Quick answer: GI pipes come in three wall-thickness classes: Light, Medium, and Heavy. The class decides pressure rating, not the outer diameter. Order by NB size AND class, or you risk pipes that either burst under pressure or cost you more than you needed.
The Order That Failed a Pressure Test
A plumbing contractor once ordered “25mm GI pipe” for a water supply line running at 10 bar. What showed up was Light class. It held for two weeks, then split at a joint during a routine pressure test. The site shut down for three days while he re-ordered, this time in Medium class, and ate the cost of re-piping.
The pipe wasn’t defective. It was the wrong class for the job. And “GI pipe” alone never tells a supplier which one you need.
What “Class” Actually Means
GI (Galvanised Iron) pipes are sold in the same nominal bore sizes, but with different wall thicknesses. A thicker wall means a higher pressure rating and a heavier pipe. IS 1239 defines three classes:
- Light (Class A): Thinnest wall. Lowest pressure rating. Used where the pipe carries load, not pressure.
- Medium (Class B): The most commonly ordered class. Balances pressure handling and cost.
- Heavy (Class C): Thickest wall. Highest pressure rating. Used where failure isn’t an option.
Same 25mm NB pipe, three different wall thicknesses, three different jobs.
Class-Wise Comparison
| Class | Wall Thickness (25mm NB) | Typical Pressure Use | Common Applications |
|---|---|---|---|
| Light (A) | ~2.6mm | Low pressure / non-pressure | Fencing, structural framing, conduit |
| Medium (B) | ~3.2mm | Medium pressure water lines | Domestic plumbing, irrigation, HVAC |
| Heavy (C) | ~4.0mm | High pressure lines | Industrial water supply, firefighting lines, boiler feed |
(Wall thickness varies slightly by NB size — always confirm the exact chart for your size before ordering.)
How to Pick the Right Class
Ask these three questions before you place the order:
- What’s the operating pressure? Anything above 7 bar, don’t go Light. Firefighting and industrial water lines almost always need Heavy.
- Is the pipe load-bearing or pressure-bearing? Fencing and structural framing rarely need more than Light class. Don’t overpay for pressure rating you’ll never use.
- What’s the application’s failure cost? If a burst pipe means a shut site or a safety risk, spend the extra on Heavy. If it means a minor drip you can fix same-day, Medium or even Light will do.
A Buyer’s Checklist
- Specify both NB size and class on every PO — never just “GI pipe”
- Ask your supplier for the IS 1239 wall-thickness chart for your exact size
- For pressure applications, confirm the hydro-test rating, not just the class name
- Don’t assume “Medium” is a safe default — check your actual operating pressure first
Why This Matters More Than People Think
Most GI pipe disputes don’t happen because the pipe was faulty. They happen because the PO said “GI pipe, 25mm” and left the class to guesswork. The supplier ships what’s in stock. If that’s Light and the job needed Heavy, you find out during the pressure test, not before.
At Sanjay Sales, every GI pipe order is confirmed against class and IS 1239 specs before dispatch, so you know exactly what’s arriving before it leaves the yard.
Need GI pipes in a specific class or size? Contact us for current stock across Light, Medium, and Heavy classes.
