Your search did not yield any results

Site Pages

Dr. Galv KnowledgeBase

News

How can I keep fabricated pipework from floating in the bath? 

When fabricated pipework designs contain five or more horizontal components or rails, galvanizers often report these products can have a tendency to float within the zinc bath if provided standard vent and drain hole details.  Floating structures cause headaches for the galvanizer because these articles are difficult to handle safely in the galvanizing kettle, experience longer-than-normal processing times, and often result in poor galvanizing quality. To mitigate against floating, additional venting and drainage holes are needed to improve the flow of zinc within the fabrication.

To describe one example, the below drawing illustrates desirable design features for fabrication of handrail containing five or more rails to prevent issues with floating. External vents should be provided with one vent hole in each side of the internal intersections.

Vent Holes Illustration1 Dr Galv
Fig. Handrail – Five or More Parallel Components

For clarity, the following notes provide additional information regarding placement and sizing of the venting/drainage holes:

  1. Each vent hole shall be as close to the weld as possible with the edge of the hole less than 0.5 in [12 mm] from the edge of the weld bead, and not less than 3/8 in. [9.5 mm] in diameter. The two holes at each intersection shall be 180° apart and in the proper location as shown.
  2. Vent holes in end sections or in similar sections shall be at minimum ½ in. (12.7 mm) in diameter, but may be considered optional depending on lifting orientation during galvanizing or to achieve higher coating quality.
  3. Any device used for erection in the field that prevents full openings on vertical legs shall be attached after galvanizing.
  4. Vent holes shall be visible on the outside of any pipe assembly prior to hot-dip galvanizing.

AGA recently proposed the addition of this diagram to expand upon the existing guidance on venting and drainage details within ASTM A385 Practice for Providing High-Quality Zinc Coatings (Hot-Dip). For more information on specification news, AGA provides regular updates via the News section of the website and our monthly member newsletter, AGA Update.


Was this answer helpful? YES       | NO

Are you still looking for the right answer? Ask an Expert

Add Your Comment