Galvanized Iron And Steel: Characteristics, Uses And Problems - GSA

CSI Division Division 5 - Metals Section Metal Materials Last Modified

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This standard includes general information on the characteristics and common uses of galvanized iron and steel and identifies typical problems associated with these materials along with common causes of its deterioration.

Introduction

Galvanizing is a process of coating iron or steel with zinc in order to provide greater protection against corrosion for the iron or steel base. The process of galvanizing sheet iron was developed simultaneously in France and England in . Both of these methods employed a “hot dipping” process to coat sheet iron with zinc. Like tinplate, early galvanized metals were hand dipped. Today almost all galvanized iron and steel is electroplated.

The following are the most common methods for applying protective coatings of zinc to iron and steel:

Hot-dip Galvanizing:

• The immersion of iron or steel in molten zinc, after the surface of the base metal has been properly cleaned.
  • This process gives a relatively thick coating of zinc that freezes into a crystalline surface pattern known as spangles.
  • During the process, a multiple layered structure of iron- or steel-zinc alloys is formed between the inner surface of the zinc coating and the iron or steel. These middle layers tend to be hard and brittle and may peel or flake if the iron or steel element is bent.

Electrogalvanizing:

• The immersion of iron or steel in an electrolyte, a solution of zinc sulfate or cyanide. Electrolytic action deposits a coating of pure zinc on the surface of the iron or steel.

Advantages:

• The thickness of the coating can be accurately controlled using this process.

Limitations:

• The thick coatings provided by the hot-dip galvanizing process are not usually possible with this method.

Sherardizing:

The placing of a thoroughly cleaned iron or steel element in an air-free enclosure where it is surrounded by metallic zinc dust. The architectural element is then heated and a thin, zinc alloy coating is produced.

Advantages:

• The coating will conform to the configurations of the element.

Limitations:

• This process is usually limited to relatively small objects.

Metallic Spraying:

The application of a fine spray of molten zinc to a clean iron or steel element. The coating can then be heated and fused with the surface of the iron or steel to produce an alloy.

Advantages:

• Coating is less brittle than those produced by some of the other processes.
• Coating will not peel or flake on bending.

Limitations:

• The coating is more porous and becomes impermeable with time as products of corrosion fill in the pores.

Painting:

Paint containing zinc dust pigments may be applied as a protective Advantages

Advantages

• The paint may be applied in situ.

Limitations:

• This is a less effective method of zinc coating than the others listed above. Paint does not adhere well to pure zinc, nor to galvanized iron or steel.
• When paint peels from galvanized iron and steel, it usually comes off completely along with the primer, exposing a clean metal surface.
• If sheet metal features are well-painted, it is difficult to identify whether they are zinc or galvanized iron or steel.
  • If the metal is galvanized, it will have a spangled appearance and may show some rust or rust stains from the iron or steel base metal. Both galvanized iron and steel are magnetic
  • If the metal is cast or pressed zinc, it will have a grayish-white appearance. Pure zinc is not magnetic so a magnet will not stick.
  • A magnet test will also reveal whether a painted sheet metal feature is zinc or galvanized iron or steel. Both galvanized iron and steel are magnetic, pure zinc is not.

Typical Uses

Typical historical uses for galvanized iron and steel included:

• Cornices and other wall ornaments
• Door and window hoods
• Decorative formed shingles and pantiles designed to imitate
  other materials
• Roof ornaments such as crestings and finials
• Typical uses today include:
• Sheet metal for flashing, and gutters and downspouts.
• Hot-dipped galvanized steel nails.

Problems and Deterioration

Problems may be classified into two broad categories:

• Natural or inherent problems based on the characteristics of the material
  and the conditions of the exposure
• Vandalism and human-induced problems.

Although there is some overlap between the two categories, the inherent material deterioration problems generally occur gradually over long periods of time, at predictable rates and require appropriate routine or preventive maintenance to control.

• Conversely, many human induced problems, (especially vandalism), are random in occurrence; can produce catastrophic results; are difficult to prevent, and require emergency action to mitigate. Some human induced problems, however, are predictable and occur outinely.

