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Technical Reference
IS 1239 Class A, B, C Pipe Thickness Chart
Light, Medium and Heavy wall thickness in millimetres for every common NB from 15 to 150. Use this chart when you enquire for Class B GI and MS pipe.
Under IS 1239, Class A is Light, Class B is Medium and Class C is Heavy. Wall thickness depends on nominal bore (NB). It is not one fixed millimetre for every size. For the widely searched 25 NB size, Class A is 2.6 mm, Class B is 3.2 mm and Class C is 4.0 mm.
When an approved MS or GI ERW requirement uses the IS 1239 three-class system, the order line still needs a nominal bore and millimetre wall. A line that says only Light, Medium or Heavy is not enough. Searches such as "b class pipe thickness in mm" show that missing dimensional detail. The chart below puts the class wall next to the OD for NB 15-150. It does not tell you which class a service needs.
Use the table for RFQs, BOQ checks and weight estimates. Pair it with the IS 1239 standard reference for marking and tolerance context, and with the steel pipe weight calculator when you need kg/m for freight. Indicative MS and GI bands are on the MS pipe price list and GI pipe price list.
You convert these walls into tonnage in Kanpur before you raise a purchase order. A 50 NB Medium line with 60.3 mm OD and 3.6 mm wall weighs 5.03 kg per metre.
Piece count, length, actual or theoretical billing basis, packing, vehicle payload, consolidation, route, access and unloading still determine truck fill and freight. Send us those fields with the BOQ. The written Kanpur quotation covers rate, documents, freight and dispatch timing.
Note: Values below are IS 1239 Part 1 ground-truth dimensions for Class A (Light), Class B (Medium) and Class C (Heavy). Write NB, class or exact wall (mm), material (MS/GI), length and end finish on the purchase order. Colour-band trade practice is a field aid, not a substitute for mill marking and MTC.
IS 1239 Class A / B / C Wall Thickness Chart (mm)
Columns show NB (mm), OD (mm) and wall thickness for Class A (Light), Class B (Medium) and Class C (Heavy). All wall values are millimetres.
| NB (mm) | OD (mm) | Class A / Light WT (mm) | Class B / Medium WT (mm) | Class C / Heavy WT (mm) |
|---|---|---|---|---|
| 15 | 21.3 | 2.0 | 2.6 | 3.2 |
| 20 | 26.9 | 2.3 | 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 | 2.9 | 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 | 4.8 |
| 100 | 114.3 | 3.6 | 4.5 | 5.4 |
| 125 | 139.7 | 4.5 | 4.8 | 5.4 |
| 150 | 165.1 | 4.5 | 4.8 | 5.4 |
What is Class B pipe thickness in mm?
Class B (Medium) thickness depends on NB. At 25 NB it is 3.2 mm; at 50 NB it is 3.6 mm; at 80 NB it is 4.0 mm; at 100 NB it is 4.5 mm. There is no single "Class B millimetre" for every size.
That is why a "b class pipe thickness in mm" enquiry needs the full chart rather than a single value. Medium is a class name. It is not a default for water, structural, plumbing or pressure duty. The approved design and project specification must select the product standard, grade, class or exact wall for the stated loads and service. When a BOQ says only "B class GI", get NB, grade, metres, coating requirement, end finish, tolerance and inspection scope confirmed before we quote. Cross-check the chart before you convert an old "Medium" note into a purchase order.
Which class for home plumbing / borewell / fire line?
A service label does not select Light, Medium or Heavy class. Copy the class or exact wall from the approved design and BOQ after you check pressure, temperature, corrosion, supports, joining, handling, testing and authority requirements. Borewell casing and fire systems may require another standard.
Installation details such as threading, clamping, burial, corrosion exposure and handling affect the design. They do not create a universal Medium or Heavy rule. Fire systems and borewell casing can also fall under different product standards and authority requirements. Read the drawing legend and governing specification first. If either is incomplete, obtain design clarification. Do not increase class by rule of thumb. We quote alternatives only as clearly identified options subject to your technical approval. Product-family references for ERW pipes and tubeshelp separate the enquiry from schedule pipe, structural section and water-well casing.
How are classes marked?
