What is A537 Class 3?
A537 Class 3 (or ASTM A537/ASME SA537 Class 3) refers to a heat-treated, quenched, and tempered carbon-manganese-silicon steel plate designed for fusion-welded pressure vessels and boilers, offering higher strength (Yield 380 MPa / 55 ksi min) and toughness than Class 1, ideal for moderate temperature services in oil, gas, and chemical industries. It's known for balanced strength and improved impact properties, with specific tempering requirements (not less than 1150°F / 620°C).
Key Characteristics of A537 Class 3:
1.Heat Treatment: Like Class 2, it is supplied in the quenched and tempered (Q&T) condition. This process gives it a fine-grained microstructure that delivers an optimal combination of high strength and excellent impact resistance.
Mechanical Properties (Typical for plates ≤ 2.5 in / 63.5 mm):
2.Minimum Yield Strength: 80 ksi (550 MPa)
Minimum Tensile Strength: 95 ksi (655 MPa)
Strength values decrease for thicker plates, as defined in the ASTM standard tables.
3.Primary Distinguishing Feature – Enhanced Toughness:
The main difference between Class 3 and Class 2 lies in its stringent toughness (impact) requirements.
While Class 2 is typically specified for service down to -50°F (-46°C), Class 3 is engineered for even more demanding low-temperature applications, often requiring Charpy V-Notch testing at -75°F (-60°C) or lower, with higher minimum absorbed energy values. This must be explicitly specified by the purchaser.
4.Common Applications:
Critical low-temperature and cryogenic pressure vessels
Storage tanks for liquefied gases (e.g., LNG, ethylene)
Offshore structures in arctic environments
Heavy-duty mining and construction equipment operating in extreme climates
How to Select & Specify A537 Class 3:
Class 3 is not a one-size-fits-all material. To use it correctly:
The purchase order must explicitly state the required lowest service temperature.
It must specify the corresponding Charpy test temperature and minimum absorbed energy (per ASME BPVC Section VIII or other governing codes).
Welding procedures must be rigorously qualified with impact testing to ensure the weld zone matches the base metal's toughness.
ASTM boiler grade A537 class 3 pressure vessel steel plate chemical composition:
| Grade | C | Mn | P | S | Si | Cu | Ni | Cr | Mo |
| A537 class 3 | 0.24 | 0.92-1.72 | 0.035 | 0.035 | 0.13-0.55 | 0.38 | 0.28 | 0.29 | 0.09 |
The mechanical properties of A537 class 3 steel plate at ambient temperature:
| Grade | Thickness(mm) | Min Yield (Mpa) | Tensile(MPa) | Elongation(%) |
| A537 class 3 | 8mm-65mm | Min 380Mpa | 550-690Mpa | 22% |
| 66mm-100mm | Min 345Mpa | 515-655Mpa | 22% | |
| 101mm-150mm | Min 275Mpa | 485-620Mpa | 20% |
Other trade names of A537 class 3 plate:
A537 plate
A537 steel
A537 class 3 steel
ASTM A537 steel
A537 carbon steel
A537 steel plate
ASTM A537 plate
A537 grade plate
The following A537 grades are also available:
ASTM A537 / ASME SA537 class 1 / A537CL1
ASTM A537 / ASME SA537 class 2 / A537CL2
1.What is A537 Class 3?
Answer: A537 Class 3 is a high-strength, heat-treated carbon-manganese-silicon steel plate designed for welded pressure vessels, offering superior notch toughness and higher strength than Class 1 and Class 2 for specific thickness ranges.
2.What are the mechanical properties of A537 Class 3?
Answer: For plates up to 2.5 inches thick, A537 Class 3 typically has a minimum yield strength of 80 ksi (550 MPa) and a minimum tensile strength of 95 ksi (655 MPa), with impact toughness requirements often more stringent than Class 2.
3.What is the heat treatment for A537 Class 3?
Answer: A537 Class 3 is supplied in the quenched and tempered condition, similar to Class 2, but may involve stricter process controls to achieve enhanced toughness properties.
4.What is the difference between A537 Class 2 and Class 3?
Answer: The key difference lies in toughness requirements and sometimes strength for thicker plates. Class 3 is specified for enhanced low-temperature impact toughness, often with stricter Charpy V-Notch requirements, making it suitable for more critical low-temperature applications.
5.What is the Charpy impact requirement for A537 Class 3?
Answer: While specific values depend on thickness and ordering requirements, Class 3 generally requires Charpy V-Notch testing at lower temperatures (e.g., -75°F/-60°C) with higher absorbed energy minima (e.g., 40-50 ft-lbs) compared to Class 2.
6.Where is A537 Class 3 commonly used?
Answer: It is used in critical low-temperature applications such as liquefied gas storage tanks, offshore platforms in arctic environments, and pressure vessels subject to extremely cold service conditions.
7.Is A537 Class 3 weldable?
Answer: Yes, but it requires strict welding procedures similar to Class 2, including the use of low-hydrogen electrodes, controlled preheat, and often post-weld heat treatment to maintain toughness in the heat-affected zone.
8.What is the maximum thickness available for A537 Class 3?
Answer: The standard covers plates up to 6 inches (150 mm), but mechanical properties, especially toughness, are thickness-dependent and must be verified per ASTM A537 tables for Class 3.
9.Is A537 Class 3 suitable for cryogenic service?
Answer: Yes, its enhanced toughness qualifications make it suitable for cryogenic and sub-zero applications, often down to -75°F (-60°C) or lower, depending on specified impact test requirements.
10.How does A537 Class 3 compare to ASTM A553 Type I?
Answer: Both are quenched and tempered steels for low-temperature service. A553 Type I is a 9% nickel alloy steel for extremely low temperatures, while A537 Class 3 is a carbon-manganese-silicon steel with enhanced toughness for moderately low temperatures, offering a more cost-effective solution for specific ranges.
Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.
