ASTM

1. ASTM G36 A7 0759530 00550ïLl 2
(# Designation:G 36 -87
Standard Practicefor
AMERICAN SOCIETY FOR TESTING AND MATERIALS
1916 Race St., Philadelphia, Pa. 19103
Reprinted from the Annual Book of ASTM Standards, Copyright ASTM
If not listed In lhe current combined index, will appear in the next edition.
Evaluating Stress-Corrosion-Cracking Resistance of Metals
and Alloys in a BoilingMagnesium Chloride Solution'
This standard is issued under the fixed designation G36; the number immediately foilowing the designation indicates the year of
originaladoption or, in the case of revision, the yeat of last revision. A number i
n parenthesesindicatesthe year of last reapproval.A
superscriptepsilon(e) indicatesan editorialchangesince the last revision or reapprovai.
1. Scope
1.1 This mactice describes a mocedure for conducting
G 30 Practice for Making and Using U-Bend Stress-Cor-
rosion Test Specimens'
stress-corrosion crackingtests in boiling magnesium chi;
ride solution. Although this test may be performed using
variousconcentrationsof magnesiumchloride,thisprocedure
covers a test solution held at a constant boiling temperature
of 155.0 f 1.0"C (311.0 & 1.8"F). The boiling points of
aqueous magnesium chloride solutions at one atmosphere
pressureas a functionof concentrationare showngraphicalIy
in Fig. 1,2 A suggestedtest apparatus capableof maintaining
solutionconcentrationand temperaturewithintheprescribed
limits for extendedperiods of time is also described herein?
1.2 The boiling magnesium chloride test is applicable to
wrought, cast, and welded stainlesssteels and related alloys.
It is a method for detecting the effects of composition, heat
treatment, surface finish, microstructure, and stress on the
susceptibility of these materials to chloride stress corrosion
~racking.~
1.3 This practice is concerned primarily with the test so-
lution, which may be used with a variety of stress corrosion
test specimens, surface finishes, and methods of applying
stress.
1.4 This standard may involvehazardous materials, oper-
ations, and equipment. This standard does not purport to
addressall of the safety problemsassociated with its use. It is
the responsibility of the user of this standasd to establish
appropriate safety and health practices and determine the
applicabilityof regulatory limitationsprior to use.
2. ReferencedDocuments
2.1 ASTMStandasds:
G 1Practice for Preparing,-Cleaning,and EvaluatingCor-
rosion Test Specimens'
'Thispracticeis under thejurisdiction of ASTM Committee G-1 on Corrosion
of Metals, and is the direct responsibility of Subcommittee Gû1.06 on Stress
Corrosion Crackingand Corrosion Fatigue.
Current edition approved Sept. 25, 1987. Published May 1988. Originally
published as G 36 -73. Last previousedition G 36 -73 (1981).
*Available data on the relationship of concentrations and boiling points of
magnesium chloride solutions are critically reviewed and supplemented by I. B.
Casale in "Boiling Pointsof MagnesiumChlorideSolutions-Their Applicationin
Stress CorrosionStudies," Corrosion,Vol 23, 1967,pp. 314-17.
'The apparatus and tesf procedures for maintaining constant boiling tempera-
tures of magnesium chloridesolutionsfor stresscorrosiontestsaredescribedby M.
A. Streicherand A. J. Sweetin Corrosion,Vol 25, 1969,pp. 1-6.
4The use of concentrated magnesium chloride solutions for determining the
susceptibilityto stress corrosion cracking of austenitic and ferritic stainless steels
and related nickel-base alloys was first described by M. A. Scheil, Symposium on
Stress Corrosion Cracking o
f Metals, S T M STP 64, ASTM, 1945, p. 395.
(Althoughcurrently ouf of print, copies may be obtained from UniversityMicro-
Ums, Inc., 300North Zceb Rd., Ann Arbor, MI 48106.)
Anniial Book o
fASTMStandards,Vol 03.02.
3. Summary of Practice
3.1 A predeterminedquantityof reagentgrade magnesium
chloride and some distilled water are added to a container.
Thecontainerandcontents,withthermometerand condenser
affied, are placed on a sourceof heat. When the magnesium
chloride solutionboils, it is adjustedto maintain the desired
concentrationand boilingpoint throughthe additionof small
quantitiesof eitherwater or salt.
