Specification Basis of ASTM A515 Grade 70 Plate
ASTM A515 Grade 70 is a carbon-silicon steel plate intended for pressure vessels and boilers in intermediate- and higher-temperature service. The specification covers chemical composition, heat treatment, tensile properties and permissible variations of the product, and ASME SA515 applies the same requirements within the boiler and pressure vessel code. Grade 70 is the highest strength level of the A515 series and is normally ordered for boiler drums, shells, heads and hot process vessels where the design stress is high but a low-alloy steel is not required.
Chemical Composition
| Element | Typical limit, % |
|---|---|
| Carbon (C) | 0.31 max, ladle |
| Manganese (Mn) | 1.20 max |
| Phosphorus (P) | 0.035 max |
| Sulfur (S) | 0.035 max |
| Silicon (Si) | 0.13 - 0.45 |
Ladle analysis and product analysis limits are not identical: the specification allows a small increase over the ladle range when the analysis is taken from the finished plate, so a certificate can show a carbon content slightly above the ladle limit and still comply. Silicon is the deliberate alloying addition. It acts as a deoxidizer and raises the strength of the ferrite, which is the practical difference between the A515 grades and the silicon-killed A516 plate used at lower service temperatures. The exact limits that apply depend on plate thickness and on the edition of the standard named in the purchase order.
Mechanical Properties
| Property | Requirement |
|---|---|
| Minimum yield strength | 260 MPa (38 ksi) |
| Tensile strength | 485 - 620 MPa (70 - 90 ksi) |
| Minimum elongation, 50 mm gauge | 21 % |
| Minimum elongation, 200 mm gauge | 17 % |
| Typical hardness | Under 200 HB |
| Density | 7.80 g/cm3, 0.284 lb per cubic inch |
| Modulus of elasticity | About 200 GPa |
Tensile properties are verified on test specimens taken in the direction of rolling and, for thicker plate, after the heat treatment that will be applied in production, so that the certificate represents the delivered condition. Impact testing is not part of the base requirement for this higher-temperature grade, and a low-temperature impact figure should not be expected on the certificate; where impact toughness is a design condition, an A516 grade ordered with impact testing is the correct choice. The nearest European reference is the pressure vessel grade EN 10028-2 P265GH, which is broadly comparable in strength but not identical in chemistry.
Thickness Range, Plate Forms and Processing
Thickness: 6 mm to 300 mm, selected to suit the design pressure and the rolling capability of the mill.
Width: 1500 mm to 4050 mm; length: 3000 mm to 15000 mm, with 6 m and 12 m the usual stock lengths.
Forms: plain hot rolled plate, cut-to-size rectangles, circle-cut blanks for heads, and plate formed into welded heads in custom sizes.
Processing: thermal and profile cutting, drilling, tapping, bevelling, miter cutting, coping and edge finishing.
Surface: plate is supplied hot rolled, with surface quality judged against the plate specification rather than against a decorative finish.
Heat Treatment, Surface Condition and Documentation
Grade 70 plate is supplied as-rolled, normalized, normalized and tempered, or quenched and tempered. Normalizing is the usual condition for boiler and pressure vessel work, because it refines the grain and produces a uniform ferrite-pearlite structure with consistent tensile results. When stress relieving is required after forming or welding, it is carried out below the lower critical temperature so that the normalized structure is retained.
Documentation normally consists of a mill test certificate to EN 10204 3.1, with 3.2 certification and inspection by an independent third party or classification society available when the purchaser or the end user requires an external witness of the tests. The certificate should state the heat number, the grade, the heat treatment, the chemical analysis and the tensile results so that the plate can be traced through fabrication and any later heat treatment.
Frequently Asked Questions
Q: What is the tensile strength of ASTM A515 Grade 70 plate?
The specified tensile range is 485 - 620 MPa, equivalent to 70 - 90 ksi, which is where the grade number comes from.
Q: What is the minimum yield strength?
260 MPa, equivalent to 38 ksi, with a minimum elongation of 21 % on a 50 mm gauge length and 17 % on a 200 mm gauge length.
Q: Is A515 Gr 70 impact tested at low temperature?
No. It is a higher-temperature carbon-silicon grade and low-temperature impact toughness is not part of its base requirement; a vessel needing that property is built from an A516 plate with impact testing.
Q: What is the difference between ASTM A515 Grade 70 and ASME SA515 Grade 70?
They carry the same requirements for composition, heat treatment and properties. The SA designation is the form used within the boiler and pressure vessel code.
Q: What thickness and sizes can be supplied?
Common supply covers 6 mm to 300 mm thick, 1500 mm to 4050 mm wide and 3000 mm to 15000 mm long, in plain, cut-to-size or circle-cut form.
Q: What condition and certification are standard?
Normalized plate with a mill test certificate to EN 10204 3.1 is the usual supply; 3.2 certification and third-party inspection are available when the project calls for them.
