P91 Steel Pipe vs P22 Steel Pipe

When it comes to high-temperature and high-pressure applications, both P91 and P22 steel pipes are popular choices under the ASME SA335 standard. While they may seem similar at first glance, the differences in composition, performance, and long-term reliability make P91 the superior option for modern power and boiler systems.
The most significant distinction lies in their alloy composition. P22 contains chromium and molybdenum, offering moderate heat and oxidation resistance. In contrast, P91 introduces additional elements—vanadium (V) and niobium (Nb)—which refine grain size and form strong carbides, greatly improving creep strength and high-temperature stability.
In terms of mechanical performance, P91 delivers nearly twice the strength of P22 at elevated temperatures. This allows for thinner wall designs, lighter systems, and extended service life. It also resists creep deformation far better, making it ideal for superheaters, reheaters, and steam pipelines operating above 550°C.
However, P91’s advantages come with greater processing challenges. Its welding and heat treatment require strict temperature control to preserve its tempered martensitic structure. P22, being less complex, is easier to fabricate but offers lower performance in severe service environments.
Ultimately, the choice between P91 and P22 depends on operating demands. For standard high-pressure applications, P22 remains economical. But for next-generation power plants and long-term reliability at extreme temperatures, P91 steel pipe stands unmatched—a true evolution in alloy engineering.