Pipe marking standards are provided by both the American Society of Mechanical Engineers (ASME) and the American National Standards Institute (ANSI) Code. Both organizations have published the same code and both have numbered it A13.1.
The 2007 edition of joint ANSI / ASME Standard A13.1 introduced a new color system for labeling pipe contents, based on six standard color combinations plus four user-defined colors. Previous versions used a four-color scheme. The colors used are based on the contents of the pipe; in general, the most hazardous feature of the contents should determine the colors used.
| Pipe Contents | Background Color | Text Color |
| Fire-quenching fluids | Red | White |
| Toxic and corrosive fluids | Orange | Black |
| Flammable fluids | Yellow | Black |
| Combustible fluids | Brown | White |
| Cooling, boiler feed, & other water | Green | White |
| Compressed air | Blue | White |
| User-defined | Purple | White |
| User-defined | White | Black |
| User-defined | Grey | White |
| User-defined | Black | White |
Pipe markers should be positioned so that they can be easily seen from the normal angle of approach. For instance, place the pipe marker below the centerline of the pipe if the pipe is overhead and above the centerline if the pipe is below eye level. Arrows should be used to indicate the direction of flow if necessary.
Pipe Markers are required at the following locations:
• Adjacent to all valves and flanges
• Adjacent to all changes of direction
• On both sides of wall or floor penetrations
• At regular intervals on straight runs
(50′ is the acceptable maximum spacing, but closer spacing might
be necessary for visibility.)
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