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ASTM A239 - 14.pdf

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ASTM A239 - 14.pdf

Designation A239 − 14Standard Practice forLocating the Thinnest Spot in a Zinc Galvanized Coatingon Iron or Steel Articles1, 2This standard is issued under the fixed designation A239; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 This practice covers the procedure for locating, by theuse of a solution of copper sulfate, the thinnest spot in a zinccoating hot dipped, electroplated, or sprayed on iron or steelarticles that are coated after the shape is produced by casting,drawing, pressing, or other forming methods. Examples areelectrical metallic tubing and rigid conduit pipe, castings andforgings, and structural steel; on special hardware, such aspoleline, builder’s, and farm implement hardware; bolts, nuts,screws, and other miscellaneous general hardware.1.2 The use of this practice with zinc coating depositedthrough different processes such as hot dipped, electroplated,or sprayed requires caution in interpretation since the endpoint may vary considerably between different zinc-coatingsystems.1.3 Excluded from this practice is sheet steel from hot-dipor electrocoating lines as the sheet products are normallysubject to additional forming after the coating process. Alsoexcluded from this practice are all zinc-coated wire and wireproducts either continuously or batch coated before or afterforming. WarningPast research dating from around 1963has indicated that this practice can be influenced by operatortechnique. Variations can be due to the difference in handpressure used to wipe the sample or the inability of the operatorto recognize the end point.1.4 This technique removes the zinc coating on the surfaceof the part being examined. This coating removal makes thepart or article unusable after testing. This technique may not besuitable for parts fabricated into their final configuration, sincethey will not be acceptable after testing.1.5 The results of this practice should not be used to predictthe service life of the galvanized coating. Other factors such aslocation of the thinnest spot, orientation of the part in service,and specific environmental conditions will also affect theservice life.1.6 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its 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.2. Significance and Use2.1 This practice is designed to locate the thinnest portionsof the zinc coating on newly coated items see Appendix X1.Variations in coating thickness can be due to the process bywhich the zinc is applied hot dipped, electroplated, or sprayedor by the geometry of the part that is coated. During hot-dipgalvanizing, the coating thickness is affected by the drainagepattern of the molten zinc, while during zinc sprayingmetallizing, coating thickness can be dependent on theoperator’s manipulation of the spray nozzle. The geometry ofthe part can also influence coating thickness especially duringhot-dip galvanizing, where peaks and valleys on the part cancause molten zinc to build up or thin out. This practice isdesigned to identify those areas of the part where the coating isthin.3. Copper Sulfate Solution3.1 The copper sulfate solution shall be made by dissolvingapproximately 36 parts by weight of commercial cupric sulfatecrystals CuSO45H2O in 100 parts by weight of distilledwater see 3.1.1. Heat may be used to complete the solution ofcupric sulfate crystals. If heated, the solution shall be allowedto cool. The solution shall then be agitated with an excess ofpowdered cupric hydroxide CuOH2, about 0.13 oz/gal 1.0g/L of solution. The presence of an excess of cupric hydroxidewill be shown by the sediment of this reagent at the bottom of1This practice is under the jurisdiction of ASTM Committee A05 on Metallic-Coated Iron and Steel Productsand is the direct responsibility of SubcommitteeA05.07 on Methods of Testing.Current edition approved May 1, 2014. Published May 2014. Originallyapproved in 1940. Last previous edition approved in 2009 as A239 - 952009ε1.DOI 10.1520/A0239-14.2This practice is used to locate the thinnest spot only, and is not intended as a testfor coating weight. This practice is to be used only within the limits of Section 1,Scope.