Products in Contact
Another type of surface defect is caused by products that come in contact with each other or are stuck together. This usually occurs when many small products are hung on the same fixture, which creates the chance products may become connected or overlapped during the galvanizing process, as seen in Figure 38. The galvanizer is responsible for proper handling of all products in order to avoid this defect. In addition, if the surface of a product has a larger bare area than the specified repair requirement allows, then that product must be rejected and regalvanized.
Rough Surface Condition
Rough surface condition or appearance is a uniformly rough coating with a textured appearance over the entire product. The cause for this rough surface condition is hot-rolled steel with a high level of silicon content. This can be avoided by purchasing steel with a silicon content less than 0.03% of the steel by weight. Rough surface condition, as seen in Figure 39, can actually have a positive effect on corrosion performance because of the thicker zinc coating produced. One of the few situations where rough coating is cause for rejection is if it occurs on handrails. The corrosion performance of galvanized steel with rough coatings is not affected by the surface roughness.
Runs
Runs are localized thick areas of zinc on the surface. Runs occur when zinc freezes on the surface of the product during removal from the zinc bath. This is more likely to occur on thinner sections with large surface areas that cool quickly. In order to avoid runs, as seen in Figure 40, adjustments of the dipping angles can be made, if possible, to alter the drainage pattern to a more acceptable mode. If runs are unavoidable and will interfere with the intended application, they can be buffed. Runs are not cause for rejection.
Rust Bleeding
Rust bleeding appears as a brown or red stain that leaks from unsealed joints after the product has been hot-dip galvanized. It is caused by pre-treatment chemicals that penetrate an unsealed joint. During galvanizing of the product, moisture boils off the trapped treatment chemicals leaving anhydrous crystal residues in the joint. Over time, these crystal residues absorb water from the atmosphere and attack the steel on both surfaces of the joint, creating rust that seeps out of the joint. Rust bleeding, as seen in Figure 41, can be avoided by seal welding the joint where possible or by leaving a gap greater than 3/32” (2.4mm) wide in order to allow solutions to escape and zinc to penetrate during hot-dip galvanizing. If bleeding occurs, it can be cleaned up by washing the joint after the crystals are hydrolyzed. Bleeding from unsealed joints is not the responsibility of the galvanizers and is not cause for rejection.
