The carbon steel grades used on air storage tanks

Carbon steel is the most widely used material of pressure vessels (including air storage tanks) due to its high strength, cost-effectiveness, and mature manufacturing process. However, carbon steel comes in different grades, and when customizing a carbon steel air tank, customers should specify exact grade to the air tank manufacturer.

In the previous article How to customize air receiver tanks from air tank manufacturers, we mentioned that carbon steel air storage tanks are usually made from Q235B and Q345R. In this article, we will list the advantages and disadvantages of these two grades, so that customers can make proper choice when customizing air receiver tanks.

Q235B

A common carbon steel. "Q" stands for yield strength, "235" indicates a yield strength of 235 MPa, and "B" indicates a quality grade, guaranteeing impact toughness at 20°C.

Advantages: Lowest cost, best economy, and easy processing.

Disadvantages:

1. Lower strength, so requires thicker walls for air tanks at the same pressure, the whole air tanks will be heavy.
2. Relatively poor toughness and fatigue resistance,particularly sensitivity to low temperatures, fracture risk.
3. Poor corrosion resistance, easy to rust.

Applications:

Suitable for air or other inert gas storage tanks with low operating pressures (typically ≤0.8 MPa) and small volumes. Typically used in non-critical, low-demand applications.

Q345R

Designed grade for pressure vessels. Its yield strength is 345 MPa, significantly superior to Q235B.

Advantages:

1. High strength: At the same pressure, the required wall thickness is thinner than Q235B, makes the air storage tank lighter.
2. Excellent impact toughness, high safety, and strong resistance to fracture.
3. Mature process: Designed specifically for pressure vessels, with stricter control over chemical composition and mechanical properties, resulting in excellent weldability.
4. Regulatory compliance: Widely recognized and recommended by chinese and international pressure vessel standards.

Disadvantages:

1. Expensive than Q235B.
2. Still a carbon steel,not corrosion-resistant and requires internal anti-corrosion coatings (such as epoxy resin). YCZX air tanks have inside rustproof coating, if customers have such requirement on their customized air receiver tanks, please specify during the initial communications.
3. 

Applications:

1. The standard and preferred material for most medium- and high-pressure (0.8MPa - 3.0MPa and above) air and nitrogen storage tanks.
2. It is the mainstream, safe, and reliable choice on the market.

Summary

For most compressed air, nitrogen, and other inert gas storage applications, Q345R offers the best balance of safety, cost-effectiveness, and performance. When OEM and customizing air tanks, specify Q345R and require the material certificate from the air tank manufacturers.

If your budget is very limited and the operating conditions are extremely simple (low-pressure, dry, non-critical), Q235B is also a good choice. But be aware of its limitations.

No matter which grades of carbon steel used, internal corrosion brings the greatest safety threat to air tanks (causing wall thickness reduction and decreased strength). Therefore, ensure that the air tank has an internal anti-corrosion coating.

After getting the air storage tanks from the air storage tank manufacturers, customers also need to strictly perform regular inspections (including macroscopic inspections, thickness measurements, and non-destructive testing), and promptly detect and handle corrosion issues.