Potential for stress-corrosion cracking

The critical potential for stress-corrosion cracking of moderately cold-worked 18-8 stainless steel in deaerated MgCb solution at 130°C is -0.145V (S.H.E.). 

Avoid mechanical stresses. Excess mechanical stresses and stress concentrations increase the potential for stress corrosion cracking. 

USNRC IN 96-11, Ingress of demineralized resins increased potential for stress corrosion cracking of control rod drive mechanism penetrations. 

Note Many practitioners use 80-90% of the yield stress for 40 ksi steel anchors and 50-70% of the yield stress for ASTM A193 Grade B7 steel anchors because of the potential for stress corrosion cracking at higher stresses. 

The requirements for stress-corrosion cracking to occur are a susceptible alloy, the presence of stress, an appropriate environment and a particular range of potentials. Cracking can be prevented by altering one or more of these. The general comments made by Hines" are still valid and worth reiterating with some minor supplementation in the light of more recent data. 

Fig. 15 Plots of coupling current versus ECP (corrosion potential) for a range of ECLs extending from 0.1 to 50 cm for the conditions shown in the figure. The horizontal line corresponds to the calculated critical coupling current, as determined from Fig. 14, which defines the critical potential, Eicscc for stress corrosion cracking [54].

Yamakawa, K. Inoue, H. Analysis of corrosion potential fluctuation for stress corrosion cracking, Corros. Sci. 31 (1990) 503. 

The higher-strength martensitic steels are at risk for stress corrosion cracking in seawater. The stress corrosion cracking can be prevented by means of cathodic corrosion protection, but the protective potential must be limited to about Uh = -0.5 V, since otherwise hydrogen-induced stress corrosion cracking may occur. 

Duplex stainless steels (ca 4% nickel, 23% chrome) have been identified as having potential appHcation to nitric acid service (75). Because they have a lower nickel and higher chromium content than typical austenitic steels, they provide the ductabdity of austenitic SS and the stress—corrosion cracking resistance of ferritic SS. The higher strength and corrosion resistance of duplex steel offer potential cost advantages as a material of constmction for absorption columns (see CORROSION AND CORROSION CONTROL). 

Titanium is resistant to nitric acid from 65 to 90 wt % and ddute acid below 10 wt %. It is subject to stress—corrosion cracking for concentrations above 90 wt % and, because of the potential for a pyrophoric reaction, is not used in red filming acid service. Tantalum exhibits good corrosion resistance to nitric acid over a wide range of concentrations and temperatures. It is expensive and typically not used in conditions where other materials provide acceptable service. Tantalum is most commonly used in appHcations where the nitric acid is close to or above its normal boiling point. 

Fig. 2-17 Relation between the time to failure by intergranular stress corrosion cracking and potential for tensile specimens of soft iron (a) boiling 55% Ca(N03)2 solution, 5 = 0.65 R a = 0.90 R (b) 33% NaOH, a = 300 N mm, at various temperatures.

Fig. 8.6 Potential and pH ranges for the stress-corrosion cracking of ferritic steels in various environments, together with the pH-dependent equilibrium potentials for reactions involving Fe - Fej04, H - H and Fej04 - Fe203 (after Congleton eial. ...

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