Pitting corrosion ferric chloride solution

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. 

Specimen 7 displays irregular corrosion spread over the entire surface of the specimen. It takes the form of wide depressions with pitting corrosion. The test solution is rust-brown and cloudy with a rust-coloured sediment, the main component of which is ferric hydroxide. This picture is typical of contact corrosion between unalloyed steel and copper in sodium chloride solutions (Figure 11.85(g)). 

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. 

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

Salinas-Bravo, V. M. and Newman, R. C., An Alternative Method to Determine Critical Pitting Temperature of Stainless Steels in Ferric Chloride Solution, Corrosion Science, Vol. 36, No. 1, 1994, pp. 67-77. 

ASTM G 48, Test Method for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by the Use of Ferric Chloride Solution, covers procedures for determination of the resistance of stainless steels and related alloys to pitting and crevice corrosion when exposed to an oxidizing chloride environment (6 % FeCls). Four procedures are identified as Methods A, B, C, and D. 

ASTM Standard Recommended Practice G48, Pitting and crevice corrosion resistance of stainless steels and related alloys by the use of ferric chloride solution ... 

If chlorides are present, the pH of the electrolyte under the biofilm may further decrease, leading to more severe corrosion. When some types of bacteria such as iron-oxidising bacteria (lOB) [32] are present, the tubercule conditions may become very acidic due to combining of the chloride ions with the ferric ions that are produced by the bacteria to form acidic ferric chloride solution inside the tubercule (or biofilm) that is highly corrosive [30]. Pitting is the predominant morphology of MIC [21,46, 104]. 

Most simple inorganic salt solutions cause virtually no attack on aluminium-base alloys, unless they possess the qualities required for pitting corrosion, which have been considered previously, or hydrolyse in solution to give acid or alkaline reactions, as do, for example, aluminium, ferric and zinc chlorides. With salts of heavy metals —notably copper, silver, and gold —the heavy metal deposits on to the aluminium, where it subsequently causes serious bimetallic corrosion. 

Fig. 4 Example of the results of crevice corrosion. Type 304 SS exposed to 6 wt.% ferric chloride for 48 h at room temperature with castellated crevice washer applied around center hole. Pitting also occurred at several sites outside the crevice. The draining of the occluded solution from the crevice sites (and pits) led to the river pattern of...

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