What is the Difference Between GI and MS Pipe?
MS (Mild Steel) pipe is bare steel pipe made from low-carbon steel. It has no protective coating and will rust when exposed to moisture and air. It is the most economical option for dry or protected environments.
GI (Galvanized Iron) pipe is MS pipe that has been coated with a layer of zinc through a hot-dip galvanizing process. The zinc coating provides excellent corrosion resistance, making it suitable for water supply, outdoor, and damp environments.
Manufacturing Difference
- MS Pipe: Steel billet → rolled/welded into tube → cut to length. No surface treatment.
- GI Pipe: MS pipe → cleaned → dipped in molten zinc at ~450°C → cooled → inspected. The zinc coating adds 2–3% to the weight.
Weight Difference — How Much Heavier is GI?
GI pipe is approximately 2–3% heavier than MS pipe of the same nominal size. This extra weight comes from the zinc coating applied during galvanizing. The zinc layer thickness is typically 45–85 microns depending on pipe size.
For practical purposes, most engineers use the same weight tables for GI and MS pipe since the difference is within manufacturing tolerance (±3.5%). However, for large quantity orders, this 2–3% difference can be significant.
GI vs MS Pipe — Side-by-Side Weight Chart
The following table compares standard weights for both pipe types as per IS:1239 Medium class:
| Size (NB) | 🔵 MS Pipe (kg/m) | 🟢 GI Pipe (kg/m) | Difference | 6m MS (kg) | 6m GI (kg) |
|---|---|---|---|---|---|
| ½″ (21.3mm) | 1.21 | 1.24 | +2.5% | 7.27 | 7.44 |
| ¾″ (26.7mm) | 1.56 | 1.60 | +2.5% | 9.38 | 9.60 |
| 1″ (33.4mm) | 2.41 | 2.47 | +2.5% | 14.44 | 14.82 |
| 1¼″ (42.2mm) | 3.10 | 3.18 | +2.6% | 18.61 | 19.06 |
| 1½″ (48.3mm) | 3.58 | 3.67 | +2.5% | 21.47 | 22.01 |
| 2″ (60.3mm) | 5.10 | 5.23 | +2.5% | 30.60 | 31.37 |
| 2½″ (76.1mm) | 6.51 | 6.67 | +2.5% | 39.06 | 40.03 |
| 3″ (88.9mm) | 8.64 | 8.85 | +2.4% | 51.84 | 53.11 |
| 4″ (114.3mm) | 12.30 | 12.60 | +2.4% | 73.80 | 75.61 |
* GI weights include approximately 2.5% additional zinc coating weight. Actual weights may vary by manufacturer.
Cost Difference
GI pipe is consistently more expensive than MS pipe due to the additional galvanizing process. The cost premium varies by market conditions but is typically:
- GI pipe costs 15–25% more than MS pipe per kg
- For smaller sizes (½″ to 1½″), the premium can be 20–30% due to higher zinc-to-steel ratio
- For larger sizes (3″ to 6″), the premium is typically 12–18%
When to Use GI vs MS Pipe
| Application | Recommended | Reason |
|---|---|---|
| Drinking water supply | 🟢 GI Pipe | Corrosion resistance, health safety |
| Outdoor plumbing | 🟢 GI Pipe | Weather and moisture exposure |
| Underground water lines | 🟢 GI Pipe | Soil moisture and corrosion |
| Fire-fighting systems | 🟢 GI Pipe | IS:1239 compliance for fire lines |
| Structural columns/frames | 🔵 MS Pipe | Lower cost, will be painted/coated |
| Industrial dry process | 🔵 MS Pipe | No moisture, paint protection sufficient |
| Compressed air lines (indoors) | 🔵 MS Pipe | Dry air, no corrosion risk |
| Gas pipelines (natural gas) | 🔵 MS Pipe | Coated externally, IS:1239 spec |
Formula Difference
Both GI and MS pipes use the same base weight formula since they have the same steel dimensions. The only difference is the zinc coating adds ~2–3% to the final weight:
×1.025 (zinc factor)