1、Designation: G 28 02Standard Test Methods ofDetecting Susceptibility to Intergranular Corrosion inWrought, Nickel-Rich, Chromium-Bearing Alloys1This standard is issued under the fixed designation G 28; the number immediately following the designation indicates the year of originaladoption or, in the
2、 case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 These
3、 test methods cover two tests as follows:1.1.1 Method A, Ferric Sulfate-Sulfuric Acid Test (3-10 ,inclusive)This test method describes the procedure forconducting the boiling ferric sulfate50 % sulfuric acid testwhich measures the susceptibility of certain nickel-rich,chromium-bearing alloys to inte
4、rgranular corrosion (see Ter-minology G 15), which may be encountered in certain serviceenvironments. 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 ra
5、te on alloys N10276,N06022, N06059, and N06455.1.1.2 Method B, Mixed Acid-Oxidizing Salt Test (Sections11-18, inclusive)This test method describes the procedurefor conducting a boiling 23 % sulfuric + 1.2 % hydrochlo-ric+1% ferric chloride+1% cupric chloride test whichmeasures the susceptibility of
6、certain nickel-rich, chromium-bearing alloys to display a step function increase in corrosionrate when there are high levels of grain boundary precipitation.1.2 The purpose of these two test methods is to detectsusceptibility to intergranular corrosion as influenced by varia-tions in processing or c
7、omposition, or both. Materials shown tobe susceptible may or may not be intergranularly corroded inother environments. This must be established independently byspecific tests or by service experience.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its
8、 use. 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. Hazard advisorystatements are given in 5.1.1, 5.1.3, 5.1.9, 13.1.1, and 13.1.11.2. Referenced Document2.1 ASTM Sta
9、ndards:A 262 Practices for Detecting Susceptibility to Intergranu-lar Attack in Austenitic Stainless Steels2D 1193 Specification for Reagent Water3G 15 Terminology Relating to Corrosion and CorrosionTesting4METHOD AFerric SulfateSulfuric Acid Test3. Significance and Use3.1 The boiling ferric sulfate
10、-sulfuric acid test may beapplied to the following alloys in the wrought condition:Alloy Testing Time, hN06007 120N06022 24N06030 120N06059 24N06200 24N06455 24N06600 24N06625 120N06686 24N06985 120N08020 120N08367 24N08800 120N08825A120N10276 24_AWhile the ferric sulfate-sulfuric acid test does det
11、ect susceptibility to inter-granular corrosion in Alloy N08825, the boiling 65 % nitric acid test, PracticesA 262, Practice C, for detecting susceptibility to intergranular corrosion in stainlesssteels is more sensitive and should be used if the intended service is nitric acid.3.2 This test method m
12、ay be used to evaluate as-receivedmaterial and to evaluate the effects of subsequent heat treat-ments. 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.1These test methods are un
13、der the jurisdiction of ASTM Committee G01 onCorrosion of Metals and are the direct responsibility of Subcommittee G01.05 onLaboratory Corrosion Tests.Current edition approved Oct. 10, 2002. Published January 2003. Originallypublished as G 28 71. Last previous edition G 28 97.2Annual Book of ASTM St
14、andards, Vol 01.03.3Annual Book of ASTM Standards, Vol 11.01.4Annual Book of ASTM Standards, Vol 03.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Apparatus4.1 The apparatus (Note 1) is illustrated in Fig. 1.FIG. 1 Apparatus f
15、or Ferric Sulfate-Sulfuric Acid TestG280224.1.1 Allihn or Soxhlet Condenser, 4-bulb,5with a 45/50ground-glass joint, overall length about 330 mm, condensingsection about 240 mm.4.1.2 Erlenmeyer Flask, 1-L, with a 45/50 ground-glassjoint. The ground-glass opening shall be 40 mm wide.4.1.3 Glass Cradl
16、e (Fig. 2)To pass through the ground-glass joint on the Erlenmeyer flask, the width of the cradleshould not exceed 40 mm and the front-to-back distance mustbe such that the cradle will fit the 40-mm diameter opening. It5To avoid frequent chipping of the drip-tip of the condenser during handling, the
17、modified condenser described by Streicher, M. A., and Sweet, A. J., Corrosion,Vol25, 1969, pp. 1, has been found suitable for this use.FIG. 2 Glass CradleG28023should have three or four holes to increase circulation of thetest solution around the specimen (Note 2).NOTE 1Substitution for this equipme
18、nt may not be used. The cold-finger type of standard Erlenmeyer flask may not be used.NOTE 2Other equivalent means of specimen support, such as glasshooks or stirrups, may also be used.4.1.4 Boiling Chips,6or some other boiling aids must beused to prevent bumping.4.1.5 Silicone Grease,7is recommende
19、d for the ground-glass joint.4.1.6 Electrically Heated Hot Plate, or equivalent to pro-vide heat for continuous boiling of the solution.4.1.7 Analytical Balance, capable of weighing to the nearest0.001 g.5. Test Solution5.1 Prepare 600 mL of 50 % (49.4 to 50.9 %) solution asfollows:5.1.1 WarningProt
