Corrosion: Stress-Corrosion Cracking Of Austenitic Stainless Steels in Chemical Plant Equipment

Rion, W.C.

doi:10.1021/ie51392a009

Cited by 3 publications

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“…Although chlorides are the common constituent of a variety of environments which induce cracking, their presence does not seem to be altogether necessary. Transgranular cracking of 18-8 has been observed, for example, in caustic soda solutions at 350~ (660~ under pressure (1), in acid sulfite cooking liquors (1), in 12% hydrofluoric acid plus 0.2% fluosilicic acid at 80~ (180~ (3) and in molten NaOH (4) at 370~ (700~ Furthermore, cracking of 18-8 has been observed in hot water containing very little chloride (5), in steam condensate containing less than 0.5 ppm total solids (6), and in cooling waters containing 25 ppm or more of chloride (7). Williams and Eckel (2) report that oxygen is necessary for cracking of 18-8 in hot water or in steam containing small quantities of chloride.…”

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Chemical Factors Affecting Stress Corrosion Cracking of 18–8 Stainless Steels

Uhlig¹,

Lincoln

1958

J. Electrochem. Soc.

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Transgranular stress corrosion cracking of 18–8 Type 304 specimens in boiling 42% MgCl2 does not depend on rate of stressing (<1 sec to 10 min) nor on small variations in degree of plastic deformation. Cold worked specimens fail in shorter times than annealed, sheared specimens. Addition of normalHCl to MgCl2 decreases cracking time whereas addition of normalNaOH increases the time. Pre‐exposure of unstressed specimens to MgCl2 slightly decreases cracking times of the same specimens subsequently stressed. Cracks occur along sheared edges of unstressed specimens despite stress relief anneal at 375°C for 2 hr.Cracks propagate along sheared edges of U‐bend specimens at 0.5 to 1 cm/hr through that portion of the specimen cross section in tension, the rate being much slower through the remaining cross section. No induction time for cracks to initiate was observed.Sizeable pits are not necessary for cracking in MgCl2 , but appear to be essential in media like normalNaCl which in absence of pitting is not particularly active in causing cracking. The pitting mechanism produces concentrated low pH metal chlorides false(normale.normalg.,FeCl2false) within the pit, which like MgCl2 cause immediate cracking. Oxygen is required for pitting of 18–8 by normalNaCl solutions as shown by Uhlig and Morrill, and hence also for stress corrosion cracking as observed by Williams and Eckel, but oxygen is not necessary in MgCl2 or FeCl2 .Cracking can be prevented by cathodic protection at a CD. of 0.03 ma/cm2 or higher. Anodic CD. up to 0.01 ma/cm2 were found to have no effect on cracking tendency, nor did coupling of 18–8 to Pt.

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