Galvanized steel tubing is a great way to cut costs if you're currently working with stainless steel or painted metal tubes. There's a good reason galvanization is the most popular way to protect steel tubing.
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What Is Galvanization?
Galvanization is a process used to make steel more durable and resistant to corrosion. The tube is given a generous coat of zinc, which protects the metal from scratching, other surface damage, and rust.
How Is It Done?
Usually, the tube is hot-dipped in melted zinc. This submersion process allows the zinc to bind tightly to the metal's surface. There are other galvanization methods, such as painting, spraying, sheet galvanizing, and electroplating, but none offer the complete coverage or durability of hot-dipping.
Pros:
Cost
Compared to other protective coatings and methods, galvanization is incredibly affordable. Labor-intensive coatings such as painting cost more to cover the salary of the painters; with hot-dipping and other machining methods, the client pays much less for the cost of factory operations. Similarly, compared to the cost of stainless steel, galvanized steel is quite cheap.
Further, galvanization lasts longer than other coatings, and requires less maintenance. Even tubes with small damaged areas will not need touch-ups, which saves in upkeep costs.
Coverage
Due to the complete submersion of the hot-dipping method, every inch of the metal will be protected. Even the most difficult corners and pockets will receive a generous protective layer.
Durability
Galvanized steel tubing can last more than 50 years in most conditions. The coating itself is bonded permanently to the metal, making transportation and installation stress-free for both the metal and its owner.
Due to a phenomenon called preferential corrosion, the zinc coating will rust and corrode before the steel, even if small areas of the zinc are damaged. This means the metal won't need touch-ups, unlike many organic coatings.
Environmentally Friendly
Galvanization is considered the most environmentally friendly protective coating. It produces only small amounts of waste and is recyclable without losing any beneficial properties of the metal.
Cons:
Not as Effective in Extreme Conditions
Although galvanized steel tubes have the potential to last more than 50 years without maintenance, that number gets cut in half in extreme conditions. In cases where the metal is exposed to the elements (salt water, rain, harsh weather) the zinc coating will corrode more quickly. Typically, even under stressful conditions, a galvanized steel component can last more than 25 years.
Physical Limitations
Some objects can't be hot-dipped due to their size. A tube that is too large or small will be difficult to get through the process.
Manufacturer Errors
If the manufacturer makes an error (such as cooling too quickly), the zinc layer will peel or chip off the tube.
Is It Right for You?
Despite the potential cons of galvanized steel, many industries benefit greatly from its low cost and long life. Even in the most extreme conditions, such as marine applications, galvanized tubing demonstrates high quality and durability.
If your project requires a cost-effective coated metal tube, galvanized steel is the most economical option.
The steps in the galvanizing process are as follows:
- The steel is cleaned in a degreasing solution
- After being cleaned, the steel is pickled by being lowered into a vat of diluted hot sulfuric acid
- The steel is then fluxed in an aqueous solution (typically zinc-ammonium chloride)
- After the flux, the steel is galvanized through immersion in a vat of molten zinc
- Afterward, the steel is inspected for consistency and a complete coating
What are the advantages of galvanized steel?
Many different industries utilize galvanized steel primarily because it has such a wide array of benefits for industries to take advantage of, including having:
Low initial cost compared to most treated steels. In addition, galvanized steel is immediately ready to use when delivered. It does not require additional preparation of the surface, inspections, painting/coatings, etc. sparing companies more costs on their end.
Longer life. With galvanization, a piece of industrial steel is expected to last more than 50 years in average environments, and can last over 20 years with severe water exposure. There is no maintenance required. The increased durability of the steel’s finished product also increases the product’s reliability.
The sacrificial anode ensures that any damaged steel is protected by the surrounding zinc coating. It doesn’t matter if the steel section is completely exposed; the zinc will still corrode first. The coating will corrode preferentially to the steel, creating a sacrificial protection to the areas that are damaged.
Rust resistance from the zinc coating. The iron elements in steel are incredibly prone to rusting, but the addition of zinc acts as a protective buffer between the steel and any moisture or oxygen. Galvanized steel is very protective, including sharp corners and recesses that couldn’t be protected with other coatings, making it resistant to damage.
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Different methods of galvanizing
As stated above, there are several different processes for galvanizing steel.
