General Introduction
The 9% nickel steel is a low-carbon nickel alloy steel with nominal composition of 9Ni, which is particularly used for low-temperature or cryogenic pressure vessels and plants for processing, transportation, and storage of LNG down to -196°C [-320°F]. The steel is originated from International Nickel Company’s lab in 1940’s. It has relatively higher strength and allowable stress than austenitic stainless steels, aluminum and copper. The 9% nickel steel exhibits excellent fracture toughness even at cryogenic temperatures. It also has high melting point and retention of strength at elevated temperatures, which provide fire-safe integrity for the LNG pressure vessels. Besides, the relatively low thermal expansion, low thermal conductivity and good corrosion resistance make the steel applicable for ethylene, methane, LNG, oxygen, and nitrogen applications.
ASME, ASTM Standards & International Equivalent
The 9% nickel steel is designated as UNS K81340. Various international equivalent are available such as GB-24510 9Ni490, 9Ni590A, 9Ni590B (China); EN 10028-4 X8Ni9+NT640, X8Ni9+QT680, X7Ni9+QT680 (Europe); JIS G3127 SL9N520, SL9N590 (Japan); CCS 9Ni; DIN 17280 X8Ni9/1.5662 (Germany). The 9Ni steel can be furnished as pressure vessel plates, pipes, tubes, fittings, flanges, valves or valve parts, and other forgings in accordance with relative ASTM or ASME standards.
| ASTM/ASME Grade | Product Form |
|---|---|
| ASTM A353, ASME SA-353 Grade 9%-Ni Steel | Double-normalized and tempered 9% nickel steel pressure vessel plates |
| ASTM A553/ ASME SA-553 Type I | Quenched and tempered 9% nickel steel pressure vessel plates |
| ASTM A333/ ASME SA-333 Grade 8 | Seamless and welded 9%-Ni alloy steel pipes for low-temp. service |
| ASTM A334/ ASME SA-334 Grade 8 | Seamless and welded 9% nickel steel tubes for low-temp. service |
| ASTM A420/ ASME SA-420 Gr. WPL8 | Wrought pipe fittings for low-temp. service |
| ASTM A522/ ASME SA-522 Type I | 9% nickel alloy steel forged flanges, fittings, valves, and parts. |
| ASTM A844/ ASME A844 9Ni | 9%-Ni steel pressure vessel plates, by direct-quenching process |
| ASTM A352/ ASME SA-352 Gr. LC9 | 9% nickel steel castings for low-temp. service |
| ASTM A671/ ASME SA-671 Gr. CG 100 & Gr. CH 100 | EFW 9%-Ni steel pipe for low-temp. |
*The 9% nickel steel pressure vessel plates made to ASTM A553 and ASTM A353 are most widely used.
*The ASME SA-671 Gr. CH 100 and Gr. CG 100 were removed from its 2013 revision.
*For ASTM A352 Gr. LC9 castings, the UNS designation is J31300.
Typical Chemical Composition of 9% Nickel Steel
| Element | C | Mn | P | S | Si | Ni |
|---|---|---|---|---|---|---|
| Content, wt. % | ≤0.13 | ≤0.90 | ≤0.015 | ≤0.015 | 0.15~0.30 | 8.5~9.5 |
*All values are for heat analysis. Carbon equivalent CE shall be calculated.
Typical Mechanical Properties of 9% Nickel Steel
| Tensile Strength, ksi [MPa] | Yield Strength, ksi [MPa] | Elongation in 2″, % |
|---|---|---|
| ≥ 100 [690] | ≥ 75 [515] | ≥ 20.0 |
*The tabulated values shall be tested at room temperatures.
*Charpy V-Notch impact tests shall be conducted at different low temperatures.
*Fracture toughness in transverse or longitudinal orientation shall be measure upon request.
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