Ferric sulfate-50% sulfuric acid test

It was known that alloy C (Table 1) could also become susceptible to intergranular attack as a result of exposure to a range of elevated temperatures. However, there was no reliable quantitative method available for detecting this condition until the publication in 1963 [24] of the results shown in Fig. 18. To demonstrate the applicability of the ferric sulfate-50 % sulfuric acid test, specimens were heat-treated for 1 h at temperatures between 900 and 2450°F (482-1343 C), and tested for 24 h. (This is much shorter than the 120-h period used for Typ e 304 because of the 2 % lower chromium content and the 16 % molybdenum in alloy C.) It was found in the ferric sulfate test that there are two maxima in corrosion rates one at 1300 F (704°C), which is... 

FIG. 19—Effect of carbon content in Ni-Cr-Mo alloys on corrosion in the ferric sulfate-50 % sulfuric acid test [25]. ( NACE International. All Rights Reserved by NACE reprinted with permission.)... 

FIG. 21—Intergranular attack on weldmant In ferritic stainless steel caused by high nitrogen content (5x). Autogenous weld In 28.5 %Cr<4.2 %Mo alloy with 22 ppm carbon and 388 ppm nitrogen after exposure In ferric sulfate-50 % sulfuric acid test. 

FIG. 10—Apparatus for ferric sulfate-sulfuric acid test. 

Acid corrosion of stainless steels in the various test media, such as nitric acid and ferric sulfate-sulfuric acid, also takes place at essentially constant electrode potential. 

Ferric Sulfate-Sulfuric Acid (Streicher Test) A 262[B]... 

Ferric Sulfate TS, Acid Add 7.5 mL of sulfuric acid to 100 mL of water, and dissolve 80 g of ferrous sulfate in the mixture with the aid of heat. Mix 7.5 mL of nitric acid and 20 mL of water, warm, and add to this the ferrous sulfate solution. Concentrate the mixture until, upon the sudden disengagement of ruddy vapors, the black color of the liquid changes to red. Test for the absence of ferrous iron, and, if necessary, add a few drops of nitric acid and heat again. When the solution is cold, add sufficient water to make 110 mL. 

Test for Cyanide Ion. Place 3 ml of alkaline filtrate in a small beaker or a large test tube, and add 5 drops of freshly prepared 10 per cent ferrous sulfate solution, 2 drops of 6 N sodium hydroxide solution and 5 drops 10 per cent potassium fluoride solution, then boil. Add 1 drop of 10 per cent ferric chloride solution and then add dilute sulfuric acid drop by drop until the solution is acid, in order to dissolve the oxides of iron. Allow to stand for five minutes. A clear solution of a yellow color indicates absence of cyanide ion and hence of nitrogen. The formation of a greenish-blue... 

B) Other ferric complexes. In three test tubes place a few milliliters of dilute (0.02-molar or less) solutions of ferric sulfate, ferric nitrate, and ferric chloride. Note their colors, and add to the three tubes 6N sulfuric, nitric, and hydrochloric acids, respectively. Divide the solution of ferric chloride in hydrochloric acid into three parts. To one portion add one-quarter its volume of sirupy phosphoric acid, and to another add a gram or so of potassium fluoride, shaking till it dissolves. Keep the third portion as a control. You now have five solutions. Note their colors then add to each a little potassium thiocyanate. If two test tubes seem to be giving an equally dark color, dilute the solutions by equal amounts and see if you notice any difference. Record the results of the tests in tabular form, thus ... 

A more refined test is the Schultz (1924) method for cholesterol, which involves the application of a mixture of concentrated sulfuric acid and glacial acetic acid to sections which have been oxidized with ferric ammonium sulfate (iron alum). A blue-green color results. The iron alum apparently oxidizes 3-hydroxy steroids and their esters to 7-oxy steroids, which give the Lifschlltz color reaction on the application of the acids. (Fieser and Fieser, 1949, p. 234). This test is considered to be more specific for a limited group of steroids than is the sulfuric acid method cited above, which reveals a large number of unsaturated polycyclic compounds. Recently, however, Kent (1952) has reported that a positive reaction also occurs with carotene. 

Generally, evaluation in the 50 % sulfuric acid ferric sulfate test is by weight-loss. However, on alloys C and C-276 the relatively low chromium content of about 15 % (i.e., 3 % less than in Type 304 steel) results in a somewhat high rate of general corrosion that tends to mask low rates of intergranular attack. Therefore, to establish evidence of intergranular attack, microscopic examination is recommended in ASTM G 28 to supplement the corrosion rate (weight-loss) data. The newer C-type alloys (Table 1) have 20 to 23 % chromium, and therefore do not pose this problem. 

Metal salts, such as ferric and cupric sulfate, are oxidizing and will passivate stainless steel when added to sulfuric acid. The salt concentration may be controlled so that passivity will occur at a specific chromium concentration. Stainless steels or areas of a stainless surface (such as sensitized grain boundary areas) with lower chromium content will not be passivated. This is the basis for the intergranular corrosion tests for stainless steels. 

Sulfuric Acid 10-15 234 112 — G E u reacts with feme oxide to produce ferric sulfate, field test. 10 days, aeration — moderate, agitation — 6 ft./sec. 

Sulfur often obscures the test for nitrogen. If sulfur is present, proceed as follows To a portion of the solution add 5 drops of ferrous sulfate solution and 5 drops of fluoride solution, then add sodium hydroxide until the mixture is alkaline. Heat to boiling, and filter from any precipitate. Acidify with dilute hydrochloric acid, and add a drop of ferric chloride to obtain a precipitate of Prussian blue. 

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