Here are the 10 most frequently asked questions about GI coils:
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A GI (Galvanized Iron) Coil Is A Type Of Steel Coil That Has Been Coated With A Layer Of Zinc Through A Process Called Galvanization. This Coating Helps To Protect The Underlying Steel From Corrosion, Making The GI Coil More Durable And Long-Lasting Compared To Untreated Steel Coils. GI Coils Are Commonly Used In A Variety Of Applications Including Construction, Automotive Manufacturing, Appliances, And General Engineering. They Are Known For Their Strength, Corrosion Resistance, And Affordability, Making Them A Popular Choice In Many Industries.
2. What Are The Advantages Of Using GI Coils?
Galvanized iron (GI) coils offer 8 advantages, making them popular in various industries:
1. Corrosion Resistance
2. Longevity
3. Strength and Toughness
4. Versatility
5. Cost-Effectiveness
6. Aesthetic Appeal
7. Recyclability
8. Protection for Base Metal
Overall, the advantages of using GI coils make them a preferred choice for a wide range of applications, including construction, automotive manufacturing, appliances, agricultural equipment, and more.
3. How Are GI Coils Manufactured?
GI (Galvanized Iron) coils are manufactured through a process called hot-dip galvanizing. Here's 7 general of the process:
The resulting GI coils are highly corrosion-resistant and are commonly used in a wide range of applications, including construction, automotive, and manufacturing industries.
Galvanized Iron (GI) coils find applications across various industries due to their corrosion resistance and durability. Some of the industries that typically use GI coils include:
Galvanized Iron (GI) coils are available in different grades, which are typically categorized based on the thickness of the zinc coating applied to the steel substrate. The most common grades of GI coils include:
1. SGCC (DX51D):
This is one of the most widely used grades of GI coils. SGCC stands for "Hot-Dip Galvanized Steel Sheet and Coil", and DX51D is the European equivalent. These coils have a standard zinc coating thickness and are suitable for general applications in various industries.
2. SGCD (DX52D)
SGCD or DX52D grade GI coils have a higher zinc coating thickness compared to SGCC/DX51D coils. They offer improved corrosion resistance and are often used in environments with higher levels of moisture or exposure to corrosive elements.
3. SGCE (DX53D)
SGCE or DX53D grade GI coils have an even higher zinc coating thickness than SGCD/DX52D coils. These coils provide enhanced corrosion protection and are suitable for applications where extended durability is required, such as in coastal areas or harsh industrial environments.
4. SGCF (DX54D):
SGCF or DX54D grade GI coils have the highest zinc coating thickness among the commonly available grades. These coils offer superior corrosion resistance and are suitable for demanding applications where maximum protection against corrosion is essential, such as in marine environments or chemical processing plants.
It's important to note that the specific grades and designations may vary slightly depending on regional standards and specifications. Additionally, there may be other specialized grades of GI coils available for specific applications or industries, but the ones mentioned above are the most commonly used grades in general industrial and commercial applications.
The standard sizes and dimensions of Galvanized Iron (GI) coils can vary depending on the manufacturer, region, and specific requirements of the customer. However, there are some common size ranges that are widely available:
GI coils typically come in widths ranging from 600mm to mm (approximately 24 inches to 59 inches). The choice of width depends on factors such as the intended application, machinery constraints, and transportation considerations.
The thickness of GI coils can vary from as thin as 0.12mm to as thick as 4.0mm (approximately 0. inches to 0.157 inches). The specific thickness required depends on the strength and durability requirements of the application.
The weight of GI coils can range from a few hundred kilograms to several metric tons, depending on the width, thickness, and length of the coil. Common coil weights range from 3 to 15 metric tons (approximately to pounds).
The inner diameter of GI coils typically ranges from 508mm to 610mm (approximately 20 inches to 24 inches). This inner diameter is standardized to fit various types of coil handling and processing equipment.
The outer diameter of GI coils can vary depending on factors such as coil width, thickness, and weight. However, common outer diameters range from mm to mm (approximately 39 inches to 79 inches).
GI coils are usually supplied in continuous lengths, with typical coil lengths ranging from mm to mm (approximately 39 inches to 118 inches). However, longer or custom lengths may be available upon request.
It's important to note that these dimensions are general guidelines, and actual sizes may vary depending on the specific specifications provided by the customer or the manufacturing capabilities of the supplier. Additionally, GI coils can be cut to custom lengths or slit to narrower widths to meet the requirements of different applications.
