Pipe Marking: The ANSI/ASME A13.1 Guide

Pipe marking is labeling the pipes in a facility so that anyone, including a maintenance tech on a night shift or a firefighter who has never been in the building, can tell what is in a line, how dangerous it is, and which way it flows. The standard that governs it in the United States is ANSI/ASME A13.1, Scheme for the Identification of Piping Systems, which sets the color code, the label and letter sizes, and where markers go. It is short, it is consistent across facilities by design, and it is the standard an OSHA inspector or a customer auditor will measure your pipes against.

What is actually required

This is where most pipe marking articles overstate things, so to be precise:

• ANSI/ASME A13.1 is a voluntary consensus standard. OSHA incorporates it by reference in one place, the pulp, paper, and paperboard mills standard (29 CFR 1910.261). There is no general-industry OSHA rule that says "mark your pipes to A13.1."
• Hazard Communication (1910.1200) does apply. OSHA has said in interpretation letters that pipes are not "containers" that must carry a HazCom label, but the employer must still tell workers what hazardous chemicals are in unlabeled pipes and how to protect themselves, through the written program, training, or other means. Marking the pipes is the simplest way to meet that.
• The General Duty Clause covers recognized hazards, and an unmarked line carrying steam, ammonia, or acid is a recognized hazard. When OSHA cites unmarked piping outside pulp and paper, that is usually how.
• Customers, insurers, and fire marshals often require A13.1 outright, and some sectors have their own mandatory standards (below).

In practice: follow A13.1. It is what everyone checks against; it is the easiest way to satisfy HazCom for piping, and the cost of labels is trivial next to one wrong valve opened.

A short history

The idea of color-coding plant piping came up at an ASME meeting in 1908, prompted by a paper on identifying power house piping by color. Facilities adopted their own schemes, which solved nothing for anyone who moved between plants, so in 1928 the American Standards Association (ANSI's predecessor) published the first common scheme as A13. It has been revised periodically since; the 2007 edition established the current six-color code, and the 2020 edition added oxidizing fluids to the yellow category and allowed GHS pictograms on labels. The standard is sold by ASME and ANSI; the current edition is on the ANSI webstore.

The color code

Color is read first, from a distance, before the words. A13.1 assigns six combinations by hazard and reserves four for the facility to define.

Two things trip people up. Steam has no assigned color in A13.1; most facilities use one of the user-defined combinations and post it on the legend chart. And a fluid that is both flammable and toxic takes the color of its greater hazard, which the facility decides and documents.

Label size and letter height

Readability scales with pipe diameter. The standard sets minimums by outside diameter, including insulation.

Measure the pipe with its insulation and jacket on, not the bare pipe size. A 2" line with 1" of insulation is a 4" OD pipe and needs the 12" label.

What goes on the label

• The legend: the name of the contents, brief and unambiguous. "SULFURIC ACID," "HOT WATER," "NATURAL GAS." Abbreviations are allowed if they are defined on the facility's posted legend chart. The standard's own wording is that legends should be brief, informative, pointed, and simple.
• Flow direction arrows, on the label or next to it, pointing the way the fluid moves. Arrows at both ends for bidirectional flow.
• Optional additional information: pressure, temperature, or GHS pictograms (allowed since 2020) where they help.

Where to place markers

One label on a long run is not marking; the standard requires markers wherever someone would need to identify the pipe:

• At every valve and flange, so the contents are visible before anyone operates or opens the line.
• At every change of direction, on both legs.
• On both sides of every wall, floor, or ceiling penetration.
• At every branch or tee, on each branch.
• Near every point where a pipe enters or leaves the facility or a room, and at equipment connections.
• At intervals on straight runs close enough that a marker is always in view. The standard does not give a number; 25 to 50 feet is the common recommendation, and closer where sight lines are short or the hazard is high.

Orient labels to the normal line of sight. On a pipe overhead, that means below the horizontal centerline; on a pipe at floor level, above it. Where the pipe is in a dark chase or ceiling, add lighting or use a photoluminescent or reflective marker; a label nobody can read does not count.

Abandoned and empty pipes

A13.1 does not separately require labeling abandoned piping, but it is standard practice and most facilities treat it as mandatory, because a pipe that looks unused may still hold residual product, pressure, or a nitrogen blanket, and because nobody wants to cut into it to find out. Label abandoned lines "ABANDONED" with the former contents if known, usually on the white/black user-defined combination, and record them on the legend chart. Empty lines kept for future use are labeled the same way with their intended service.

