1、Designation: G 36 94 (Reapproved 2006)Standard Practice forEvaluating Stress-Corrosion-Cracking Resistance of Metalsand Alloys in a Boiling Magnesium Chloride Solution1This standard is issued under the fixed designation G 36; the number immediately following the designation indicates the year of ori
2、ginaladoption or, in the 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.1. Scope1.1 This practice describes a procedure for conductingstress-corro
3、sion cracking tests in a boiling magnesium chloridesolution. Although this test may be performed using variousconcentrations of magnesium chloride, this procedure covers atest solution held at a constant boiling temperature of 155.0 61.0C (311.0 6 1.8F). The boiling points of aqueous magne-sium chlo
4、ride solutions at one atmosphere pressure as afunction of concentration are shown graphically in Fig. 1.2Asuggested test apparatus capable of maintaining solution con-centration and temperature within the prescribed limits forextended periods of time is also described herein.31.2 The boiling magnesi
5、um chloride test is applicable towrought, cast, and welded stainless steels and related alloys. Itis a method for detecting the effects of composition, heattreatment, surface finish, microstructure, and stress on thesusceptibility of these materials to chloride stress corrosioncracking.41.3 This pra
6、ctice is concerned primarily with the test solu-tion, which may be used with a variety of stress corrosion testspecimens, surface finishes, and methods of applying stress.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility
7、 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. See Section 7 forspecific safety precautions.2. Referenced Documents2.1 ASTM Standards:5D 1193 Specification for Reagent WaterG1 Practice for P
8、reparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG15 Terminology Relating to Corrosion and CorrosionTestingG30 Practice for Making and Using U-Bend Stress-Corrosion Test Specimens3. Terminology3.1 DefinitionsFor definitions of terms used in this prac-tice see Terminology G15.4. Summary of
9、 Practice4.1 A predetermined quantity of reagent grade magnesiumchloride and some distilled water are added to a container. Thecontainer and contents, with thermometer and condenser af-fixed, are placed on a source of heat. When the magnesiumchloride solution boils, it is adjusted to maintain the de
10、siredconcentration and boiling point through the addition of smallquantities of either water or salt.4.2 After the solution has stabilized at the desired boilingpoint for the test, the stressed specimens are added. Dependingupon the intent of the test, the specimens should be givenperiodic inspectio
11、ns. If the duration of test exceeds 7 days, thesolution should either be changed or the suggested or similartest apparatus used.5. Significance and Use5.1 For most applications, this environment provides anaccelerated method of ranking the relative degree of stress-corrosion cracking susceptibility
12、for stainless steels and relatedalloys in aqueous chloride-containing environments. Materialsthat normally provide acceptable resistance in hot chlorideservice may crack in this test. The test may not be relevant tostress-corrosion cracking in polythionic acid or caustic envi-ronments.1This practice
13、 is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.06 on Environmen-tally Assisted Cracking.Current edition approved Nov. 1, 2006. Published December 2006. Originallyapproved in 1973. Last previous edition approved in 2000 as G
14、 36 94 (2000).2Available data on the relationship of concentrations and boiling points ofmagnesium chloride solutions are critically reviewed and supplemented by I. B.Casale in “Boiling Points of Magnesium Chloride SolutionsTheir Application inStress Corrosion Studies,” Corrosion , Vol 23, 1967, pp.
