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How To: Understand Data Tags

Every pressure vessel manufactured by Wessels Company is equipped with a metal data tag affixed to its front side, positioned below the smart bracket system. This data tag serves as a quick reference for essential vessel information.

All vessels that adhere to the ASME code have a corresponding U stamp on the tag. You can learn more about the ASME code and Wessels’s certification here: Wessels and ASME Specification | Wessels Company (

Each vessel that adheres to the ASME code is also given a specific National Board number, which is the manufacturing organization’s sequential identifier for a specific pressure-retaining item so it can be tracked. The number circled is either a five- or six-digit number, found in the upper right corner of the data tag. Maintenance engineers can use the National Board number as a reference for technical support or warranty information.

Crucial operational parameters such as maximum and minimum working pressures and temperatures are prominently featured on the tag. These values are denoted as Maximum Allowable Working Pressure (MAWP) and Minimum Design Metal Temperature (MDMT), respectively. For instance, the specified MAWP for this vessel is 200 pounds per square inch (psi), accompanied by a maximum working temperature of 240°F.

Additionally, the tag includes the manufacturing year, affirming its origin in the United States. H.D. denotes Head Dimension, indicating the size of the vessel’s top, while SH signifies the shell thickness or steel gauge employed in its construction.

In the lower left corner of the tag you can find the CRN (Canadian Registration Number), a mandatory identifier for vessels intended for installation and registration within Canada. Meanwhile, the tank type is often delineated on the lower right side; for example, this particular vessel is identified as a 35-gallon expansion tank.

The name of the manufacturer can also be found on the tag, and in this case, the manufacturer is Wessels Company. For more information about data tags, you can call our warehouse at 317-888-9800 or watch this short video.