Effects of flow rate on crack growth in sensitized type 304 stainless steel in high-temperature aqueous solutions

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Effects of flow rate on intergranular crack growth in sensitized Type 304 stainless steel (UNS S30400) in distilled water containing 15 ppm or 25 ppm (2.59 x 10(-4) or 4.31 x 10(-4) m) sodium chloride (NaCl) at 250 degreesC were examined using compact tension (CT) specimens under constant loading conditions. On increasing the flow rate, the crack growth rate (CGR) drastically increased, but later decreased to a level that was lower than the initial value. The initial increase in CGR was attributed to an enhanced rate of mass transfer of oxygen to the external surface, where it consumed the current emanating from the crack mouth. However, the subsequent decrease in CGR was attributed to crack flushing, which is a delayed process because of the time required to destroy the aggressive conditions that exist within the crack. Once flushing destroyed the aggressive crack environment, CGR decreased with increasing flow rate. The time over which CGR increased after an increase in the flow rate depended on how fast crack flushing occurred by fluid flow; the higher the flow rate and the greater the crack opening, the faster the crack flushing and the shorter the transition time. Finally, intergranular cracks propagated faster in regions nearer both sides of the CT specimens, where the oxygen supply to the external surface was enhanced under stirring conditions and where minimal resistance existed to current four from the crack tip to the external surfaces. This observation provided evidence that the crack's internal and external environments were coupled electrochemically.
Publisher
National Assoc. of Corrosion Engineers International
Issue Date
2000-05
Language
English
Article Type
Article
Keywords

STRESS-CORROSION CRACKING; FLUID-FLOW; ENVIRONMENTS; SYSTEMS; WATER

Citation

CORROSION, v.56, no.5, pp.482 - 491

ISSN
0010-9312
URI
http://hdl.handle.net/10203/77875
Appears in Collection
MS-Journal Papers(저널논문)
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