In high-temperature and high-pressure industrial sectors, material selection is crucial for equipment safety and operational efficiency. T91 and P91, as two commonly used martensitic heat-resistant steels, are widely applied in power generation, petrochemical, and related industries. Although their names are similar and chemical compositions are close, their performance characteristics and application scenarios show significant differences.

Fundamental Differences Between T91 and P91

Definitions and Standards

T91 (T91 Tube ) is a tubing-grade steel primarily used for manufacturing boiler tubes, superheater and reheater tubes, and other tubular components. It conforms to ASME SA-213 standards.

P91 (P91 Pipe ) is a piping-grade steel used for manufacturing main steam lines, headers, and other pressure components. It follows ASME SA-335 standards.

Chemical Composition Differences

Both steels share essentially the same chemical composition, with minor variations:

Aluminum content: T91 typically has lower aluminum content (≤0.04%), while P91 may have slightly higher levels (≤0.06%)

Manufacturing process: T91 is usually produced as seamless tubing, while P91 can be manufactured as either seamless or welded pipe

Mechanical Properties Differences

Strength requirements: P91 has slightly higher strength requirements to accommodate larger diameters and thicker walls

Impact toughness: P91 generally has stricter impact toughness requirements

Heat treatment: Both require normalizing and tempering, but specific parameters may vary based on section thickness

Application Areas

Primary Applications of T91

Superheater and reheater tubes in power plant boilers

High-temperature, high-pressure tubing systems

Heat exchanger tube bundles

Tubular components operating at 593-649°C

Primary Applications of P91

Main steam lines and hot reheat lines in power plants

High-temperature, high-pressure headers and manifolds

Piping in petrochemical hydrocracking units

Nuclear power system piping

Thick-walled pressure components operating at 593-649°C

Selection Considerations

Operating conditions: Temperature, pressure, and media corrosiveness

Component type: Piping, headers, or tubular heat exchange components

Manufacturing requirements: Weldability and formability

Economic factors: Initial cost and total lifecycle cost

Regulatory compliance: Must meet relevant industry standards and codes

Development Trends

With the advancement of supercritical and ultra-supercritical power generation technology, the application range of T91/P91 steels continues to expand. Current research focuses include:

Further improving long-term high-temperature creep strength

Enhancing long-term stability of welded joints

Developing more economical manufacturing processes

Exploring applicability in carbon dioxide cycle systems

Although T91 and P91 share similar chemical compositions, they have distinct differences in application scenarios, performance requirements, and manufacturing standards. Proper selection and use of these materials are essential for ensuring safe operation and extending service life of high-temperature, high-pressure equipment. Engineers should make informed choices based on specific application conditions, design requirements, and industry standards.