3.2 After the solution has stabilizedat the desiredboiling
point for the test, the stressedspecimensare added. Depend-
ing upon the intent of the test, the specimensshouldbe given
periodic inspections. Ethe duration of test exceeds 7 days,
the solution should either be changed or the suggested or
similartest apparatusused.
4. Significance and Use
4.1 For most applications, this environment provides an
accelerated method of ranking the relative degree of stress-
corrosion cracking susceptibilityfor stainless steels and re-
lated alloys in aqueous chloride-containing environments.
Materials that normally provide acceptableresistance in hot
chloride service may crack in this test. The test may not be
relevant to stress-corrosion cracking in polythionic acid or
causticenvironments.
4.2 Resistanceto stress-corrosioncrackingin boiling mag-
nesium chloride (155.0"C (311.0"F))should, where possible,
be correlated to resistance in service for the materials of
interest. However, such correlationsmay not always be pos-
sible.
4.3 Boiling magnesium chloridemay also cause pitting of
many stainlessalloys.Thisleadsto thepossibilityofconfusing
stress-corrosionfailureswith mechanical failuresinduced by
corrosion-reducednet cross sections. This danger is particu-
larly great when smaíl cross section samples, high applied
stress levels, long exposureperiods, stress-corrosionresistant
alloys, or a combination thereof are being used. Careful
examination is recommended for correct diagnosis of the
causeof failure.
5. Apparatus
5.1 Any inert, transparent apparatuswith provisionsfor a
thermometer and water-cooled condenser can be used, pro-
vided that it has been designed to contain the stressed speci-
men whiíe maintaining a constant temperature and concen-
tration of the magnesiumchloridesolutionby minimizingor
preventinglosses of condensate and water vapor during pro-
longed periods of test. Small losses of water from a solution'
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2. ASTM G3b 87 0754510 0055045
170 , , , , , , I I , , , , , I , , , , , ,
t
t
O I
O 20 30 40 50
90L"" " I ' I ' ' ' " I ' ' " I
WEIGHT PERCENT MgCl,
FIG. 1 BoilingPointsof Aqueous MagnesiumChloride Solutions
at One Atmosphereas a Functionof Concentration2
of magnesium chloride will lead to large increases in the
boiling point of the solution with a reduction in the time to
failureof a specimenby stresscorrosioncracking.Asuggested
apparatus, shown in Figure Al, meets these requirements.
Design details of this apparatus are given in Annex A1.
6. Reagents
6.1 Purity o
f Reagents-Reagent grade chemicalsshall be
used in all tests. Unless otherwise indicated, it is intended
that all reagents shall conform to the specifications of the
Committeeon Analytical Reagents of the American Chemi-
cal Society, where such specificationsare available.6 Other
grades may be used, provided it is first ascertained that the
reagent is of sufficientlyhigh purity to permit its use without
lesseningthe accuracy of the determination.
6.2 Purity o
f Water-Distilled water or water of equal
purity shall be used to prepare the test solutions.
6.3 Magnesium Chloride (MgC12*6H*O)-A solution of
magnesium chloride that boils at 155.0 & 1.0"C (311.0 &
1.8"F) is used in this test. A second 25 weight % solution of
magnesiumchlorideisrequiredforthetrapifthetestduration
exceeds 7 days without a solution change and the suggested
apparatusis used.
6.3.1 To prepare about 400 mL of the test solutionfor use
in a l-L Erlenmeyerflaskor other container,weigh 600 g of
reagentgrade MgC12.6H20
and add this to the flask contain-
ing a thermometer alongwith 15mLof distilledwater.
"ReagentChemicals,American ChemicalSocietySpecifications,"Am. Chem-
ical Soc.,Washington,DC.For suggestions on the testing of reagents not iisted by
theAmerican ChemicalSociety,see"ReagentChemicalsandStandards,"byJoseph
Rosin, D. Van Nostrand Co., Inc., New York, NY, and the "United States
Pharmacopeia.''
6.3.2 Add 10to 15boiling chips or other boiling aids.
6.3.3 Heat by placing the flask on a hot plate or other
suitablesourceof heat and put the condenserin place, leaving
off the trap. Hook up the cooling water supply to the con-
denser.
