HR Sheets in Racking Systems
Hot Rolled (HR) sheets are widely used in the design and fabrication of industrial racking systems (such as warehouse storage racks, pallet racks, and shelving systems). Their role is mainly structural, providing load-bearing strength and durability.
Where HR Sheets are Used in Racking Systems
- Base Plates & Brackets
- HR sheets (6–12 mm thick) are cut and fabricated into base plates and brackets.
- Function: Distribute load to the floor, anchor uprights, and provide stability.
- Upright Frames & Columns
- HR sheets are rolled into angles, channels, or box sections.
- High strength grades (IS 2062 E250/E350 or ASTM A36/A572) are used for heavy load capacity.
- Beam Connectors
- HR sheets are fabricated into gussets and connector plates.
- Ensure strong joints between vertical uprights and horizontal beams.
- Shelving Panels (for Heavy Duty Racks)
- Thick HR sheets (2.5–6 mm) are used for decking or shelving in heavy-load racks.
- Sometimes reinforced with corrugation or ribs for extra load-bearing strength.
- Cross Bracing & Stiffeners
- HR sheets cut into flat bars or strips are used as cross bracing.
- Maintain rigidity and prevent sway of tall rack structures.
Why HR Sheets are Preferred
- High Load Capacity – Can handle the static and dynamic loads in warehouses.
- Weldability – Easy to fabricate into custom shapes for racking.
- Durability – Resistant to impact from forklifts or shifting loads.
- Cost-Effective – Less expensive compared to cold rolled sheets for heavy structures.
Grades Commonly Used
- IS 2062 E250/E350 – Structural quality steel for uprights, beams, base plates.
- ASTM A36 / A572 – Structural HR sheets for heavy-duty racking.
- EN 10025 S235/S275 – European grades for structural racking systems.
Thickness Range in Racking
| Component | Typical HR Sheet Thickness |
|---|---|
| Base plates | 6 – 12 mm |
| Uprights (formed sections) | 2.5 – 6 mm |
| Beams (formed from HR sheet sections) | 3 – 6 mm |
| Shelves (flat or ribbed panels) | 2 – 6 mm |
| Braces & gussets | 2 – 5 mm |
Metal Pretreatments Recommended for HR Sheets
Hot Rolled (HR) sheets have a rough surface with mill scale (iron oxides) and sometimes oil/grease contamination. Because of this, they require more intensive pretreatment compared to cold rolled (CR) sheets before painting, powder coating, or galvanizing.
Stepwise Pretreatment Sequence for HR Sheets
- Degreasing / Alkaline Cleaning
- Removes oil, grease, and dirt.
- Chemicals: Alkaline cleaners with surfactants (NaOH, sodium carbonate, phosphate-based).
- Method: Spray or dip.
- Derusting / Descaling (Pickling)
- Removes mill scale (FeO, Fe₂O₃, Fe₃O₄) formed during hot rolling.
- Chemicals:
- Acid pickling: HCl (10–15%) or H₂SO₄ (10–20%) at 50–70°C.
- Eco-friendly options: Phosphoric acid + additives, chelating agents.
- In some cases, mechanical descaling (shot blasting, wire brushing) is combined with chemical treatment.
- Water Rinsing
- Thorough rinsing with fresh water after acid pickling.
- Sometimes followed by DM water rinse for critical applications.
- Surface Conditioning (Optional)
- To activate and prepare surface for conversion coating.
- Chemicals: Titanium or zirconium salts, proprietary conditioners.
- Phosphating / Conversion Coating
- Provides adhesion base + corrosion resistance.
- Types used for HR sheets:
- Iron Phosphate – economical, thin layer (for indoor/non-critical).
- Zinc Phosphate – crystalline, heavy-duty corrosion protection (automotive, appliances).
- Manganese Phosphate – wear resistance (for engineering parts).
- Passivation / Sealing
- Improves corrosion resistance, prevents underfilm rusting.
- Chemicals: Chromates, non-chrome passivation (zirconium, silane-based).
- Drying
- Hot air drying at 100–120°C.
- Ensures no retained moisture before painting/powder coating.
Recommended Pretreatment Combinations for HR Sheets
| Application | Pretreatment Process |
|---|---|
| General fabrication (indoor use) | Degreasing → Derusting → Iron Phosphate → Passivation |
| Automotive / Structural | Degreasing → Pickling → Zinc Phosphate → Passivation |
| Engineering parts (wear resistance) | Degreasing → Pickling → Manganese Phosphate + Oil |
| Powder Coating | Degreasing → Pickling → Zinc Phosphate → Passivation → Drying |
| Galvanizing (Pre-treatment) | Degreasing → Pickling (HCl/H₂SO₄) → Fluxing → Galvanizing |
⚠️ Key Note: For HR sheets, acid pickling is mandatory to completely remove mill scale before any phosphate or paint coating. Without scale removal, adhesion failures and underfilm corrosion occur.
