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Frequently Asked Questions About Corten Weathering Steel

What is Corten®?

COR-TEN® is a trademarked name owned by U.S. Steel.

COR-TEN® steel is becoming more popular by roll formed product end-users. Its unique look and naturally oxidizing finish make it especially desirable for many architectural projects. Weathering steel, best-known under the trademark COR-TEN® steel, is a group of steel alloys which were developed to obviate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years. Weathering steel has increased resistance to atmospheric corrosion when compared to other steels. COR-TEN® resists the corrosive effects of rain, snow, ice, fog, and other meteorological conditions by forming a coating of dark brown oxidation over the metal, which inhibits deeper penetration and negates the need for painting and costly rust-prevention maintenance over the years. In simple terms the steel is allowed to rust and that rust forms a protective coating that slows the rate of future corrosion.

A588 OR A606-4
Both A588 and A606-4 are weathering steel specifications and have similar chemical compositions that meet the ASTM G101 of 6.0 or higher on the atmospheric corrosion-resistance index. The difference in our products is:

A606-4 is considered weathering steel sheet with thicknesses beginning at 22 Gauge and thicker available up to 3/16”. We stock A606-4 in flat sheets, coil, and panels.

A588 is available in steel plate and starts at 3/16” thickness and increases up to 5” thickness. A588 is a high strength low alloy plate used for structural applications such as buildings and bridges.

Dual Mill Certifications of ASTM A606-4 and ASTM A588 are provided for thicknesses 14 Gauge and thicker.

Can A606-4/A588/A847 be welded?

You can weld weathering steel using the same flux combinations so that the tensile strength of the deposited weld metal (welding rod or wire) is consistent with the tensile strength of the base metal (weathering steel). Typical tensile strength of based metal (weathering steel) is 68-78 KSI. We would advise only welding A606-4 or A588 together. Welding to other metals can lead to a dissimilar metal reaction with A606-4 or A588.

Corten Roofing vs. Bare Cold Rolled Roofing

Bare Cold rolled steel is used as a less expensive option to A606 Type 4 ( Commonly referred to as Corten ). Bare Cold Rolled is widely manufactured for a variety of different purposes including metal roofing and costs less. Both of these panels are completely different. However, they look similar in appearance. After installation and exposure to normal weather the surface of the panel develops a gorgeous rustic finish and texture. Corten contains copper, chromium, manganese, and nickel which makes this material more expensive. Corten resists the corrosive effects of rain, snow, ice, fog, and other meteorological conditions by forming a coating of dark brown oxidation over the metal, which inhibits deeper penetration and negates the need for painting and costly rust-prevention maintenance over the years. Corten will last longer and would be more desirable in harsh climates.

WHAT Flat Sheet/Flat Stock Thickness Do I need?

Since flat sheets can be used in a variety of applications and are considered a DESIGN-BUILD application, we recommend consulting with the designer or engineer of your project to determine the gauge/thickness required. Once the gauge/thickness is determined please use our online chart to review and submit an online quote for the gauge/thickness required.


Coil is used typically to roll form into panels. Flat sheets are used in various applications, including landscaping, architectural buildings and multiple other applications.
Since most individuals do not have the proper equipment to load/unload/process coils-we typically recommend flat sheets. Unless you are able to roll form panels from coil, we recommend you use flat sheets. Always make sure to follow proper safety and lifting protocols when manually handling material.


Flat sheets (also referred to as flat stock) are construction materials usually purchased for design and build projects. Unlike a common pre-formed metal panel, there are no specific installation instructions. Installation of flat sheets will vary depending on your specific need. We recommend consulting with the installer, designer or engineer of your project to determine the best installation method.

Can we apply a clear coat to A606-4/A588 Weathering Steel?
If you choose to clear coat the material, do it after the A606-4/A588 has a good rust/patina set into the steel. If you do it prior to a good rust/patina, then it is very likely your clear coat will take off the rust.

If you add a clear coat to the A606-4/A588 material it will likely change the surface color due to the additives in your clear coat.

We do not have a specific recommendation on clear coatings. We recommend you check with your local paint supplier and get their recommendation as they are the coating experts.


In general do NOT use dissimilar metals with COR-TEN®.
Galvanized, Galvalume®®®®®®®®®®®®®®®®, and zinc should NOT come into contact with COR-TEN®.
Stainless steel is compatible with COR-TEN®.


A606-4 and A588 steel arrives UNRUSTED and will rust with naturally exposure to the weather.

Can I buy COR-TEN®?

No, COR-TEN® is not available. What is available is steel in an A606-4 or an A588 finish. If somebody tells you that they are supplying you COR-TEN® they are almost certainly unaware of their own product. Simply ask them if their steel was purchased from U.S. Steel. If the answer is " No " or " I don't know " it's almost certainly NOT COR-TEN®. When someone needs COR-TEN® they are normally referring to A606 Type 4 or A588. If you want COR-TEN® this will be the best available option. Weathering steels, such as ASTM A588, A242, A606 and COR-TEN® exhibit superior corrosion resistance over regular carbon steel as a result of the development of a protective oxide film on the metals surface which slows down further corrosion. A606-4 steel is available in metal roofing/siding panels, standing seam panels, flat sheets, and coil form.


There are no warranties for A606-4 or A588 Steel.


Yes, rust runoff will likely stain the surrounding areas.


Screws are furnished in a Stainless Steel/Painted Koko Brown.

How do I get Cor-ten® Steel to rust?

Nothing. This material will rust on its own if left exposed to the weather. Getting the material wet will increase the speed in which it rust.


