AASHTO M 232M M 232-2010 Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware.pdf

1、Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware AASHTO Designation: M 232M/M 232-10 (2015) ASTM Designation: A153/A153M-09 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-4h M 232M/M 23

2、2-1 AASHTO Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware AASHTO Designation: M 232M/M 232-10 (2015)1ASTM Designation: A153/A153M-09 1. SCOPE 1.1. This specification covers zinc coatings applied by the hot-dip process on iron and steel hardware. The hot-dip galvanizing

3、process consists of parts being immersed in molten zinc for a time sufficient to allow a metallurgical reaction between iron from the steel surface and the molten zinc, resulting in the formation of Zn/Fe alloy layers bonding the coating to the steel surface. 1.2. This specification is intended to b

4、e applicable to hardware items that are centrifuged or otherwise handled to remove excess galvanizing bath metal (free zinc). Coating thickness grade requirements reflect this. 1.3. The values stated in SI units are to be regarded as the standard. The equivalent inch-pound units may only be approxim

5、ate. 1.4. This 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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. REFER

6、ENCED DOCUMENTS 2.1. AASHTO Standard: T 65M/T 65, Mass Weight of Coating on Iron and Steel Articles with Zinc or Zinc-Alloy Coatings 2.2. ASTM Standards: A143/A143M, Standard Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting E

7、mbrittlement A780/A780M, Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings A902, Standard Terminology Relating to Metallic Coated Steel Products B6, Standard Specification for Zinc B487, Standard Test Method for Measurement of Metal and Oxide Coating Thickness

8、 by Microscopical Examination of Cross Section B690, Standard Specification for Iron-Nickel-Chromium-Molybdenum Alloys (UNS N08366 and UNS N08367) Seamless Pipe and Tube E376, Standard Practice for Measuring Coating Thickness by Magnetic-Field or Eddy-Current (Electromagnetic) Testing Methods 2015 b

9、y the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-4h M 232M/M 232-2 AASHTO F1470, Standard Practice for Fastener Sampling for Specified Mechanical Properties and Performance Inspection F1789, Standard Termino

10、logy for F16 Mechanical Fasteners 3. TERMINOLOGY 3.1. Definitions: 3.1.1. The following terms and definitions are specific to this specification. ASTM A902 contains other terms and definitions relating to metallic coated steel products. ASTM F1789 contains other terms and definitions relating to mec

11、hanical fasteners. 3.2. Definitions of Terms Specific to This Standard: 3.2.1. average coating thickness, nthe average of the specimen coating thickness values for the samples in an inspection lot. 3.2.2. bare spots, nuncoated areas on the surface of the steel part that contain no measurable zinc co

12、ating. 3.2.3. dross inclusions, nthe iron/zinc intermetallics, oxides, and flux remnants present in a galvanized coating in a form other than the layer growth of the coating. 3.2.4. individual measurement, nthe reading from a magnetic thickness gauge of a single coating spot thickness, or the micros

13、copic reading of a coating thickness as seen in an optical microscope at one spot. 3.2.5. inspection lot, nthe quantity of identical parts cleaned, fluxed, and galvanized together at one time in an appropriate container that is being submitted for acceptance as a group. 3.2.6. malleable casting, na

14、steel article that has been subjected to a prolonged anneal to decarburize or graphitize the part to remove as much of the carbon as possible or to convert the carbon to graphite, which permits plastic deformation in compression without rupture. 3.2.7. sample, na collection of individual units of pr

15、oduct from a single inspection lot selected in accordance with Section 6 and intended to represent that inspection lot for acceptance. 3.2.8. specimen, nan individual test article upon which thickness measurements or mass weight determinations are performed. 3.2.9. specimen coating thickness, nthe a

16、verage thickness from no fewer than five test measurements on a specimen, when each measurement location is selected to provide the widest dispersion (in all applicable directions) of locations within the specimen volume. 3.2.10. threaded areas, nthe sections of a steel part that have threads formed

17、 before hot-dip galvanizing. 4. MATERIALS AND MANUFACTURE 4.1. Steel or IronFerrous articles to be hot-dip zinc coated shall conform to specifications designated by the purchaser. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a vio

18、lation of applicable law.TS-4h M 232M/M 232-3 AASHTO 4.2. ZincThe zinc used for the coating shall conform to ASTM B6 or ASTM B690, or both, and shall be at least equal to the grade designated as “Prime Western.” 4.2.1. If a zinc alloy is used as the primary feed for the galvanizing bath, then the ba

