Introduction: Why A537 vs A516 Matters for Pressure Vessel Design?
Specifying the wrong pressure vessel steel plate can lead to catastrophic wall failure, cost overruns of 
15–30%, and project delays that cascade through your entire supply chain. When engineers and procurement teams face the choice between ASTM A537 Class 2 and ASTM A516 Grade 70, the decision must be driven by engineering requirements - not by price alone or by what happens to be in stock.
ASTM A516 Grade 70 is the global benchmark carbon steel for welded pressure vessels - cost-effective, versatile, and proven in tens of thousands of installations. ASTM A537 Class 2 is the high-performance alternative - quenched and tempered to deliver 60% higher yield strength, engineered for high-pressure, low-temperature, and weight-optimized designs.
Are you unsure which grade fits your vessel design? Contact GNEE Steel for a free material selection consultation - our engineers will review your design pressure, temperature, and code requirements and recommend the most cost-effective compliant grade. Request a material selection consultation →
A537 vs A516 Quick Reference Comparison Table
| Property | ASTM A516 Grade 70 | ASTM A537 Class 2 |
|---|---|---|
| Standard | ASME SA-516/SA-516M (2021) | ASME SA-537/SA-537M (2021) |
| Steel Type | Carbon Steel | Carbon-Manganese-Silicon Steel |
| Heat Treatment | As-rolled or Normalized | Quenched & Tempered |
| Yield Strength (≤40 mm, MPa min) | 260 | 415 |
| Tensile Strength (≤65 mm, MPa) | 485–620 | 550–690 |
| Elongation (50 mm gauge, % min) | 21 | 22 |
| Typical Service Temp | Above −29°C (−20°F) | Down to −45°C (−49°F) |
| Weldability | Excellent - forgiving | Good - requires preheat + PWHT |
| Cost Level | Baseline (lowest) | +$100–180/ton (Q&T premium) |
| Best For | Standard tanks, boilers, general vessels | LPG spheres, high-pressure reactors, offshore |
What Is ASTM A516 Grade 70 Pressure Vessel Plate?
ASTM A516 Grade 70 is governed by ASME SA-516/SA-516M (2021 edition), titled Pressure Vessel Plates, Carbon Steel, for Moderate- and Lower-Temperature Service. It is a killed carbon steel plate designed for fusion-welded pressure vessels where improved notch toughness is required.
The standard defines four strength grades - 55, 60, 65, and 70 - where the number indicates the minimum tensile strength in kilopounds per square inch (ksi). Grade 70, with a tensile range of 70–90 ksi (485–620 MPa), is the most widely specified and represents the highest strength in the A516 series.
Key characteristics
Heat treatment
Supplied as-rolled for thinner plates, or normalized (900–950°C) for thicker plates to refine grain structure and improve toughness
Weldability
Excellent - compatible with standard low-hydrogen electrodes (AWS E7018), minimal preheat requirements
Availability
Readily available in thicknesses from 6 mm to 250 mm from multiple Chinese mills
Typical applications
Storage tanks (API 650/620), boiler drums, heat exchanger shells and tubesheets, air receivers, general-purpose pressure vessels
What Is ASTM A537 Class 2 Carbon-Mn-Si Steel Plate?
ASTM A537 is governed by ASME SA-537/SA-537M (2021 edition), titled Pressure Vessel Plates, Heat-Treated, Carbon-Manganese-Silicon Steel. Unlike A516, which is a carbon steel, A537 is a carbon-manganese-silicon steel strengthened through mandatory heat treatment.
The standard defines three classes:
| Class | Heat Treatment | Tempering Temp | Yield (≤40 mm) | Tensile Strength |
|---|---|---|---|---|
| Class 1 | Normalized | - | 345 MPa (50 ksi) | 485–620 MPa (70–90 ksi) |
| Class 2 | Quenched & Tempered | ≥595°C (1100°F) | 415 MPa (60 ksi) | 550–690 MPa (80–100 ksi) |
| Class 3 | Quenched & Tempered | ≥620°C (1150°F) | 380 MPa (55 ksi) | 515–655 MPa (75–95 ksi) |
This article focuses on A537 Class 2 - the most commonly specified high-strength class for demanding pressure vessel applications.