15、 31417.3The apparatus and test procedures for maintaining constant boiling tempera-tures of magnesium chloride solutions for stress corrosion tests are described by M.A. Streicher and A. J. Sweet in Corrosion, Vol 25, 1969, pp. 16.4The use of concentrated magnesium chloride solutions for determining
16、 thesusceptibility to stress corrosion cracking of austenitic and ferritic stainless steelsand related nickel-base alloys was first described by M. A. Scheil, Symposium onStress Corrosion Cracking of Metals, ASTM STP 64, ASTM, 1945, p. 395.(Although currently out of print, copies may be obtained fro
17、m University Micro-films, Inc., 300 North Zeeb Rd., Ann Arbor, MI 48106.)5For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe A
18、STM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.5.2 Resistance to stress-corrosion cracking in boiling mag-nesium chloride (155.0C (311.0F) should, where possible,be correlated to resistance in service for the materials o
19、finterest. However, such correlations may not always be pos-sible.5.3 Boiling magnesium chloride may also cause pitting ofmany stainless alloys. This leads to the possibility of confusingstress-corrosion failures with mechanical failures induced bycorrosion-reduced net cross sections. This danger is
20、 particu-larly great when small cross section samples, high appliedstress levels, long exposure periods, stress-corrosion resistantalloys, or a combination thereof are being used. Carefulexamination is recommended for correct diagnosis of the causeof failure.6. Apparatus6.1 Any inert, transparent ap
21、paratus with provisions for athermometer and water-cooled condenser can be used, pro-vided that it has been designed to contain the stressed specimenwhile maintaining a constant temperature and concentration ofthe magnesium chloride solution by minimizing or preventinglosses of condensate and water
22、vapor during prolonged periodsof test. Small losses of water from a solution of magnesiumchloride will lead to large increases in the boiling point of thesolution with a reduction in the time to failure of a specimen bystress corrosion cracking.Asuggested apparatus, shown in Fig.X1.1, meets these re
23、quirements. Design details of this appara-tus are given in Appendix X1.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the A
24、merican Chemical Society,where such specifications are available.6Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Purity of WaterReagent water Type IV (SpecificationD 119
25、3) shall be used to prepare the test solutions.7.3 Magnesium Chloride (MgCl26H2O)A solution ofmagnesium chloride that boils at 155.0 6 1.0C (311.0 61.8F) is used in this test. A second 25 weight percent solutionof magnesium chloride is required for the trap if the testduration exceeds seven days wit
26、hout a solution change and thesuggested apparatus is used.7.3.1 To prepare about 400 mL of the test solution for use ina 1-L Erlenmeyer flask or other container, weigh 600 g ofreagent grade MgCl26H2O and add this to the flask containinga thermometer along with 15 mL of reagent water.7.3.2 Add 10 to
27、15 boiling chips or other boiling aids.7.3.3 Heat by placing the flask on a hot plate or othersuitable source of heat and put the condenser in place, leavingoff the trap. Hook up the cooling water supply to the condenser.7.3.4 When the solution boils vigorously and there is nomore dripping of conden
28、sate, slowly add small quantities (4 to5 mL) of reagent water at the top of the condenser to reduce thetemperature to 155.0C (311.0F). Use extreme caution whenadding the water to the boiling magnesium chloride solution.Cool water can form a layer on top of the magnesium chloride,and when it reaches
29、the bottom of the flask, bumping can occur.Use a protective shield.NOTE 1If too much water has been added, add some crystals ofMgCl26H2O through the condenser until a temperature of 155.0C(311.0F) is attained.7.4 To prepare the 25 weight percent solution for the trap(Fig. X1.3), place 53.4 g of MgCl
30、26H2O and 46.6 mL ofreagent water in a flask and allow the crystals to dissolve atroom temperature.8. Safety Precautions8.1 When cold, magnesium chloride can be handled withthe minimum protective equipment of rubber gloves andgoggles. Maximum protective measures should be taken toprevent boiling mag
31、nesium chloride from coming into contactwith the skin. Severe burns can result as the hot magnesiumchloride adheres to the skin forming a crust which causes deepburns. The severity of the burns can be reduced by takingproper and immediate first aid measures and by contacting aphysician.8.1.1 In the
32、advent of a spill or accident, the hot magnesiumchloride should be quickly flushed from the skin with largequantities of cold water to minimize the burning, followed byimmediate first aid and medical attention.6Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, W
33、ashington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.FIG. 1
