ASTM A516 Grade 70 Carbon Steel: Pressure Vessel Plate for Moderate & Lower-Temperature Service
ASTM A516 Grade 70 (UNS K02700) is a carbon-manganese-silicon steel plate specifically designed for welded pressure vessels operating in moderate and lower-temperature environments (down to -20°C/-4°F). Its fine-grained microstructure, achieved through normalized rolling, delivers superior notch toughness, weldability, and consistent mechanical properties across thick sections (up to 150mm). This grade is the industry standard for boilers, storage tanks, and industrial pressure equipment where ASME BPVC Section II compliance is required. Below, we examine its chemical composition, mechanical properties, manufacturing process, and critical application considerations.
1. Chemical Composition (ASTM A516/A516M Standard)
| Element | Content Range (wt%) | Function |
|---|---|---|
| Carbon (C) | ≤ 0.31% | Primary strengthening element; controlled to balance strength and weldability (Pcm ≤ 0.25%) |
| Manganese (Mn) | 0.79 – 1.30% | Enhances hardenability and deoxidation; compensates for sulfur effects (Mn/S ≥ 20:1) |
| Phosphorus (P) | ≤ 0.035% | Impurity; minimized to prevent temper embrittlement and reduce segregation |
| Sulfur (S) | ≤ 0.035% | Impurity; controlled to improve anisotropy and Z-direction properties (optional Z15/Z25/Z35 testing) |
| Silicon (Si) | 0.13 – 0.45% | Deoxidizer; improves strength via solid-solution hardening (killed steel process) |
| Copper (Cu) | ≤ 0.30% | Residual element; limited to avoid hot shortness during rolling |
| Nickel (Ni) | ≤ 0.30% | Residual; may improve low-temperature toughness in trace amounts |
| Chromium (Cr) | ≤ 0.25% | Residual; higher levels may require impact testing per ASME requirements |
| Molybdenum (Mo) | ≤ 0.08% | Residual; not intentionally added (unlike A537 Class 1) |
2. Mechanical Properties (Normalized Condition)
- Tensile Strength: 70-90 ksi (485-620 MPa) — ensures structural integrity under internal pressure
- Yield Strength (0.2% offset): ≥ 38 ksi (260 MPa) — minimum guaranteed for design calculations
- Elongation (200mm gauge): ≥ 17% (transverse), ≥ 21% (longitudinal) — indicates formability for rolling/flanging
- Charpy V-Notch Impact: ≥ 20 ft-lb (27 J) at -20°C — critical for fracture resistance in low-temperature service
- Brinell Hardness (HB): ≤ 187 — limits susceptibility to hydrogen-induced cracking (HIC)
- Reduction of Area: ≥ 35% — measures ductility for high-strain applications
3. Manufacturing Process & Quality Control
- Steelmaking: Electric arc furnace (EAF) + ladle refining (LF) + vacuum degassing (VD) to achieve ultra-low hydrogen (< 2ppm) and inclusion control (Type II MnS ≤ 1.5 per ASTM E45).
- Rolling: Thermomechanical controlled processing (TMCP) with finish rolling at 850-950°C to refine austenite grain size (ASTM E112 Grain Size ≥ 5).
- Normalizing: Heated to 900-950°C, soaked for 1 hour per 25mm thickness, air-cooled to ensure uniform microstructure and relieve residual stresses.
- Ultrasonic Testing: 100% UT per ASTM A435/A577/A578 (calibration to FBH Ø1.6mm) for internal defect detection in plates > 50mm thick.
- Surface Condition: Shot blasted to Sa2.5 (ISO 8501-1) with roughness 3-6µm Ra; optional primer coating (15-25µm DFT) for corrosion protection during storage.
- Certification: Mill Test Reports (MTR) per EN 10204 3.2 with PMI verification (OES analysis) and NDE records traceable to heat numbers.
4. Key Application Scenarios
Petrochemical Industry
Crude oil storage tanks (API 650), spherical LPG/NH₃ vessels (API 620), and separator drums — resistant to H₂S-induced cracking (NACE MR0175 compliant with supplementary requirements).
Power Generation
Boiler drums, steam separators, and feedwater heaters in fossil fuel/biomass plants — operates continuously at temperatures up to 450°C with ASME Section I stamp.
Water Treatment
Potable water tanks, desalination pressure vessels, and wastewater digesters — NSF/ANSI 61 certified for contact with drinking water when coated with approved epoxy systems.
Industrial Gas Storage
CO₂, N₂, and air receiver tanks for process industries — designed per PD 5500 or AD 2000 Merkblatt with 100% radiography (RT) for critical welds.
Mining & Mineral Processing
Slurry tanks, leach autoclaves, and thickener mechanisms — abrasion-resistant with optional hardness testing (HB 170-187) for extended service life.
Transportation
Rail tank cars (AAR S-60) and ISO containers for hazardous materials — DOT/TC compliance with supplemental Charpy testing at -40°C for Arctic service.
5. Comparison with Related Grades
| Grade | Key Alloying | Tensile Strength (ksi) | Primary Advantage | Typical Use Case |
|---|---|---|---|---|
| ASTM A516 Gr. 60 | Lower C (≤ 0.27%) | 60-80 | Better weldability for thin sections | Non-critical tanks, structural supports |
| ASTM A516 Gr. 70 | Balanced C-Mn | 70-90 | Optimal strength-toughness balance | Pressure vessels, boilers, API tanks |
| ASTM A537 Cl. 1 | Ni-Cr-Mo added | 70-90 | Higher toughness at -45°C | Cryogenic service, sour gas environments |
| ASTM A285 Gr. C | Higher P/S (≤ 0.04%) | 55-75 | Lower cost for non-critical apps | Water tanks, low-pressure containers |
| EN 10028 P355GH | Al-killed | 65-85 (450-585 MPa) | European equivalent with CE marking | PED-certified pressure equipment |
6. Engineering & Fabrication Guidelines
- Welding Procedures: Preheat to 95-150°C for plates > 25mm (interpass max 300°C); use low-hydrogen electrodes (E7018) to prevent cold cracking. PWHT at 595-650°C required for thicknesses > 38mm per ASME Sec. VIII Div. 1 UCS-56.
- Post-Weld Testing: Mandatory 100% VT (visual) + 10% RT (radiography) for Category D welds; hydrostatic test at 1.3× design pressure with hold time ≥ 30 minutes.
- Corrosion Allowance: Add 3mm (0.125″) for mild corrosive environments; 6mm (0.25″) for cyclic wet/dry service (e.g., seawater ballast tanks).
- NDE Requirements: UT thickness mapping (per ASTM E797) for plates in hydrogen service; AET (Acoustic Emission Testing) for spherical vessels during commissioning.
- Coating Systems: For atmospheric exposure, 3-coat epoxy/polyurethane system (250µm DFT) per NORSOK M-501; internal linings (e.g., rubber or glass-flake) for chemical resistance.
- Temperature Limits: Maximum continuous service at 450°C (840°F); avoid prolonged exposure above 425°C to prevent graphitization (per API 941).
7. Request a Carbon Steel Plate Quote
Need ASTM A516 Grade 70 plates with customized dimensions, NDE levels, or supplementary requirements (e.g., HIC testing, Z-direction properties)? Contact our technical sales team for mill-direct pricing, lead times, and certification packages tailored to your project specifications. We stock thicknesses from 6mm to 150mm with widths up to 3,800mm, and offer plasma/oxy-fuel cutting to your drawings.