Ferric chloride environment

Hibner, E. L., Modification of Critical Crevice Temperature Test Procedures for Nickel Alloys in a Ferric Chloride Environment, Materials Performance, Vol. 26, No. 3, 1987, pp. 37-40. 

The Materials Technology Institute of the Chemical Process Industry (MTI) has identified five corrosion tests for iron- and nickel-based alloys, out of which two concern the resistance to crevice corrosion. The method MTI-2, originating from ASTM G48, involves the use of 6% ferric chloride solution for determining the relative resistance of alloys to crevice corrosion in oxidizing chloride environment. The method MTI-4 uses an increase in neutral bulk Cl- concentration at eight levels, ranging from 0.1 to 3% NaCl, to establish the minimum critical Cl concentration that produces crevice corrosion at room temperature (20-24°C).43,44... 

Gu, B. Dong, W. Brown, G. M. Cole, D. R. Complete Degradation of Perchlorate in Ferric Chloride and Hydrochloric Acid under Controlled Temperature and Pressure, Environ. Sci. Technol. 2003,37,2291-2295. 

What s in a letter With nickel alloys it is important to make no mistake in entering the specification. For example, Hastelloy C-276 is used in many demanding chemical environments. Hastelloy B-2 also possesses exceptional chemical resistance, but to niche environments like hot hydrochloric acid. It fails rapidly if substituted for Hastelloy C-276 in a service like ferric chloride. Never call out a material merely as Hastelloy, Inconel, etc. It is best to identify any nickel alloy by its UNS designation, such as UNS N102756 for Hastelloy C-276 and N10665 for Hastelloy B-2. 

In a recent investigation of the corrosion resistance of as-welded C-276, C-22, and alloy 686 specimens, Saldanha [47] has shown that such weld metal is also susceptible to rapid and severe pitting in a simulated plant solution, boiling 80 % acetic acid with 1000-5000 ppm ferric chloride. There was severe pitting on all three alloy weldments see Fig. 23 for pitting in C-276 weld metal in only five days of testing. There was no attack in the heat-affected zones or in the base-plate. Thus, there are plant environments in which... 

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. 

Stainless Steels. In this method, ferric chloride has been used to detect the precipitation of harmful intermetallic phases rather than indicate the performance of the steel in other corrosive environments. 

The composition of the etchant is mainly ferric chloride in water, with concentrations ranging from 28 to 42 percent by weight. Free acid is present because of the hydrolysis reaction and the need to maintain an acid environment. The natnral acidity is usually supplemented by additional amounts of HCl (up to 5 percent) to prevent formation of insoluble precipitates of ferric hydroxide. Commercial formulations for copper alloy etching are usually 36 Be, or approximately 4.0 Ib/gal FeCls, and may contain antifoam and wetting agents. Customary add operating HCl content is 1.5 to 2.0 percent. 

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