6.3.4 When the solution boils vigorously and there is no
more dripping of condensate, slowly add s m d quantities (4
to 5 mL) of distilled water at the top of the condenser to
reduce the temperature to 155.0"C (311.o"F). Use extreme
caution when adding the water to the boiling magnesium
chloride solution. Cool water can form a layer on top of the
magnesium chloride, and when it reaches the bottom of the
flask, bumping can occur. Use a protectiveshield.
NOTE-iftoo muchwaterhasbeenadded,addsomecrystalsofMgC12.
6H20
through the condenseruntil a temperatureof 155.0"C(31 1 . O g i
s
attained.
6.4 To prepare the 25 weight % solution for the trap (Fig.
A1.3), place 53.4 g of MgC12.6H20and 46.6 mL of distilled
water in a flask and allow the crystals to dissolve at room
temperature.
7. Safety Precautions
7.1 When cold, magnesium chloride can be handled with
the minimum protective equipment of rubber gloves and
goggles. Maximum protective measures should be taken to
prevent boiling magnesium chloride from coming into con-
tact with the skin. Severebums can result as the hot magne-
sium chloride adheres to the skin forming a crust which
causes deep burns. The severity of the bums can be reduced
by taking proper and immediate first aid measures and by
contacting a physician.
7.1.1 In the advent of a spill or accident, the hot magne-
sium chloride should be quicklyflushedfrom the skin with
large quantities o
f cold water to minimize the burning,fol-
lowed by immediatejrst aid and medical attention.
7.1.2 A
i
l heating or boiling of magnesium chloride should
be done in a shielded area with protectionby hood or shield,
or both.
7.1.3 Minimum personal protective equipment for han-
dling boihg magnesium chloride should include safety
glasses or goggles, face shield, laboratory coat, and rubber
gloveswith cotton inner gloves.
7.1.4 Dispose of boiling magnesium chloride by letting it
cool. When the solutionhas solidified,run tap water into the
containerto dissolveand flush the solutiondown the drain,
7.1.5 Do not remelt the solidified magnesium chloride.
Localized melting adjacent to the heat source and below the
solidlayerof magnesiumchloridecan causesufficientstresses
through volume expansionto crack the containingvessel.
8. Test Specimens
8.1 Any type of stresscorrosion test specimencan be used
with this test solution.'
8.2 The test specimen must be thick enough so that the
applied stress does not cause mechanical rupture when the
'Foracomprehensivediscussionofthevarioustypesoftestspecimensavailable,
see"StressCorrosionT
e
s
t
i
n
gMethods,"Stress CorrosionTesting,ASTMSTP425,
ASTM. (Althoughcurrently out of print, copies maybe obtainedf
r
o
m University
Microfilms,Inc., 300 North Zeeb Rd., Ann Arbor, M
i 48106.) See also W o n 2
ofthispractice.
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3. ASTM G36 87 0757530 0055096 b
cross section is reduced by pitting or generalcorrosion.
8.3 Wheneverpossible,onlyonespecimenshouldbetested
in each flask. If more than one specimen is tested in a flask,
the specimensshould be of the same-alloyin order to avoid
the possible deleterious effects of the corrosion products of
one alloy on the performance of.the other alloy.
8
.
4 The test specimens must be kept from direct contact
with heated surfacesby glasssupports. Metal specimenhold-
ers used for stressingspecimensshouldalso be supportedon
glassrods or tubes.The designfor twotypes of test specimens
that can be used with the suggested apparatus can be found
in footnote 3.
9. Procedure
9.1 Collectthe apparatusandtest specimensin preparation
for the test. If the suggestedtest apparatus is used, assemble
as outlined in Annex A1,
9.2.Prepare the test solution by adding a known quantity
of reagent grade MgC12.6H20, distilled water, and some
boiling aids to the container fitted with a thermometer and
water-cooledcondenser. After applyingheat, adjust the con-
centration of the solution by slowly adding small quantities
(4to 5 mL) of distilled water until the solution reaches the
constant-boilingtemperatureof 155f 1.0"C(311.O 0 1.8"F).
Now place the previously prepared test specimens in the
contäiner.