A516 Gr70 and A537 Cl2 Chemical Composition Comparison
Both grades share a carbon-manganese-silicon base, but the differences in composition limits - combined with fundamentally different heat treatment routes - drive their performance divergence.
| Element | A516 Grade 70 (%) | A537 Class 2 (%) |
|---|---|---|
| Carbon (C) | 0.27 (≤12.5 mm) / 0.28 (>12.5 mm) | 0.24 |
| Silicon (Si) | 0.15–0.40 | 0.15–0.30 |
| Manganese (Mn) | 0.85–1.20 | 0.70–1.60 (by thickness) |
| Phosphorus (P) | 0.035 max | 0.030 max |
| Sulfur (S) | 0.035 max | 0.030 max |
| Copper (Cu, if specified) | 0.20 | 0.35 |
| Nickel (Ni, if specified) | 0.25 | 0.50 |
A516 vs A537 Mechanical Properties by Thickness
| Property | A516 Grade 70 | A537 Class 2 |
|---|---|---|
| Yield Strength (≤40 mm, MPa min) | 260 | 415 |
| Yield Strength (>40–65 mm, MPa min) | 260 | 380 |
| Yield Strength (>65–100 mm, MPa min) | 260 | 345 |
| Tensile Strength (≤65 mm, MPa) | 485–620 | 550–690 |
| Tensile Strength (>65–100 mm, MPa) | 485–620 | 515–655 |
| Elongation (50 mm gauge, % min) | 21 | 22 |
| Impact Toughness | Good (per purchaser spec) | Superior (CVN at −45°C, min 27J) |
A537 Cl2 vs A516 Gr70 Steel Plate Heat Treatment: Q&T vs Normalized
Heat treatment is the single most important factor distinguishing A537 from A516. The same carbon-manganese-silicon chemistry, processed differently, produces dramatically different mechanical properties.
A516 Grade 70: As-Rolled or Normalized
- As-rolled: Supplied directly after hot rolling. Suitable for thinner plates with moderate toughness requirements.
- Normalized (900–950°C): Heated above the upper critical temperature (Ac3) and air-cooled. This refines the ferrite-pearlite grain structure, improving toughness and uniformity. Typically applied to thicker plates per ASTM A20 supplementary requirement S4.
The normalized microstructure of A516 Grade 70 is a fine-grained ferrite-pearlite - strong, tough, and highly weldable, but limited in yield strength to 260 MPa.
A537 Class 2: Quenched and Tempered
- Austenitizing (870–900°C): Heated above Ac3 to fully transform to austenite.
- Quenching (water): Rapid cooling produces martensite or bainite - hard, strong, but brittle.
- Tempering (≥595°C / 1100°F): Reheating tempers the martensite, trading some hardness for improved toughness and ductility. The result is a tempered martensite/bainite microstructure with high yield strength (415 MPa) and excellent low-temperature toughness.
Key insight: Normalizing gives A516 moderate strength and good toughness. Quenching and tempering give A537 Class 2 substantially higher strength and superior impact resistance - at the cost of more complex processing, stricter welding requirements, and higher mill cost.
A537 Cl2 and A516 Gr70 Pressure Vessel Steel Plate Applications
A516 Grade 70
- Storage tanks (API 650 / API 620) for water, diesel, chemicals, and crude oil
- Boiler drums and steam generators (moderate pressure, ≤450°C service)
- Heat exchanger shells and tubesheets in refineries and petrochemical plants
- Air receivers and accumulators for compressed gas systems
- General-purpose pressure vessels where cost-effectiveness and weldability are primary
A537 Class 2
- LPG and propane storage spheres - high yield enables thinner walls for large-diameter spheres, reducing steel tonnage and foundation load
- High-pressure reactors and separators in oil refineries and petrochemical plants
- Offshore platform pressure vessels - weight savings are critical for offshore structural load limits
- Low-temperature service vessels - superior Q&T impact toughness at −45°C and below
- Mobile pressure vessels and gas bullet tanks - weight reduction directly improves payload efficiency
- NACE MR0175 / ISO 15156 sour service vessels - A537 Cl2's lower P/S limits support HIC resistance
A537 vs A516 Selection Guide: 5 Key Decision Factors
Choosing between A516 Grade 70 and A537 Class 2 comes down to five engineering factors:
1. Design Pressure
- Low to moderate pressure (standard wall thickness acceptable) → A516 Grade 70 - more economical and readily available
- Medium to high pressure (requiring reduced wall thickness or weight optimization) → A537 Class 2 - 60% higher yield allows thinner design
2. Operating Temperature
- Moderate temperature (above −29°C / −20°F) → A516 Grade 70 - sufficient toughness at lower cost
- Low-temperature service (below −29°C, down to −45°C) → A537 Class 2 - superior Q&T impact toughness engineered for cryogenic-adjacent service
3. Weight and Space Constraints