19、se material used to make that alloy shall conform to ASTM B6 or ASTM B690, or both. 4.2.2. The molten metal in the working volume of the galvanizing bath shall contain not less than an average value of 98.0 percent zinc by mass weight. Note 1The galvanizer may choose to add trace amounts of certain

20、elements (for example, aluminum, nickel, bismuth, or tin) to the zinc bath to help in the processing of certain reactive steels or to enhance the cosmetic appearance of the finished product. The elements can be added to the galvanizing bath as a master feed alloy, or they can be added to the bath by

21、 the galvanizer as individual feeds. 4.2.3. If high-grade or special high-grade zinc is used, the molten metal in the working volume of the galvanizing bath shall contain not less than an average value of 99.8 percent zinc by mass weight. 4.3. Minimum Coating Mass Weight or Minimum Coating Thickness

22、The minimum coating mass weight or the minimum coating thickness shall conform to the requirements prescribed in Table 1 for the material category and thickness of material in which the article belongs. Table 1Thickness or Mass Weight of Zinc Coating for Various Classes of Material Mass Weight of Zi

23、nc Coating, g/m2oz/ft2 of Surface, Min Coating Thickness, m mils, Min Class of Material Average of Specimens Tested Any Individual Specimen Average of Specimens Tested Any Individual Specimen Class ACasingsMalleable iron, steel 610 2.00 550 1.80 86 3.4 79 3.1 Class BRolled, pressed, and forged artic

24、les (except those that would be included under Classes C and D): B-14.75 mm 3/16in. and more in thickness and more than 380 mm 15 in. in length 610 2.00 550 1.80 86 3.4 79 3.1 B-2less than 4.75 mm 3/16in. in thickness and more than 380 mm 15 in. in length 458 1.50 381 1.25 66 2.6 53 2.1 B-3any thick

25、ness and 380 mm 15 in. and less in length 397 1.30 336 1.10 56 2.2 48 1.9 Class CFasteners more than 9.5 mm 3/8in. in diameter and similar articles. Washers 4.75 mm and 6.35 mm 3/16in. and 1/4in. in thickness 381 1.25 305 1.00 53 2.1 43 1.7 Class DFasteners 9.5 mm 3/8in. and less in diameter, rivets

26、, nails, and similar articles. Washers less than 4.75 mm 3/16in. in thickness 305 1.00 259 0.85 43 1.7 36 1.4 Note: Length of the piece, stated in Classes B-1, B-2, and B-3, refers to the finished dimension of the piece after fabrication. 4.4. Threaded ArticlesThe zinc coating on threads shall not b

27、e subjected to a cutting, rolling, or finishing-tool operation unless specifically authorized by the purchaser. In order to meet overtapping allowances, tapping the threads of nuts or tapped holes after galvanizing is not prohibited. 4.5. Touch-up and RepairBare spots that are found on parts after g

28、alvanizing shall be renovated by use of the methods found in ASTM A780/A780M if the following criteria are met. The bare spots shall have an area totaling not more than 1 percent of the surface area to be coated excluding threaded areas of the piece, and the bare spots shall not include any threaded

29、 areas of the piece. The thickness of the repair shall be equal to the surrounding galvanized coating except for repairs made by paints containing zinc dust, in which case the thickness of the repair shall be 50 percent greater than the thickness of the galvanized coating required for the class of m

30、aterial but shall not be greater than 100 m (4.0 mils). Repair thickness measurements shall be made in accordance 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-4h M 232M/M 232-4 AASHTO with ASTM A78

31、0/A780M. The galvanizer shall make repairs unless directed by the purchaser to deliver items unrepaired for subsequent renovation by the purchaser. 5. WORKMANSHIP, FINISH, AND APPEARANCE 5.1. The zinc-coated articles shall be free from uncoated areas, blisters, flux deposits, dross inclusions, and o

32、ther types of projections that would interfere with the intended use of the articles, or other defects not consistent with good galvanizing practice. 5.2. The zinc coating shall be smooth and reasonably uniform in thickness. Note 2Smoothness of surface is a relative term. Minor roughness that does n

33、ot interfere with the intended use of the part or roughness that is related to the as-received (ungalvanized) surface condition of the part shall not be grounds for rejection. Note 3Because this specification is applicable to items that are centrifuged or otherwise handled to remove excess bath meta