GI coils have superior corrosion resistance compared to other types of steel coils. This is because they are coated with a layer of zinc, which acts as a sacrificial anode, protecting the underlying steel from rust and corrosion. This makes GI coils ideal for outdoor or humid environments where corrosion is a concern.
The galvanization process adds an extra layer of protection to GI coils, making them more durable compared to other types of steel coils. They are less likely to rust or corrode over time, resulting in a longer lifespan.
While GI coils may be slightly more expensive upfront due to the galvanization process, they are generally more cost-effective in the long run because of their extended lifespan and reduced maintenance requirements. They may require less frequent replacement or repair compared to other types of steel coils.
GI coils typically have similar strength characteristics to other types of steel coils of comparable thickness. The galvanization process does not significantly alter the mechanical properties of the steel, so GI coils retain their strength and structural integrity.
GI coils have a characteristic shiny, metallic appearance due to the zinc coating. This can be desirable for certain applications where aesthetics are important. However, for applications where appearance is not a concern, other types of steel coils may be preferred.
Overall, GI coils offer excellent corrosion resistance, durability, and cost-effectiveness compared to other types of steel coils, making them a popular choice for a wide range of applications, including roofing, automotive, construction, and manufacturing.
The process of galvanizing GI coils involves several steps:
The steel coils are cleaned to remove any surface contaminants such as oil, grease, or dirt. This is typically done using a chemical cleaning process or by immersing the coils in a degreasing solution.
The coils are then immersed in a pickling solution, usually an acidic bath such as hydrochloric acid or sulfuric acid. This removes any remaining oxides and mill scale from the surface of the steel, preparing it for the galvanizing process.
After Pickling, The Coils Are Rinsed To Remove Any Residual Pickling Solution And Then Immersed In A Flux Solution. The Flux Helps To Prevent Oxidation Of The Steel Surface Before It Is Galvanized And Promotes The Adhesion Of The Zinc Coating.
The prepared steel coils are passed through a bath of molten zinc at temperatures typically around 450°C (850°F). The coils are carefully submerged in the zinc bath, ensuring that the entire surface is coated with a layer of molten zinc. This process is known as hot-dip galvanizing.
Once the steel coils have been galvanized, they are removed from the zinc bath and allowed to cool in the open air or by quenching in water. This solidifies the zinc coating and ensures that it adheres firmly to the surface of the steel.
After cooling, the galvanized GI coils may undergo further processing such as skin-pass rolling or tension leveling to improve surface finish and flatness. They may also be cut to size and coil-wound for shipment to customers.
The galvanizing process creates a durable, corrosion-resistant coating of zinc on the surface of the steel coils, providing long-lasting protection against rust and corrosion in a variety of environments.
The lifespan of GI (Galvanized Iron) coils can vary depending on factors such as the thickness of the zinc coating, the environmental conditions they are exposed to, and the quality of the galvanizing process. However, in general, GI coils are known for their durability and long lifespan.
Under normal conditions, where they are not subjected to extreme corrosion or mechanical damage, GI coils can last for several decades. It's not uncommon for properly galvanized GI coils to remain corrosion-free and structurally sound for 20 to 50 years or even longer.
Factors that can affect the lifespan of GI coils include exposure to corrosive environments such as coastal areas with high salt content in the air, industrial environments with chemical pollutants, or frequent exposure to moisture and harsh weather conditions.
Regular maintenance, such as periodic inspections for damage or signs of corrosion, can help extend the lifespan of GI coils. Additionally, applying protective coatings or sealants as needed can provide extra protection against corrosion and prolong the lifespan of the coils.
Overall, GI coils are valued for their longevity and resistance to corrosion, making them a popular choice for a wide range of applications where durability and reliability are important.
Several factors can influence the price of GI (Galvanized Iron) coils:
The price of GI coils is heavily influenced by the cost of raw materials, primarily steel and zinc. Fluctuations in the prices of these materials due to factors such as supply and demand, tariffs, and currency exchange rates can impact the overall cost of GI coils.
The process of galvanizing involves several steps, including surface preparation, pickling, fluxing, and hot-dip galvanizing. The cost of these processes, including labor, energy, and overheads, can affect the price of GI coils.
3. Zinc Coating Thickness:
The thickness of the zinc coating applied to GI coils can vary depending on the desired level of corrosion resistance and durability. Thicker coatings require more zinc and may result in higher production costs, which can influence the price of GI coils.
Like any commodity, the price of GI coils is influenced by supply and demand dynamics in the market. Increased demand for GI coils, particularly during periods of high construction activity or infrastructure development, can drive prices higher.
