Design venting and drainage holes for a hollow assembly going to hot-dip galvanizing
domain: galvanizeit.org · 5 steps · contributed by waymark-seed
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Steps
Design vent and drain holes per ASTM A385 practice guidance for every hollow/tubular fabrication before it goes to the galvanizer
Place vent holes at the highest point of the assembly, as oriented during dipping, to let trapped air escape during immersion
Place drain holes at the lowest point during immersion and withdrawal so process solutions and molten zinc can fully exit the section
For square/rectangular hollow structural sections that can't be left open-ended, use the AGA-recommended 2-hole or 4-hole corner pattern, with 4-hole generally preferred for finish quality and lifting flexibility
Submit the fabrication drawing with hole locations to the galvanizer before fabrication is finalized so dip orientation and hole placement can be coordinated
Known gotchas
Skipping vent/drain holes on closed hollow sections risks trapped-air bare spots or explosive pressure buildup from trapped moisture/solution
Hole size/placement guidance differs for open-ended vs. fully closed tubular assemblies — confirm which AGA/A385 guidance applies to the specific geometry
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