A106 Grade B steel (K03006): properties, composition, equivalents
ASTM A106 Grade B / ASME SA-106 Gr B (UNS K03006): the standard seamless carbon steel pipe for high-temperature and pressure service — 240 MPa (35 ksi) yield, 415 MPa (60 ksi) tensile. Grades A/B/C, composition, A106 vs A53 vs API 5L, P235GH/P265GH/STPG370 equivalents.
What is A106 Grade B?
ASTM A106 Grade B (ASME SA-106 Gr B) is the seamless carbon steel pipe of refineries, power plants, chemical plants and process piping everywhere ASME B31.1/B31.3 apply: 240 MPa (35 ksi) minimum yield, 415 MPa (60 ksi) tensile, killed steel with a silicon minimum, intended for high-temperature service (ASME allowables run to 538 °C, practical use to about 425 °C). UNS K03006. Grade A is the softer version for bending and cold-forming, Grade C the stronger one (275/485 MPa) for higher pressure.
The specification is often confused with A53 Grade B, which has identical strength: the differences are that A106 is seamless only, must be fully killed (Si ≥ 0.10 %), has tighter chemistry with residual limits, and requires hydrostatic and NDE testing suited to pressure work. In practice most seamless pipe from NPS 1/2 to 24 is triple-stencilled A106 B / A53 B / API 5L B because it meets all three. Wall schedules follow ASME B36.10M (Sch 40, 80, 160, XXS…), and the pipe is supplied hot-finished (or cold-drawn in small sizes) with bevelled ends for butt welding.
For temperatures below −29 °C, A333 Grade 6 (same strength, Charpy-tested at −45 °C) replaces it; above 425 °C the Cr-Mo grades A335 P11/P22. European P235GH/P265GH (EN 10216-2), JIS STPG370/STPT410, GB 20/20G and GOST 20 are the near matches.
A106 Grade B chemical composition
| Element | Mass % | Note |
|---|---|---|
| C | ≤ 0.3 | Grade A: 0.25; Grade B: 0.30; Grade C: 0.35 |
| Mn | 0.29 – 1.06 | Grade A: 0.27–0.93; Grade B: 0.29–1.06; Grade C: 0.29–1.06 |
| P | ≤ 0.035 | |
| S | ≤ 0.035 | |
| Si | ≥ 0.1 | |
| Cr | ≤ 0.4 | Cr + Cu + Mo + Ni + V ≤ 1.00 (Grade B/C) |
| Cu | ≤ 0.4 | |
| Mo | ≤ 0.15 | |
| Ni | ≤ 0.4 | |
| V | ≤ 0.08 |
ASTM A106/A106M-19a Table 1. Killed steel (Si ≥ 0.10 %) — the essential difference from A53 (which may be semi-killed). For each 0.01 % C below 0.30, Mn may rise 0.06 % to a maximum of 1.35 % (Grade B/C).
A106 Grade B mechanical properties
| Thickness / condition | Yield strength ReH / Rp0.2 MPa (ksi) | Tensile strength Rm MPa (ksi) | Elongation A % | Hardness |
|---|---|---|---|---|
| Grade A | 205 (29.7) | ≥ 330 (≥ 47.9) | 35 (L) / 25 (T), ≥ 8 mm wall | — |
| Grade B (standard) | 240 (34.8) | ≥ 415 (≥ 60.2) | 30 (L) / 16.5 (T), ≥ 8 mm wall | ≈ 130–170 HB (typ.) |
| Grade C | 275 (39.9) | ≥ 485 (≥ 70.3) | 30 (L) / 16.5 (T) | — |
| Grade B — typical mill certificate | ≈ 280–340 (≈ 40.6–49.3) | ≈ 450–520 (≈ 65.3–75.4) | ≈ 35–45 (L) | ≈ 140–160 HB |
| Grade B — ASME II-D allowable stress at 20–400 °C | S = 118 MPa (17.1 ksi) (S = 17.1 MPa (2.5 ksi)) | — | — | — |
| Grade B — allowable stress at 425 °C (800 °F) | S ≈ 91 MPa (13.2 ksi) (S ≈ 13.2 MPa (1.9 ksi)) | — | — | — |
ASTM A106/A106M-19a Table 2; elongation in 50 mm longitudinal (L) and transverse (T), reduced for thinner walls by the A106 formula. Bend and flattening tests are required; hydrostatic test to ASME B31.3 / A106 §17. No Charpy unless S5 ordered (ASME B31.3 requires impact tests below −29 °C).
Impact toughness
A106 Grade B requires a minimum Charpy V-notch energy of 18 J at -29 °C (typical, seamless Grade B ≤ 12 mm wall; not required by default). ASME B31.3 exempts A106-B from impact testing down to −29 °C (−20 °F) for most wall thicknesses; below that, order S5 Charpy or use A333 Grade 6 (low-temperature seamless pipe with 27 J at −45 °C).
