Here's a technical comparison of A285 Grade C and A516 Grade 70 steel plates, crucial for selecting materials in pressure vessel and storage tank fabrication:
| Characteristic | A285 Grade C | A516 Grade 70 |
|---|---|---|
| Key Application | Moderate pressure/vacuum tanks | Critical pressure vessels, low-temp service |
| Governing Standard | ASTM A285 (Pressure Vessel Plates, Carbon Steel, Low- and Intermediate-Tensile Strength) | ASTM A516 (Pressure Vessel Plates, Carbon Steel, for Moderate- and Lower-Temperature Service) |
| ASME Section VIII | Division 1 only | Division 1 & 2 |
| Min. Yield Strength | 30 ksi (205 MPa) | 38 ksi (260 MPa) |
| Min. Tensile Strength | 55-75 ksi (380-515 MPa) | 70-90 ksi (485-620 MPa) |
| Max. Thickness w/o Post-Weld Heat Treat | 1.25 in (32 mm) | 2 in (50 mm) at 650°F (343°C) design temp |
| Typical Chemistry | Higher max S (0.045%) & P (0.045%) | Tighter controls: Max S (0.035%), P (0.035%) |
| Notch Toughness | Optional per purchase order | Mandatory (Impact testing required) |
| Low-Temperature Suitability | Limited to -10°C (14°F) MDMT* | Down to -50°C (-60°F) MDMT* after normalization |
| Relative Cost | Lower | Higher (+~15-25%) |
Critical Design Considerations:
Temperature is Decisive:
A285 Gr C: Max MDMT (Minimum Design Metal Temp) is -10°C (14°F), even normalized. Unsuitable for sub-zero applications.
A516 Gr 70: Readily achieves -30°C (-20°F) MDMT as-rolled. Normalized can reach -50°C (-60°F). Essential for refrigerated tanks.
Thickness & Stress:
Use A516 Gr 70 for thicker sections (>32mm/1.25") to avoid costly PWHT, or where higher strength reduces plate thickness/weight.Safety Criticality:
A516 Gr 70's mandatory notch toughness testing ensures fracture resistance in shock/vibration-prone or low-temperature environments.Code Compliance:
For Division 2 pressure vessels or ASME stamping below -10°C, A516 Gr 70 is required. A285 Gr C is Division 1 only.When to Choose:
A285 Grade C: Atmospheric/low-pressure storage tanks operating above freezing, water tanks, non-critical applications with MDMT > -10°C. Offers cost savings where applicable.
A516 Grade 70: ASME Boiler & Pressure Vessel Code stamped vessels, low-temperature service (refrigerants, LNG), high-pressure storage, thick-walled vessels, or where impact toughness is mandated.
Key Takeaway: While both steels serve pressure containment, A516 Grade 70 provides superior low-temperature toughness, higher strength, and stricter quality control, making it essential for critical applications. A285 Grade C remains a cost-effective choice for simpler, ambient-temperature tanks where code allows. Always verify material selection against ASME BPVC Section VIII requirements and specific design conditions.
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