Natural or Inherent Problems

Corrosion:

• Galvanized iron and steel’s resistance to corrosion depends largely
  on the type and thickness of the protective zinc coating and the
  type of corrosive environment.
• The zinc coating on galvanized iron and steel may be corroded by:
  Acids, strong alkalis, and is particularly vulnerable to corrosion
  by sulfur acids produced by hydrogen sulfide and sulfur dioxide
  pollution in urban atmospheres.

Natural Corrosion:

• The zinc coating on galvanized iron and steel develops a natural carbonate on its surface by exposure to the atmosphere and by the action of rainwater. This coating, however, is usually not thick enough to protect the metal from further corrosion.
• The carbonate can become brittle and crusty and eventually split, exposing fresh zinc for corrosion. Since the zinc coating on the iron or steel is very thin, it can corrode up to the base metal exposing the base to the atmosphere as well.
• In industrial atmospheres, the zinc carbonate coating can be broken down by the same acids that attack zinc. These acids convert the carbonate to zinc sulfate, which is water soluble and washes away with rainwater, often staining the adjacent building elements.

Chemical Corrosion:

• Galvanized iron and steel have good corrosion resistance to: Concrete, mortar, lead, tin, zinc and aluminum.
• Galvanized iron and steel have poor corrosion resistance to: Plasters and cements (especially Portland cements) containing chlorides and sulfates, acidic rainwater run- off from roofs with wood shingles (redwood, cedar, oak, and sweet chestnut), moss, or lichen, condensation on the underside of zinc plates and ponded water on the exterior surfaces of the zinc features
• Galvanic (Electrochemical) Corrosion: This type of corrosion is an electrolytic reaction between the zinc coating and dissimilar metals when in the presence of an electrolyte such as rain, dew, fog or condensation.
• To prevent the corrosion of the zinc coating due to galvanic action, contact between galvanized items and copper or pure iron or steel should be avoided.
• Galvanized iron and steel are corrosive to all metals except lead, tin, zinc and aluminum.
• Applying a protective coating such as paint to galvanized iron and steel will alleviate the problems caused by corrosion of the protective zinc coating.

Vandalism or Human-induced Problems

Mechanical or Physical Deterioration:

• Causes removal of the protective metal surface. The soft zinc coating on galvanized iron and steel make it vulnerable to abrasion damage, especially at roof valleys and gutters where the coating can be worn paper-thin by the scouring of rainwater.
• Fatigue: A type of deterioration caused by cyclical expansion and contraction of sheet metal features, especially roofs, without adequate provisions for this movement.
• Zinc is very vulnerable to fatigue failure because it has a relatively high coefficient of thermal expansion.
• Fatigue failure may also occur when the metal sheets are too thin to resist buckling and sagging. It results in the bulging and tearing of the zinc coating and resembles a cut or a crack.
• Creep: The permanent distortion of a soft metal which has been stretched due to its own weight. Thin areas of the metal are especially prone to failure. Creep may be prevented by the use of properly sized individual sheets and bays, properly designed joints, and an adequate number of fasteners.
• Distortion: Permanent deformation or failure may occur when a metal is overloaded beyond its yield point because of increased live or dead loads, thermal stresses, or structural modifications altering a stress regime

Connection Failure:

• Wind and thermal stress can damage a roof by pulling joints apart and loosening fasteners.

Galvanized Steel: Exploring Types, Uses, and Benefits

Welcome to the Worthington Steel blog! In this article, we will delve into the world of galvanized steel. Whether you're new to the industry or a seasoned professional, understanding galvanized steel's different types, uses, and benefits is essential.

First, we'll provide a comprehensive overview of galvanized steel, explaining its unique properties and how it is manufactured. Next, we'll explore the wide range of applications where galvanized steel excels, from construction and automotive to agriculture and beyond.

One of the main reasons galvanized steel is so popular is its numerous advantages. We'll discuss these benefits, including its exceptional corrosion resistance, durability, and cost-effectiveness. Additionally, we'll provide insights into the considerations and maintenance required to keep galvanized steel in optimal condition.

Finally, as a leading provider of high-quality flat-rolled steel products, we'll highlight why choosing galvanized steel from Worthington Steel could benefit you. Our commitment to excellence as a solutions provider sets us apart from the competition.

