What Is ASTM A213?
ASTM A213, formally A213/A213M, covers seamless ferritic and austenitic alloy-steel boiler, superheater and heat exchanger tubes. These tubes are pressure-tight and designed for heat transfer in enclosed systems, typically smaller in diameter than pipe and often used in tube bundles. The specification is the backbone of high-temperature heat exchange equipment in power and process industries.
Grades are organized into ferritic alloy steels with T designations and austenitic stainless steels with TP designations.
Ferritic and Austenitic Grade Families
| Grade | Type | Typical Composition | Key Characteristic |
|---|---|---|---|
| T11 | Ferritic | 1.25Cr-0.5Mo | Standard moderate-temperature grade |
| T22 | Ferritic | 2.25Cr-1Mo | Most common Cr-Mo tube grade |
| T91 | Ferritic | 9Cr-1Mo-V-Nb | High strength, creep resistant |
| TP304H | Austenitic | 18Cr-8Ni high carbon | High-temperature strength |
| TP316L | Austenitic | 16Cr-12Ni-2.5Mo low carbon | Superior corrosion resistance |
| TP321H | Austenitic | 18Cr-10Ni-Ti high carbon | Stabilized against sensitization |
Ferritic grades offer better thermal conductivity, lower thermal expansion and lower cost, while austenitic grades provide superior corrosion resistance and high-temperature strength.
Heat Treatment Requirements
| Grade Type | Required Treatment | Typical Range |
|---|---|---|
| Ferritic T11, T22 | Full anneal or normalize and temper | 870-925 degrees C |
| T91, T92 | Normalize and temper | Normalize 1040-1090 degrees C, temper 730-800 degrees C |
| Austenitic TP grades | Solution anneal and rapid cool | 1040 degrees C minimum |
Heat treatment is mandatory for every A213 tube because it develops the microstructure that provides the specified strength and toughness.
Mechanical Properties and Testing
| Grade | Tensile, min MPa | Yield, min MPa | Hardness, max |
|---|---|---|---|
| T11, T22 | 415 | 205 | 163 HB |
| T91 | 585 | 415 | 250 HB |
| TP304H, TP316L | 515 | 205 | 192 HB |
Every tube is hydrostatically tested unless replaced by non-destructive examination, and eddy current or ultrasonic testing is mandatory to detect longitudinal defects. Tensile, hardness, flattening and intergranular corrosion tests complete the program.
Applications
A213 tubes serve boiler water walls, superheaters, reheaters and economizers in power plants, heat exchangers and reformer tubes in petrochemical plants, furnace and transfer lines in refineries, and condensers and reactors in chemical processing. When specified for ASME Code construction they are designated SA213.
FAQ
Q1. What is the difference between A213 and A335?
A213 covers boiler and heat exchanger tubes in smaller diameters with mandatory non-destructive examination, while A335 covers larger-diameter pipe for high-temperature piping systems.
Q2. What does the T in T22 stand for?
The T prefix denotes tube form in the A213 specification, while the P prefix in A335 denotes pipe form of the same alloy.
Q3. Why is T91 heat treated by normalizing and tempering?
This treatment forms a tempered martensite structure with fine precipitates that give T91 its high creep strength at elevated temperatures.
Q4. What is sensitization in austenitic tubes?
Sensitization is chromium depletion at grain boundaries caused by welding or service in the 425-815 degrees C range, which low-carbon L grades and stabilized grades such as TP321 resist.
Q5. Are A213 tubes seamless only?
Yes, A213 covers seamless tubes only. Welded versions are covered by specifications such as A249 or A688.
Q6. What dimensions are A213 tubes produced in?
Typical outside diameters range from about 1.6 mm to 127 mm, with wall thicknesses from 0.8 mm to 12.7 mm, in random or cut lengths.
