ASTM A516 Pressure Vessel Plate Grades Explained

When you're specifying carbon steel plate for a pressure vessel or boiler, ASTM A516 is likely the first standard that comes to mind. It's the go-to specification for moderate- and lower-temperature services where notch toughness matters. But choosing the right grade isn't just about picking the highest number—it's about matching the plate's mechanical properties to your design temperature, thickness, and fabrication method.

This guide walks through the four A516 grades, what sets them apart, and how to make a practical selection without over-specifying.

What ASTM A516 Covers

ASTM A516/A516M covers carbon steel plates intended primarily for welded pressure vessels and boilers. The standard is split into four grades—55, 60, 65, and 70—based on minimum tensile strength. The higher the grade number, the stronger the plate.

The specification is commonly used for service temperatures down to about -20°F (-29°C) when impact testing is performed. Above that, it's a workhorse material for ambient and elevated temperature applications up to roughly 1000°F (538°C), though creep becomes a factor well before that.

All grades are killed steel, which means they're deoxidized with silicon or aluminum. That's a key difference from some other carbon steel plates—it gives better uniformity and improves notch toughness, which is why A516 is preferred for low-temperature service.

Grade-by-Grade Breakdown

Here's the short version of what each grade delivers:

• Grade 55 – Minimum tensile 55 ksi (380 MPa). Lowest strength, best formability. Often used for thinner sections where welding and cold forming dominate.
• Grade 60 – Minimum tensile 60 ksi (415 MPa). The most common general-purpose grade. Balances strength and weldability for a wide range of vessel shells and heads.
• Grade 65 – Minimum tensile 65 ksi (450 MPa). A step up for thicker walls or higher design pressures, but still very weldable.
• Grade 70 – Minimum tensile 70 ksi (485 MPa). The highest strength in the A516 family. Used when you need to minimize plate thickness or where design pressure is high.

Don't assume Grade 70 is always the right choice. It requires more care in welding and forming, and it's not always available in the same thickness range as lower grades. Many fabricators prefer Grade 60 for routine work because it's forgiving in the shop.

Chemical Composition Limits

The standard sets maximums for key elements, but the exact values depend on the grade and the plate thickness. For example, carbon is capped at 0.26% for Grade 70, but Grade 55 allows up to 0.24% in plates 1 inch and under. Manganese limits range from 0.60–1.20% depending on grade and thickness.

Phosphorus and sulfur are both limited to 0.035% max. These are typical for carbon steel, but if you're doing heavy welding, you may want to specify a lower sulfur content via supplementary requirements. Silicon is in the 0.15–0.40% range, which helps with deoxidation.

One thing to watch: the standard has a table that ties carbon and manganese limits to thickness. For plates over 2 inches thick, the carbon max drops, and manganese can increase slightly. Always check the current edition of ASTM A516/A516M for the exact table—don't rely on memory or old data.

Mechanical Properties and Testing

Each grade has a specified minimum yield strength and tensile range. For example, Grade 60 has a minimum yield of 32 ksi (220 MPa) and a tensile range of 60–80 ksi (415–550 MPa). Grade 70 goes to 38 ksi (260 MPa) yield and 70–90 ksi (485–620 MPa) tensile.

Elongation requirements also vary by thickness. Thinner plates typically require higher elongation—for instance, 23% in 8 inches for Grade 60, but 21% for Grade 70. These are minimums; actual values are usually higher.

If you're designing for low-temperature service, you'll need to specify impact testing. ASTM A516 doesn't automatically include Charpy V-notch (CVN) testing unless you call it out. The standard references ASTM A20/A20M for the general requirements, and you can add Supplementary Requirement S5 for impact tests. That's where you'll define the test temperature and energy absorption values, which are often set by the applicable construction code like ASME BPVC Section VIII Div. 1.

Practical Selection Guide

When you're deciding between grades, think about three things: design pressure, plate thickness, and fabrication method.

1. Design pressure – Higher pressure means higher hoop stress, so you might need a higher grade to keep thickness down. But don't jump to Grade 70 if Grade 65 will do—check your allowable stress table first.
2. Plate thickness – Thicker plates are harder to form and weld. A lower grade might allow you to use a thicker plate that's easier to handle, especially for dished heads.
3. Welding and forming – If you're doing extensive cold forming or welding, lower carbon content (Grades 55 or 60) reduces the risk of cracking. For thick sections, you'll also need to consider preheat and post-weld heat treatment.

Also, remember that A516 is not the same as A36 structural steel. A36 has no impact testing requirements and is not intended for pressure vessel service. Don't substitute one for the other.

Common Misconceptions

One myth is that Grade 70 is always better because it's stronger. That's not true if your design doesn't need the extra strength—you'll pay more per ton and may face longer lead times. Another is that A516 is only for low temperatures; it's actually fine for elevated temperature service up to about 1000°F, though you'll need to check creep properties above 700°F.

Some engineers also assume that all A516 plates are the same regardless of the mill. In practice, the heat treatment and quality vary. If you need guaranteed through-thickness properties, specify supplementary requirements like S3 (ultrasonic examination) or S6 (higher tensile testing) from A20. These add cost but can be worth it for critical service.

Closing Takeaway

The best A516 grade for your job is the one that meets your design requirements with the least cost and fabrication risk. Start with Grade 60 as your baseline, then move up or down based on thickness and pressure. Always verify the current edition of the standard for chemical and mechanical limits, and don't forget to specify impact testing if your service temperature is below 0°F. When in doubt, talk to your plate supplier early—they can tell you what's in stock and what's going to cost you extra.

A516 is a reliable, well-understood material. The key is not to over-specify. Match the grade to the service, and you'll keep your project on budget and on schedule.