Mild steel plate for storage tanks is most often a choice between ASTM A36 and ASTM A516 Grade 70. This guide compares the two grades on notch toughness, weldability and pressure vessel code compliance, with selection guidance for atmospheric and low-pressure storage tanks.
Carbon steel storage tanks (for water, fuel, chemicals, oil and other liquids) are built from welded plate, and the grade choice between ASTM A36 and ASTM A516 Grade 70 is one of the most consequential specification decisions. A36 is a structural plate grade widely used for atmospheric tanks and general fabrication. A516 Grade 70 is a pressure vessel plate grade with guaranteed notch toughness, mandatory for low-temperature service and for tanks designed to ASME BPVC Section VIII.
Strength and Notch Toughness
ASTM A36 plate has minimum yield strength of 36,000 psi (250 MPa) and tensile strength of 58–80,000 psi (400–550 MPa). ASTM A516 Grade 70 plate has minimum yield strength of 38,000 psi (260 MPa) and tensile strength of 70–90,000 psi (485–620 MPa), slightly higher than A36, with mandatory Charpy V-notch impact testing at a specified temperature (typically -46 °C for the standard Class). The notch toughness is what differentiates A516 from A36 for low-temperature service, where brittle fracture is a risk if the plate lacks impact resistance.
When A36 Is the Right Specification
ASTM A36 plate is the right specification for atmospheric storage tanks (no internal pressure, or very low pressure) operating above about -10 °C, for water storage tanks, for fire water reservoirs, for chemical tanks with non-corrosive contents at ambient temperature, and for general welded plate fabrication that does not fall under ASME BPVC. A36 is widely stocked, readily available in thicknesses from 5 to 100 mm, and significantly cheaper than A516.
When A516 Grade 70 Is the Required Upgrade
ASTM A516 Grade 70 is the required specification for storage tanks designed to ASME BPVC Section VIII (pressure vessel code), for low-temperature service (below about -10 °C), for tanks storing hazardous or flammable liquids where brittle fracture is a safety concern, and for any tank where the customer or insurer specifies impact-tested plate. A516 is also the conservative choice for crude oil and hydrocarbon storage, LNG and LPG facilities, and for tank farms in cold-climate regions.
Plate Thickness, Welding and Code Compliance
Tank shell thickness is calculated from the API 650 (for atmospheric tanks) or ASME BPVC Section VIII (for pressure vessels) code, based on diameter, design pressure, joint efficiency and corrosion allowance. Allow 1.0–1.5 mm corrosion margin for carbon steel tanks with mildly aggressive contents. Use low-heat-input SMAW or GMAW with E7018 or E7016 electrodes for A36, or matching low-hydrogen electrodes for A516. All butt welds in pressure vessels require 100% radiographic or ultrasonic examination, while atmospheric tanks per API 650 allow spot radiography on critical joints.
What to Specify on the Tank Plate RFQ
State the standard (ASTM A36 or ASTM A516 Grade 70), the thickness, the plate size, the design code (API 650 or ASME BPVC Section VIII), the design temperature, the Charpy impact requirement (Class 1, 2, or 3 per A516, or A36 with supplementary Charpy if needed), and the test report per EN 10204 3.1. For low-temperature or pressure vessel service, default to A516 Grade 70; for ambient atmospheric tanks, A36 is acceptable and saves cost. Always confirm the mill supplies the actual Charpy values at the design temperature, not just the certificate reference.
Related Resources from Baobin Steel
- Steel sheet and plate catalog – A36, A516 and structural grades
- Structural steel overview – grades and standards
- Request a quote – send your tank design code and dimensions for plate pricing