10. Report
10.1 Record starting time, type of specimen, stress, and
type exposure. A clear distinction must be made in the type
of exposure;that is, complete immersion, vapor phase expo-
sure, or a combination of immersion and exposure to the
vapor phase. Thetime required to initiate cracks, the rate of
crack growth,and the time to failure may be of importance,
dependingupon the purpose of the test.
10.1.1 Periodicremoval of thespecimenfrom the solution
may be necessary to determine the time when cracks first
appear and the rate of crack propagation. Microscopical
examination of polished surfaces is required to detect crack
initiation. Ali stressed surfaces should be examined at mag-
nificationsup to 2OXrMefallographicexaminationofexposed
surfaces and of polished and etched cross sections at higher
magnificationsare necessaryat the end of the test to establish
the type of cracking: transgranular, intergranular,or mixed.
10.1.2 Ruptured specimens should also be examined for
evidence of mechanical failure resulting from the action of
applied stress on specimens whose cross sections have been
reducedby generalor pitting corrosion,or both. Suchfailures
usually show evidence of ductility. Duplicate tests with
thicker specimensshouldbe made in caseof doubt.
-
ANNEX
(MandatoryInformation)
Al. TEST APPARATUS
Al.1 Thefollowingtest apparatusissuggested-or itsability
to maintain a constant temperature and solution concentra-
tion over a long period of time. Use of this apparatus is not
mandatory and is presented here only as a guide.
A1.2 The suggested test apparatus is shown in Fig. Al.l
and the design details aregiven below:
A1.2.1 Flasl-the 1-LErlenmeyer flask (Fig. A1.2) has a
ground-glass 45/50 outer joint at the mouth and a 10/30
ground-glassouterjoint to hold the thermometer.
NOTEAl.I-Other flasksor containers may be used. For tests requit-
ing a larger container, a 3-L round bottom flask with a 71/60 ground-
glass outer joint can also be used.Theheight of the condenser (A1.2.2)
and thedimensions of the trap (Fig. A1.3) can be the same as for the 1-
L Erlenmeyer flask.
A1.2.2 Condenser (Fig. Al.4)-a modified Allihn con-
denser with a 45/50 ground-glassinnerjoint. In place of the
drip tip on the conventional condenser, the exit must be
formedasshownin Fig.Al.4.
Asmoothexiton thecondenser
is essential to prevent dripping. The water jacket of the
condenser should be at least 250 mm long. At the top of the
condenser, a 29/26 ground-glass outer joint is required to
hold the trap in place.
NOTEA1.2 -Dripping of condensate into hot magnesium chloride
solution from the "drip tip" of a conventional Allihn condenser results
in a pulsating generation of water vapor. These pressure waves lead to
the loss of water vapor at the top of the condenser. Initially, there may
be some dripping from the condenser until there is completewetting of
the walls of the flask by the condensate.
A1.2.3 Trap-containing a 25 weight % solution of mag-
nesium chloride (Fig. A1.3), and affixed to the top of the
condenserto eliminatevapor losses by diffusion during tests
in excess of 7 days. The trap is joined to the condenser by a
29/26 ground glassinnerjoint,
Al,2.4 Thermometer-required to adjust the boiling
point, and therebythe concentrationof the magnesium chlo-
ridesolutionwhenit is prepared,and to monitor the solution
temperature throughout the test. The graduations must
clearly show 1°Cincrements in the range of 130 to 170°C
(266 to 338°F').When the speciallydesignedthermometer of
Fig. AL5 is used in the i-L Erlenmeyerflaskof Fig. A1.2, no
more spaceis needed on hot pIatesthan that taken up by the
flasksthemselves.AmodifiedASTM Thermometer86Dwith
a temperature range from 95 to 170°C(203 to 338°F)in 1°C
subdivisionscan also be used with this apparatus.
NOTEA1.3-The thermometer should be checkedfor the presenceof
gasbubbles beforeeach use. These can be removed by coolingthe lower
part ofthebulb (dryice) andgentlytapping the thermometer. Storageof
a thermometet in a verticalposition willprevent appearance of bubbles.
Ai.2.5 Adapter-a fluorocarbon resin adapter containing
~ a rubberO-ring seal fora 10/30 ground-glassouterjoint must
be used to hold the thermometerin place in the flask.
