Designation:G1–03
Standard Practice for
Preparing,Cleaning,and Evaluating Corrosion Test Specimens1
This standard is issued under thefixed designation G1;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon(e)indicates an editorial change since the last revision or reapproval.
1.Scope
1.1This practice covers suggested procedures for preparing bare,solid metal specimens for tests,for removing corrosion products after the test has been completed,and for evaluating the corrosion damage that has occurred.Emphasis is placed on procedures related to the evaluation of corrosion by mass loss and pitting measurements.(Warning—In many cases the corrosion product on the reactive metals titanium and zirco-nium is a hard and tightly bonded oxide that defies removal by chemical or ordinary mechanical means.In many such cases, corrosion rates are established by mass gain rather than mass loss.)
1.2This standard does not purport to address all of the safety concerns,if any,associated with its use.It is the responsibility 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.For specific precautionary statements,see1and7.
2.
2.Referenced Documents
2.1ASTM Standards:
A262Practices for Detecting Susceptibility to Intergranu-lar Attack in Austenitic Stainless Steels2
D1193Specification for Reagent Water3
D1384Test Method for Corrosion Test for Engine Coolants in Glassware4
D2776Test Methods for Corrosivity of Water in the Ab-sence of Heat Transfer(Electrical Methods)5
G15Terminology Relating to Corrosion and Corrosion Testing6
G16Guide for Applying Statistics to Analysis of Corrosion Data6
G31Practice for Laboratory Immersion Corrosion Testing of Metals6
G33Practice for Recording Data from Atmospheric Cor-rosion Tests of Metallic-Coated Steel Specimens6
G46Guide for Examination and Evaluation of Pitting Corrosion6
G50Practice for Conducting Atmospheric Corrosion Tests on Metals6
G78Guide for Crevice Corrosion Testing of Iron Base and Nickel-Base Stainless Alloys in Seawater and Other Chloride-Containing Aqueous Environments6
3.Terminology
3.1See Terminology G15for terms used in this practice.
4.Significance and Use
4.1The procedures given are designed to remove corrosion products without significant removal of base metal.This allows an accurate determination of the mass loss of the metal or alloy that occurred during exposure to the corrosive environment.
4.2These procedures,in some cases,may apply to metal coatings.However,possible effects from the substrate must be considered.
5.Reagents and Materials
5.1Purity of Reagents—Reagent grade chemicals shall be used in all tests.Unless otherwise indicated,it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where such specifications are available.7Other grades may be used, provided it isfirst ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.
5.2Purity of Water—Unless otherwise indicated,references to water shall be understood to mean reagent water as defined by Type IV of Specification D1193.
1This practice is under the jurisdiction of ASTM Committee G01on Corrosion of Metals and is the direct responsibility of Subcommittee G01.05on Laboratory Corrosion Tests.
Current edition approved October1,2003.Published October2003.Originally approved in1967.Last previous edition approved in1999as G1–90(1999)e1.
2Annual Book of ASTM Standards,V ol01.03.
3Annual Book of ASTM Standards,V ol11.01.
4Annual Book of ASTM Standards,V ol15.05.
5Discontinued,replaced by Guide G96.See1990Annual Book of ASTM Standards,V ol03.02.
6Annual Book of ASTM Standards,V ol03.02.
7Reagent Chemicals,American Chemical Society Specifications,American Chemical Society,Washingt
on,DC.For suggestions on the testing of reagents not listed by the American Chemical Society,see Analar Standards for Laboratory Chemicals,BDH Ltd.,Poole,Dorset,U.K.,and the United States Pharmacopeia and National Formulary,U.S.Pharmacopeial Convention,Inc.(USPC),Rockville, MD.
1
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6.Methods for Preparing Specimens for Test
6.1For laboratory corrosion tests that simulate exposure to service environments,a commercial surface,closely resem-bling the one that would be used in service,will yield the most meaningful results.
6.2It is desirable to mark specimens used in corrosion tests with a unique designation during preparation.Several tech-niques may be used depending on the type of specimen and test.
6.2.1Stencil or Stamp—Most metallic specimens may be marked by stenciling,that is,imprinting the designation code into the metal surface using hardened steel stencil stamps hit with a hammer.The res
ulting imprint will be visible even after substantial corrosion has occurred.However,this procedure introduces localized strained regions and the possibility of superficial iron contamination in the marked area.
