What is tube steel, and what are its common names?
Tube steel is hollow structural steel formed into cylindrical or rectangular shapes. It is commonly called steel tubing, structural tubing, or hollow structural sections (HSS). In industrial applications, it is also referred to as steel tubes, mechanical tubing, or simply “tubing” when the context is clear.
Terminology can vary depending on the industry and application. In construction, you will often hear it called structural steel tubing or HSS. Maritime and offshore industries frequently use terms such as steel tubes or marine-grade tubing. The manufacturing sector typically refers to it as mechanical tubing, especially when it is used for machinery components or hydraulic systems.
Steel tubes serve countless applications across industries, from structural frameworks in buildings to fluid-transport systems on ships. The hollow design provides an excellent strength-to-weight ratio while allowing for the internal flow of liquids, gases, or cables when needed.
What’s the difference between steel tube and steel pipe?
Steel tubes are manufactured for structural and mechanical applications with precise dimensions and wall thicknesses, while steel pipes are designed primarily for fluid transport, with specifications focused on pressure ratings and flow capacity.
The key distinction lies in how they are measured and specified. Steel tubes are dimensioned by their outside diameter (OD) and wall thickness, ensuring consistent external dimensions for structural connections and mechanical fits. Steel pipes, however, are specified by nominal pipe size (NPS) and schedule ratings such as Schedule 40 or Schedule 80, which indicate wall thickness and pressure capability.
Manufacturing processes also differ. Tubes typically undergo more precise forming and finishing processes to achieve tighter dimensional tolerances. Pipes prioritize internal surface quality and pressure resistance over external precision. This difference makes tubes ideal for structural frameworks, machinery components, and architectural applications, while pipes excel in plumbing, process systems, and fluid handling.
In practice, the terms are sometimes used interchangeably, especially in general conversation. However, when specifying materials for critical applications, understanding these distinctions helps ensure you get the right product for your specific requirements.
What are the main types of steel tubing available?
The main types of steel tubing include structural tubing (round, square, and rectangular HSS), mechanical tubing for machinery applications, and specialized variants such as stainless steel tubing and high-pressure hydraulic tubing.
Structural steel tubing forms the backbone of construction and framework applications:
- Round structural tubing – Offers uniform strength in all directions, ideal for columns and supports
- Square tubing – Provides flat surfaces for easy connections and mounting
- Rectangular tubing – Combines directional strength with efficient material use
Mechanical tubing serves precision applications in manufacturing and machinery. This category includes drawn-over-mandrel (DOM) tubing for high-precision requirements and cold-finished tubing for improved surface quality and dimensional accuracy.
Material grades add another layer of classification. Carbon steel tubing offers strength and affordability for general applications. Stainless steel tubing provides corrosion resistance essential in marine and chemical environments. Alloy steel tubing delivers enhanced properties for demanding conditions such as high temperatures or extreme pressures.
Our steel tubes inventory covers these major categories, ensuring maritime, offshore, and industrial clients can source complete packages from a single supplier.
How is steel tubing classified and specified?
Steel tubing is classified by dimensions (outside diameter and wall thickness), material grade (such as ASTM specifications), manufacturing method (welded or seamless), and end finish (plain end, beveled, or threaded).
Dimensional specifications follow standardized systems. Outside diameter typically ranges from small fractional sizes up to 20 inches or more for large structural applications. Wall thickness is specified in decimal inches or gauge numbers, with thicker walls providing higher strength and pressure ratings.
Material classifications use established standards such as ASTM (American Society for Testing and Materials) specifications. Common grades include:
- ASTM A500 – Standard for cold-formed welded structural tubing
- ASTM A513 – Specification for electric-resistance-welded carbon steel mechanical tubing
- ASTM A269 – Covers seamless and welded austenitic stainless steel tubing
- ASTM A106 – For high-temperature service applications
Manufacturing methods significantly impact performance characteristics. Seamless tubing offers superior pressure capability and uniform properties but costs more than welded alternatives. Electric-resistance-welded (ERW) tubing provides good strength at a lower cost, while drawn-over-mandrel processing achieves the tightest tolerances.
Certifications and documentation accompany properly specified tubing, including material test reports (MTRs) and compliance certificates. These documents prove the material meets specified standards, which is crucial for maritime and offshore applications where safety regulations are stringent.
How Marine Steel helps with steel tube specification and supply
We provide comprehensive steel tube solutions that eliminate the complexity of sourcing from multiple suppliers. With over 11 years of experience serving maritime, offshore, and industrial sectors, we understand the time pressure and technical requirements our clients face.
Our steel tube services include:
- Complete inventory, from small mechanical tubing to large structural sections up to 20 inches
- ASTM-certified materials with proper documentation and material test reports
- Custom processing, including cutting, bending, and surface treatments
- Fast turnaround from our Rotterdam and Houston locations
Whether you need standard structural tubing for a construction project or specialized marine-grade materials for offshore applications, we work with you to ensure the specifications are correct. Because vessel delays can cost thousands per day, we maintain extensive stock and provide rapid quotations to keep your projects moving. Contact our team to discuss your steel tube requirements and experience the difference of working with a true one-stop shop.
