Galvanised (GI)
/glossary/galvanisedSteel pipe coated with zinc layer for corrosion resistance in outdoor and wet environments.
Galvanised (GI) pipe is steel tube with a hot-dip zinc coating. The tube follows IS 1239 Part 1 and the coating follows IS 4736, whose amended minimum is 360 g/m². Kanpur JJM and PWD contractors buy it by NB and Light, Medium, or Heavy class with threaded and coupled ends. In the dated site table GI lands 15 to 25 percent above black MS. Quotes from RP Sales are ex-warehouse Kanpur, GST 18% extra.
In detail
Galvanised (GI) pipe is steel tube with a hot-dip zinc coating. The tube follows its own product standard, usually IS 1239 Part 1 for NB 15 to 150, and the coating follows IS 4736, whose amended minimum is 360 g/m². Zinc gives sacrificial corrosion protection, but service life depends on exposure, water chemistry, jointing, and maintenance. GI suits plumbing, water distribution, fencing, and selected fire-system work only where the approved specification calls for galvanized steel.
What galvanised pipe is, and what it is not
GI pipe is steel pipe protected by a hot-dip zinc coating. IS 1239 Part 1 supplies the dimensional and product basis for common steel tubes, while IS 4736 addresses the hot-dip zinc coating.
IS 4736:1986 stays Active on the BIS e-sale catalogue, reaffirmed in 2021 with 4 amendments. The BIS steel-tube certification manual ties Cl. 5.1 to a minimum zinc mass of 360 g/m² for tubes up to 6 mm thick, checked on 100 mm pieces per IS 6745.
Galvanized is not a grade and not a pressure rating. The zinc layer is a corrosion-control measure; it does not replace the steel-tube class, pressure design, joint specification, or project inspection needs.
GI tubes follow IS 1239 Part 1, while Part 2 covers wrought-steel fittings and tubulars. A purchase order that says only galvanized leaves the edition, coating evidence, surface condition, and acceptance basis unclear.
Who should order GI, and who should order black or another product
GI suits above-ground water distribution, building plumbing, exposed utility lines, agricultural installations, fencing, and selected fire-system work when the approved specification calls for galvanized steel.
JJM and PWD contractors preserve the exact NB, class, ISI marking, coating, and document wording from the tender schedule. Building plumbers state threaded and coupled or plain ends before comparing bundles.
Do not select GI only because the service contains water. Buried lines, chemical service, high-temperature lines, and fire networks can need a different material, coating system, or wall class under the project design.
Heavily welded structural work starts from black MS where the drawing wants an uncoated substrate, since welding burns the zinc at every joint. IBR boiler and steam-piping tubes never take GI as a substitute, because zinc adds no strength.
For saline zones, specify galvanised or coated casing separately, since zinc improves corrosion life but never compensates for a thin wall. No material follows from the word saline alone; the water and soil analysis goes to the designer.
GI versus black MS price bands
Both columns come from the dated site tables for Medium class. Premiums divide same endpoints and round to whole percent.
| Size | MS Medium (₹/kg) | GI Medium (₹/kg) | GI premium, min end | GI premium, max end |
|---|---|---|---|---|
| 50 NB (2 inch) | 53-60 | 65-73 | 23% | 22% |
| 80 NB (3 inch) | 52-58 | 63-71 | 21% | 22% |
| 100 NB (4 inch) | 51-57 | 62-70 | 22% | 23% |
The site table premium statement is 15-25% over equivalent black MS. Service life depends on exposure, water or soil chemistry, fabrication damage, installation, and maintenance; no fixed number of years follows from the premium.
How to specify galvanised pipe on an RFQ
A galvanized RFQ needs two standards on one line plus the commercial details, so a price comparison never alters the technical basis.
- Tube: IS 1239 Part 1, nominal bore, Light, Medium, or Heavy class, and grade.
- Coating: IS 4736:1986 with applicable amendments, minimum 360 g/m² where the amended clause governs.