What is Galvanized Steel?

Galvanized steel is a type of steel that has been coated with a metallic layer to protect the base steel substrate from corrosion. Types of galvanized coatings include zinc (Zn), aluminum (Al), combinations of zinc & aluminum, and combinations of zinc & aluminum & magnesium.  These metal coatings can be added electrolytically or through the hot dip galvanizing.  The hot dip galvanizing process can be performed through brief immersion in a molten metal bath (batch process) or more efficiently through a continuous process where steel passes through a molten metal pot.  These metals offer galvanic protection to the steel substrate, sacrificially corroding themselves before the underlying steel substrate due to the higher electrochemical potential of the metal layers.  This process provides a durable, long-lasting finish, making galvanized steel highly popular in various steel-intensive industries.

Where is Galvanized Steel Used?

Galvanized steel is widely used in various industries for its exceptional properties and durability. Let's explore some of the key applications of galvanized steel:

Galvanized steel in construction and infrastructure:

Galvanized steel is extensively used in the construction industry for its corrosion resistance and strength. It is commonly used for roofing, wall panels, framing, and structural components. The coating protects the steel from rusting, increasing its lifespan and reducing maintenance costs.

Galvanized steel in automotive manufacturing

Galvanized steel is vital in the automotive industry, where safety and durability are paramount. It produces car bodies, chassis, and various structural components. The galvanized coating provides excellent protection against corrosion, ensuring the longevity of vehicles even in harsh environments.

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Galvanized steel in electrical and telecommunications

Galvanized steel is widely used in electrical and telecommunications infrastructure. It is used for cable trays, poles, towers, utility boxes, cabinets, enclosures, outlet boxes, lighting equipment, and conduits. The galvanized coating provides excellent corrosion resistance, making it suitable for outdoor installations and ensuring the reliability of these critical systems.  

Galvanized steel in agriculture

Galvanized steel is utilized in several applications in the agricultural industry.  It protects high-tech center-point irrigation systems as they irrigate crops in the fields. It is also widely utilized to manufacture shiny grain bins that withstand all weather environments. 

Galvanized Steel in Solar Energy

Galvanized steel is an important material in the manufacture of solar racking and solar ground mounts, protecting them from weather conditions.

Worthington Steel offers many galvanized steel products that meet the highest quality standards. Our galvanized steel is known for its exceptional performance, reliability, and long-lasting protection. Whether you require galvanized steel for construction, automotive, or electrical applications, we have the right solutions to meet your needs. Please reach out to us today to learn more about our galvanized steel products and how they can benefit your projects.

What is Hot-Dipped Galvanized Steel?

Worthington Steel produces a type of galvanized steel known as hot-dipped galvanized steel. When producing hot-dipped galvanized steel, the steel is first cleaned to remove any surface impurities and then dipped into a bath of molten zinc. The zinc coating bonds with the steel by developing an intermetallic layer, which forms a protective layer that acts as a sacrificial barrier against moisture, chemicals, and other environmental factors that can cause steel corrosion.  The zinc coating sits on top of steel and isn’t chemically bonded, making it more prone to chips. Galvanized coating is best for non-surface critical applications requiring high corrosion resistance, such as culverts, grain bins, and guard rails. 

What Other Types of Hot-Dipped Coatings Does Worthington Offer?

Galvanneal

A galvanneal coating is produced by annealing galvanized steel. During the annealing process, the zinc bonds to the iron in the steel, producing a zinc-iron alloy. The galvanneal coating is smoother and harder than the galvanized coating, making it superior for exposed painted applications and more resistant to surface damage.   Galvanneal is often selected for car bodies.

Aluminized (type I,II)

"Aluminized Type 1" steel refers to steel coated with a layer of aluminum-silicon alloy through a hot-dipping process. This coating provides several benefits to the steel, including enhanced corrosion resistance, improved heat resistance, and increased reflectivity.  This protective barrier is beneficial in environments where exposure to moisture, chemicals, or high temperatures is a concern. Typical applications are heat exchangers and automotive exhaust systems.

