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Revision Date: September 04, 2009
Updated On: September 10, 2009
This practice is designed to locate the thinnest portions of the zinc coating on newly coated items (see Appendix X1). Variations in coating thickness can be due to the process by which the zinc is applied (hot dipped, electroplated, or sprayed) or by the geometry of the part that is coated. During hot-dip galvanizing, the coating thickness is affected by the drainage pattern of the molten zinc, while during zinc spraying (metallizing), coating thickness can be dependent on the operator's manipulation of the spray nozzle. The geometry of the part can also influence coating thickness especially during hot-dip galvanizing, where peaks and valleys on the part can cause molten zinc to build up or thin out. This practice is designed to identify those areas of the part where the coating is thin.
1.1 This practice covers the procedure for locating, by the use of a solution of copper sulfate, the thinnest spot in a zinc coating (hot dipped, electroplated, or sprayed) on iron or steel articles that are coated after the shape is produced by casting, drawing, pressing, or other forming methods. Examples are: electrical metallic tubing and rigid conduit pipe, castings and forgings, and structural steel; on special hardware, such as poleline, builder's, and farm implement hardware; bolts, nuts, screws, and other miscellaneous general hardware.
1.2 The use of this practice with zinc coating deposited through different processes (such as hot dipped, electroplated, or sprayed) requires caution in interpretation since the end point may vary considerably between different zinc-coating systems.
1.3 Excluded from this practice is sheet steel from hot-dip or electrocoating lines as the sheet products are normally subject to additional forming after the coating process. Also excluded from this practice are all zinc-coated wire and wire products either continuously or batch coated before or after forming. Warning—Past research (dating from around 1963) has indicated that this practice can be influenced by operator technique. Variations can be due to the difference in hand pressure used to wipe the sample or the inability of the operator to recognize the end point.
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
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