Quick Answer
Quick Answer
IS 1161 is the Bureau of Indian Standards specification for steel tubes used in structural applications — handrailing, scaffolding, general construction, and light structural frames. It covers three grades: YSt 210, YSt 240, and YSt 310, defined by minimum yield strength. BIS certification is mandatory for IS 1161 tubes sold in India.
IS 1161 (IS 1161:2014 with amendments) is published by the Bureau of Indian Standards (BIS) and governs welded and seamless circular steel tubes used for structural purposes — not for pressure service (covered by IS 1978/IS 3589) or conveying fluids under pressure (IS 1239). The standard is widely used for handrail systems, scaffolding, trusses, bus-body frameworks, light columns, and general structural tubework where the tube is used as a structural member rather than a pressure conduit. Grades are designated with the prefix "YSt" followed by the minimum yield strength in MPa. IS 1161 is mandatory BIS-certified (Schedule II).
Scope and Applicability
IS 1161 covers:
- Welded (ERW) and seamless circular steel tubes
- Nominal bore: 6 mm to 150 mm (NB)
- Wall thickness: 1.6 mm to 10 mm depending on NB
- Applications: structural frameworks, handrails, scaffolding, furniture frames, vehicle body structures, light trusses, purlins
IS 1161 does not cover:
- Pressure vessels or boiler tubes (IS 1914, IS 3074)
- Water / gas supply pipes in pressure service (IS 1239)
- Hot-formed hollow sections (IS 4923)
- Cold-formed rectangular/square hollow sections (IS 12778)
- Precision tubes (IS 3601)
Grade Coverage
| Grade | Yield Strength Basis | Minimum Yield Strength | Typical Application |
|---|---|---|---|
| YSt 210 | Lower bound | 210 MPa | Light scaffolding, furniture, handrails, light frames |
| YSt 240 | Medium | 240 MPa | General structural tubes, scaffolding standards, purlins |
| YSt 310 | High strength | 310 MPa | Structural trusses, light columns, vehicle body frames |
The grade prefix "YSt" stands for yield strength steel tube (Y = Yield, St = Steel tube). YSt 240 is the most commonly stocked grade in India, corresponding broadly to general structural use.
Chemical Composition Requirements
Ladle (heat) analysis. All values are weight percent maximum.
| Element | YSt 210 | YSt 240 | YSt 310 |
|---|---|---|---|
| Carbon (C) max | 0.20 | 0.20 | 0.22 |
| Manganese (Mn) max | 1.20 | 1.20 | 1.40 |
| Silicon (Si) max | 0.35 | 0.35 | 0.40 |
| Sulphur (S) max | 0.050 | 0.050 | 0.050 |
| Phosphorus (P) max | 0.050 | 0.050 | 0.050 |
| S + P max | 0.090 | 0.090 | 0.090 |
No minimum alloy addition requirements; these are plain carbon-manganese steels. For tubes requiring weldability calculations, the approximate CEV for YSt 310 (using maximum values) = 0.22 + 1.40/6 = 0.45, indicating preheat may be required for heavy section connections.
Mechanical Properties
Tensile test per IS 1608. Test pieces are flattened (for tubes) or ring specimens. Elongation measured on gauge length = 5.65√A.
| Grade | Yield Strength (0.2% PS) min (MPa) | UTS min (MPa) | Elongation min % |
|---|---|---|---|
| YSt 210 | 210 | 330 | 20 |
| YSt 240 | 240 | 360 | 20 |
| YSt 310 | 310 | 450 | 15 |
Notes:
- For ERW (electric resistance welded) tubes, the test piece may be a strip cut longitudinally from the tube, with the weld zone in the gauge length
- For seamless tubes, test pieces are longitudinal strips or rings
- Hardness test (Rockwell B) is not mandated by IS 1161 but may be agreed between supplier and purchaser
Dimensions: Outside Diameter and Wall Thickness
IS 1161 specifies dimensions by Nominal Bore (NB) designation. Selected sizes with standard outside diameter (OD) and wall thickness (WT):
| NB (mm) | OD (mm) | WT Light (mm) | WT Medium (mm) | WT Heavy (mm) |
|---|---|---|---|---|
| 15 | 21.3 | 2.0 | 2.6 | 3.2 |
| 20 | 26.9 | 2.0 | 2.6 | 3.2 |
| 25 | 33.7 | 2.6 | 3.2 | 4.0 |
| 32 | 42.4 | 2.6 | 3.2 | 4.0 |
| 40 | 48.3 | 2.6 | 3.2 | 4.0 |
| 50 | 60.3 | 2.9 | 3.6 | 4.5 |
| 65 | 76.1 | 3.2 | 3.6 | 4.5 |
| 80 | 88.9 | 3.2 | 4.0 | 5.0 |
| 100 | 114.3 | 3.6 | 4.5 | 5.4 |
| 125 | 139.7 | 4.0 | 5.0 | 5.4 |
| 150 | 168.3 | 4.5 | 5.4 | 6.3 |
Light, Medium, and Heavy refer to wall thickness series. "Heavy" is used for structural applications requiring higher section modulus. All three series share the same OD for a given NB, enabling common end fittings.
