Best practice also recommends studs and bolted assemblies be sent to the galvanizer disassembled. Â Masking to prevent galvanizing threads on pipe or fittings is very difficult. The recommended practice is to clean and tap after galvanizing. Anchoring devices (such as threaded rods and anchor bolts)Â sometimes are specified to be galvanized in the threaded areas only or in the areas to be exposed above ground. This can be more expensive than galvanizing the complete unit because of the additional handling required. Complete galvanizing can be specified for items to be anchored in concrete.
Manufacturers of threaded parts recognize special procedures must be followed in their plants when certain items are to be galvanized. Following are some examples:
The table below shows the recommended overtapping for nuts and interior threads as detailed in ASTM A563, Specification for Carbon and Alloy Steel Nuts. On threads over 1.5 inches (38 mm) it is often more practical, if design strength allows, to have the male thread cut 0.031″ (0.8 mm) undersize before galvanizing so a standard tap can be used on the nut.
Design considerations courtesy of American Galvanizers Association. The AGA also has the publication, The Design of Products to be Hot-Dip Galvanized After Fabrication, available for download.Â
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