Prepping your products for Hot Dip Galvanizing

There are some important things to keep in mind in the preparation of your metal fabrications before you ship them to be galvanized.

Design considerations prior to fabrication

Prior to fabrication, communication between the galvanizer, designer, and the fabricator will ensure that all materials are galvanized safely, economically, and effectively. Most ferrous metals including hot and cold rolled steels, castings, as well as stainless steels can be galvanized.

photo: Galvanizing prepDesign requirements for galvanizing include putting in holes in the proper location for filling and draining hollow structures while allowing for air to escape from within. Proper hole location is crucial, not just for the effectiveness of the galvanizing, but also because the release of trapped super heated steam from inside the fabrication is very dangerous. Sealed pipe or HSS (tubing) can and will explode in the kettle if holes are not properly installed.

Because hot dip galvanizing is a coating of zinc on bare steel, the original steel becomes slightly thicker. Typical galvanized coatings range from 3-8 mils (75-200 microns). When designing and detailing tapped holes, the increased thickness is important.

Hole sizes in certain fabricated steel products must be oversized to account for the zinc that bonds to the edges. If after galvanizing the hole is still not large enough, it can be retapped. Retapping will not necessitate regalvanizing. Because of the zinc coating’s cathodic properties, the coating on the mating fastener will protect chased or retapped nuts.

What preparation is required during fabrication

To ensure that welded sections will galvanize properly, all welding flux residues must be removed at the time of fabrication. Welds that are not slaged will not galvanize properly. Avoid using anti-spatter sprays when welding prior to galvanizing, as they are often not removed by chemical cleaning and must be mechanically removed. Avoid using welding rod high in silicon or use uncoated electrodes when possible.

Painted materials or materials with a black lacquer coating (typically found on pipe) must first be abrasive shot blasted or wheelabrated as our chemical cleaning process does not remove these coatings. Identification markings, such as paint markings, need to be removed before galvanizing or the material will not be galvanized in these areas.

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