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1the vessel. The neutralized solution shall be allowed to standfor 24 h and then filtered or decanted.3.1.1 Cupric oxide CuO, 0.11 oz/gal 0.8 g/L may besubstituted for cupric hydroxide, provided the solution isallowed to stand not less than 48 h after this addition beforedecanting or filtering.3.2 The solution shall have a specific gravity of 1.186 at18C 65F. To adjust a solution of improper specific gravity,add distilled water when the specific gravity is high, and add acopper sulfate solution of a higher specific gravity when thesolution is low in specific gravity.4. Specimen Rinse Water4.1 Ordinary, clean tap water may be used for rinsingspecimens. If no running tap water is available, the rinse watershall be changed after each dip. The temperature of the rinsewater shall be from 15 to 21C 60 to 70F.5. Quantity of Copper Sulfate Solution5.1 Hardware and Similar Articles For evaluating hard-ware and similar articles, the quantity of copper sulfatesolution required for each evaluation will depend on thesuperficial area of the specimen being evaluated and the weightof coating. The quantity should not be less than 1.2 qt/oz/ft240.5 mL/g/m2 of zinc coating on the specimen Note 1 andshall be sufficient to cover the specimen so that the top surfaceof the solution is at least1⁄2 in. 12.7 mm above the top of thesection of the specimen under evaluation. The solution shall bediscarded after completion of the evaluation, and fresh solutionshall be used for any additional evaluations.NOTE 1The theoretical minimum amount of copper sulfate solutionrequired to dissolve zinc is 0.4 qt/oz 13.5 mL/g. The quantity specifiedin 5.1 is three times this minimum to ensure adequate rate of solution.6. Preparation of Specimens6.1 The specimens selected for evaluation shall be free ofabrasion or cuts in the zinc coating, except those which mayoccur during manufacture of the specimen. Where the area ofuncoated surface to be immersed is more than 10 of the totalimmersed surface area, precautions, such as plugs for tubularmaterial, or lacquer, paraffin, or other suitable coatings for theuncoated surfaces must be taken so as not to deplete thestrength of copper sulfate solution.6.2 Clean the specimens with a suitable volatile organicsolvent and finally, thoroughly wash with clean water and wipedry with a clean cotton cloth. Unless otherwise specified,remove lacquer or varnish coatings with a suitable clean,volatile organic solvent such as acetone, which will not attackthe zinc coating or leave a greasy or waxy deposit. Thoroughlyrinse the specimens in clean water and wipe dry with a cleancotton cloth. Bring the specimens to a temperature between 15and 21C 60 and 70F prior to the beginning of theimmersion series.6.3 Abnormal cases may arise when, by reason of unusualsurface conditions, the copper sulfate solution will not actnormally on the zinc coating. For example, the solution mayhave no apparent attack on all or part of the surface, or falsedeposits of copper may appear on the zinc coating. If there isany question of abnormality of performance of specimens,discard the specimens and select new ones. Clean the newspecimens in alcohol, rinse, and wipe dry. Then immerse for 3min in a solution consisting of 1 part by volume of ammoniumhydroxide sp gr 0.90 and 9 parts of water. The specimens maybe scrubbed with a cotton cloth during this immersion. Aftercleaning, wash the specimens and wipe dry, then subject themto the procedure described in Section 7.7. Procedure7.1 Immerse the specimens in the copper sulfate solution,which shall be maintained at a temperature of 16 to 20C 61to 68F. Allow the specimens to remain in a fixed position inthe solution for exactly 1 min. Do not agitate the solutionduring the immersion period, nor allow the specimens to toucheach other or the sides of the container. After each 1-minimmersion, wash the specimens immediately in the rinse water,and use a fiber bristle brush to remove any copper deposit thatmay have formed on the zinc coating. Before returning thespecimens to the copper sulfate solution, drain thoroughly ofexcess rinse water and wipe dry with a clean cloth.7.2 Continue successive immersions of 1 min each, washingand wiping the specimens after each immersion until the endpoint has been reached see Appendix X2.NOTE 2Zinc coatings on threads are usually difficult to test. It hasbeen found advantageous to saw female-threaded parts longitudinally,exposing the threads to full view and facilitating cleaning to removesponge copper after each immersion in the copper sulfate solution.Brushing should be parallel to the threads.8. End Point8.1 The end point shall be recognized by the appearance ofbright, adherent copper deposits. However, if such a depositfails to form after the complete disappearance of the zinccoating, the immersion succeeding the disappearance of thezinc shall be recognized as representing the end point.8.2 Confirm adherence of the bright copper deposit by apeeling test. If it is possible to remove the copper with an inkeraser or to peel the copper with the edge of a blunt tool suchas the back of a knife blade, and zinc appears underneath