Cast Iron vs. Cast Steel Mooring Bollards: Which One Should You Choose?

Are you struggling to decide between cast iron and cast steel for your next mooring bollard project? Making the wrong choice can compromise safety and lead to long-term issues.

The best choice between cast iron and cast steel bollards depends on your project's specific needs. Cast steel offers superior ductility, meaning it will bend before breaking under extreme load. Ductile cast iron, on the other hand, provides higher yield strength and better wear resistance.

Choosing the right material is a critical first step. But there's much more to consider, from the specific grade of the material to the manufacturing process and even the supplier's capabilities. These details can make or break the quality and safety of your final installation. To make an informed decision, you need to understand the nuances of each material and how they perform in the real world.

Which is better, cast iron or cast steel?

Picking a winner between cast iron and cast steel¹ feels impossible. Each has its champions, and the technical data can be confusing, leaving you unsure which is truly superior.

Neither material is inherently "better" overall; the ideal choice depends on the application. Cast steel excels in ductility² and impact toughness³, making it safer for critical applications. Ductile cast iron⁴ boasts higher strength and better corrosion resistance⁵, which can be advantageous in certain environments.

When I work with clients like Tommy, we often focus on the two most common materials available from quality suppliers in China: Ductile Cast Iron⁶ (specifically, grade QT450-10⁷) and Cast Steel (grade ZG230-450⁸). Historically, the industry started with gray iron, which was brittle. We then moved to the much-improved cast steel and ductile iron options we have today. The key difference lies in how they react under stress. Cast steel's main advantage is its ductility², or elongation. It can deform significantly before it fractures, which provides a visual warning of overload. Ductile iron has higher yield strength⁹ but is less ductile.

To make it clearer, here is a simple breakdown:

Property	Cast Steel (ZG230-450)	Ductile Cast Iron (QT450-10)	What it means for you
Yield Strength	≥ 230 MPa	≥ 300 MPa	Ductile iron resists permanent bending better.
Tensile Strength	≥ 450 MPa	≥ 450 MPa	Both have similar ultimate breaking points.
Ductility (Elongation)	≥ 20%	≥ 10%	Cast steel visibly bends more before it fails.
Impact Resistance	Higher	Lower	Cast steel is better at absorbing sudden shocks.

Ultimately, for most port projects, owners and engineering firms can be flexible. After discussing the pros and cons, they usually accept either ZG230-450 or QT450-10 because both are reliable choices when sourced from a reputable manufacturer.

What are the different types of mooring bollards?

Are you wondering what your options are beyond the material itself? With so many different shapes and names, it can be hard to know which bollard type fits your specific needs.

Mooring bollards come in various designs to suit different mooring styles, vessel sizes, and wharf layouts. Common types include the T-Head¹⁰, Horn (or Staghorn), Kidney, and Double Bitt, each offering unique advantages for securing mooring lines efficiently and safely.

The design of a bollard is just as important as the material it's made from. The shape determines how easily and securely ropes can be handled, especially under heavy loads or at sharp angles. For example, I remember a project where the client initially specified a simple single bitt bollard, but after reviewing the mooring analysis¹¹, we realized a Horn-type bollard would be much safer. It allowed for lines from two different vessels without the risk of them slipping over each other. This is a common part of my discussion with a client like Tommy; we need to ensure the selected shape works for the planned operations. The choice isn't just about aesthetics; it's about operational safety and efficiency for the port.

Here’s a look at the most common types:

Common Bollard Designs

• T-Head / T-Bollard: A very popular and versatile design. Its shape is excellent for handling steep mooring line angles and can accommodate lines from multiple vessels.
• Horn / Staghorn Bollard: The "horns" are perfect for securing lines quickly and preventing them from accidentally releasing, especially in areas with significant tidal change.
• Kidney / Cleat Bollard: A low-profile, simple design that is common for smaller vessels and marinas. It's economical and effective for moderate loads.
• Double Bitt / Twin Horn Bollard¹²: These are robust bollards, often used in high-traffic commercial ports. They provide high holding capacity and can handle multiple mooring lines simultaneously.

Each of these designs is engineered to distribute the load from the mooring line into the concrete dock structure safely. The selection process should always consider the vessel types, mooring patterns, and environmental forces at the specific berth.

What are mooring bollards made of?

Are you feeling overwhelmed by material specifications like ZG230-450 or QT450-10? These technical names can seem complex, making it difficult to understand exactly what you are buying.