Hot-Dip Galvanizing
The first and foremost method for galvanization is hot-dip galvanizing. The process is very similar to what the name suggests! In this method, steel or iron is dipped in a molten pool of zinc that maintains a temperature of around 860°F (460 °C). This molten bath begins a metallurgical bond between the zinc and the receiving metal. After the metal is pulled from the bath, it reacts to being exposed to the atmosphere, and the pure zinc mixes with oxygen to form zinc oxide. The zinc-oxide further reacts to carbon dioxide and forms zinc carbonate, which makes up the final protective coating on the material. The tell-tale sign of a hot-dipped galvanized material is the presence of a crystalline-like pattern on the surface, sometimes referred to as “spangle.”
The hot-dipped galvanizing method is an economical choice that can be quickly executed on both simple and complex shapes.
The new coated material can be worked and machined in a similar fashion to uncoated materials. Galvanized steel can be used in high-temperature applications up to 392 °F, but use in temperatures exceeding that level will cause the zinc-carbonate layer to peel off.
Galvannealing
Galvannealing is the outcome of combining the annealing and hot-dip galvanizing processes in order to produce a specialized coating on steel. The process of galvanization is performed via hot-dipping and instantaneous annealing, which produces a matte gray finish.
Galvannealed steel is a zinc-iron alloy product, where the base metal is coated by the hot-dip process, then heated to induce alloying between the molten zinc coating and the steel. The resulting finish is a dull matte surface. Galvannealed steel is conducive to welding and the surface is excellent for paint adhesion.
Pre-galvanizing
Also similar to the hot-dip galvanizing method, but performed at the very first stage of production. Pre-galvanizing is a process that involves rolling the sheet metal through a cleaning agent to quickly prime material for galvanizing. Then, the metal is passed through a pool of molten liquid zinc and is immediately recoiled. The primary advantage of this method is that coils of steel sheet can be rapidly galvanized on a large scale with a more unified coating than the traditional hot-dipped method.
Electrogalvanizing
The most unique of these outlined methods, electrogalvanizing does not involve dipping the material in a molten vat of zinc. Instead, an electric current is introduced to an electrolyte solution that is applied to the steel, which reduces positively charged zinc ions to zinc metal – which is then deposited on the positively charged steel. Like pre-galvanizing, this method is typically done at the first stage of production.
Galvanizing advanced high-strength steel
For more information about the galvanization process for advanced high-strength steel, as well as our partner National Galvanizing, please click here.
What industries utilize galvanized steel?
Galvanized metals are used everywhere!
The bodies of cars and many bicycles are made from galvanized metals. Some drinking water pipes are still made from galvanized steel. Cool rolled sheet metal is also frequently galvanized. Nuts, bolts, tools, and wires of all kinds are now galvanized because it is a cheap process, and helps boost the metal’s lifespan!
Galvanized steel, in particular, is often what is used in modern “steel frame” buildings. Galvanized steel is also used to create structures like balconies, verandahs, staircases, ladders, walkways, and more. Galvanized metal is the ideal choice if your project will live outside after it’s done. Fences, roofs, outdoor walkways, these are all great choices for galvanized metal!
- Wind & solar industries – Solar projects must have a continuous workflow once installed and any repairs/maintenance results in disruption to service (a.k.a. revenue loss). This means that hot-dipped galvanized steels are popular in solar projects for their corrosion protection. It is also popular for its ‘environmental’ friendliness because it does not produce emissions and ensures decades without maintenance. For example, it is often utilized in the agriculture industry because the equipment is susceptible to being easily corroded, creating a demand for tougher, more resilient equipment. Hot-dip galvanized steel provides corrosion protection that can often last for decades, even when exposed to the harsh environment of farming.
- Automotive industry – Though only used on luxury models up until the s, the use of zinc-coated bodies for automobiles is now the norm in auto manufacturing. The ‘body-in-white’ of a car makes up about 80% of the body, all using galvanized steel. The rust -resistance of galvanized steel is also a good marketing tool for the automotive industry because it can provide ‘anti-rust warranties’ to customers.
- Construction industry – Whether for residential or commercial, the durability of galvanized steel has made it popular for over a century in the construction industry. It is also selected for construction because of its aesthetics; The ‘shine’ that galvanized steel provides gives it a contemporary feel and is popular in modern architectural designs. Also, it isn’t just used for large structural pieces but things like fencing, gutters, rails, tubing, poles, and much more.
- Telecommunication industry – lines are not an easy maintenance job, they are tall and often difficult to reach. Hot-galvanized steel can be used on wiring and equipment boxes which decreases the risk of damage and need for maintenance at all.
Well, there you have it! With our partner Heidtman Steel, National Galvanizing runs a 245,000-square-foot facility, featuring pickling, galvanizing, galvannealing, and slitting, all in one location, convenient to major markets. This combination of capabilities provides our customers with unparalleled responsiveness to meet the ever-changing demands of today’s market.
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