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All galvanization is the same, right?

Jeff Bowman for Progressive Dairyman Published on 29 March 2019
This type of galvanization may hold up better in dry, open-lot settings.

When buying equipment for a freestall barn, all owners want equipment that will stand the test of time, bringing them the most value for the money spent. Shy of purchasing stainless-steel headlocks and loops, how can you be sure your hard-earned dollars are going into a product that will last?

A common conversation had with both dairy owners and farm managers has been around the perception all galvanized products are equal.

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In their eyes, selection should only be on product design or which salesman brought them the nicest hat (I hand out a stylish camo cap).

However, in this case, perception is myth. Galvanization takes many forms, and while the common denominator is all products labeled “galvanized” include corrosion-inhibiting zinc, there is great variation in how it’s applied to the metal and the actual level of corrosion resistance.

Many people don’t realize “galvanized” can be a loosely used term but, armed with knowledge, dairy owners can make informed decisions that may mean the difference between getting 10 years or 20 years out of barn equipment.

When it comes to freestall equipment, the common types of galvanization in the market are as follows:

  • Hot-dip galvanized: A common practice not proprietary to any steel manufacturer or company.

  • Coated tubing

  • Pre-galvanized, which can vary greatly in process; for this, I’ll speak to the different products I’ve seen on the market.

Hot-dipped galvanized products

The hot-dip process has remained mostly unchanged for almost 200 years. It has several stages, beginning with:

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  • Cleaning/degreasing to remove biological contaminants and oils from the steel surface

  • Pickling to remove mill scale and rust (iron oxide) from the surface of the steel

  • Fluxing (dipped in zinc ammonium chloride) to prevent oxidation and contamination before the actual dipping

These products have lost the critical protection at the weld points provided by hot dipping.

Cleanliness of the steel is necessary for even coverage of the zinc, as oils will create a barrier to contact.

The actual process of “dipping” the steel is as basic as it sounds, as the pipes or manufactured product is dropped into a tank containing molten zinc.

The final step of the hot-dip process is to remove excess zinc (that zinc costs money) from the product as it cools, typically in a liquid bath. Quick temperature changes cause deformation, so proper timing on this step is critical.

Full immersion in the tank ensures hot-dipped products are galvanized inside and out, which is not possible with an inline galvanizing process.

Due to the reaction and coverage of zinc on the steel with the hot-dipping process, it has long been considered the superior treatment for protecting steel in a variety of environments. However, with that coverage comes a heavy cost.

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It requires high-energy inputs of both time and equipment, and releases byproducts in the form of gases and emissions, increasing environmental impact. For this reason, it has become costly to hot dip, particularly in countries where environmental regulations are more stringent.

Coated-tubing products

Another tubing option features an inline galvanizing process that pushes the tubing through a molten zinc bath immediately as it is formed at the mill.

This process features additional coatings after the zinc is applied, essentially a clear coating and a layer of protection for the zinc layer.

While the number of layers and type of coating varies with each manufacturer, these additional layers create improved corrosion resistance at the surface by stopping contact between the contaminant and the steel (think varnish on your stained-wood furniture), as shown in the photo.

However, this process has a couple of key limitations. Maintaining the necessary temperature to penetrate the layers of steel with zinc isn’t possible with this system. So as a result, the thickness of the zinc layer is about one-third that of the traditional hot-dip processes.

The exterior coatings mentioned above, depending on composition and quality, bring the surface corrosion resistance back to nearly that of hot-dip galvanizing.

Here’s the kicker: Because the steel is coated continuously in the inline bath, the zinc cannot reach the inside of the tubing. Spraying zinc paint to coat the inside of the steel provides a less effective layer of protection.

This type of product has found a particular fit in highway and industrial applications, where corrosion resistance of the exterior surface protects the steel in the application.

For example, think about salt spray on a highway post: The coating prevents the corrosive from reaching the steel; rain later washes the salt away. The interior of the post is never exposed to the elements because it is capped and sealed.

For dairy operations, this creates a problem: Dairy barns don’t stop at surface corrosion.

