Can Carbon Steel Pipes be Used for Potable Water?

Can carbon steel pipes be used for potable water?

Carbon steel pipe itself is not suitable for direct use as potable water pipes because it easily rusts, affecting water quality and shortening the pipe's lifespan. Therefore, it must undergo special treatment and meet specific standards before it can be used safely under certain conditions.

When considering pipe materials for domestic or public drinking water systems, safety, durability, and cost are all important factors. So, is carbon steel, a common metal, suitable for use as potable water pipes?

First, we need to understand the basic properties of carbon steel. Composed primarily of iron and carbon, carbon steel has excellent mechanical properties and workability, but it is prone to rusting in humid environments. This characteristic is a major concern for potable water pipes, as rust not only affects water quality but also poses a potential threat to human health.

Potential Risks of Carbon Steel Pipes:

1. Water Contamination: When carbon steel rusts, the rust dissolves into the water, increasing the iron content. Long-term consumption of water with excessive iron content may have adverse health effects, such as gastrointestinal discomfort and impaired nutrient absorption.

2. Microbial Growth: Rusted pipe surfaces easily develop uneven structures, creating a breeding ground for microorganisms such as bacteria and algae. These microorganisms can further contaminate water quality and endanger human health.

Improvements and Applications of Carbon Steel - Internal Corrosion Treatment:

Despite the aforementioned drawbacks of carbon steel, special treatments can improve its performance to a certain extent, making it suitable for drinking water systems under certain conditions.

The only viable way to use carbon steel pipes for drinking water is to reliably treat the internal walls with corrosion protection. The most common treatment is galvanizing.

1. Galvanizing

A dense layer of zinc is applied to the carbon steel surface. Zinc acts as a sacrificial anode, corroding before the iron, thereby protecting the steel pipe from rust. While galvanized steel pipes improve corrosion resistance and service life to a certain extent, water quality monitoring and regular maintenance are still necessary.

Implementation Standards:
Generally, the requirements for galvanized pipes are followed in ASTM A53 (American Standard) or GB/T 3091 (National Standard "Welded Steel Pipes for Low-Pressure Fluid Transportation").

Advantages: High strength and impact resistance.

Disadvantages:
Rust: After years of use, the zinc coating gradually wears out, causing the steel pipe to rust and contaminate the water.
Bacterial Harvest: The rough inner surface is prone to scaling, creating a breeding ground for bacteria (such as Legionella).
Heavy weight and inconvenient installation.

Therefore, in most developed countries, as well as new residential and municipal projects in China, galvanized carbon steel pipes are banned or no longer recommended for use in drinking water systems.

2. Internal Anti-corrosion Treatment

Carbon steel pipes used directly for drinking water transportation require IPN8710 anti-corrosion treatment to prevent corrosion. Otherwise, rust may occur over long-term use. Plastic-coated carbon steel pipes (e.g., with a smooth inner coating) can reduce water flow resistance and energy consumption, making them more suitable for demanding applications.

Plastic lining (e.g., PE lining) can maintain the mechanical strength of carbon steel while isolating the water from the metal, ensuring water quality safety. This type of composite pipe must pass hygienic performance tests (such as immersion tests and toxicology tests) and obtain a national health permit.

3. Stainless Steel Coating

Applying a stainless steel coating to the surface of carbon steel can also effectively prevent rust. This treatment combines the mechanical properties of carbon steel with the corrosion resistance of stainless steel, making the pipe safer and more reliable. However, it should be noted that while technically feasible, economic and process complexity limit its widespread application. It cannot completely replace solid stainless steel pipe, but it does offer unique advantages in specific scenarios. The coating may wear or peel during use, so regular inspection and maintenance are also required.

Modern Preferred Options:

For drinking water pipes, the following safer and more durable materials should be preferred.

a. Plastic pipes: Such as PP-R pipes (random copolymer polypropylene) are currently the absolute mainstay for hot and cold water supply in homes. They are low-cost, rust-free, corrosion-resistant, and easy to install.

b. Stainless Steel Pipes: Such as 304 or 316 stainless steel pipes are food-grade, high-strength, and excellently corrosion-resistant. They are the highest-quality choice and are commonly used in hospitals, high-end hotels, and direct drinking water systems. 

c. Copper pipe: A traditional, high-end pipe material with natural antibacterial properties, but at a relatively high cost.

Applications of Carbon Steel Pipe in Water Supply:

Carbon steel pipe is widely used in the following water supply and drainage applications:

1. Drinking Water Pipe Networks: Carbon steel pipe is a key material for drinking water pipeline network construction, meeting the water source and water quality requirements of different regions and scales.
2. Sewage Treatment: Carbon steel pipe can be used in the inlet and outlet pipe networks of sewage treatment plants, offering corrosion resistance and high pressure resistance.
3. Building Water Supply: Carbon steel pipe can be used in the construction of building water supply networks, offering advantages such as safety, reliability, and a long service life.
4. Agricultural Irrigation: Carbon steel pipe can be used in agricultural irrigation systems, offering corrosion resistance, wear resistance, and high-pressure resistance.

Conclusion:
From a technical and hygienic perspective, untreated carbon steel is not suitable for direct use as drinking water pipes. Do not use carbon steel pipe (including galvanized pipe) in new or renovated drinking water systems. However, with appropriate anti-corrosion measures, carbon steel pipe can be safely used in drinking water systems under certain conditions. Regardless, we should closely monitor changes in water quality and regularly inspect and maintain pipes to ensure drinking water safety.

In addition, for new or renovated drinking water systems, consider using more corrosion-resistant and non-toxic pipe materials, such as plastic pipes like PPR and PE, or metal pipes like stainless steel or copper. These materials offer greater safety and durability, ensuring better drinking water safety.

Read more: Food-grade Stainless Steel Pipe or Carbon steel tube vs Stainless steel tube