SA204 Grade B STEEL PLATE
SA204 Grade B is an alloy steel plate standardized under the ASME Boiler and Pressure Vessel Code (Section II, Part A). It is a molybdenum steel specifically designed for moderate to high-temperature service in welded pressure vessels, particularly boiler drums and shells.
Key Characteristics:
1. Chemical Composition (Defining Feature):
Molybdenum (Mo): 0.45–0.60%. This is the primary alloying element, which enhances strength at elevated temperatures and provides some resistance to creep.
Carbon (max 0.20%), Manganese (0.55–0.85%), Silicon (0.15–0.40%).
It is a relatively simple, low-alloy steel without chromium.
2. Mechanical Properties (for plates ≤ 2 in / 50 mm):
Tensile Strength: 65 – 85 ksi (450 – 585 MPa)
Yield Strength (Minimum): 37 ksi (255 MPa)
Elongation (Minimum): 23% (Longitudinal), 17% (Transverse)
3. Heat Treatment:
Supplied in the normalized or normalized and tempered condition.
4. Temperature Service Range:
Its primary application is for components operating at elevated temperatures, typically up to about 850°F (454°C). It is not primarily designed for low-temperature/cryogenic service.
Primary Applications:
Boiler Drums and Shells: Its classic use is in the construction of fossil-fuel power plant boilers.
Moderate-Temperature Pressure Vessels: Vessels in refinery and chemical process services where temperatures are elevated but not extreme.
Heat Exchanger Shells.
Comparison within the SA204 Family:
The SA204 standard has three grades based on increasing molybdenum content and strength:
Grade A: 0.45–0.60% Mo (lower strength than B)
Grade B: 0.45–0.60% Mo (standard strength for boiler applications)
Grade C: 0.90–1.10% Mo (highest strength and temperature capability)
Why It's Used:
It offers a cost-effective balance of strength, fabricability (good weldability), and elevated temperature performance for a specific industrial niche. For more severe high-temperature/hydrogen service, chromium-molybdenum steels (like SA387) are typically specified.
Key Distinction:
Unlike SA203 (nickel steel for low temperatures), SA204 (molybdenum steel) is designed for elevated temperature service.
Chemical Composition and Mechanical Properties:
| SA204 Grade B Chemical Composition | |||||
| Grade | The Element Max (%) | ||||
| C | Si | Mn | P | S | |
| A204 Grade B | 0.20-0.27 | 0.13-0.45 | 0.90-0.98 | 0.035 | 0.035 |
| Mechanical Property of SA203 Grade A steel plate | SA204 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 |
ASME SA204 Gr.B Pressure vessel steel plate Specification
Thickness:1.5mm -260mm
Width:1000mm-4000mm
Length:1000mm-18000mm
1.What is SA204 Grade B?
SA204 Grade B is a molybdenum alloy steel plate designed for service in welded boilers and other pressure vessels operating at moderate to high temperatures.
2.What is the chemical composition of SA204 Grade B?
Its composition includes Molybdenum (0.45-0.60%), Carbon (max 0.20%), Manganese (0.55-0.85%), Silicon (0.15-0.40%), and controlled Phosphorus and Sulfur.
3.What are the mechanical properties of SA204 Grade B?
For plates up to 2 inches thick, key properties include a minimum tensile strength of 65-85 ksi (450-585 MPa) and a minimum yield strength of 37 ksi (255 MPa).
4.Is SA204 Grade B a carbon steel or alloy steel?
It is classified as an alloy steel due to its intentional and specified molybdenum content, which provides enhanced strength at elevated temperatures.
5.What is the primary application of SA204 Grade B?
It is primarily used for parts of boilers and pressure vessels where moderate elevated temperature strength and resistance to creep are required.
6.What is the maximum service temperature for SA204 Grade B?
It is commonly used for service temperatures up to approximately 850°F (454°C) in applications such as boiler drums and shells.
7.How does SA204 Grade B compare to SA204 Grade A and C?
Grade B has higher molybdenum content than Grade A, providing better elevated temperature strength. Grade C has even higher molybdenum content (0.90-1.10%) for the highest strength.
8.Is SA204 Grade B suitable for hydrogen service?
It can be used in certain hydrogen service applications, but its suitability depends on specific temperature, pressure, and hydrogen partial pressure conditions. Often, chrome-molybdenum steels like SA387 are preferred for severe service.
9.What is the heat treatment for SA204 Grade B?
SA204 Grade B plates are typically supplied in the normalized or normalized and tempered condition to achieve the required mechanical properties.
10.Can SA204 Grade B be welded easily?
Yes, it has good weldability. Welding should follow standard practices for low-alloy steels, including proper preheat and post-weld heat treatment (PWHT) for thicker sections to maintain properties.
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.
