IS 1161 is the Bureau of Indian Standards (BIS) specification for steel tubes used for structural purposes and general engineering — primarily circular hollow sections that carry load rather than convey fluid under a piping code. Grades are ordered by minimum yield strength: YSt 210, YSt 240, and YSt 310. Size is commonly designated by nominal bore (NB) with a wall class or explicit thickness. Manufacturing is typically ERW, the same welded route familiar from IS 1239 stock, but the governing purpose differs: IS 1161 is selected for structural load-bearing members, while IS 1239 is selected for water, gas, and sewage conveyance with Light/Medium/Heavy classes and mandatory hydrostatic testing. Buying the wrong standard creates inspection failures even when the tube looks identical on a rack. For square and rectangular structural sections, use IS 4923 instead of IS 1161.
Scope of IS 1161 structural tubes
IS 1161 covers steel tubes intended for structural use — columns, struts, trusses, scaffolding structures, handrails, idler frames, and similar load-bearing or fabricated assemblies. Designers rely on the yield-strength grade and section properties rather than a water-service pressure class.
Tubes are typically circular. Dimensions are designated by nominal bore (NB) and wall, with mechanical properties tied to YSt 210 / YSt 240 / YSt 310. Confirm the BIS revision cited in the tender and match markings on the tube and MTC to that reference.
Grades and size designation
- YSt 210 — 210 MPa min yield; general structural and light fabrication
- YSt 240 — 240 MPa min yield; common industrial structural choice
- YSt 310 — 310 MPa min yield; higher-strength structural members
- Size: nominal bore (NB) plus wall class or explicit thickness — never grade alone
- Finish: black or galvanized when corrosion protection is ordered separately
IS 1161 vs IS 1239
Both standards often share an ERW manufacturing base and similar NB size ranges, which is why buyers and site teams confuse them. The governing purpose is different. IS 1239 is a conveyance standard for water, gas, and sewage: class (Light / Medium / Heavy) defines wall thickness, and hydrostatic testing is a core acceptance check. IS 1161 is a structural standard: yield-strength grade governs material selection for load-bearing duty.
If the drawing says structural column, truss chord, handrail post, conveyor idler frame, or scaffolding structure, specify IS 1161 with YSt grade. If the line is a water riser, plumbing main, or gas distribution pipe, specify IS 1239 with class. Do not accept a substitution without design approval — hydrotested conveyance pipe is not automatically a structural grade package, and structural tube is not automatically a pressure-service package.
| Point | IS 1161 | IS 1239 |
|---|---|---|
| Governing use | Structural / general engineering load-bearing | Water, gas, sewage conveyance |
| Grades / classes | YSt 210 / YSt 240 / YSt 310 (yield grades) | Light / Medium / Heavy wall classes |
| Testing emphasis | Mechanical properties for structural grade; project tests as specified | Mandatory hydrostatic test for conveyance acceptance |
| Typical buyers | Fabricators, PEB/structural contractors, OEMs, scaffolding & material-handling buyers | Plumbing, utilities, municipal water, gas distribution, MEP contractors |
Search queries for “IS 1161 vs IS 1239” almost always come from buyers who received mixed stock or a tender that cites one standard while the drawing implies the other. Resolve the conflict on paper before dispatch — not after fabrication.
Applications
- Structural columns, props, and compression members
- Roof and floor trusses, lattice frames, and bracings
- Scaffolding structures and temporary works (as design permits)
- Handrails, balustrades, and guard systems
- Conveyor idler frames, supports, and plant fabrication
Procurement notes for Indian RFQs
State: IS 1161 × NB (or OD) × wall/class × YSt grade × length × finish × quantity. Ask for MTC 3.1 with heat number, chemistry, and mechanical results. If galvanizing is required, cite the coating standard separately.
Where the project mixes circular structural tubes with SHS/RHS members, keep standards separate on the BOM: circular → IS 1161; square/rectangular → IS 4923. RP Sales can quote structural tubes and hollow sections together when both size lists are clear.