NOTE
A1A-Use of a thermometer with a ground-glassinnerjoint in
place of the adapter resultsin appreciableloss of water vapor at this hot
joint.
A1.2.6 When assembling the above components, do not
-
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4. ASTM G3b 87 0757530 0055097 @i
FIG. 141.1 Assembly o0 Glase Apparatus fer Stresa-CorrosionTest in BoilingMagnesiumChloride with CI-Bend Specimen in Place
use any lubricantson any of the ground-glassjoints.
A1.3 Assembly:
Al .3.1 The thermometeralong with its adapter is inserted
into the side arm of the Erlenmeyer flask and positioned so
that the bulb is located about 7.5 mm (5/16 in.) from the
bottom of the flask.The adapter is tightened to prevent the
loss of water during the test and the MgC12.6H20,distilled
water, and boiling aids are added to the flask. After position-
ingthe water-cooledcondenseron top of the flask,the whole
assembly is placed on a hot plate or other suitable source of
heat. Do not attach the trap at this time.
A1.3.2 The solution concentration is adjusted by slowly
addingsmall portions (4 to 5 mL) of distilled water until the
constantboiling temperatureof 155& 1°C(311.0 f 1.8"F)is
attained. The previously prepared test specimensand holder
are now ready to be placed in the flask.This is accomplished
by removing the condenser from the flask, immersing the
specimen and specimen holder in the boiling solution (with
caution),and quicklyreplacing the condenser.
A1.3.3 Cut a 50 by 450-mm (2 by 18-in.)strip of com-
mercial aluminum foil. Wrap this foil around the outside of
the joint between the condenser and the flask and press the
foilagainstthe giass so that thejoint iswell coveredand none
of the foil is in contactwith the hot flask below thejoint.
4
,
-
,
,
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5. ASTM G36 87 0759530 0055098 T
-
I
;
'
62
tis
'jL
I 7 0
L
FIG. A1.2 ModifiedErlenmeyer Flask(1000 mL)
ALL DIMENSIONS IN
MILLIMETERS
, 65 4 "L"= LIQUID LEVEL LINE
(INSCRIBE)
FIG. A1.3 Trap for Top of Condenserto PreventLoss of Vapor
MODIFIED
REGULAR
FIG. A1.4 Modificationof Allihn Condenserto Prevent Loss of
Vapor
5
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6. ASTM G36 87 m 0757530 0055077 1 m
MERCURY EXPANSION BULB
LIQUID LEVEL 0.7 cm
I
4
.
0
c
m
- 10.0 cm 5
.
1crn 4 k--
I1
.
7 crn
YELLOW BACK
kMERCURY COLUMN
NUMBERS
@ YELLOW BACK PLACED AS
@
@) I°C INCREMENTS
FIG. A1.5 Design of Thermometerfor Use in Flask of Fig. A2
ACCURACY OF f 1/2OC OR BETTER
GRADUAT IONS
NOTE
A1.5-The purpose of the aluminum foil is to prevent loss of
condensate by evaporation where the top of the ground-glass surface of
thejoint is exposedto the air. Condensate rises by capillaryaction in the
joint and evaporatesin the warm air.
A1.3.4 If the period of exposure exceeds 7 days, a liquid
trap is required at the top of the condenser to maintain the
constant boiling point of 155.0 f 1.o"C (311.0 f 13°F)
without new additionsof water to the boilingMgC12solution.
Fill the trap to the liquid level line with a 25% solution of
MgC12(see 5.4). As soon as the condensate stops dripping
from the condenser and flows down the wall of the Erlen-
meyer flask in a continuous stream,placethe trap on top of
the condenser.
NOTE
Aí.6-Whenever the trap is needed, it must be used with the
modified condenser because the pressure pulses generated by "drip tip"
condensers exceed the capacity of the trap to absorb sudden changes in
pressurewithin the flask.
A1.3.5 During long-time tests, there may be a slow drop
in the level of liquid in the trap because of evaporation of
water at the top of the trap from the 25 weight % MgCh
solution.This level should be brought up to the liquid level
line by additionsof distilled water every 7 to 14days.
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and should be addressed to ASTM Headquarters. Your comments wiil receive careful consideration at a meeting of the responsible
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views known to the ASTM Committeeon Standards, 1916RaceSt., Philadelphia,PA 19103.
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