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ASME Pipe Marking Standard

Quick Tips #203

Hazardous materials flow through miles of piping in a wide variety of facilities. Just like hazardous materials in other ”containers,” piping systems should be appropriately labeled. The American Society of Mechanical Engineers (ASME) A13.1 Scheme for the Identification of Piping Systems standard addresses pipe marking by offering a common labeling method for use in all industrial, commercial and institutional facilities as well as in buildings used for public assembly. This standard does not apply to buried pipelines or electrical conduit.

Label Requirements

Pipe marking labels must effectively communicate the contents of the pipes and give additional detail if special hazards (such as extreme temperatures or pressures) exist. The legend should be short in length and easy to understand. For example, the legend "Steam 100 PSIG" specifies the contents as well as the additional pressure hazard. An arrow should be used in conjunction with the legend to show which direction the material flows. If flow can be in both directions, arrows in both directions should be displayed.

ASME A13.1 was updated in 2007 and reaffirmed in 2013. It uses a color code chart with six standard color combinations and four user-defined combinations as shown below. The colors are based on the contents of the pipe and in general, the most hazardous feature of the contents is used to determine the colors used.

Label Size

Pipe diameter determines the appropriate label and text sizes as shown below.

Label Placement

Labels should be positioned on the pipes so they can be easily seen and read from the normal angle of approach. For example, labels should be placed below the centerline of the pipe if the pipe is overhead and above the centerline if the pipe is below eye level. Labels should be located adjacent to valves and fittings, adjacent to changes of direction, on both sides of wall or floor penetrations, and at regular intervals on straight segment runs with spacing between that allows for easy identification (50 feet is the suggested maximum spacing, but closer spacing may be needed for visibility).


Unmarked pipes are a danger to both people and property. Accidents, injuries and damage to equipment can be caused by not knowing what is flowing through the pipes that surround us. By marking and identifying pipes, errors and accidents can be prevented. It also makes maintenance work easier and helps prevent time-consuming searches.

Commonly Asked Questions
Q. What if I have a pipe smaller than 0.75 inches in diameter?
A. For pipes of less than 0.75 inches in diameter, the use of a permanently legible tag is suggested. On many piping systems, there may be valves, actuators and transmitters that can be tricky to label with standard pipe markers. Valve tags can make labeling these awkward places quick and easy.
Q. Are particular shades of yellow, green, red and blue required for pipe labels?
A. Yes, ASME A13.1- 2007 (R2013) references the technical definitions, color standards and color tolerances set forth in the American National Standards Institute (ANSI)/National Electrical Manufacturers Association (NEMA) Z535.1- 2006 (R2011) Safety Colors. The color shades suggested are intended to give the highest level of recognition to employees with both normal and color-deficient vision.
Q. Has this ASME pipe marking standard been adopted by the Occupational Safety and Health Administration (OSHA)?
A. No, it is still considered an industry voluntary consensus standard. Even though it has not been specifically adopted by OSHA, industry voluntary consensus standards may be evidence that a hazard is recognized and there is a feasible means of correcting such a hazard. If you do not follow a voluntary consensus standard, it is possible to be cited under OSHA’s General Duty Clause.

ASME A13.1-2007 (R2013) Scheme for the Identification of Piping Systems

ANSI/NEMA Z535.1-2006 (R2011) Safety Colors

(Rev. 10/2015)

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Please Note:
The content in this newsletter is intended for general information purposes only. This publication is not a substitute for review of the applicable government regulations and standards, and should not be construed as legal advice or opinion. Readers with specific compliance questions should refer to the cited regulation or consult with an attorney.

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