate intergranular stress corrosion cracking (IGSCC) and then the water was deaerated and hydrogenated to see if IGSCC continued in 250 C DPW. Tests were performed with and without 200 ppb SO{sub 4}{sup =}. The 304 SS test materials were evaluated in either the as-received, heavily sensitized (649 C for 1 h), fully sensitized (1099 C for 1 h/water quench/621 C for 17 h) or 20% cold rolled condition. At the beginning of each test sequence, specimens were subjected to continuous cycling with a 500s rise/500s fall or a 5000s rise/500s fall to promote the transition from a transgranular (TG) precrack to an IG crack. After generating a uniform crack under continuous cycling conditions, a trapezoidal waveform with 500s rise/9000s hold/500s fall was used to characterize the SCC behavior. Crack growth rates (CGRs) were monitored continuously with the electric potential drop (EPD) method and were corrected based on physical crack length measurements obtained when specimens were destructively evaluated. Continuous cycling with a 500s or 5000s rise time was found to produce both TG faceting and IGSCC in fully sensitized 304 SS tested in 75 C APW with 7 ppm O{sub 2} and 200 ppb SO{sub 4}{sup =}. However, no measurable crack extension occurred when a 9000 s hold time was introduced. Extensive IGSCC occurred in heavily sensitized and fully sensitized 304 SS in 250 C APW with 1 ppm O{sub 2} and 200 ppb SO{sub 4}{sup =}. IGSCC initiated under continuous cycling conditions with a 500 s rise time, and rapid IGSCC occurred when a 9000 s hold time was introduced. During the trapezoidal waveform test with a 9000 s hold, CGRs ranged from 1 to 3 mils/day for the heavily sensitized material and 5 to 10 mils/day for the fully sensitized material. When the test environment was dearated and hydrogenated to 30 cc H{sub 2}/kg H{sub 2}O, CGRs decreased by an order of magnitude ({approx}0.1 mils/day), and the cracking mode in 250 C DPW was predominantly TG. The only material that exhibited evidence of IGSCC in 250 C DPW was 20% cold rolled 304 SS. IGSCC readily initiated in 250 C APW and continued in 250 C DPW. Metallographic and fractographic examinations showed that the IG cracking was highly branched and discontinuous. Results from the scoping SCC tests have revealed significant information regarding the nature of IG and TG cracking of 304 SS in APW and DPW. The key finding is that cold work appears to be more important than sensitization in producing IGSCC in DPW.
- Research Organization:
- Bettis Atomic Power Laboratory (BAPL), West Mifflin, PA
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC11-98PN3820
- OSTI ID:
- 923319
- Report Number(s):
- B-T-3697; TRN: US200804%%1063
- Resource Relation:
- Conference: EPRI-MRP Expert Panel on Crack Growth
- Country of Publication:
- United States
- Language:
- English
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