20、ect the eyes and use rubber gloves forhandling acid. Place the test flask under a hood.5.1.2 First, measure 400 mL of Type IV reagent water(Specification D 1193) in a 500-mL graduate and pour into theflask.5.1.3 Then measure 236 mL of reagent-grade sulfuric acid(H2SO4) of a concentration which must
21、be in the range from95.0 to 98.0 weight percent in a 250-mL graduate. 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 3Loss of vapor results in concentration of the a
22、cid.5.1.4 Weigh 25 g of reagent grade ferric sulfate (containsabout 75 % Fe2(SO4)3(Note 4) and add to the H2SO4solution. A trip balance may be used.NOTE 4Ferritic sulfate is a specific additive that establishes andcontrols the corrosion potential. Substitutions are not permitted.5.1.5 Add boiling ch
23、ips.5.1.6 Lubricate the ground glass of the condenser joint withsilicone grease.5.1.7 Cover the flask with the condenser and circulatecooling water.5.1.8 Boil the solution until all ferric sulfate is dissolved.5.1.9 WarningIt has been reported that violent boilingcan occur resulting in acid spills.
24、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.66. Test Specimens6.1 A specimen having a total surface area of 5 to 20 cm2isrecommended.6.2 The intent is to test a s
25、pecimen representing as nearly aspossible the material as used in service. 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 fin
26、ishing should be performed as is required toremove foreign material and obtain a standard, uniform finishas specified in 6.4. For very heavy sections, specimens shouldbe maintained to represent the appropriate surface whilemaintaining reasonable specimen size for convenience intesting. Ordinarily, r
27、emoval 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
28、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.6.3 When specimens are cut by shearing, the deformedmaterial must be removed by machining or grinding to a depthequ
29、al to the thickness of the specimen to remove cold workedmetal.6.4 All surfaces of the specimen, including edges, should befinished using wet No. 80-grit or dry No. 120-grit abrasivepaper. If dry abrasive paper is used, polish slowly to avoidoverheating. Sand blasting should not be used.6.5 Residual
30、 oxide scale has been observed to cause spuri-ous specimen activation in the test solution. 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.6.6 The sp
31、ecimen dimensions should be measured includingthe edges and inner surfaces of any holes and the total exposedarea calculated.6.7 The specimen should then be degreased using suitablenonchlorinated agents such as soap and acetone, dried, andthen weighed to the nearest 0.001 g.7. Procedure7.1 Place the
32、 specimen in the glass cradle, remove thecondenser, immerse the cradle by means of a hook in theactively boiling solution (Fig. 1), and immediately replace thecondenser. A fresh solution should be used for each test.7.2 Mark the liquid level on the flask with wax crayon toprovide a check on vapor lo
33、ss which would result in concen-tration of the acid. If there is an appreciable change in the level(a 0.5-cm or more drop), repeat the test with fresh solution andwith a fresh specimen or a reground specimen.7.3 Continue immersion of the specimen for the length oftime specified in Section 3, then re
34、move the specimen, rinse inwater and acetone, and dry.7.4 Weigh the specimen and subtract this mass from theoriginal mass.7.5 Intermediate weighing is not necessary, except as notedin 7.7. The tests can be run without interruption. However, ifpreliminary results are desired, the specimen can be remo
35、ved atany time for weighing.7.6 Replacement of acid is not necessary during the testperiods.6Amphoteric alundun: granules, Hengar Granules, from the Hengar Co.,Swedesboro, NJ have been found satisfactory for this purpose.7Stopcock grease has been found satisfactory for this purpose.G280247.7 If the
36、corrosion rate is extraordinarily high in Method A,as evidenced by a change in color (green) of the solution,additional ferric sulfate must be added during the test. Theamount of ferric sulfate that must be added, if the total massloss of all specimens exceeds2gasindicated by an interme-diate weight
37、, is 10 g for each1gofdissolved alloy. This doesnot apply to Method B.7.8 In Method A, several specimens of the same alloy maybe tested simultaneously. 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 s
38、ample shouldbe tested in a flask for Method B.7.9 During testing, there is some deposition of iron oxideson the upper part for the flask. This can be readily removedafter test completion by boiling a solution of 10 % hydrochlo-ric acid (HCl) in the flask.8. Calculation and Interpretation of Results8
39、.1 CalculationMeasure the effect of the acid solution onthe matCorrosion Rate 5 K 3 W!/A 3 T 3 D! (1)where:K = a constant (see 8.1.1),T = time of exposure, h, to the nearest 0.01 h,A = area, cm2, to the nearest 0.01 cm2,W = mass loss, g, to the nearest 0.001 g, andD = density, g/cm3(see 8.1.2).=8.1.
