Venting & drainage

This is the biggest fabrication design issue faced by hot dip galvanizers and mostly applies to hollow sections with capped ends.

The galvanizing process involves us submerging your steelwork into liquid zinc that must contact and therefore coat every square inch of the steel surface area, inside and out.

Firstly, you have to envisage how the steelwork will be hung for dipping.  If it is a complex fabrication then we would always recommend you contact us first and preferably before or during the design phase rather than post fabrication.

Once you have a good idea of how your fabrication will be hung for galvanizing you will be able to determine where to place your venting and drainage holes.  The first part of every closed hollow section to submerge into the zinc requires a drainage hole (to let zinc in and out) and the last part to submerge requires a vent hole (to let the air out).  See our Design It guide for more information.


If a steel section’s drainage hole is missing then it will either not submerge at all or will fill with zinc costing both galvanizer and customer money.

If a section’s vent hole is missing then it will either not submerge into the molten zinc at all or will explode due to the trapped and now super heated air.  Exploding fabrications are bad for you and potentially dangerous for us to process.

Please do not scrimp on those holes.  As far as we are concerned: the more the merrier and the bigger the better.  Refer to our hole size guide for the minimum vent/drainage hole sizes required but remember; the bigger the holes = the quicker the dip = the better the finish!  Thanks.