Circular Steel Hollow Section (CHS): IS 3601 Manufacturer in India
If you're sourcing a round pipe, ERW pipe, CHS pipe, round steel pipe, or circular hollow section for a structural, mechanical, or architectural project, this page covers what you need to specify one correctly: size range, grade, applicable IS code, and where a circular profile fits best on a project. SRMB Realfabrica manufactures circular hollow sections at SRMB Srijan's integrated steel plant in Durgapur, West Bengal, rolling our own hot rolled coil into finished circular sections on Cold Formed ERW lines, under IS 3601.
What Is a Circular Hollow Section?
A circular hollow section (CHS) is a structural steel tube with a round cross section and a hollow core, manufactured for mechanical and general engineering purposes as well as structural use. Depending on the industry and the person searching, you'll see this same product called round pipe, ERW pipe, ERW steel pipe, CHS pipe, round steel pipe, tubular steel pipe, or circular steel tube. Because our sections are formed by Electric Resistance Welding, they also fall under the broader category of ERW pipe and carbon steel pipe, terms commonly used across the Indian steel pipe market for the same welded tube family.
Unlike a square or rectangular section, a CHS has no corners or flat faces, which means stress applied to the tube, whether from bending, internal pressure, or twisting, is distributed evenly around its circumference rather than concentrated at a joint or edge. That single geometric difference is what makes circular hollow sections the preferred shape wherever torsion, rotation, wind load, or pressure containment matter more than axial load alone.
Full Specifications
| Specification | Detail |
|---|---|
| Product standard | IS 3601 (Steel tubes for mechanical and general engineering purposes) |
| Size range | 15mm NB to 80mm NB |
| Thickness range | 1.8mm to 5.4mm |
| Grade (tube designation) | WT 160, WT 210, WT 240, WT 310 |
| Standard length | 6 metres to 7 metres, custom cutting available on request |
| Surface finish | Black, smooth, consistent finish |
| Input material | Hot rolled coil conforming to IS 10748 |
| Forming process | Cold Formed ERW (Electric Resistance Welded) |
Grades and Mechanical Properties
| Tube Designation | Min Tensile Strength (MPa) | Min Yield Strength (MPa) | Elongation, up to 33.7mm OD | Elongation, above 33.7mm OD |
|---|---|---|---|---|
| WT 160 | 310 | 160 | 15.0% | 22.0% |
| WT 210 | 330 | 210 | 12.0% | 20.0% |
| WT 240 | 410 | 240 | 10.0% | 15.0% |
| WT 310 | 450 | 310 | 6.0% | 10.0% |
Choosing the Right Grade and Size
For light duty applications such as handrails, flag poles, and general architectural framing, WT 160 or WT 210 typically provide sufficient strength while keeping the section lightweight and easy to fabricate. For structural supports exposed to higher wind load, or for mechanical applications carrying torsional or rotational stress, WT 240 offers a meaningful step up in both tensile and yield strength. WT 310 is generally reserved for applications with the most demanding strength requirements, where a smaller, thinner section still needs to carry substantial load.
Nominal bore size should be selected based on the diameter your application calls for, from 15mm NB at the small end for lighter fittings and railings, up to 80mm NB for larger structural and mechanical applications. As with grade selection, your structural or mechanical engineer's load calculation should guide the final size and thickness choice rather than nominal bore alone.
Dimensional Conformity
SRMB Realfabrica circular hollow sections are manufactured to hold outside diameter and wall thickness within the tolerances specified under IS 3601 for the selected tube designation. Because exact tolerance figures vary by size and grade combination, our technical team can share the specific tolerance data sheet for whichever size and grade you're specifying, alongside a formal quotation.
Where Circular Hollow Sections Are Used
Flag poles and street light structures
Handrails and balustrades
Structural supports in high wind exposure areas
Mechanical applications involving torsional forces
Aesthetic architectural elements
Conveyor systems and material handling equipment
Why Circular Hollow Sections Are Specified Over Other Shapes
Optimum Wind Resistance
A round profile presents a lower and more consistent drag coefficient to wind from any direction, reducing lateral load on tall or exposed structures such as poles and masts.
Superior Torsional Strength
The uniform distribution of material around a circular section gives it a higher torsional stiffness per unit weight than a square or rectangular section of similar size, making it the natural choice for rotating or twisting loads.
Pressure Resistance
Because a circular shape has no flat faces or corners to concentrate stress, it resists internal and external pressure more evenly, which matters for tubular components carrying fluids or gases.
Aesthetic Appeal
The clean, continuous profile of a circular section is often preferred in architectural and public-facing applications where visual finish matters as much as structural performance.
Manufacturing Quality Behind Every Length
Primary Steel Producer
Manufactured from our own hot rolled coil at an integrated steel plant, not sourced or re-rolled from external material.
Batch Level Testing
Every batch is tested against IS 3601 requirements for dimensions and mechanical properties before dispatch.
IMS Certification
Manufacturing operates under an Integrated Management System covering quality, environment, and safety standards.
On-Product Traceability
Each section carries markings that trace it back to its batch and production line for full quality accountability.
Handling and Site Considerations
Weldability
SRMB Realfabrica circular hollow sections can be welded using standard MS electrodes without preheating, allowing straightforward fabrication and site jointing.
Open Ends
Sections are supplied with open ends. We recommend sealing exposed ends with a welded end plate on site to prevent moisture ingress and internal corrosion over the working life of the structure.
Packaging
Sections are bundled and strapped for transit to minimise surface damage, with bundle-level identification for easy tracking on site and at stockyards.
How to Order
To place an order or request a quotation, share your required nominal bore size, grade (tube designation), wall thickness, and length with our technical team. For projects where the exact size and grade combination needs confirming, we'll validate availability and share a formal specification sheet alongside your quote.
Frequently Asked Questions
A circular hollow section is a structural steel tube with a round cross section and hollow core. It's also called round pipe, ERW pipe, CHS pipe, round steel pipe, or circular steel tube.
We manufacture circular hollow sections from 15mm NB to 80mm NB in 1.8mm to 5.4mm wall thickness, under IS 3601. Not every size is available in every thickness, so please confirm with our technical team.
SRMB Realfabrica circular hollow sections conform to IS 3601, which covers steel tubes for mechanical and general engineering purposes.
We manufacture circular hollow sections in four IS 3601 tube designations: WT 160, WT 210, WT 240, and WT 310, classified by minimum tensile and yield strength.
WT 310 has a higher minimum yield strength (310 MPa) and tensile strength (450 MPa) than WT 160 (160 MPa yield, 310 MPa tensile), making it suited to more demanding structural applications.
Standard supply length is 6 metres to 7 metres. Custom cut lengths can be arranged on request for specific project requirements.
Circular hollow sections are used for flag poles, handrails, balustrades, wind exposed structural supports, mechanical torsional applications, architectural elements, and conveyor systems.
Yes, in practice. ERW (Electric Resistance Welded) pipe and circular hollow section both describe the same welded round steel tube, formed on the same manufacturing process.
Circular sections handle torsional and rotational load, wind resistance, and pressure containment better than square or rectangular sections, which are optimised for axial and one-directional bending load instead.
Controlled chemistry and a smooth surface finish support good corrosion resistance. Sealing all open ends with a welded end plate further protects against internal corrosion over the section's working life.
Yes. SRMB Realfabrica circular hollow sections can be welded using standard MS electrodes without any preheating required beforehand.
For outside diameter and thickness tolerance, along with weight per length for your selected size and grade, please contact our technical team or download our product brochure for current data.
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