40、1 Many different units are used to express corrosionrates. Using the above units for T, A, W, and D, the corrosionrate can be calculated in a variety of units with the followingappropriate value of K:Corrosion Rate Units DesiredConstant K in Corrosion RateEquationAmils per year (mpy) 3.45 3 106inche
41、s per year (ipy) 3.45 3 103inches per month (ipm) 2.87 3 102millimeters per year (mm/Y) 8.76 3 104micrometers per year (m/y) 8.76 3 107picometers per second (pm/s) 2.78 3 106grams per square meter-hour (g/m2-h) 1.00 3 1043 DBmilligrams per square decimeter-day (mdd) 2.40 3 1063 DBmicrograms per squa
42、re meter-second (g/m2-s) 2.78 3 1063 DB_AIf desired, these constants may also be used to convert corrosion rates fromone set of units to another. To convert a corrosion rate in units X to a rate in unitsY, multiply by KY/KX. For example:15 mpy 5 15 3 2.78 3 106!/3.45 3 106!# pm/s5 12.1 pm/sBDensity
43、is not needed to calculate the corrosion rate in these units. The densityin the constant K cancels out the density in the corrosion rate equation.8.1.2UNS Designation Density, g/cm3N06007 8.31N06022 8.69N06030 8.22N06059 8.80N06200 8.50N06455 8.64N06600 8.41N06625 8.44N06686 8.73N06985 8.31N08020 8.
44、05N08367 8.06N08800 8.03N08825 8.14N10276 8.878.2 Interpretation of ResultsThe presence of intergranularcorrosion is usually determined by comparing the calculatedcorrosion rate to that for properly annealed material. Even inthe absence of intergranular corrosion, the rate of general orgrain-face co
45、rrosion of properly annealed material will varyfrom one alloy to another. These differences are demonstratedin Refs. (1-7).88.3 As an alternative or in addition to calculating a corro-sion rate from mass loss data, metallographic examination maybe used to evaluate the degree of intergranular corrosi
46、on. Thedepth of attack considered acceptable shall be determinedbetween buyer and seller.9. Report9.1 Record the test procedure used, specimen size andsurface preparation, time of test, temperature, and mass loss.9.2 Report following information:9.2.1 Alloy number and heat number,9.2.2 Chemical comp
47、osition and thermal treatment,9.2.3 Test method used, and9.2.4 Calculated corrosion rate in units desired.10. Precision and Bias910.1 The precision of the procedure in Test Method A ofTest Methods G 28 was determined in an interlaboratory testprogram with six laboratories running duplicate tests of
48、threeheat treatments of a single material. Precision consists ofrepeatability, that is, the agreement that occurs when identicalspecimens are run sequentially with the same test method in thesame laboratory by the same operator and equipment, andreproducibility, that is, the agreement that occurs wh
49、en iden-tical specimens are run with the same test method at differentlaboratories.10.1.1 The interlaboratory test program produced repeat-ability statistics consisting of the repeatability standard devia-tion, srand the 95 % repeatability limits, r. These values wererelated to the average corrosion rate, x, in mpy by the followingexpressions:sr562.84 * 1026x!3(2)r 567.95 * 1026x!3(3)where:r = 2.8srThe units of r and srare mpy.8The boldface numbers refer to the list of references at the end of these testmethods.9Supporting data is
