SA516 Gr 70 and SA 285 Gr C are both carbon steel plates produced for pressure equipment, and both carry the SA prefix because they are used under the ASME Boiler and Pressure Vessel Code as well as their original ASTM specifications. The essential difference is strength: SA516 Gr 70, from ASTM A516/A516M, develops a much higher minimum yield and tensile strength than SA 285 Gr C from ASTM A285/A285M, so the two grades are used at different pressure ratings and different design temperatures. Selecting the wrong plate affects allowable stress, wall thickness and, in many jurisdictions, code compliance. This article sets out the composition, mechanical property and temperature limits of each grade, and explains when a normalized plate such as SA516 Gr 70N should be ordered instead of the as-rolled product.
What SA516 Gr 70 and SA 285 Gr C Are
SA516 Gr 70 is a killed, fine-grain treated carbon steel plate intended for moderate and lower temperature pressure vessel service. The Gr 70 designation refers to a minimum tensile strength of 70 ksi, roughly 485 MPa, and the grade is normally supplied in the as-rolled condition for thin plate, with normalizing applied when toughness in thicker sections or lower service temperatures has to be guaranteed. It is one of the most widely used vessel steels in petroleum refining, power generation, boiler drums and chemical processing, and it is available in thicknesses from about 5 mm to 200 mm with ultrasonic testing and Charpy impact testing available on request.
SA 285 Gr C belongs to a family of low and intermediate tensile strength carbon steel plates for pressure vessels. It is intended for service where a lower allowable stress is acceptable, typically for storage vessels, low pressure tanks, water and utility service and general welded equipment. ASTM A285 plates are made of carbon, manganese, phosphorus and sulfur with specified limits on each element, and Gr C is the highest strength level of the three grades in the specification, above Grades A and B. Because the strength level is lower, thicker walls are needed for the same design pressure compared with SA516 Gr 70.
Chemical Composition Compared
Both are plain carbon steels with deliberate limits on carbon, manganese and residuals. The tighter strength requirement of SA516 Gr 70 is supported by a higher manganese level together with killing and fine-grain treatment, while SA 285 Gr C keeps alloying simpler.
| Element (max %, heat analysis) | SA516 Gr 70 | SA 285 Gr C |
|---|---|---|
| Carbon (C) | 0.28 | 0.28 |
| Manganese (Mn) | 0.85-1.20 | 0.90 (for thickness over 20 mm) |
| Phosphorus (P) | 0.035 | 0.035 |
| Sulfur (S) | 0.035 | 0.035 |
| Silicon (Si) | 0.13-0.45 | not specified as a minimum |
| Deoxidation practice | fully killed, fine grain | killed or semi-killed |
Mechanical Properties Compared
The strength gap is the decisive difference between the two grades, and it directly controls the design allowable stress and therefore the required plate thickness of a vessel or drum.
| Property, plate up to 25 mm | SA516 Gr 70 | SA 285 Gr C |
|---|---|---|
| Tensile strength (MPa) | 485-620 | 380-515 |
| Yield strength, min (MPa) | 260 | 205 |
| Elongation, min (%) | 21 | 25 |
| Typical Charpy requirement | 20 J average at the agreed temperature when impact tested | impact testing not normally specified |
Normalizing, Impact Testing and ASME Temperature Limits
SA516 Gr 70 plate is supplied as-rolled in the common commercial condition, while the suffix N in SA516 Gr 70N means the plate has received an additional normalizing heat treatment. Normalizing refines the grain structure, removes rolling directionality and improves notch toughness, which is required by many specifications for thicker plate or for vessels operating at low temperature. Where the design calls for impact tested material, the order should state the test temperature, the minimum energy and the delivery condition, because as-rolled plate may not satisfy the same acceptance criteria as normalized plate of the same grade.
Under ASME BPVC Section II the permitted application of these steels depends on the construction code section rather than on the steel alone:
SA516 Gr 70 under ASME Section I: up to 850 °F (454 °C) for boiler construction.
SA516 Gr 70 under ASME Section III, Classes 2 and 3: up to 700 °F (371 °C) for nuclear components.
SA285 grades are restricted to lower design pressures and are not applied to the same high duty boiler and nuclear components.
Low temperature service below the impact test exemption curve requires impact tested plate with a documented Charpy energy value.
Which Grade Should Be Specified
SA516 Gr 70: boiler drums, refinery and petrochemical pressure vessels, heat exchangers, separators and any component where the allowable stress must be maximised to keep wall thickness down.
SA 285 Gr C: low pressure storage vessels, water and utility tanks, general welded fabrication and non-critical equipment where a lower allowable stress and a heavier wall are acceptable.
SA516 Gr 70N: thick plate, low temperature service or any specification that requires guaranteed Charpy impact energy.
Frequently Asked Questions
Q: What is the main difference between SA516 Gr 70 and SA 285 Gr C?
Strength. SA516 Gr 70 has a minimum yield of 260 MPa and a tensile range of 485-620 MPa, well above SA 285 Gr C at 205 MPa minimum yield and 380-515 MPa tensile, so it carries a higher allowable stress in pressure equipment.
Q: Are SA516 Gr 70 and SA 285 Gr C interchangeable?
Not directly. A lower strength plate can rarely be substituted where the design thickness was calculated on the higher allowable stress of SA516 Gr 70, and any substitution must be re-checked against the governing code.
Q: What does the SA prefix mean?
It identifies the ASTM specification as adopted by the ASME Boiler and Pressure Vessel Code, so SA516 Gr 70 and ASTM A516 Gr 70 describe the same material, as do SA 285 Gr C and ASTM A285 Grade C.
Q: What is the maximum service temperature of SA516 Gr 70?
Under ASME Section I it is limited to 850 °F (454 °C), and under Section III Classes 2 and 3 to 700 °F (371 °C). The applicable limit for a given vessel comes from the code section used for its design.
Q: What is the difference between SA516 Gr 70 and SA516 Gr 70N?
N denotes normalizing. As-rolled SA516 Gr 70 is the standard commercial condition, while SA516 Gr 70N is given an extra normalizing treatment for improved grain refinement and notch toughness.
Q: Which grade is better for low temperature service?
SA516 Gr 70 in an impact tested and normalized condition is the usual choice, because its fine-grain treatment and Charpy testing allow documented toughness at the design metal temperature.
Q: What is the equivalent Indian or European grade for SA516 Gr 70?
Equivalent pressure vessel grades are defined in national standards, and boiler quality carbon steel plate to a recognised pressure vessel specification is the usual route when a direct cross reference does not exist.