- No weight restriction (stationary vessels, ground-level tanks) → A516 Grade 70
- Weight-critical (spheres, offshore, mobile, transport) → A537 Class 2 - approximately 30% weight reduction
4. Fabrication Complexity and Budget
- Standard fabrication, budget-sensitive → A516 Grade 70 - easier welding, no mandatory PWHT, lower consumable costs
- Controlled fabrication, performance-critical → A537 Class 2 - requires preheat and PWHT but delivers superior mechanical performance
5. Code Compliance and Standard Requirements
- ASME BPVC Section VIII Div. 1 - standard construction → Both grades accepted; A516 Gr70 is the default for moderate service
- API 620 / API 650 - storage tanks → A516 Gr70 is the primary specified grade; A537 Cl2 may be specified for higher-pressure spheres
- NACE MR0175 / ISO 15156 - sour service → A537 Cl2 preferred due to lower P/S limits and mandatory impact testing; A516 Gr70 acceptable with S ≤ 0.003% and HIC testing per NACE TM0284
- ASME IX P-Number → Both grades are P-No. 1 (Group 1 for A516, Group 2 for A537); WPS requalification may be required when switching between them
Decision summary:
| If your priority is... | Choose... |
|---|---|
| Lowest cost, standard service | A516 Grade 70 |
| Highest strength, thinnest walls | A537 Class 2 |
| Low-temperature toughness | A537 Class 2 |
| Easiest fabrication, field welding | A516 Grade 70 |
| Sour service (HIC resistance) | A537 Class 2 (or A516 with S ≤ 0.003%) |
| Offshore / weight-critical | A537 Class 2 |
A516 Gr70 / A537 Cl2 Pressure Vessel Steel Plates Specifications
| Specification | A516 Grade 70 | A537 Class 2 |
|---|---|---|
| Standard | ASME SA-516/SA-516M (2021) | ASME SA-537/SA-537M (2021) |
| Thickness Range | 6–250 mm | 6–200 mm |
| Width Range | 1,500–3,500 mm | 1,500–3,500 mm |
| Length Range | 3,000–12,000 mm | 3,000–12,000 mm |
| Surface Finish | Shot blasted (Sa 2.5) / Pickled / As-rolled | Shot blasted (Sa 2.5) / Pickled |
| Heat Treatment | As-rolled or Normalized | Quenched & Tempered |
| Ultrasonic Testing | ASTM A435/A578 | |
| HIC Testing | NACE TM0284 (if specified) | |
| Certification | EN 10204 3.1 / 3.2 | |
| Third-Party Inspection | SGS / BV / DNV / TÜV | |
| Packaging | Sea-worthy wooden pallets / steel frame | |
| Delivery Condition | Cut to size, beveled, or pre-machined | |
GNEE Steel supplies both A516 Grade 70 and A537 Class 2 pressure vessel plates with full traceability and quality assurance:
- Quality certification: ISO 9001 certified, EN 10204 3.1/3.2 MTC on every order, NACE TM0284 HIC testing available on request
- Third-party inspection: SGS, BV, DNV, TÜV all accepted on every order
- Value-added services: Cutting to size, beveling, UT testing, shot blasting, painting, custom packaging, and third-party inspection coordination
Learn more about GNEE Steel qualifications →
FAQ
1. Is A537 stronger than A516?
Yes. A537 Class 2 has significantly higher yield strength (415 MPa vs. 260 MPa for ≤40 mm thickness) and a higher tensile strength range (550–690 MPa vs. 485–620 MPa). Both grades have similar elongation values (22% vs. 21% in 50 mm gauge), meaning A537 maintains good ductility despite its higher strength.
2. Can A516 Grade 70 substitute A537 Class 2?
No - not directly. The 60% gap in yield strength means substituting A516 Gr70 for A537 Cl2 would require significantly thicker plates, increasing vessel weight, welding volume, and overall cost. Additionally, if the design specifies A537 Class 2 for low-temperature service (−45°C), A516 Gr70 may not meet the required impact toughness without supplementary impact testing. Any substitution must be approved by the vessel's design engineer and verified against the applicable code (ASME BPVC, EN 13445, etc.). Under ASME IX, both grades are P-No. 1 but in different groups, so WPS requalification may be required.
3. What is A537 Class 2 equivalent to?
There is no exact equivalent. The closest EN standard grade is P460NH (EN 10028-3), and the closest JIS grade is SPV490 (JIS G3115). However, composition, heat treatment, and impact requirements differ across standards. For ASME code compliance, SA-537 Cl2 is the definitive specification.
Whether you need cost-effective A516 Grade 70 for standard vessels or high-strength A537 Class 2 for demanding applications, GNEE Steel delivers certified plates with EN 10204 3.1/3.2 MTC, third-party inspection by SGS/BV/DNV/TÜV, NACE TM0284 HIC testing on request, and fast global shipping to 50+ countries. Contact GNEE Steel today for a quotation →
