MS vs. GI Pipes: Which Is Better for Industrial Plumbing?

Choosing between Mild Steel (MS) and Galvanized Iron (GI) pipes is a critical decision for industrial plumbing systems, as it directly impacts performance, lifespan, and cost.

This guide will provide a comprehensive comparison of MS and GI pipes for industrial applications, analyzing their differences, performance characteristics, installation, maintenance, and cost factors.

The aim is to equip readers with the knowledge to select the optimal piping solution for their specific industrial needs, ensuring reliability and longevity.

What Are MS and GI Pipes? The Fundamentals

To properly compare Mild Steel and Galvanized Iron pipes, we must first understand what each material is and how it is produced. This foundational knowledge is crucial for understanding their distinct properties and performance characteristics.

Mild Steel (MS) Pipes: The Backbone of Basic Piping

Mild steel, also known as low-carbon steel, is a type of carbon steel characterized by a low carbon content (typically ranging from 0.05% to 0.25% by weight). This low carbon content makes it relatively soft, ductile, and easy to form, weld, and machine. Unlike higher carbon steels, it is not easily hardened through heat treatment. It contains other elements, such as manganese, silicon, sulfur, and phosphorus, but in much smaller quantities.

Manufacturing Process

MS pipes are typically manufactured through two primary methods:

Seamless: Produced from a solid round billet, which is heated and then pushed or pulled over a piercing rod to create a hollow tube without any weld seam.
Welded (ERW or SAW): Produced from steel strips or plates that are rolled into a cylindrical shape and then welded along the seam.
Electric Resistance Welding (ERW): The edges of the rolled strip are heated and fused by an electric current.
Submerged Arc Welding (SAW): The edges are welded using an arc submerged in granular flux, creating a strong, but sometimes thicker, weld seam.

Galvanized Iron (GI) Pipes: Adding a Protective Layer

The term “Galvanized Iron” is commonly used, but it’s technically a misnomer in modern piping. The pipes are made of steel (mild steel, specifically) that has undergone a process called galvanization. Therefore, it’s more accurate to refer to them as “Galvanized Steel” pipes, but the industry frequently uses “GI pipes.”

Galvanization is the process of applying a protective zinc coating to steel or iron to prevent rust and corrosion. Zinc serves as a barrier coating and also acts as a sacrificial anode, meaning it corrodes preferentially to the steel underneath, providing cathodic protection even if the layer is scratched or damaged.

Galvanization Process (Hot-Dip Galvanizing)

The most common method for galvanizing pipes is hot-dip galvanizing. The process involves several steps:

Cleaning: The steel pipe is thoroughly cleaned to remove dirt, grease, oil, and other impurities. This is typically accomplished through degreasing and pickling (an acid bath) to remove mill scale and rust.
Fluxing: The cleaned pipe is then dipped in a flux solution (typically zinc ammonium chloride), which removes any remaining oxides and prevents further oxidation before galvanizing.
Dipping: The pipe is immersed in a bath of molten zinc, heated to around 450°C (840°F). The steel reacts with the molten zinc, forming a series of zinc-iron alloy layers on the surface, topped by a layer of pure zinc.
Cooling: After withdrawal from the zinc bath, the pipe is cooled, usually in water or ambient air.

Key Differences: A Comparison for Industrial Use

Comparing MS and GI pipes goes beyond just the presence of a zinc coating. Their distinct properties impact performance in critical areas for industrial plumbing. Let’s break down the key differences:

Corrosion Resistance

MS Pipes: Highly susceptible to corrosion, especially rust (iron oxide), when exposed to moisture and oxygen. In industrial environments, this can be accelerated by humidity, chemicals in the air or carried by the fluid, and stagnant water.
GI Pipes: Offers significantly higher corrosion resistance due to the protective zinc coating. The zinc acts as a barrier and a sacrificial anode, protecting the underlying steel even if the layer is scratched.

