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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 Because items being galvanized are immersed in and withdrawn from all cleaning solutions and molten zinc at an angle, vent holes should be located at the highest point and drain holes at the lowest point as mounted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 Venting & Drainage page in the Design section includes links for more information and diagrams with examples of good venting and draining. 

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Pallab Dutta

My client is worried about galvanizing covering of handrail pipe inside surface. The pipe diameter 1-1/2" SCH40. Is this something covered under ASTM A123? If yes, please let us know, how to ensure without destructive testing.


Hello Pallab, Hot-dip galvanizing is a total immersion process, meaning the steel is fully submerged into cleaning solutions and the molten zinc coating all interior and exterior surfaces. This complete coverage ensures even the insides of hollow and tubular structures, like handrail pipe, and the threads of fasteners are coated and protected.

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