When you’re choosing PPGI (pre-painted galvanized iron) and PPGL (pre-painted Galvalume), finding the right specification is a decisive factor. Both PPGI and PPGL offer a wide range of grades, offering different properties suitable for various roofing, construction, and automotive applications.
PPGI and PPGL steel specifications are a broad topic with several categories. In this article, we explain the most important pre-painted steel specifications in a buyer-focused way. This includes specifications mainly related to paint system composition, coating thickness and weight, sheet width, corrosion performance, durability, surface finish, and mechanical properties.
Structure of Pre-Painted Steel and Specification Categories
To understand detailed PPGI and PPGL specifications clearly, you must first know how prepainted steel is actually structured. Pre-painted steels are not just materials; they are multi-layer engineered systems. To study, we can mainly separate prepainted steel into three layers:
- Base Metal – mostly cold-rolled steel coils or sheets
- Metallic Coating – zinc for galvanized steel and aluminum-zinc (AluZinc) for Galvalume
- Paint System – non-metallic coating systems such as PE, SMP, and PVDF
Here is a concise breakdown of important coated steel specifications related to the above three layers.
Layer | PPGI (Galvanized) | PPGL (Galvalume) | Related Specifications |
Base Metal | Cold-rolled steel | Cold-rolled steel substrate | Base metal thickness (BMT) Base metal grade (DX51D, SGCC, S250–S550) Mechanical strength Formability |
Metallic Coating | Zinc (Z) coating | Aluminum-zinc alloy (55% Al, 43% Zn, 1.5% Si) | Coating weight/grade (G60, G90, Z100, Z275, AZ70, AZ150) Corrosion resistance Environmental Durability |
Paint System | Primer + topcoat (PE, SMP, HDP, PVDF) | Primer + topcoat (PE, SMP, HDP, PVDF) | Type of paint system Coating thickness (μm) Color specifications (RAL) UV resistance Surface finish (matte, glossy, textured) |
Pre-Painted Steel Thickness Specifications (BMT, TCT)
When it comes to PPGI and PPGL thickness, we can also break it down into the above three layers: base metal thickness, metallic coating thickness, and paint system thickness. Out of them, base metal thickness (BMT) and total coating thickness (TCT) are the values you’ll see in standard coated-steel specification sheets.
Base Metal Thickness (BMT)
This is the thickness of the steel substrate (usually cold-rolled steel). It generally ranges from 0.12 mm to 1.2 mm and can be increased up to 2.00 mm upon customization requirements. The thickness of the base metal is the primary contributor to the overall strength, stiffness, and load-bearing capacity of the final product.
Some of the common industrial applications for different thickness ranges of steel are given below.
BMT Range | Applications |
0.12 – 0.30 mm | Light-duty panels, decorative panels, ceiling panels, and other non-structural applications |
0.30 – 0.60 mm | Roofing sheets, wall cladding, partition panels, and general building applications |
≥0.60 – 1.20 mm | Industrial panels, shutter panels, stronger formed sections, and applications requiring higher rigidity and durability |
1.20 – 2.00 mm | Customized heavy-duty applications, project-specific industrial or structural uses |
Total Coating Thickness (TCT)
Total coating thickness (TCT) indicates the sum of the thicknesses of both the metallic coating (zinc or Aluzinc) and the paint system.
- Metallic Coating Thickness: This is the main corrosion protection layer of the product. The thickness of this layer is not measured in mm but in grams per square meter (g/m²). This is the quantity that is represented by the pre-painted steel grades as well.
- Thickness of the Paint System: This is the thickness of both the topcoat and the backcoat. This is usually measured in microns. Generally, the topcoat is around 15-25 μm and the back coat is around 5 – 10 μm.
The sum of BMT and TCT gives you the total thickness of the final pre-painted steel product. If your goal is to improve corrosion protection, you should improve the components in TCT.
Standard Dimensions of Pre-Painted Steel Coils
When considering standard steel coil dimensions, thickness, width, and inner diameter are the values usually provided in many specification sheets. Since we already discussed thickness, let’s study more on width and the inner diameter.
Standard Widths of Pre-Painted Steel Coils
In the stock form, pre-painted steel usually comes as coils formed by rolling the sheets. In PPGI and PPGL coil specifications, width is the distance between the two edges of the metal strip.
The most common standard widths of pre-painted steel coils are 600 mm, 762 mm, 914 mm, 1000 mm, 1200 mm, 1219 mm, and 1250 mm. You might not be able to source all the standard widths from a single manufacturer, but these are the popular grades available in the global market. Also, many manufacturers today also provide customized options such as slitting, cut-to-length sheets, custom widths, and narrow coil supply.
For roofing and construction, buyers usually decide the width including the final effective cover after corrugation and profiling. Also, when choosing coils for fabrication work, you must pick a sufficient strength to reduce scrap, especially during shearing and stamping.
