What Is Tube Steel?

Navigating the world of metal manufacturing can be confusing, but if you’re wondering what tube steel is, we can help. Special Metal Alloys UK Ltd is an esteemed International Trading House. We are authorised sales representatives and distributors of a few of the most prominent producers across the globe, primarily dealing with nickel alloys and stainless steel products.

In its simplest form, tube steel is a type of steel that is used in the manufacture of hollow metal tubes. It is made from hot-rolled steel that has been shaped into a hollow tube by rolling and welding it. Tube steel is heat-treated to increase its strength and durability, making it suitable for use in a variety of applications such as structural supports, frames, and pipes. Tube steel can be used for both commercial and residential applications, making it an ideal material for construction projects.

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Why should tube steel be used?

Tube steel, with few exceptions, is highly resistant to corrosion, rust, and chemicals and requires little maintenance. If used for structural purposes with a larger diameter, it is highly durable and has a high tensile and compressive strength.

What are the different types of steel called?

To standardise steel grades internationally, the SAE has designated 9 major classifications, Carbon steel; nickel steel; nickel-chromium steel; molybdenum steel; chromium steel; tungsten steel; nickel-chromium-molybdenum steel; and silicon-manganese steel. Each of these classes is subdivided into grades according to type and composition.

In the steel industry, for practical purposes four main types of steel are distinguished, carbon steels, alloy steels, stainless steels, and tool steel.

What material is tube steel?

Depending on the application, steel tubing can be manufactured from a variety of raw materials, like iron, carbon, manganese, vanadium, and zirconium. The specific type of tube stainless steel will be categorised according to its chemical composition, crystalline structure, and method of manufacturing.

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Is stainless steel a form of tube steel?

One of the most common types of tube steel is stainless steel alloys, mainly of the austenitic, ferritic, martensitic, or a combination called duplex types, each with different grades, quality, durability, and temperature resistance.

If this sounds confusing, let us unpack some of these concepts first.

Austenitic stainless steel:

Its primary crystalline structure is austenite and it contains at least 10.5% nickel, chromium, carbon, nitrogen and a variety of other elements.
Chromium makes it highly resistant to corrosion and nitrogen is a stiffening agent.
Some of the most important qualities distinguishing austenitic stainless steel include its excellent toughness, resistance to extremely low temperatures, is not hardened by heat, essentially non-magnetic, and can be welded.
Its main applications are in heat exchangers, chemical processing, and cryogenic applications.

Ferritic stainless steel:

Its primary crystalline structure is a body-centred cubic crystal and it contains iron, between 8 and 10% nickel, 10 to 30% chromium, and less than 0.2% carbon.
It has good heat and corrosion resistance, in particular to chloride corrosion.
Its mechanical properties and low-temperature toughness are generally less than austenitic stainless steel.
It is non-hardenable by heat and only marginally hardenable by cold rolling, but highly formable and can be welded.
Its main applications are in the automotive industry, water-heating appliances, and industrial machinery.

Martensitic stainless steel:

Its primary crystalline structure is a body-centred tetragonal crystal and it contains between 10.5 and 18% chromium, nickel, manganese, molybdenum, and up to 1.2% carbon, adjusted in a way to obtain the optimal structure.
The high amount of carbon adds to its toughness, but the lower amount of nickel makes it less corrosion-resistant.
It can be hardened by high temperatures followed by rapid cooling. When hardened, it can become brittle and is therefore reheated at low temperatures to temper the material to intermediate hardness levels.
Low-carbon martensitic stainless steel tubes have higher corrosion resistance and can be formed more easily, whereas the high-carbon type is stronger, but more brittle and cannot be formed as easily and cannot be welded.
Its main application is in structural steel and surgical instruments and in a solid form typically for automotive parts and cutlery.

Duplex (austenitic-ferritic) stainless steel:

This is commonly a two-phase alloy made from a form of austenitic-ferritic stainless-steel, based upon iron with alloying additions of up to 25% chromium, 7% nickel and molybdenum.
The combination benefits from the properties of both crystalline structures which makes it suitable for a wide variety of uses but also subjects it to particular weaknesses.
It has good weldability, good toughness, and high resistance to corrosion and cracking.
Its weakness includes brittleness at extreme temperatures.
Its main applications include heat exchanger tubes; structural tanks; seawater tubes; oil, gas, chemical, and nuclear processing.