Indian trade practice commonly marks Light / Class A with a yellow band, Medium / Class B with blue and Heavy / Class C with red. Check NB, wall and mill marking. Paint can be wrong after rework.
Colour bands are a yard and site convention. They are not a substitute for the permanent mill stencil and the inspection documents. Bundles get mixed when multiple classes share a truck. On incoming inspection you should measure a sample OD and wall with a micrometer or vernier, match heat or batch marks to the MTC and reject mixed classes that lack clear identification. For tender work, write both the class name and the wall in millimetres on the BOQ so a disputed blue band cannot override a measured 3.2 mm requirement. For a Kanpur enquiry, send us NB, class or exact wall, grade, finish, quantity, document scope and delivery PIN so the accepted quotation and purchase order identify the wall before we release material.
Class vs schedule: are they the same?
No. IS 1239 Class A/B/C is not the same system as ASME pipe schedule (Sch 40, Sch 80). Compare actual wall thickness in millimetres. Use the pipe schedule chart for ASME values.
Schedule numbers come from the ASME B36.10M family used heavily in process and imported equipment packages. Class A/B/C language dominates Indian MS/GI ERW tube trade for water, structural and general utility pipe. A drawing that says "Sch 40" and a quotation that names "B class" are not automatically interchangeable even when walls look close at one NB. Convert both to OD and wall in mm, then to kg/m if freight or support design depends on mass. Mixing the two vocabularies without a conversion step is a common cause of wrong wall on site and failed hydro or fit-up checks.
Buying IS 1239 pipe in Kanpur
For Kanpur, Unnao and Kanpur Dehat tender work, you should reproduce the applicable BOQ and drawing. Do not infer a class from the authority, industry, burial condition or pressure label. A fire-system line, process-water line, steam pipe, precision component and water-well casing can require different standards, design checks and inspection records even when nominal dimensions look similar. Separate each material line and obtain approval for any proposed class, schedule, grade or product-standard substitution.
We confirm dispatch timing from the Bartan Bazar yard in the written quotation for the specific order. Share the delivery PIN, total tonnage and required-at-site time so the quote separates dispatch from arrival. We do not promise a universal lead time. Mixed loads may consolidate ERW, seamless and precision tubes into one truck when the quotation allows. Start from the steel pipes Kanpur page, pick GI lines on GI pipes Kanpur or MS ERW on the MS ERW supplier page, and read the Kanpur steel market guide for freight and documentation practice.
MS versus GI price bands in Kanpur
The ordered class identifies the nominal wall for the listed size. Price still depends on size, grade, finish or coating requirement, coating mass, source, quantity, commercial terms and quotation date. Indicative bands below are ex-warehouse Kanpur, reviewed 24 May 2026, and exclude GST at 18 percent as published on the linked price lists on that date. They track coil and zinc markets and are not firm quotes.
| Product family | Size range | Indicative band (₹/kg) | Bands as of |
|---|---|---|---|
| MS ERW, IS 1239 Light / Medium / Heavy | 15 to 150 NB | 47 to 70 | 24 May 2026 |
| GI pipe, IS 1239 galvanized | 15 to 150 NB | 57 to 86 | 24 May 2026 |
The dated bands shown span ₹47-70/kg for MS ERW and ₹57-86/kg for GI as of 24 May 2026, but their endpoints do not establish a reusable coating premium for a particular size or order. Size-wise detail sits on the MS pipe price list and the GI pipe price list. Compare current written quotations only after class, grade, coating requirement, quantity, billing weight basis, documents and delivery terms match.
Worked example: 200 lengths of 25 NB Class B
Take the most quoted domestic size: 25 NB Class B with OD 33.7 mm and wall 3.2 mm. The weight formula gives (33.7 minus 3.2) times 3.2 times 0.02466, which is 2.41 kg per metre. One 6 m trade length weighs about 14.5 kg.
An order of 200 lengths therefore totals about 2,900 kg, which is 2.9 MT. You fill the balance of a load with other ordered sizes only when packing and document segregation permit. For GI, do not add a universal percentage to black-pipe mass. Use the applicable coating requirement and the offered or measured coated mass stated for the lot.
RFQ checklist for IS 1239 pipe
Send us these ten items with every class enquiry so we price the exact line you need.
- NB with OD in mm, since nominal bore alone does not define diameter.