GI coils manufactured to higher quality standards or certifications may command a premium price due to their superior performance and reliability. Customers may be willing to pay more for GI coils that meet specific industry standards or regulatory requirements.
The cost of transporting GI coils from the manufacturing facility to the customer's location can impact the overall price. Factors such as distance, mode of transportation, and fuel prices can influence transportation costs and, consequently, the final price of GI coils.
Economic conditions, trade policies, and geopolitical events can also affect the price of GI coils. Trade tariffs, sanctions, or changes in government regulations can lead to fluctuations in prices or supply chain disruptions.
Overall, the price of GI coils is influenced by a combination of factors related to raw materials, manufacturing processes, market dynamics, quality standards, and external economic and political factors. Understanding these factors can help manufacturers, suppliers, and customers make informed decisions regarding the purchase and sale of GI coils.
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The following is a list of frequently asked questions about hot-dip galvanizing. Click on the question to be taken to the answer listed further down on the page. If you do not see your question listed here, try searching using the links above, the search engine on the top right of the page, or contact the AGA for assistance.
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Zinc metal used in the galvanizing process provides an impervious barrier between the steel substrate and corrosive elements in the atmosphere. It does not allow moisture and corrosive chlorides and sulfides to attack the steel. Zinc is more importantly anodic to steel – meaning it will corrode before the steel, until the zinc is entirely consumed.
There are four steps:
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When compared with paint systems, hot-dip galvanizing after fabrication has comparable initial application costs and, almost always, lower life-cycle costs. In fact, the lower life-cycle costs of a hot-dip galvanized project make galvanizing the smart choice for today and tomorrow.
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Hot-dip galvanized steel resists corrosion in numerous environments extremely well. It is not uncommon for galvanized steel to last more than 70 years under certain conditions. To get a good idea of how long your project will last, see the service-life chart.
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The three intermetallic layers that form during the galvanizing process are all harder than the substrate steel and have excellent abrasion resistance.
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Zinc on newly galvanized steel is very reactive and wants to form zinc oxide and zinc hydroxide corrosion products that eventually become the stable zinc carbonate. When galvanized steel is tightly stacked or stored in wet boxes that don’t allow for free flowing air, the zinc forms excessive layers of zinc hydroxide, otherwise known as wet storage stain. Most wet storage stain can be easily removed with a cleaner or nylon brush. To prevent wet storage stain, store galvanized steel indoors or block it so that there is ample free flowing air between each galvanized article.
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The steel chemistry is the primary determinant of galvanized coating thickness and appearance. Continuously cast steel produced by the steel companies has a wide variety of chemistries, thus the different coating appearances.
There are several different additives that galvanizers may put in their zinc kettle to enhance the coating appearance by making it shiny, spangled or matte gray. The appearance of the coating (matte gray, shiny, spangled) does nothing to change the corrosion protection of the zinc coating.
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Constant exposure to temperatures below 390F (200C) is a perfectly acceptable environment for hot-dip galvanized steel. Good performance can also be obtained when hot-dip galvanized steel is exposed to temperatures above 390F (200C) on an intermittent basis.
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Called duplex coatings, zinc and paint in combination (synergistic effect) produce a corrosion protection approximately 2X the sum of the corrosion protection that each alone would provide. Additionally, duplex coatings make for easy repainting, excellent safety marking systems, and good color-coding. Painting over galvanized steel that has been in service for many years also extends the life of the zinc coating.
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Structural steel (plate, wide-flange beams, angles, channels, pipe, tubing) are galvanized to ASTM A 123/A 123M. Fasteners and small parts that fit into a centrifuging basket are galvanized to ASTM A 153/A 153M. Reinforcing steel is galvanized to ASTM A 767/A 767M.
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Depending on the product mix, square feet per ton, and condition of the steel surface, galvanizing is often less expensive on an initial cost basis. However, as with any purchase, the lifetime costs should be considered when making a project decision on the corrosion prevention system to utilize. And, with galvanizing, the life cycle cost, i.e. the cost per year to maintain, is almost always less than a paint system. Paint systems require maintenance, partial repainting and full repainting several times over a 30-year project life. The costs can be staggering, making the decision to paint a costly one in the long run.
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Galvanizers can progressively dip such a fabrication or article of steel. They dip one half in the molten zinc bath, remove it, turn it around or over and immerse the other half in the zinc. This method is often erroneously referred to as ‘double dipping’.
