CYLINDER REFURBISHING   DOT mandates that cylinders be hydrostatically recertified every five years. At a minimum, this requires the cylinder to be tested and certified that it is safe for continued use. NRI is a DOT-approved hydrostatic test facility and offers these and other cylinder refurbishing services: Internal cleaning Dip tube replacement Internal drying Removal of old paint Valve replacement Application of industry color standard paint  NRI is the first company in the US offering this service to contractors and end users through distributors. These services are available for refrigerant and recovery cylinders in the most frequently used sizes.