- Class name plus exact wall in mm, for example Class B 3.2 mm at 25 NB.
- Material or grade only as named by the applicable product standard, approved design and BOQ; do not select it from threading alone.
- Black or galvanized finish only as specified, with the applicable coating requirement and offered inspection evidence confirmed in the written quotation and PO.
- Length: standard 6 m trade lengths or exact cut-to-length sizes.
- End finish: plain end or threaded and coupled for site jointing.
- Required MTC type and heat traceability, named in the RFQ and confirmed in the quotation.
- Any third-party agency or approval process, scope, hold points, location, fees and release evidence; we confirm allocation in the written quotation.
- Quantity in lengths and MT, so we can plan truck fill and freight.
- Delivery PIN with ex-warehouse Kanpur versus delivered terms stated.
Common mistakes in class procurement
Class and grade get mixed up more than anything else. Class sets wall thickness. Grade sets yield strength through YST 210, 240 or 310. A Class C YST 210 pipe is thick but not high-strength, while a Class A YST 310 pipe is strong but thin. Orders that name only one of the two get quoted both ways and compared wrongly.
Threading is the next failure point. Light class thins further at threads and dents in handling, so thread preparation can reduce effective section or damage a tube when it does not follow the ordered standard and approved joint detail. Do not infer a permissible threaded, buried, pressurised or fire duty from the class name alone. Do not accept a mixed bundle on colour bands alone. Verify sampled dimensions, permanent markings and the traceability records required by the purchase order.
Standards and compliance
IS 1239 Part 1 (2004) defines the Light, Medium and Heavy walls for welded tubes from 15 to 150 mm NB, with grades drawn from the YST system: 210, 240 and 310 MPa minimum yield. Use the ordered edition and test clause for the exact product. Do not apply one hydrotest statement to every size. Hot-dip galvanizing for GI lines follows IS 4736. The original 1986 clause used 400 g/m² minimum average coating mass, and Amendment 3 substituted 360 g/m². Confirm the current ordered requirement and lot record. The full clause context is on the IS 1239 standard reference. Schedule conversions are on the pipe schedule chart.
Key points
- Class A is Light, Class B is Medium and Class C is Heavy; wall varies by NB, never one fixed mm.
- 25 NB Class B at 33.7 mm OD and 3.2 mm wall weighs 2.41 kg per metre, about 14.5 kg per 6 m.
- Order class plus grade plus exact wall; colour bands are a field aid, not proof.
- Do not apply a universal GI price premium or mass uplift; compare the dated quotation and the offered coated mass for the same size, class and quantity.
- Send us NB, finish, MTC and delivery PIN when you ask us to quote IS 1239 from Kanpur.
References
- IS 1239 (Part 1):2004: Steel Tubes for Water and Sewage, Specification, Part 1, Bureau of Indian Standards. Cited by code and clause; no specific catalogue page was reachable from this environment.
- IS 1161:2014: Steel Tubes for Structural Purposes and General Engineering, Specification, Bureau of Indian Standards. Cited by code for YST 210, 240 and 310 grades.
- IS 4736: Hot-Dip Zinc Coating on Steel Tubes, Bureau of Indian Standards. The original 1986 clause used 400 g/m² minimum average coating mass; Amendment 3 substituted 360 g/m². Confirm the current ordered requirement and lot record.
- ASME B36.10M: Welded and Seamless Wrought Steel Pipe, American Society of Mechanical Engineers. Catalogue page (fetched HTTP 200, 3 Sep 2026): asme.org: B36.10M welded and seamless wrought steel pipe.
Frequently Asked Questions
Related Resources
- IS 1239 Standard: Full Reference
- Pipe Schedule Chart (ASME)
- MS Pipe Price List
- GI Pipe Price List
- Steel Pipe Weight Calculator
- ERW Pipes & Tubes
- Steel Pipes Supplier in Kanpur
- GI Pipes Supplier in Kanpur
- MS ERW Pipe Supplier in Kanpur
- Kanpur Steel Market Buyer Guide
Need IS 1239 Class A / B / C pipe?
Send us NB, class or wall (mm), MS or GI, quantity and delivery PIN. We quote wholesale from Kanpur with the document scope confirmed in the written offer.
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