ASTM A213 T91 pipe belong to ASTM A213 which do Ferrite and Austenitic boiler superheater and heat exchanger seamless steel tube.
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ASTM A213 T91
ASTM A213 T91 is a seamless ferritic and austenitic alloy steel boiler tube used in superheaters, and heat exchangers.
But for ASTM A335 P91 tubing, they intended for Ferritic and alloy seamless steel tubes intended for high-temperature service. 91 grade steel, its excellent performance at room temperature and 650°C under creep properties, low linear expansion coefficient, good manufacturability, low cost (9.5-11.5% alloy quantity), excellent long-term organizational stability, achieve rapid promotion and development. Grade 91 included in ASME (American Society of Mechanical Engineers) or ASTM (American Society for Testing Material) referred to various specifications such as “T-91 steel”, “P-91 steel”, “F-91 steel”, etc. Here we will discuss the difference between T91 pipe and P91 pipe, if you are interested, read on, you will not regret it.
ASTM A335 P91
ASTM A335 P91 is a ferritic alloy steel that has very high strength properties, which do not deteriorate with time, and are creep resistant. It is also called 9 Cr 1 Mo steel, or chrome moly pipe, based on its composition.
First, they are attributed to different standard categories. T91 tubes belong to ASTM A213, which manufacture ferrite and austenitic overheating seamless steel pipes and heat exchanger. But for ASTM A335 P91 pipes, they were intended for ferritic and alloy seamless steel pipes intended for high-temperature service.
Alloyed by almost 9% chromium and 1% molybdenum, they are also called 9 Cr 1 Mo steel according to their composition. Chromium improves resistance to high temperatures and increases resistance to oxidation. Molybdenum increases creep resistance. Except for the small differences in carbon content, they are basically the same in chemical composition and physical property.
It is designed for enhanced creep strength, making it a creep strength enhanced ferritic (CSEF). This metal is made by normalizing at 1050 °C, air cooling to 200 °C, and then tempered through heating to 760 °C. This process is the main reason behind P91’s creep strength and durability. P91 stands for the metal’s composition of 9% chrome and 1% molybdenum plus vanadium. The chrome increases temperature strength and oxidation resistance. The molybdenum increases the elasticity, resistance to wear, and high temperature creep strength. More characteristics to note of ASTM A335 P91 Type 2:
- Non-deteriorating
- Decreased thickness
- Higher creep strength
Chemical composition of ASTM A335 P91 and ASTM A213 T91
The chemical composition of P91 and T91 steel pipes and the comparison of physical properties are detailed below:
| Material | C max | Minnesota | Cr | Month | Not even max | Yes | P max | S max |
| ASTM A213 T91 | 0.07-0.14 | 0.3-0.6 | 8.0-9.5 | 0.85-1.05 | 0.4 | 0.2-0.5 | 0.02 | 0.01 |
| ASTM A335 P91 | 0.08-0.12 | 0.3-0.6 | 8.0-9.5 | 0.85-1.05 | 0.4 | 0.2-0.5 | 0.02 | 0.01 |
Both can be used in engineering components, superheater coils, collectors and steam pipes with less thickness. This contributes to an increased thermal fatigue life of almost ten times. This allows them to increase the operating temperature to a higher level, increasing the efficiency of the power plant. In short, T is used for tubes and P denotes tubes. When you need small diameter tubes as a superheater, reheater and economizer, choose T91, while for large diameter tubes, P91 is more suitable.
Recently, a study developed by the European Nuclear Society focused on the radiation resistance of ASTM A213 T22 and ASTM A335 P22 steel tubes using two different positron annihilation techniques (positron lifetime measurements and Doppler widening). He showed that the differences between ASTM A213 T91 and ASTM A335 P91 is the microstructure and the results showed greater radiation resistance for T91 steel than for P91.