MS (mild steel) and GI (galvanised iron) pipe share the same carbon-steel ERW substrate; GI adds a hot-dip zinc coating of 400 to 600 g/m² that delays corrosion for 15 to 50 years. GI costs 15 to 25 percent more, is the default for water and outdoor use, and complicates welding because the zinc burns off at the joint.
MS vs GI side-by-side — buyer table
| Attribute | MS pipe (black) | GI pipe (galvanised) |
|---|---|---|
| Base material | Mild-steel ERW substrate | Mild-steel ERW substrate + zinc coating |
| Manufacturing route | Hot-rolled coil → forming → ERW seam | Same as MS, then hot-dip galvanising bath |
| Zinc coating mass | None | 400-600 g/m² typical (IS 4736) |
| Corrosion life (outdoor) | 1-3 years before red-rust visible | 15-50 years depending on humidity / salinity |
| Pressure rating | Same as base wall class | Same as base wall class (zinc adds no strength) |
| Cost premium | Baseline | +15-25% over equivalent MS |
| Weldability | Direct MIG/TIG/arc, no prep | Grind zinc 25 mm either side; fume hazard |
| Indian standard | IS 1239 Pt 1 (NB sizes); IS 3589 (water mains) | IS 1239 Pt 1 + IS 4736 (zinc coating spec) |
| End finish typical | Plain, bevelled or screwed | Threaded and coupled per IS 1239 |
| Primary applications | Frames, scaffolding, painted structures, fabrication | Plumbing, potable water, outdoor rails, agriculture |
When to choose MS pipe
If the line will be welded into a fabricated assembly, MS wins — the absence of zinc keeps the weld procedure simple and avoids the zinc-burn-and-repair loop at every joint. If the installation is indoors and dry (machine frames, conveyor supports, painted railings), MS wins because the cost saving is real and the corrosion risk is limited. If a downstream paint or coating system will be applied anyway (epoxy, polyurethane, 3LPE for buried), MS plus that coating is usually cheaper than GI plus the same coating.
When to choose GI pipe
If the line carries potable or process water that contacts the pipe wall, GI is the default because uncoated MS quickly causes red-water discoloration and customer complaints. If the line is exposed outdoors (rooftop plumbing, agricultural irrigation, perimeter fencing), the zinc layer delays corrosion long enough to make the cost premium worth it. If the joinery is threaded-and-coupled rather than welded (most building plumbing), GI ships ready to install with the coating intact across the run.
Welding GI — what changes
Hot-dip zinc vaporises around 907 °C, well below typical arc-weld temperatures. Welding straight through the zinc produces dense white fume (zinc oxide) that triggers metal-fume fever and contaminates the weld pool. Standard remediation is to grind the zinc back 25 mm either side of the joint, weld the bare steel with normal procedure, then repair the burned zone with zinc-rich epoxy primer (90 percent zinc by dry mass) or two coats of cold-galvanising paint. For shop fabrication, the cleaner approach is to buy black MS, weld the assembly, then hot-dip galvanise the finished item.
Standards to put on the RFQ
For MS, specify the substrate standard and class: “ERW MS pipe to IS 1239 Part 1, 50 NB Medium class, black, 6 m random”. For GI, add the coating standard and minimum mass: “ERW pipe to IS 1239 Part 1, 50 NB Medium class, hot-dip galvanised to IS 4736 minimum 400 g/m², threaded & coupled, 6 m random”. Without the IS 4736 callout, suppliers can ship a lighter electroplated coating that fails outdoor service in months rather than decades. See our IS 1239 reference and ERW pipes product page for stock.
FAQ — MS vs GI pipe procurement
What is the difference between MS and GI pipe?
Is GI pipe stronger than MS pipe?
How much more expensive is GI than MS pipe?
Can GI pipe be welded?
Which Indian standard governs MS and GI pipe?
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