- Length: standard 6 m; ends threaded and coupled with GI socket, or plain end, with coupling quantity.
- Quantity in metres or MT, with marking, packing, and inspection needs.
- Documents: MTC plus the galvanising certificate or coating record; BIS licence details where required; TPI stage.
- Delivery: ex-warehouse Kanpur or delivered, with consignee and e-way bill address; GST stated separately.
- Tender supply: attach the BOQ page and ask the supplier to reproduce the description on the quotation.
Worked example: 200 lengths of 50 NB Medium GI
50 NB Medium has OD 60.3 mm and wall 3.6 mm on the site weight chart. W = (60.3 − 3.6) × 3.6 × 0.02466 = 56.7 × 3.6 × 0.02466 = 5.03 kg/m, so a 6 m length is 30.2 kg of steel.
Zinc adds roughly 3-6% over the plain-end MS weight depending on coating class and surface area. A coated 6 m length is therefore about 31.1 to 32.0 kg.
Two hundred lengths are 200 × 30.2 = 6,040 kg (6.04 MT) of steel, or about 6.22-6.40 MT coated. The lot sits below the 9 MT truck band, so it moves as part-load or a combined load.
The GI band for 50 NB Medium is ₹65-73 per kg ex-warehouse Kanpur as of 24 May 2026. The steel line is 6,040 × 65 = ₹392,600 (about ₹3.93 lakh) to 6,040 × 73 = ₹440,920 (about ₹4.41 lakh), before GST and freight. Confirm whether the invoice uses theoretical mass or coated weighment on the MTC.
Common mistakes on GI orders
In practice, buyers write galvanized alone on the PO. That single word leaves the edition, coating mass, evidence, surface condition, and acceptance basis unclear.
A second mistake names only IS 1239. That controls the steel substrate but does not state the zinc-coating requirement, so the coating line must join it.
A third mistake copies an older class table into a new PO. The amended basis is 360 g/m² where that clause governs, not the superseded earlier figure.
A fourth mistake welds GI freely on structural work. Each weld burns the zinc and leaves the weld zone uncoated, which the drawing must address.
A fifth mistake translates every coated BOQ item into IS 1239 GI. Borewell casing keeps its own product specification with the specified thread form, and fire lines follow the approved riser and hydrant specification.
Standards and compliance for galvanised pipe
IS 1239 Part 1 (2004) defines Light, Medium, and Heavy walls for welded tubes from 15 to 150 mm NB with YST grade designations. Take the test method, pressure, sampling, and acceptance from the ordered edition and inspection plan.
IS 4736 governs the coating: mass of zinc (Cl. 5.1, 360 g/m² minimum average) and free bore (Cl. 5.3), plus freedom from defects, uniformity and adhesion tests.
Acceptance tests on the site IS 4736 guide are the hydrochloric-acid strip for mass in g/m² and repeated copper-sulphate (Preece) dips for uniformity. Adhesion is judged under handling and bending, and visual checks cover blistering, peeling, bare spots, ash, and lumps.
EN 10204 Type 3.1 is the standard mill certificate for the coating and the substrate alike. Galvanizing must be explicitly ordered and reconciled with threading, welding, coating continuity, and site needs.
Galvanizing delays corrosion but sets no fixed service life and proves nothing about potable, buried, fire, or structural duty by itself. Each use needs its governing code, chemistry, dimensions, joints, and inspection.
Buying GI pipe in Kanpur
Latouche Road and Bartan Bazar yards move stocked GI by the bundle, like black ERW. Kanpur plumbing contractors, PWD and JJM tender buyers, fire-system installers, and agricultural buyers name NB, class, coating, ends, and quantity on the RFQ.
RP Sales quotes stocked GI ex-warehouse Kanpur from the Latouche Road and Bartan Bazar yards, GST 18% extra.
JJM house-connection and PWD distribution lots follow the class the tender schedule states. Copy it instead of applying a universal class rule, and compare the ex-warehouse or delivered basis with freight and taxes stated separately.
