Wall Thickness (WT)
/glossary/wall-thicknessRadial steel between the bore and the outside diameter of a pipe or tube.
Wall thickness is the radial steel between the bore and the OD, written in millimetres or as Light, Medium, Heavy or a schedule. At 50 NB the site weight table uses 3.6 mm for Medium class; the schedule chart uses 3.91 mm for 2 inch Sch 40. Kanpur PWD, JJM, and fire contractors must copy the wall the BOQ names. RP Sales prices pipe ex-warehouse Kanpur with GST 18% extra on the invoiced steel.
In detail
Wall thickness (WT) is the radial distance between the inner and outer surfaces of a pipe or tube. It enters mass, geometry, and design calculations, but it is not the only input to pressure or structural capacity. Indian class pipe uses Light, Medium, and Heavy walls by NB. ASTM and ASME pipe uses schedule or a stated millimetre wall. Tolerances sit in the product standard: IS 1239 Part 1 clause 9 for class tube, ASTM A530/A530M-18 Table 1 for the pipe specifications that invoke it. Write OD or NB together with the wall or class.
What wall thickness is, and what it is not
Wall thickness is a measured radial dimension. On a round pipe it is (OD − ID) / 2 when both diameters are taken at the same cross-section. Buyers write it in millimetres, as a class word, or as a schedule number. The class thickness chart and the pipe schedule chart are the two tables this site uses for those languages.
ASTM A53/A53M-24 Note 2 states that nominal wall thickness exists in name only and is used to distinguish it from the actual wall, which may vary over or under that nominal. A PO that copies only Sch 40 without a millimetre check leaves that variation unexamined.
Wall is not a pressure rating. Size, material allowable stress, corrosion allowance, joint type, and the governing design code also set capacity. A schedule number alone does not fix a working pressure. Wall is not a grade. IS 1239 class describes wall only; the standard's own steel requirements set the material basis, and Medium class is a different field on an IS 1239 line from either.
Wall is not coating. Zinc under IS 4736 adds mass and changes the outside dimension after dipping. Phosphate on a precision tube is a film, not a structural increase. Design on the steel wall, then treat coating as a finish line.
Who should write class, and who should write schedule
Write Light, Medium, or Heavy (Class A / B / C) when the BOQ is IS 1239 Part 1 for 15 to 150 mm NB. Kanpur JJM house connections, PWD water laterals, and most plumbing take Medium unless the schedule says otherwise. NBC 2016 Part 4, already cited on the IS 1239 standard page, sends wet-riser and hydrant pipe to Heavy class GI. Light class is disallowed on that fire service.
Write schedule or a millimetre wall when the drawing is ASTM A106, A53, or ASME B36.10M pipe. Panki process isometrics use Sch 40 or Sch 80. Borewell casing follows IS 4270 light or heavy duty, not a pipe schedule nickname. Hydraulic barrels in Dada Nagar use a stated OD × wall after finishing, because skiving removes stock.
Do not write Sch 40 on an IS 1239 line. Do not write Medium on an A106 line. Do not borrow a 50 NB Medium wall for a 25 NB take-off. Class wall changes with NB on the weight table.
Sugar-mill boiler tubes are ordered by OD and minimum wall, not by class and not by NPS. A 50.8 mm tube is not 2 inch pipe. Printing-cylinder and honed-bore work also lives on millimetre wall after the finishing pass.
Class walls versus schedule walls at 50 NB
The same 60.3 mm OD appears on both charts. The walls do not. Use the table to stop a Medium-versus-Sch-40 argument at the RFQ, not at the weighbridge.
| Call-out | OD (mm) | Wall (mm) | Mass (kg/m) | 6 m mass (kg) | Where it belongs |
|---|---|---|---|---|---|
| IS 1239 Light | 60.3 | 2.9 | 4.10 | 24.6 | Only if the BOQ names Light |
| IS 1239 Medium | 60.3 | 3.6 | 5.03 | 30.2 | Usual Kanpur water / plumbing class |
| IS 1239 Heavy | 60.3 | 4.5 | 6.19 | 37.1 | Fire hydrant / wet riser when NBC applies |
| 2 in Sch 40 | 60.3 | 3.91 | 5.44 | 32.6 | A53 / A106 schedule pipe |
| 2 in Sch 80 | 60.3 | 5.54 | 7.48 | 44.9 | Heavier schedule on the same NPS |
Sch 40 at 3.91 mm is thicker than Medium at 3.6 mm and thinner than Heavy at 4.5 mm. None of those three walls is a substitute for the other. The 24 May 2026 MS ERW Medium band at 50 NB is ₹53-60 per kg; the seamless Sch 40 band at 2 inch is ₹80-98 per kg.
How to specify wall on an RFQ
Put the millimetre wall on the same line as the NB or NPS. A class or schedule word without that number is how two suppliers quote two products. Use the RFQ form so size, wall, and documents stay together.
