ASTM A522 Type I – 9% Ni steel – UNS K81340
Forged 9% nickel ferritic steel for cryogenic service down to −196 °C
Low-carbon steel with 8.5–9.5% Ni, forged and rolled to ASTM A522/A522M for flanges, fittings and valves in cryogenic service. Supplied double normalized and tempered (NNT) or quenched and tempered (QT), it keeps its toughness at −196 °C and is the standard material for LNG tanks and lines.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | K81340 |
| W.Nr./EN | X8Ni9 – 1.5662 (EN 10222-3, forgings) |
| DIN | X8Ni9 |
| JIS | SL9N520 / SL9N590 (plate, JIS G3127) |
| Trade names | 9% Ni, 9Ni |
| Others | Plate A353/A553 Type I; pipe A333 Gr 8; fittings A420 WPL8 |
Standards by product form
| Form | Standard |
|---|---|
| Forging (flanges, fittings, valves) | ASTM A522/A522M Type I; ASME SA-522 |
| Plate | ASTM A353 (NNT) / A553 Type I (QT) |
| Pipe/tube | ASTM A333 Gr 8 / A334 Gr 8 |
| Butt-welding fittings | ASTM A420 WPL8 |
| EN bar/forging | EN 10222-3 X8Ni9 |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7228.40.00 | 7228.40 | 7228.40.0000 | 7228 40 90 |
| Hot-rolled bar | 7228.30.00 | 7228.30 | 7228.30.8041 | 7228 30 61 |
| Plate (> 10 mm, width ≥ 600 mm) | 7225.40.90 | 7225.40 | 7225.40.3050 | 7225 40 40 |
| Seamless pipe | 7304.19.00 | 7304.19 | 7304.19.5050 | 7304 19 10 |
| Welded pipe | 7306.19.00 | 7306.19 | 7306.19.5150 | 7306 19 00 |
| Flange and fitting | 7307.91.00 | 7307.91 | 7307.91.5030 | 7307 91 00 |
Tariff class: alloy steel (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
Pipe: 7304.19 and 7306.19 are line pipe for oil and gas pipelines; boiler, heat exchanger or process tubes go under 7304.39/7304.59 (seamless) and 7306.30/7306.50 (welded).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM A522/A522M – Type I
| Element | Range (%) |
|---|---|
| C | ≤ 0.13 |
| Mn | ≤ 0.90 |
| P | ≤ 0.025 |
| S | ≤ 0.025 |
| Si | 0.15 – 0.30 (≤ 0.10 with vacuum deoxidation) |
| Ni | 8.5 – 9.5 |
Mechanical properties
NNT or QT – ASTM A522 Type I, room temperature
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 515 MPa |
| Tensile strength | ≥ 690 MPa |
| Elongation | ≥ 22% |
| Reduction of area | ≥ 45% |
| Impact at −196 °C | Charpy lateral expansion ≥ 0.38 mm |
Typical physical properties
| Property | Value |
|---|---|
| Density | ≈ 7.86 g/cm³ (typical) |
| Modulus of elasticity | ≈ 195 GPa (typical) |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | −196 °C to 121 °C (scope of A522). |
| Heat treatment | NNT: 900 °C in air + 790 °C in air + tempering 565–605 °C. QT: austenitize 800 ± 14 °C, water quench + tempering 565–605 °C. Cooling after tempering in air or water at ≥ 167 °C/h. Stress relief 550–585 °C. |
| Welding | Weldable with nickel-based consumables (do not use ferritic consumables): AWS ENiCrMo-6 / ENiCrFe-9 (A5.11), ERNiMo-8 / ERNiCr-3 (A5.14). Control residual magnetism (arc blow) and heat input; PWHT normally waived per code. |
| Machining | Similar to a 690 MPa low-alloy steel; good with carbide. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Flanges and fittings for LNG
- Cryogenic valves
- Tanks and lines for liquid nitrogen, oxygen and argon (down to −196 °C)
- Regasification terminals and LNG carriers
- Cryogenic vessel nozzles
Alternatives: A350 LF3 (3.5% Ni) down to −101 °C, cheaper; 304L/316L stainless (A182) when an austenitic without ductile-brittle transition is wanted; Invar 36 for low-expansion piping.
ASTM A522 Type I: complete guide
What ASTM A522 Type I steel is
A522 is the forged version of the 9% nickel steel of ASTM A353 and A553 plates. It belongs to the family of alloy steels, but with a function opposite to that of the Cr-Mo grades: instead of resisting heat, it keeps toughness at cryogenic temperatures at which ordinary carbon and low-alloy steels become brittle.
Chemical composition and role of nickel
Nickel (8.5 – 9.5%) lowers the ductile-brittle transition temperature and, with the correct heat treatment, produces a microstructure of tempered martensite with stable reverted austenite (formed during tempering), responsible for toughness at −196 °C. Carbon is kept low (≤ 0.13%) and phosphorus and sulfur are limited to 0.025% to preserve toughness.
Heat treatment
Double normalized and tempered or quenched and tempered, with tempering between 565 and 605 °C. Dustre performs the cycle in its own furnaces, with temperature records, as part of its heat treatment service, and confirms the result with impact testing.
Welding
The critical point of fabrication with 9% Ni is the consumable: welding must be done with a nickel alloy (ENiCrMo-6 / ERNiMo-8 or ENiCrMo-3), because ferritic consumables do not reach the toughness required at −196 °C. Preheating is unnecessary or low, and normally there is no post-weld heat treatment. The material is strongly magnetic, so parts must be demagnetized before welding.
Applications
Flanges, fittings, valves, nozzles and forged parts of LNG tanks and piping, air separation plants (liquid nitrogen and oxygen), ethylene and other liquefied gases, between −196 °C and about 120 °C.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, heat treatment in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of ASTM A522 Type I?
Per ASTM A522/A522M – Type I: C ≤ 0.13; Mn ≤ 0.90; P ≤ 0.025; S ≤ 0.025; Si 0.15 – 0.30 (≤ 0.10 with vacuum deoxidation); Ni 8.5 – 9.5.
Which standards cover ASTM A522 Type I?
Forging (flanges, fittings, valves): ASTM A522/A522M Type I; ASME SA-522. Plate: ASTM A353 (NNT) / A553 Type I (QT). Pipe/tube: ASTM A333 Gr 8 / A334 Gr 8. Butt-welding fittings: ASTM A420 WPL8. EN bar/forging: EN 10222-3 X8Ni9.
Up to what temperature can ASTM A522 Type I be used?
−196 °C to 121 °C (scope of A522).
Which materials can replace ASTM A522 Type I?
A350 LF3 (3.5% Ni) down to −101 °C, cheaper; 304L/316L stainless (A182) when an austenitic without ductile-brittle transition is wanted; Invar 36 for low-expansion piping.
Why is A522 Type I used in cryogenic flanges and valves?
Nickel of 8.5 to 9.5%, with NNT or QT treatment, keeps toughness at −196 °C, a temperature at which ordinary carbon and low-alloy steels become brittle. That is why it is standard in LNG, liquid oxygen, nitrogen and argon.
Is A522 Type I suitable for high temperature?
No. The scope of ASTM A522 runs from −196 °C to 121 °C. For high temperature, use Cr-Mo steels such as F11 or F9 (ASTM A182).