Dimensional Tolerances
Outside Diameter Tolerances
| OD (mm) | Tolerance |
|---|---|
| Up to 48.3 | ± 0.5 mm |
| 48.3 to 114.3 | ± 0.8 mm |
| 114.3 to 168.3 | ± 1.0 mm |
Wall Thickness Tolerances
| Wall Thickness | Tolerance |
|---|---|
| ≤ 4.0 mm | ± 10% |
| > 4.0 mm | ± 10% |
Minimum wall thickness at any point: not less than 90% of the specified nominal WT (i.e., tolerance is one-sided for minimum).
Length
Standard lengths: 4 m, 5.5 m, and 6 m. Random lengths between 4 m and 7 m are acceptable unless fixed lengths are specified. Length tolerance: +50 mm / −0 mm for cut-to-length orders.
Straightness
Camber (bow): maximum 1.5 mm per metre of length.
Mass Tolerance
Mass per metre: ± 7.5% for individual tubes; ± 5% for batch average (for lots > 10 tonnes).
Hydrostatic Test Requirements
All tubes must pass a hydrostatic test unless the purchaser agrees to substitute an eddy-current or other non-destructive test:
| Grade | Test Pressure (MPa) — Light series | Test Pressure (MPa) — Medium series | Test Pressure (MPa) — Heavy series |
|---|---|---|---|
| YSt 210 | 5.0 | 5.0 | 7.0 |
| YSt 240 | 5.0 | 7.0 | 7.0 |
| YSt 310 | 7.0 | 7.0 | 10.0 |
The test pressure is held for a minimum of 5 seconds. No leakage or visible deformation is acceptable. ERW tubes are additionally subject to weld integrity inspection — either 100% eddy-current testing or hydrostatic test at the above pressures.
Weld Seam Quality (ERW Tubes)
The weld bead (flash) on the inside of ERW tubes must be removed (scarfed) to ensure the internal profile is substantially round. External flash removal is required if specified. Weld zone hardness must not exceed 300 HV on a Vickers traverse across the weld.
Surface Condition and Coating
Tubes are supplied in one of the following conditions:
- Plain (black): as-rolled/welded, without coating
- Hot-dip galvanised: to IS 4736, minimum average zinc coating 42.5 µm (for scaffolding and handrails)
- Bright drawn / cold-finished: for close-tolerance applications (must be specified)
BIS Mandatory Certification
IS 1161 is under mandatory BIS certification (Schedule II):
- All structural tubes sold as IS 1161 must carry the ISI Mark with the producer's BIS licence number
- Grade, nominal bore, wall thickness, and BIS licence number must be stamped/stencilled on the tube at intervals not exceeding 2 m
- MTCs must state the BIS licence number, heat number, grade, and dimensions
Cross-Standard Equivalents
| IS 1161 Grade | EN 10210 Equivalent | ASTM Equivalent | BS Equivalent |
|---|---|---|---|
| YSt 210 | S195T (EN 10217-1 welded) | A500 Gr A (approximate) | BS 1387 Light / BS EN 10255 |
| YSt 240 | S235JRH (EN 10210-1) | A500 Gr B (approximate) | BS EN 10210 S235JRH |
| YSt 310 | S355J2H (EN 10210-1) | A500 Gr C / A501 (approximate) | BS EN 10210 S355J2H |
EN 10210 covers hot-finished structural hollow sections; EN 10219 covers cold-formed. ASTM A500 covers cold-formed welded circular hollow sections. Exact equivalence depends on tube formation method, OD, and WT; verify section-by-section before substituting.
