At present, in the newly-built subcritical unit, the material of the hot section of the main steam pipe and the reheat steam pipe has been replaced by P91 steel instead of P22 steel.
For this reason, the analysis and comparison of P91 steel and P22 steel from the aspects of chemical elements, room temperature mechanical properties, allowable stress and creep strength, linear expansion coefficient and thermal conductivity, and welding performance show that P91 steel is more superior.
Finally, through practical application in engineering, it is further explained that the use of P91 steel can save pipes, facilitate design and installation, and have significant economic benefits.
P91 steel is used to fill the 600～650℃ temperature range between pearlitic heat-resistant steel and austenitic heat-resistant steel. P91 steel belongs to martensitic heat-resistant steel, and its maximum service temperature is 650 ℃. In fact, on the basis of the original 9Cr-1Mo steel, strengthening elements such as V, Nb, and N are added to form a new grade of modified steel.