6.2.2Electric engraving by means of a vibratory marking tool may be used when the extent of corrosion damage is known to be small.However,this approach to marking is much more susceptible to having the marks lost as a result of corrosion damage during testing.
reactive metal6.2.3Edge notching is especially applicable when extensive corrosion and accumulation of corrosion products is antici-pated.Long term atmospheric tests and sea water immersion tests on steel alloys are examples where this approach is applicable.It is necessary to develop a code system when using edge notches.
6.2.4Drilled holes may also be used to identify specimens when extensive metal loss,accumulation of corrosion products, or heavy scaling is anticipated.Drilled holes may be simpler and less costly than edge notching.A code system must be developed when using drilled holes.Punched holes should not be used as they introduce residual strain.
6.2.5When it is undesirable to deform the surface of specimens after preparation procedures,for exam
ple,when testing coated surfaces,tags may be used for specimen identi-fication.A metal or plastic wire can be used to attach the tag to the specimen and the specimen identification can be stamped on the tag.It is important to ensure that neither the tag nor the wire will corrode or degrade in the test environment.It is also important to be sure that there are no galvanic interactions between the tag,wire,and specimen.
6.3For more searching tests of either the metal or the environment,standard surfacefinishes may be preferred.A suitable procedure might be:
6.3.1Degrease in an organic solvent or hot alkaline cleaner. (See also Practice G31.)
N OTE1—Hot alkalies and chlorinated solvents may attack some metals. N OTE2—Ultrasonic cleaning may be beneficial in both pre-test and post-test cleaning procedures.
6.3.2Pickle in an appropriate solution if oxides or tarnish are present.In some cases the chemical cleaners described in Section6will suffice.
N OTE3—Pickling may cause localized corrosion on some materials.
6.3.3Abrade with a slurry of an appropriate abrasive or with an abrasive paper(see Practices A262and
Test Method D1384).The edges as well as the faces of the specimens should be abraded to remove burrs.
6.3.4Rinse thoroughly,hot air dry,and store in desiccator.
6.4When specimen preparation changes the metallurgical condition of the metal,other methods should be chosen or the metallurgical condition must be corrected by subsequent treat-ment.For example,shearing a specimen to size will cold work and may possibly fracture the edges.Edges should be ma-chined.
6.5The clean,dry specimens should be measured and weighed.Dimensions determined to the third significantfigure and mass determined to thefifth significantfigure are sug-gested.When more significantfigures are available on the measuring instruments,they should be recorded.
7.Methods for Cleaning After Testing
7.1Corrosion product removal procedures can be divided into three general categories:mechanical,chemical,and elec-trolytic.
7.1.1An ideal procedure should remove only corrosion products and not result in removal of any base
metal.To determine the mass loss of the base metal when removing corrosion products,replicate uncorroded control specimens should be cleaned by the same procedure being used on the test specimen.By weighing the control specimen before and after cleaning,the extent of metal loss resulting from cleaning can be utilized to correct the corrosion mass loss.
N OTE4—It is desirable to scrape samples of corrosion products before using any chemical techniques to remove them.These scrapings can then be subjected to various forms of analyses,including perhaps X-ray diffraction to determine crystal forms as well as chemical analyses to look for specific corrodants,such as chlorides.All of the chemical techniques that are discussed in Section7tend to destroy the corrosion products and thereby lose the information contained in these corrosion products.Care may be required so that uncorroded metal is not removed with the corrosion products.
7.1.2The procedure given in7.1.1may not be reliable when heavily corroded specimens are to be cleaned.The application of replicate cleaning procedures to specimens with corroded surfaces will often,even in the absence of corrosion products, result in continuing mass losses.This is because a corroded surface,particularly of a multiphase alloy,is often more susceptible than a freshly machined or polished surface to corrosion by the cleaning procedure.In such cases,the following method of determi
ning the mass loss due to the cleaning procedure is preferred.
7.1.2.1The cleaning procedure should be repeated on speci-mens several times.The mass loss should be determined after each cleaning by weighing the specimen.
7.1.2.2The mass loss should be graphed as a function of the number of equal cleaning cycles as shown in Fig.1.Two lines will be obtained:AB and BC.The latter will correspond to corrosion of the metal after removal of corrosion products.The mass loss due to corrosion will correspond approximately to point B.
7.1.2.3To minimize uncertainty associated with corrosion of the metal by the cleaning method,a method should be chosen to provide the lowest slope(near to horizontal)of line
BC.