See GI pipes in Kanpur, the GI pipe price list, MS vs GI, the class thickness chart, and the Kanpur steel market.
Coating tests and goods-receipt checks
Ask for the galvanising certificate with the MTC. The mass-of-coating result in g/m² must meet the 360 minimum where the amended clause governs; hold a lower or missing result for written technical review.
Check uniformity through the Preece dip count, adhesion through handling and bend behaviour, and surface through visual examination. The free-bore check runs a 230 mm rod of suitable size through the tube.
Reconcile pipe stencil, bundle tag, heat identity, dimensions, coating, certificate, and test reports before release. A generic test sheet does not supply the coating evidence the contract states.
Where TPI applies, name the agency and hold points on the PO. SGS, Bureau Veritas, Lloyds, and TUV are the inspection agencies the Kanpur yard coordinates with when the RFQ names one.
Threads, welding, and coating continuity
Standard GI supply is 6 m threaded and coupled with a GI socket. State threaded and coupled or plain ends before comparing bundles, since re-threading and re-coupling change the delivered cost.
Order galvanizing explicitly and reconcile it with threading, welding, and coating continuity on the same line. Cut ends, threads, and weld zones follow the project specification for coating acceptance.
Handle bundles so cutting, welding, storage, and transport do not strip the zinc before installation. The galvanising certificate covers the mill coating, not site workmanship.
Fire-system installers match the approved riser, hydrant, and branch-line specification rather than choosing by colour or coating alone. NBC 2016 practice points wet risers to Heavy class GI, but the fire consultant confirms the class.
Delivery basis and dispatch from Kanpur
Use ex-warehouse Kanpur when the buyer arranges transport and the delivered PIN when the supplier does. Freight is quoted for the actual load and PIN code, with dedicated-truck versus part-load as a quote field.
Daily dispatch from Kanpur covers Uttar Pradesh, Bihar, Madhya Pradesh, Delhi NCR, and Uttarakhand. State the city route and PIN for Lucknow, Agra, Prayagraj, Varanasi, Gorakhpur, Jhansi, Bareilly, or Patna on the RFQ.
Put the consignee and e-way bill address on the order with the coating and document needs. A 6.04 MT GI lot like the worked example can share a truck with black ERW when bundle sizes and handling stay compatible.
Send NB, class, coating, ends, quantity, and inspection scope on the RFQ for a technical and commercial offer within 4 working hours.
Where you'll meet this in procurement
You will meet Galvanised (GI) when choosing process route and product family. Match Galvanised (GI) to pressure, temperature, corrosion duty, and standard (IS, ASTM, ASME, or API) so the mill route and documentation line up with the application.
Related terms
Related resources
Key points
- GI pipe is IS 1239 Part 1 steel tube plus a separate IS 4736 hot-dip zinc coating line on the PO.
- The amended IS 4736 minimum is 360 g/m² where that clause governs; IS 1239 alone does not state zinc.
- In the dated site table GI costs 15-25% above equivalent black MS, with no fixed service life attached.
- Zinc burns off at welds, so welded structural work and IBR boiler tubes stay off GI.
- Quotes are ex-warehouse Kanpur, GST 18% extra; ask for the galvanising certificate with the MTC.
Frequently asked questions
Sources
- IS 4736:1986. Hot-dip Zinc Coatings on Mild Steel Tubes; Active, reaffirmed 2021, 4 amendments (BIS e-sale catalogue fetched 2026-09-05) (Bureau of Indian Standards)
- BIS steel-tube certification manual. Manual for certification of steel pipes, tubes and fittings; IS 4736 Cl. 5.1 minimum 360 g/m², Cl. 5.3 free-bore 230 mm rod (PDF fetched 2026-09-05) (Bureau of Indian Standards)
- IS 1239 (Part 1):2004. Steel tubes, tubulars and other wrought steel fittings (tube basis for common GI) (Bureau of Indian Standards)
- EN 10204:2004. Metallic products. Types of inspection documents (European Committee for Standardization (CEN))