Pitting corrosion, stainless steels

In soil, stainless steel is fairly resistant to uniform corrosion, which occurs over the entire surface however, it may be subject to pitting corrosion. Stainless steel is most often used in situations where contamination of the material carried in the pipe is the prime concern. However, as pitting of the buried structures might occur, where soil conditions surrounding the pipe vary, it would be prudent to install stainless steel pipe with a uniform, well-installed backfill where differential oxygen corrosion cells will not occur. Coatings and cathodic protection of buried pipehnes in corrosive soils should be considered. In noncorrosive soils, coatings for stainless steel are recommended. 

Szklarska-Smialowska, Z., Electron Microprobe Study of the Effect of Sulphide Inclusions on the Nucleation of Corrosion Pits in Stainless Steels , Br. Corros. J., S, 159 (1970) Weinstein, M. and Speirs, K., Mechanisms of Chloride-activated Pitting Corrosion of Martensitic Stainless Steels , J. Electrochem. Soc., 117, 256 (1970)... 

Freiman, L. 1. and Kolotyrkin, Ya. M., Pitting Corrosion of Aluminium in Solutions of Sodium Perchlorate and Perchloric Acid , Zashch. Melal, 2, 488 (1966) C.A., 65, 19674d Novakovskii, V. M. and Sorokina, A. N., Comparative Electrochemistry of Stress Corrosion and Pitting of Stainless Steels in Chloride Solutions , Zashch. Melal, 2, 416 (1966) C.A., 65, 18152g... 

Potential-time relationships have been widely used for studying film formation and film breakdown, as indicated by an increase or decrease in the corrosion potential, respectively. May studied the corrosion of 70/30 brass and aluminium brass in sea-water and showed how scratching the surface resulted in a sudden fall in potential to a more negative value followed by a rapid rise due to re-formation of the film conversely, the pitting of stainless steel in chemical plant may be detected by a sudden decrease in potential... 

Chlorides are responsible for the pitting corrosion of steel parts. Normal carbon steel can stand 1000 ppm of chlorides (=1000 g M 3), but stainless steel starts to corrode severely from 100 ppm on Attention for ladders, illumination sets etc. 

G.T. Burstein and P C. Pistorius, Surface Roughness and the Metastable Pitting of Stainless Steel in Chloride Solutions, Corrosion, Vol 51, 1995, p 380-385... 

K. OsozawaandN. Okato, Effect of Alloying Elements, Especially Nitrogen, on Initiation of Pitting in Stainless Steel, Passivity and Its Breakdown in Iron and Iron-Base Alloys, R.W. Staehle and H. Okada, Ed., National Association of Corrosion Engineers, 1976, p 135-139... 

Aluminum alloys are susceptible to underdeposit corrosion. Stainless steels are also susceptible to underdeposit corrosion as well as deep pitting. Anodic, cathodic, and filming inhibitors are used to mitigate corrosion (40). 

P.S. Pistorius, G.T. Burstein, Growth of corrosion pits on stainless steel in chloride solution containing dilute sulfate, Corros. Sci. 33 (1992) 1885—1897. 

G.S. Frankel, L. Stockert, F. Hunkeler, H. Boehni, Metastable pitting of stainless steel. Corrosion 43 (1987) 429-436. 

R.C. Newman, W.P. Wong, H. Ezuber, A. Gamer, Pitting of stainless steels by thiosulfate ions. Corrosion 45 (1989) 282-287. 

An IPEN rack containing 1060, 6061 and 6262 alloys, used in fuel assembly manufacture, was also immersed in the basin. After 16 months of exposure, it was observed that some pitting had occurred on the uncoupled coupons, mostly on the top surfaces. The aluminium couples were stained inside the crevices but were not pitted. The stainless steel-aluminium galvanic coupons were much more severely corroded. Additional laboratory tests were conducted to determine whether increased levels of silver in the basin water could have increased the corrosion of the aluminium cladding in the IPEN basin. Results indicated no pitting but an increase in darkness of the surface oxide colour with the increase of silver concentration. 

Bemhardsson, S., Mellstrdm, R., and Brox, B., Limiting Chloride Contents and Temperatures with Regtird to Pitting of Stainless Steels." Paper 85, NACE CORROSION/80 Conference, Anaheim, CA, 1980. 

Garner. A., Newmann, R. C. (1991), Thiosulfate pitting of stainless steels, NACE Corrosion/91, Paper No. 186. 

Chamritsld IG, Bums GR, Webster BJ, Laycock NJ (2004) Effect of iron-oxidizing bacteria on pitting od stainless steels. CORROSION 60(7)... 

Sulfate-reducing bacteria have also been reported to be responsible for pitting corrosion on stainless steels in aqueous environments. The mechanisms proposed are mostly related to iron and steel. However, a different mechanism has been proposed in which the role of thiosulfate in the microbial pitting of stainless steel has been emphasized [137]. The same authors have also demonstrated clearly that SRB-induced pitting corrosion of stainless steel is unlikely to occur in a uniformly anaerobic SRB medium, whereas it will occur when the anaerobic sites are coupled to an oxygen cathode [136]. 

In contrast to the situation for aluminum, electrochemical studies on the pitting of stainless steels are fi aught with contradictions because of the effect of experimental factors. Several investigations have used breakthrough potential or breakdown potential, as a measure of pitting susceptibility. As pointed out earlier, the current increases rapidly at the breakdown potential (Fig. 4.24), this is considered as an indication of a breakdown of the passive, corrosion-resistant steel film and initiation of pitting. 

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