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Hot-dip fasteners generally have about 10 times as much zinc on the surface and are suitable for use in all exterior and interior applications. Zinc-plated fasteners will provide a disappointing performance if used outside, especially when used to connect hot-dip galvanized structural steel members.
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The corrosion rate of zinc and how long it will provide protection is a function of the coating thickness and the amount of corrosive elements in the atmosphere. For example, in rural settings where there is less automotive/truck exhaust and plant emissions, galvanized steel can easily last for 100 – 150 years without maintenance. Industrial and marine locations contain significantly more aggressive corrosion elements such as chlorides and sulfides and galvanized steel may last for 50 – 100 years in those cases. The relationship between coating thickness and atmospheric conditions is contained in a popular graph developed by the AGA. Please see the publication Hot-Dip Galvanizing for Corrosion Protection: A Specifier’s Guide on this web site.
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Yes. Specifically, fabricated steel must allow for easy flow of the cleaning chemicals and molten zinc metal over and through it. This means that gussets must be cropped, holes put in the proper location for draining and venting of zinc from tubular configurations, weld flux removed, overlapping surfaces must be seal-welded, and light gauge material temporarily braced. The details of design and fabrication are contained in the AGA publication The Design of Products to be Hot-dip Galvanized After Fabrication, found on this web site.
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First of all, the variety of things galvanized is broad. Structural steel (angles, channels, wide-flange beams, I-beams, H-beams), grating, expanded metal, corrugated sheets, wire, cables, plate, castings, tubing, pipe, bolts & nuts. The industries that utilized hot-dip galvanized steel range from bridge & highway (reinforcing steel for decks and column concrete, girders, stringers, light and signposts, guardrail, fencing), water & wastewater treatment plants (walkway grating/expanded metal, handrails) architectural (facades, exposed structural steel, lentils), parking garages (reinforcing steel for concrete decks, exposed structural steel columns and barriers), pulp & paper plants (structural steel, walkways, handrail), OEMs (motor housings, electrical cabinets, frames, heat exchanger coils), electrical utilities (transmission towers, distribution poles, substations, wind turbine poles), communication (cell towers), rail transportation (poles, switchgear, miscellaneous hardware), chemical/petro-chemical (pipeline hardware, manufacturing buildings, storage tanks, walkways), recreation (boat trailers, stadiums, arenas, racetracks), and many more.
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The hot-dip galvanizing process can accommodate various different shapes and sizes of steel. Kettle sizes vary in dimensions from one galvanizer to the next. You can view the online listing of all the galvanizers in North America and their kettle sizes.
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Numerous different fabrications for a variety of applications are galvanized each year. To view a list of the different types of products that have been hot-dip galvanized click here.
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The galvanized coating appearance may either be bright and shiny resulting from the presence of an outer layer of pure zinc, or duller, matte gray as the result of the coating’s intermetallic layers being exposed. Performance is not affected. Coating appearance depends on the amount of zinc in the coating.
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Coating thickness depends on the thickness, roughness, chemistry, and design of the steel being galvanized. Any or all of these factors could produce galvanized coatings of non-uniform thickness. Members of the American Galvanizers Association galvanize to ASTM standards, which define minimum average coating thickness grades for various material categories.
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Minimizing potential warpage and distortion is easily done in the project’s design stages by selecting steel of equal thicknesses for use in every separate subassembly that is to be hot-dip galvanized, using symmetrical designs whenever possible, and by avoiding the use of light-gage steel (<1/16” / 1.6 mm). Some structures may benefit from the use of temporary bracing to help maintain their shape and/or alignment.
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Galvanized coatings can be easily and effectively painted, not only for aesthetics but also to extend the structure’s service life. The age and extent of weathering of the galvanized coating dictate the extent of surface preparation required to produce a quality paint system over galvanized steel. ASTM D , Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting, should be consulted for suggested surface preparation methods for galvanized coatings of varying ages.
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As an average, the weight of the article will increase by about 3.5% due to zinc picked up in the galvanizing process. However, that figure can vary greatly based on numerous factors. The fabrication’s shape, size, and steel chemistry all play a major role, and other factors like the black weight, the different types of steel that get welded together, and the galvanizing bath chemistry can also have an effect.
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When galvanized parts are used for slip-critical connections, they must either be brushed, abrasive blasted, or painted with zinc-silicate paint to increase the surface roughness and, thus, the slip factor.
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Rebar is commonly fabricated after galvanizing. In order to minimize the possibility for coating damage, avoid bending the rebar at a radius of more than 8 times its radius. ASTM A 767, Specification for Zinc-Coated (Galvanized) Steel Bars for Concrete Reinforcement, has a table that provides maximum bend diameters for various-sized rebar.