7.1.3Repeated treatment may be required for complete removal of corrosion products.Removal can often be con-firmed by examination with a low power microscope (for example,73to 303).This is particularly useful with pitted surfaces when corrosion products may accumulate in pits.This repeated treatment may also be necessary because of the requirements of 7.1.2.1.Following the final treatment,the specimens should be thoroughly rinsed and immediately dried.7.1.4All cleaning solutions shall be prepared with water and reagent grade chemicals.
7.2Chemical procedures involve immersion of the corro-sion test specimen in a specific solution that is designed to remove the corrosion products with minimal dissolution of any base metal.Several procedures are listed in Table A1.1.The choice of chemical procedure to be used is partly a matter of trial and error to establish the most effective method for a specific metal and type of corrosion product scale.(Warning—These methods may be hazardous to personnel).7.2.1Chemical cleaning is often preceded by light brushing (non metallic bristle)or ultrasonic cleaning of the test speci-men to remove loose,bulky corrosion products.
7.2.2Intermittent removal of specimens from the cleaning solution for light brushing or ultrasonic cleaning can often facilitate the removal of tightly adherent corrosion products.7.2.3Chemical cleaning is often followed by light brushing or ultrasonic cleaning in reagent water to remove loose products.
7.3Electrolytic cleaning can also be utilized for removal of corrosion products.Several useful methods for corrosion test specimens of iron,cast iron,or steel are given in Table A2.1.7.3.1Electrolytic cleaning should be preceded by brushing or ultrasonic cleaning of the test specimen to remove loose,bulky corrosion products.Brushing or ultrasonic cleaning should also follow the electrolytic cleaning to remove any loose slime or deposits.This will help to minimize any redeposition of metal from reducible corrosion products that would reduce the apparent mass loss.
7.4Mechanical procedures can include scraping,scrubbing,brushing,ultrasonic cleaning,mechanical shocking,and im-pact blasting (for example,grit blasting,water-jet blasting,and so forth).These methods are often utilized to remove heavily encrusted corrosion products.Scrubbing with a nonmetallic bristle brush and a mild abrasive-distilled water slurry can also be used to remove corrosion products.
7.4.1Vigorous mechanical cleaning may result in the re-moval of some base metal;therefore,care should be exercised.These should be used only when other methods fail to provide adequate removal of corrosion products.As with other meth-ods,correction for metal loss due to the cleaning method is recommended.The mechanical forces used in cleaning should be held as nearly constant as possible.
8.Assessment of Corrosion Damage
8.1The initial total surface area of the specimen (making corrections for the areas associated with mounting holes)and the mass lost during the test are determined.The average corrosion rate may then be obtained as follows:
Corrosion Rate 5~K 3W !/~A 3T 3D !
(1)
where:
K =a constant (see 8.1.2),T =time of exposure in hours,A =area in cm 2,
W =mass loss in grams,and
D =density in g/cm 3(see Appendix X1).
8.1.1Corrosion rates are not necessarily constant with time of exposure.See Practice G 31for further guidance.
8.1.2Many different units are used to express corrosion rates.Using the units in 7.1for T,A,W ,and D ,the corrosion rate can be calculated in a variety of units with the following appropriate value of K :
Corrosion Rate Units Desired
Constant (K )in Corrosion
Rate Equation mils per year (mpy) 3.453106inches per year (ipy) 3.453103inches per month (ipm) 2.873102millimetres per year (mm/y)8.763104micrometres per year (um/y)8.763107picometres per second (pm/s)
2.783106grams per square meter per hour (g/m 2·h)
1.0031043D milligrams per square decimeter per day (mdd)
2.4031063D micrograms per square meter per second (µg/m 2·s)
2.7831063D
N OTE 5—If desired,these constants may also be used to convert corrosion rates from one set of units to another.To convert a corrosion rate in units X to a rate in units Y ,multiply by K Y /K X ;for example:
15mpy 5153~2.783106!/~3.453106!pm/s
(2)
8.1.3In the case of sacrificial alloy coatings for which there is preferential corrosion of a component whose density differs from that of the alloy,it is preferable to use the density of the corroded component (instead of the initial alloy density)for calculating average thickness loss rate by use of Eq 1.This is done as follows:(1)cleaning to remove corrosion products only and determine the mass loss of the corroded component;(2)stripping the remaining coating to determine the mass of the uncorroded component;(3)chemical analysis of the stripping solution to determine the composition of the
uncorroded
FIG.1Mass Loss of Corroded Specimens Resulting from
Repetitive Cleaning
Cycles
component;(4)performing a mass balance to calculate the composition of the corroded component;(5)using the mass and density of the corroded component to calculate the average thickness loss rate by use of Eq 1.An example of this procedure is given in Appendix X2.