What is HSS tube steel?

HSS in this context means Hollow Structural Sections and it refers to high-strength welded steel which is used as structural elements in buildings and other structures.

Like all steel tubing, it is produced in round, oval, square, rectangular, octagonal, and a variety of other shapes and is manufactured in a broad range of sizes and lengths, with different specifications.

What is the difference between tube steel and HSS?

In this context, HSS means high-speed steel. Structurally they are the same, but the applications are very different.

Carbon tube steel

Carbon tube steel is an iron-carbon alloy with a carbon content of between 0.02 and 2% carbon, small amounts of silicon, manganese, sulphur and phosphorous. The higher the carbon content, the harder and tougher the tube steel, but with less plasticity.

Steel hollow sections made from carbon tube steel have very high tensile and compressive strength; highly durable; resistant to fire, earthquakes, hurricanes, and tornadoes; and invulnerable to pests; but susceptible to corrosion. These qualities make them highly suitable for application in heavy-duty industries, infrastructure, and construction.

Tungsten tube steel:

Tungsten is the strongest and toughest of all metals, and also has the highest melting point of any unalloyed metal and a very high resistance to corrosion.

The term tungsten steel refers to any steel alloy that includes tungsten and which provides the steel with enhanced toughness and hardness, tensile and compressive strength, durability, heat resistance, and corrosion resistance. The main alloying elements found in tungsten tube steel include carbon, cobalt, chromium, and vanadium.

Tungsten tube steel is highly-sought after in heat exchangers, heating elements, chemical processing, atomic energy plants, induction furnaces, rare earth smelting systems, quartz glass smelting systems, and the LED industry.

Titanium tube steel

Titanium has the same or higher tensile and compressive strength as steel, and much higher chemical resistance than stainless steel, but is much lighter, making it highly suitable for a diverse range of tubing. Even though it is not technically correct to call it tube steel, it is included here because of its growing popularity and application in tubes with a thin wall thickness and small outer diameter, used in automotive mechanical applications, aircraft, instrumentation systems, and brachytherapy where radioactive implants are inserted directly into the cancerous tissue.

Titanium hollow sections are completely rust and corrosive-resistant in normal environments but will corrode in vacuums and environments where oxygen is limited.

Are all steel tubes manufactured in the same way?

In addition to understanding the different types of tube steel, the selection of the right steel tube requires knowledge of the production method and the difference between steel tubes and steel pipe.

Welded steel tube

A welded hollow section is formed either as hot rolled or cold rolled and the seams are welded longitudinally.
It is used both for transporting liquids and structural purposes, depending on the properties of the tubes.
It is used widely for geological drilling, in the petrochemical industry and as high-precision structural tubing in the automotive and aviation industry. and in pressure equipment.

Seamless steel tube

Seamless steel tubes do not have weld joints or seams and are produced through a hot or cold process of extrusion, where long sections of steel billets are forced through a die that blocks out the intended shape of the tubes.
They can withstand intense or extreme temperatures and pressure and are typically used in fertilizer, petroleum, shipping and the chemical industry.

What is the difference between steel tube and steel pipe?

These terms are often, erroneously, used as synonyms.

Shape

Steel tube can be produced in round, square, rectangular, octagonal and oval hollow sections, while steel pipe is round.

Tolerance and Application

Normally, steel pipes transport or dispense gases and liquids and it is therefore critical to know the liquid capacity, outside diameter, wall thicknesses, and tolerance of the steel pipe or tubing.
Tubes are used for transporting liquids and structural purposes.

Size

Pipe accommodates larger nominal pipe size for conveyance capacity and larger applications.
Tube is measured by outside diameter or wall thickness and pipe by inside diameter.

Manufacturing process

Steel tubes are usually submitted to more stringent inspections and testing processes.
More intense labour, energy, and material, generally make the tubes of higher quality and more expensive.

What is the main disadvantage of tube steel?

Tube steel has poor thermal conductivity, which complicates bonding with other metals.

Special Metal Alloys is a specialist stainless steel tube supplier and because each case is different, our qualified professionals can provide you with expert advice on all aspects of selecting and ordering the correct type of stainless steel tubing. Visit our contact page to get in touch or alternatively, email us at sales@specialmetalalloys.co.uk for more information.