Weathering Steel never completely stops rusting. The weathering process occurs after the panel is installed. It eventually decreases and from that point on the finish acts as a protective coating for the base metal. This protective coating essentially stops the corrosion. Laboratory analysis of the rust film have shown that the alloying elements in the steel, particularly copper, chromium, and nickel produced insoluble compounds that clogged the pores at the rust/steel interface, thereby ending the regeneration.

What is the lifespan of Cor-ten® steel?

There is no definitive answer to this question. It depends on the environment and the way in which it was installed. Many projects using bare cold rolled and Corten products were installed in excess of forty years ago and there are no problems. Corten will have a longer life-span than bare cold rolled steel. One of the most common problems is using a light gauge steel. Using a heavier gauge steel is the most important thing you can do to increase the longevity of Corten steel.


COR-TEN® steel requires alternating wet and dry cycles to form a properly adhered protective layer. Areas that have salt laden air, high rainfall, humidity, or persistent fog are typically not the proper environment for COR-TEN®.

What does it cost to deliver Cor-ten Steel?

It can be shipped anywhere in the country very inexpensively on one of our route trucks. The price depends on the job location, length and weight of panels. Just request a quote and we will quote the delivery price.


The original COR-TEN® received the standard designation A 242 ("COR-TEN® A") from the ASTM International standards group. Newer ASTM grades are A 588 ("COR-TEN® B") and A606 for thin sheet. All alloys are in common production and use.


It is recommended to use a high temperature underlayment. We do not sell underlayment. Contact an expert in underlayment for further details.

What is Corten Tube and pipe?

If you are looking for Corten Steel (also known as weathering steel) tube or pipe it is not available. We can offer the equivalent and it is produced under ASTM A847 (American Society Testing Materials). ASTM A847-HSS-Hollow Structural Steel is a cold-formed high strength-low alloy steel that is welded and shaped into square tube, rectangular tube and pipe.

Will the ASTM A847 HSS tube and pipe rust the same as the sheets that I am getting?

Yes, the same alloys are used in all weathering steel products when they are produced at the mill. There is a special group of alloys that are used when produced at the mill. Copper, manganese, silicon and nickel are just a few of the alloys used. This group of alloys is very different than standard steel and, when combined, these alloys exhibit superior corrosion resistance over regular carbon steel. The result is a protective oxide film on the metal’s surface which slows down future corrosion. This alloy mix creates a beautiful rust (patina) when exposed to the elements of nature.

How do I know I got HSS Weathering Steel Tube or Pipe vs standard HSS-Hot Roll Tube or Pipe?

There are a couple of ways to make sure you received “the real” weathering steel aka Corten. One is to get a mill certification from your supplier at the time of shipment. The other is the visual test.

The visual test is to look for the orange color when the material patinas. Standard hot roll will rust, just not the same as weathering steel. Why? ASTM A847 HSS tube and pipe has copper & manganese that creates a beautiful orange rust patina. If you get the orange color-then most likely you got Weathering Steel, but we would recommend you get a mill certification just to be sure.

Western States Metal Roofing will always provide a mill certification at time of shipment when required.

Can I weld the Corten (HSS-Weathering Steel tube and pipe)? If so, how do that and will it look the same?

Yes, you can weld ASTM A847 HSS Tube or Pipe. You can weld weathering steel using the same flux combinations so that the tensile strength of the deposited weld metal (welding rod or wire) is consistent with the tensile strength of the base metal (weathering steel). Typical tensile strength of based metal (weathering steel) is 68-78 KSI. We advise only welding A606-4 or A588 together. Welding A606-4 or A588 to other metals can lead to a dissimilar metal reaction.

Please note, there isn't a specific welding wire for ASTM A847 HSS tube and pipe. We advise using the above flux combinations and using your local welding supply company for welding materials. Since the weld is not comprised of weathering steel, the weld will rust over time and the patina from the weathering steel tube will blend together nicely.

What are the typical applications for the ASTM A847 HSS tube and pipe?

Typical applications for ASTM A847 HSS tube are bridges, hand rails, and any other applications where high-strength low-alloy (HSLA) and superior corrosion resistance steel is required. It can also be used in your landscape and architectural applications where no future maintenance of material is required. The pipe can be used in fence applications, artistic structures and many other applications where you desire strength in the steel, longevity and visually pleasing.

You indicate that it is weldable. Will the weld look and rust the same?

You can weld weathering steel using the same flux combinations so that the tensile strength of the deposited weld metal (welding rod or wire) is consistent with the tensile strength of the base metal (weathering steel). Since the deposit of the welded area is not the same material as A606-4, the weld will take a bit longer to rust. Once the A606-4 oxidizes with the weld it will blend together in a nice orange-brown oxide finish.

How long will it take to develop the patina finish?

There is no specific timeline on how long the “full” patina finish will take to develop. There are multiple factors when it comes to getting the orange-brown oxide finish. Those factors are the environment, moisture, weather, and humidity. A606-4 develops the patina faster when it can go through wet and dry cycles. When A606-4 gets wet the orange-brown oxide finish will develop. When A606-4 dry’s from the moisture the “natural rust” will begin to set into the steel. If you need it to develop faster there are some natural solutions that when applied over and over will assist you in developing that beautiful patina.

Where does that orange color finish come from in A606-4?

The orange-brown finished color in A606-4 comes mainly from the copper content. With 5% copper in the alloy mix, the copper immediately comes to the top as the patina process begins. Additionally, the copper along with manganese, silicon and nickel content in A606-4 creates that protective layer as the material continues to patina. Standard carbon steel will rust but it will not have the beautiful colors that come from A606-4.