Welding/Restoring Corrosion Resistance
The following article will cover the process of welding and restoring corrosion resistance.
Restoring Corrosion Resistance to Welds and Zinc Rich Coatings
The heat generated from the welding process vaporizes the protective zinc coating near the weld. Even though the remaining zinc continues to provide some protection to the zinc-free areas, the appearance is poor and the zinc-free area will rust when exposed to the environment. The same applies to the interior (ID) of the tube, except exposure to the environment is minimal.
There are several zinc rich paints available which will restore corrosion protection to the weld areas on both the ID and OD, with varied application methods.
Note: It is necessary to take the proper steps in cleaning the surface of weld slag and oil to insure a strong mechanical bond..
Some of the coatings are for use “as is” and some are for use as a base coat in powder coating applications.
OD Applications
When coating the weld area of a tube to be used in the shiny galvanized state, a standard cold galvanizing compound should be used. There are numerous manufacturers and various brand names commercially available. The key to choosing a corrosion resistant cold galvanizing compound is the percentage of zinc dust present in the compound. Some of the recommended compounds are listed in the table below.