A106 Grade B equivalent grades
| Grade | System | Match | Why / differences |
|---|---|---|---|
| A53 Gr. B (Type S) | ASTM / ASME | Near | Same 240/415 MPa; A53 may be semi-killed and is intended for general (not high-temperature) service; most seamless pipe is dual-certified A106-B/A53-B. |
| API 5L Gr. B | ASTM / ASME | Near | Line pipe: yield 241 MPa (35 ksi), tensile 414 MPa (60 ksi); PSL1/PSL2 with different testing; often triple-certified. |
| A333 Gr. 6 | ASTM / ASME | Near | Same strength as A106-B with guaranteed 18 J (avg 13.5 J) Charpy at −45 °C for low-temperature service; normalized. |
| P235GH / P265GH | EN (European) | Near | EN 10216-2 seamless pressure tube: P235GH (yield 235, Rm 360–500) is the usual substitute; P265GH (265 / 410–570) matches A106-B tensile. Both guarantee yield to 400–450 °C. |
| P235TR2 / P265TR2 | EN (European) | Near | EN 10216-1 non-alloy tubes for pressure (room temperature) — the A53-type equivalents. |
| 20 / 20G | GB/T (China) | Near | GB/T 8163 grade 20 (fluid) and GB/T 5310 20G (boiler): C 0.17–0.24, yield ≥ 245, Rm ≥ 410 MPa. |
| 20 / 10 | GOST (Russia/CIS) | Near | GOST 8731/8732 Steel 20 seamless tube: yield ≥ 245, Rm ≥ 412 MPa. |
| STPG370 / STPG410 | JIS (Japan) | Near | JIS G3454 STPG370 (Rm ≥ 370, yield ≥ 215) and STPG410 (Rm ≥ 410, yield ≥ 245) — pressure piping to 350 °C; STPT410 (G3456) for high temperature ≈ A106-B. |
| A335 P11 / P22 | ASTM / ASME | Functional | Cr-Mo seamless pipe for service above ~425 °C where carbon steel graphitizes. |
| IS 1239 / IS 3589 | IS (India) | Functional | Indian ERW pipe specs; IS 1239 Heavy (yield 195–320) is the water/gas pipe; for seamless pressure pipe India uses A106/SA-106 directly. |
Identical = same composition and mechanical limits within rounding. Near = one limit differs (e.g. carbon max or impact temperature). Functional = interchangeable for most uses after an engineering check. Full cross-reference for A106 Grade B →
Old and superseded designations
| Old name | Standard | Note |
|---|---|---|
| K03006 (Gr B), K02501 (Gr A), K03501 (Gr C) | UNS | |
| SA-106 | ASME BPVC Section II Part A | ASME adoption; pipe is dual-marked A106/SA-106 and usually also A53 B and API 5L B (triple stencil). |
| A53 Grade B | ASTM A53 (Type S) | General-service seamless/welded pipe with the same strength; A106 adds killed steel, Si min and high-temperature intent. |
| API 5L Grade B | API 5L | Line pipe with the same 241/414 MPa; triple-certified pipe is common. |
| St 35.8 / St 45.8 | DIN 17175 (withdrawn) | German boiler tube grades now P235GH/P265GH (EN 10216-2). |
Product forms and tolerance standards
Product forms: seamless pipe NPS 1/8 to 48 (DN 6–1200), wall schedules per ASME B36.10M (Sch 10–XXS), hot-finished (standard) or cold-drawn (small sizes, closer tolerance), ends: plain, bevelled (30° ±5°), threaded, NOT welded — A106 is seamless only (welded equivalents: A53 Type E/F, A672).
Dimensional tolerances: dimensions: ASME B36.10M (OD ±1 % or ±0.4 mm small sizes; wall −12.5 %); hydrostatic test and NDE (eddy current/UT) per A106 §17–18; supplementary: S1–S9 (product analysis, transverse tension, flattening, metal structure, Charpy, etc.).
Key property values
A106 Grade B yield strength
Minimum 240 MPa (35 ksi); typical 280–340 MPa. Grade A: 205 MPa (30 ksi); Grade C: 275 MPa (40 ksi).
A106 Grade B tensile strength
Minimum 415 MPa (60 ksi), no maximum; typical 450–520 MPa. Grade A: ≥ 330 MPa; Grade C: ≥ 485 MPa.
ASME allowable stress (SA-106 B)
118 MPa (17.1 ksi) from −29 °C to 400 °C; 116 MPa at 425 °C (B31.3 values differ slightly by edition); 85 MPa at 455 °C; creep-governed above ~425 °C; listed to 538 °C (1000 °F). B31.3 exempts from impact testing down to −29 °C for most walls.
Elongation, hardness, bend
Elongation ≥ 30 % longitudinal / 16.5 % transverse (Grade B, wall ≥ 8 mm; reduced for thinner walls). Hardness not specified; typical 130–170 HB (NACE ≤ 22 HRC easily met). Bend test 180° around 12 × wall (Grade B) without cracking; flattening test per §14.
