AD 296: Liquid metal assisted cracking and cold formed light gauge steel

The occurrence of Liquid Metal Assisted Cracking (LMAC) in galvanized hot rolled and welded steel members has been highlighted by articles in the construction press.  However, LMAC has not been observed in cold formed light gauge steel sections.

It is thought that galvanizing a steel section which contains residual stresses will make the section susceptible to LMAC.  Hot rolled and welded sections contain residual stresses from the rolling and welding processes which are carried out before they are dipped in the galvanizing bath. Normal cold formed light gauge steel sections are formed from sheets or strips that have been galvanized before they are rolled in to the required shape.

Designers can be assured that LMAC is not a problem with cold formed light gauge sections   manufactured from strip or sheet that was galvanized prior to being formed into the required shape. Such sections include:

• Purlins
• Cladding rails
• Light steel channel and z sections
• Floor decking
• Cladding systems.