What are the standards for pipe marking labels?

The American National Standards Institute sets standards for the color and location of pipe marking labels. Pipes that carry flammable substances must be marked with a yellow label with black text. Corrosive substances require an orange label with black text.

If a pipe carries more than one type of liquid, use the labeling standards for the most hazardous substance. Place a label next to all valves, flanges and changes of direction. Straight sections of pipe should have one label for every 50 feet of pipe. For overhead pipes, affix the label below the centerline. Place the label below the centerline if the pipe is below eye level.