Inner Diameters of Pre-Painted Steel Coils
Inner diameter (ID) is the diameter of the hollow center of the steel coil. The most common standard diameters are 508 mm and 610 mm. This is an important specification because the coil ID must match your decoiling, handling, and processing equipment. It’s critical for safe loading, smooth uncoiling, and efficient production.
Standard Grades Related to PPGI and PPGL
Here, both the base metal grade and the metallic coating weight grades are equally important.
Base Metal Grades
Base metal grade is the primary factor that provides the strength and formability to your product. In PPGI and PPGL, the two most common standard systems are EN grades such as DX51D, S250GD, and S350GD, and JIS grades such as SGCC.
- DX51D and SGCC usually mean general forming grades. These are suitable when you need to bend, roll, form, or shape easily.
- S250GD and S350GD are structural grades. The number shows the minimum yield strength in MPa (e.g., S250GD has 250 MPa minimum yield strength).
Metallic Coating Grades / Galvanized and Galvalume Grades
Metallic coating grade indicates the weight of the protective coating applied to the steel surface. The G series and Z series are the most common grade systems for galvanized steel. Galvalume grades are usually indicated with the AZ series.
Steel Type | Grade System | Example Grades | Meaning | Unit System |
Galvanized (PPGI) | Z series | Z100, Z180, Z275 | Z = Zinc coating. | g/m² (metric) |
Galvanized (PPGI) | G series | G60, G90 | G = Galvanized coating | oz/ft² (imperial) |
Galvalume (PPGL) | AZ series | AZ50, AZ70, AZ150 | AZ = Aluminum-Zinc alloy coating | g/m² (metric) |
In all these series, the number always indicates the total coating mass. A higher number means better corrosion resistance and durability. Also, you must know that some grades, such as G90 and Z275, are equivalent in performance.
Paint Coating System Specifications for PPGI and PPGL
The paint coating system is the outermost layer applied right after the zinc/AluZinc coating. This layer acts as a protective barrier for the steel, preventing exposure to moisture, salt, and pollutants.
Types of Paint Systems: PE, SMP, HDP, and PVDF
PE (Polyester) coating is the most common and cost-effective option. It offers good flexibility, appearance, and cost efficiency for general roofing and cladding applications.
SMP (Silicone Modified Polyester) is an improved version of the PE coating. It provides improved weather resistance, gloss retention, and UV performance compared to PE.
HDP (High Durability Polyester) is also a further modified version of polyester. It can provide higher durability and longer outdoor life than PE and SMP, without reaching premium coating cost levels.
PVDF (Polyvinylidene Fluoride) is the grade system with the highest protection and also the highest cost. PVDF provides excellent UV resistance, superior color retention, low chalking, and long-term performance. This is the ideal coating system for coastal and high-exposure industrial environments.
Coating Structure and Thickness Specifications
According to the structure, there are two types of paint systems defined:
- 2/1 coating system: two coating layers on the exposed front side and one layer on the back side.
- 2/2 coating system: two coating layers on both the front and back sides
When you mainly need the appearance and higher performance of the front side, you can choose a 2/1 coating system to reduce the cost. But in more demanding environments (coastal, industrial, and high humidity), you’ll have to use a 2/2 system with increased coating thickness for improved long-term corrosion protection.
Color Specifications
Color is important not only for appearance but also for UV performance. Colors of pre-painted steel are usually indicated using the RAL system. RAL is a standardized color coding system that supports:
- Exact shade matching
- Color consistency between batches
- Clear communication between buyer and supplier
As an example, RAL 9003 represents signal white, RAL 3005 means wine red, and RAL 5015 means sky blue.
Surface Finish Specifications
Surface finish is also equally important for appearance and usability in service. The most common finishes are glossy, matte, textured, wrinkled, embossed, patterned, and wood-grain or printed finishes.
For roofing and panels, glossy surfaces are preferred. Also, many modern architectural designs use matte finishes for aesthetics. Textured, embossed, and patterned finishes are mainly used for decorative purposes, especially when you need to reduce the visibility of scratches.
How to Read a Full PPGI or PPGL Coil Specification
A complete coated-steel specification looks like the following. It tells the buyer all the required specifications he should know before purchasing.
0.50 mm x 1000 mm, AZ150, S350GD, PVDF, RAL 9003, matte finish
As an example, you can decode each component of the above specification as follows.
- 0.50 mm – thickness (BMT or BMT+TCT, depends on supplier’s convention)
- 1000 mm – width
- AZ150 – aluminum-zinc coating mass
- S350GD – substrate grade / strength level
- PVDF – paint system
- RAL 9003z – color code
- matte finish – final surface appearance
This level of clean and detailed specifications provides you many advantages, including reduced disputes, improved quote accuracy, and helps you meet your exact requirements easily.
Contact Us for Custom PPGI or PPGL Coil Specifications
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