34、 Boiling Points of Aqueous Magnesium Chloride Solutionsat One Atmosphere as a Function of Concentration2G 36 94 (2006)28.1.2 All heating or boiling of magnesium chloride shouldbe done in a shielded area with protection by hood or shield, orboth.8.1.3 Minimum personal protective equipment for handlin
35、gboiling magnesium chloride should include safety glasses orgoggles, face shield, laboratory coat, and rubber gloves withcotton inner gloves.8.1.4 Disposal of the magnesium chloride should be accom-plished in accordance with the material safety data suppliedwith the chemical or by the chemical manuf
36、acturer or supplier.8.1.5 Do not remelt the solidified magnesium chloride.Localized melting adjacent to the heat source and below thesolid layer of magnesium chloride can cause sufficient stressesthrough volume expansion to crack the containing vessel.9. Test Specimens9.1 Any type of stress corrosio
37、n test specimen can be usedwith this test solution.7See Practice G1and G30.9.2 The test specimen must be thick enough so that theapplied stress does not cause mechanical rupture when thecross section is reduced by pitting or general corrosion.9.3 Whenever possible, only one specimen should be tested
38、in each flask. If more than one specimen is tested in a flask, thespecimens should be of the same alloy in order to avoid thepossible deleterious effects of the corrosion products of onealloy on the performance of the other alloy.9.4 The test specimens must be kept from direct contactwith heated sur
39、faces by glass supports. Metal specimen holdersused for stressing specimens should also be supported on glassrods or tubes. The design for two types of test specimens thatcan be used with the suggested apparatus can be found infootnote 3.10. Procedure10.1 Collect the apparatus and test specimens in
40、preparationfor the test. If the suggested test apparatus is used, assemble asoutlined in Appendix X1.10.2 Prepare the test solution by adding a known quantity ofreagent grade MgCl26H2O, reagent water, and some boilingaids to the container fitted with a thermometer and water-cooled condenser. After a
41、pplying heat, adjust the concentrationof the solution by slowly adding small quantities (4 to 5 mL)of distilled water until the solution reaches the constant-boilingtemperature of 155 6 1.0C (311.0 6 1.8F). Now place thepreviously prepared test specimens in the container.11. Report11.1 Record starti
42、ng time, type of specimen, stress, and typeexposure. A clear distinction must be made in the type ofexposure; that is, complete immersion, vapor phase exposure,or a combination of immersion and exposure to the vaporphase. The time required to initiate cracks, the rate of crackgrowth, and the time to
43、 failure may be of importance, depend-ing upon the purpose of the test.11.1.1 Periodic removal of the specimen from the solutionmay be necessary to determine the time when cracks firstappear and the rate of crack propagation. Microscopic exami-nation of polished surfaces is required to detect crack
44、initiation.All stressed surfaces should be examined at magnifications upto 203. Metallographic examination of exposed surfaces andof polished and etched cross sections at higher magnificationsare necessary at the end of the test to establish the type ofcracking: transgranular, intergranular, or mixe
45、d.11.1.2 Ruptured specimens should also be examined forevidence of mechanical failure resulting from the action ofapplied stress on specimens whose cross sections have beenreduced by general or pitting corrosion, or both. Such failuresusually show evidence of ductility. Duplicate tests with thickers
46、pecimens should be made in case of doubt.12. Keywords12.1 accelerated test; apparatus; boiling magnesium chlo-ride; glassware; nickel containing alloy; stainless steels; stress-corrosion crackingAPPENDIX(Nonmandatory Information)X1. TEST APPARATUSX1.1 The following test apparatus is suggested for it
47、sability to maintain a constant temperature and solution concen-tration over a long period of time. Use of this apparatus is notmandatory and is presented here only as a guide.X1.2 The suggested test apparatus is shown in Fig. X1.1and the design details are given below:X1.2.1 Flaskthe 1-L Erlenmeyer
48、 flask (Fig. X1.2) has aground-glass 45/50 outer joint at the mouth and a 10/30ground-glass outer joint to hold the thermometer.NOTE X1.1Other flasks or containers may be used. For tests requiringa larger container, a 3-L round bottom flask with a 71/60 ground-glassouter joint can also be used. The
49、height of the condenser (X1.2.2) and thedimensions of the trap (Fig. X1.3) can be the same as for the 1-LErlenmeyer flask.X1.2.2 Condenser (Fig. X1.4)a modified Allihn con-denser with a 45/50 ground-glass inner joint. In place of thedrip tip on the conventional condenser, the exit must be formedas shown in Fig. X1.4. A smooth exit on the condenser isessential to prevent dripping. The water jacket of the condenser7For a comprehensive discussion of the various types of test specimensavailable, see “Stress Corrosion Testing Methods,” Stress Corrosion Testing
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