The procedure described above gives an average penetration rate of the coating,but the maximum penetration for a multiphase alloy may be larger when the corroded phase is not uniformly distributed across the surface.In such cases,it is generally considered good practice to obtain a cross section thro
ugh the corroded surface for microscopic examination. This examination will reveal the extent of selective corrosion of particular phases in the coating,and help in understanding the mechanism of attack.
8.2Corrosion rates calculated from mass losses can be misleading when deterioration is highly localized,as in pitting or crevice corrosion.If corrosion is in the form of pitting,it may be measured with a depth gage or micrometer calipers with pointed anvils(see Guide G46).Microscopical methods will determine pit depth by focusing from top to bottom of the pit when it is viewed from above(using a calibrated focusing knob)or by examining a section that has been mounted and metallographically polished.The pitting factor is the ratio of the deepest metal penetration to the average metal penetration (as measured by mass loss).
N OTE6—See Guide G46for guidance in evaluating depths of pitting. N OTE7—See Guide G78for guidance in evaluating crevice corrosion.
8.3Other methods of assessing corrosion damage are:
8.3.1Appearance—The degradation of appearance by rust-ing,tarnishing,or oxidation.(See Practice G33.)
8.3.2Mechanical Properties—An apparent loss in tensile strength will result if the cross-sectional area of the specimen (measured before exposure to the corrosive environment)is reduced by corrosion.(See Practice G50.)Loss in tensile strength will result if a compositional change,such as dealloy-ing taking place.Loss in tensile strength and elongation will result from localized attack,such as cracking or intergranular corrosion.
8.3.3Electrical Properties—Loss in electrical conductivity can be measured when metal loss results from uniform corrosion.(See Test Methods D2776.)
8.3.4Microscopical Examination—Dealloying,exfoliation, cracking,or intergranular attack may be detected by metallo-graphic examination of suitably prepared sections.9.Report
9.1The report should include the compositions and sizes of specimens,their metallurgical conditions,surface preparations, and cleaning methods as well as measures of corrosion damage,such as corrosion rates(calculated from mass losses), maximum depths of pitting,or losses in mechanical properties.
10.Precision and Bias
10.1The factors that can produce errors in mass loss measurement include improper balance calibration and stan-dardization.Generally,modern analytical balances can deter-mine mass values to60.2mg with ease and balances are available that can obtain mass values to60.02mg.In general, mass measurements are not the limiting factor.However, inadequate corrosion product removal or overcleaning will affect precision.
10.2The determination of specimen area is usually the least precise step in corrosion rate determinations.The precision of calipers and other length measuring devices can vary widely. However,it generally is not necessary to achieve better than 61%for area measurements for corrosion rate purposes. 10.3The exposure time can usually be controlled to better than61%in most laboratory procedures.However,infield exposures,corrosive conditions can vary significantly and the estimation of how long corrosive conditions existed can present significant opportunities for error.Furthermore,corro-sion processes are not necessarily linear with time,so that rate values may not be predictive of the future deterioration,but only are indications of the past exposure.
10.4Regression analysis on results,as are shown in Fig.1, can be used to obtain specific information on precision.See Guide G16for more information on statistical analysis. 10.5Bias can result from inadequate corrosion product removal or metal removal caused by overcleaning.The use of repetitive c
leaning steps,as shown in Fig.1,can minimize both of these errors.
10.5.1Corrosion penetration estimations based on mass loss can seriously underestimate the corrosion penetration caused by localized processes,such as pitting,cracking,crevice corrosion,and so forth.
11.Keywords
11.1cleaning;corrosion product removal;evaluation;mass loss;metals;preparation;
specimens
ANNEXES
(Mandatory Information)
A1.CHEMICAL CLEANING PROCEDURES
TABLE A1.1CHEMICAL CLEANING PROCEDURES FOR REMOVAL OF CORROSION PRODUCTS
Designation Material
Solution
Time Temperature Remarks
C.1.1
Aluminum and Alu-minum Alloys
50mL phosphoric acid (H 3PO 4,sp gr 1.69)20g chromium trioxide (CrO 3)Reagent water to make 1000mL 5to 10min
90°C to Boiling
If corrosion product films remain,rinse,then follow with nitric acid procedure (C.1.2).C.1.2Nitric acid (HNO 3,sp gr 1.42)
1to 5min 20to 25°C
Remove extraneous deposits and bulky corrosion products to avoid reactions that may result in excessive removal of base metal.
