ASME SA515 Grade 70 (also known as ASTM A515 Gr 70) is a high-strength carbon-silicon steel plate specifically designed for intermediate and higher-temperature service in boilers and other pressure vessels.
Key Technical Specifications
The "70" in the name represents its minimum tensile strength of 70 ksi.
| Property | Value (Metric) | Value (Imperial) |
|---|---|---|
| Tensile Strength | 485 – 620 MPa | 70 – 90 ksi |
| Yield Strength (min) | 260 MPa | 38 ksi |
| Elongation (min) | 17% (200mm) / 21% (50mm) | 17% (8") / 21% (2") |
CHEMICAL COMPOSITION OF A515 BQ GR.70 STEEL PLATES
| C | Si | Mn | P | S | Al | Cr | Cu | Ni | Mo | Nb | Ti | V |
| 0.18 | 0.4 | 0.95/1.50 | 0.015 | 0.008 | 0.02 (Min) | 0.3 | 0.3 | 0.3 | 0.08 | 0.01 | 0.03 | 0.02 |
MECHANICAL PROPERTIES OF BOILER QUALITY STEEL PLATES
| Tensile strength (ksi) | Yield strength (ksi) | Elongation min, % 200 mm (8 in) | Elongation min, % 50 mm (2 in) |
| 485-620 (70-90) | 260 (38) | 17 | 21 |
EQUIVALENT GRADE OF A515 GRADE 70 BOILER PLATES
| British Standard | European Norm | ASTM/ASME | DIN |
| BS1501-224-490A/B | EN10028 P355GH | A/SA515 - Grade 70 | - |
Distinctive Features
Coarse Grain Structure: Unlike the fine-grained SA516 Grade 70 (used for low-temperature toughness), SA515 is produced to a coarse grain practice to improve its resistance to creep and graphitization at elevated temperatures.
High Strength: It offers the highest tensile strength among the three grades (60, 65, and 70) defined in the ASTM A515 specification.
Weldability: It maintains good weldability using standard methods like SMAW or TIG, provided appropriate procedures for carbon steel are followed.
SA 515 Grade 70 Processing
1. Cutting
Common methods include plasma cutting, oxy-fuel cutting and mechanical shearing. Oxy-fuel cutting is preferred for thick plates (＞20mm) due to high efficiency, while plasma cutting suits thin plates (≤20mm) to ensure smooth edges. Mechanical shearing is applied for regular-shaped workpieces, with pre-heating to 100-150℃ recommended for plates over 30mm to avoid edge cracking.
2. Forming
Mainly involves bending, rolling and stamping. Cold forming is suitable for plates ≤12mm, with bending radius not less than 1.5 times the plate thickness. Hot forming (200-350℃) is required for thicker plates to reduce forming resistance and prevent material damage. Rolling should be done at a uniform speed, and stress relief annealing is necessary after forming to eliminate residual stress.
3. Welding
Use low-hydrogen electrodes (E7018) or flux-cored wires (E71T-8) to avoid hydrogen cracking. Pre-heat to 80-150℃ before welding, and maintain interpass temperature below 300℃. Post-weld heat treatment (PWHT) at 595-650℃ for 1-2 hours is mandatory for welded joints to improve toughness and reduce stress.
4. Heat Treatment
Normalization (890-920℃, air cooling) is the key process to refine grain structure and enhance strength. Stress relief annealing (550-600℃, furnace cooling) is performed after processing to reduce residual stress. For thick-walled components, tempering at 600-620℃ is added to improve ductility.
5. Surface Treatment
Remove oxide scale and rust via sandblasting or pickling. Clean the surface with acetone to remove oil and impurities before welding or painting. Anti-corrosion coating (e.g., epoxy resin) is applied after processing to extend service life in harsh environments.
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What heat treatment is SA515 Grade 70 subjected to?
It is usually supplied in the as-rolled or normalized condition. Normalization (heating to 890-950°C, holding, then air cooling) refines grain structure, improves toughness, and ensures consistent mechanical properties across the plate.
What is the hardness of SA515 Grade 70?
The Brinell hardness (HB) of SA515 Grade 70 is typically between 137 and 187 HB. This moderate hardness balances strength and ductility, making it easy to machine and form into pressure vessel components.
Can SA515 Grade 70 be used for cryogenic applications?
No, it is not suitable for cryogenic applications (temperatures below -29°C). For cryogenic services, SA516 Grade 70 (with lower carbon content) or other low-temperature steels are preferred to avoid brittle fracture.
What is the difference between SA515 Grade 70 and SA516 Grade 70?
SA515 is for moderate-temperature pressure vessels, while SA516 is for low-temperature service. SA516 has stricter toughness requirements (Charpy V-notch test) and lower carbon content, suitable for colder environments than SA515.
What is the elongation requirement of SA515 Grade 70?
SA515 Grade 70 requires a minimum elongation of 21% in a 50 mm gauge length. This high elongation indicates good ductility, allowing the material to deform without breaking under stress, critical for pressure vessel safety.
How to inspect SA515 Grade 70 plates for defects?
Common inspection methods include visual inspection (VI), ultrasonic testing (UT) for internal defects, magnetic particle testing (MT) or liquid penetrant testing (PT) for surface defects, ensuring compliance with ASME quality standards.
What is the density of SA515 Grade 70?
The density of SA515 Grade 70 is approximately 7.85 g/cm³ (0.283 lb/in³), the same as standard carbon steel. This value is used for weight calculation in pressure vessel design and manufacturing.
Can SA515 Grade 70 be machined easily?
Yes, SA515 Grade 70 is easy to machine. Its moderate hardness and good ductility allow for turning, milling, drilling, and other machining operations with standard tools, reducing production time and costs.
What is the melting point of SA515 Grade 70?
The melting point range of SA515 Grade 70 is 1425-1538°C (2597-2800°F), similar to other carbon steels. This high melting point ensures it can withstand high-temperature environments in boiler and pressure vessel applications.
What is the corrosion resistance of SA515 Grade 70?
It has basic corrosion resistance in mild environments but is not resistant to strong acids, alkalis, or saltwater. For corrosive services, it requires protective coatings (e.g., paint, galvanizing) or liners to extend service life.