34、l (Section 1.2), irregular coating distribution is not normally encountered. Drainage problems, which manifest themselves as local excess coating thickness that would interfere with function or as edge tears or spikes that present a safety hazard because of their sharpness, are grounds for rejection

35、 under the terms of Section 5.1. 5.3. Embrittlement is a potential condition of steel that is cold-worked, depending on factors such as the steel type (strength level, aging characteristics), thickness, degree of cold work, and galvanizing process. The galvanizer, the designer, and the fabricator sh

36、all take precautions against embrittlement. The precautions to fabricate properly and prepare the material for galvanizing to prevent embrittlement are described in ASTM A143/A143M. Note 4Low service temperatures increase the risk of brittle failure of all plain carbon steels, including those that h

37、ave been galvanized. This temperature embrittling effect varies with type of steel. The expected service temperature should thus be taken into account when selecting steels for galvanizing. Note 5Tin is often added to hot-dip zinc baths to control spangle in the galvanized finish. However, the prese

38、nce of tin, antimony, or arsenic in the zinc bath can contribute to embrittlement in structural steels, particularly if the steels contain more than 0.10 percent copper. The concentrations of tin, antimony, or arsenic should be individually restricted for each element to 0.01 percent maximum. Use of

39、 high-grade or special high-grade zinc restricts the presence of these deleterious elements. 5.4. Malleable castings shall be of such composition as will preclude the possibility that they become embrittled by the galvanizing process or they shall be either cooled from the anneal or subsequently hea

40、t treated so as to immunize them against embrittlement. 5.5. The zinc coating shall adhere tenaciously to the surface of the base metal. 5.6. If the galvanized material covered by this specification is bent or otherwise fabricated to a degree that causes the zinc coatings to stretch or compress beyo

41、nd the limit of elasticity, any cracking or flaking of the coating resulting from bending or fabricating shall not be cause for rejection. 6. SAMPLING 6.1. Test specimens shall be selected at random from each inspection lot. 6.2. The method of selection and sample size shall be agreed upon between t

42、he galvanizer and the purchaser. Otherwise, the sample size selected from each lot shall be as follows: 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-4h M 232M/M 232-5 AASHTO Number of Pieces in Lot

43、 Sample Size 3 or fewer All 4 to 500 3 501 to 1,200 5 1,201 to 3,200 8 3,201 to 10,000 13 10,001 and over 20 6.3. A specimen that fails to conform to a requirement of this specification shall not be used to determine the conformance to other requirements. 6.4. The method of sampling for fasteners th

44、at are required to meet the standards of the Fastener Quality Act is described in ASTM F1470. Sample quantities and definitions of terminology are included in the referenced specification. 7. TEST METHODS 7.1. Tests shall be made to ensure that the zinc coating is being furnished in accordance with

45、this specification and as specified for the following: 7.1.1. Minimum coating mass weight or minimum coating thickness in Section 4.3. 7.1.2. Finish and appearance in Sections 5.1 and 5.2. 7.1.3. Embrittlement in Sections 5.3 and 5.4. 7.1.4. Adherence in Section 5.5. 7.2. Average Mass Weight of Coat

46、ing: 7.2.1. The average mass weight of the zinc coating shall be determined by weighing specimens after pickling and drying and again after galvanizing, unless the method described in Section 7.2.2 is used. The number of specimens that are used to determine the average of an inspection lot shall be

47、derived from Section 6. Note 6This method does not take into account the mass weight of iron reacted from the article that is incorporated into the coating. It will thus underestimate coating mass weight by up to approximately 10 percent. Base metal reactivity will affect the extent of underestimati

48、on. 7.2.2. In the case of materials inspected after galvanizing, the average mass weight of coating shall be determined by stripping the number of specimens derived in Section 6 in accordance with T65M/T65, and averaging the results of the individual specimens, unless the method described in Section

49、 7.2.1 is used. 7.3. Average Thickness of Coating: 7.3.1. In the case of fasteners such as bolts, nuts, and screws, the determination of the thickness of coating shall be made on a portion of the article that does not include any threads. 7.3.2. The average thickness of coating shall be determined by magnetic thickness gauge in accordance with ASTM E376 unless the method described in Section 7.3.3 is used. The thickness shall be measured