- Identity: IS 1239 class pipe, ASTM A53 / A106 schedule pipe, or boiler tube by OD.
- Size: NB in mm, or NPS, plus OD in millimetres from the chart.
- Wall: Light / Medium / Heavy with the chart millimetres, or Sch 40 / 80 / 160 with the chart millimetres, or a stated min wall.
- Material basis: IS 1239 class tube per the applicable revision, A53 A/B, A106 A/B/C, or the SA grade on the drawing. YST 210 / 240 / 310 are IS 1161 structural-tube grades, not an IS 1239 finished-pipe designation; do not write them on an IS 1239 line.
- Length 6 m unless cut-to-length. Ends: PE, T&C, or bevel.
- Coating: black or IS 4736 zinc. Documents: MTC 3.1, heat, BIS licence on IS 1239.
- Inspection: mill or named TPI. Delivery ex-warehouse Kanpur. Add GST at 18% on the invoiced steel value.
Worked mass for 50 NB Medium
Mass on this page uses W = (OD − t) × t × 0.02466 kg/m. For 50 NB Medium the weight table uses OD 60.3 mm and wall 3.6 mm. W = (60.3 − 3.6) × 3.6 × 0.02466 = 56.7 × 3.6 × 0.02466 = 5.03 kg/m. A 6 m length is 30.2 kg.
Eighty lengths are 80 × 30.2 = 2,416 kg (2.42 MT) before zinc or threads. The MS ERW price list Medium band at 50 NB is ₹53-60 per kg ex-warehouse Kanpur as of 24 May 2026. That steel line is 2,416 × 53 = ₹1,28,048 to 2,416 × 60 = ₹1,44,960 before GST and freight.
The schedule chart already lists 2 inch Sch 40 as 5.44 kg/m on the same OD. Do not rerun the formula on that row on this page. If the isometric wanted Sch 40, the lot mass would be 80 × 32.6 = 2,608 kg, not 2,416 kg. That 192 kg gap is why class and schedule cannot share a rate.
Common wall mistakes in Kanpur procurement
In practice, buyers write Heavy grade when they mean Heavy class. IS 1239 tubes are specified by class (Light, Medium, Heavy) and the standard's own steel requirements, not by a YST grade letter; YST 210 / 240 / 310 belong to IS 1161 structural tube. The inspector reads L, M, or H embossed on the tube per the BIS product manual marking clause.
A second failure is Light class on a wet riser. NBC 2016 Part 4 wants Heavy class GI. The lot then fails TPI and the occupancy file.
A third failure is a Sch 40 offer against a Medium BOQ, or the reverse, because both say 2 inch. Measure 3.6 mm versus 3.91 mm with a micrometer. The BIS product manual lists a micrometer among the clause 8 dimension tools.
A fourth failure is designing a hydraulic barrel on the mother-tube wall after a skiving pass. Remaining wall is the design wall. Record it on the drawing before the RFQ.
A fifth failure is using one under-tolerance percentage on class tube, schedule pipe, and precision tube. Those percentages live in different standards.
Standards that set wall and tolerance
IS 1239 (Part 1):2004 clause 8 covers dimensions against Tables 3 to 5. Clause 9 covers tolerances on thickness and mass against the same tables. The BIS product manual (PM/1239 (Part 1)/4, Feb 2022) assigns those checks to every hour of production. This page does not reprint unpublished table percentages from that manual.
ASTM A530/A530M-18 is the general-requirements specification invoked by A106 and the other product specs listed in its scope 1.5. That edition sets wall variation for seamless and welded pipe with no filler metal at a minimum wall not more than 12.5% under the nominal wall stated, the same under-tolerance already used on the A106 standard page on this site. A530 scope 1.5 names A106. It does not name A53.
ASME B36.10M standardises welded and seamless wrought-steel pipe OD and nominal walls. The word pipe in that standard is distinct from tube. NPS 12 and smaller have OD numerically larger than the size name. Schedule 40 and Standard are identical through NPS 10 on the edition this site already cites for 3.91 mm at 2 inch.
DIN 2391 and EN 10305 use tolerance classes, not Light / Medium / Heavy. Copy T3 or the EN equivalent from the drawing. IBR tubes use the minimum-wall basis on SA192 or SA210, not a plus/minus class word.
How Kanpur contractors specify wall
JJM and PWD bidders copy the BOQ class word and then add the millimetre wall from the class thickness chart. Intra-city work to Panki, Dada Nagar, and Jajmau still needs that millimetre on the PO, because a Fazalganj plumber and a Chakeri fire contractor do not share one default class.
Fire-system installers in Kanpur stay on Heavy GI. Borewell contractors stay on the IS 4270 duty wall named on the well drawing; see drill and borewell pipes in Kanpur. Hydraulic shops state remaining wall after hone or SRB.
Loads leave the Bartan Bazar / Basanti Nagar (208014) yard for Lucknow, Agra, Varanasi, Gorakhpur, Jhansi, Bareilly, and Patna. Steel pipes in Kanpur is the local landing page. Read Kanpur steel market for the yard address and industrial-area map.