Pipe marking in a 5S program

Pipe marking is the overhead part of the visual workplace that 5S builds on the floor and the labels and signs page covers at the station. It belongs in the Standardize step: the facility's color scheme, legend abbreviations, and user-defined colors are written down once and applied the same way in every area, and the legend chart is posted where maintenance and visitors will see it. It belongs in the Sustain step as an audit item: markers present at valves and penetrations, legible, correct color, arrows pointing the right way. And it is a hazard-communication item in 6S, where it usually earns its place after the first near miss involving a hot water or chemical line.

Other standards that may apply

A13.1 is the general scheme. Some facilities have a sector standard that overrides or adds to it:

• Ammonia refrigeration: IIAR Bulletin 114 (International Institute of Ammonia Refrigeration) specifies orange markers with physical state, pressure level, and flow direction, and is referenced by many authorities having jurisdiction.
• Medical gases: NFPA 99 and CGA C-9 for hospitals and clinics, with their own color scheme for oxygen, nitrous oxide, medical air, and vacuum.
• Water and wastewater treatment: the Recommended Standards for Water Works and Wastewater Facilities, usually called the Ten States Standards, specify a color scheme for treatment plant piping.
• Marine: ISO 14726 for piping on ships.
• Specific chemicals and gases: NFPA, CGA, and manufacturer requirements for chlorine, hydrogen, and others.

For a fuller treatment of the specialty standards, the guide to pipe marking standards on Creative Safety Supply covers each in more depth than fits here.

Doing the project

1. Get the standard. Buy A13.1 and any sector standard that applies. It is a few pages and inexpensive, and labeling a facility from a summary is how the wrong color gets on a hundred markers.
2. Walk the facility and inventory the lines. Contents, diameter with insulation, flow direction, every valve, penetration, and change of direction. A floor plan with the runs sketched on it is the deliverable.
3. Write the scheme. The facility's assignments for the user-defined colors, the abbreviations, and any sector overrides, on one page. This is the legend chart that gets posted.
4. Size and count the labels from the inventory. The count is always higher than expected.
5. Print or order. Pre-printed pipe marking labels are quick for standard contents. An industrial label printer handles the facility-specific legends, the odd sizes, and the ongoing changes, and most facilities end up with both.
6. Install to the placement rules, with the surface clean and dry, and orient to the line of sight.
7. Train. Everyone who works near the lines learns the color code and where the legend chart is. New hires get it in orientation; contractors get it at sign-in.
8. Audit. Add pipe markers to the 5S audit. Lines get rerouted, insulation gets replaced, and markers disappear.

5S Today's pipe marking guide is a free download that walks through the standard with reference tables for the job.

Frequently asked questions

Is pipe marking required by OSHA?

Not by a general pipe-marking rule. A13.1 is incorporated by reference only for pulp and paper mills. Hazard Communication requires employers to inform workers about hazardous chemicals in unlabeled pipes, and the General Duty Clause covers recognized hazards, so unmarked hazardous lines can be cited. Marking to A13.1 is the practical way to comply.

What color is a steam pipe?

A13.1 does not assign one. Most facilities use a user-defined combination, commonly purple/white or black/white, and post it on the legend chart. Some use orange/black on the grounds that high-pressure steam is a burn hazard; either is acceptable if documented.

How often do labels need to repeat on a straight run?

The standard says often enough that a marker is always visible; it does not give a distance. Every 25 to 50 feet is the usual practice, closer where sight lines are obstructed.

Do I measure the pipe or the insulation?

The outside diameter including insulation and jacketing. That is the surface the label goes on and the size a reader sees.

Do abandoned pipes need labels?

The standard does not explicitly require it, but it is standard practice and strongly recommended. Label them "ABANDONED" with the former contents.

Can I use GHS pictograms on pipe labels?

Yes, since the 2020 edition, as an addition to the color, legend, and arrows, not a replacement for them.

Related resources

Pipe marking is one part of the visual workplace covered on the 5S, 6S, floor marking, and labels and signs pages. For the compliance side, see compliance audits. 5S Today stocks pipe marking labels and the label printers to make your own, and the pipe marking guide is a free download.