Strength and Structural Integrity

MS Pipes: Offer excellent tensile strength and structural integrity, making them suitable for various pressure applications. The strength is inherent in the steel itself.
GI Pipes: The zinc coating itself is relatively thin. GI pipes have similar structural strength to equivalent MS pipes in terms of pressure-bearing capacity.

Weight

MS Pipes: The weight is determined by the steel’s density and the pipe’s dimensions (diameter and wall thickness).
GI Pipes: Slightly heavier than equivalent MS pipes due to the added weight of the zinc coating.

Temperature Tolerance

MS Pipes: Can handle a wide range of temperatures, limited primarily by the properties of steel itself and the pressure ratings at elevated temperatures.
GI Pipes: While the steel pipe can withstand high temperatures, the zinc coating starts to degrade and oxidize rapidly above certain thresholds (around 200°C or 392°F).

Cost

MS Pipes: Generally have a lower upfront material cost compared to GI pipes of the same size and schedule.
GI Pipes: Have a higher initial cost due to the extra manufacturing step (galvanization).

Joining Methods

MS Pipes: Can be joined using various methods, including welding, threading, flanging, and mechanical couplings.
GI Pipes: Can also be joined by threading, flanging, and mechanical couplings.

Surface Finish

MS Pipes: Typically have a darker, mill-finish surface that is prone to rust unless painted or coated externally.
GI Pipes: Have a distinct grayish, often crystalline (spangled) zinc-coated surface.

Installation and Fabrication

MS Pipes: Easier to cut, bend, and weld due to the absence of the zinc coating.
GI Pipes: Cutting and threading require care to ensure the zinc coating is not excessively damaged at the ends.

Performance and Suitability in Industrial Plumbing

The choice between MS and GI pipes in industrial plumbing depends heavily on the specific fluid being transported, the operating conditions (pressure and temperature), the surrounding environment, and regulatory requirements. Let’s look at typical industrial applications and the suitability of each pipe type.

Process Water Piping

Application: Transporting water used in manufacturing processes, cooling systems, boiler feed, etc. Water quality can vary (raw, treated, demineralized, chilled).

Considerations: Internal corrosion is a significant concern, particularly with untreated or partially treated water that contains dissolved oxygen and minerals.

Recommendation: GI is generally preferred for standard process water lines where temperatures are moderate (<60-70°C) due to superior corrosion resistance. For high-purity or aggressive water, or high temperatures, other materials such as stainless steel or plastics may be better suited.

Compressed Air Systems

Application: Distributing compressed air throughout the plant for tools, machinery, and instrumentation.

Considerations: Compressed air often contains moisture (condensate), which can cause internal corrosion. External corrosion can also be a factor, depending on the environment. Pressure ratings are typically higher than water lines.

Recommendation: GI pipes are a common and reliable choice for compressed air distribution due to their resistance to internal corrosion from moisture.

Steam Piping

Application: Conveying low, medium, or high-pressure steam for heating, process use, or power generation.

Considerations: High temperatures and pressures are involved. Condensate (hot water) also contributes to corrosion.

Recommendation: MS pipes (or specialized alloys for extremely high temperatures and pressures) are the standard for industrial steam piping. GI is unsuitable.

Firefighting Systems (Hydrants, Sprinklers)

Application: Distributing water for fire suppression. These systems are typically either dry (filled with air or nitrogen) or wet (filled with water) when not in use, but must deliver water reliably under pressure during an emergency.

Considerations: Reliability is paramount. Internal corrosion must be minimized to prevent blockages in sprinkler heads and ensure the structural integrity of the system under pressure. External corrosion is also a concern.

Recommendation: GI pipes are highly recommended and widely used for firefighting systems due to their proven corrosion resistance and reliability in water-filled or intermittently wet conditions.

Chemical Process Piping

Application: Transporting various chemicals, acids, alkalis, solvents, etc., used in manufacturing processes.

Considerations: Chemical compatibility is the most critical factor to consider. Both MS and GI pipes (and their zinc coating) can be highly reactive or quickly corroded by specific chemicals.

