Pipe Color Code Chart and Pipe Labeling Standards (ASME A13.1)

Pipe labeling standards tell a plant how to show what each pipe carries, and the United States reference is ASME A13.1: a lettered legend naming the contents, an arrow showing the direction of flow, and a color field keyed to the hazard. This reference is written for maintenance leads, safety managers and engineers who need the values quickly. The color chart, size chart and placement rules come first. After those are a lookup by fluid, the OSHA position, ammonia and sprinkler practice, the separate underground code, and a method for surveying a plant and handing over the records.

Pipe color code chart (ASME A13.1)

A13.1 fixes six color combinations by the hazard of the contents and leaves four more for each plant to define. The legend is the primary identifier and color is the secondary one, so a colored pipe with no words on it does not meet the scheme.

This chart shows the scheme of the 2023 edition, whose revisions included the Color section and the Designation of Colors table. ASME now lists a 2026 edition that revises the 2023 text, so compare these values with whichever edition your specification names. The swatches are screen approximations; exact safety colors are defined in ANSI/NEMA Z535.1.

What do pipe labeling standards require?

They require positive identification by words, with direction of flow and a color that signals the hazard. A13.1 covers aboveground piping in industrial, commercial, transmission, distribution and institutional installations and in buildings used for public assembly; electrical conduit and buried lines sit under other rules. Each marker carries these elements:

• Legend. The name of the contents, in full or abbreviated, with whatever further detail identifies the hazard, such as temperature or pressure. Brief, plain names work best, and they should match the names on the P&IDs.
• Flow arrow. It sits with the legend and points away from it. Lines that run both ways get arrows in both directions.
• Color. It appears on or next to the pipe by any physical means, always together with a legend, and may run the full length or appear intermittently.
• Optional hazard content. GHS pictograms may form part of the legend. Where a line connects to a container labeled under GHS, a matching pipe label can repeat the product identifier, pictogram, signal word and hazard statements.
• Type. A readable sans serif bold face in a contrasting color, generally at least half an inch tall.

Abandoned piping has its own treatment: black letters on a white field with a black border. If the dead line holds a pressurized preservation fluid or residual hazardous material, the legend says so, because that is exactly what a demolition crew needs to read before cutting it.

Pipe label size chart by outside diameter

Letter height and minimum field length are set by the outside diameter of the pipe or its covering, so an insulated line is measured over the jacket.

Below about 3/4 inch outside diameter, and for valves and fittings, a permanent legible tag does the job in place of a wrapped marker. Older charts show nearly the same values in gapped bands (2-1/2 to 6 inches, then 8 to 10 inches), which leaves sizes such as 7 inches unassigned; the continuous bands above close those gaps.

The band follows actual diameter, and nominal size can mislead. Use the pipe schedule chart for pipe outside diameters and the sanitary tube size chart for tube, then add twice the insulation thickness:

The insulated 6 inch line is the case takeoffs get wrong: its bare size calls for a 12 inch field, while its jacket calls for 32 inches. Field length is a minimum as well, so a long legend such as a full chemical name simply runs longer.

Where do pipe labels go?

Markers go wherever a person needs to confirm the contents: at valves and flanges, at changes of direction and branches, on both sides of penetrations, and along straight runs. A13.1 states the straight-run spacing as a functional test, close enough to identify the line, and plants turn that test into a number in their own scheme.

Test a placement from the normal approach, standing where the operator stands. In a stacked rack, the side facing the aisle is the only side that counts, and a marker that needs a ladder to read has failed even if the spacing is correct.

What color is each pipe? Pipe color codes by contents

Markers follow the hazard class, so the color for a given fluid comes from asking which class it falls in; the table gives the usual answers under the 2023 scheme. For anything unusual, classify from the safety data sheet, and where a fluid fits two classes, take the more severe one and add the second hazard to the legend.

Water pipe color code

A13.1 sets water markers by temperature: white on green for potable, cooling and other cold or tepid water, and black on gray for boiler feedwater and other hot water. Write a temperature breakpoint into the site key, because the two colors will meet on the same system at a heat exchanger or mixing valve. A dual-temperature line on a hydronic system needs its own decision; marking it gray with a plain legend treats it by its worst case.

Steam pipe color code

Steam takes black letters on a gray field, a value that arrived with the 2023 edition. Steam had no assigned color before that, so older plants carry yellow from the 1996 scheme or a site-defined choice. Put the pressure in the legend, since 15 psi and 150 psi steam look identical on a jacket. Steam and condensate piping runs are usually insulated, which pushes them up a size band, and the marker must tolerate the jacket temperature.

