In the steel procurement world, confusing different grades of carbon steel can lead to disastrous consequences. One of the most common questions we hear from EPC contractors and fabrication buyers is: "What is the difference between ASTM A36 and ASME SA516 Grade 70?"
While both are widely used carbon steel plates, they belong to completely different engineering universes. A36 is the king of structural frames, whereas SA516 Gr 70 is the lifeblood of pressure vessels.
Here is a deep dive into their differences in application, chemical composition, mechanical properties, and sourcing costs.
The Fundamental Difference: Structural vs. Pressure Vessel
The easiest way to understand the difference is to look at their intended end-use.
- ASTM A36 (The Structural Workhorse): This is a general-purpose, low-carbon structural steel. It is designed for riveting, bolting, and welding in the construction of bridges, buildings, and general machinery. It is an "ASTM" standard, meaning its primary focus is on basic structural integrity.
- ASME SA516 Grade 70 (The Pressure Vessel Specialist): This is a premium-grade carbon steel specifically engineered for moderate to low-temperature pressure vessels. Because it holds highly pressurized gases or liquids, it is governed by the strict ASME (American Society of Mechanical Engineers) boiler and pressure vessel codes. Safety and fracture resistance are its top priorities.
SA516 Grade 70 VS A36 Chemical Composition and Mechanical Properties
|
Element |
ASTM A516 GR 70 (% by weight) |
ASTM A36 (% by weight) |
|---|---|---|
|
Carbon (C) |
0.27 max |
0.26 max |
|
Manganese (Mn) |
0.85–1.20 |
1.03 max (varies by thickness) |
|
Phosphorus (P) |
0.035 max |
0.040 max |
|
Sulfur (S) |
0.035 max |
0.050 max |
|
Silicon (Si) |
0.15–0.40 |
0.40 max |
|
Aluminum (Al) |
0.02 min (for killed steel) |
Not specified |
|
Iron (Fe) |
Balance |
Balance |
|
Property |
ASTM A516 GR 70 |
ASTM A36 |
|---|---|---|
|
Tensile Strength |
485–620 MPa (70–90 ksi) |
400–550 MPa (58–80 ksi) |
|
Yield Strength (min) |
260 MPa (38 ksi) |
250 MPa (36 ksi) |
|
Elongation (min, 200 mm) |
17% |
20% |
|
Elongation (min, 50 mm) |
21% |
23% |
|
Hardness (HB, typical) |
140–200 HB |
120–150 HB |
|
Impact Toughness (Charpy V-notch) |
Meets ASTM requirements at -46°C |
Not typically specified |
Can A36 Replace SA516 70?
From a procurement standpoint, A36 is cheaper and more readily available. This leads some buyers to wonder if they can substitute it. The answer is a hard NO for pressure applications.
If your engineering drawings specify ASME SA516 Gr 70 for an oil storage tank or a boiler, substituting it with A36 is a massive safety and compliance violation. A36 cannot withstand the internal pressure fluctuations and temperature extremes, risking catastrophic explosions.
Conversely, if you are building a simple structural steel frame, using SA516 Gr 70 instead of A36 would technically work (since it's stronger), but it would be a complete waste of your project budget.
Weldability and Fabrication
Both steels are weldable, but their applications influence welding considerations:
A36: Excellent weldability due to lower carbon content and fewer alloying elements. It's commonly welded using SMAW, GMAW, or GTAW with fillers like AWS A5.1 E7018. No preheating is typically needed for thinner sections.
A516 Gr 70: Also weldable, but its higher carbon and manganese content may require preheating (100-150°C) and post-weld heat treatment for thicker plates, especially in A516 GR 70 Material specification applications. Recommended fillers include E7018 or ER70S-6.
Key Difference: A36 is easier to weld for general structural work, while A516-70 carbon steel plate requires more care in pressure vessel fabrication due to its higher strength and potential for cracking in sour gas environments.
Source High-Quality SA516 Gr 70 and A36 with GNEE Steel
Whether you are fabricating massive pressure vessels for the petrochemical industry or erecting commercial buildings, choosing the right steel grade and a reliable supplier is crucial.
At GNEE Group, we maintain a massive inventory of both ASTM A36 structural plates and ASME SA516 Grade 70 boiler plates. For our SA516 materials, we provide comprehensive MTCs (EN 10204 3.1/3.2), including Ultrasonic Testing (UT) and Charpy V-Notch (CVN) impact test reports upon request.