Recommendation: For chemical process piping, the choice of material is particular to the chemical(s) involved. While MS might be used with liners for some applications, GI is rarely suitable.

HVAC Systems

Application: Piping for chilled water, hot water, or condenser water in large industrial HVAC systems.

Considerations: Water quality, temperature (chilled vs. hot), potential for oxygen ingress, and scale build-up.

Recommendation: GI pipes are often preferred for chilled water and condenser water lines in industrial HVAC systems due to their corrosion resistance. MS is acceptable for closed-loop hot water systems.

Installation, Joining, and Maintenance Considerations

Beyond material properties and application suitability, practical aspects like installation, joining, and long-term maintenance significantly influence the choice between MS and GI pipes for industrial projects.

Installation and Fabrication

Cutting and Threading: While the sacrificial action of the surrounding zinc offers some protection to the immediately exposed area, it’s best practice to apply a zinc-rich paint or cold galvanizing compound to these areas after cutting and threading to restore corrosion protection.
Bending: Both MS and GI pipes can be bent cold or hot. However, bending GI pipes aggressively can sometimes cause the zinc coating to flake or crack on the outer radius of the bend, compromising protection.

Joining Methods

Choosing the appropriate joining method is crucial for system integrity and safety.

Welding: As discussed earlier, welding MS pipes is a standard and effective practice, producing strong, permanent joints. Welding GI pipes is more complex due to the toxic zinc fumes and potential issues with weld quality.
Threading and Screwing: This is a prevalent method for joining smaller diameter MS and GI pipes (typically up to NPS 4 or 6).
Flanging: A highly reliable and versatile joining method suitable for both MS and GI pipes, especially in larger diameters or applications requiring periodic dismantling for maintenance or inspection.
Mechanical Couplings: Various mechanical couplings (e.g., grooved fittings like Victaulic) can be used for both MS and GI pipes.

Maintenance and Lifespan

MS Pipes: Require regular maintenance, especially in environments with corrosive conditions. This often includes external painting or coating touch-ups to prevent rust from forming.
GI Pipes: Offer a significantly longer lifespan in corrosive water or humid air environments compared to uncoated MS pipes, due to the inherent protection provided by the zinc coating.
Inspection: For both MS and GI pipes, regular inspection is crucial as part of a proactive maintenance program.

Regulatory Standards and Compliance

Industrial plumbing systems must comply with various national and international standards, codes, and regulations to ensure safety, reliability, and performance. These standards often dictate acceptable materials, manufacturing processes, pressure ratings, testing procedures, and installation practices.

Both MS and GI pipes used in industrial plumbing are manufactured and specified according to relevant standards. Some key standards include:

Indian Standards (BIS)

IS 1239 (Part 1): Covers specifications for MS pipes for ordinary uses (water, air, gas). Includes requirements for material, dimensions, tolerances, and testing.
IS 3589: Specifies steel pipes for water and sewage (often used for larger diameters, available in MS or coated versions).
IS 4270: Covers steel tubes for structural purposes (MS, often used for supports).

International Standards (ASTM, API, BS, EN)

ASTM A53: Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless (covers both MS and GI).
ASTM A106: Standard Specification for Seamless Carbon Steel Pipe for High-Temperature Service (typically MS).
API 5L: Specification for Line Pipe (often MS, used for oil and gas, but principles apply).
BS 1387 / EN 10255: Specifications for Steel Tubes for Screw Threading and for Ordinary Purposes (covers both black and galvanized).

Compliance Implications

Material Specification: Projects for specific applications often require pipes that are manufactured and tested to exact standards.
Galvanization Requirements: Standards such as ASTM A53 specify the minimum zinc coating thickness for galvanized iron (GI) pipes, ensuring adequate corrosion protection.
Pressure and Temperature Ratings: Standards provide tables or formulas to determine the maximum allowable working pressure for pipes of different materials, sizes, and schedules at various temperatures.
Joining Methods: Codes often specify acceptable joining methods for different applications.
Testing and Quality Control: Standards mandate various tests to verify the quality and integrity of the pipes.

