Tubes and Pipes – Importance of Tubular Structures

Tubular Structures are one of most economical structures. Tube sections have small self weights which lowers their cost and increases their efficiency. In normal conversation, tubes are often referred as pipes too. They come in various shapes, round and rectangular being the most common.

Earlier, angles and girders were more used compared to tubes because of the high manufacturing cost of tubular sections. Some of the reasons for this are: (a) Difficult to have smooth cut surface and (b) Difficulty in making connections between tube sections. Development of oxyacetylene cutting machine helped to get smooth cut surface and correct profiling of edges. Improvements in welding technique made it easier to have connections between tubes.

Tubes have found increased usage in industrial buildings and warehouses with roofing systems. Large span roof trusses can be made using tubes more economically. Tubes are generally available in lengths of 4 meter to 6 meter.

Classification

IS: 1161 lists the following manufacturing processes for tubes:

• HFW: Hot Finished Welded
• HFS/CDS: Hot Finished Seamless
• ERW/HFIW: Electrical Resistance Welded or Induction Welded

Tubes can be of mild steel material or stainless steel with different grades. They can be galavanized with zinc coating or painted with red oxide.

There is wide range of tubes available of different sizes and thickness. They are classified as light, medium and heavy depending upon their wall thickness. Wall thickness is generally measured in mm or gauge, with different values for each available size.

Grades according to Yield Strength

Tubes are also graded according to their yield strength. As per IS, they are:

• YSt 210: Minimum Yield Strength 210 MPa, Minimum Tensile Strength 330 MPa
• YSt 240: Minimum Yield Strength 240 MPa, Minimum Tensile Strength 410 MPa
• YSt 310: Minimum Yield Strength 310 MPa, Minimum Tensile Strength 450 MPa
• YSt 355: Minimum Yield Strength 355 MPa, Minimum Tensile Strength 490 MPa

Uses and Advantages

Tubular sections can be used as compression members. For this diameter of the tube should be as large as possible with the ratio diameter/thickness as small as possible. Tubes are generally uneconomical as tension members. Let us list down some of the advantages of Tubes:

• For the same load, surface area of a tube section is less compared to other rolled sections.
• Because of the less surface area, wind forces are small in tubular structures.
• Small self weights make tubular structures economical in use.
• In case of tubular columns, internal hollow space can be filled with concrete to increase the load carrying capacity and improve fires resistance.
• Internal hollow space of tubes can be used for carrying drain pipes, cables, etc.
• Can be easily welded with other tube sections for varied applications and uses.