A wall dispute at the gate is a micrometer job, not a nickname job. Hold the bundle if the stencil says M and the PO says Heavy.
Barlow pressure is not a rating
Barlow's formula is P = 2 · S · t / D, where S is the stress the calculation assumes, t is wall, D is OD, and P is the resulting internal pressure. Use it once here to show that wall is an input, not a stamp. Take 2 inch Sch 40 at D = 60.3 mm and t = 3.91 mm, and take S = 240 MPa, the A106 Grade B minimum yield already tabulated on the A106 standard page. P = 2 × 240 × 3.91 / 60.3 = 1,876.8 / 60.3 = 31.1 MPa.
That 31.1 MPa figure is the Barlow pressure this wall and stress combination would carry at minimum yield. It is not an ASME B31.3 allowable working pressure. It is not a hydrostatic test pressure. It is not a reason to thin the wall. Code design uses the allowable-stress table for the exact material line, edition, and metal temperature, plus corrosion allowance and joint efficiency.
IS 1239 leak-proof testing on the BIS product manual is 5 MPa on each tube, eddy-current or hydrostatic. That shop test is not the 31.1 MPa Barlow figure above and not a working-pressure approval for a buried JJM main.
Measuring wall at incoming inspection
The BIS product manual lists a micrometer, vernier, and steel scale for clause 8 dimensions. Measure wall at the ends and at mid-length on the sample the ITP names. Record the lowest reading. Compare it with the ordered millimetre wall and with the product-standard under-tolerance, not with a remembered percentage.
On IS 1239 the colour band and the embossed L, M, or H must match the PO class. On schedule pipe the stencil should show NPS, schedule, and specification. Heat numbers still have to match the MTC.
A short weighbridge ticket against theoretical mass is a prompt to re-measure wall and count lengths. It is not, by itself, proof of a thin wall. Threads, couplings, and zinc change finished mass. The pipe-weight chart and the weight calculator use the same 0.02466 formula for the planning number.
Mass, freight, and GST from the yard
The 2.42 MT Medium lot above sits well below a 9 MT truck band used elsewhere on this site for part-load talk. It usually travels as part of a mixed Kanpur load. Keep class bundles tagged so a Heavy fire lot cannot mix with Medium plumbing on the same challan line.
Ex-warehouse Kanpur is the comparison basis. A delivered PIN adds carriage. GST at 18% extra applies to the invoiced steel. Theoretical 5.03 kg/m is the bid check. Weighbridge mass is the commercial mass when the PO sells by actual weight.
Stock class pipe follows the 3-7 day window on the lead-time entry. Changing Medium to Heavy after the PO is a new line, not a free wall upgrade.
Where you'll meet this in procurement
You will meet Wall Thickness (WT) on size charts, mill quotes, and fitment checks. Cross-check Wall Thickness (WT) against OD, wall thickness or schedule, length, and end finish so the delivered pipe matches flanges, fittings, and pressure duty—not just a familiar nominal label.
Related terms
Related resources
Key points
- Wall is a radial millimetre dimension. Class and schedule are names for series of walls, not pressure ratings.
- 50 NB Medium is 60.3 × 3.6 mm and 5.03 kg/m. 2 inch Sch 40 is 60.3 × 3.91 mm and 5.44 kg/m.
- IS 1239 Part 1 clause 9 covers thickness and mass tolerances. A530/A530M-18 Table 1 covers A106-family pipe, not class tube.
- NBC wet-riser and hydrant pipe is Heavy class GI. Light class fails that fire service.
- Barlow P = 2·S·t/D at S = 240 MPa, t = 3.91 mm, D = 60.3 mm gives P = 31.1 MPa, not a code allowable.
Frequently asked questions
Sources
- ASTM A53/A53M-24. Note 2: nominal wall thickness exists in name only and may vary over or under the nominal (store abstract) (ASTM International)
- ASTM A530/A530M-18. General Requirements for Specialized Carbon and Alloy Steel Pipe, Table 1 wall tolerances (12.5% under nominal wall, as also stated on this site's A106 standard page); scope 1.5 includes A106 (ASTM International)
- PM/1239 (Part 1)/4 Feb 2022. IS 1239 (Part 1):2004 product manual: Cl. 8 dimensions, Cl. 9 tolerances on thickness and mass, Cl. 13 leak-proof 5 MPa, colour bands Cl. 17.2-17.4 (Bureau of Indian Standards)
- ASME B36.10M. Welded and Seamless Wrought Steel Pipe: schedule walls; Sch 40 = Standard through NPS 10; 2 inch Sch 40 wall 3.91 mm as used on this site (American Society of Mechanical Engineers)
- NBC 2016 Part 4. Fire and Life Safety: Heavy class GI for wet-riser and hydrant pipe (as already cited on the site IS 1239 page) (Bureau of Indian Standards / Ministry of Housing and Urban Affairs)