Making the Right Choice for Your Factory

Deciding between MS and GI pipes for your industrial plumbing system requires a structured approach, moving beyond general comparisons to consider your specific circumstances and needs. Here’s a framework to guide your decision:

Identify the Application and Fluid

What fluid(s) will be transported? (Water, steam, air, chemical, etc.)
What are the properties of the fluid? (Corrosiveness, temperature, pressure, viscosity, purity requirements)
What is the purpose of the piping system? (Process, utility, safety, structural)

Assess the Operating Conditions

What are the maximum and minimum operating temperatures? (Crucial for GI above ~70°C and especially above ~200°C)
What are the design pressure requirements?
Are there significant pressure or temperature fluctuations?
Is vibration or mechanical stress a factor?

Consider Lifecycle Cost, Not Just Upfront Price

Calculate the estimated total cost of ownership over the expected life of the system, including initial material and installation, energy costs, routine maintenance, potential repairs, and eventual replacement.

Review Installation and Maintenance Capabilities

What joining methods are feasible and preferred (welding, threading, flanging, mechanical)? Does your team or contractor have experience with these methods for both MS and GI?
What level of ongoing maintenance is acceptable or feasible for your plant?
How critical is uninterrupted operation? (Higher reliability of GI in corrosive settings reduces downtime risk.)

Check Applicable Standards and Codes

What industry standards, local building codes, or specific project specifications apply to this piping system? Does the chosen material comply?

Consult with Experts

Engaging with experienced piping material suppliers and engineers is invaluable. They can provide insights based on experience with similar applications, offer specific product data, and help you interpret standards and performance characteristics. [MS and GI Pipe Difference]

Conclusion

Choosing between Mild Steel (MS) and Galvanized Iron (GI) pipes for industrial plumbing is crucial, as it impacts performance, reliability, and cost. While MS is cost-effective, strong, and easy to fabricate, its susceptibility to corrosion limits its use in environments with corrosive conditions or high temperatures.

GI pipes, with their protective zinc coating, offer superior corrosion resistance and a longer lifespan for water, compressed air, and humid applications, justifying their higher initial cost. However, GI is unsuitable for high temperatures due to zinc degradation and welding complexities.

The optimal choice depends on specific application, operating conditions, environment, and a thorough analysis of both upfront and lifecycle costs. Expert consultation, like with SRJ Piping India, is highly recommended for tailored material selection.

Confused Between MS and GI Pipes?

SRJ Piping India helps you make the right industrial plumbing choice. From corrosion resistance to cost analysis, our experts guide you through MS and GI pipe selection for your unique needs.

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MS vs. GI Pipes: Which Is Better for Industrial Plumbing?

Table of Contents

What Are MS and GI Pipes? The Fundamentals

Mild Steel (MS) Pipes: The Backbone of Basic Piping

Manufacturing Process

Galvanized Iron (GI) Pipes: Adding a Protective Layer

Galvanization Process (Hot-Dip Galvanizing)

Key Differences: A Comparison for Industrial Use

Corrosion Resistance

Strength and Structural Integrity

Weight

Temperature Tolerance

Cost

Joining Methods

Surface Finish

Installation and Fabrication

Performance and Suitability in Industrial Plumbing

Process Water Piping

Compressed Air Systems

Steam Piping

Firefighting Systems (Hydrants, Sprinklers)

Chemical Process Piping

HVAC Systems

Installation, Joining, and Maintenance Considerations

Installation and Fabrication

Joining Methods

Maintenance and Lifespan

Regulatory Standards and Compliance

Indian Standards (BIS)

International Standards (ASTM, API, BS, EN)

Compliance Implications

Making the Right Choice for Your Factory

Identify the Application and Fluid

Assess the Operating Conditions

Consider Lifecycle Cost, Not Just Upfront Price

Review Installation and Maintenance Capabilities

Check Applicable Standards and Codes

Consult with Experts

Conclusion

Confused Between MS and GI Pipes?

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