Tube Specification & Overfill Rule

The three major types of cylinder (tube) specifications are DOT, UN and ASME. The most common DOT cylinders are of 3T and 3AAX specifications which are of 22 inch outside diameter and are used on a jumbo tube trailer. 3A and 3AA specifications are normally of 9-5/8 inches outside diameter which is used on a multi tube trailer. Following table shows tube specification and overfill rule for DOT tubes. Some gases like Helium and Nitrogen can be filled on both 3T and 3AAX tubes but 3T tubes are recommended because they are lighter in weight. Products like hydrogen, hydrogen mixtures and CNG can only be filled on a 3AAX tube. DOT 3AAX can be filled with CNG only if the tube is stamped CNG at the time of manufacture. 3T tubes are recommended for most of the gases other than hydrogen or hydrogen mixture. DOT tubes can always be replaced with its UN tube equivalent. Please contact us for more details.