What Is ASME SA 516 GR 70 Steel Plate?
ASME SA 516 GR 70 is a carbon steel plate specification for welded pressure vessels that operate at moderate and low temperatures. It is technically identical to ASTM A 516 GR 70, and both documents describe a killed steel with a fine austenite grain size produced under ASTM A20/A20M practice. The grade combines a tensile strength range of 485–620 MPa with a minimum yield strength of 260 MPa and a minimum elongation of 17% in a 200 mm gauge length.
Because phosphorus and sulfur are each capped at 0.025%, SA 516 GR 70 is the usual choice where hydrogen induced cracking (HIC) resistance has to be demonstrated by testing to NACE TM0284 for sour gas service. Thickness also matters: plates up to 40 mm are commonly supplied as-rolled, while heavier plates are normalized, and a notch toughness test ordered on a plate of 40 mm or less also calls for the normalizing treatment.
What Is ASME SA 285 GR C Steel Plate?
ASME SA 285 GR C is a lower-strength carbon steel plate intended for low and intermediate pressure vessels and for general fabrication. The SA 285 specification covers three strength levels, GR A, GR B and GR C, and GR C is the strongest of the three, with a tensile strength range of 380–515 MPa and a minimum yield strength of 205 MPa.
A tensile range of 310–450 MPa is sometimes quoted for GR C in second-hand tables, but that range actually belongs to SA 285 GR A, so grade identity should always be confirmed against the mill certificate rather than a comparison chart. The specification sets no notched impact requirement and no hardness limit, which is why SA 285 GR C is not intended for low-temperature or sour service.
Chemical Composition Comparison
| Element | ASME SA 516 GR 70 | ASME SA 285 GR C |
|---|---|---|
| Carbon (C) | ≤0.27% up to 12.5 mm; ≤0.28% for 12.5–50 mm; ≤0.30% for 50–100 mm; ≤0.31% above 100 mm | ≤0.28% |
| Manganese (Mn) | 0.85–1.20% | ≤0.90% |
| Phosphorus (P) | ≤0.025% | ≤0.035% |
| Sulfur (S) | ≤0.025% | ≤0.035% |
| Silicon (Si) | 0.15–0.40% | 0.10–0.35% |
| Aluminium (Al) | ≥0.02%, killed steel with fine grain practice | Not specified |
The chemistry explains most of the performance gap. SA 516 GR 70 is a fully killed, aluminium-treated steel that must satisfy fine austenite grain size requirements, whereas SA 285 GR C carries no grain size or aluminium requirement at all. SA 516 GR 70 also halves the residual element allowances, and it is exactly that tighter sulfur limit which makes HIC testing meaningful in wet sour service. Note that the carbon limit of SA 516 GR 70 is graded by thickness; the single figure of 0.27–0.31% that circulates in some comparisons is a misreading of the thickness table rather than a fixed requirement.
Mechanical Properties Comparison
| Property | ASME SA 516 GR 70 | ASME SA 285 GR C |
|---|---|---|
| Tensile strength | 485–620 MPa | 380–515 MPa |
| Yield strength, minimum | 260 MPa | 205 MPa |
| Elongation, minimum (200 mm) | 17% | 23% |
| Charpy V-notch impact | 27 J at −46 °C when specified | Not required by the specification |
| Hardness | ≤200 HBW | Not specified |
| Typical delivery condition | As-rolled up to 40 mm, normalized above 40 mm | As-rolled |
SA 516 GR 70 is roughly a third stronger in tension and about 27% higher in specified yield strength than SA 285 GR C, while still guaranteeing 27 J of absorbed energy at −46 °C whenever impact testing is ordered. SA 285 GR C answers with higher ductility and a lower price per tonne, which is why it is normally reserved for tanks and lightly loaded vessels.
Applications and Selection Guidance
SA 516 GR 70: high-pressure vessels, oil and gas separators, wet sour gas equipment that must pass HIC testing, petrochemical reactors and heat exchangers, and boiler components operating at pressures up to about 500 bar and temperatures up to about 450 °C.
SA 285 GR C: atmospheric and low-pressure storage tanks, water and non-corrosive fluid tanks, simple industrial vessels, and general fabricated structures where ductility and cost matter more than strength.
A simple selection rule: specify SA 516 GR 70 whenever design pressure, wall thickness or service temperature is demanding, or when sour service requires HIC testing; specify SA 285 GR C when the duty is mild, the fluid is benign and lowest installed cost is the priority. Both grades weld readily with conventional carbon steel consumables, but SA 516 GR 70 gives fabricators more margin for thick-section welding because of its lower carbon and sulfur levels.
Frequently Asked Questions
Q: Is ASME SA 516 GR 70 the same as ASTM A 516 GR 70?
The two documents are technically identical. ASME SA 516/SA 516M is the version adopted for ASME Boiler and Pressure Vessel Code construction, and either designation may legitimately appear on a mill certificate or inspection report.
Q: What is the maximum carbon content of SA 516 GR 70?
It depends on thickness: 0.27% up to 12.5 mm, 0.28% for 12.5–50 mm, 0.30% for 50–100 mm and 0.31% above 100 mm. Reporting a single figure of 0.27–0.31% as the grade limit is incorrect.
Q: Why is 310–450 MPa often quoted for SA 285 GR C?
That tensile range belongs to SA 285 GR A. Grade C of the same specification is specified at 380–515 MPa, so a drawing that quotes 310–450 MPa for GR C should be checked against the applicable edition of the standard.
Q: Can SA 285 GR C be used in sour gas service?
No. It carries no low-temperature impact requirement and permits higher sulfur and phosphorus than SA 516 GR 70, so it is not the normal choice where HIC testing to NACE TM0284 is mandatory.
Q: Why does SA 516 GR 70 have a minimum aluminium content?
The aluminium addition (0.02% minimum) is part of the fine grain practice that refines the ferrite grain structure, and fine grain size is what delivers the 27 J impact toughness at −46 °C.
Q: Can the two grades be welded to each other?
Yes. Both are carbon steels of similar carbon equivalent, and they are routinely joined with standard low-hydrogen consumables; the joint should simply be qualified against the lower-strength grade in the design calculation.