thecopper, such an appearance of deposited copper shall not beconstrued as an end point.8.3 A fine line appearance of copper on the top of screwthreads or on sharp edges of articles, or within 1 in. 25 mmof a cut portion of a specimen, shall not be judged as an endpoint. Likewise, the indication of bright adherent deposits ofcopper at or adjacent to any cut or abrasion present on theoriginal specimen shall not be considered an end point.9. Supplementary Tests9.1 If at any time during the immersion procedure there isany doubt as to the presence of exposed base metal, asdetermined by visual inspection, there are several supplemen-tary tests described in Section 10, one or more of which may beused depending on the type of coating being evaluated.A239 − 14210. Supplementary Test for All Types of Zinc Coatings10.1 Microscopical TestSection the specimen through thecopper deposit, mount, and polish it for metallographic analy-sis. Etch the polished surface using an etching solutioncomposed of 20 g of chromic acid, 1.5 g of sodium sulfate, and100 mL of distilled water Palmerton reagent. After etching,wash the specimen with alcohol. Examine the etched specimenunder a microscope, using a magnification of 100 diameters orgreater if necessary.10.2 Qualitative Test for Zinc3Apply a drop or severaldrops of diluted hydrochloric acid to the area in questiondepending on its size. The presence of zinc is indicated byimmediate vigorous effervescence evolution of hydrogen. Ifno appreciable zinc is present, the effervescence will be mild.By carefully removing the acid, a confirming test for zinc maybe made as follows neutralize the acid with ammoniumhydroxide, acidify with acetic acid, and pass hydrogen sulfideinto the solution; a white precipitate zinc sulfide, ZnSconfirms the presence of zinc.11. Keywords11.1 bolts; electroplated; hardware; hot dipped; nuts;screws; thinnest spot; zinc coating thicknessAPPENDIXESNonmandatory InformationX1. APPLICATION OF THIS PRACTICE TO WEATHERED GALVANIZED WAREX1.1 This practice is not applicable to aged or weatheredmaterial because of the corrosion film present on the zinccoating. If it is desired to use this practice on such material, thecorrosion film should be removed before conducting thisprocedure by immersing the specimens for 3 min in anammonium hydroxide solution 1 part by volume of ammo-nium hydroxide sp gr 0.90 to 9 parts by volume of distilledwater then rinsing the specimens in clean water and wipingthem dry.X2. STANDARD FOR COMPARISONX2.1 If it is desired to show the character of the brightmetallic copper deposit on an exposed iron or steel surface, areference standard for comparison may be prepared as followsPartially submerge a zinc-coated specimen in strong hydro-chloric acid until violent action ceases. Immediately removethe specimen, wash, and wipe it dry. The specimen with an areaof bare surface thus exposed, including a portion with zinccoating intact, is then dipped for a few seconds in the coppersulfate solution at a temperature of 16 to 20C 61 to 68F,removed, washed, and wiped dry. This copper-coated referencestandard should be prepared at the time this practice is beingconducted.X3. ACTION OF COPPER SULFATE SOLUTION ON ZINC COATINGSX3.1 The fact that this practice cannot be used for deter-mining the weight of zinc coating is due to the wide variationin the rate of solubility of the various types of coating resultingfrom differences in the composition and structure of thecoatings. For instance, electroplated and sprayed-zinc coatingsconsist essentially of pure zinc; the outer part of hot-dippedcoatings consists of nearly pure zinc; whereas, the portion nextto the steel base is composed of zinc-iron alloys; in the case ofhot-dipped coatings heated after galvanizing, the coating con-sists almost entirely of zinc-iron alloys.X3.2 In view of these differences in the makeup of the zinccoatings applied by the different processes, it has been foundby Groesbeck and Walkup4in tests on a limited number ofsamples that electroplated and flame-sprayed coatings, byreason of their high pure-zinc content, dissolve rather rapidlyin the copper sulfate solution; that the conventional hot-dipcoatings dissolve only about two thirds as fast as the pure zinccoatings; and that the hot-dip coatings heated after galvanizingdissolve only about half as fast as the pure zinc coatings.3Only an outline of the test is given. The details of the test may be found intechnical literature.4For further information on this test method, reference may be made to thefollowing papersWalkup, H. H., and Groesbeck, E. C., “Some Factors Affecting the Preece Testfor Zinc Coatings,” Proceedings, ASTM, Vol 32,

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