Required vent & drain holes for hollow structural sections & handrail tubing
In order to ensure that all interior and exterior surfaces are protected from corrosion, entire steel fabrications are lowered into and raised out of cleaning solutions, flux solutions, and molten zinc metal. In order to facilitate interior and exterior cleaning and coating, it is necessary to provide holes in fabrications to be galvanized.
The primary reason for vent and drain holes is to allow air to be evacuated from within and around the fabrication, allowing it to be completely immersed in the cleaning solutions and molten zinc and for the excess zinc and solutions to drain out and away from the part.
The secondary reason is that if fabrications to be galvanized are not properly vented, cleaning solutions or rinse waters trapped in overlapping or contacting surfaces flash to steam. The resulting pressure increase (up to 3600 psi [25MPa]) can rupture the fabrication. Additionally, trapped moisture that flashes to steam can result in localized uncoated surfaces.
Because items being galvanized are immersed in and withdrawn from all cleaning solutions and molten zinc at an angle, vent holes should be located at the highest point and drain holes at the lowest point as mounted during the galvanizing process. A variety of products require vent and drain holes and the size and location are critical to achieve successful and safe galvanizing. The links below lead to diagrams with examples of good venting and draining.
See Also:
Handrail
Tube Truss
Pipe Truss 3 inches and Larger
Pipe Columns, Girders, & Poles
Box Sections
Tapered- Single Arm
Enclosed & Semi-Enclosed Products
Drainage
I could not find vent holes examples for monopoles for example 45m monopole with base diameter of around 2m
According to the AGA Design Guide (www.galvanizeit.org/images/uploads/publicationPDFs/Design_Guide_Galvanized_Steel_Structures.pdf), if the height + width of a box section is less than 8 inches (20 cm) you would need to leave the ends completely open to allow for venting/drainage. The Design Guide gives additional venting information. You can also contact your galvanizer to help you with venting requirements.
One more note in reference to the above question and answer. It would also be necessary to have no internal gussets in the pickets. Also, the above information is for box sections only, not rectangular sections.
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