Stainless Steels In Chloride-containing Solutions Research Articles

Crevice Corrosion Performance of 436 Ferritic Stainless Steel Studied by Different Electrochemical Techniques in Sodium Chloride Solutions with Sulfate Addition

The crevice corrosion behaviors of 436 stainless steels in chloride-containing solutions with sulfate addition were studied using potentiodynamic, galvanostatic and repassivation potential measurements. The results of these electrochemical tests were compared and discussed. Galvanostatic test was proved to be the most powerful technique in detecting the crevice corrosion of 436 stainless steels, while the repassivation potential measurement was the most time-saving method in this study. Sulfate ions have inhibited the crevice corrosion of 436 stainless steels in chloride-containing solution, which may result from the effects of competitive adsorption and the IR drop mechanism.

Photo-inhibition of pitting corrosion on types 304 and 316 stainless steels in chloride-containing solutions

The influence of incident monochromatic uv light on the susceptibility of types 304 and 316 stainless steels to pitting corrosion in chloride-containing solutions is described. Illumination of the immersed surfaces, in neutral and acidic solutions, gave rise to an enhanced resistance to the onset of pitting corrosion that persisted for some 220 h after the irradiation had been removed. This was evident from an increase in the breakdown potential, longer induction periods, and notable changes in the current noise at constant potentials for specimens polarized under illumination. It was found that the degree of inhibition to pitting attack depended on the photon energy, the illumination period and the nature of the passive film. Higher breakdown potentials and longer induction periods were observed with high energy photons ( λ < 375 nm); these photons having energies in excess of the bandgap energy. Also, the photo-inhibition effect increased with the period of illumination; the maximum effect being observed following a 5-h illumination period. A much reduced photo-inhibition effect was observed for specimens polarized in alkaline solutions. This was attributed to the formation of a precipitate layer at the film-solution interface, which hindered the interaction of the incident photons with the barrier layer.

A statistical evaluation of crevice corrosion on type 304 stainless steel

A multiple crevice corrosion monitor has been developed in order to evaluate the susceptibility to crevice corrosion for Type 304 stainless steel in chloride-containing solution, in terms of the probability distribution for occurrence of crevice corrosion. The potentials within crevices formed by a polyacetal washer, which is designed by referring to ASTM G78-83, have been monitored to detect the generation of crevice corrosion. The survival (i.e. no corrosion) probability, P, with times is described as, ln P = − γ(t−t 0) where t 0 is the incubation time before which no crevice corrosion initiates. The crevice corrosion generation rate, λ, was described as a function of the applied potential and the temperature.

Initiation events for pitting corrosion of stainless steel?

Events which could conceivably trigger off pitting corrosion of 18Cr-8Ni stainless steel in chloride-containing solution have been observed upon potentiostatic polarization of microelectrodes (10 μm diameter) of the steel. These events were undetectable on larger electrodes because they could not be distinguished above the background current. The events had amplitude 30–80 pA, frequency up to about 0.05 s−1, and lifetime around 50 s. The average charge carried by an event was ∼100 pC, rather less than the charge required to dissolve one monolayer of the steel over the entire micro-electrode surface (∼600 pC). Most of the events were characterised by a sharp rise and slow fall of the current, in contrast to the current transients (slow rise, sharp fall) associated with the nucleation and temporary propagation of micropits on larger electrodes. It is inferred that the transients were associated with a microstructural feature in the microwire used to fabricate the electrodes. The results are rationalized with a model of very slow dissolution of one component of a binary alloy, and rapid dissolution of the other, with a different rate for different types of surface site.

Electrochemical Methods in Crevice Corrosion Testing: Report prepared for the European Federation of Corrosion Working Party ‘Physico-chemical testing methods of corrosion: Fundamentals and applications’

Abstract In the first part of this review a number of theoretical aspects of the mechanism of crevice corrosion are dealt with, mainly related to the crevice attack of stainless steels in chloride-containing solutions. Next the test methods are discussed, paying attention to the geometrical conditions and the electrochemical test procedure. A number of practical applications are given, both as regards mechanistic testing and also for ranking purposes. Finally a selected review is given of the results obtained during the past few years.

Electrochemical investigations of pitting corrosion

By using chronopotentiostatic and stepwise potential change experiments with potentiokinetic and galvanostatic testing, the following types of pitting corrosion of stainless steels in chloride-containing solutions have been investigated: sulphate inhibition of pitting; 35%Cr-Fe alloy; Cr-Ni-Mo stainless steels. The circuit resistance was found to be of fundamental importance. The pit passivation potential depends on the intensity of a corrosion attack before potential change only in the case of inhibited solutions. In uninhibited solutions passivation and formation potentials are nearly equal only in the case of potentiostatic circuit conditions. The Cr-Fe alloy and the Cr-Ni-Mo stainless steels show a potential range of repassivating pitting. Of practical interest is the critical potential of stable pitting which decreases with increasing circuit resistance. The beneficial effect of Mo is only valid for the pitting potential obtained potentiostatically and not at higher circuit resistances. Considering the practical meaning of the addition of Mo it may be concluded that this element is probably essentially connected with repassivation of pits and conditioning effects of the passive layer.