In the United States, Occupational Safety and Health Administration regulations recommend following American Society of Mechanical Engineers Standard A13.1-2015 - Scheme for the Identification of Piping Systems.
The standard states that labels should be placed where easily viewed by a person standing near the pipe at any of the following points:
* Valves and flanges.
* Approximately every  to  on straight sections.
* A pipe passes through a wall or floor.
* Any pipe direction changes, such bends or junctions.