C.2.1Copper and Copper Alloys
500mL hydrochloric acid (HCl,sp gr 1.19)Reagent water to make 1000mL 1to 3min 20to 25°C Deaeration of solution with purified nitrogen will minimize base metal removal.
C.2.2
4.9g sodium cyanide (NaCN)Reagent water to make 1000mL 1to 3min
20to 25°C
Removes copper sulfide corrosion products that may not be removed by hydrochloric acid treatment (C.2.1).
C.2.3100mL sulfuric acid (H 2SO 4,sp gr 1.84)Reagent water to make 1000mL
1to 3min 20to 25°C
Remove bulky corrosion products before treatment to minimize copper redeposition on specimen surface.
C.2.4120mL sulfuric acid (H 2SO 4,sp gr 1.84)30g sodium dichromate (Na 2Cr 2O 7·2H 2O)Reagent water to make 1000mL
5to 10s 20to 25°C
Removes redeposited copper resulting from sulfuric acid treatment.
C.2.554mL sulfuric acid (H 2SO 4,sp gr 1.84)Reagent water to make 1000mL
30to 60min 40to 50°C
Deaerate solution with nitrogen.Brushing of test specimens to remove corrosion
products followed by re-immersion for 3to 4s is recommended.
C.3.1Iron and Steel
1000mL hydrochloric acid (HCl,sp gr 1.19)20g antimony trioxide (Sb 2O 3)50g stannous chloride (SnCl 2)1to 25min 20to 25°C
Solution should be vigorously stirred or
specimen should be brushed.Longer times may be required in certain instances.C.3.2
50g sodium hydroxide (NaOH)200g granulated zinc or zinc chips Reagent water to make 1000mL 30to 40min 80to 90°C
Caution should be exercised in the use of any zinc dust since spontaneous ignition upon exposure to air can occur.
C.3.3
200g sodium hydroxide (NaOH)20g granulated zinc or zinc chips Reagent water to make 1000mL 30to 40min 80to 90°C
Caution should be exercised in the use of any zinc dust since spontaneous ignition upon exposure to air can occur.
C.3.4
200g diammonium citrate ((NH 4)2HC 6H 5O 7)
Reagent water to make 1000mL
20min 75to 90°C
Depending upon the composition of the corrosion product,attack of base metal may occur.
C.3.5
500mL hydrochloric acid (HCl,sp gr 1.19)3.5g hexamethylene tetramine Reagent water to make 1000mL 10min 20to 25°C
Longer times may be required in certain instances.C.3.6
Molten caustic soda (NaOH)with 1.5–2.0%sodium hydride (NaH)
1to 20min 370°C
For details refer to Technical Information Bulletin SP29-370,“DuPont Sodium Hydride Descaling Process Operating Instructions.’’C.4.1Lead and Lead Alloys
10mL acetic acid (CH 3COOH)Reagent water to make 1000mL
5min Boiling ...C.4.250g ammonium acetate (CH 3COONH 4)Reagent water to make 1000mL
10min 60to 70°C ...C.4.3
250g ammonium acetate (CH 3COONH 4)Reagent water to make 1000mL 5min
60to 70°C
...
C.5.1
Magnesium and Mag-nesium Alloys
150g chromium trioxide (CrO 3)10g silver chromate (Ag 2CrO 4)Reagent water to make 1000mL 1min Boiling
The silver salt is present to precipitate chloride.C.5.2200g chromium trioxide (CrO 3)10g silver nitrate (AgNO 3)20g barium nitrate (Ba(NO 3)2)Reagent water to make 1000mL
1min 20to 25°C
The barium salt is present to precipitate sulfate.
C.6.1Nickel and Nickel Alloys
150mL hydrochloric acid (HCl,sp gr 1.19)Reagent water to make 1000mL
1to 3min 20to 25°C ...C.6.2100mL sulfuric acid (H 2SO 4,sp gr 1.84)Reagent water to make 1000mL
1to 3min 20to 25°C ...C.7.1
Stainless Steels
100mL nitric acid (HNO 3,sp gr 1.42)Reagent water to
make 1000mL
20min
60°C
...
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