JIS G 3125 SPA-H steel plate is a hot-rolled atmospheric corrosion resistant steel, commonly classified as weathering steel (Corten steel).
Compared with conventional carbon steel (with or without copper addition), SPA-H steel exhibits significantly superior resistance to atmospheric corrosion in most outdoor environments.
When exposed to air and moisture, SPA-H steel forms a dense and adherent rust layer (patina) on its surface. This patina acts as a protective barrier, slowing down further corrosion and eliminating the need for additional coatings such as paint or galvanizing.
Standard of JIS G 3125 SPA-H Steel Plate
Standard: JIS G 3125
Description: Hot rolled steel plates, sheets, and strips for superior atmospheric corrosion resistance
Country / Authority: Japan Industrial Standards (JIS)
Chemical Composition of JIS G 3125 SPA-H Steel Plate
| Grade | C ≤ | Si | Mn ≤ | P | S ≤ | Cu | Cr | Ni ≤ |
|---|---|---|---|---|---|---|---|---|
| SPA-H | 0.12 | 0.20–0.75 | 0.60 | 0.070–0.150 | 0.035 | 0.25–0.55 | 0.30–1.25 | 0.65 |
Note:
The alloying elements Cu, Cr, and Ni are the key contributors to SPA-H's weathering performance, enabling stable patina formation and improved long-term corrosion resistance.
Mechanical Properties of JIS G 3125 SPA-H Steel Plate
| Grade | Plate Thickness | Yield Strength | Tensile Strength | Elongation |
|---|---|---|---|---|
| SPA-H | ≤ 6.0 mm | ≥ 355 MPa | ≥ 490 MPa | ≥ 22% |
| SPA-H | ＞ 6.0 mm | ≥ 355 MPa | ≥ 490 MPa | ≥ 15% |
These mechanical properties make SPA-H suitable for load-bearing and structural applications, while also meeting architectural performance requirements.
Application of JIS G 3125 SPA-H Steel Plate
JIS G 3125 SPA-H weathering steel plate is widely used in industrial, infrastructure, transportation, and architectural projects where long-term atmospheric corrosion resistance and structural reliability are required.
With a minimum yield strength of 355 MPa and tensile strength of at least 490 MPa, SPA-H is suitable for load-bearing structures such as bridges, building frames, and façade support systems, where it provides stable mechanical performance while reducing the need for protective coatings.
In power generation and industrial facilities, SPA-H plates are commonly applied in air preheaters, economizers, and exhaust duct structures, as they withstand humid, temperature-fluctuating environments and form a dense protective patina that slows material loss.
The steel is also extensively used in railway carriages, rolling stock, and transportation equipment, where its resistance to rain, snow, and atmospheric pollutants helps extend service life and minimize repainting cycles.
In addition, SPA-H is a proven material for containers and outdoor structural panels, offering reliable corrosion protection during long-term exposure to varying climates. Its predictable weathering behavior, low maintenance requirements, and long service life make SPA-H an economical and durable choice for projects designed for decades of outdoor operation.
Steel Category of JIS G 3125 SPA-H
SPA-H belongs to the Corten steel / weathering steel category.
"Cor-Ten" is a trademark originally developed by United States Steel, referring to steel that combines corrosion resistance (Cor) and tensile strength (Ten).
Weathering steels like SPA-H were developed to reduce or eliminate the need for protective coatings, relying instead on their naturally forming rust layer for protection.
Specification of JIS G 3125 SPA-H Steel Plate
Thickness: ≤ 16 mm
Width: ≤ 2000 mm
Length: Customized according to project requirements
Equivalent Grades of JIS G 3125 SPA-H Steel Plate
| Japan (JIS) | EU (EN) | Germany (DIN/WNr) | France (AFNOR) | UK (BS) | China (GB) | ISO |
|---|---|---|---|---|---|---|
| SPA-H | S355J0WP (1.8945) | 9CrNiCuP324 | E36WA3 | WR50A / WR50B / WR50C | 09CuPCrNi-A | Fe355W-1A |
Q1: What is SPA-H Corten steel?
SPA-H is a Japanese standard weathering steel grade specified in JIS G 3125. It contains alloying elements such as copper, chromium, and nickel, which allow it to form a dense protective rust layer on the surface. This patina significantly slows down further corrosion and improves long-term durability in atmospheric environments.
Q2: What are the main advantages of SPA-H weathering steel?
The key advantages of SPA-H steel include excellent atmospheric corrosion resistance, high strength, and low maintenance cost. Unlike ordinary carbon steel, SPA-H does not require frequent painting or coating, which helps reduce lifecycle costs while maintaining a unique natural appearance.
Q3: Where is SPA-H Corten steel commonly used?
SPA-H steel is widely used in bridges, building structures, architectural façades, railway carriages, containers, air preheaters, and economizers. It is especially suitable for outdoor structures exposed to changing weather conditions for long periods.
Q4: Does SPA-H steel need painting or surface treatment?
In most outdoor applications, no additional painting is required. SPA-H naturally forms a stable rust layer after exposure to the atmosphere. However, in highly corrosive environments (such as marine or high-salt areas), additional surface protection may be recommended to extend service life.
Q5: How long does it take for SPA-H steel to form a stable patina?
Under normal atmospheric conditions, SPA-H steel typically forms a stable protective patina within 6 to 24 months
