TECHNICAL

Draining and Venting

Tubular assemblies such as handrails, pipe columns, pipe girders, steel light poles, transmission poles, pipe trusses, and sign bridges are commonly galvanized.

It is mandatory that tubular fabrications and hol­low sections be properly vented.

Any pickling acid or rinse waters that might be trapped in a blind or closed joint connection will be converted to super-heated steam. This is a serious potential hazard to galvanizing equipment and to personnel.

Galvanizing demands completely cleaned and coated with zinc, air and ash must be allowed to flow in and completely wet the surfaces.

In all tables of draining, venting and gusset bevel calculations, allowance has been made for the speedy and total expulsion of entrapped air and ‘ash’ produced during the galvanizing process.

Simply stated, the structure must be lowered into the solution without trapping any air. It must be raised from the solution without trapping any solution. Consequently, ample passageways which allow flow in and out must be designed into the assemblies.

Since items to be galvanized are immersed and withdrawn at an angle, the vent holes should be located at the highest point and drainage holes at the lowest point in each hollow member.

All components of fabricated hollow sections can be inter-connected with full open tee or with mi­tred joints. Each closed section must be provided with a vent hole and drain hole.

Base plates and end plates must be designed to facilitate venting and draining. Fully cutting the plate provides minimum obstruction to a full, free flow into and out of hollow sections. Since this is not always possible, the use of vent holes in the plate often provides a solution.

Refer to our Design Principles booklet for more detail.