Instruction Manual for Pre-Painted Steel Coil (PPGI/PPGL)

What Are PPGI and PPGL Coils?

Pre-painted steel coil, commonly abbreviated as PPGI (pre-painted galvanized iron) and PPGL (pre-painted galvalume), is a flat steel product coated with an organic paint system on a metallic-coated substrate. The substrate is usually hot-dip galvanized steel (GI) or zinc-aluminum coated steel (GL, 55% Al-Zn), and the topcoat is applied on continuous coil coating lines. The result is a corrosion-resistant, decorative material widely used in building roofing, wall cladding, home appliances, and light steel structures.

Selection Precautions

Selection should follow the end use and the atmospheric environment. Corrosivity classes are generally divided into rural, urban, industrial, and marine atmospheres, and the actual service conditions (acid, alkali, salt, humidity, UV exposure, and ventilation) determine the required coating system:

Rural atmosphere: standard polyester (PE) systems are usually sufficient.

Urban atmosphere: PE or SMP systems with adequate film thickness.

Industrial atmosphere: HDP (high-durability polyester) or PVDF systems with higher corrosion resistance.

Marine atmosphere: PVDF or special anti-corrosion systems are recommended.

Reference standards for the coating and substrate include GB/T 12754, EN 10169, and ASTM A755.

Storage, Transportation, and Handling

Store coils in a dry, ventilated warehouse, away from organic solvents and corrosive media such as acids, alkalis, and salts.

Keep the original packaging intact; do not stack coils directly on wet floors.

Protect the coil from rain, snow, fog, and condensation during transport; cover the truck load with waterproof sheeting.

Avoid bumps, extrusions, and sharp contact that can damage the paint film and cause edge rust.

Use soft slings and lifting beams; never drop or drag coils.

Processing and Installation Precautions

For one project, use material from the same manufacturer and the same batch to avoid color difference on the facade.

Process at an ambient temperature above 7 degrees Celsius to prevent paint film cracking during bending and roll forming.

Check surface quality, adhesion, and film thickness during processing; stop and investigate if defects appear.

Remove metal burrs from cut edges and apply edge protection or touch-up paint where the cut edge is exposed.

During installation, walk on support zones only and avoid dragging profiles across each other.

Quality Inspection Points

Common Mistakes to Avoid

The most frequent failures are caused by condensation storage (coil edge rust), dragging coils on rough floors, cutting at low temperature, mixing batches with different coating lots, and exposing cut edges without touch-up in marine environments. Each of these can be avoided with the storage and processing controls described above.

Frequently Asked Questions

Q: What is the difference between PPGI and PPGL?
PPGI uses a hot-dip galvanized (zinc) substrate, while PPGL uses a zinc-aluminum (galvalume, typically 55% Al-Zn) substrate. PPGL generally offers better corrosion resistance and heat reflectivity, while PPGI is more common and cost-effective.

Q: How long can pre-painted steel coil be stored?
With proper indoor storage and intact packaging, 6 to 12 months is typical; longer storage increases the risk of condensation and edge staining, especially in humid climates.

Q: Can pre-painted steel be cut with a plasma cutter?
Guillotine shears, slitters, and fine-blade saws are preferred. High-heat cutting such as plasma or oxy-fuel damages the paint film along the cut edge and requires complete re-coating.

Q: Why does color difference occur between batches?
Paint batches, coating line conditions, and substrate surface texture can vary slightly. Ordering the full project quantity from one production batch minimizes visible difference.

Q: What temperature is safe for bending and roll forming?
Most paint systems should be processed above 7 degrees Celsius; below this temperature the film becomes brittle and may crack at bends. In cold weather, pre-warm the coil or schedule processing indoors.

Q: What should be checked when a pre-painted steel coil is delivered?
Verify the coil weight, width, thickness and coating mass against the mill certificate, then inspect for edge damage, scratches, indentations, wrap tightness and any dampness under the packaging. Confirm the protective film and the batch number, and reject or segregate coils showing white rust, blistering or colour mismatch, because paint defects present on delivery can limit both processing yield and the appearance of the finished panel.