Steel A387 Gr 21L Class 1
ASTM A387 Gr 21L Class 1
A387 Grade 21L Class 1 is the low-carbon version of the 3Cr-1Mo chromium-molybdenum pressure vessel plate in the ASTM A387 family, with restricted carbon for better weldability, toughness and resistance to temper embrittlement.
Reference datasheet — A387 Gr 21L Class 1 is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the N+T condition
A387 Gr 21L Class 1 tempers and conditions
A387 Gr 21L Class 1 is supplied in 5 conditions, soft to hard. N+T is the default FabDigit quotes; the values on this page are for it.
Compare all 5 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Solution annealed | Alternative Class 1 heat treatment permitted by A387; softest condition, easiest cold forming and machining, lowest strength. | 235 | 440 | 31 | 128 HB | 7.8 % IACS |
Post-weld heat treated | Properties certified after the fabricator's simulated PWHT soak — the condition specified for reactor shells and heads. | 245 | 450 | 29 | 133 HB | 7.8 % IACS |
N+TDefault Normalized and tempered | Standard supply condition for A387 Gr 21L Class 1 plate: normalize ~900–940 °C, temper ≥650 °C for best toughness/HTHA resistance. | 265 | 470 | 28 | 140 HB | — |
Normalized and Tempered + step-cooled | Supplementary-requirement order where the plate is step-cooled and Charpy-tested to prove low temper-embrittlement shift (J-factor / X-bar limits) for hydroprocessing reactors. | 265 | 470 | 28 | 140 HB | 7.8 % IACS |
Quenched and tempered | Ordered when maximum through-thickness toughness is wanted in heavy sections; still tempered back into the Class 1 strength band. | 350 | 520 | 25 | 160 HB | 7.7 % IACS |
What is A387 Gr 21L Class 1?
A387 Grade 21L Class 1 is the low-carbon version of the 3Cr-1Mo chromium-molybdenum pressure vessel plate in the ASTM A387 family, with restricted carbon for better weldability, toughness and resistance to temper embrittlement. In the Class 1 normalized-and-tempered condition it provides 265 MPa yield, 470 MPa tensile, 28 % elongation and about 140 HB, with service to 540 °C in heavy-wall hydroprocessing equipment. It is not corrosion resistant in wet service, so internal surfaces are stainless weld overlaid, and PWHT near 690 °C is mandatory. Grade 22L is the nearest alternative for higher strength. A387 Gr 21L Class 1 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F). A387 Gr 21L Class 1 has a yield strength of 265 MPa (38.4 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Elongation at break is 28% and the elastic modulus is 207 GPa (30 Msi).
What is A387 Gr 21L Class 1 used for?
- hydrocracker vessels
- welded pressure vessel shells requiring PWHT control
- refinery reactors
Advantages
- Tough — resists crack growth — 160 MPa·√m (145.6 ksi·√in), better than 98% of steel grades
- High service temperature — 540°C (1,004 °F), better than 93% of steel grades
- Good corrosion resistance — 22/100, better than 90% of steel grades
- Ductile — tolerates forming and impact — 28%, better than 89% of steel grades
Limitations
- Low strength — 265 MPa (38.4 ksi), worse than 92% of steel grades
A387 Gr 21L Class 1 properties
Typical room-temperature values for A387 Gr 21L Class 1-N+T; bars are the position among steel grades.
Physical3
A387 Gr 21L Class 1 has a density of 7.85 g/cm³ (0.284 lb/in³), heavier than 56% of steel grades. It melts at 1,425°C (2,597 °F).
Mechanical16
A387 Gr 21L Class 1 has a yield strength of 265 MPa (38.4 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Elongation at break is 28% and the elastic modulus is 207 GPa (30 Msi).
Thermal6
A387 Gr 21L Class 1 is rated for continuous service to 540°C (1,004 °F). It conducts heat at 36 W/m·K (20.8 BTU/hr·ft·°F), worse than 73% of steel grades. Thermal expansion is 12 µm/m·K (6.67 µin/in·°F).
Electrical3
A387 Gr 21L Class 1 conducts electricity at 7.8 % IACS, worse than 57% of steel grades.
Chemical & Environmental3
Corrosion resistance is poor (22/100), better than 90% of steel grades.
Sustainability4
Producing a kilogram of A387 Gr 21L Class 1 takes about 31 MJ of energy and emits 2.3 kg of CO₂ — more than 64% of steel grades. Typical recycled content is 25%.
Manufacturability6
A387 Gr 21L Class 1's machinability is good (55/100, better than 62% of steel grades); weldability good (62/100); formability good (55/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the steel family
Yield strength against density for every steel grade FabDigit runs. A387 Gr 21L Class 1 is highlighted; hover a dot for its name, or open the interactive family chart.
Working with A387 Gr 21L Class 1
Is A387 Gr 21L Class 1 easy to machine?
Machines like annealed low-alloy steel (~55–60 % of 1212); use rigid setups, sharp carbide and generous coolant, and rough before final PWHT to avoid distortion.
