What Do the Numbers Stamped on a Compressed Gas Cylinder Mean?

The numbers stamped on a compressed gas cylinder give you a lot of useful information. Typical stamps look something like this:

DOT3AA-2265

12345

4-99

3-09

2-19

The first line is the DOT Specification (DOT3AA). That tells you it is a seamless alloy steel cylinder. Other common DOT specifications include:

The number after the dash gives you the maximum service pressure (2265 psig). Common standard DOT service pressures are:

Higher pressures are also available up to 10,000 psig but are less common. Different DOT specifications are also common as shown in the first table.

The longer number series is the cylinder’s serial number which uniquely identifies it to the manufacturer and gas supplier.

The last series of numbers tell you the month and year the cylinder was hydrostatically tested by the manufacturer (April of 1999, March of 2009, and February of 1019). A cylinder cannot be refilled by the manufacturer if it is out of test date, but the cylinder can be transported, and the contents used even if it is out of its test date. The most common test intervals are every 3, 5, 10, or 12 years. A star after the date indicates a 10 year frequency. (Note, however, that not every 10 year cylinder is always so marked.)

For more information on this and many other safety and operational topics concerning compressed gas cylinders you may want to consider the University of Wisconsin one day virtual course Compressed Gases: Safe Installations and Safe Operations given on January 27, 2021. For more information see https://epd.wisc.edu/courses/compressed-gases-safe-installations-and-safe-operations/ .