IS 1161: Structural Steel Tubes: Grades YSt 210/240/310, Sizes & vs IS 1239

Overview

IS 1161 is the Bureau of Indian Standards (BIS) specification for steel tubes used for structural purposes and general engineering. The usual product is a circular hollow section that carries load rather than conveying 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. The purpose is different. IS 1161 is selected for structural load-bearing members. 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.

What IS 1161 is, what governs it, and what it is not

IS 1161 is the Bureau of Indian Standards specification titled Steel Tubes for Structural Purposes. The BIS product manual for IS 1161:2014 is the public certification reference buyers can read without buying the full standard text. It governs circular tubes made by hot-finished welded, hot-finished seamless, cold-finished seamless, electric-resistance welded, or high-frequency induction welded routes.

The entity is a load-bearing circular hollow section. Designers select it by yield-strength grade and section size, not by a water-service wall class. It is not IS 1239 water or gas tube, not IS 3589 large-diameter water main pipe, and not IS 4923 square or rectangular hollow section. A tube that looks like IS 1161 on a rack still fails inspection if the MTC cites the wrong standard number.

Who should specify IS 1161 on Kanpur fabrication jobs

Specify IS 1161 when the drawing treats the tube as a structural member: columns, struts, truss chords, scaffolding standards, handrail posts designed as CHS, conveyor frames, and plant fabrication. PWD, CPWD and MES structural BOQs that name IS 1161 expect YSt grade language and mechanical results on the MTC. Kanpur contractors should keep water and gas lines on IS 1239 even when the tube looks the same on the rack.

Do not specify IS 1161 for fluid conveyance merely because the OD matches; use the product standard and wall basis named by the design. For boiler, steam, or sour service, follow the approved material and regulatory documents. IBR tubes use Form III-B where applicable; steam pipes use III-A; H2S service needs the full approved ISO 15156/NACE basis rather than an acronym.

• Use: structural CHS members, scaffolding systems the designer allows, industrial frames
• Do not use: IS 1239 water or gas lines, IS 3589 rising mains, IBR boiler tubes
• Do not use: SHS or RHS columns (order IS 4923), sour-service line pipe (order NACE / API 5L)

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.

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.

RFQ checklist for IS 1161 tubes

Write the line so a mill or stockist can price one product, not three. The BIS product manual requires the test certificate to show grade, size, cast or control-unit number, type or class, and the matching test results. Missing any of those fields is how mixed IS 1239 stock enters a structural BOQ.

• Size: NB or OD in mm (licence scope in the BIS manual starts at 15 mm NB and runs up to 1200 mm NB)
• Wall: class or explicit thickness in mm; never grade alone
• Grade: YSt 210, YSt 240 or YSt 310 as on the drawing; name YSt 355 / 420 / 460 only when the design and mill licence include them
• Length: 6 m is the common commercial length on this site; state project cut lengths if needed
• End finish: plain or bevel, as the BIS licence scope allows
• Coating: black, or galvanized with IS 4736 called out separately
• Certificate: MTC 3.1 with heat number, chemistry and mechanicals against IS 1161
• Inspection: mill only, or TPI hold points if the tender names an agency
• Packing: bundle marks for grade, size, licence number (CM/L) and lot identity
• Delivery basis: ex-works Kanpur, quantity in metres or MT, with legally applicable tax and charges stated in the current quotation

Worked mass example for a 50 NB structural tube

Theoretical plain-end steel mass on this site uses W = (OD − t) × t × 0.02466 kg/m, with OD and wall in millimetres. The constant 0.02466 is the carbon-steel factor at 7850 kg/m³ used on the pipe-weight chart.

Take 50 NB with OD 60.3 mm and a 3.6 mm wall (the Medium-class wall already tabulated for that OD). W = (60.3 − 3.6) × 3.6 × 0.02466 = 5.03 kg/m. A 6 m length is 30.2 kg. One hundred lengths are 3.02 MT before coating, threading or tolerance. Use the same arithmetic on the drawing wall; do not borrow an IS 1239 class wall unless the structural note actually states that thickness.

Common procurement mistakes on IS 1161 lots

In practice, inspectors fail lots when the BOQ names IS 1161 and the MTC names IS 1239, or the reverse. The tubes can share an ERW look and the same NB. The certificate number is what the PWD or TPI clerk matches.

• RFQ written as MS pipe 50 NB with no standard, so three suppliers quote three products
• IS 1239 Medium bought for scaffolding because it was cheaper that week
• IS 1161 stock used on a water header because the OD matched
• Class words (Light / Medium / Heavy) written onto an IS 1161 line
• YSt grade omitted, so the mill ships the lowest yield it has licensed
• Colour band used instead of stencil and MTC (yard colour is trade practice only)

Standards and compliance clauses for IS 1161

The BIS product manual for IS 1161:2014 points inspectors to the clauses that appear on a factory surveillance. Clause 5 covers material and chemistry (Table 3 in the standard). Clause 6 and Table 1 cover outside diameter, thickness and mass. Clause 8 sends galvanizing to IS 4736. Clause 9 is straightness. Clause 10 is length. Clause 11 covers mechanical tests.

Tensile strength and elongation are run to IS 1608 (Part 1). Cold bend, where applicable, is IS 2329. Flattening, where applicable, is IS 2328. Raw strip for welded tube is IS 10748 or IS 2062. Each BIS-marked consignment must carry a test certificate with Standard Mark, cast or control-unit number, type, class, size and the results. Ask for that package on the PO, not a generic MS pipe MTC.

• Governing standard: IS 1161:2014, Steel Tubes for Structural Purposes (BIS)
• Related: IS 1239-1:2004 conveyance; IS 4923:2017 SHS/RHS; IS 4736 galvanizing
• Licence grades in the product manual: YSt 210, 240, 310, 355, 420, 460

Key points for IS 1161 buyers

• IS 1161 is a structural circular-tube standard ordered by YSt grade, not by water-pipe class.
• Common commercial grades are YSt 210, YSt 240 and YSt 310; higher YSt grades need design and licence cover.
• The BIS product manual names NB from 15 mm to 1200 mm and ERW, HFIW, HFW, HFS and CDS routes.
• A 50 NB tube at 60.3 mm OD and 3.6 mm wall weighs 5.03 kg/m on the site formula.
• Do not substitute IS 1239, IS 3589 or IS 4923 because the metal looks the same.