Modern mooring bollards are primarily made from either Cast Steel (like ZG230-450) or Ductile Cast Iron (like QT450-10). These materials are chosen for their high strength, durability, and ability to be cast into the complex shapes required for bollard designs.

The material you choose is the foundation of the bollard's performance. As I mentioned, most projects today use either cast steel or ductile iron. But it's important to understand that the supplier landscape is not what you might expect. Most of the suppliers you'll find, including my company, are not the foundries themselves. Bollards are a relatively low-volume, niche product, so large-scale foundries rarely focus on them. Instead, suppliers are typically either marine steel structure fabricators who have their own advanced coating facilities, or they are integrators who manage a supply chain of foundries and specialized painting workshops. This is a critical point because the anti-corrosion treatment is extremely important. The process involves sandblasting the raw casting and then applying a marine-grade paint¹³ system according to standards like ISO 12944¹⁴. Most foundries simply don't have the professional painting workshops required to do this properly. This supply chain structure is key to getting a quality final product.

What is the biggest disadvantage of cast iron?

Worried about cast iron's reputation for being brittle? This common concern could make you hesitant to select it, even when it might be a suitable and cost-effective option for your project.

The biggest disadvantage of cast iron in general is its brittleness. However, it's crucial to distinguish between old gray cast iron and modern Ductile Cast Iron⁶. While gray iron can fracture without warning, ductile iron (like QT450-10) offers significantly improved ductility².

Let's be very clear here. When people talk negatively about "cast iron," they are often thinking of gray cast iron⁴, which is not suitable for modern, high-load mooring bollards. The game changed with the development of ductile cast iron. By adding magnesium to the molten iron, we change the graphite structure from sharp flakes (which create stress points) to rounded spheres. This small change makes a massive difference in performance. Ductile iron is not as ductile as cast steel¹—it will stretch about half as much before failing—but it is far from brittle. It has a higher yield strength⁹ than its cast steel counterpart (ZG230-450), meaning it can handle a higher load before it starts to permanently deform. For many standard mooring applications where sudden, extreme impacts are less likely, ductile iron is an excellent and often more economical material choice, providing a great balance of strength and reliability.

What are the disadvantages of cast steel?

Thinking cast steel is the perfect solution with no downsides? This assumption might lead you to overlook potential issues like higher costs or susceptibility to corrosion if not properly treated.

The main disadvantages of cast steel are its lower corrosion resistance⁵ compared to ductile cast iron and potentially higher material cost. It absolutely requires a high-performance coating system to protect it from the harsh marine environment, which adds to the overall expense.

While cast steel's ductility is a major safety advantage, it doesn't come without trade-offs. The first is its performance in a marine environment. On its own, steel corrodes much faster than iron. This is why the surface preparation and coating process are non-negotiable and must be done perfectly. Any flaw in the paint job, like improper surface blasting or incorrect paint thickness, will quickly become a rust spot, compromising the integrity of the bollard over time. The second point is cost. Generally, producing cast steel is more expensive than producing ductile iron. While the price difference can vary based on the market, it's a factor you need to consider in your project budget. For a client like Tommy, balancing the superior impact performance of cast steel against the higher initial cost and strict reliance on the coating system is a key part of the decision-making process.

What is the best material for bollards?

Are you still searching for a single "best" material for all situations? This quest for a simple answer can lead to overlooking the most important factor: the specific needs of your project.

There is no single "best" material for all bollards. The best material is the one that is correctly specified for the project's loads, environmental conditions, and safety requirements, and is sourced from a high-quality, verifiable manufacturer, complete with proper anti-corrosion treatment.

This leads me to a serious issue in our industry. Because bollards are covered in thick layers of paint, it is nearly impossible for a buyer to visually inspect the quality of the underlying casting. The quality level among foundries varies enormously. Some may use subpar raw materials or have poor casting techniques¹⁵, resulting in internal defects like porosity or cracks. These defects are completely hidden by the paint. A low-quality bollard might look identical to a high-quality one. The danger is that bollards are designed with a high safety factor¹⁶, so they won't fail under normal daily use. This allows low-price, low-quality products to enter the market. A buyer might think they got a great deal, but they have installed a hidden safety risk on their jetty. A sudden, high load from a storm or an operational error could cause this flawed bollard to fail catastrophically. This is why the "best" material is one that comes with trust, transparency, and traceability from your supplier.

Conclusion

In summary, choosing between cast steel and ductile iron depends on balancing ductility against strength. The most critical factor, however, is ensuring high-quality casting and coating from a reputable supplier.

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