What Is SA553 Type 1 Steel?
SA553 Type 1 is a quenched and tempered alloy steel plate containing nominally 9% nickel. It was developed to deliver outstanding fracture toughness, yield strength, and weldability at cryogenic temperatures, where standard carbon steels become dangerously brittle. The ASME SA-553/SA-553M specification covers Type I (9% nickel) and Type II (8% nickel), and Type 1 is the most widely specified grade for the most demanding cryogenic service because of its impact resistance at -195 °C. The designation SA553 Type 1, SA553 Type I, and ASTM A553 Type I all refer to the same material.
Chemical Composition
The table below presents the composition limits for SA553 Type 1 per ASME SA-553, as heat analysis requirements:
Carbon (C), max: 0.13% | Manganese (Mn), max: 0.90% | Phosphorus (P), max: 0.035% | Sulfur (S), max: 0.040% | Silicon (Si): 0.15-0.40% | Nickel (Ni): 8.50-9.50% | Iron (Fe): balance.
Product analysis tolerances apply to manganese (up to 0.98%), silicon (0.13-0.45%), and nickel (8.40-9.60%). The low carbon limit minimizes the risk of cold cracking in the heat-affected zone during welding.
Mechanical Properties and Impact Requirements
Tensile strength (ultimate): 690-825 MPa (100,000-120,000 psi).
Yield strength (0.2% offset), min: 585 MPa (84,800 psi).
Elongation at break (in 50 mm), min: 20%.
Impact test temperature (Type I): -195 °C (-320 °F).
Minimum Charpy V-notch impact energy at -195 °C (transverse): 27 J.
Minimum lateral expansion at -195 °C: 0.381 mm.
These requirements provide a statistically robust safety margin validated by decades of field service in LNG storage tanks and cryogenic transport vessels.
Heat Treatment Requirements
All SA553 Type 1 plates must undergo a controlled two-stage heat treatment: austenitizing at 800-925 °C (1475-1700 °F), holding long enough to reach uniform temperature through the full thickness, followed by rapid water quenching. The plates are then tempered at 565-635 °C (1050-1175 °F), with a minimum holding time of 30 minutes per inch (1.2 min/mm) of thickness but not less than 15 minutes, followed by air cooling or equivalent. This quench and temper (Q+T) condition is mandatory and provides the balance of strength and cryogenic toughness that defines the material.
SA553 Type 1 versus Type 2
Type 1 contains 8.50-9.50% nickel and is impact-tested at -195 °C, with a minimum service temperature of -196 °C for LNG, liquid oxygen, nitrogen, and argon service. Type 2 contains 7.50-8.50% nickel and is impact-tested at -170 °C. Type 1 is the clear choice for the most demanding applications such as LNG peak-shaving plants, ethylene storage terminals, and air separation unit storage, while Type 2 is more economical for less severe temperature requirements.
Applications
SA553 Type 1 is the reference material for large LNG flat-bottom above-ground storage tanks serving at about -163 °C, and it is approved for the inner shell of double-walled LNG storage systems. It is also used for cryogenic gas transport and storage of nitrogen, oxygen, and argon below -196 °C, for inner vessel shells in air separation units, and for ethylene storage spheres and cryogenic transport tanks in petrochemical plants.
Frequently Asked Questions
Is SA553 Type 1 the same as ASTM A553 Type I? Yes. ASME SA-553 Type I is identical to ASTM A553 Type I; the SA prefix indicates the ASME Boiler and Pressure Vessel Code designation, while the A prefix denotes the ASTM standard, and both reference the same material, chemical, and mechanical requirements.
What is the difference between Type 1 and Type 2? The primary difference is nickel content and impact test temperature: Type 1 has 8.50-9.50% nickel and is tested at -195 °C, while Type 2 has 7.50-8.50% nickel and is tested at -170 °C.
What impact energy is required at -195 °C? minimum Charpy V-notch impact energy of 27 J and a minimum lateral expansion of 0.381 mm are required at -195 °C for Type 1.
How is SA553 Type 1 heat treated? Plates are austenitized at 800-925 °C, water quenched, and tempered at 565-635 °C with a minimum hold time of 30 minutes per inch of thickness.
Is SA553 Type 1 weldable? Yes. The low carbon content minimizes cold cracking risk, and conventional fusion processes such as SMAW, SAW, GMAW, and TIG can be used with properly matched nickel-based filler metals.
What is the maximum thickness available? The specification sets no absolute maximum; the limit is determined by the ability to meet mechanical and impact requirements through the full thickness, and current mill practice routinely covers plate up to 50 mm and beyond.