MTC Verification Checklist
When verifying a mill test certificate for IS 1161 structural tubes, confirm:
- Standard stated as IS 1161:2014 with grade (YSt 210, YSt 240, or YSt 310)
- BIS licence number of the producing mill present
- Heat number traceable to tube bundle/end-stamps
- Nominal bore and wall thickness (series — Light/Medium/Heavy) stated
- OD and WT within IS 1161 tolerance limits for the declared size
- Chemical analysis: C, Mn, Si, S, P within grade limits
- Tensile test: YS ≥ grade minimum, UTS ≥ minimum, elongation ≥ minimum
- Hydrostatic test result: stated as passed (or eddy-current test if agreed)
- ERW weld quality: flash removal and weld hardness compliance noted (for ERW tubes)
- If galvanised: coating mass per IS 4736 stated
Frequently Asked Questions
What is the difference between IS 1161 and IS 1239 steel tubes?
IS 1161 covers tubes for structural use — acting as structural members in frames, handrails, scaffolding, and trusses, where the load is primarily axial or bending. IS 1239 covers tubes for water, gas, and other fluid conveyance at low pressure. IS 1239 tubes have similar dimensions but are tested primarily for hydraulic pressure integrity and corrosion resistance in service. IS 1239 is also listed under mandatory BIS certification. Never substitute IS 1239 pipes for IS 1161 structural tubes without verifying the grade and mechanical properties, as IS 1239 uses different grade designations and the yield strength requirements differ.
Is IS 1161 YSt 310 equivalent to IS 2062 E350?
They are close but not identical. IS 2062 E350 structural steel has YS min 350 MPa versus 310 MPa for YSt 310. The yield strength of YSt 310 is lower, but its UTS minimum (450 MPa) is higher than IS 2062 E250 (410 MPa) and slightly below E350 (490 MPa). For structural design of tubular members, use the actual grade properties stated on the MTC rather than assuming equivalence. EN 10210 S355J2H is the closest European equivalent to YSt 310 in terms of yield strength class.
What does the hydrostatic test pressure prove about a structural tube?
The hydrostatic test primarily verifies weld integrity (for ERW tubes) and the absence of through-thickness defects (seams, laminations) in both ERW and seamless tubes. For structural (non-pressure) use, it is a manufacturing quality check, not a service pressure rating. The test pressures in IS 1161 (5–10 MPa) are much lower than those in IS 1239 (up to 50 MPa for water/gas pipes). The test does not define the service pressure rating of the tube; for pressure service, a separate pressure calculation under the applicable piping code must be performed.
Can IS 1161 tubes be used for scaffolding in India?
Yes. IS 3696 (Safety Code for Scaffolding) specifies that scaffold poles, ledgers, and transoms shall conform to IS 1161 (Grade YSt 240 or higher, Medium or Heavy series, NB 40 or NB 50). Scaffold tubes must carry the ISI Mark and be in straight condition. Bent, kinked, or heavily corroded tubes must not be used. For modular scaffolding systems (cup-lock, ring-lock), tube compliance with IS 1161 YSt 240 medium series is typically the minimum specified in safety standards and contractor specifications.
How do I calculate the section modulus and moment capacity of an IS 1161 tube?
For a circular hollow section (CHS), the elastic section modulus Zxx = π/32 × (OD⁴ − ID⁴) / OD, where ID = OD − 2 × WT. Example: NB 50 Medium series, OD = 60.3 mm, WT = 3.6 mm, ID = 53.1 mm. Zxx = π/32 × (60.3⁴ − 53.1⁴) / 60.3 = approximately 5.42 cm³. Moment capacity (elastic) = Zxx × fy = 5.42 cm³ × 310 N/mm² (for YSt 310) = 1.68 kN·m. For plastic design, use the plastic section modulus Zpxx, which is 4/3 × Zxx for a thin-walled CHS approximation. IS 800 (the design code) provides the full CHS design procedure including section classification and local buckling checks.
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