Pipe sizes can be confusing compared to "tube".
For exact OD, ID and Wall download our Pipe Size Chart (PDF).
Welded vs. Seamless Pipe. Welded pipe has the "flash" or seam removed from the outside diameter and generally has little or no evidence of a weld. Seamless pipe can withstand greater pressures and is commonly used where a perfectly smooth surface is required on the inside of the pipe for transporting of fluids and materials.