OSHA has no requirements for the interval at which to apply pipe labels. However, employers may wish to check with state and local authorities to see if there are any state regulations that would apply. The local fire marshal may be able to supply information on both state and local regulations.
If no requirements apply, employers may wish to use the standard interval recommended by the American Society of Mechanical Engineers (ASME) in ASME Standard A13.1-2020, Scheme for the Identification of Piping Systems. This standard simply calls for intervals “sufficient for identification.” The standard adds that markings should be placed where pipes bend, divide, or go through surfaces. Also, markings are recommended near flanges/valves.