THIS CONTAINER MUST BE REPAIRED ONLY WITH CORTEN STEEL
On containers intended for transporting goods around the world, you will often find a prominent warning:
“Warning – THIS CONTAINER MUST BE REPAIRED ONLY WITH CORTEN STEEL”
This notice is not merely a recommendation, but a fundamental safety and technical rule that significantly affects the lifespan, safety, and value of the container.
Using Corten steel in repairs is key to maintaining:
- Structural integrity
- Corrosion resistance
- Compliance with international standards in the transport industry
In this glossary entry, you will find an explanation of the physical and chemical principles of Corten steel, the reasons for this strict warning, proper repair procedures, comparison with common carbon steel, and the broader context in the container shipping industry.
Corten Steel – A Unique Material for Containers
History and Chemical Composition
Corten steel, also known as weathering steel, is a special alloy steel developed in the USA in the 1930s for railway cars and later standardized for shipping containers. The name CORTEN is derived from two key properties:
- COR (corrosion resistance)
- TEN (tensile strength)
Chemical Composition (example of typical Corten steel for containers):
| Element | Typical Content (%) |
|---|---|
| Carbon (C) | up to 0.12 |
| Manganese (Mn) | up to 0.50 |
| Phosphorus (P) | 0.07–0.15 |
| Sulfur (S) | max 0.03 |
| Silicon (Si) | 0.25–0.75 |
| Chromium (Cr) | 0.40–0.65 |
| Nickel (Ni) | 0.40–0.65 |
| Copper (Cu) | 0.25–0.55 |
| Iron (Fe) | remainder |
Thanks to this precise combination of alloying elements, Corten steel acquires unique properties that predestine it for the extremely demanding environment typical of shipping containers.
Scientific Principle: Protective Patina
Unlike common steel, where corrosion is a destructive process, Corten steel uses controlled corrosion to create:
- Stable protective oxide layers (patina)
- Self-regenerating capabilities
- Slowing of further corrosion to a negligible level
How the protective layer works:
- Forms through alternating moisture and dryness
- The layer is dense, compact, and firmly adherent
- Does not flake off like common rust on carbon steel
- After damage (for example, after repair or scratching), the patina regenerates itself
Significance for containers:
- Significantly extends lifespan: in demanding environments (salt water, moisture, UV radiation), Corten steel has a lifespan of up to 25 years, while common steel undergoes destructive corrosion within 6–10 years.
- Reduces maintenance and coating needs: most containers are not painted with anti-corrosion paints because protection is ensured by the material’s properties.
Mechanical Properties and Use in Containers
| Property | Corten Steel (e.g., S355J2W) | Standard Carbon Steel (A36) |
|---|---|---|
| Tensile Strength | > 485 MPa | approx. 400–550 MPa |
| Hardness | High | Medium |
| Weldability | Good (special wires) | Excellent (common wires) |
| Corrosion Resistance | Excellent (protective patina) | Poor (progressive rust) |
| Lifespan | 15–25+ years | 6–10 years |
| Maintenance | Minimal | Regular coatings |
Why this matters:
- Containers are often stacked up to 9 stories high – Corten provides sufficient strength for these extreme loads.
- Resistance to mechanical stress – ship transport, rail transport, road transport.
Container Repairs – Why ONLY Corten Steel
Fundamental Dangers of Improper Repairs
Using steel other than Corten steel (e.g., common carbon steel) results in:
- Galvanic corrosion – at the contact point of two different metals and moisture, an electrochemical cell forms where the less noble metal (common steel) corrodes more rapidly.
- Rapid breakdown of the repaired area – common steel will rust through much faster than Corten, endangering the container’s tightness and cargo safety.
- Loss of certification and container value – an improperly repaired container may not pass inspection or be insured.
Technological Procedure for Proper Repair
- Selection of the correct material:
- Always use sheet/panel from the same class of Corten steel (e.g., S355J2W, ASTM A588, etc.)
- Special welding materials:
- Use of low-hydrogen electrodes or wires compatible with Corten steel (e.g., AWS E8018-W, E7018-W).
- Surface preparation:
- Thorough cleaning and degreasing of the repair area, removal of rusty parts down to healthy material.
- After repair:
- Allow a new protective patina to form in the air; it is not advisable to cover with common paint.
Expert Recommendations (according to IICL and ISO standard 1161):
- Every intervention must be documented and approved by a responsible person.
- Repairs should be performed only by qualified welders with experience in container repairs.
Corten Steel in the Container Industry
Standardization and Global Significance
- Since the 1990s, Corten steel has been the only accepted material for manufacturing standard ISO containers.
- Ensures compatibility within the global intermodal system (ships, trains, trucks).
- Enables long-term recycling – containers can be 100% recycled into new steel at the end of their lifespan.
Ecological and Economic Benefits
- Long lifespan = fewer containers need to be manufactured, lower carbon footprint.
- Minimal maintenance = lower consumption of protective coatings and VOC emissions.
- Recyclability = no loss of quality during reprocessing.
Overview of Technical Parameters of Corten Sheets for Containers
| Parameter | Typical Values |
|---|---|
| Container wall thickness | 1.6–2.0 mm |
| Container frame thickness | 3.0–5.0 mm |
| Density | 7.85 g/cm³ |
| Minimum yield strength | 355 MPa (S355J2W) |
| Lifespan in aggressive environment | 20–25 years |
Warning in Practice: Digitalization and Repair Monitoring
- From 2025 onwards, the industry expects widespread implementation of digital repair protocols.
- Each container will have a digital record of maintenance, repairs, and materials used.
- Use of incorrect steel will lead to container disqualification from transport and loss of warranty.
Frequently Asked Questions and Myths About Corten Steel in Containers
Myth: Any steel is fine as long as it’s strong enough?
Fact: No. Using steel other than Corten steel leads to rapid destruction of the repaired area and loss of container value.
Myth: Patina is just “rust” and has no significance?
Fact: The protective patina is essential for the container’s long lifespan and minimal maintenance.
Myth: Repair with common steel is cheaper?
Fact: In the short term, yes, but in the long term it leads to significantly higher costs for repeated repairs, downtime, and risk of cargo loss.
The warning “THIS CONTAINER MUST BE REPAIRED ONLY WITH CORTEN STEEL” is a fundamental rule of safety and efficiency in container shipping.
Corten steel, through its chemistry, self-protective capability, and high strength, made possible the emergence of modern global logistics.
Failure to follow this rule leads to material failure, financial losses, and safety risks.
Proper repair always with Corten = long lifespan, safety, value!
Czech Republic, Pardubice 
WITHOUT SHIPPING 