"Aluminized Type 2" steel also utilizes an aluminum-silicon alloy, but there are differences in the coating processes and properties.  This type of coating is best for applications where extremely high-temperature environments and corrosion are significant concerns.  Aluminized Type 2 offers superior corrosion protection to aluminized Type 1.  Applications for type 2 would be heavy-duty industrial equipment exposed to harsh conditions and applications involving chemical processing where heat and chemical exposure are factors.

Galvalume

Galvalume is a coating made of zinc and aluminum. The name “galvalume” is a combination of “galvanized” and “aluminum – the two main components of the coating.  Before the steel is dipped into the zinc bath, it is coated with a thin aluminum-silicon alloy layer.  This aluminum-silicon coating provides several advantages over traditional galvanized coating: enhanced corrosion resistance, improved heat resistance, better formability, and a longer lifespan.  The heat tolerance and formability make this coating ideal for metal roofing and siding in hot climates.

Advantages of Galvanized Steel

Galvanized steel offers several advantages, making it a popular choice in various industries. Let's explore some of the key benefits:

Enhanced Corrosion Resistance

One of the primary advantages of galvanized steel is its exceptional protection of base steel substrate. The galvanization process involves applying a protective zinc coating to the steel surface, which forms a barrier against moisture, chemicals, and other corrosive elements. This zinc coating acts as a sacrificial layer, protecting the underlying steel from rust and corrosion. As a result, galvanized steel exhibits superior resistance to environmental factors, making it ideal for outdoor applications.

Longevity and Durability

Galvanized steel is known for its long-lasting durability. The protective zinc coating provides an additional layer of defense against wear and tear, extending the steel's lifespan. This makes galvanized steel a cost-effective choice in the long run, as it requires minimal maintenance and replacement. Whether used in construction projects, automotive manufacturing, or infrastructure development, galvanized steel stands the test of time.

Cost-effectiveness in the Long Run

While the upfront cost of galvanized steel may be slightly higher than that of other materials, its long-term cost-effectiveness must be considered. Galvanized steel's enhanced corrosion resistance and durability reduce the need for frequent repairs, replacements, and maintenance. Additionally, its resistance to rust and corrosion eliminates the need for protective coatings or sealants, further reducing costs. Its longevity and low maintenance requirements make it an economical choice for various applications. It also acts as a natural lubricant in roll-forming operations.

Considerations and Maintenance

Regarding galvanized steel, proper handling, and storage are crucial to maintaining its quality and effectiveness. Here are some guidelines to follow:

Handling

Handle with care: Galvanized steel is coated with a protective layer of zinc, which can be scratched or damaged if mishandled. Avoid dropping, dragging, or sliding galvanized steel to prevent any potential damage to the coating.

Storage

Store in a dry, well-ventilated environment. Moisture can accelerate corrosion on galvanized steel, resulting in white rust caused by zinc oxidization. Before fabricating, storing galvanized steel in a dry environment is essential to minimize exposure to moisture or humidity. Regardless, a well-ventilated storage area with low humidity levels is ideal for long-term storage—ceiling fans are an excellent solution to prevent white rust from occurring.

Choosing Galvanized Steel from Worthington Steel

Worthington Steel offers a wide range of galvanized steel products designed to meet our customers' diverse needs. Whether you are in construction, automotive, or any other industry that requires durable and corrosion-resistant materials, our galvanized steel is the perfect choice.

Our galvanized steel products are available as master coil, slit, or cut-to-length sheets, and our customers fabricate, stamp, roll form, or bend. We understand that different projects have different requirements, which is why we offer customization options to ensure that our galvanized steel meets your exact specifications and can offer you galvanized, galvanneal, and type I or type II aluminized (used for heat-resistant applications or culvert, respectively).

When it comes to quality, Worthington Steel is committed to delivering nothing but the best. Our galvanized steel undergoes a rigorous process to ensure its strength, durability, and corrosion resistance. We adhere to strict quality standards and continuously invest in advanced technology and innovation to provide our customers with the highest quality products with the consistency you demand.

Contact us to discuss your requirements of Galvanized Steel Sheet. Our experienced sales team can help you identify the options that best suit your needs.