SA213 T11 vs T22 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
SA213 T11 and SA213 T22 are two widely used chromium‑molybdenum low‑alloy steels for boiler, superheater, and heat‑exchanger tubes. Engineers and procurement professionals frequently weigh tradeoffs between upfront material cost, ease of fabrication and welding, and in‑service high‑temperature strength (creep resistance). In many projects the decision reduces to whether the higher alloy content and elevated‑temperature capability of T22 justify its higher cost and slightly more demanding welding and heat‑treatment controls compared with T11.
The primary technical distinction is that T22 is alloyed to provide substantially better strength and creep resistance at elevated temperatures than T11; T11 is typically chosen where good ductility, easier weldability, and lower cost are priorities for lower to moderate service temperatures.
1. Standards and Designations
- Major standards:
- ASTM/ASME: SA213 (tubes for high‑temperature service), A335 (pipes) — T11 and T22 correspond to Cr‑Mo grades commonly aligned with P11 and P22 in pipe specifications.
- EN / DIN: Comparable grades are 13CrMo44/14MoV6‑3 family members, but direct cross‑references require caution.
- JIS / GB: National standards have similar Cr–Mo series but verify exact designations and property tables for substitution.
- Classification:
- SA213 T11 and T22 are low‑alloy ferritic steels (alloy steel) designed for high‑temperature service; they are not stainless steels nor HSLA in the typical sense (their alloying is targeted at elevated‑temperature strength and creep rather than corrosion resistance alone).
2. Chemical Composition and Alloying Strategy
The table below gives typical composition ranges (weight percent) encountered in industry practice and per commonly used ASME/ASTM ranges. Exact limits depend on the specific mill and standard version; always consult the controlling material specification for purchase or design.
| Element | Typical T11 (approx. wt%) | Typical T22 (approx. wt%) |
|---|---|---|
| C | 0.05 – 0.15 | 0.05 – 0.15 |
| Mn | 0.30 – 0.65 | 0.30 – 0.60 |
| Si | 0.10 – 0.50 | 0.10 – 0.50 |
| P | ≤ 0.035 | ≤ 0.035 |
| S | ≤ 0.035 | ≤ 0.035 |
| Cr | ~0.9 – 1.4 (nominal ~1.0–1.25) | ~2.0 – 2.5 (nominal ~2.25) |
| Ni | ≤ 0.40 (trace) | ≤ 0.40 (trace) |
| Mo | ~0.44 – 0.65 (nominal ~0.5) | ~0.85 – 1.06 (nominal ~1.0) |
| V | trace / optional | trace / optional |
| Nb (Cb) | trace / not specified | trace / not specified |
| Ti | trace | trace |
| B | trace | trace |
| N | trace | trace |
How alloying affects performance: - Chromium increases hardenability and high‑temperature strength and promotes formation of stable carbides that improve creep resistance. - Molybdenum improves creep strength and resistance to softening at temperature by stabilizing carbides and hindering diffusion. - Carbon and manganese control basic strength and hardenability; higher carbon increases strength but reduces weldability and toughness. - Silicon is a deoxidizer and provides modest strength and oxidation resistance. - Trace microalloying additions (V, Nb, Ti) can influence grain size, precipitation strengthening and impact toughness, but these are typically minor in standard T11/T22 compositions.
3. Microstructure and Heat Treatment Response
Typical microstructures: - In delivered (normalized and tempered) condition both T11 and T22 exhibit tempered martensite / tempered bainitic microstructures with a dispersion of alloy carbides (Cr‑ and Mo‑rich). Grain size and carbide distribution are controlled by normalization temperature and tempering regime. - T22, with higher Cr and Mo, tends to form a higher fraction of stable alloy carbides and a microstructure that resists coarsening at elevated temperatures better than T11.
Heat treatment effects: - Normalizing (air cooling from above the critical range) refines prior austenite grain size and dissolves carbides; followed by tempering to develop the desired toughness/strength balance. - Quenching and tempering control room‑temperature toughness versus strength but are less common for as‑rolled tube products intended for service — standard practice is normalization and tempering appropriate to the product form. - For both grades, post‑weld heat treatment (PWHT) is commonly used to temper weld HAZ and reduce residual stresses and hardness; T22 typically requires stricter control (minimum PWHT temperature, hold time) to meet creep performance. - Thermo‑mechanical controlled processing (TMCP) can be used to refine grain size and improve toughness in thick sections, but for tubing the dominant variables are normalization and tempering cycles.
4. Mechanical Properties
The mechanical properties below are indicative ranges for normalized and tempered tubing and depend strongly on wall thickness, exact heat treatment and finish. Use the applicable code tables for design.
| Property | Typical T11 (normalized & tempered) | Typical T22 (normalized & tempered) |
|---|---|---|
| Tensile strength (MPa) | ~420 – 560 MPa | ~450 – 620 MPa |
| Yield strength (0.2% offset, MPa) | ~240 – 360 MPa | ~300 – 420 MPa |
| Elongation (%) | ~20 – 25% | ~18 – 22% |
| Impact toughness (Charpy V, room temp) | Moderate; depends on heat treatment | Moderate; often slightly lower than T11 if carbon/hardenability are higher |
| Hardness (HB) | ~150 – 220 HB | ~160 – 240 HB |
Interpretation: - T22 generally offers higher yield and tensile strength, especially at elevated temperatures, because of the higher Cr and Mo content which enhances creep strength. - T11 may provide marginally better ductility and can be easier to meet toughness requirements for some geometries, because of its lower alloy content and lower hardenability. - The room‑temperature toughness difference is modest in properly processed materials; the key service advantage for T22 is retention of strength at temperature (creep resistance).
