ASTM A533 Grade A and Grade B are low-alloy steels for welded pressure vessels, with Grade B being the more common, offering higher strength and toughness, especially in thicker sections, due to its manganese-molybdenum (and sometimes nickel) composition, suited for demanding applications like nuclear reactors, while Grade A provides a lower strength, more general-purpose option, both typically supplied quenched and tempered. The primary differences lie in their specified mechanical properties (yield/tensile strength) and intended service conditions, with Grade B's enhanced toughness making it a workhorse for high-stress, thick-section vessels.
Chemical composition of ASTM A533 Grade A
|
Grade |
C % |
Mn %(<40mm) |
P% |
S% |
Si% |
Mo% |
Ni% |
|
A533 Grade A |
0.25 |
1.07-1.82 |
0.035 |
0.035 |
0.13-0.45 |
0.41-0.84 |
-- |
Chemical composition of ASTM A533 Grade B
|
Grade |
C % |
Mn %(<40mm) |
P% |
S% |
Si% |
Mo% |
Ni% |
|
A533 Grade B |
0.25 |
1.07-1.82 |
0.035 |
0.035 |
0.13-0.45 |
0.41-0.84 |
0.37-0.73 |
Mechanical Property of ASTM A533 Grade A
|
Grade |
Min Yield |
Tensile |
Thicknesss |
Elongation |
|
A533 Grade A |
345 Mpa |
550-690Mpa |
<50MM |
18% |
Mechanical Property of ASTM A533 Grade B
|
Grade |
Min Yield |
Tensile |
Thicknesss |
Elongation |
|
A533 Grade B |
485 Mpa |
620-795Mpa |
<50MM |
16% |
ASTM A533
Type: Alloy steel plates for pressure vessels, often manganese-molybdenum (Mn-Mo) or Mn-Mo-Ni.
Heat Treatment: Usually supplied quenched and tempered (Q&T) for improved strength and toughness.
Classes: Available in different classes (e.g., Class 1, 2, 3) indicating strength levels, with Grade B Class 3 being the strongest.
Key Differences: Grade A vs. Grade B
Strength: Grade B provides higher tensile and yield strength than Grade A, especially in thicker plates.
Usage: Grade B (especially Class 1 and 3) is the preferred choice for heavy-section nuclear reactor vessels and high-pressure components. Grade A offers sufficient properties for lower-strength, less critical pressure vessel applications.
Composition: While both are alloy steels, Grade B often incorporates nickel (Mn-Mo-Ni), contributing to its superior notch toughness, a crucial property for thick components, notes ASM International.