Types of Paints Recommended for Racking Systems (Made from HR Sheets)
Racking systems (warehouse racks, pallet racks, shelving) require coatings that combine mechanical durability, corrosion resistance, and aesthetic appeal. The choice depends on whether the racks are for indoor use, heavy-duty industrial environments, or outdoor storage.
1. Powder Coatings (Most Preferred for Racks)
- Epoxy Powder Coating
- High mechanical strength, abrasion resistance.
- Smooth finish, excellent adhesion.
- Best for indoor warehouse racks (no UV exposure).
- Epoxy-Polyester Hybrid Powder Coating
- Balanced chemical resistance + UV resistance.
- Good for general-purpose indoor racking.
- Pure Polyester Powder Coating
- UV-stable, weather-resistant.
- Recommended for outdoor racking systems (open yards, ports).
2. Liquid Paints (Conventional Systems)
- Epoxy Paints (2K Epoxy)
- Primer + topcoat system.
- Excellent corrosion and chemical resistance.
- Ideal for heavy-duty racks in corrosive/chemical environments.
- Polyurethane Paints (PU Paints)
- Glossy, UV-resistant, scratch resistant.
- Used as a topcoat over epoxy primer.
- Suitable for racks in exposed environments.
- Alkyd Enamel Paints (Economical)
- Single-component, air drying.
- Moderate durability, only for low-cost indoor racks.
3. Specialized Coatings
- Zinc-Rich Epoxy Primer + PU Topcoat
- For maximum corrosion resistance.
- Recommended in coastal / high humidity storage yards.
- Nano-ceramic or Silane Pre-treatment + Powder Coating
- Eco-friendly, improves powder adhesion & life.
- Now common in modern racking system manufacturers.
Recommended Coating Systems (Summary Table)
| Environment | Recommended Paint System |
|---|---|
| Indoor warehouses | Epoxy powder coating / Epoxy-Polyester hybrid powder |
| Outdoor storage yards | Polyester powder coating / Epoxy primer + PU topcoat |
| Heavy-duty / chemical plants | Zinc phosphate pretreatment + Epoxy primer + Epoxy/PU topcoat |
| Low-cost economy racks | Alkyd enamel air drying paints |
✅ Best Industry Practice:
- Pretreatment of HR sheets (degreasing + pickling + phosphating) before coating.
- Powder coating is preferred due to high durability, uniform finish, and eco-friendly process.
Salt Spray Resistance Parameters for Racking Systems (HR Sheet + Coating)
Salt spray testing (ASTM B117 / ISO 9227) is widely used to evaluate the corrosion resistance of racking system coatings (powder-coated or liquid-coated). Since racking systems are exposed to humidity, warehouse conditions, and sometimes outdoor storage, the required resistance varies by application environment.
Recommended Parameters
| Application Environment | Coating System | Salt Spray Test (ASTM B117) Requirement |
|---|---|---|
| Indoor warehouses (normal humidity, no chemical exposure) | Iron phosphate pretreatment + Epoxy/Polyester powder coating (60–80 µm) | > 500 hours without red rust |
| Heavy-duty indoor / industrial (higher humidity, forklift traffic) | Zinc phosphate pretreatment + Epoxy primer (20–30 µm) + PU/Polyester powder topcoat (60–80 µm) | 750–1000 hours without red rust |
| Outdoor / Semi-outdoor storage (UV, rain, coastal exposure) | Zinc phosphate pretreatment + Zinc-rich epoxy primer (30–40 µm) + PU / Polyester powder topcoat (70–100 µm) | 1000–1500 hours without red rust |
| Coastal / Harsh chemical environment | Zinc phosphate or nano-ceramic pretreatment + Zinc-rich epoxy primer (40 µm) + PU / Super durable polyester powder coat (80–120 µm) | 1500–2000 hours without red rust |
Key Notes
- Pretreatment is critical – HR sheets must undergo pickling + phosphating before coating.
- Film thickness – Minimum 60–80 µm for powder coating, higher (100–120 µm) for outdoor.
- Edge coverage – Sharp rack edges must be rounded or sealed, since corrosion starts at edges.
- Testing standard – ASTM B117 (Neutral Salt Spray), some OEMs also demand Cyclic Corrosion Tests (Prohesion ASTM G85) for stricter evaluation.
- Performance indicator – No red rust at specified hours; white rust (zinc corrosion products) may be acceptable if zinc-rich primers are used.
👉 For global racking manufacturers, a benchmark is ≥ 1000 hours NSS (Neutral Salt Spray) for high-quality racks.
Corrosion Resistance Standards for Racking Systems
(Salt Spray Test Benchmarks from International Standards & Guidelines)
1. European Standards (EN / FEM)
- EN 15512 – Steel static storage systems – Adjustable pallet racking systems – Principles for structural design.
- Requires durability against corrosion but refers to coating suppliers’ performance specs.