5. Weldability
Weldability considerations revolve around carbon content, overall hardenability (Cr + Mo + other alloying), and the need for preheat/PWHT.
- Hardness and martensite formation in heat‑affected zones increase with higher alloying and hardenability; thus, T22's higher Cr and Mo raise the risk of HAZ hardening and hydrogen‑induced cold cracking if welding controls are inadequate.
- Common weldability indices useful for qualitative interpretation:
- Carbon equivalent (IIW):
$$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ - Pcm (more conservative index):
$$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$ - Interpretation (qualitative): higher CE or Pcm implies more preheat, slower cooling, and often mandatory PWHT to avoid brittle HAZ microstructures. T22 will usually have a higher CE than T11 at equal carbon, indicating stricter welding procedures.
- Recommended practice: control hydrogen in weld consumables, apply appropriate preheat, and perform PWHT per code and material datasheets — more stringent PWHT is commonly specified for T22 to meet creep performance and toughness requirements.
6. Corrosion and Surface Protection
- Both T11 and T22 are non‑stainless alloy steels and do not provide significant resistance to wet corrosion or aggressive environments by chemistry alone.
- Typical protections: painting, primers, high‑temperature coatings, or metallurgical coatings where appropriate. For outdoor/atmospheric service, galvanizing may be used for some components but is uncommon for high‑temperature tubing.
- For high‑temperature oxidation (steam/furnace), surface oxide scales form; alloying (Cr) improves scale adhesion and high‑temperature oxidation resistance — here T22 benefits from higher Cr content.
- Stainless corrosion indices such as PREN are not applicable to these low‑alloy steels: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$ This index is intended for stainless steels and does not meaningfully describe corrosion behavior of Cr–Mo ferritic steels.
7. Fabrication, Machinability, and Formability
- Machinability: Both grades machine reasonably well when normalized and tempered; T22 can be slightly more difficult due to higher alloy content and stronger carbide dispersions.
- Formability and cold bending: Lower alloyed T11 is generally more forgiving in bending and forming operations; T22 may require tighter bend radii control or elevated‑temperature forming to avoid cracking in thicker sections.
- Surface finishing: Grinding, polishing and nondestructive testing are standard; for welding and fabrication, shop controls for hydrogen and PWHT are more frequently applied to T22.
8. Typical Applications
| SA213 T11 – Typical Uses | SA213 T22 – Typical Uses |
|---|---|
| Economical superheater and reheater tubing for lower‑temperature steam circuits, feedwater heaters, and general boiler tubes where moderate temperature strength is sufficient | Superheater tubes, steam piping and headers in power plants, petrochemical high‑temperature process piping, and components where higher creep strength and longer life at elevated temperature are required |
| Economical heat exchanger tubing for moderate temperatures | Critical high‑temperature pressure parts and piping requiring higher allowable stresses at temperature |
| Replacement parts in systems originally designed for 1–1.25% Cr service where weldability and cost control are important | New designs where extended service life, higher allowable stress at temperature, or reduced wall thickness for weight/space savings are desired |
Selection rationale: - Choose T11 when service temperatures and stresses are moderate and when lower cost, easier fabrication, and simpler welding/PWHT controls are priorities. - Choose T22 when higher creep strength and oxidation/scale stability at elevated temperatures are required and when longer life or higher allowable stress at temperature justifies higher material cost and more stringent fabrication controls.
9. Cost and Availability
- Cost: T22 typically costs more than T11 due to higher Cr and Mo content; Mo is particularly expensive and contributes disproportionately to price.
- Availability: Both grades are widely available in tube and pipe forms, but lead times and cost volatility can be driven by alloy demand (Mo availability). Standard tube sizes and common wall thicknesses are readily stocked by major suppliers; specialty sizes may have longer lead times.
- Product forms: seamless and welded tubing, pipes, fittings and flanges are common; availability in plates and forgings varies with market demand.
10. Summary and Recommendation
| Attribute | SA213 T11 | SA213 T22 |
|---|---|---|
| Weldability | Better (lower hardenability) | More demanding (higher hardenability; stricter PWHT) |
| Strength – Toughness balance | Good at room & moderate temp | Superior high‑temperature strength / creep resistance |
| Cost | Lower | Higher |
Conclusions: - Choose SA213 T11 if: your design operates at moderate steam or process temperatures where exceptional creep resistance is not required, you prioritize lower material cost, simpler welding and fabrication controls, and you need good ductility and toughness in service. - Choose SA213 T22 if: the application involves higher steam temperatures or sustained stresses where creep resistance and retained strength at temperature are critical, you accept higher material cost and more stringent welding/PWHT procedures, and you need longer in‑service life or higher allowable stresses at temperature.
Final recommendation: base the selection on the project’s maximum operating temperature and stress (creep life requirements), welding procedure capability (preheat/PWHT), and life‑cycle cost analysis. When in doubt, consult the applicable ASME/ASTM material tables and perform a design review that includes allowable stresses at the intended service temperature and weld procedure qualifications.