48567

Corrosion potential: stainless equipment outdoors w/ galvanized anchors [Arkansas] 

April 22, 2008

My company makes a product that is installed on side walks and in parking lots. The installation base is a galvanized mild steel plate affixed to the ground by either wedge anchors or J bolts set in concrete. Onto this galvazied plate is a peice of equipment that has a 316 stainless steel base. Both parts come into contact over a wide surface area. Will there be any galvanic corrosion problems between the galvanized plate and the stainless plate? If so, what can be used between the two plates? The installtion sites see varying weather conditions in various climates.

Todd Magness
product designer - Harrison, AR, USA

Hi, Todd. A galvanic corrosion cell requires 3 things: metals of differing potential, a metallic path between them, and an ionic path (wet path) between them. It's severity depends on how far the metals differ in potential (stainless and zinc are far away), how wet and conductive the wet path is, and sometimes the relative surface areas (a large area of nobler metal if worse that a large area of active metal).

In this case you have a large area of the nobler metal (stainless) available to corrode a small area of active metal (galvanizing and then steel) under unfavorable environmental conditions. The two parts should be electricaly isolated with plastic shims, bushings, and washers, I think.

Regards,

Ted Mooney, P.E.  finishing.com Brick, NJ

Ted is right...If you look at galvanized boat trailers, it is common to see the frame and parts hot dipped, and the fasteners SS. They use plastic washers and inserts to break the path.

David Jaye
Houston, TX, USA