- FEM 10.2.02 (Federation Europeenne de la Manutention)
- Recommends coating systems tested for ≥ 500 hrs (indoor) and ≥ 1000 hrs (outdoor/semi-outdoor) in salt spray (ASTM B117 / ISO 9227).
2. American Standards (ANSI / RMI)
- ANSI MH16.1 (RMI Standard) – Specification for the design, testing, and utilization of industrial steel storage racks.
- Refers to coating performance requirements defined by the user’s environment.
- General industry benchmark: ≥ 750 hrs for indoor racks, ≥ 1000 hrs for outdoor racks.
3. ISO Standards
- ISO 9227 – Corrosion tests in artificial atmospheres (Salt Spray Test).
- Widely used to qualify racking coatings.
- Coating manufacturers align with:
- Indoor storage: 500–750 hrs NSS.
- Outdoor/severe: 1000–1500 hrs NSS.
4. OEM / Industry Benchmarks
Many global rack manufacturers and paint suppliers (AkzoNobel, Jotun, PPG, Asian Paints Industrial) recommend:
- Indoor racks: Iron phosphate + epoxy/polyester powder → 500–750 hrs NSS.
- Outdoor racks: Zinc phosphate + epoxy primer + polyester/PU topcoat → 1000–1500 hrs NSS.
- Harsh/coastal racks: Zinc-rich epoxy primer + PU/polyester powder → 1500–2000 hrs NSS.
Comparison Table
| Standard / Guideline | Indoor Rack Requirement | Outdoor Rack Requirement | Extreme/Coastal |
|---|---|---|---|
| FEM 10.2.02 (Europe) | ≥ 500 hrs NSS | ≥ 1000 hrs NSS | Case-specific (OEM defined) |
| ANSI MH16.1 (USA) | ≥ 750 hrs NSS | ≥ 1000 hrs NSS | ≥ 1500 hrs (OEM/OEM spec) |
| ISO 9227 (General Ref.) | 500–750 hrs NSS | 1000–1500 hrs NSS | 1500–2000 hrs NSS |
| Industry/OEM Practice | 500 hrs (minimum) | 1000 hrs (standard) | 1500–2000 hrs (premium) |
✅ Takeaway:
For world-class racking systems, a minimum of 1000 hours NSS is expected for outdoor use, and 1500–2000 hours for coastal/chemical conditions. Indoor racks can be validated at 500–750 hrs.
Here’s a consolidated reference table of standards for HR sheets, pretreatment, coatings, and salt spray testing in racking systems:
Reference Standards for Racking Systems
| Standard / Guideline | Scope / Title | Relevance to Racking Systems |
|---|---|---|
| IS 1079 (India) | Hot rolled carbon steel sheet and strip | Base material specification for HR sheets used in racks |
| IS 2062 (India) | Hot rolled medium & high tensile structural steel | Structural steel grade for uprights, beams, base plates |
| IS 2002 (India) | Steel plates for pressure vessels/boilers | Boiler quality plates; sometimes referenced for high-toughness HR sheets |
| IS 3589 (India) | Steel pipes for water/sewage | HR plates rolled into tubular rack sections |
| IS 3618 (India) | Phosphate treatment of iron and steel | Pretreatment standard for phosphating before painting |
| ASTM A36 (USA) | Carbon structural steel | Common HR sheet grade for structural applications |
| ASTM A1011 (USA) | Hot-rolled sheet, high-strength low-alloy | HR sheets with higher strength for racks |
| ASTM A572 (USA) | High-strength low-alloy structural steel | Used for heavy-duty racking components |
| ASTM A516 (USA) | Pressure vessel plates, carbon steel | Boiler-quality steel reference |
| ASTM B117 (USA) | Salt spray (fog) testing | Benchmark test for coating corrosion resistance |
| ASTM G85 (USA) | Modified salt spray (cyclic corrosion tests) | Advanced testing for high-performance racks |
| ISO 9227 (Global) | Corrosion tests in artificial atmospheres – Salt spray tests | International reference for NSS testing of coatings |
| ISO 12944 (Global) | Corrosion protection of steel structures by paint systems | Paint system design for different environments (indoor/outdoor/coastal) |
| ISO 8501/8502/8503 (Global) | Surface preparation standards | Surface cleaning and profile inspection for coating |
| EN 10025 (Europe) | Hot rolled products of structural steels | European equivalent for HR sheet grades |
| EN 15512 (Europe) | Steel static storage systems – Design principles | Design code for pallet racking systems |
| FEM 10.2.02 (Europe) | Federation Europeenne de la Manutention guideline | Corrosion protection & coating recommendations for racks |
| ANSI MH16.1 / RMI (USA) | Industrial steel storage racks – Design, testing & use | US racking system design and durability guideline |
| JIS G3101 (Japan) | Rolled steels for general structure | Japanese reference for HR steels |
| DIN 17100 (Germany) | Structural steel grades | German HR steel standard |
✅ This table connects base material standards, pretreatment standards, and corrosion testing standards with their direct relevance to racking systems.
