ASTM A203 Grade D and B are both nickel alloy steel plates for pressure vessels, but differ in nickel content and strength; Grade B is typically 2% nickel (2-Ni), while Grade D is ~3.5% nickel (3.5-Ni), offering better toughness for low-temperature service, with Grade D having slightly higher yield and tensile strength requirements, commonly used in demanding oil, gas, and cryogenic applications.
Chemical Composition
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A203 Grade BChemical Composition |
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Grade |
The Element Max (%) |
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|
C |
Si |
Mn |
P |
S |
|
|
A203 Grade B |
0.17 |
0.13-0.45 |
0.78-0.88 |
0.035 |
0.035 |
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A203 Grade DChemical Composition |
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|
Grade |
The Element Max (%) |
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|
C |
Si |
Mn |
P |
S |
|
|
A203 Grade D |
0.17 |
0.13-0.45 |
0.70-0.80 |
0.035 |
0.035 |
Mechanical Property
|
Mechanical Property of A203 Grade B steel plate |
A203 Grade B |
|
Tensile strength, kis [MPa] |
70-90[485-620] |
|
Yield strength, min, kis [MPa] |
40 [275] |
|
Elongation in 8 in. [200 mm], min, % |
17 |
|
Elongation in 2 in. [50 mm], min, % |
21 |
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Mechanical Property of A203 Grade D steel plate |
A203 Grade D |
|
Tensile strength, kis [MPa] |
65-85 [450-585] |
|
Yield strength, min, kis [MPa] |
37 [255] |
|
Elongation in 8 in. [200 mm], min, % |
19 |
|
Elongation in 2 in. [50 mm], min, % |
23 |
Key Differences & Similarities:
Standard: Both fall under ASTM A203 (or ASME SA-203), a specification for Nickel-Alloy Steel Plates for Pressure Vessels.
Nickel Content:
Grade B: ~2% Nickel (often called "2% nickel steel").
Grade D: ~3.5% Nickel (often called "3.5% nickel steel").
Properties: The higher nickel in Grade D provides superior toughness and impact resistance, especially at low (cryogenic) temperatures, making it suitable for harsher conditions than Grade B.
Mechanical Properties (Typical for normalized plates):
Grade B: Minimum Yield Strength ~37 ksi (255 MPa), Tensile Strength ~60-72 ksi (415-495 MPa).
Grade D: Minimum Yield Strength ~37 ksi (255 MPa), Tensile Strength ~65-77 ksi (450-530 MPa). (Note: Grade D has a higher tensile requirement).
Heat Treatment: Both are typically supplied normalized.
Applications: Both serve pressure vessels, but Grade D is preferred for very low-temperature applications, like in CO2 capture or air separation units, due to its enhanced toughness.
