Galvanizing overlapping surfaces presents two concerns.

1. Trapped pickle solutions may weep out after galvanizing and stain the surrounding steel.  On the rare occasions that this does happen, it is strictly an aesthetic consideration and does not affect the corrosion resistance of the stained area.  In areas of critical aesthetics, preventative action may have to be taken.
   
2. Overlapping surfaces can present a corrosion problem in severely corrosive environments.  We know of very few applications in Alberta where this would be a concern.  In fact, of the many thousands of tonnes we have galvanized over the last three and one half decades, we know of no problems in this area.  In addition, a Dow chemical marine terminal at Joliet, Illinois was galvanized after the angle clips were bolted on with excellent results.

Hot dip galvanizing does not prevent corrosion between overlapped surfaces.  However, due to the lack of cathodic protection, paint systems provide even less protection.  Therefore, if seal welding is not required with a paint system, it is definitely not required with hot dip galvanizing.  Seal welding is only required when specified.  The specifier should base this decision on the severity of the environment and independant of the corrosion protection system to be used.

For appropriate detailing for corrosion resistance, regardless of the corrosion protection system used, refer to the SSPC "Steel Structures Painting Manual, Volume 1, Chapter 25 - Design of Corrosion Safe Structures".

Note: Seal welded areas larger than 200 sq.cm. must be vented (by the fabricator) to prevent explosions in the galvanizing bath.  Consult the galvanizer on the best method and size of the venting.