Hollow section steel is one of the most widely used structural materials in the world, yet many buyers are not entirely sure what it is, how it differs from other steel profiles, or which type suits their application. Whether you are sourcing for a shipbuilding project, an offshore platform, or a construction job, understanding hollow sections helps you make faster, smarter decisions without relying on guesswork.
This guide covers everything you need to know: what hollow section steel is, the different types available, common applications, and how to choose the right section for your project.
What is hollow section steel?
Hollow section steel is a type of structural steel profile with a hollow interior running along its full length. Unlike solid bars or open profiles such as I-beams and angle iron, hollow sections are completely enclosed, which gives them a distinctive combination of strength, stiffness, and relatively low weight.
They are manufactured by forming flat steel strip into a tube shape and welding the seam, or by hot-rolling steel into seamless tubular profiles. The result is a clean, closed profile that performs well under a wide range of structural loads, including compression, bending, and torsion.
Hollow sections are sometimes referred to as structural tubes or hollow structural sections (HSS), and they are available in a broad range of sizes, wall thicknesses, and steel grades to suit different load requirements and environments.
What are the different types of hollow section steel?
There are three main types of hollow section steel, each defined by its cross-sectional shape:
- Circular Hollow Sections (CHS): Round tubes with a circular cross-section. These offer excellent resistance to torsion and are commonly used in applications where loads come from multiple directions, such as columns, handrails, and offshore structures.
- Rectangular Hollow Sections (RHS): Flat-sided profiles with a rectangular cross-section. These are easier to connect and fabricate than circular sections, making them popular in frames, supports, and architectural steelwork.
- Square Hollow Sections (SHS): A specific type of rectangular section where all four sides are equal. These are a practical choice when uniform load distribution and clean aesthetics are both important.
Each type has its own structural characteristics, and the right choice depends on the loads involved, the connection method, and the practical demands of the application.
What is hollow section steel used for?
Hollow section steel is used across a wide range of industries because of its structural efficiency and versatility. Common applications include:
- Structural frameworks and building construction: Columns, beams, and trusses in commercial and industrial buildings frequently use hollow sections because they carry loads efficiently while keeping weight down.
- Maritime and offshore structures: Offshore platforms, ship structures, and marine infrastructure rely on circular hollow sections in particular, due to their resistance to multi-directional forces and their performance in harsh, corrosive environments.
- Mechanical and industrial equipment: Hollow sections are used in machine frames, conveyor systems, and support structures where strength and dimensional accuracy are critical.
- Cranes and lifting equipment: The high strength-to-weight ratio of hollow sections makes them well suited for crane booms and other load-bearing structures where minimising dead weight matters.
- Architectural and infrastructure projects: Bridges, canopies, and public structures often feature hollow sections for both structural and visual reasons.
The breadth of applications is one reason hollow section steel is such a core product for procurement professionals working in maritime, offshore, and construction sectors alike.
What’s the difference between hollow section steel and solid bar or open sections?
The key difference comes down to how each profile distributes material relative to its structural performance.
A solid bar places material throughout its entire cross-section. This makes it very strong in tension and compression, but the material at the centre contributes relatively little to bending or torsional resistance. For structural applications, this means a solid bar often uses more material than necessary to achieve the same performance as a hollow section.
Open sections such as I-beams, channels, and angles are efficient in bending along one axis but are weaker in torsion and under loads from multiple directions. They are also harder to seal against corrosion, which is a significant limitation in maritime and offshore environments.
Hollow sections distribute material at the outer edges of the profile, where it does the most structural work. This makes them highly efficient under bending, compression, and torsion, while also being easier to protect against corrosion because there are no open flanges or exposed edges to seal.
For applications where weight, multi-directional loading, and durability all matter, hollow sections typically offer the best overall performance.
What steel grades are used for hollow sections?
Hollow sections are produced in a range of steel grades depending on the required strength, weldability, and environmental resistance. The most common grades include:
- S235 and S275: General structural grades suitable for standard construction and fabrication work where high strength is not the primary requirement.
- S355: A higher-strength structural grade widely used in construction, offshore, and heavy engineering applications. It offers a good balance of strength, toughness, and weldability.
- ASTM A500 and A501: American standard grades for structural hollow sections, commonly specified in projects following US codes or for clients in North America.
- Stainless steel grades (such as 316L): Used where corrosion resistance is critical, particularly in marine environments, chemical processing, or food-grade applications.
Choosing the correct grade matters not just for structural reasons but also for compliance. Many projects in maritime, offshore, and industrial sectors require material certificates and traceability documentation, so working with a supplier who can provide the right certifications alongside the product is essential.
You can explore the full range of steel products and grades available from Marine Steel to find the specification that fits your project.
How do you choose the right hollow section for your project?
Selecting the right hollow section comes down to a few key factors:
Load type and direction: If loads come from multiple directions or torsion is a concern, circular hollow sections are usually the stronger choice. For connection and fabrication ease, rectangular or square sections are often more practical.
Wall thickness: This determines the section’s resistance to buckling and its overall load-bearing capacity. Thicker walls are needed for high-stress applications, while lighter wall thicknesses work well for secondary structures or architectural elements.
Steel grade: Match the grade to the structural demands and any applicable standards or certifications required by the project or classification society.
Environment: In corrosive environments such as offshore platforms or marine structures, consider whether additional surface treatment, galvanizing, or a stainless steel grade is appropriate.
Connection method: How the section will be welded, bolted, or joined to other components can influence the profile choice. Rectangular and square sections are generally easier to connect using standard fabrication techniques.
If you are not sure which section fits your application, a knowledgeable supplier can help you work through the requirements quickly, saving time and avoiding costly specification errors.
How Marine Steel helps you source hollow sections with confidence
At Marine Steel, we stock a broad range of hollow section steel across circular, rectangular, and square profiles, in multiple grades and dimensions. Our team understands the time pressure that comes with maritime, offshore, and construction procurement, and we are set up to respond quickly with the right product and documentation.
Here is what we offer:
- Extensive stock of hollow sections in Rotterdam and Houston for fast turnaround
- Multiple steel grades, including structural grades and stainless steel options
- Material certificates and traceability documentation as standard
- Custom tube processing, including cutting to size, bending, drilling, and surface treatment
- A single point of contact who thinks along with you, not just fulfils the order
Whether you need standard sections off the shelf or custom-processed tubes to a specific drawing, we handle it all in one place. Contact our team to discuss your requirements and receive a fast, accurate quotation.