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No, the steel chemistry and surface condition are the primary determinants of zinc coating thickness. Leaving the steel in the molten zinc a little longer than optimal may have one of two effects: 1) it may increase the coating thickness, but only marginally; 2) it may significantly increase the coating thickness and cause a brittle coating.
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“Double-dipping” is the progressive dipping of steel that is too large to fit into the kettle in a single dip. Double-dipping cannot be used to produce a thicker hot-dip galvanized coating.
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The primary reason for vent holes is to allow otherwise trapped air and gases to escape; the primary reason for drain holes is to allow cleaning solutions and molten zinc metal to flow entirely into, over, and throughout the part, and then back into the tank or kettle.
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When stitch-welding is used, there is a possibility of gas release between gaps, which will prevent the galvanized coating from forming in these areas. By leaving at least a 3/32” (2.4 mm) gap between the contacting surfaces, gases are allowed to escape and cleaning solutions and molten zinc are allowed to flow in between the surfaces for a complete and uniform coating.
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“White rust” is the term mistakenly applied to wet storage stain, which actually is a milder corrosion product than white rust. Wet storage stain can be avoided by properly stacking freshly galvanized articles, avoiding unprotected exposure to wet or humid climates, or by using a surface passivation treatment after galvanizing. Wet storage stain typically weathers away once the part is in service. (True “white rust” is most commonly associated with galvanized cooling towers.)
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Yes, but because masking or stop-off materials may not be 100% effective, contact your galvanizer for suggestions.
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There are no known studies to suggest zinc corrosion products cause any harm to the environment. Zinc is a naturally occurring element (25th most abundant element in the earth), and necessary for all organisms to live. It is a recommended part of our diet (RDA 15 mg) and necessary for reproduction. It is used in baby ointments, vitamins, surgical instruments, sunscreens and cold lozenges.
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Zinc is a noble metal and will sacrifice itself (i.e. corrode, give up its electrons and create a bi-metallic couple) to protect most metals. So, it is recommended to insulate galvanized steel so that it doesn’t come in direct contact with dissimilar metals. Rubber or plastic, both non-conductive, are often used to provide this insulation.
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The process steps are similar but the production equipment is very different. After fabrication galvanizing is a more manual process where structural steel (fabricated plate, wide-flange beams, angles, channels, tube, pipe, fasteners) is suspended by wire, chain or hook from crane hoists and immersed in the cleaning solutions and zinc. Continuous sheet galvanizing involves uncoiling sheet, passing it through the cleaning steps and molten zinc bath at speeds up to 500 feet per minute, drying and recoiling.
The uses of after-fabrication galvanized steel are usually exterior in nature because the zinc coating is relatively thick (3.0 – 6 mils, 75 – 150 microns, 1.7 to 3.6 oz/sq. ft.) and will protect steel from corrosion in most atmospheric conditions for 50 to 100 years. Galvanized sheet is suitable for interior applications because of the relatively thin coating (0.45 oz on each side), unless it is painted after galvanizing.
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G90 is a grade of galvanized sheet produced to ASTM A653. It has 0.90 oz/sq. ft. of zinc overall or 0.45 oz/sq. ft. per side. A60 is also a grade, has 0.30 oz/sq. ft. per side, and has been annealed after galvanizing to produce a surface that promotes good adhesion of paint.
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In order for zinc to develop its protective patina of zinc carbonate that is very stable and non-reactive, it requires a wetting and drying cycle like that produced by nature. Salt spray tests keep the zinc wet and essentially wash the zinc corrosion products off as they develop, inflating the corrosion rate of zinc. This lab test is not reflective of real-world performance of zinc coatings.
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Constant exposure to temperatures below 390 F (200 C) is a perfectly acceptable environment for hot-dip galvanized steel. Good performance can also be obtained when hot-dip galvanized steel is exposed to temperatures above 390 F (200 C) on an intermittent basis.
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No, the steel chemistry and surface condition are the primary determinants of zinc coating thickness. Leaving the steel in the molten zinc a little longer than optimal may have one of two effects: 1) it may increase the coating thickness, but only marginally; 2) it may significantly increase the coating thickness and cause a brittle coating.
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There is no such thing as cold galvanizing. The term is often used in reference to painting with zinc-rich paint. Galvanizing by definition means a metallurgical reaction between zinc and iron to create a bond between the zinc and the steel of approximately psi. There is no such reaction when zinc-rich paints are applied and the bond strength is only several hundred psi.
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