Immersion is common, not only with manure but with saliva and mucus on stall loops and, most importantly, dairy barns have a continual gas immersion, with concentrations of ammonia and methane constantly attacking steel surfaces.

Exposed ends of this tubing allow gas penetration and separate the layers protecting the raw steel. This can greatly affect longevity in the freestall environment.

Make no mistake, these products have their place too. Open-lot environments, where gas trapping is not an issue, can see long life from these products.

The inline nature of the process means tubing can be manufactured in any length, allowing greater manufacturing flexibility in some situations.

Most importantly, the cost of manufacturing is less, making these products cost-competitive. I, unfortunately, have yet to meet a dairy farmer who has told me money is no object; when I do that, stainless-steel headlocks may become a reality.

Pre-galvanized products

Again, this category can be pretty vague, so buyer beware. The only firm definition is: The product was galvanized before the manufacturing process by any of the methods above, typically then welded or shaped into the final product.

If your product is a loop, this means the galvanization and or coating was stretched as the straight tube is turned 180 degrees.

Most manufacturers utilize this method, as only the most humid and corrosive environments (i.e., Florida) can attack the loop to the severity to make post-manufacturing protection necessary on this item.

For headlocks, loop mounts or gates, this means the product was welded together using galvanized components.

Welding, by nature, burns away the zinc layer of the steel as the two pieces are joined. Most pre-galvanized products apply a zinc-rich paint to re-protect the weld but, as you can imagine, this protection is never as good as the original.

That said, these products are common in dry, arid environments and typically provide satisfactory service in feedlots and open applications.

Watch for material buildup around the welds; make sure headlocks are up off the curb so contaminants can’t build on corrosion points.

Here are the words of caution when dealing with pre-galvanized equipment: Watch out for products assembled from hot-dip galvanized materials, welded together and then labeled as hot-dipped.

These products have lost the critical protection at the weld points hot dipping provides and, in fact, are not hot dipped at all.

Conclusion

When outfitting your dairy barn with the equipment it needs, how that product is protected can make a huge difference in both the cost of the material and longevity of the product.

Some products will last effectively to validate their lower cost of galvanizing in more forgiving environments, while corrosive environments dictate the best protection possible.

The amount of zinc and the way it is applied can be the difference between getting eight to 10 years of service from the equipment and getting 20-plus years, as well as a stylish hat.  end mark

PHOTO 1: Coated tubing may resist corrosion on the outside, but because the interior of the tube may only have a light coating of zinc, a freestall barn environment can have deleterious effects on the life of the product. This type of galvanization may hold up better in dry, open-lot settings.

PHOTO 2: Some barn products are assembled from hot-dip galvanized materials, welded together and then labeled as hot dipped. These products have lost the critical protection at the weld points provided by hot dipping. Photos provided by Jeff Bowman, Artex Barn Solutions.

Jeff Bowman
  • Jeff Bowman

  • Artex Barn Solutions Ltd.
  • Email Jeff Bowman

Has it been hot dipped?

hot dipped

Let’s see if your product has been hot dipped. First, look for places on your product that could hold air (i.e., tubing with welded-on caps) and look for a bleeder hole. The temperature from hot dipping will cause air trapped inside of steel to expand (like a hot air balloon) and cause a rupture of the product. No bleeder hole for air to escape means no hot dipping.

Fun fact

Temperature is critical in the hot-dipping process. The melting point of zinc is 432°C, and it begins a chemical breakdown at temperatures above 471°C, which can result in poor performance.

Maintaining the temperature at about 450°C is critical to the galvanization process itself. Once immersed, the steel temperature rises to meet that of the molten zinc bath. A metallurgical change happens at the interface between the steel and the zinc. As the steel reaches the bath temperature, alloys of iron and zinc develop in the first three interface layers.

This unique characteristic of the hot-dip galvanization process yields abrasion-resistant iron/zinc alloy layers. These layers bond the zinc tightly to the surface of the steel, approximately 3,600 psi. Other coatings bond at much lower strengths, 300 to 600 psi.

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