ASTM G28 PDF

This document describes all three of these tests for four common standards, and describes the differences. Just remember that these tests were devised for specific groups of alloys and should not be applied to all CRAs! This document also points out which alloys the tests are intended for, and recommends the most appropriate test when none is specified. Why were these tests designed?

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Anumber in parentheses indicates the year of last reapproval. This standard has been approved for use by agencies of the U. Department of Defense. The uniform corrosion rate obtained by this testmethod, which is a function of minor variations in alloycomposition, may easily mask the intergranular corrosioncomponents of the overall corrosion rate on alloys N,N, N, and N Materials shown tobe susceptible may or may not be intergranularly corroded inother environments.

This must be established independently byspecific tests or by service experience. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Warning statementsare given in 5. Referenced Documents2.

Significance and Use3. In the case of nickel-rich, chromium-bearing alloys, thetest method may be applied to wrought and weldments ofproducts. The test method is not applicable to cast products. Current edition approved Nov. Published November Originallyapproved in Last previous edition approved in as G28—02 United States The ground-glass opening shall be 40 mm wide. Itshould have three or four holes to increase circulation of thetest solution around the specimen Note 2.

NOTE 1—Substitution for this equipment may not be used. Thecold-finger type of standard Erlenmeyer flask may not be used. NOTE 2—Other equivalent means of specimen support, such as glasshooks or stirrups, may also be used. Test Solution5. Place the test flask under a hood. Add the acidslowly to the water in the flask to avoid boiling by the heatevolved Note 3. Externally cooling the flask with waterduring the mixing will also reduce overheating. NOTE 3—Loss of vapor results in concentration of the acid.

A trip balance may be used. NOTE 4—Ferritic sulfate is a specific additive that establishes andcontrols the corrosion potential. Substitutions are not permitted. It is important to ensure thatthe concentration of acid does not increase and that an adequatenumber of boiling chips which are resistant to attack by thetest solution are present. Test Specimens6. The specimens shouldbe cut to represent the grain flow direction that will see service,for example, specimens should not contain cross-sectionalareas unless it is the intent of the test to evaluate these.

Onlysuch surface finishing should be performed as is required toremove foreign material and obtain a standard, uniform finishas specified in 6. For very heavy sections, specimens shouldbe maintained to represent the appropriate surface whilemaintaining reasonable specimen size for convenience intesting.

Ordinarily, removal of more material than necessarywill have little influence on the test results. However, in thespecial case of surface decarburization or of carburization thelatter is sometimes encountered in tubing when lubricants orbinders containing carbonaceous materials are employed , itmay be possible by heavy grinding or machining to remove theaffected layer completely. Such treatment of test specimens isnot permissible, except in tests undertaken to demonstrate suchsurface effects.

If dry abrasive paper is used, polish slowly to avoidoverheating. Sand blasting should not be used. Therefore, theformation of oxide scale in stamped codes must be prevented,and all traces of oxide scale formed during heat treatment mustbe thoroughly removed prior to stamping identification codes.

Your comments will receive careful consideration at ameeting of the responsible technical committee,1which you may attend. A fresh solution should be used for each test.

If there is an appreciable change in the level a 0. The tests can be run without interruption. However, ifpreliminary results are desired, the specimen can be removed atany time for weighing. Theamount of ferric sulfate that must be added, if the total massloss of all specimens exceeds 2 g as indicated by an interme-diate weight, is 10 g for each 1 g of dissolved alloy. This doesnot apply to Method B. The number 3 or 4 is limited onlyby the number of glass cradles that can be fitted into the flaskand the consumption of ferric sulfate.

Only one sample shouldbe tested in a flask for Method B. Calculation and Interpretation of Results8. Forexample mpyfs2. The densityin the constant K cancels out the density in the corrosion rate equation. Even inthe absence of intergranular corrosion, the rate of general orgrain-face corrosion of properly annealed material will varyfrom one alloy to another. These differences are demonstratedin Refs Thedepth of attack considered acceptable shall be determinedbetween buyer and seller.

Precision and Bias Precision consists of6The boldface numbers in parentheses refer to a list of references at the end ofthis standard.

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