When engineers, builders, or procurement teams search for ERW, GP, GI, and MS pipes, they usually face the same problem: the terms look similar, but they refer to different things—a manufacturing process, a coating type, or a steel material. Choosing the wrong one can lead to higher maintenance, premature corrosion, or failed inspections.
Here is the simple explanation up front:
- ERW Pipe refers to how the pipe is made (Electric Resistance Welded).
- MS Pipe refers to the base material (mild steel).
- GP Pipe and GI Pipe refer to the type of zinc coating applied (electro-galvanized vs hot-dip galvanized).
This guide explains each type clearly, how they’re manufactured, how they differ, and where they’re used so you can choose confidently for any project.
Understanding ERW, GP, GI, And MS Pipes
What Is ERW Pipe?
ERW (Electric Resistance Welded) Pipe is formed by shaping steel strips into a tube and welding the seam using high-frequency current. It provides:
- Consistent dimensions
- Smooth internal surface
- Reliable weld quality
- Competitive cost
Because of its balance of strength and efficiency, ERW Pipe is widely used in construction, fire protection systems, HVAC, and general mechanical lines.
What Is GP Pipe?
GP (Galvanized Plain) pipe is steel coated using electro-galvanizing, which applies a thin, uniform zinc layer. This coating offers light to moderate corrosion resistance.
Common uses include:
- Indoor plumbing
- Furniture and racks
- Light structural frames
GP pipes are best for controlled indoor environments rather than harsh outdoor conditions.
What Is GI Pipe?
GI (Galvanized Iron) pipes are hot-dip galvanized, forming a thick, bonded zinc layer that protects steel from corrosion.
They are widely used for:
- Outdoor water supply
- Agricultural irrigation
- Building exteriors
- Humid or coastal regions
In the GP vs GI comparison:
GP = thin zinc for indoor use
GI = thick zinc for outdoor use
What Is MS Pipe?
MS (Mild Steel) pipes are uncoated low-carbon steel pipes with excellent weldability and workability. They are used for:
- Structural frames
- Fabrication work
- Machinery and automotive parts
However, MS pipe needs paint or coating if exposed to moisture.
How These Pipes Are Manufactured?
ERW Pipe Manufacturing
- Slitting steel coils
- Forming into a round shape
- High-frequency welding
- Straightening and sizing
- Dimensional and weld testing
ERW manufacturing is efficient, repeatable, and suitable for large-scale production.
GP Pipe Manufacturing (Electro-Galvanizing)
- Steel pipe is cleaned
- Immersed in a zinc solution
- Electrical current deposits a uniform zinc layer
This process creates a bright, smooth finish ideal for indoor applications.
GI Pipe Manufacturing (Hot-Dip Galvanizing)
- Steel pipe is cleaned and pre-treated
- Dipped into molten zinc
- Coating bonds metallurgically
- Cooled and inspected
This thicker coating gives GI pipe its well-known outdoor durability.
MS Pipe Manufacturing
MS pipes are formed (often by ERW welding) but without any zinc coating, making them more affordable but requiring protective paint or powder coating for outdoor use.
Key Differences Between ERW, GP, GI, And MS Pipes
Coating & Corrosion Protection
- MS Pipe – no coating, lowest corrosion resistance
- GP Pipe – thin electro-galvanized layer, indoor use
- GI Pipe – thick hot-dip zinc layer, outdoor use
- ERW Pipe – can be MS, GP, or GI depending on coating
GI pipes last the longest in harsh conditions.
Strength & Performance
ERW Pipe has a strong, reliable weld seam and consistent diameter.
GP and GI pipes primarily differ in coating—not strength.
Cost Differences
Lowest → Highest:
MS → ERW → GP → GI
GI pipes cost more but often provide the best lifecycle value outdoors.
Recommended Reading
If you want a deeper comparison of manufacturing methods, read:
What Is the Difference Between ERW and SMLS Pipe? Your Complete Guide for Global Buyers
Practical Uses Of Each Pipe Type
Uses Of ERW Pipes
- Fire protection systems (with FM/UL approval)
- HVAC and mechanical lines
- Structural construction
- Water distribution and utilities
ERW Pipe is one of the most versatile and widely used steel tube types.
Uses Of GP Pipes
- Indoor plumbing
- Handrails and furniture
- Interior frames and supports
GP pipes perform best where corrosion risk is moderate.
Uses Of GI Pipes
- Residential and commercial water supply
- Irrigation systems
- Outdoor structural applications
- Humid or coastal environments
GI pipe offers excellent long-term durability outdoors.
Uses Of MS Pipes
- Fabrication and machinery
- Automotive frames
- Building frames
- Industrial support structures
MS pipe is easy to weld and cost-effective for indoor or protected environments.
How To Choose The Right Pipe Type?
Choose Based On Environment
- Indoor → MS or GP
- Outdoor → GI
- Fire protection → ERW with FM/UL
- Coastal regions → GI or specially coated ERW
Choose Based On Corrosion Protection
- Minimal → MS
- Moderate → GP
- High/Outdoor → GI
Choose Based On Budget & Lifespan
MS is cheapest but needs coating;
GI has higher upfront cost but lowest long-term maintenance.
Choose Based On Standards
Check project requirements for:
- ASTM or EN structural standards
- GI coating standards (ASTM A123, EN 10240)
- Fire protection approvals (FM/UL for ERW Pipe)
Common Mistakes To Avoid
Using MS Pipes Outdoors Without Coating
Rust forms quickly without paint or protection.
Selecting GP Pipes For Humid Or Coastal Areas
Electro-galvanized coating is too thin for harsh environments.
Using GI Pipes In Fire Systems Without Certification Check
Some fire systems require ERW Pipe with FM/UL approval.
Buying ERW Pipes Without Test Reports
Always request MTC, weld inspection, and coating data.
FAQs
Q: Is ERW Pipe suitable for structural and fire uses?
Yes—when certified and tested, ERW Pipe is widely used in these applications.
Q: What’s the difference between GP and GI pipes?
GP = thin electro-galvanized zinc
GI = thick hot-dip zinc for heavy corrosion protection.
Q: Can MS pipes be used outdoors?
Yes, but only with paint or protective coating.
Q: Are GI pipes safe for water supply?
Commonly used for water lines; check local standards for specifics.
Baolai Steel — Reliable Supplier For ERW, GP, GI & MS Pipes
Baolai Steel manufactures ERW pipes, GP and GI galvanized pipes, and MS pipes with full traceability, export-grade quality, and consistent dimensions. Our ERW Pipe solutions for fire protection are available with FM/UL approvals, supporting projects worldwide.
Final Thoughts
Understanding the differences between ERW, GP, GI, and MS pipes helps avoid costly mistakes and ensures long-term performance. Whether your project involves water supply, construction, fire protection, or fabrication, selecting the right pipe type is essential for safety and durability.
If you need help choosing the correct material, Baolai Steel’s technical team can provide project-specific recommendations and support.
Looking for certified ERW, GP, GI, or MS pipes for your next project? Visit our Contact Us page and speak directly with our technical team for specifications, pricing, and expert guidance.