Can A387 Gr 21L Class 1 be welded?
SAW/SMAW/GTAW with matching 3Cr-1Mo (or low-C 2.25Cr-1Mo) consumables, 200–250 °C preheat/interpass, low-hydrogen practice, and mandatory PWHT ~690 °C; control weld-metal J-factor/X-bar and step-cool test for reactor service.
Can A387 Gr 21L Class 1 be formed, bent or molded?
Hot form heads and shells at 900–1000 °C followed by re-normalizing and tempering; cold forming is limited and should be followed by stress relief.
A387 Gr 21L Class 1 chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| CL grade: carbon restricted vs Gr 21 | ≤ 0.1 | 0.08 |
| Mn | 0.3 – 0.6 | 0.45 |
| Poften ≤0.008 for temper-embrittlement control | ≤ 0.04 | 0.01 |
| S | ≤ 0.03 | 0.01 |
| Sioften ≤0.10 with X-bar control | ≤ 0.5 | 0.2 |
| Cr | 2.75 – 3.25 | 3 |
| Mo | 0.9 – 1.1 | 1 |
| Fe | balance |
What surface finishes work on A387 Gr 21L Class 1?
Not corrosion resistant in wet service — internal surfaces are weld-overlaid with 309L/347 stainless or Alloy 625; external surfaces are shop-primed and insulated.
Surface treatments FabDigit runs on steel parts — pick them in the quote configurator or call them out on the drawing. Each links to its datasheet in the surface-finish library (thickness, specs, call-out, material verdicts).
Organic Coating
Black / Phosphate
Thermal Spray
Equivalent designations
Standards and trade names that resolve to Steel A387 Gr 21L Class 1 in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- A387 Grade 21L Class 1
How much does A387 Gr 21L Class 1 cost?
A387 Gr 21L Class 1 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
A387 Gr 21L Class 1 — frequently asked
What is A387 Gr 21L Class 1 used for?
A387 Gr 21L Class 1 is typically used for hydrocracker vessels, welded pressure vessel shells requiring PWHT control and refinery reactors. In short: low-carbon 3Cr-1Mo plate; temper-embrittlement resistant; hydroprocessing vessel grade.
What is the yield strength of A387 Gr 21L Class 1?
A387 Gr 21L Class 1 has a typical yield strength of 265 MPa (38.4 ksi) and a tensile strength of 470 MPa (68.2 ksi) — weaker than 92% of steel grades. Strength varies by condition: see the 5 listed tempers.
Is A387 Gr 21L Class 1 easy to machine?
Reasonably — machinability is rated good (55/100, better than 62% of steel grades). Machines like annealed low-alloy steel (~55–60 % of 1212); use rigid setups, sharp carbide and generous coolant, and rough before final PWHT to avoid distortion.
Can A387 Gr 21L Class 1 be welded?
Yes — weldability is rated good (62/100). SAW/SMAW/GTAW with matching 3Cr-1Mo (or low-C 2.25Cr-1Mo) consumables, 200–250 °C preheat/interpass, low-hydrogen practice, and mandatory PWHT ~690 °C; control weld-metal J-factor/X-bar and step-cool test for reactor service.
What surface finishes work on A387 Gr 21L Class 1?
Not corrosion resistant in wet service — internal surfaces are weld-overlaid with 309L/347 stainless or Alloy 625; external surfaces are shop-primed and insulated.
Can A387 Gr 21L Class 1 be formed, bent or molded?
Hot form heads and shells at 900–1000 °C followed by re-normalizing and tempering; cold forming is limited and should be followed by stress relief.
What is the maximum service temperature of A387 Gr 21L Class 1?
A387 Gr 21L Class 1 is rated for continuous use to about 540°C (1,004 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between A387 Gr 21L Class 1 N+T and A387 Gr 21L Class 1-A?
N+T is the default condition — standard supply condition for A387 Gr 21L Class 1 plate: normalize ~900–940 °C, temper ≥650 °C for best toughness/HTHA resistance. A: alternative Class 1 heat treatment permitted by A387; softest condition, easiest cold forming and machining, lowest strength. Yield strength is 265 MPa in N+T versus 235 MPa in A.
How much does A387 Gr 21L Class 1 cost?
A387 Gr 21L Class 1 is a standard-cost steel ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM A387/A387M — Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum — ASTM International (2021)
- ASTM A20/A20M — General Requirements for Steel Plates for Pressure Vessels — ASTM International (2020)
- ASME BPVC Section II Part D — Material Properties (allowable stress, E, α, k) — ASME (2023)
- API RP 934-A — Materials and Fabrication of 2¼Cr-1Mo, 2¼Cr-1Mo-¼V, 3Cr-1Mo and 3Cr-1Mo-¼V Heavy-Wall Pressure Vessels — API (2019)
- API RP 941 — Steels for Hydrogen Service at Elevated Temperatures (Nelson curves) — API (2016)
- ASM Handbook Vol.1 — Properties and Selection: Irons, Steels, and High-Performance Alloys — ASM International (1990)
- Mysteel / SMM (2025)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.