Compressed air pipe color code

Compressed air takes white letters on blue, and that row has not moved through any of the editions compared below. Blue identifies air only by class, so use the legend to separate plant air, instrument air and breathing air, and to carry the pressure. Distinct legends matter most at drops, where a wrong connection can reach a tool, a cylinder or a person. More on layout is on the compressed air piping page.

Natural gas pipe color code and gas pipe labeling

Natural gas takes black letters on yellow, the same marker as any other flammable gas, and hydrogen and propane look identical, so the legend does the separating. Fuel gas codes add their own layer of marking. The International Fuel Gas Code, section 401.5, calls for a yellow label marked “Gas” in black letters at intervals of 5 feet or less on exposed piping other than steel pipe and CSST in the 2021 wording, and adopting jurisdictions change it: New York City applies it to all new piping, and Minnesota adds the operating pressure on medium and high pressure systems. Read the code your jurisdiction adopted. Welding gas systems covered by 29 CFR 1910.253 must also mark each station outlet with the name of the gas.

Chilled water pipe marking

Chilled water pipe marking is white on green, with separate supply and return legends and arrows, because the two lines usually run side by side at the same size. Measure over the insulation, keep the marker on the jacket and never cut into the vapor retarder to fix a tag, since that is where a condensation problem starts. If the loop carries glycol, name the mix in the legend and check the safety data sheet for the class. Layouts are covered under chilled water systems.

Why your plant does not match the chart: edition changes

A plant that looks wrong against the chart is often correct for an older edition, because A13.1 has changed its color assignments more than once after the 1996 edition. Many charts in circulation, including recent ones, still show the 2007 to 2020 values, with brown for combustible fluids.

Two traps follow from the swap. Brown and gray traded places: brown now has no fixed meaning, while gray now means steam and hot water, so a plant that used white on gray for nitrogen under the old scheme sits close to a marker with a new meaning. Published industry guidance reads a new edition as applying to new installations and leaves markers in service alone. The real exposure is an undocumented mix, where two people read the same color two ways. State the edition on the site key and mark the boundary wherever a new area meets an old one.

ANSI vs ASME: one pipe labeling standard, two names

The ANSI pipe marking standard and ASME A13.1 are the same document: ASME publishes it and ANSI approves it as an American National Standard, so requests for the ANSI pipe color code, ANSI pipe labeling standards or ANSI pipe marking color codes all lead to the table above. The older ANSI name survives because federal regulations and many legacy specifications still print it. Its full title is Scheme for the Identification of Piping Systems. When a specification says ASME pipe labeling standards or quotes an ASME pipe color code, ask which year it means; that one question settles most marking disputes during submittal review. Mechanical specifications commonly adopt it by reference, with a line requiring the color scheme and lettering to comply with A13.1, which is how a voluntary consensus document becomes a contract requirement. Treat this page as a pipe marking guide for planning, and the purchased standard as the governing text.

OSHA pipe labeling requirements

OSHA pipe labeling requirements appear in a few specific places, and in those places they cite an old edition of A13.1 by name. For most general industry plants the duty arises through hazard communication, process safety and the General Duty Clause, while the marking method comes from A13.1.

The hazard communication pair is the one most plants overlook. Pipes fall outside the container labeling rule, yet the employer still owes workers a method of knowing what is inside them, and a complete marking scheme is the plainest way to meet that duty. State plans and local fire or mechanical codes can go further, so check them for each site. Where a rule names a decades-old edition, record in the site key how the current markers meet its legend and color intent.

Ammonia pipe color code and ammonia pipe labeling requirements

Under A13.1, ammonia falls in the toxic and corrosive class, black letters on orange. Refrigeration plants normally go further and follow IIAR Bulletin 114, which adds the refrigerant state, the relative pressure and an abbreviation for the line. The bulletin now sits inside IIAR 2 as informative Appendix Q, so a facility has more than one way to meet the labeling section of IIAR 2, Section 5.16.4.

Pipe paint is a separate question from the marker. The bulletin’s guideline colors are orange for liquid over 70 psig, yellow for vapor over 70 psig and for booster discharge at any pressure, light blue for low pressure high temperature lines, dark blue for low pressure low temperature lines, purple for the lowest pressure and temperature lines, gray for relief vent piping, and green for condenser water and brine or glycol secondary coolant. White PVC or gray aluminum insulation jacket is acceptable, and the label background need not match the pipe color.

Systems holding 10,000 pounds or more of anhydrous ammonia fall under OSHA process safety management, where labeling is judged as good engineering practice. These color schemes are guidelines, so a facility may run its own, provided it documents the scheme, trains employees and contractors on it, and records the training along with proof of understanding. Component labels should use the same unique identifiers as the P&IDs, such as AU-2 for an air unit, because a generic name stops identifying anything once the nameplate is gone.

