Boiler Tube Material: Types, Grades and Selection

In boiler design, material selection is primarily driven by operating temperature. Once the temperature range is defined, suitable material categories — carbon steel, alloy steel, and stainless steel — can be determined accordingly.

1. Types of Boiler Tube Materials

Boiler tube materials are generally classified based on their allowable temperature range and service environment. Each material group has a well-defined role in boiler design, with corresponding grades and typical applications.

2. How to Select Boiler Tube Materials

In practical engineering applications, temperature is the primary design constraint, as it directly defines the applicable material range. Once the operating temperature is established, pressure level, design life, and cost considerations are evaluated to further refine the material selection.

Figure: Typical boiler tube material selection based on operating temperature ranges.

Typical Material Selection Practice

In most power plant projects, material selection is driven primarily by operating temperature. Once the temperature range is identified, the material choice is usually quite straightforward.

Carbon steel is used by default in lower temperature sections (≤500℃), where performance requirements are moderate.

As temperature increases to 500–600℃, alloy steels such as T11 and T22 are introduced, with T22 preferred for its better creep resistance.

For temperatures above 600℃, materials like T91/T92 become necessary, while stainless steels are reserved for sections with higher oxidation or corrosion risks.

2.1 Low to Medium Temperature Conditions (≤500℃)

Below 500℃, most heat transfer surfaces operate within the conventional material range. In this region, material selection is not driven by performance limits, but rather by long-term stability and cost efficiency.

Carbon steel is typically the default choice, with grades such as ASTM A192 and SA210 C widely used and well proven in long-term service.

These materials provide sufficient strength and oxidation resistance for low-temperature applications, while offering low cost and good manufacturability.

As a result, carbon steel is mainly used in water walls, economizers, and low-temperature superheaters.

2.2 Medium to High Temperature Conditions (500–600℃)

In the 500–600℃ range, material behavior is no longer governed by strength alone. Creep resistance, microstructural stability, and oxidation/steam corrosion resistance become the dominant factors.

Commonly used grades include SA213 T11 and SA213 T22. In practical design, T22 is generally preferred near the upper end of this temperature range, as it provides better long-term creep performance and a wider safety margin compared to T11.

2.3 High and Ultra-High Temperature Conditions (≥600℃)

At temperatures above 600℃, material degradation is no longer primarily strength-related, but is driven by long-term creep deformation and microstructural instability.

In engineering practice, the main material solutions fall into two categories:

① Martensitic Heat-Resistant Steels (T91 / T92)

T91 and T92 are primarily used in components where high creep strength and pressure-bearing capability are the key design requirements, such as high-temperature superheaters and reheaters.

Among them, T91 is widely regarded as a baseline material for supercritical units and has extensive, proven service experience in applications around 600℃. T92 is typically selected for higher operating parameters or where additional design margin is required.

② Austenitic Stainless Steels (e.g., TP347H)

As operating temperatures increase further, or when steam oxidation and corrosion become more severe, creep strength alone is no longer sufficient to ensure service life. In such cases, austenitic stainless steels are introduced.

TP347H and its modified grades (such as TP347HFG and Super304H) are commonly used in high-temperature heat transfer sections. Their main advantage lies in superior oxidation resistance and long-term microstructural stability under elevated temperature service.

3. Common ASTM / ASME Standards for Boiler Tubes

ASTM and ASME standards are the most widely adopted specifications in international boiler and power plant projects. Each standard corresponds to specific material types and service conditions.

In practical applications, SA192 and SA210 primarily cover carbon steel systems, while SA213 and SA335 represent high-temperature alloy and stainless steel grades, forming the core material standards in high-specification boiler design.

4. Boiler Tube Material Selection by Application

In practical engineering projects, material selection is typically driven by component location and operating conditions. Since different heat transfer surfaces operate under varying temperature and media environments, material combinations are generally well established in boiler design practice.

4.1 Power Plant Boilers

In conventional thermal power plants as well as supercritical and ultra-supercritical units, boiler systems operate under long-term high temperature and high pressure conditions. As a result, high-temperature strength and creep resistance are key material selection criteria.

Commonly used materials include:

- SA213 T22: Applied in medium to high temperature sections (approximately 540–580℃). It is widely used in superheaters, reheaters, and main steam lines, and is considered a mature and well-established alloy steel grade in power plant applications.

- SA213 T91: Used in higher temperature service (≥600℃), offering superior creep strength. It is commonly applied in critical components of supercritical and ultra-supercritical boiler systems.

In most power plant designs, T22 and T91 are typically used in a graded configuration to achieve an optimal balance between cost and performance.

4.2 Superheaters and Reheaters

Superheaters and reheaters operate in some of the most demanding regions of a boiler, where both temperature and service conditions are severe. In addition to high-temperature strength, materials must also provide strong resistance to oxidation and steam-side corrosion.

Common material selections include:

- TP347H / TP347HFG: Austenitic stainless steels used in high-temperature regions, capable of service temperatures up to approximately 650℃.

- In higher specification units, advanced grades such as Super304H or HR3C may also be applied.

These materials are typically used in final-stage high-temperature heat transfer sections, where long-term stability and service life have a direct impact on overall boiler reliability.

4.3 Economizer and Water Wall

For economizers and water wall systems, cost-effectiveness is typically the primary consideration. As a result, carbon steel remains the default material choice in most applications.

Typical materials include SA210 C and ASTM A192.

These grades are widely used in economizers, water walls, and other low-temperature heat transfer surfaces. Under operating conditions below 500℃, they offer a well-established balance of cost efficiency

5. FAQs

Q1: What material is used for boiler tubes?

Boiler tubes are typically made from carbon steel, alloy steel, and stainless steel, and are widely supplied as seamless steel pipes for high-pressure and high-temperature applications.

The choice depends mainly on operating temperature, pressure, and corrosion conditions, with higher temperatures requiring alloy or stainless steel grades.

Q2:What is the best material for high-pressure boiler tubes?

For high-pressure and high-temperature applications, alloy steels such as SA213 T22, T91, and T92 are commonly used.

These materials provide excellent creep strength and long-term stability under demanding service conditions.

Q3: What is the difference between T22 and T91 boiler tubes?

The main difference lies in temperature capability and creep strength.

T22 is typically used in the 500–580℃ range, while T91 is designed for higher temperatures (≥600℃) and provides significantly better long-term performance.

Q4：How to choose the right boiler tube material?

The selection is primarily based on operating temperature, followed by pressure, corrosion conditions, and design life.

In practice, carbon steel is used for lower temperatures, alloy steel for medium ranges, and stainless steel for high-temperature or corrosive environments.

6. Conclusion

In practice, boiler tube material selection is always a balance between temperature capability and cost.

For project-specific selection (e.g., T22 vs T91, or stainless steel upgrade), we can help evaluate based on your operating conditions and recommend suitable grades and specifications.

Read more: How To Weld Boiler Tubes? or Methods for Cleaning Boiler Tubes