49 C.F.R. § 180.403
In addition to the definitions contained in §§ 171.8 , 178.320(a) and 178.345-1 of this subchapter, the following definitions apply to this subpart:
Corroded or abraded means any visible reduction in the material thickness of the cargo tank wall or valve due to pitting, flaking, gouging, or chemical reaction to the material surface that effects the safety or serviceability of the cargo tank. The term does not include cosmetic or minor surface degradation that does not effect the safety or serviceability of the cargo tank
Corrosive to the tank or valve means that the lading has been shown through experience or test data to reduce the thickness of the material of construction of the tank wall or valve.
Delivery hose assembly means a liquid delivery hose and its attached couplings.
Modification means any change to the original design and construction of a cargo tank or a cargo tank motor vehicle that affects its structural integrity or lading retention capability including changes to equipment certified as part of an emergency discharge control system required by § 173.315(n)(2) of this subchapter. Any modification that involves welding on the cargo tank wall must also meet all requirements for "Repair" as defined in this section. Excluded from this category are the following:
Owner means the person who owns a cargo tank motor vehicle used for the transportation of hazardous materials, or that person's authorized agent.
Piping system means any component of a cargo tank delivery system, other than a delivery hose assembly, that contains product during loading or unloading.
Rebarrelling means replacing more than 50 percent of the combined shell and head material of a cargo tank.
Repair means any welding on a cargo tank wall done to return a cargo tank or a cargo tank motor vehicle to its original design and construction specification, or to a condition prescribed for a later equivalent specification in effect at the time of the repair. Excluded from this category are the following:
Replacement of a barrel means to replace the existing tank on a motor vehicle chassis with an unused (new) tank. For the definition of tank, see § 178.320 , § 178.345 , or § 178.338-1 of this subchapter, as applicable.
Stretching means any change in length, width or diameter of the cargo tank, or any change to a cargo tank motor vehicle's undercarriage that may affect the cargo tank's structural integrity.
49 C.F.R. §180.403