Sprinkler pipe labeling requirements and fire protection marking

The fire protection pipe color code in A13.1 is white letters on red, covering water, foam and CO2 in sprinkler and firefighting piping, and green is kept for other water. The rules for sprinkler systems then come mainly from NFPA 13, which focuses on signs at valves and system data rather than on the pipe wall.

• Valve signs. The 2022 edition, section 16.9.11, calls for permanently marked, weatherproof metal or rigid plastic signs on control, drain, venting and test connection valves, fastened with corrosion-resistant wire, chain or another approved method.
• Control valves. Each sign names the part of the building served. If more than one valve must close to work on a system, a sign points to the others.
• Design data. Hydraulically calculated systems carry a permanent sign or label with the design basis, and acceptance checklists look for it at the riser.

Section numbers move between editions, so confirm the one your authority adopted. Whether the pipe itself is painted red is usually set by the owner’s specification and the local fire authority, some of which also set colors for fire department connections and exterior riser valves. If you do paint, mask the sprinklers: NFPA 25 calls for replacing a sprinkler carrying non-manufacturer paint that is detrimental to its performance.

Underground pipe color code

Buried lines follow the APWA Uniform Color Code, a separate system from A13.1 used to mark them on the ground surface before digging. It draws on the ANSI Z535.1 safety colors, and the One-Call center is contacted before excavation.

Watch the two meanings when a plant project crosses from yard to building. Blue marks potable water below ground and compressed air above it; green marks sewers below ground and clean water above it; red marks power below ground and fire water above it. Some states publish their own rules, so check the state one-call guidance for the site.

Industrial pipe color codes outside A13.1

Several other schemes are in use, and imported skids or overseas owner standards may arrive marked to one of them. The main difference is that A13.1 sorts by hazard, while these schemes usually sort by substance.

• BS 1710, common in the UK and Commonwealth countries: green for water, silver-gray for steam, light blue for air, brown for oils, violet for acids and alkalis, and red for fire protection.
• ISO 14726: identification colors for piping contents on ships and marine structures.
• IS 2379, India: a ground color for the fluid group with narrower bands for the specific fluid.
• PFI ES-22: color coding of pipe material grades for fabrication shops and laydown yards. These stripes identify the alloy and say nothing about contents, so a green stripe on carbon steel has no connection to water. Material traceability during pipe fabrication rests on mill records and markings, with color as a supplement.
• Medical gases follow healthcare codes with their own colors; see medical gas piping.

Sanitary plants add their own layer: hygienic standards shape tube and finish, and an owner’s site scheme usually decides how polished lines are identified in product areas. On a skid built to a foreign scheme, re-mark to the receiving plant’s key at installation, so one system does not read differently from the rest of the building.

How to run a pipe labeling survey

A pipe labeling survey is a line-by-line walk that confirms what each pipe carries, then records the legend, color, size and location of every marker it needs. Marking comes last, after the contents are confirmed, because a confident label on a misidentified line is worse than no label at all. Use it as a pipe marking color code guide for your own site key, and follow these steps in order.

Arrows cause more errors than colors do. Check them against the actual flow at recirculation loops, headers fed from both ends and bypasses, and use two-way arrows where flow really reverses. Marking fits best as a final step of a plant utilities tie-in or shutdown, when lines are already being traced and accessed.

What goes in the turnover package

A marking turnover lets the next person maintain the scheme without repeating the survey. Include the site key with its edition, the marker schedule by line number, as-built P&IDs with matching line names, the valve tag list, the abandoned line list, marker material data and temperature limits, the signed walkdown and the training record. On regulated systems, this feeds the wider turnover package and commissioning and validation walkdowns, where the legend on the pipe has to agree with the drawing being verified. Writing these deliverables into an RFQ at the start costs far less than a survey after startup.

Pipe marking on Paul Industries jobs

Paul Industries labels and marks the piping it designs, fabricates, installs and turns over, as part of the job on process piping and plant utility work, and it surveys and re-labels existing plant piping to a written site key, including replacing obsolete markers and marking abandoned lines. Crews work in all 50 states, and the marker schedule, walkdown and key go into the same turnover as the weld and test records. Send your line list or P&IDs through request a quote for a survey, a re-labeling scope or a new install with marking included.

Standards referenced: ASME A13.1 · ANSI/NEMA Z535.1 · 29 CFR 1910.253 · 29 CFR 1910.261 · 29 CFR 1910.262 · 29 CFR 1910.1200 · 29 CFR 1910.119 · IIAR 2 · IIAR Bulletin 114 · NFPA 13 · NFPA 25 · International Fuel Gas Code · APWA Uniform Color Code · BS 1710 · ISO 14726 · PFI ES-22

Frequently asked questions

What is the latest edition of ASME A13.1?

