Crevice corrosion resistant

Recommended practice for examination and evaluation of pitting corrosion Test method for determining susceptibility to stress corrosion cracking of high-strength aluminium alloy products Test method for pitting and crevice corrosion resistance of stainless steels and related alloys by the use of ferric chloride solution Recommended practice for preparation and use of direct tension stress corrosion test specimens... 

A common chemical laboratory test for corrosion resistance is a simple exposure test using metal coupons. The ASTM standard G48 —Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution—describes a simple exposure test. The material coupons (e.g., 60 x 60 mm) are placed on a glass cradle and immersed in the solution in such a way that the coupons are evenly exposed. 

Two recent studies have used surface techniques to examine the protective layers formed in various oxidation conditions and related the nature of the oxide to the corrosion rates in specific environments. Hultquist and Leygraf (43, 44) have examined crevice corrosion resistance in a NaCl solution at room temperatures while Baer (45) has looked at higher temperature (800°C) air oxidation. Oxygen potential, or partial pressure, is an important parameter in both studies where it was found that controlled oxidation can tailor the Cr profile in the alloy and surface oxide for maximum corrosion protection. Specific goals in each experiment were oxide characterization and comparison to corrosion rates... 

Crevice Corrosion resistance of Alpha Titanium Alloys depends on Impurity Content/Alloying Additions... 

Austenitic SS s are also used in freshwater. However, because of cost their use is limited mainly to applications in which copper-zinc alloys are unsuitable, as in tubes in which the process side is incompatible with copper base alloys. To avoid pitting, type 304 (UNS S30400) SS is normally limited to services in which the chloride ion concentration is at a maximum of 100 ppm, and type 316 SS is limited to services in which the chloride ion is a maximum of 500 ppm. The relative pitting and crevice corrosion resistance of SS alloys can be approximated by the following equation ... 

The main approach to improving the pitting and crevice corrosion resistance of the basic 35% nickel, 19% chromium, and 2% molybdenum alloy was to increase the molybdenum content. Among the first of the newer alloys introduced was 904 L (UNS N08904), which boosted the molybdenum content to 4% and reduced the nickel content to 25%. The reduction in nickel content was beneficial as a costsaving factor, with minimal loss of general corrosion resistance and sufficient resistance to chloride SCC. 

ASTM G48-76, Standard Methods for Pitting and Crevice Corrosion, Resistance of stainless steel and Related AUoys by Use of Ferric Chloride Solution, American Society for Testing and Materials, Philadelphia, Pa. 

Y.C. Lu, M.B. Ives, Chemical treatment with cerium to improve the crevice corrosion resistance of austenitic stainless steels, Corros. Sci. 37 (1995) 145—155. 

Oldfield JW. Test techniques for pitting and crevice corrosion resistance of stainless steels and nickel alloys in chloride containing environments. International Materials Review, 32, 1987 3 153—170. 

Alloy C-22 and Alloy 59 were developed for applications where resistance to corrosion under highly oxidizing conditions is required. The high chromium content in these alloys, 22% and 23% for C-22 and 59, respectively, imparts excellent corrosion resistance of these alloys to nitric acid [23]. In addition, these alloys have been found to have superior crevice corrosion resistance in seawater [24]. 

Zinc may also be used to prevent crevice corrosion of other materials. Work by Ito et al. (1989) shows that crevice corrosion resistance of zinc-plated stainless steels is superior to that of unplated in an NaCl solution. Good general corrosion resistance was also obtained. It seems that these beneficial results are due not only to sacrificial dissolution of zinc, but also to suppression of the cathodic reaction of dissolved oxygen by the corrosion products. A buffer action by the corrosion product also seems to play an important part in the prevention of corrosion. 

G 48 Test Method for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by the Use of Ferric... 

Testing for shorter periods may be appropriate when the test sample configuration intentionally provides more severe conditions than anticipated in service. Crevice corrosion tests using severe artificial crevice geometries may only require 30-90 days of exposure to establish relative crevice corrosion resistance. 

Several tests have been developed over the years to determine the crevice corrosion resistance of alloys. The objectives of these tests include comparison of alloys, qualification of alloys for a given service, evaluation of the effects of fabrication processes on crevice corrosion resistance, quality control, and life prediction. This chapter will briefly describe the types of tests, and their applicability and limitations, with a focus on tests that have been or are now being considered by ASTM Committee G-1 on Corrosion of Metals. While these test principles are applicable to a wide variety of alloys, the information presented is focused on stainless and nickel-base alloys. 

REVIEW OF TEST METHODS FOR CREVICE CORROSION RESISTANCE... 

These techniques for evaluating crevice corrosion resistance involve holding (static) or incrementally changing (step or scan) the potential or current. Some of the more frequently used techniques for evaluating crevice corrosion resistance are listed below, following the definitions given in ASTM G 15 ... 

Critical potentials axe important in determining the resistance of a mefed to localized corrosion because they have a mechanistic underpinning and they are rapid measurements. Two potentials have been used as a measure of the crevice corrosion resistance—crevice/pit initiation potential (Ee or Ep) and crevice/pit repassivation potential (Ei ev or E ). The E or Ep is the potential at which the current... 

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