Dimensions and pressure rating
OD per ASME B36.10M (NPS 1/8–48); wall tolerance −12.5 %. Working pressure per B31.3: P = 2·S·E·t/(D − 2·Y·t) with S = 118 MPa, E = 1.0 (seamless) — e.g. NPS 4 Sch 40 (114.3 × 6.02 mm, t_min 5.27) ≈ 8.7 MPa (1260 psi) at 400 °C before corrosion allowance.
Physical properties
Density 7.85 g/cm³, E = 200 GPa (29 × 10⁶ psi) at 20 °C, 186 GPa at 400 °C; expansion 11.7 × 10⁻⁶/K (20–100 °C), 13.9 (20–400 °C); conductivity ≈ 50 W/m·K.
Heat treatment
Supplied hot-finished (as-rolled) or, for cold-drawn pipe, normalized or stress-relieved (A106 §6: cold-drawn pipe must be heat-treated at ≥ 650 °C). Normalize 870–930 °C if specified. PWHT 595–650 °C required by B31.1/B31.3 above 19 mm wall (P-No. 1) or for specific services.
Weldability
Excellent weldability (CE ≈ 0.35–0.45): GTAW root (ER70S-2/-6) with SMAW/FCAW fill (E7018 / E71T-1), or full SMAW with E6010 root in pipelines; procedures per ASME IX / B31.3. Preheat 10 °C minimum, 80–95 °C for wall > 25 mm or C > 0.30; PWHT 595–650 °C above 19 mm wall (P-No. 1 Group 1) per B31.3 Table 331.1.1. Bevel 37.5° per B16.25; back-purge not required for carbon steel. Weld to stainless with ER309L; to Cr-Mo with the lower-alloy filler.
Machining, forming and heat treatment
Threading (NPT per B1.20.1) and grooving (Victaulic) are routine on Sch 40/80; machinability ≈ 65–70 % of B1112. Cold bending: minimum radius 5 D (Grade A) to 6 D (Grade B) without heat; hot bending 900–1050 °C followed by normalizing when required; induction bending common. Flaring and swaging in the annealed state. Cut by saw, abrasive, plasma or oxy-fuel; grind heat-affected edges before welding.
Typical applications
- Refinery and petrochemical process piping (ASME B31.3) to ~425 °C
- Power-plant steam and feedwater piping (ASME B31.1), boiler external piping
- Steam headers, condensate and hot-oil systems, heat-transfer fluid loops
- Pressure-vessel nozzles, manways and long-weld-neck fittings machined from pipe
- Hydraulic and pneumatic lines at high pressure (Sch 160 / XXS)
- Fire-water and utility piping in plants (often A53-B)
- Structural columns and mechanical tubing where seamless pipe is specified
Frequently asked questions
What is the difference between A106 Grade B and A53 Grade B?
Same strength (240 / 415 MPa). A106 is seamless only, fully killed with Si ≥ 0.10 %, has tighter chemistry and residual limits, and is intended for high-temperature pressure service; A53 may be seamless (Type S) or welded (Types E/F), may be semi-killed, and is for general service. Most seamless pipe is dual-certified A106-B/A53-B, so buying A106-B covers both.
What is the maximum temperature for A106 Grade B?
ASME lists allowable stresses to 538 °C (1000 °F), but long-term use is limited to about 425 °C (800 °F) because carbon steel graphitizes and loses creep strength above that; Cr-Mo pipe (A335 P11/P22) takes over.
Can A106 Grade B be used at low temperature?
ASME B31.3 exempts it from impact testing to −29 °C (−20 °F) for most wall thicknesses. Below that, use A333 Grade 6 (same strength, Charpy-tested at −45 °C) or order A106 with supplementary S5 impact testing.
What is the European equivalent of A106 Grade B?
EN 10216-2 P235GH (yield 235, Rm 360–500 MPa) is the usual substitute; P265GH (265 / 410–570 MPa) matches the tensile more closely. Both are seamless pressure tubes with guaranteed elevated-temperature yield. Cross-use in ASME systems requires the pipe to be also certified to SA-106 or accepted by the owner.
What are A106 Grades A, B and C?
Grade A: 205 MPa yield / 330 MPa tensile, C ≤ 0.25 % — for bending and cold forming. Grade B: 240 / 415 MPa, C ≤ 0.30 % — the standard. Grade C: 275 / 485 MPa, C ≤ 0.35 % — for higher pressure, less weldable.
Does A106 pipe need PWHT after welding?
Per ASME B31.3, P-No. 1 carbon steel needs PWHT at 595–650 °C when the wall exceeds 19 mm (3/4 in), or regardless of thickness for certain services (caustic, amine, wet H₂S, lethal). Below that, no PWHT.
Related grades
Verified against ASTM A106/A106M-19a; ASTM A106/A106M-19a Tables 1–2; ASME B36.10M-2018; ASME B31.3-2022 Table A-1 and 331.1.1; ASME BPVC II-D. Last checked: September 2026.