ASME lists a 2026 edition, which revises the 2023 edition. Before that came 2020, 2015 and 2007. The title has stayed Scheme for the Identification of Piping Systems, and the document is short at 19 pages, so a plant can reasonably keep a current copy with its safety records.

Is ASME A13.1 mandatory?

It is a voluntary consensus standard that becomes binding in three ways: a regulation cites it, a contract or specification adopts it, or a code or insurer requires it. Without any of those, it still serves as the recognized benchmark an auditor or investigator is likely to measure a plant against.

How far apart should pipe labels be?

The standard asks for spacing sufficient to identify the line and leaves the distance open. Plants often write 25 feet into their site scheme because it is easy to audit, then tighten it in congested racks and relax it on long, visible yard runs. Whatever number you pick, write it down.

Do I size a pipe label by nominal size or actual diameter?

By actual outside diameter, including any insulation or covering. Nominal size works as a shortcut only for bare pipe at NPS 14 and up, where nominal and actual diameter match. For everything smaller, look up or measure the true figure.

Which way does the arrow go on a pipe marker?

It points in the direction of flow and away from the legend. Separate arrow markers are common because they let an installer set flow independently of which way the legend reads, which helps when a line is read from the far side of an aisle.

Does the whole pipe need to be painted?

Full-length color is one option; the scheme equally accepts intermittent color next to a legend. Many plants leave stainless and insulated lines unpainted and rely on markers alone, which also keeps coatings away from weld inspection areas.

Can a plant keep its old pipe color scheme?

Yes, provided the scheme is written down and people are trained on it, and it does not conflict with a regulation or contract. Plants often adopt the current edition for new work and retrofit older areas during turnarounds. The record of which area follows which edition is what keeps that workable.

Which marker does nitrogen piping take?

Nitrogen has no assigned row in the 2023 table, so it takes a user-defined combination recorded in the site key. Add a warning about asphyxiation in the legend or at access points where the plant's hazard review calls for it, since inert gas gives no sensory warning at all.

What color is diesel or fuel oil piping?

Under the 2023 scheme, combustible fluids are black on yellow, grouped with flammable fluids. A plant marked between 2007 and 2020 will show white on brown for the same oil, so read the legend first and the color second during any changeover.

How does a pipe marker differ from a valve tag?

A marker identifies the contents and flow of the line, while a tag identifies a specific valve by number and ties it to a valve chart or lockout procedure. A valve in a line usually needs both, because the procedure names the tag and the operator confirms the service from the marker.

Should ammonia insulation jacket match the pipe color?

Matching is optional. Plain white PVC or gray aluminum jacket is common and acceptable as long as the markers follow the chosen practice. An orange marker on an orange pipe can actually be harder to read, which is one argument for keeping jackets neutral.

Where do abbreviations belong on a pipe label?

They are acceptable in the legend when the site key explains them, and the same abbreviation should appear on the P&IDs. Avoid invented short forms that only one shift understands, and spell out the name wherever a contractor or emergency responder is likely to be the reader.

Can GHS pictograms replace the pipe legend?

They supplement the name and flow arrow, which remain the primary identifier. Pictograms are most useful on lines connected to labeled tanks and totes, where a worker can match the pipe to the container and read the same hazard information on both.

How do I label a pipe when I do not know what is in it?

Treat it as unknown until proven: trace it to both ends, check isolation and maintenance records, and sample under the site's line-break procedure if needed. Hold the marker until the contents are confirmed, and keep the line on the open list so it is resolved instead of forgotten.

How should pipes be marked in hot or washdown areas?

Choose the marker for the worst condition on that pipe: jacket temperature, chemical cleaning, ultraviolet exposure and abrasion. Mechanically fastened markers tend to outlast adhesive ones on hot or frequently cleaned surfaces, and food plants often have a site rule on what may be used in product zones.

Who is responsible for pipe marking on a new installation?

The specification should assign it, and it is cleanest when the installing contractor owns it, because the crew knows the contents, flow and routing as the lines go in. Name the edition, the site key and the walkdown in the scope, so the marking closes out with the rest of the turnover.

How often should pipe labels be audited?

Set the check on events and on a calendar: after any line change, tie-in or insulation repair, and on a routine walk such as an annual safety inspection. Missing markers cluster where insulation was opened, so start any audit around recently repaired valves and flanges.

How long does a pipe labeling survey take?

Effort scales with line count and congestion, so count lines before estimating. A current line list and accurate P&IDs shorten the walk considerably, while undocumented retrofits take the most time because each unknown line has to be traced. Sharing drawings at the start gives the most reliable scope.

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