Introduction: Why Pressure Vessel Steel Is Not Just Thicker A36
Buyers new to steel procurement sometimes assume that ASTM A516 and ASTM A36 are interchangeable if the thickness is the same. They are not. A36 is a structural steel with modest chemistry control and no mandatory impact testing. A516 is a pressure vessel quality steel with tightly controlled chemistry, mandatory notch toughness, and a testing regime designed to keep boilers, tanks, and pressure vessels from failing in service.
This guide compares A516 vs A36 for buyers who need to choose between them for tanks, pressure vessels, or structural supports near process equipment.
The Standards Behind the Grades
ASTM A36 / A36M covers carbon structural steel shapes, plates, and bars. It sets minimum mechanical properties and broad chemistry limits. It does not require impact testing, does not limit carbon equivalent tightly, and is not intended for pressure-retaining equipment.
ASTM A516 / A516M covers carbon steel plates for moderate- and lower-temperature service in pressure vessels. It is divided into grades by tensile strength:
- A516 Grade 55: 55–75 ksi tensile
- A516 Grade 60: 60–80 ksi tensile
- A516 Grade 65: 65–85 ksi tensile
- A516 Grade 70: 70–90 ksi tensile
The most commonly supplied grade for export is A516 Grade 70, often written simply as A516-70. It delivers higher strength than A36 and includes mandatory Charpy V-notch impact testing when ordered to Supplementary Requirement S5.
Chemical Composition Comparison
| Element | A36 (max %) | A516 Grade 70 (max %) |
|---|---|---|
| Carbon (C) | 0.29 | 0.27 (varies by thickness) |
| Manganese (Mn) | 0.80–1.20 | 0.85–1.20 |
| Phosphorus (P) | 0.04 | 0.025 |
| Sulfur (S) | 0.05 | 0.025 |
| Silicon (Si) | 0.15–0.40 | 0.15–0.40 |
A516 carries significantly lower phosphorus and sulfur limits. That matters because P and S promote brittle fracture and lamellar tearing, both unacceptable in welded pressure vessels. A36’s looser limits are acceptable for structural loads but not for pressure containment.
Mechanical Properties Comparison
| Property | A36 | A516 Grade 70 |
|---|---|---|
| Yield strength | ≥ 250 MPa (36 ksi) | ≥ 260 MPa (38 ksi) |
| Tensile strength | 400–550 MPa | 485–620 MPa |
| Elongation | ≥ 20% | ≥ 17% |
| Impact testing | Not required | Required (S5) for low-temp service |
The tensile strength gap is the practical difference. A516-70 delivers roughly 15–20% higher tensile strength than A36, which allows thinner vessel walls for the same design pressure and reduces weld metal volume.
Temperature Service Limits
A36 has no official low-temperature qualification in the standard. It is routinely used down to about −20°C in structural applications by engineering judgment, but the code does not guarantee toughness.
A516 is specifically designed for lower-temperature service. Grade 70 is qualified down to −20°F (−29°C) for normal thicknesses and can be ordered with impact tests at lower temperatures through supplementary requirements. This makes it the default choice for cryogenic and cold-climate storage tanks.
Weldability and Heat Treatment
Both grades weld with standard processes, but A516 pressure vessel work demands more control:
- Preheat: A516 thick sections generally require preheat to control hydrogen cracking. A36 often does not.
- Post-weld heat treatment (PWHT): required for most pressure vessels per ASME Section VIII. A36 structural work rarely needs PWHT.
- Consumables: A516 vessels typically require low-hydrogen electrodes and filler metal matched to the grade. A36 is more forgiving.
A516 plates are normally supplied in the as-rolled condition. Normalizing is available as Supplementary Requirement S1 and is often required for vessels in low-temperature or corrosive service because it improves toughness and homogeneity.
When to Specify A36
- Structural supports, platforms, and stairways around pressure equipment
- Brackets, base plates, and non-pressure retaining parts
- Projects governed by AISC or general structural codes
- Applications where low cost and easy weldability matter more than pressure integrity
When to Specify A516
- Pressure vessels, boilers, and process columns
- Storage tanks for liquids or gases under pressure
- Low-temperature or cryogenic equipment
- Any equipment designed to ASME Section VIII or similar pressure codes
- Welded tanks where brittle fracture must be prevented
International Equivalents
| Standard | Equivalent to A516 Grade 70 | Equivalent to A36 |
|---|---|---|
| EN 10025-2 | P355GH | S235JR |
| JIS | SPV355 | SS400 |
| GB | Q345R (pressure vessel) | Q235B |
Chinese mills commonly supply Q345R as the domestic equivalent of A516-70 and Q235B as the equivalent of A36. For code-stamped vessels, the substitute must be approved by the design authority and the inspecting agency.
Buyer Checklist for Pressure Vessel Plate
- Specify grade, thickness, and standard: “ASTM A516 Grade 70 plate, normalized per S1 if required.”
- Request impact test temperature and energy if the vessel will operate below −20°C.
- Require EN 10204 3.1 certificate with full chemistry, mechanical properties, and heat treatment records.
- Confirm ultrasonic testing (UT) for internal defects if thickness exceeds 25 mm.
- Define dimensional tolerances per ASTM A20.
- Arrange third-party inspection by an ASME-accredited or recognized body.
Frequently Asked Questions
1. Can I use A36 for a pressure vessel?
Only if the design code explicitly permits it. Most pressure vessel codes require pressure-retaining materials to meet specific standards with impact testing. A36 does not meet those requirements by default.
2. What is the main difference between A516 and A36?
A516 is pressure vessel quality steel with lower P/S limits and mandatory toughness testing. A36 is general structural steel with broader chemistry and no impact requirement.
3. Is A516 Grade 70 stronger than A36?
Yes. A516-70 has higher tensile strength (485–620 MPa vs 400–550 MPa) and slightly higher yield strength. The bigger advantage is its guaranteed toughness at lower temperatures.
4. Should A516 plate be normalized?
Normalizing improves toughness and homogeneity. It is required for many low-temperature vessels and thick sections. Order per Supplementary Requirement S1 if your design calls for it.
5. What certificate do I need for a code-stamped vessel?
You need an EN 10204 3.1 or 3.2 mill test certificate, impact test reports if required, and inspection by an authorized third party such as Lloyd’s, BV, DNV, or TUV.
Conclusion
A516 and A36 are not competitors; they serve different risk models. A36 is the economical choice for structural work where ductility and weldability matter. A516 is the safety-critical choice for pressure vessels where chemistry control, toughness, and traceability are mandatory. Specifying the wrong grade can invalidate a vessel certification and create liability that far exceeds the material cost.
Huaxia-Steel supplies ASTM A516 Grade 55/60/65/70 pressure vessel plate and ASTM A36 structural plate with EN 10204 3.1 certificates, normalized processing, and third-party inspection. Send us your vessel drawing and quantity for a same-week quotation.
